CK-12 Life Science
Page 46
Two Blood Circulation Systems
The blood is pumped around in two large “loops” within the body. One loop moves blood around the body—to the head, limbs, and internal organs. The other loop moves blood to and from the lungs where carbon dioxide is released and oxygen is picked up by the blood. A simple version of these two “loops” is shown in Figure below. Systemic circulation is the portion of the cardiovascular system which carries oxygen-rich blood away from the heart, to the body, and returns oxygen-poor blood back to the heart. The pulmonary circulation is the part of the cardiovascular system which carries oxygen-poor blood away from the heart to the lungs, and returns oxygen-rich blood back to the heart. This oxygen-rich blood then gets pumped around the body in the systemic circulation. These two circulations will be further discussed in Lesson 2.
Figure 18.6
The double circulatory system; blood in one circuit has to go through the heart to enter the other circuit.
The Lymphatic System
The lymphatic system is a network of vessels and tissues that carry a clear fluid called lymph. The lymphatic system, shown in Figure below, extends all around the body. Lymph tissues include lymph nodes, lymph ducts, and lymph vessels. Lymph vessels are tube-shaped just like blood vessels. The lymphatic system works with the cardiovascular system to return body fluids to the blood. The lymphatic system and the cardiovascular system are often called the body’s two circulatory systems.
Figure 18.7
The lymphatic system helps return fluid that leaks from the blood vessels back to the cardiovascular system.
The lymphatic system has two main jobs:
Removing excess fluids from body tissues.
Making certain types of white blood cells.
Role of the Lymphatic System in Circulation
The lymphatic system collects and returns fluid to the cardiovascular system. A small amount of fluid leaks from the blood vessels when blood is pumped around your body. This fluid collects in the spaces between cells and tissues. Some of the fluid returns to the cardiovascular system, and the rest is collected by the lymph vessels of the lymphatic system, which are shown in Figure below.
The fluid that collects in the lymph vessels is called lymph. The lymphatic system then returns the lymph to the cardiovascular system. Unlike the blood system, the lymphatic system is not closed and has no central pump. Lymph moves slowly in lymph vessels. It is moved along in the lymph vessels by the squeezing action of smooth muscles and skeletal muscles.
Figure 18.8
Lymph capillaries collect fluid that leaks out from blood capillaries.
Role of the Lymphatic System in the Body’s Defenses
The lymphatic system also plays an important role in the immune system. The lymphatic system makes certain blood cells, and also filters, or traps foreign particles. The lymphatic system contains white blood cells to protect the body from infection.
Organs of the Lymphatic System
Along with the lymph vessels, lymph ducts, and lymph nodes, the lymphatic system also includes many organs. The tonsils, thymus, and spleen, which are shown Figure above, each have a role in the defense of the body against infection. Many of these organs are also part of the immune system.
Tonsils
The tonsils are areas of lymphoid tissue on either side of the throat. The term tonsils refers most often to the tonsils in the back of the throat as shown in Figure below. But, there are tonsils in the nasal cavity and behind the tongue too. Like other organs of the lymphatic system, the tonsils are also part of the immune system. The immune system helps protect the body against infection. The tonsils are believed to help fight off nose and throat, and other upper respiratory tract infections such as colds. Tonsils tend to reach their largest size near puberty, after which they get smaller. Tonsillitis is an infection of the tonsils that can cause a sore throat and fever.
Figure 18.9
The term refers most often to the tonsils in the back of the throat, but there are tonsils in the nasal cavity and behind the tongue too.
Bone Marrow
Bone marrow is the tissue found in the middle of bones. The marrow in the large bones of adults makes new blood cells. Certain white blood cells, called T-cells, are made in the bone marrow and move to the thymus to mature. Other white blood cells called B-cells, move from the bone marrow to the spleen after they have matured.
Thymus
The thymus is found in the upper chest. Chemicals made by the thymus help the production of certain infection-fighting cells. The thymus is where certain white blood cells called lymphocytes mature. These cells move from the bone marrow to the thymus to finish growing. The thymus grows to its largest size near puberty, and gets smaller as a person ages. If a person’s thymus is surgically removed or damaged by disease while they are young, the person will be very prone to infections.
Spleen
The spleen is in the abdomen, as shown in Figure below. In an area of the spleen called red pulp, materials are filtered from the blood, including old and dead red blood cells. The spleen also makes red blood cells. Areas called white pulp help fight infections by making white blood cells. If a person’s spleen is surgically removed, or does not work properly, the person is prone to certain infections.
You can learn more about the roles of the lymphatic system and white blood cells in the Diseases and the Body’s Defenses chapter.
Structures and Functions of the Cardiovascular and Lymphatic Systems System Structure (organs and tissues) Function
Lymphatic Lymph vessels Transport fluid (lymph) from between body cells back to blood
Lymph nodes Trap invading microbes, foreign particles, cancerous cells
Spleen, tonsils, and adenoids Trap invading microbes and foreign particles
Thymus Site of white blood cell (lymphocyte)maturation
Cardiovascular Blood vessels Transport blood around the body
Blood Transport of oxygen and nutrients; also carries white blood cells to sites of infection and inflammation
Heart Pumps blood around the body
Figure 18.10
In the spleen, the white pulp makes white blood cells, while the red pulp acts like a filter and removes dead and dying cells from the blood.
Lesson Summary
The cardiovascular system consists of the heart, the blood vessels, and the blood. There are three main types of blood vessels in the body; arteries, veins, and capillaries.
The systemic circulation is the portion of the cardiovascular system, which carries oxygen-rich blood away from the heart, to the body, and returns oxygen-poor blood back to the heart. The pulmonary circulation is the part of the cardiovascular system, which carries oxygen-poor blood away from the heart to the lungs, and returns oxygen-rich blood back to the heart.
Lymph tissues include lymph nodes, lymph ducts, and lymph vessels. Organs of the lymphatic system include the tonsils, thymus, and spleen. The lymphatic system works with the cardiovascular system to return body fluids to the blood. Taken together the two are often called the body’s circulatory systems.
Review Questions
Identify the main structures of the cardiovascular system.
Identify three types of blood vessels found in the body.
Which blood vessels transport blood away from the heart?
What are the smallest blood vessels in the body called?
What blood vessels bring blood back to the heart?
Where does blood in the pulmonary system go after it leaves the heart?
Where does blood in the systemic circulation go after it leaves the heart?
What does blood that leaves the heart in the systemic circulation have that body cells need?
Identify the main tissues and organs of the lymphatic system.
Outline how the cardiovascular and the lymphatic systems work together.
What is lymph, and where does it come from?
Name one function of tonsils.
What might happen if a
person did not have a spleen?
Name the two circulatory systems of the body.
Further Reading / Supplemental Links
http://en.wikipedia.org/wiki/Heart
Vocabulary
arteries
Blood vessels that carry blood away from the heart.
blood
A body fluid that is a type of connective tissue; moves oxygen and other compounds throughout the body.
capillaries
The smallest and narrowest blood vessels in the body.
cardiovascular system
The organ system that is made up of the heart, the blood vessels, and the blood.
lymphatic system
A network of vessels and tissues that carry a clear fluid called lymph; includes lymph nodes, lymph ducts, and lymph vessels.
plasma
The straw-colored fluid in blood.
pulmonary circulation
The part of the cardiovascular system which carries oxygen-poor blood away from the heart to the lungs, and returns oxygen-rich blood back to the heart.
systemic circulation
The portion of the cardiovascular system which carries oxygen-rich blood away from the heart to the body, and returns oxygen-poor blood back to the heart.
veins
Blood vessels that carry blood back to the heart.
Points to Consider
Consider how the structure of the heart helps to maintain the systemic and pulmonary circulations.
Consider how problems with the coronary circulation can affect the entire body.
How would a hole in the heart muscle that allowed blood in the two ventricles to mix affect the rest of the body?
Lesson 18.2: Heart and Blood Vessels
Lesson Objectives
Describe the structure of the heart.
Outline how blood moves through the heart.
Describe the importance of valves in the heart.
Describe the coronary circulation.
Check Your Understanding
What is the role of the cardiovascular system?
What is the main function of the heart?
Introduction
The heart is divided into four chambers, the left and right atria and the left and right ventricles. An atrium is one of the two small, thin-walled chambers on the top of the heart that blood first enters. A ventricle is one of the two muscular V-shaped chambers that pump blood out of the heart. The four chambers of the heart are shown in Figure below. The atria receive the blood, and the ventricles pump the blood out of the heart. Each of the four chambers of the heart have a specific job, these are:
The right atrium receives oxygen-poor blood from the body.
The right ventricle pumps oxygen-poor blood toward the lungs.
The left atrium receives oxygen-rich blood from the lungs.
The left ventricle pumps oxygen-rich blood out of the heart to the rest of the body.
The heart is usually found in the left to middle of the chest with the largest part of the heart slightly to the left. The heart is usually felt to be on the left side because the left ventricle is bigger and stronger than the right ventricle. The heart is surrounded by the lungs.
Figure 18.11
The atria receive blood and the ventricles pump blood out of the heart.
Blood Flow Through the Heart
Blood flows through the heart in two separate loops; you could think of them as a “left side loop” and a “right side loop”. The right side and left side of the heart refer to your heart as it sits inside your chest. Its left side is your left side and, its right side is your right side.
The right side of the heart collects deoxygenated blood from the body and pumps it into the lungs where it releases carbon dioxide and picks up oxygen. The left-side carries the oxygenated blood back from the lungs, into the left side of the heart which then pumps the oxygenated blood throughout the rest of the body.
The Heartbeat
To move blood through the heart, the cardiac muscle needs to contract in an organized way. Blood first enters the atria, as shown in Figure below. When the atria contract blood is pushed into the ventricles. After the ventricles fill with blood, they contract and blood is pushed out of the heart. Valves in the heart keep the blood flowing in one direction. You can see some of the valves in Figure below. The valves do this by opening and closing in one direction only. Blood moves only forward through the heart. The valves stop the blood from flowing backward. There are four valves of the heart:
The two atrioventricular (AV) valves stop blood from moving from the ventricles to the atria.
The two semilunar (SL) valves are found in the arteries leaving the heart, and they prevent blood flowing back from the arteries into the ventricles.
The “lub-dub” sound of the heartbeat is caused by the closing of the AV valves (lub), and SL valves (dub), after blood has passed through them.
Figure 18.12
Blood flows in only one direction in the heart; blood enters the atria, contracting and pushing blood into the ventricles, the atria relax, the ventricles fill with blood, contract, and push blood around the body.
Control of the Heartbeat
The heart is a made up of cardiac muscle cells. Cardiac cells are able to contract by themselves. They do not need help from the nervous system. This is different than skeletal muscle, which needs messages from nerve to contract. But the contractions of cardiac muscle still need to be coordinated to make sure the cells contract as a group.
The contraction rate of cardiac muscle is controlled by two small groups of cardiac muscle cells called the sinoatrial (SA) and atrioventricular (AV) nodes. The SA node is found in the wall of the right atrium. It starts the contraction of muscle cells in the atria. The contracting cells send electrical messages called impulses to other muscle cells. The impulses then reach the AV node. The AV node is found in the lower part of the right atrium. The AV node conducts the impulses that come from the SA node through the atria to the ventricles. The impulses then spread around the ventricles and they contract.
The frequency of the heart's contractions, called the heart rate, can be changed by nervous or hormonal signals. Activities such as exercise or getting frightened can make the heart rate increase. After the exercise is over, or the fright has passed, the heart rate returns to normal.
Blood Circulation and Blood Vessels
There are actually two separate circulation systems within the heart. Both of these together make up the complete circulatory system of humans and other animals. Neither system can work alone. These are the pulmonary circulation and the systemic circulation. The human heart is made up of two separate pumps, the right side which pumps deoxygenated blood into the pulmonary circulation, and the left side which pumps oxygenated blood into the systemic circulation. Blood in one circuit has to go through the heart to enter the other circuit.
The blood vessels are an important part of the cardiovascular system. They connect the heart (the pump), to every cell in the body. Arteries carry blood away from the heart, while veins return blood to the heart. The main arteries and veins of the heart are shown in Figure below.
Figure 18.13
The right side of the heart pumps deoxygenated blood into the pulmonary circulation; the left side pumps oxygenated blood into the systemic circulation.
The veins that return oxygen- poor blood to the heart are the superior vena cava and the inferior vena cava. The pulmonary veins return oxygen-rich blood to the heart. The pulmonary veins are the only veins that carry oxygen-rich blood all other veins carry oxygen-poor blood.
The pulmonary arteries carry oxygen-poor blood away from the heart to the lungs. These are the only arteries that carry oxygen-poor blood. The aorta is the largest artery in the body. It carries oxygen-rich blood away from the heart. Further away from the heart, the aorta branches into smaller arteries.
Pulmonary Circulation
The pulmonary circulation is the part of the cardiovascular system wh
ich carries oxygen-poor blood away from the heart and brings it to the lungs. Oxygen-poor blood returns to the heart from the body and leaves the right ventricle through the pulmonary arteries, which carry the blood to each lung. Once at the lungs, the red blood cells release carbon dioxide and pick up oxygen during respiration. The oxygen-rich blood then leaves the lungs through the pulmonary veins which return it to the left side of the heart. This completes the pulmonary cycle.
The oxygenated blood is then pumped to the body through the systemic circulation before returning again to the pulmonary circulation.
Systemic Circulation
The systemic circulation is the part of the cardiovascular system which carries oxygen-rich blood away from the heart, to the body, and returns oxygen-poor blood back to the heart. Oxygen-rich blood leaves the left ventricle through the aorta, from where it goes to the body's organs and tissues. The blood vessels that supply oxygen and nutrients to organs and tissues are much smaller than the vessels that leave the heart. Recall that capillaries are the smallest blood vessels. The tissues and organs absorb the oxygen, through the capillaries. Oxygen-poor blood is collected from the tissues and organs by tiny veins, which then flow into bigger veins. The inferior and superior venae cavae, are the large veins that return oxygen-poor blood to the right side of the heart. This completes the systemic cycle. The blood releases carbon dioxide and gets more oxygen in the pulmonary circulation before returning to the systemic circulation.