Chapter 18
Circulation and Respiration
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Life Science
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1. Circulatory System – The circulatory system circulates blood throughout the body, delivers
essentials substances to the cells, and removes wastes. It is often called the cardiovascular
system. It consists of the heart, blood vessels, and blood. (386)
2. Heart – The heart is a cone shaped muscle that pumps 2 million liters of blood per year. It
consists of cardiac muscle tissue. The right side of the heart collects oxygen-poor blood from
the body and sends it to the lungs. There it gets rid of carbon dioxide waste and picks up
oxygen. The left side of the heart collects oxygen rich blood from the lungs and sends it out to
all the parts of the body. The heart has four chambers. The upper chambers collect blood and
are called atria. The lower chambers send blood out and are called ventricles. There are oneway valves between the chambers. Valves are flaps of tissue that prevent the backward flow of
blood. The upper chambers of the heart beat first, sending the blood down through a valve to
the ventricles. Then the ventricles beat sending blood out to the lungs and the body. This
“double beat” creates a “lub-dub” sound when you listen to your heart.(387)
3. Arteries – Arteries are blood vessels that carry blood away from the heart. With only one
exception (the pulmonary artery) all arteries carry oxygen rich blood. Arteries have three
layers to withstand the pressure from the heart beat. (388)
4. Capillaries – Arteries lead to capillaries, which are the smallest blood vessels (they are
microscopic). This is where exchange of materials with the cells takes place. The capillary
walls are only one cell thick. Oxygen and other materials are constantly diffusing through the
capillary walls. (388)
5. Veins – Capillaries pick up carbon dioxide and water waste. The blood vessels that carry this
oxygen poor blood back to the heart are called veins. With one exception (the pulmonary vein)
all veins carry oxygen-poor blood. Veins have three layers but are thinner than arteries
because they do not receive blood directly from the heart. The also have one-way valves in
them to keep blood from flowing backwards. Muscles in the legs and arms help move blood
through the veins each time they contract.(388)
6. Blood – A circulating tissue of red blood cells, white blood cells, particles of platelets, and the
fluid plasma is called blood. You have about five liters of blood. The main function of the
blood is to supply oxygen and nutrients to the tissues, and remove wastes from the cells
(carbon dioxide). Blood also transports water, hormones, enzymes, and immune cells. (389)
7. Plasma – The fluid part of the blood is a straw-colored liquid called plasma. Plasma makes up
55% of the blood. It contains water, dissolved nutrients, sugars, and proteins. (389)
8. Red Blood Cells – Red blood cells carry oxygen to your cells. They make up about 45% of
the blood. They are red because they contain a red substance called hemoglobin. Hemoglobin
carries oxygen and consists mainly of iron. Note: Red blood cells have no nucleus and do not
reproduce. They are manufactured in the bone marrow. (389)
9. White Blood Cells – Cells that destroy invaders are called white blood cells. There is
only a small fraction of these in the blood. They are part of your immune system. They help
fight invaders by destroying things like bacteria and viruses. Some also produce antibodies
and eat up dead cells.
10. Platelets – Small particles in your blood that help the blood clot to “plug” a cut are called
platelets. They also only make up a small fraction of your blood. (389)
11. Aorta – Oxygenated blood is carried away and leaves the heart traveling out to the body
through the aorta. This is the largest artery in the body. (390)
12. Atherosclerosis – Eating foods high in cholesterol & saturated fats can cause a build up of fatty
deposits on the insides of the artery walls that clog the arteries. This can eventually lead to heart
attacks, hypertension, and strokes of the brain. This disease is called atherosclerosis.
13. Blood Pressure & Hypertension - Contractions of the heart generate blood pressure. Blood
pressure is a measurement of the force of blood pushing against the artery walls. Systolic
pressure is the maximum force exerted when the heart contracts (beats). Diastolic pressure
is the force exerted when the heart is relaxed (between beats). It is measured in millimeters of
mercury. Normal pressure is 120/80 mm Hg. High blood pressure causes a disorder called
hypertension. High blood pressure is often caused by clogged arteries. (390)
14. Respiration & Respiratory System – Respiration is the process in which the body takes in
oxygen and gets rid of carbon dioxide and excess water. The respiratory system consists of
the lungs and the passageways that lead to the lungs. These include: 1) The nose and mouth.
2) The pharynx (throat). 3) The larynx, that also contains your voice box. 4) The trachea,
also called the windpipe. 4) The trachea branches into two tubes called bronchi, one leading
to each lung. 5) Each bronchus branches into many tinier tubes called bronchioles. 6) The
bronchioles end in tiny bundles of air sacs called alveoli. They are surrounded by capillaries
and this is where the exchange of gases (oxygen and carbon dioxide) takes place. (391)
15. Diaphragm – The sheet of muscle that works the respiratory system and helps draw air into
your lungs is called the diaphragm. When the diaphragm contracts and pulls downward the
chest cavity increases (gets bigger) and you breath in (inhale). When the diaphragm relaxes
and folds upward, pushing against the lungs, the chest cavity decreases (gets smaller), and
you breath out (exhale). Muscles between the ribs also help in this process. (391)
16. Blood Flow – All blood, except from the lungs, enters the right side of the heart (right
atrium) through two veins. The superior vena cava brings blood in from the upper part of
the body. The inferior vena cava brings blood in from the lower part of the body. When the
right atrium of the heart contracts blood moves through a valve into the right ventricle.
Valves in the heart keep blood from flowing backwards. When the right ventricle
contracts blood moves through a valve into the pulmonary artery. This splits and takes blood
to each lung so that oxygen can be picked up and carbon dioxide removed. The oxygen rich
blood is carried back to the heart through the pulmonary veins. It is dumped into the left
atrium. When it contracts blood goes through a valve into the left ventricle. When the left
ventricle contracts blood moves through a valve into the aorta, which sends the blood out to
the body. (392)
17. Pulmonary Circulation – Circulation from the heart, out to the lungs, and back to the heart is
called pulmonary circulation. The blood travels to the lungs through the pulmonary artery, and
oxygen-rich blood comes back to the heart through the pulmonary veins.
18. Systemic Circulation – Circulation of oxygen-rich blood from the heart, out to all of the tissues
and organs of the body (except the heart & lungs), and back to the heart is called systemic
circulation.
19. Coronary Circulation – The flow of blood to the tissues of the heart through the heart’s own
blood vessels is called coronary circulation.
20. Lymphatic System & Lymph – Some of the material in the blood is continually leaking out of
the capillaries and into the surrounding tissues of the body. The system in your body that collects
this tissue fluid, and places it back in the bloodstream is called the lymphatic system. Once the
tissue fluid is collected in the tubes of the of the lymphatic system it is called lymph. The
lymphatic system also helps defend the body against pathogens.
21. Lymph Vessels & Lymph Capillaries – The lymph is collected in tubes called lymph vessels
and lymph capillaries. There is no pump to move the lymph along these vessels. Lymph flows
through these vessels by the contraction of surrounding skeletal muscles, and smooth muscle.
Like veins, lymph vessels also have one-way valves that keep lymph from flowing backwards.
Lymph moves into the lymph vessels and capillaries by simple absorption and diffusion.
22. Lymphocytes – Special white blood cells that are found in the lymph are called lymphocytes.
Your body reacts to infection by increasing the number of these white blood cells.
23. Lymph Nodes – Before lymph enters back into the bloodstream it passes through bean-shaped
structures called lymph nodes. The lymph nodes filter out any microorganisms and foreign
material that may have been engulfed by the lymphocytes.
24. Tonsils, Spleen, & Thymus Gland - Major organs of the lymphatic system include the tonsils
in the back of the throat, the spleen behind the upper left part of the stomach, & the thymus gland
behind the sternum. The tonsils protect the mouth & throat from pathogens. The spleen, the largest
of the lymph organs, filters the blood of worn out & damaged blood cells. Special cells in the spleen
also destroy bacteria & other invaders. The thymus gland produces lymphocytes to fight infection.