CK-12 Biology I - Honors
Page 109
High cholesterol levels: High amounts of low density lipids (LDLs) in the blood, also called "bad cholesterol", are a significant risk factor.
Obesity: Being obese, especially if the fat is deposited mostly in the torso, rather than the hips and thighs, increases risk significantly.
High blood pressure: Hypertension can cause atherosclerosis.
Lack of physical activity: Aerobic activities, including walking and vacuuming, that are done for 60 minutes a day, five days a week, help keep the heart healthy.
Poor eating habits: Eating mostly foods that are nutrient poor (do not have many nutrients other than fat or carbohydrate) leads to high cholesterol levels and weight gain, among other things.
Although there are uncontrollable risk factors involved in CVD, a person whose family has a history of CVD is not destined to develop heart disease. There are many things such a person can do to help prevent CVD, even when predisposed to a disease. A person who is physically active every day, eats healthfully, and avoids tobacco can lower their chances of developing the disease.
Although men have a higher rate of cardiovascular disease than women, it is also the number one health problem for women in industrialized countries. After menopause, the risk for women is almost equal to that of men.
Cardiovascular Disease Awareness
Cardiovascular diseases are called "lifestyle diseases" because they are caused mostly by everyday choices that people make, such as what to eat for dinner, or what to do during their free time. For example, watching TV with your dog does not involve much moving around so it does not exercise the body, whereas bringing the dog for a walk outside exercises both of you. Decisions that you make today and everyday will affect your cardiovascular health many years from now, such as those shown in Figure below.
Many studies have shown that plaque buildup starts in early adolescence. However, teens are more concerned about risks such as HIV, accidents, and cancer than cardiovascular disease. One in three people will die from complications due to atherosclerosis. For this reason there is an emphasis on the prevention of CVD through risk reduction. For example, healthy eating, regular physical activity, and avoidance of smoking can greatly decrease a person’s chance of developing a CVD.
Figure 22.23
Limiting sedentary activities such as watching TV, and making more time for walking, hiking, cycling, or running will help develop a healthy heart.
Congenital Heart Defects
A congenital heart defect is a problem with the structure of the heart that is present at birth. Such heart defects are the most common type of major birth defect. Most heart defects either obstruct blood flow in the heart or vessels near it, or cause blood to flow through the heart in an abnormal pattern, although other defects affecting heart rhythm can also occur.
Treatment for a defect can include medicines, surgery, and other medical procedures and heart transplants. The treatment depends on the type and severity of the defect and the child's age, size and general health. Also, certain mild defects that some children are born with are repaired over time by the body.
Lesson Summary
The main components of the cardiovascular system are the heart, the blood vessels, and the blood. It moves nutrients, hormones, gases and wastes to and from body cells, and distributes heat to maintain homeostasis.
Deoxygenated blood enters the right atrium from the body through the vena cava; oxygenated blood coming from the lungs through the pulmonary vein enters the left atrium. The atria then contract, pushing the blood into the ventricles. After a short delay, the ventricles contract, the oxygenated blood gets pushed through the aorta to the rest of the body, and the deoxygenated blood gets pushed to the lungs through the pulmonary arteries.
Arteries have thick walls that have three major layers; an inner endothelial layer, a middle layer of smooth muscle, and an outer layer of stretchy connective tissue (mostly collagen). The thick, outer layer of a vein is made up of collagen-containing connective tissue. The connective tissue is wrapped around bands of smooth muscle while the interior is lined with endothelium. Most veins have one-way flaps called valves that prevent blood from flowing backward and pooling in the legs, feet, arms or hands due to the pull of gravity. The walls of capillaries are made of only a single layer of endothelial cells.
The lymphatic system has three related functions; the removal of excess fluids from body tissues, the absorption of fats and transport of fat to the cardiovascular system, and the production of certain types of white blood cells.
Atherosclerosis, which may lead to a heart attack, is a chronic inflammatory response in the walls of arteries that leads to a buildup of plaque. Plaque is made of cell debris, cholesterol, fatty acids, calcium, and fibrous connective tissue that build up around an area of inflammation. As a plaque grows it stiffens and narrows the artery, which reduces the flow of blood through the artery.
Eating nutritious food, being physically active for 60 minutes on most days of the week, and avoiding smoking are three of the most effective things a person can do to avoid cardiovascular disease.
Summary Animation
http://www.hostos.cuny.edu/oaa/heart/heart.html
Review Questions
Why is the left ventricle generally thicker than the right ventricle?
At what point do the pulmonary and systemic circulation systems meet up?
Why do veins have valves? Use the heart Figure below to answer the following four questions:
Figure 22.24
What two structures are involved in the patent ductus arteriosus shown in this diagram. (Hint: The patent ductus arteriosus is the structure found inside the white circle at top center).
Propose what might happen to blood flow around the site of the PDA.
Would a PDA be considered a heart defect? Explain your answer.
How might the PDA affect the body? Use Figure below of the estimated prevalence of cardiovascular disease (CVD) in the U.S. population to answer the following three questions.
Figure 22.25
What is the overall trend in the prevalence of CVD in the U.S. population?
In what age group does the prevalence of CVD in the female population equal that of the male population?
At what point does 50 percent of the male and female population have CVD?
Further Reading / Supplemental Links
Vanhecke et al. Awareness, knowledge, and perception of heart disease among adolescents. EJCPR 2006;13:718-723.
Strong, J.P., et al. Prevalence and Extent of Atherosclerosis in Adolescents and Young Adults JAMA. 1999;281:727-735. Available online at:
http://jama.ama-assn.org/cgi/content/full/281/8/727
http://www.estrellamountain.edu/faculty/farabee/biobk/BioBookcircSYS.html
http://training.seer.cancer.gov/ss_module08_lymph_leuk/lymph_unit01_sec01_intro.html
http://www.nlm.nih.gov/medlineplus/ency/article/000171.htm#Causes,%20incidence,%20and%20risk%20factors
http://www.nlm.nih.gov/medlineplus/congenitalheartdefects.html
http://www.americanheart.org
http://www.accessexcellence.org/
http://whyfiles.org/090doping_sport/3.html
http://whyfiles.org/
http://en.wikipedia.org
Vocabulary
arteriole
Small diameter blood vessel that extends and branches out from an artery and leads to capillaries.
artery
Large, muscular vessels that carry blood away from the heart.
atria
Thin-walled blood collection chambers of the heart, pump blood into the ventricles (singular, atrium).
atrioventricular node
Conducts the electrical impulses that come from the SA node through the atria to the ventricles.
atrioventricular valves
Ensure blood flows from the atria to the ventricles.
blood pressure
The force exerted by circulating blood on the walls of blood vessels.
Bundle of His
A collection of heart muscle cells (fibers) specialized for electrical conduction that transmits the electrical impulses from the AV node.
cardiovascular system
An organ system that moves nutrients, hormones, gases and wastes to and from body cells, and distributes heat to maintain homeostasis.
capillary
Smallest of the body's blood vessels, connects arterioles and venules, and are important for the interchange of gases and other substances between blood and body cells.
coronary circulation
Supplies the heart tissue with blood.
diastole
Period of time when the heart relaxes after contraction.
heart
The muscular organ that pumps blood through the blood vessels by repeated, rhythmic contractions.
hypertension
Condition in which a person’s blood pressure is chronically high.
pulmonary circulation
Portion of the cardiovascular system which carries deoxygenated blood away from the heart, to the lungs, and returns oxygenated blood back to the heart.
Purkinje fibers
Specialized cardiac muscle cells that conduct action potentials into the ventricles, causing the cardiac muscle of the ventricles to contract in a controlled fashion.
semilunar valves
Present in the arteries leaving the heart, prevent blood flowing back from the arteries into the ventricles.
sinoatrial node
Known as the "cardiac pacemaker," found in the upper wall of the right atrium, is responsible for the wave of electrical stimulation that starts atrial contraction by creating an action potential.
sphygmomanometer
Measures arterial pressure.
systemic circulation
Portion of the cardiovascular system which carries oxygenated blood away from the heart, to the body, and returns deoxygenated blood back to the heart.
systole
Contraction of the heart chambers, which drives blood out of the chambers.
vascular resistance
Resistance to flow that blood must overcome to be pumped through your circulatory system.
vasoconstriction
Constriction of blood vessels by contracting the vascular smooth muscle in the vessel walls.
vasodilatation
Process by which blood vessels in the body become wider due to the relaxation of the smooth muscle in the vessel wall.
vein
Vessel that carries blood toward the heart.
ventricles
Heart chambers which collect blood from the atria and pump it out of the heart.
venule
Small vessel that allows deoxygenated blood to return from the capillaries to veins.
Points to Consider
How may factors such as the region of the world in which you live or your type of employment contribute to your risk of developing cardiovascular disease?
Hypothesize about the role of blood in your excretory system.
Lesson 22.2: Blood
Lesson Objectives
List three functions of blood.
Describe the composition of blood.
Outline the process of blood clotting.
Identify two major blood group systems.
Outline the significance of blood type in transfusions.
Describe two diseases of the blood.
Introduction
Blood is a fluid connective tissue. It circulates around the body through the blood vessels by the pumping action of the heart. Arterial blood carries oxygen and nutrient to all the body’s cells, and venous blood carries carbon dioxide and other metabolic wastes away from the cells.
In addition to the transport of gases, nutrients, and wastes, blood has many other functions that include:
The removal of waste such as carbon dioxide, urea and lactic acid from the body tissues.
The defense of the body against infection by microorganisms or parasites.
The repair of damage to the body tissues.
The transport of chemical messages, such as hormones and hormone-like substances.
The control of body pH (the normal pH of blood is in the range of 7.35 - 7.45).
The control of body temperature.
The Composition of Blood
Blood is a colloidal solution, it is made up of particles suspended in a fluid. It accounts for about 7% of the human body weight. The average adult has a blood volume of roughly 5 liters, composed of a fluid called plasma, and several kinds of cells. Within the blood plasma, are erythrocytes (red blood cells), leukocytes (white blood cells), thrombocytes (platelets) and other substances. The cells that make up the blood can be seen in Figure below.
Figure 22.26
A scanning electron microscope (SEM) image of normal circulating human blood. One can see red blood cells, several white blood cells including knobby lymphocytes, a monocyte, a neutrophil, and many small disc-shaped platelets.
Plasma
Plasma is the golden-yellow liquid part of the blood. Plasma is 90% water and 10% dissolved materials including proteins, glucose, ions, hormones, and gases. It acts as a buffer, maintaining pH near 7.4. Plasma is about 54% the volume of blood; cells and fragments make up about 46% of the volume.
Red Blood Cells
Red blood cells, also known as erythrocytes, are flattened, doubly concave cells that carry oxygen. There are about 4 to 6 million cells per cubic millimeter of blood. Red blood cells make up about 45% of blood volume, as shown in Figure below. Each red blood cell has 200 million hemoglobin molecules. Humans have a total of 25 trillion red blood cells (about 1/3 of all the cells in the body). Red blood cells are continuously made in the red marrow of long bones, ribs, skull, and vertebrae. Each red blood cell lives for only 120 days, after which they are destroyed in liver and spleen.
Figure 22.27
The components of blood. Red blood cells make up about 45% of the blood volume, white blood cells, about one percent, and platelets less than one percent. Plasma makes up the rest of the blood.
Mature red blood cells do not have a nucleus or other organelles. They contain the protein hemoglobin which gives blood its red color. The iron-containing heme portion of hemoglobin enables the protein to carry oxygen to cells. Heme binds to molecules of oxygen, which increases the ability of the blood to carry the gas.
Iron from hemoglobin is recovered and reused by red marrow. The liver degrades the heme units and secretes them as pigment in the bile, responsible for the color of feces. Each second two million red blood cells are produced to replace those thus taken out of circulation.
White Blood Cells
White blood cells, also known as leukocytes, are generally larger than red blood cells, as shown in Figure below. They have a nucleus, but do not have hemoglobin. White blood cells make up less than one percent of the blood's volume. They are made from stem cells in bone marrow. They function in the cellular immune response. There are five types of white blood cells. Neutrophils enter the tissue fluid by squeezing through capillary walls and phagocytizing (swallowing) foreign bodies. Macrophages also swallow and destroy cell debris and bacteria or viruses. In Figure below, a macrophage is shown phagocytizing two particles, possibly pathogens. Macrophages also release substances that cause the numbers of white blood cells to increase. Antigen-antibody complexes are swallowed by macrophages. Lymphocytes fight infection. T-cells attack cells containing viruses. B-cells produce antibodies. To learn more about the role of white blood cells in fighting infection, refer to the Immune System and Disease chapter.
Figure 22.28
Relative sizes of red and white blood cells. a - red blood cells; b neutrophil; c - eosinophil; d lymphocyte. b, c, and d are different types of white blood cells.
Figure 22.29
Macrophage showing cytoplasmic extensions that allow it to swallow particles or pathogens. In the image here, a mouse macrophage stretches its arms to engulf two partic
les at once.
Platelets
Platelets, also known as thrombocytes, are important in blood clotting. Platelets are cell fragments that bud off bone marrow cells called megakaryocytes. A platelet is shown in Figure below. They make up less than one percent of blood volume. Platelets carry chemicals essential to blood clotting. They change fibrinogen into fibrin, a protein that creates a mesh onto which red blood cells collect, forming a clot. This clot stops more blood from leaving the body and also helps to prevent bacteria from entering the body. Platelets survive for 10 days before being removed by the liver and spleen. There are 150,000 to 300,000 platelets in each milliliter of blood. Platelets stick to tears in blood vessels and they release clotting factors.
Figure 22.30
Cells of the blood. From left to right: Red blood cell, platelet, white blood cell. The concave side of red blood cells can be seen. Both sides of red blood cells are concave. The biconcave shape gives the red blood cells a smaller surface to volume ratio, which allows them to pick up large amounts of oxygen.
Other Blood Components