the circulatory system assignment

• Biology Article
• Human Circulatory System Transportation

Human Circulatory System

The human body is a complex machine, requiring many processes to function efficiently. To keep these crucial processes running without any hitches, vital elements and components need to be delivered to the various parts of the body.

This role of transportation is undertaken by the human circulatory system, moving essential nutrients and minerals throughout the body and metabolic waste products away from the body. Below is a neat labelled  Circulatory system diagram.

Read more:  Human Body Anatomy

Read on to explore intricate about the human circulatory system and its components in greater detail.

Table of Contents

Double Circulation

• Blood Cells

Blood Vessels

Lymphatic system, human circulatory system diagram.

The human circulatory system consists of a network of arteries, veins, and capillaries, with the heart pumping blood through it. Its primary role is to provide essential nutrients, minerals, and hormones to various parts of the body. Alternatively, the circulatory system is also responsible for collecting metabolic waste and toxins from the cells and tissues to be purified or expelled from the body.

Features of Circulatory System

The crucial features of the human circulatory system are as follows:

• The human circulatory system consists of blood, heart, blood vessels, and lymph.
• The human circulatory system circulates blood through two loops (double circulation) – One for oxygenated blood, another for deoxygenated blood.
• The human heart consists of four chambers – two ventricles and two auricles.
• The human circulatory system possesses a body-wide network of blood vessels. These comprise arteries, veins, and capillaries.
• The primary function of blood vessels is to transport oxygenated blood and nutrients to all parts of the body. It is also tasked with collecting metabolic wastes to be expelled from the body.
• Most circulatory system diagrams do not visually represent its sheer length. Theoretically, if the veins, arteries, and capillaries of a human were laid out, end to end, it would span a total distance of 1,00,000 kilometres (or roughly eight times the diameter of the Earth).

Organs of Circulatory System

The human circulatory system comprises 4 main organs that have specific roles and functions. The vital circulatory system organs include:

• Blood (technically, blood is considered a tissue and not an organ)
• Lymphatic system

The heart is a muscular organ located in the chest cavity, right between the lungs. It is positioned slightly towards the left in the thoracic region and is enveloped by the pericardium. The human heart is separated into four chambers; namely, two upper chambers called atria ( singular: atrium ), and two lower chambers called ventricles.

Heart, a major part of the human circulatory system

Though other animals possess a heart, the way their circulatory system functions is quite different from humans. Moreover, in some cases, the human circulatory system is much more evolved when compared to insects or molluscs.

Read More:   Human Heart

The way blood flows in the human body is unique, and it is quite efficient too. The blood circulates through the heart twice, hence, it is called double circulation. Other animals like fish have single circulation, where blood completes a circuit through the entire animal only once.

The main advantage of double circulation is that every tissue in the body has a steady supply of oxygenated blood, and it does not get mixed with the deoxygenated blood.

Further Reading: Double circulation

Circulation of blood in humans – Double circulation

Blood is the body’s fluid connective tissue, and it forms a vital part of the human circulatory system. Its main function is to circulate nutrients, hormones, minerals and other essential components to different parts of the body. Blood flows through a specified set of pathways called blood vessels. The organ which is involved in pumping blood to different body parts is the heart.  Blood cells, blood plasma, proteins, and other mineral components (such as sodium, potassium and calcium) constitute human blood.

Blood is composed of:

• Plasma  – the fluid part of the blood and is composed of  90%  of water.
• Red blood cells, white blood cells and platelets constitute the solid part of blood.

Types of Blood Cells

The human body consists of three types of blood cells, namely:

• Red blood cells (RBC) / Erythrocytes

Red blood cells are mainly involved in transporting oxygen, nutrients, and other substances to various parts of the body. These blood cells also remove waste from the body.

• White blood cells (WBC) / Leukocytes

White blood cells are specialized cells, which function as a body’s defence system. They provide immunity by fending off pathogens and harmful microorganisms.

• Platelets / Thrombocytes

Platelets are cells that help to form clots and stop bleeding. They act on the site of an injury or a wound.

Blood vessels are a network of pathways through which blood travels throughout the body.  Arteries and veins are the two primary types of blood vessels in the circulatory system of the body.

Arteries are blood vessels that transport oxygenated blood from the heart to various parts of the body. They are thick, elastic and are divided into a small network of blood vessels called capillaries. The only exception to this is the pulmonary arteries, which carries deoxygenated blood to the lungs.

Veins are blood vessels that carry deoxygenated blood towards the heart from various parts of the body.  They are thin, elastic and are present closer to the surface of the skin. However, pulmonary and umbilical veins are the only veins that carry oxygenated blood in the entire body.

Also Read:  Blood

The human circulatory system consists of another body fluid called lymph. It is also known as tissue fluid. It is produced by the lymphatic system which comprises a network of interconnected organs, nodes and ducts.

Lymph is a colourless fluid consisting of salts, proteins, water, which transport and circulates digested food and absorbed fat to intercellular spaces in the tissues. Unlike the circulatory system, lymph is not pumped; instead, it passively flows through a network of vessels.

Functions of Circulatory System

The most important function of the circulatory system is transporting oxygen throughout the body. The other vital functions of the human circulatory system are as follows:

• It helps in sustaining all the organ systems.
• It transports blood, nutrients, oxygen, carbon dioxide and hormones throughout the body.
• It protects cells from pathogens.
• It acts as an interface for cell-to-cell interaction.
• The substances present in the blood help repair the damaged tissue.

Explore More: Circulatory System

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Frequently Asked Questions

1. how does the human circulatory system work, 2. what are the three types of circulation.

• Pulmonary Circulation
• Systemic Circulation
• Coronary Circulation

3. Is the human circulatory system open or closed?

4. what is the advantage of a closed circulatory system, 5. what is double circulation, 6. what are the dangers of high blood pressure, 7. what is a stroke, 8. what is hypertension, 9. what is hypo-tension, 10. what was the earliest circulatory system like.

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Lab 6: Circulatory Systems

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• Page ID 24395

• Susan Burran and David DesRochers
• Dalton State College via GALILEO Open Learning Materials

Most animals are complex multicellular organisms that require a mechanism for transporting nutrients throughout their bodies and removing waste products. The circulatory system has evolved over time from simple diffusion through cells in the early evolution of animals to a complex network of blood vessels that reach all parts of the human body. This extensive network supplies the cells, tissues, and organs with oxygen and nutrients, and removes carbon dioxide and waste, which are byproducts of respiration and other cellular activities.

Circulatory systems differ significantly throughout the Animal Kingdom. In all vertebrate organisms, as well as some invertebrates, this is a closed-loop system, in which the blood is not free in a cavity. In a closed circulatory system, blood is contained inside blood vessels and circulates unidirectionally from the heart around the systemic circulatory route, then returns to the heart again. As opposed to a closed system, arthropods—including insects, crustaceans, and most mollusks—have an open circulatory system. In an open circulatory system, the blood is not enclosed in the blood vessels but is pumped into a cavity called a hemocoel and is called hemolymph because the blood mixes with the interstitial fluid.

Mammalian Heart and Blood Vessels:

The mammalian circulatory system is divided into three circuits: the systemic circuit, the pulmonary circuit, and the coronary circuit. Blood is pumped from veins of the systemic circuit into the right atrium of the heart, then into the right ventricle. Blood then enters the pulmonary circuit and is oxygenated by the lungs. From the pulmonary circuit, blood re-enters the heart through the left atrium. From the left ventricle, blood re-enters the systemic circuit through the aorta and is distributed to the rest of the body.

Exercise 1: Structure of the Heart

• Human Heart Model
• Using the model of the human heart and the chart provided, locate the different structures of the heart. Write the flow of the blood and the function of each structure in the space provided:

Right atrium: __________________________________________

Tricuspid valve: __________________________________________

Right ventricle: __________________________________________

Left atrium: __________________________________________

Bicuspid/Mitral valve: __________________________________________

Left ventricle: __________________________________________

Exercise 2: Blood Type and RH factor.

Blood is important for regulation of the body’s systems and homeostasis. Blood helps maintain homeostasis by stabilizing pH, temperature, osmotic pressure, and by eliminating excess heat. Blood supports growth by distributing nutrients and hormones, and by removing waste. Blood plays a protective role by transporting clotting factors and platelets to prevent blood loss and transporting the disease-fighting agents or white blood cells to sites of infection.

Microscope work: Use one of the light microscopes to explore a slide of a human blood smear. The leukocytes (white blood cells) are stained purple (nuclear staining) and far less common than the erythrocytes (red blood cells). Count the number of leukocytes in your view at the medium magnification. How many are there?

______________________________________________________________________________________________________________________________________________

Erythrocytes outnumber leukocytes 600:1. Therefore, estimate the number of erythrocytes in your view: _________________________________________________________

Why do you think the erythrocytes outnumber the leukocytes?

__________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Red blood cells are coated in antigens made of glycolipids and glycoproteins. The composition of these molecules is determined by genetics, which have evolved over time. The two most well-known blood groups are the ABO and Rh systems. The surface antigens in the ABO blood group are glycolipids, called antigen A and antigen B. People with blood type A have antigen A, those with blood type B have antigen B, those with blood type AB have both antigens, and people with blood type O have neither antigen. Antibodies called agglutinogens are found in the blood plasma and react with the A or B antigens, if the two are mixed. When type A and type B blood are combined, agglutination (clumping) of the blood occurs because of antibodies in the plasma that bind with the opposing antigen; this causes clots that coagulate in the kidney causing kidney failure. Type O blood has neither A or B antigens, and therefore, type O blood can be given to all blood types. Type O negative blood is the universal donor. Type AB positive blood is the universal acceptor because it has both A and B antigen.

The Rh blood group was first discovered in Rhesus monkeys. Most people have the Rh antigen (Rh+) and do not have anti-Rh antibodies in their blood. The few people who do not have the Rh antigen and are Rh– can develop anti-Rh antibodies if exposed to Rh+ blood. This can happen after a blood transfusion or after an Rh– woman has an Rh+ baby. The first exposure does not usually cause a reaction; however, at the second exposure, enough antibodies have built up in the blood to produce a reaction that causes agglutination and breakdown of red blood cells. An injection can prevent this reaction.

Based on the information above, fill out the following chart regarding each blood type:

• Blood typing kit (1/each group)
• 4 unknown simulated blood dropper bottles
• Anti –A, Anti-B, Anti-D (RH) sera dropper bottles
• Place one drop of simulated blood in the middle of each depression in the blood typing tray.
• Add one drop of Anti-A serum next to the A blood cells, one drop of Anti-B serum next to the B blood cells, and one drop of Anti-D serum next to box D blood cells.
• Mix the simulated blood with the Anti-serum using the toothpick for about two minutes
• Depend on the type of the antigen in the blood, the blood mixture will clump or the mixture will not change.
• Record your observation on the following table.

Exercise 3: Measuring Blood Pressure and Pulse Rate

Blood pressure (BP) is the pressure exerted by blood on the walls of a blood vessel that helps to push blood through the body. Blood moving through the blood vessels exerts pressure against the vessel walls. This blood pressure is highest in the aorta. It decreases as the blood moves through the arterioles, capillaries, venules, and veins. Many factors can affect blood pressure, such as hormones, stress, exercise, eating, sitting, and standing. Blood flow through the body is regulated by the size of blood vessels, by the action of smooth muscle, by one-way valves, and by the fluid pressure of the blood itself.

There are two components to blood pressure:

• Systolic blood pressure: measures the amount of pressure that blood exerts on vessels while the heart is beating (contracting). The pressure in the vessel is highest at this time. The optimal systolic blood pressure is 120 mmHg.
• Diastolic blood pressure: measures the pressure in the vessels between heartbeats (resting). The pressure is at its lowest point. The optimal diastolic blood pressure is 80 mmHg.

When we measure blood pressure, we are actually measuring the systolic pressure and the diastolic pressure separately. This is why you always see blood pressure reported as two numbers, one "over" the other. For example in a blood pressure reading of 130/85, this means that the systolic pressure is 130 and the diastolic pressure is 85.

• Sphygmomanometer (pronounced sfig-mo-muh-NAM-eh-ter) consists of an inflatable cuff, an inflation pump, a gauge to register pressure, and a controlled exhaust valve.
• Stethoscope: to listen to the different sounds that occur

You will work in pairs to measure the effect of exercise on pulse rate and blood pressure.

• Have your partner sit down and relax for 2 minutes. Place your index and middle fingers in the groove on the inside of his/her wrist. Just slide your fingers across the tendons until they slip into soft tissue.
• Wait until you clearly feel beats coming with a regular rhythm.
• Count the number of pulses in 15 seconds.
• Multiply the number of pulses by 4 to get the number of beats per minute.
• Record this number in the table below.
• Attach the inflatable cuff around your partner’s arm above the elbow as shown in the figure above. Tuck the flap of the bag under the fold.
• Place the stethoscope over the brachial artery (underneath the cuff as shown in the figure above.
• You begin by inflating the cuff to about 200 mm. The blood flow below stops and you will hear no sound in the brachial artery when you listen with the stethoscope.
• If the pressure has gone below 200 mmHg, inflate the cuff again.
• Slowly begin releasing the pressure in the cuff. The blood begins to flow through the artery causing vibrations and turbulence that are audible through the stethoscope
• The first tapping sound you hear indicates that blood has entered the artery. Record this reading as the systolic pressure.
• You continue to deflate the cuff until you stop hearing any sound. The last tapping sound you hear indicates the diastolic pressure.
• Now go outside and exercise for exactly 5 minutes. You can do jumping jacks, run up and down the stairs or do push-ups.
• Immediately after sitting down measure the pulse rate/min (Steps 1–3) and the blood pressure (steps 4–10) and record your data.
• Measure the beat rate and the blood pressure of your partner. Record the results in the following table.

1. How does exercise affect pulse rate and blood pressure?

2. Explain what happens to the circulatory system during exercise. Include the major organs involved in your explanation.

3. Why does increased physical activity increases heart rate?

4. Why is heart rate lower in an individual who does aerobic exercise regularly?

5. How and why does heart rate change with body position?

Circulatory and Cardiovascular System STEM

The circulatory system is one of the most important systems in the human body. It’s responsible for transporting blood, nutrients, and oxygen to all of our cells. Keeping it healthy is essential for overall health and wellness.

This STEM lesson plan on the circulatory system is the perfect way for students to learn about this vital system and how to keep it healthy. Through a variety of engaging activities and hands-on experiments, they’ll gain a thorough understanding of its structure and function. They’ll also discover how important it is to other body systems and learn practical tips for keeping it healthy.

Description

Additional information, what our circulatory and cardiovascular system stem lesson plan includes.

Lesson Objectives and Overview: Circulatory and Cardiovascular System STEM teaches students about the structure and functions of this body system. Students will be able to explain how and why to keep the circulatory system healthy. They will also discover how it works with other body systems to function properly. This lesson is for students in 4th grade, 5th grade, and 6th grade.

Classroom Procedure

Every lesson plan provides you with a classroom procedure page that outlines a step-by-step guide to follow. You do not have to follow the guide exactly. The guide helps you organize the lesson and details when to hand out worksheets. It also lists information in the yellow box that you might find useful. You will find the lesson objectives, state standards, and number of class sessions the lesson should take to complete in this area. In addition, it describes the supplies you will need as well as what and how you need to prepare beforehand. For this lesson, you will need red and green markers, water, large containers, and measuring cups. You might also choose to get a timer for the activity.

Options for Lesson

In the “Options for Lesson” section of the classroom procedure page, you will see some suggestions for additional activities or ideas to add to the lesson if you want to. One idea is to have students calculate the mean, median, mode, and range of the heart rates of the students in the class. (You may benefit from pairing this lesson with a math lesson related to central tendency and graphing.) Students could change the amount of water or size of the measuring cup to reflect different stages in life—child versus adult—during the practice. Consider talking about different animals and their hearts and how they differ from those of humans. Another option is to have a veterinarian come to the class to talk about the different circulatory systems of animals and compare them to humans.

Teacher Notes

The teacher notes page provides an extra paragraph of information to help guide the lesson. You can use the blank lines to write down any other ideas or thoughts you have about the topic as you prepare.

CIRCULATORY AND CARDIOVASCULAR SYSTEM STEM LESSON PLAN CONTENT PAGES

Introduction to the heart.

The Circulatory and Cardiovascular System STEM lesson plan has three pages of content. Students will first learn what this body system actually is. The circulatory system comprises the heart, blood vessels, and blood. There are two circulatory systems in the human body: pulmonary circulation and systemic circulation. With pulmonary circulation blood loops from the heart to the lungs and back. And with systemic circulation, it loops from the heart to all the other parts of the body and back.

With each heartbeat, blood travels throughout the body to carry oxygen and nutrients to the cells. Without blood, we wouldn’t be alive! This is why the heart has to pump blood continuously through the body. The heart is the main organ in the circulatory system. It is a muscle about the size of a fist on the left side of the chest. Its job is to propel blood throughout the body.

Each minute, the heart beats anywhere from 60 to 100 times, but it can go even faster than that if needed. The body sends the heart signals to pump more (or less) blood depending on the situation. For example, exercising or being scared tells the heart to pump faster to get more oxygen. But when we sleep, our body tells the heart to slow down. Each day, the heart beats around 100,000 times. That’s 30 million times a year and over 2.5 billion times over an average lifespan.

Parts of the Heart

The heart has four chambers: two ventricles and two atria. The bottom two chambers are the ventricles, which are separated by a wall called the interventricular septum. Ventricles are responsible for pumping blood out of the heart. The upper two chambers of the heart are the atria. Atria have the opposite job as ventricles and receive blood as it enters the heart. The wall between them is the interatrial septum. In addition, four sets of valves in the heart ensure that the blood can only flow in one direction.

Blood enters the heart through the right atrium, passes down to the right ventricle through the tricuspid valve, and flows through the pulmonary artery. It flows through the pulmonary artery to the lungs, where it gathers oxygen and removes carbon dioxide. The aorta is the main artery that takes away blood. Something called the mitral valve separates the left atrium and left ventricle, taking away blood from the heart.

Blood Vessels

Next, students will learn about blood vessels. Blood vessels constantly circulate blood throughout the body. As the blood circulates, it picks up nutrients from food and drops them off to the cells that need energy. Then it takes the waste from the cells (carbon dioxide) and drops it off in the lungs so we can breathe it out.

Blood vessels are tubes that run through the entire body to help carry the blood. Some of these are veins, which bring blood to the heart. Others are arteries, which take blood away from the heart. Arteries have to be super strong and thick because there is more pressure on them from the heart’s pumping. Veins don’t have to be as wide because they carry the blood back to the heart.

Our blood consists of red blood cells, among other things. Red blood cells carry oxygen, which is why it looks red. Blood also contains platelets that help our blood clot when we get a cut. In addition, it has white blood cells, which are responsible for killing germs and keeping the blood free from invaders. The red blood cells, white blood cells, and platelets float around in a substance called plasma. Together they make up our blood.

There are four main types of blood—A, B, O, and AB. Each type is slightly different from the others because of antibodies and antigens. If a person needs a blood donation, they must receive blood that matches their blood type. If the blood types do not match, the person receiving the blood can get very sick.

Keeping the Circulatory System Healthy

The circulatory system works with all the other systems in the body to help supply nutrients and remove waste. Our heart is an essential part of the system as it pumps blood throughout our bodies. It is necessary to keep it healthy and working well for our whole life.

Like all muscles, we can strengthen the heart through regular exercise. For example, a brisk 10-minute walk can increase the blood flow through the heart and make it stronger. Avoiding foods that are heavy in fat and sugar can also help our circulatory system remain healthy. On the flip side, eating healthy foods and snacks like natural fruits and vegetables can strengthen our heart and circulatory systems.

Excessive stress can hurt the circulatory system because it increases the levels of chemicals in the bloodstream that injure the cells. Deep-breathing exercises and learning to manage stress are part of a heart-healthy plan. Infections can be hard on the circulatory system as well. A good habit is to wash the hands often to reduce the chances of getting sick from the flu or other diseases.

CIRCULATORY AND CARDIOVASCULAR SYSTEM STEM LESSON PLAN WORKSHEETS

The Circulatory and Cardiovascular System STEM lesson plan includes three worksheets: an activity worksheet, a practice worksheet, and a homework assignment. Each one will help students solidify their grasp of the material they learned throughout the lesson. You can refer to the classroom procedure guidelines to know when to hand out each worksheet.

PULSE RATE ACTIVITY WORKSHEET

For the activity, students will collect data on their own pulse rate. First, they will put their hands on either their neck or wrist and count their pulse for 10 seconds. After multiplying that number by 6 to get their beats per minute, they will record the answer in the table. Students will then run in place as fast as they can for 15 seconds. Again, they will count their pulse for 10 seconds, multiply by 6, and record the answer in the table.

The worksheet lists four prompts regarding the data students collected about their pulse. They must explain why the rate changed after exercising and describes things that make a pulse rate change. Then they will list three activities to increase their pulse rate and two that decrease it.

On the second worksheet page, students will collect the heart rate data from four other students and fill in their information in the table. Finally, they will create a bar graph showing each students resting pulse rate in green and active pulse rate in red.

CIRCULATORY AND CARDIOVASCULAR SYSTEM STEM PRACTICE WORKSHEET

The practice worksheet requires students to see if they can work faster than their hearts. Students will first read a short passage at the top of the page about how much blood the heart pumps through their body every day. They will fill a container with one gallon of water and set a timer for one minute. Then they will use a small cup to scoop water into another container as fast as possible. Another students will count the scoops. At the bottom of the worksheet are four prompts for students to respond to.

EXERCISES HOMEWORK ASSIGNMENT

For the homework assignment, students will mark off spots on a tic-tac-toe board as they complete the exercise on that spot. They should do as many of each exercise as they can for two minutes. Then they will check their heart rate after each exercise and record the beats per minute in the box. Exercises include jumping jacks, push-ups, squats, and jogging in place.

Worksheet Answer Keys

The lesson plan document provides answer keys for the three worksheets. All the correct answers are in red to make it easier for you to compare them with students’ work. Some of the prompts on various worksheets are objective, so students’ answers will vary. The answer keys often provide sample responses in these cases. If you choose to administer the lesson pages to your students via PDF, you will need to save a new file that omits these pages. Otherwise, you can simply print out the applicable pages and keep these as reference for yourself when grading assignments.

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Cardiovascular System Anatomy and Physiology

Journey to the heart of our being with the cardiovascular system study guide . Aspiring nurses, chart the pulsating rivers of life as you discover the anatomy and dynamics of the body’s powerful pump and intricate vessel networks.

Table of Contents

Functions of the heart, heart structure and functions, layers of the heart, chambers of the heart, associated great vessels, heart valves, cardiac circulation vessels, blood vessels, major arteries of the systemic circulation, major veins of the systemic circulation, intrinsic conduction system of the heart, the pathway of the conduction system, cardiac cycle and heart sounds, cardiac output, physiology of circulation, cardiovascular vital signs, blood circulation through the heart, capillary exchange of gases and nutrients, age-related physiological changes in the cardiovascular system.

The functions of the heart are as follows:

• Managing blood supply. Variations in the rate and force of heart contraction match blood flow to the changing metabolic needs of the tissues during rest, exercise, and changes in body position.
• Producing blood pressure. Contractions of the heart produce blood pressure, which is needed for blood flow through the blood vessels.
• Securing one-way blood flow. The valves of the heart secure a one-way blood flow through the heart and blood vessels.
• Transmitting blood. The heart separates the pulmonary and systemic circulations, which ensures the flow of oxygenated blood to tissues.

Anatomy of the Heart

The cardiovascular system can be compared to a muscular pump equipped with one-way valves and a system of large and small plumbing tubes within which the blood travels.

The modest size and weight of the heart give few hints of its incredible strength.

• Weight. Approximately the size of a person’s fist, the hollow , cone-shaped heart weighs less than a pound .
• Mediastinum. Snugly enclosed within the inferior mediastinum, the medial cavity of the thorax, the heart is flanked on each side by the lungs.
• Apex. Its more pointed apex is directed toward the left hip and rests on the diaphragm, approximately at the level of the fifth intercostal space.
• Base. Its broad posterosuperior aspect, or base , from which the great vessels of the body emerge, points toward the right shoulder and lies beneath the second rib.
• Pericardium. The heart is enclosed in a double-walled sac called the pericardium which is the outermost layer of the heart.
• Fibrous pericardium. The loosely fitting superficial part of this sac is referred to as the fibrous pericardium, which helps protect the heart and anchors it to surrounding structures such as the diaphragm and sternum .
• Serous pericardium. Deep to the fibrous pericardium is the slippery, two-layer serous pericardium, where its parietal layer lines the interior of the fibrous pericardium.

The heart muscle has three layers and they are as follows:

• Epicardium. The epicardium or the visceral and outermost layer is actually a part of the heart wall.
• Myocardium. The myocardium consists of thick bundles of cardiac muscle twisted and whirled into ringlike arrangements and it is the layer that actually contracts.
• Endocardium. The endocardium is the innermost layer of the heart and is a thin, glistening sheet of endothelium hat lines the heart chambers.

The heart has four hollow chambers, or cavities: two atria and two ventricles.

• Receiving chambers. The two superior atria are primarily the receiving chambers, they play a lighter role in the pumping activity of the heart.
• Discharging chambers. The two inferior, thick-walled ventricles are the discharging chambers, or actual pumps of the heart wherein when they contract, blood is propelled out of the heart and into circulation.
• Septum. The septum that divides the heart longitudinally is referred to as either the interventricular septum or the interatrial septum, depending on which chamber it separates.

The great blood vessels provide a pathway for the entire cardiac circulation to proceed.

• Superior and inferior vena cava. The heart receives relatively oxygen-poor blood from the veins of the body through the large superior and inferior vena cava and pumps it through the pulmonary trunk .
• Pulmonary arteries. The pulmonary trunk splits into the right and left pulmonary arteries, which carry blood to the lungs, where oxygen is picked up and carbon dioxide is unloaded.
• Pulmonary veins. Oxygen-rich blood drains from the lungs and is returned to the left side of the heart through the four pulmonary veins.
• Aorta. Blood returned to the left side of the heart is pumped out of the heart into the aorta from which the systemic arteries branch to supply essentially all body tissues.

The heart is equipped with four valves, which allow blood to flow in only one direction through the heart chambers.

• Atrioventricular valves. Atrioventricular or AV valves are located between the atrial and ventricular chambers on each side, and they prevent backflow into the atria when the ventricles contract.
• Bicuspid valves. The left AV valve- the bicuspid or mitral valve, consists of two flaps, or cusps, of the endocardium.
• Tricuspid valve. The right AV valve, the tricuspid valve, has three flaps.
• Semilunar valve. The second set of valves, the semilunar valves, guards the bases of the two large arteries leaving the ventricular chambers, thus they are known as the pulmonary and aortic semilunar valves.

Although the heart chambers are bathed with blood almost continuously, the blood contained in the heart does not nourish the myocardium.

• Coronary arteries. The coronary arteries branch from the base of the aorta and encircle the heart in the coronary sulcus (atrioventricular groove) at the junction of the atria and ventricles, and these arteries are compressed when the ventricles are contract and fill when the heart is relaxed.
• Cardiac veins. The myocardium is drained by several cardiac veins, which empty into an enlarged vessel on the posterior of the heart called the coronary sinus .

Blood circulates inside the blood vessels, which form a closed transport system, the so-called vascular system.

• Arteries. As the heart beats, blood is propelled into large arteries leaving the heart.
• Arterioles. It then moves into successively smaller and smaller arteries and then into arterioles, which feed the capillary beds in the tissues.
• Veins. Capillary beds are drained by venules , which in turn empty into veins that finally empty into the great veins entering the heart.

Except for the microscopic capillaries, the walls of the blood vessels have three coats or tunics.

• Tunica intima. The tunica intima, which lines the lumen, or interior, of the vessels, is a thin layer of endothelium resting on a basement membrane and decreases friction as blood flows through the vessel lumen.
• Tunica media. The tunica media is the bulky middle coat which mostly consists of smooth muscle and elastic fibers that constrict or dilate, making the blood pressure increase or decrease.
• Tunica externa. The tunica externa is the outermost tunic composed largely of fibrous connective tissue, and its function is basically to support and protect the vessels.

The major branches of the aorta and the organs they serve are listed next in the sequence from the heart.

Arterial Branches of the Ascending Aorta

The aorta springs upward from the left ventricle of the heart as the ascending aorta.

• Coronary arteries. The only branches of the ascending aorta are the right and left coronary arteries, which serve the heart.

Arterial Branches of the Aortic Arch

The aorta arches to the left as the aortic arch.

• Brachiocephalic trunk. The brachiocephalic trunk, the first branch off the aortic arch, splits into the right common carotid artery and right subclavian artery .
• Left common carotid artery. The left common carotid artery is the second branch of the aortic arch and it divides, forming the left internal carotid , which serves the brain, and the l eft external carotid , which serves the skin and muscles of the head and neck.
• Left subclavian artery. The third branch of the aortic arch, the left subclavian artery , gives off an important branch- the vertebral artery , which serves as part of the brain.
• Axillary artery. In the axilla, the subclavian artery becomes the axillary artery.
• Brachial artery. the subclavian artery continues into the arm as the brachial artery, which supplies the arm.
• Radial and ulnar arteries. At the elbow, the brachial artery splits to form the radial and ulnar arteries, which serve the forearm.

Arterial Branches of the Thoracic Aorta

The aorta plunges downward through the thorax, following the spine as the thoracic aorta.

• Intercostal arteries. Ten pairs of intercostal arteries supply the muscles of the thorax wall.

Arterial Branches of the Abdominal Aorta

Finally, the aorta passes through the diaphragm into the abdominopelvic cavity, where it becomes the abdominal aorta.

• Celiac trunk. The celiac trunk is the first branch of the abdominal aorta and has three branches: the left gastric artery supplies the stomach ; the splenic artery supplies the spleen , and the common hepatic artery supplies the liver.
• Superior mesenteric artery. The unpaired superior mesenteric artery supplies most of the small intestine and the first half of the large intestine or colon .
• Renal arteries. The renal arteries serve the kidneys.
• Gonadal arteries. The gonadal arteries supply the gonads, and they are called ovarian arteries in females while in males they are testicular arteries .
• Lumbar arteries. The lumbar arteries are several pairs of arteries serving the heavy muscles of the abdomen and trunk walls.
• Inferior mesenteric artery. The inferior mesenteric artery is a small, unpaired artery supplying the second half of the large intestine.
• Common iliac arteries. The common iliac arteries are the final branches of the abdominal aorta.

Major veins converge on the venae cavae, which enter the right atrium of the heart.

Veins Draining into the Superior Vena Cava

Veins draining into the superior vena cava are named in a distal-to-proximal direction; that is, in the same direction the blood flows into the superior vena cava.

• Radial and ulnar veins . The radial and ulnar veins are deep veins draining the forearm; they unite to form the deep brachial vein , which drains the arm and empties into the axillary vein in the axillary region.
• Cephalic vein. The cephalic vein provides for the superficial drainage of the lateral aspect of the arm and empties into the axillary vein.
• Basilic vein. The basilic vein is a superficial vein that drains the medial aspect of the arm and empties into the brachial vein proximally.
• Median cubital vein. The basilic and cephalic veins are joined at the anterior aspect of the elbow by the median cubital vein, often chosen as the site for blood removal for the purpose of blood testing.
• Subclavian vein. The subclavian vein receives venous blood from the arm through the axillary vein and from the skin and muscles of the head through the external jugular vein .
• Vertebral vein. The vertebral vein drains the posterior part of the head.
• Internal jugular vein. The internal jugular vein drains the dural sinuses of the brain.
• Brachiocephalic veins. The right and left brachiocephalic veins are large veins that receive venous drainage from the subclavian, vertebral, and internal jugular veins on their respective sides.
• Azygos vein. The azygos vein is a single vein that drains the thorax and enters the superior vena cava just before it joins the heart.

Veins Draining into the Inferior Vena Cava

The inferior vena cava, which is much longer than the superior vena cava, returns blood to the heart from all body regions below the diaphragm.

• Tibial veins. The anterior and posterior tibial veins and the fibular vein drain the leg; the posterior tibial veins become the popliteal vein at the knee and then the femoral vein in the thigh; the femoral vein becomes the external iliac vein as it enters the pelvis.
• Great saphenous veins. The great saphenous veins are the longest veins in the body; they begin at the dorsal venous arch in the foot and travel up the medial aspect of the leg to empty into the femoral vein in the thigh.
• Common iliac vein. Each common iliac vein is formed by the union of the external iliac vein and the internal iliac vein which drains the pelvis.
• Gonadal vein. The right gonadal vein drains the right ovary in females and the right testicles in males; the left gonadal vein empties into the left renal veins superiorly.
• Renal veins. The right and left renal veins drain the kidneys.
• Hepatic portal vein. The hepatic portal vein is a single vein that drains the digestive tract organs and carries this blood through the liver before it enters the systemic circulation.
• Hepatic veins. The hepatic veins drain the liver.

Physiology of the Heart

As the heart beats or contracts, the blood makes continuous round trips- into and out of the heart, through the rest of the body, and then back to the heart- only to be sent out again.

The spontaneous contractions of the cardiac muscle cells occurs in a regular and continuous way, giving rhythm to the heart.

• Cardiac muscle cells. Cardiac muscle cells can and do contract spontaneously and independently, even if all nervous connections are severed.
• Rhythms. Although cardiac muscles can beat independently, the muscle cells in the different areas of the heart have different rhythms.
• Intrinsic conduction system. The intrinsic conduction system, or the nodal system , that is built into the heart tissue sets the basic rhythm.
• Composition. The intrinsic conduction system is composed of a special tissue found nowhere else in the body; it is much like a cross between a muscle and nervous tissue.
• Function. This system causes heart muscle depolarization in only one direction- from the atria to the ventricles; it enforces a contraction rate of approximately 75 beats per minute on the heart, thus the heart beats as a coordinated unit.
• Sinoatrial (SA) node. The SA node has the highest rate of depolarization in the whole system, so it can start the beat and set the pace for the whole heart; thus the term “ pacemaker “.
• Atrial contraction. From the SA node, the impulse spread through the atria to the AV node, and then the atria contract.
•   Ventricular contraction. It then passes through the AV bundle, the bundle branches, and the Purkinje fibers, resulting in a “wringing” contraction of the ventricles that begins at the heart apex and moves toward the atria.
• Ejection. This contraction effectively ejects blood superiorly into the large arteries leaving the heart.

The conduction system occurs systematically through:

• SA node. The depolarization wave is initiated by the sinoatrial node.
• Atrial myocardium. The wave then successively passes through the atrial myocardium.
• Atrioventricular node. The depolarization wave then spreads to the AV node, and then the atria contract.
• AV bundle. It then passes rapidly through the AV bundle.
• Bundle branches and Purkinje fibers. The wave then continues on through the right and left bundle branches, and then to the Purkinje fibers in the ventricular walls, resulting in a contraction that ejects blood, leaving the heart.

In a healthy heart, the atria contract simultaneously, then, as they start to relax, contraction of the ventricles begins.

• Systole. Systole means heart contraction .
• Diastole. Diastole means heart relaxation .
• Cardiac cycle. The term cardiac cycle refers to the events of one complete heartbeat, during which both atria and ventricles contract and then relax.
• Length. The average heart beats approximately 75 times per minute, so the length of the cardiac cycle is normally about 0.8 seconds .
• Mid-to-late diastole. The cycle starts with the heart in complete relaxation ; the pressure in the heart is low, and blood is flowing passively into and through the atria into the ventricles from the pulmonary and systemic circulations; the semilunar valves are closed, and the AV valves are open; then the atria contract and force the blood remaining in their chambers into the ventricles.
• Ventricular systole. Shortly after, the ventricular contraction begins, and the pressure within the ventricles increases rapidly, closing the AV valves; when the intraventricular pressure is higher than the pressure in the large arteries leaving the heart, the semilunar valves are forced open, and blood rushes through them out of the ventricles; the atria are relaxed, and their chambers are again filling with blood.
• Early diastole. At the end of systole, the ventricles relax, the semilunar valves snap shut, and for a moment the ventricles are completely closed chambers; the intraventricular pressure drops and the AV valves are forced open; the ventricles again begin refilling rapidly with blood, completing the cycle.
• First heart sound. The first heart sound, “lub” , is caused by the closing of the AV valves.
•  Second heart sound. The second heart sound, “dub” , occurs when the semilunar valves close at the end of systole.

Cardiac output is the amount of blood pumped out by each side of the heart in one minute. It is the product of the heart rate and the stroke volume .

• Stroke volume. Stroke volume is the volume of blood pumped out by a ventricle with each heartbeat.
• Regulation of stroke volume . According to Starling’s law of the heart , the critical factor controlling stroke volume is how much the cardiac muscle cells are stretched just before they contract; the more they are stretched , the stronger the contraction will be; and anything that increases the volume or speed of venous return also increases stroke volume and force of contraction.
• Factors modifying basic heart rate. The most important external influence on heart rate is the activity of the autonomic nervous system , as well as physical factors (age, gender, exercise, and body temperature).

A fairly good indication of the efficiency of a person’s circulatory system can be obtained by taking arterial blood and blood pressure measurements.

Arterial pulse pressure and blood pressure measurements, along with those of respiratory rate and body temperature, are referred to collectively as vital signs in clinical settings.

• Arterial pulse. The alternating expansion and recoil of an artery that occurs with each beat of the left ventricle create a pressure wave-a pulse- that travels through the entire arterial system.
• Normal pulse rate. Normally, the pulse rate (pressure surges per minute) equals the heart rate, so the pulse averages 70 to 76 beats per minute in a normal resting person.
• Pressure points. There are several clinically important arterial pulse points, and these are the same points that are compressed to stop blood flow into distal tissues during hemorrhage , referred to as pressure points.
• Blood pressure. Blood pressure is the pressure the blood exerts against the inner walls of the blood vessels, and it is the force that keeps blood circulating continuously even between heartbeats.
• Blood pressure gradient. The pressure is highest in the large arteries and continues to drop throughout the systemic and pulmonary pathways, reaching either zero or negative pressure at the venae cavae.
• Measuring blood pressure. Because the heart alternately contracts and relaxes, the off-and-on flow of the blood into the arteries causes the blood pressure to rise and fall during each beat, thus, two arterial blood pressure measurements are usually made: systolic pressure (the pressure in the arteries at the peak of ventricular contraction) and diastolic pressure (the pressure when the ventricles are relaxing).
• Peripheral resistance. Peripheral resistance is the amount of friction the blood encounters as it flows through the blood vessels.
• Neural factors. The parasympathetic division of the autonomic nervous system has little or no effect on blood pressure, but the sympathetic division has the major action of causing vasoconstriction or narrowing of the blood vessels, which increases blood pressure.
• Renal factors. The kidneys play a major role in regulating arterial blood pressure by altering blood volume, so when blood pressure increases beyond normal, the kidneys allow more water to leave the body in the urine , then blood volume decreases which in turn decreases blood pressure.
• Temperature. In general, cold has a vasoconstricting effect, while heat has a vasodilating effect.
• Chemicals. Epinephrine increases both heart rate and blood pressure; nicotine increases blood pressure by causing vasoconstriction; alcohol and histamine cause vasodilation and decreased blood pressure.
• Diet. Although medical opinions tend to change and are at odds from time to time, it is generally believed that a diet low in salt , saturated fats , and cholesterol help to prevent hypertension , or high blood pressure.

The right and left sides of the heart work together in achieving a smooth-flowing blood circulation .

• Entrance to the heart. Blood enters the heart through two large veins, the inferior and superior vena cava, emptying oxygen-poor blood from the body into the right atrium of the heart.
• Atrial contraction. As the atrium contracts, blood flows from the right atrium to the right ventricle through the open tricuspid valve.
• Closure of the tricuspid valve. When the ventricle is full, the tricuspid valve shuts to prevent blood from flowing backward into the atria while the ventricle contracts.
• Ventricle contraction. As the ventricle contracts, blood leaves the heart through the pulmonic valve, into the pulmonary artery, and to the lungs where it is oxygenated.
• Oxygen-rich blood circulates. The pulmonary vein empties oxygen-rich blood from the lungs into the left atrium of the heart.
• Opening of the mitral valve. As the atrium contracts, blood flows from your left atrium into your left ventricle through the open mitral valve.
• Prevention of backflow. When the ventricle is full, the mitral valve shuts. This prevents blood from flowing backward into the atrium while the ventricle contracts.
• Blood flow to the systemic circulation. As the ventricle contracts, blood leaves the heart through the aortic valve, into the aorta, and to the body.

Substances tend to move to and from the body cells according to their concentration gradients.

• Capillary network. Capillaries form an intricate network among the body’s cells such that no substance has to diffuse very far to enter or leave a cell.
• Routes. Basically, substances leaving or entering the blood may take one of four routes across the plasma membranes of the single layer of endothelial cells forming the capillary wall.
• Lipid-soluble substances. As with all cells, substances can diffuse directly through their plasma membranes if the substances are lipid-soluble.
• Lipid-insoluble substances. Certain lipid-insoluble substances may enter or leave the blood and/or pass through the plasma membranes within vesicles, that is, by endocytosis or exocytosis .
• Intercellular clefts. Limited passage of fluid and small solutes is allowed by intercellular clefts (gaps or areas of plasma membrane not joined by tight junctions), so most of our capillaries have intercellular clefts.
• Fenestrated capillaries. Very free passage of small solutes and fluid is allowed by fenestrated capillaries, and these unique capillaries are found where absorption is a priority or where filtration occurs.

The capacity of the heart for work decreases with age. Older peoples’ rate is slower to respond to stress and slower to return to normal after periods of physical activity . Changes in arteries occur frequently which can negatively affect blood supply.

Health promotion teaching can include risk detection and reduction for cardiovascular diseases, blood pressure and cholesterol level monitoring, ideal weight maintenance, and a low- sodium diet.

Craving more insights? Dive into these related materials to enhance your study journey!

• Anatomy and Physiology Nursing Test Banks . This nursing test bank includes questions about Anatomy and Physiology and its related concepts such as: structure and functions of the human body, nursing care management of patients with conditions related to the different body systems.

12 thoughts on “Cardiovascular System Anatomy and Physiology”

very informative!

So great work that could help alot of nurses all over the world, I appreciate it so much.

Nurseslabs have done a very nice work. I wish them good health and strength to continue with the good work.

This excerpt was a magnificent essay of the “Heart Human”.My daughter Arlene Rivera is also an RN and this you wrote about all the heart makes me feel better to know about the knowledge you people possess.Thanks.

In the pathway above, the right subclavian vein is incorrectly labeled as the right pulmonary artery.

For the first time since i leave Nursing school I have now fully understood the cardiovascular system. Keep the good work Matt Vera, you are the best.

Hey Alex, Thank you so much for your kind words! I’m thrilled to hear that our explanations have helped you gain a better understanding of the cardiovascular system. It’s always wonderful to see the impact of educational resources on students and professionals alike.

If there are any more topics or concepts within nursing or healthcare that you’d like to explore or if you have any questions, please don’t hesitate to reach out. Your curiosity and dedication to learning are truly commendable! 🩺🫁📚✨

What is the reference?!

terimakasih atas dedikasinya. super

Enjoy your work, I saw an error in the last image. The right subclavian vein was given the wrong name.

I always found it difficult to find nursing resources since a lot of those that I have seen require payment (and pricey at that). I’m glad I found Nurseslabs. It helps me understand topics that confused me as a student and things I need to refresh since I have been in the profession for a while now.

Easily comprehensible, nice description.

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Cardiopulmonary Resuscitation

Lesson 1. review of the circulatory and respiratory systems.

LESSON 1 Review of the Circulatory and Respiratory Systems.

TEXT ASSIGNMENT Paragraphs 1-1 through 1-6.

LESSON OBJECTIVES After completing this lesson, you should be able to:

1-1. Identify the general functions of the circulatory system.

1-2. Identify the components of the circulatory system and their functions.

1-3. Identify the general functions of the respiratory system.

1-4. Identify the components of the respiratory system and their functions.

SUGGESTION After you have completed the text assignment, work the exercises at the end of this lesson before beginning the next lesson. These exercises will help you achieve the lesson objectives.

1-1. DEFINITIONS

Some of the terms used in this subcourse are defined below.

a. Casualty. The casualty is the person with the medical problem, such as a person who is not breathing. When being treated by medical personnel, the casualty may be referred to as a patient.

b. Rescuer. The rescuer is the person who is assisting the casualty; for example, the person giving mouth-to-mouth resuscitation to a casualty who is not breathing. In this subcourse, you are the rescuer.

c. Airway. The airway consists of the body structures through which air from the atmosphere passes while going to the lungs.

d. Sign. A sign is anything that the rescuer can tell about the casualty’s condition by using his (the rescuer’s) own senses. For example, a rescuer can see the casualty’s chest rise and fall, hear the sounds made by a casualty when he breathes, and feel the casualty’s pulse.

e. Symptom. A symptom is any change from the norm which is felt by the casualty but which cannot be directly or objectively sensed by the rescuer. Examples of symptoms felt by the casualty include chest pain, nausea, and headache. An injury can produce both signs and symptoms. If you bump your leg against a chair, for example, a bruise may develop. The bruise is a sign of the injury since other people can see the bruise. The pain you feel is a symptom since other people cannot feel your pain.

1-2. IMPORTANCE OF THE CIRCULATORY SYSTEM

The human body is composed of cells. The average adult human’s body is made up of around eighty trillion (80,000,000,000,000) living cells. Cells need energy to survive, repair themselves, perform their functions, and reproduce. Cells obtain this energy through cellular respiration; that is, they combine a source of potential energy with oxygen to liberate energy. The sources of potential energy come from the food (carbohydrates, fats, and proteins) that are processed into usable units by the body’s digestive system (stomach, small intestine, liver, pancreas, and so forth).

The oxygen comes from the air that is inhaled by the lungs. Oxygen in the lungs and food in the intestine cannot help the muscles and other cells unless the oxygen and food can be delivered to those cells. Delivering oxygen and food to the cells is the function of the blood in the body’s circulatory system. The circulatory system also takes waste products (by-products of cellular respiration) from the cells and delivers them to organs (lungs and kidneys) where the wastes can be expelled from the body.

1-3. THE CIRCULATORY SYSTEM

The circulatory system consists of the heart, blood vessels, and blood. The circulatory system brings oxygen and nutrients to the body’s cells and carries away waste products. The circulatory system is also called the cardiovascular system (“cardio-” means heart; “-vascular” means vessels.)

a. Heart. The heart (figure 1-1) is a strong, muscular organ that, by its rhythmic contractions, acts as a force pump maintaining blood circulation. The heart is about the size of a fist and is located in the lower left-central part of the chest cavity.

(1) Layers. The heart consists of three layers.

(a) The myocardium is the middle layer. It is composed of the actual heart muscles. (“Myo-” means muscle; “cardium” means heart.)

(b) The pericardium is the outer layer. It is a double-walled sac that surrounds the heart muscles. (“Peri-” means around.)

(c) The endocardium is the inner layer. It forms the inner lining of the four chambers. (“Endo-” means within.)

(2) Chambers. The heart can be described as being two pumps. Each side (right half and left half) of the heart has a receiving chamber for the blood (the atrium) and a pumping chamber (the ventricle). The two halves of the heart are separated by a wall-like structure called the interventricular septum.

NOTE: The plural of atrium is atria.

(3) Sinoatrial node. The sinoatrial (SA) node is a small bundle of nerve tissue located at the junction of the superior vena cava and the right atrium. The sinoatrial node is a natural pacemaker that produces an electrical stimulus. This electrical stimulus causes the muscles of the ventricles to contract and pump blood.

b. Blood Vessels. The blood vessels are firm, elastic, muscular tubes that carry the blood away from the heart and back to the heart again.

(1) Blood circulation systems. Since the heart is divided into two parts (the right half consisting of the right atrium and the right ventricle and the left half consisting of the left atrium and left ventricle), it is not surprising to find that there are actually two blood circulatory systems–the systemic and the pulmonary.

(a) Systemic. The systemic (general) circulatory system is the larger of the two systems. It takes the blood pumped by the left ventricle to all parts of the body and returns the blood to the right atrium. The oxygen content of the blood is high when it leaves the heart through the left ventricle and is low when it returns to the right atrium.

(b) Pulmonary. The pulmonary circulatory system takes the blood pumped by the right ventricle to the lungs and returns the blood to the left atrium. The oxygen content of the blood is low when it leaves the heart through the right ventricle and high when it returns to the left atrium.

(2) Types of blood vessels. Both the systemic and the pulmonary circulatory systems are composed of three major types of blood vessels–arteries, capillaries, and veins.

(a) Arteries. The arteries carry blood pumped by the ventricles away from the heart. The arteries of the systemic circulatory system carry oxygenated (oxygen rich) blood to body tissues. The pulmonary arteries carry deoxygenated (oxygen-poor) blood to the lungs. Arteries have the capacity to constrict and dilate. This constricting and dilating helps to regulate the blood pressure.

(b) Capillaries. Originally, the arteries are large blood vessels. Soon, however, they divide into smaller branches. These branches then divide again and again. With each division, the blood vessels become smaller and smaller. Finally, the blood vessels are so small that only one red blood cell can pass through at a time. When they reach this size, the blood vessels are called capillaries. When a red blood cell enters the capillaries, it is free to perform its primary functions.

In the pulmonary system, red blood cells give up carbon dioxide to the lungs and pick up oxygen. In the systemic system, red blood cells give oxygen and nutrients to the cells and pick up carbon dioxide and other waste products.

(c) Veins. Capillaries join together to form larger blood vessels, which then combine to form even larger blood vessels. These blood vessels are called veins. Veins carry the blood back to the heart. The veins of the systemic system carry oxygen-poor blood to the right atrium. The veins of the pulmonary system carry oxygen-rich blood to the left atrium. The veins are not as thick as the arteries, and they will collapse when severed. Many veins have valves, which keep blood from flowing backward (away from the heart). The term “vena” denotes a vein.

c. Blood. Blood is a viscous (thick), reddish fluid. When the blood is oxygenated (oxygen-rich), it is bright red. When the blood is low in oxygen content, it is a darker red. When the darker color is seen through a layer of skin tissue, it appears to be bluish. Blood is composed of fluid and solids.

(1) Plasma. The liquid part of the blood is called plasma. It is straw-colored (pale yellow) and carries the solid components of the blood such as erythrocytes, leukocytes, and thrombocytes.

(2) Erythrocytes. Erythrocytes (also called red blood cells or RBC) transport oxygen from the lungs and nutrients from the small intestine to the cells of the body. They also transport carbon dioxide and other waste materials from the body’s cells to the lungs and kidneys where the waste products are removed and expelled.

(3) Leukocytes. Leukocytes (also called white blood cells or WBC) assist in the body’s defense against disease by attacking and destroying bacteria and other foreign particles in the blood and body tissues.

(4) Thrombocytes. Thrombocytes (also called platelets) help to stop bleeding from a damaged blood vessel. Although thrombocytes normally show no tendency to coagulate (clot) in the blood, they change character when they approach a cut or tear in a blood vessel. The thrombocytes then combine to form a soft clot where the vessel wall is broken. This clot soon hardens to form a plug to stop the loss of blood.

1-4. BLOOD FLOW

In order to summarize how blood flows in the body, let’s take a trip through the body’s circulatory system (figure 1-2). We will enter the system at the vena cava.

a. Vena Cava. There are two major blood veins, which empty into the right atrium. The superior vena cava carries oxygen-poor blood coming from the head, arms, and chest. The inferior vena cava returns oxygen-poor blood from the lower trunk and legs.

b. Right Atrium. The right atrium receives blood from the superior vena cava and the inferior vena cava. When the right ventricle relaxes (that is, after it has contracted and pumped blood), blood flows from the right atrium into the right ventricle through the tricuspid valve. The tricuspid valve is formed so that blood cannot flow back into the right atrium when the right ventricle contracts.

c. Right Ventricle. When the right ventricle is filled with blood, it receives an impulse from the sinoatrial node. This impulse causes the muscles of the right ventricle to contract. This contraction causes the inside of the ventricle (the space where the blood is) to become smaller. The increased pressure forces blood out of the ventricle and into the pulmonary artery. The pulmonary valve located at the beginning of the pulmonary artery keeps blood from flowing back into the right ventricle when the ventricle relaxes and returns to its normal size.

d. Lungs (Pulmonary System). The pulmonary artery divides into two arteries. One artery travels to the right lung while the other artery travels to the left lung. The arteries divide until they reach the capillary stage. The capillaries surround the alveoli (air sacs) of the lungs. There the oxygen-poor blood gets rid of carbon dioxide and picks up oxygen from the air in the alveolus. The blood, now high in oxygen content, then returns to the left atrium through the pulmonary veins.

e. Left Atrium. The left atrium receives blood from the lungs through two pulmonary veins. When the left ventricle relaxes after having contracted, the blood flows from the left atrium into the left ventricle through the mitral valve. The mitral valve keeps blood from flowing back into the left atrium when the left ventricle contracts.

f. Left Ventricle. After the left ventricle is filled with oxygen-rich blood, it receives an impulse from the sinoatrial node, which causes it to contract and pump blood into the large artery call the aorta. When the blood enters the aorta, it passes through the aortic valve. This valve keeps the blood from flowing back into the heart once the left ventricle relaxes.

g. Body (Systemic System).

(1) Some arteries branch off the aorta to provide the brain, upper body, and heart with blood. Blood returns to the heart from these areas through the superior vena cava.

NOTE: If blood flow to the brain stops and is not restored (either the casualty’s heart starts beating on its own or cardiopulmonary resuscitation is administered), the brain will begin to die in six to ten minutes.

(2) The aorta turns down and divides into smaller arteries which go to the lower parts of the body. Some of the blood picks up fluids and nutrients from the intestines. Some of the blood passes through the liver and kidneys which remove bacteria and other unwanted substances from the blood. The blood returns to the heart from these areas through the inferior vena cava.

1-5. THE RESPIRATORY SYSTEM

The respiratory system consists of two lungs and the respiratory tract that carries air to and from the lungs (figure 1-3). When a person inhales, the air enters the nose or mouth, travels down the trachea, and into the two bronchi. Each bronchus divides into smaller and smaller air tubes. Finally, the air reaches the alveoli (air sacs). The red blood cells in the capillaries surrounding the alveoli absorb oxygen from the air and give off carbon dioxide, which passes into the alveoli.

When a person exhales, the air travels from the alveoli through the air tubes, up the trachea, and out the nose or mouth. Of course, not all of the air inhaled reaches the alveoli nor is all of the oxygen removed from the air in the alveoli. The average adult takes in about 500 milliliters (ml) of air each time he inhales and he exhales the same amount. Even after the person exhales, the lungs still contain about 2300 ml of air. The anatomy (structures) and the physiology (functions) of the respiratory system are briefly discussed below.

a. Nose. The nose is composed of two nostrils (openings) and two nasal cavities (air chambers above the roof of the mouth and below the cranium). A structure called the nasal septum separates the right nostril and nasal cavity from the left nostril and nasal cavity. The nose warms, moistens, and filters the inhaled air. Special nerve endings in the upper part of the nasal cavities provide the sense of smell.

b. Pharynx. The pharynx is a part of the throat that is part of both the respiratory system and the digestive system. The pharynx is divided into three parts. The nasopharynx (upper part) connects with the nasal chambers. The oropharynx (middle part) connects with the oral cavity (mouth). The laryngopharynx (lower part) connects with the larynx (respiratory system) and the esophagus (digestive system).

c. Epiglottis. The epiglottis is a flap that covers the entrance to the larynx when a person swallows. This prevents food from entering the larynx instead of the esophagus. When a person inhales, the entrance to the larynx is not covered and air enters the larynx. If a foreign object enters the airway, it can block the airway and cause breathing to stop.

d. Larynx. The larynx is a box-like structure composed of cartilage, ligaments, and muscles that sits on top of the trachea. The larynx contains the vocal cords, which produce the voice; therefore, it is sometimes called the voice box. It is also called the Adam’s apple because of the bulge it causes in the throat.

e. Trachea. The trachea (windpipe) is a tube composed of horseshoe-shaped rings of cartilage. Cilia (hair-like projections) on the inner lining of the trachea help to filter air as it passes through the trachea to the bronchi.

f. Bronchi. The bronchi are two tube-like structures at the base of the trachea. One bronchus leads toward the right lung; the other bronchus leads toward the left lung. Like the trachea, the bronchi are composed of cartilaginous rings and are lined with a mucous membrane.

g. Bronchioli. The bronchi divide and subdivide until they become small air tubes one millimeter or less in diameter call bronchioli. The bronchioli continue to subdivide until they become very small tubes ending in alveoli.

h. Alveoli. Alveoli are tiny, grape-like clusters of microscopic air sacs. Air enters the alveoli from the bronchioli. The wall of an alveolus is one cell layer thick. The alveolus is surrounded by equally thin capillaries. Oxygen (O2) molecules from the air inside the alveolus travel through the alveolus and capillary walls to the blood within the capillary. The hemoglobin in the red blood cells captures the oxygen molecules and release carbon dioxide (CO2) molecules. The carbon dioxide molecules and some water molecules travel from the blood, through the walls, and into the alveoli.

i. Lungs. The alveoli, bronchioli, and associated blood vessels make up two cone-like organs called lungs. The lungs are broad at their base (which rests on the diaphragm) and narrow at the apex (top). Each lung is surrounded by pleural membranes that prevent friction when the lung expands and contracts. The right lung is divided into three lobes; the left lung is divided into two lobes. The left lung is smaller than the right lung because the heart takes up space on the left side of the chest cavity.

1-6. MECHANICS OF BREATHING

Breathing refers to the process of moving air into and out of the lungs. The process is usually performed automatically (without conscious thought) by the respiratory control center located in the medulla oblongata of the brain stem. The normal range of breathing rates (one cycle consists of one inspiration and one exhalation) in an adult is 12 to 20 breaths per minute. Regular, easy breathing is referred to as eupnea. Difficulty in breathing is referred to as dyspnea.

a. Inhalation. During the inhalation (inspiration) phase of breathing, the diaphragm and the intercostal muscles contract. When the diaphragm muscle (located at the base of the lungs) contracts, it is pulled downward toward the abdomen. This flattening of the diaphragm enlarges the chest cavity. When the intercostal muscles (located between the ribs) contract, they lift the rib cage up and out (chest rises). This also enlarges the chest cavity. This expansion of the chest cavity causes the air pressure in the alveoli to decrease. Air from the outside environment rushes in through the nose or mouth to equalize the pressure.

b. Exhalation. During the exhalation (expiration) phase of breathing, the diaphragm and the intercostal muscles relax. When the diaphragm muscle relaxes, it resumes its dome-like shape (moves upward). When the intercostal muscles relax, they let the rib cage return to its original position (moves down and inward). Both of these actions cause the air pressure in the alveoli to increase and force air out of the lungs, through the airways, and out the nose or mouth.

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Circulatory system.

Your heart pumps blood to every nook and cranny in your body. The average heart beats approximately 72 times each minute. It weighs nine to eleven ounces in females and just an ounce or two more in males. In your lifetime, your heart will beat approximately 2.5 billion times.

Many children are aware of their heart. They can feel it beating in their chest. They can feel it race after recess on the playground and they can feel it jump when they're startled. This is the perfect place to start a unit on the circulatory system.

Teaching the Circulatory System to Your Young Students

While the heart is the center of the circulatory system, it's not alone. You have arteries, veins and of course, the blood that courses through them. Teaching the circulatory system can be fun. Watching children become more aware of their bodies and engaged in how it works can be an enriching experience. The circulatory system can be a single unit or it can be part of a larger unit on health and/or the human body.

Teacher Planet offers a variety of teaching resources to help make teaching the circulatory system simple and enjoyable. You'll find lesson plans, activities, worksheets and additional teaching resources all designed to help you bring the circulatory system alive in your classroom.