Textbook questions Flashcards
(213 cards)
1
Q
List the 5 major functions of the blood
A
transport dissolved gases, nutrients, hormones, metabolic wastes
regulate pH and ion composition of interstitial fluids
restrict fluid losses at injury sites
defend against toxins and pathogens
stabilize body temperature
2
Q
Identify 3 types of formed elements in the blood
A
RBC, WBC, platelets
3
Q
List the 3 major types of plasma proteins
A
albumins, globulins, fibrinogen
4
Q
What would be the effects of a decrease in amount of plasma proteins
A
decrease would lead to lower plasma osmotic pressure, reduced ability to fight infections, decreased transport and binding of some ions, hormones, and other molecules
4
Q
Describe the structure of hemoglobin.
A
Protein made of 4 globular subunits, each bound to a heme molecule which gives RBC ability to transport oxygen in the blood
5
Q
How would a person’s hematocrit change after a significant blood loss?
A
after significant blood loss, hematocrit would decrease
6
Q
What effect would obstruction to the renal arteries have on a person’s hematocrit?
A
The hematocrit would increase, because reduced blood flow to the kidneys triggers the release of erythropoietin, which stimulates an increase in erythropoiesis (red blood cell formation).
7
Q
How would liver disease affect the level of bilirubin in the blood?
A
Bilirubin would accumulate in the blood, producing jaundice, because diseases that damage the liver, such as hepatitis or cirrhosis, impair the liver’s ability to excrete bilirubin in the bile.
8
Q
What is the function of surface antigens on RBCs?
A
Surface antigens on RBCs are glycoproteins in the plasma membrane; they determine blood type.
9
Q
Which blood type can be safely transfused into a person with type O blood?
A
Only type O blood can be safely transfused into a person whose blood type is O.
10
Q
Why can’t a person with type A blood safely receive blood from a person with type B blood?
A
If a person with type A blood receives a transfusion of type B blood, which contains anti-A antibodies, the red blood cells will agglutinate (clump), potentially blocking blood flow to various organs and tissues.
11
Q
Identify the five types of white blood cells.
A
The five types of white blood cells are neutrophils, eosinophils, basophils, monocytes, and lymphocytes.
12
Q
Which type of white blood cell would you find in the greatest numbers in an infected cut?
A
An infected cut would contain a large number of neutrophils, because these phagocytic white blood cells are the first to arrive at the site of an injury.
13
Q
Which type of cell would you find in elevated numbers in a person who is producing large amounts of circulating antibodies to combat a virus?
A
The blood of a person fighting a viral infection would contain elevated numbers of lymphocytes, because B cells (B lymphocytes) produce circulating antibodies.
14
Q
How do basophils respond to an injury?
A
Basophils respond to an injury by releasing a variety of chemicals, including histamine and heparin. Histamine dilates blood vessels and heparin prevents blood clotting. Basophils also release other chemicals that attract eosinophils and other basophils to the injured area.
15
Q
Define thrombocytopoiesis.
A
Thrombocytopoiesis is the term for platelet production.
16
Q
List the three primary functions of platelets.
A
Platelets release chemicals important to the clotting process, they form a temporary patch in the walls of damaged blood vessels, and they reduce the size of a break in a vessel wall.
17
Q
A decreased number of megakaryocytes would interfere with what body process?
A
A decreased number of megakaryocytes would interfere with the blood’s ability to clot properly, because fewer megakaryocytes would produce fewer platelets.
18
Q
How could a fat-free diet affect blood clotting?
A
Vitamin K is necessary for blood clotting, and fats are required for vitamin K absorption. So, if a person did not eat foods containing fat, this would lead to a vitamin K deficiency, which would, in turn, result in a decreased production of several clotting factors—most notably, prothrombin. As a result, clotting time would increase.
19
Q
Unless chemically treated, whole blood will coagulate in a test tube. This clotting process begins when Factor XII becomes activated. Which clotting pathway is involved in this process?
A
The activation of Factor XII initiates the intrinsic pathway.
20
Q
The formed elements of the blood include (a) plasma, fibrin, and serum, (b) albumins, globulins, and fibrinogen, (c) WBCs, RBCs, and platelets, (d) all of these.
A
c
21
Q
In the blood of an average adult, the total number of RBCs is about ______, and the hemoglobin concentration is about _______. (a) 10 trillion, 0.15 g/dL, (b) 30 billion, 3 g/dL, (c) 5 trillion, 200 g/dL, (d) 25 trillion, 15 g/dL.
A
d
22
Q
Plasma contributes approximately ______ percent of the volume of whole blood, and water accounts for ______ percent of the plasma volume. (a) 55, 92, (b) 25, 55, (c) 92, 55, (d) 35, 72.
A
a
23
Q
Whole blood (a) is acidic, (b) is less cohesive than water, (c) is more resistant to flow than water, (d) has a temperature of about 35°C, (e) has different physical characteristics in veins and arteries.
A
c
24
The bright red color of blood is due to (a) oxyhemoglobin, (b) deoxyhemoglobin, (c) ferritin, (d) carbaminohemoglobin, (e) transferrin.
a
25
The following is a list of the phases involved in the process of hemostasis.
(1) coagulation
(2) fibrinolysis
(3) vascular spasm
(4) retraction
(5) platelet phase
The correct sequence of these phases is (a) 5, 1, 4, 2, 3, (b) 3, 5, 1, 4, 2, (c) 2, 3, 5, 1, 4, (d) 3, 5, 4, 1, 2, (e) 4, 3, 5, 2, 1.
b
26
Stem cells responsible for lymphocytopoiesis are located in (a) the thymus and spleen, (b) the lymph nodes, (c) the red bone marrow, (d) all of these structures.
d
27
_____ and ______ are also known as clotting factors I and II. (a) Tissue factor, calcium ions, (b) Fibrinogen, prothrombin, (c) Prothrombin, proconvertin, (d) Tissue factor, pro-accelerin.
b
28
What five major functions are performed by blood?
Blood (1) transports dissolved gases, nutrients, hormones, and metabolic wastes; (2) regulates pH and electrolyte composition of interstitial fluids throughout the body; (3) restricts fluid losses through damaged vessels or at other injury sites; (4) defends against toxins and pathogens; and (5) stabilizes body temperature.
29
Name the three major types of plasma proteins and identify their functions,
Major types of plasma proteins are (1) albumins, which maintain the osmotic pressure of plasma and are important in the transport of fatty acids; (2) globulins, which (a) bind small ions, hormones, or compounds that might otherwise be filtered out of the blood at the kidneys or have very low solubility in water (transport globulins), or (b) attack foreign proteins and pathogens (immunoglobulins); and (3) fibrinogen, which functions in blood clotting.
30
Which type of antibodies does plasma contain for each of the following blood types? (a) type A, (b) type B, (c) type AB, (d) type O.
(a) anti-B antibodies; (b) anti-A antibodies; (c) neither anti-A nor anti-B antibodies; (d) both anti-A and anti-B antibodies
31
What four characteristics of WBCs are important to their response to tissue invasion or injury?
WBCs exhibit (1) emigration (diapedesis), squeezing between adjacent endothelial cells in the capillary wall; (2) amoeboid movement, a gliding movement that transports the cell; (3) positive chemotaxis, the attraction to specific chemical stimuli, and (4) phagocytosis (engulfing particles for neutrophils, eosinophils, and monocytes).
32
Which three substances influence the rate of platelet formation?
The rate of platelet formation is influenced by (1) thrombopoietin or thrombocytestimulating factor, (2) interleukin-6, and (3) multi-CSF.
33
Name the three types of lymphocytes and identify their functions,
The primary lymphocytes are (1) T cells, which are responsible for cellmediated immunity; (2) B cells, which are responsible for humoral immunity; and (3) NK cells, which are responsible for immune surveillance.
34
What is the difference between prothrombin and thrombin?
Prothrombin is an inactive precursor that is converted to thrombin during coagulation. Thrombin is an enzyme that causes the clotting of blood by converting fibrinogen to fibrin.
35
What four conditions cause the release of erythropoietin?
Erythropoietin is released (1) during anemia, (2) when blood flow to the kidneys declines, (3) when the oxygen content of air in the lungs declines, and (4) when the respiratory surfaces of the lungs are damaged.
36
What contribution from the intrinsic and the extrinsic pathways is necessary for the common pathway to begin?
Initiation of the common pathway requires the activation of Factor X by the extrinsic and/or intrinsic pathways
37
Dehydration would (a) cause an increase in the hematocrit, (b) cause a decrease in the hematocrit, (c) have no effect on the hematocrit, (d) cause an increase in plasma volume.
a
38
Erythropoietin directly stimulates RBC formation by (a) increasing rates of mitotic divisions in erythroblasts, (b) speeding up the maturation of red blood cells, (c) accelerating the rate of hemoglobin synthesis, (d) all of these.
d
39
Urine is yellow due to the presence of (a) hemoglobin, (b) biliverdin, (c) stercobilins, (d) bilirubin, (e) urobilins.
e
40
A difference between the A, B, and O blood types and the Rh factor is (a) Rh agglutinogens are not found on the surface of red blood cells, (b) Rh agglutinogens do not produce a cross-reaction, (c) individuals who are Rh− do not carry agglutinins to Rh factor unless they have been previously sensitized, (d) Rh agglutinogens are found free in the plasma, (e) Rh agglutinogens are found bound to plasma proteins.
c
41
What factors determine whether myeloid stem cells develop into RBCs or WBCs?
The hormone multi-CSF stimulates myeloid stem cells to become progenitor cells. Under the influence of the hormone erythropoietin, progenitor cells develop into proerythroblasts and eventually into RBCs. Under the influence of the hormone GM-CSF, progenitor cells develop into blast cells. The hormone G-CSF induces blast cells to become myeloblasts and eventually granulocytes, whereas the hormone M-CSF induces blast cells to become monoblasts and eventually monocytes.
42
How do elements of blood defend against toxins and pathogens in the body?
White blood cells defend against toxins and pathogens. Neutrophils, eosinophils, and monocytes engulf and digest bacteria, protozoa, fungi, viruses, and cellular debris. Lymphocytes are specialized to attack and destroy specific foreign cells, proteins, and cancerous cells, directly or through the production of antibodies.
43
What is the role of blood in the stabilization and maintenance of body temperature?
Blood stabilizes and maintains body temperature by absorbing and redistributing the heat produced by active skeletal muscles.
44
What can be the consequences of having too little or too much iron in the body?
Too much iron can cause problems due to excessive buildup in secondary storage sites, such as the liver and the heart. Too little iron can result in irondeficiency anemia.
45
Why is aspirin sometimes prescribed for the prevention of vascular problems?
Aspirin helps prevent vascular problems by inhibiting clotting. It inhibits platelet enzymes involved in the production of thromboxane A2 and prostaglandins, thereby inhibiting clotting. It also prolongs bleeding time.
46
Damage to the semilunar valve of the right ventricle would affect blood flow into which vessel?
Damage to the semilunar valve of the right ventricle, or pulmonary valve, would affect blood flow to the pulmonary trunk.
47
What prevents the AV valves from swinging into the atria?
Contraction of the papillary muscles (just before the rest of the ventricular myocardium contracts) pulls on the chordae tendineae, which prevent the AV valves from opening back into the atria.
48
Why is the left ventricle more muscular than the right ventricle?
The left ventricle is more muscular than the right ventricle because the left ventricle must generate enough force to propel blood throughout the body, except the lungs, whereas the right ventricle must generate only enough force to propel blood a few centimeters to the lungs.
49
Define autorhythmicity.
Autorhythmicity is the ability of cardiac muscle tissue to contract without neural or hormonal stimulation.
50
Which structure of the heart is known as the cardiac pacemaker?
The sinoatrial (SA) node is known as the cardiac pacemaker or the natural pacemaker.
51
If the cells of the SA node did not function, how would the heart rhythm change and the heart rate be affected?
If the cells of the SA node did not function, the AV node would act as the pacemaker and set the heart rhythm. The heart would still continue to beat, but at a slower rate.
52
Why is it important for impulses from the atria to be delayed at the AV node before they pass into the ventricles?
If the impulses from the atria were not delayed at the AV node, they would be conducted through the ventricles so quickly by the bundle branches and Purkinje cells that the ventricles would begin contracting immediately, before the atria had finished their contraction. As a result, the ventricles would not be as full of blood as they could be, and the pumping of the heart would not be as efficient, especially during physical activity.
53
Give the technical terms for heart contraction and heart relaxation.
The technical term for heart contraction is systole, and the term for heart relaxation is diastole.
54
List the phases of the cardiac cycle.
The phases of the cardiac cycle are atrial systole, atrial diastole, ventricular systole, and ventricular diastole.
55
Is the heart always pumping blood when pressure in the left ventricle is rising? Explain.
No. When pressure in the left ventricle first rises, the heart is contracting but no blood is leaving the heart. During this initial phase of contraction, both the AV valves and the semilunar valves are closed. The increase in pressure is the result of increased tension as the cardiac muscle contracts. When the blood pressure in the ventricle exceeds the blood pressure in the aorta, the aortic semilunar valves are forced open, and blood is rapidly ejected from the ventricle.
56
What could cause an increase in the size of the QRS complex in an electrocardiogram
An increase in the size of the QRS complex indicates a larger-than-normal amount of electrical activity during ventricular depolarization. One possible cause is an enlarged heart. Because more cardiac muscle is depolarizing, the magnitude of the electrical event would be greater.
57
Define cardiac output.
Cardiac output is the amount of blood pumped by the left ventricle in 1 minute.
58
Caffeine has effects on cardiac conducting cells and contractile cells that are similar to those of NE. What effect would drinking large amounts of caffeinated drinks have on the heart?
Caffeine acts directly on the conducting system and contractile cells of the heart, increasing the rate at which they depolarize. Drinking large amounts of caffeinated drinks would increase the heart rate.
59
Why is it a potential problem if the heart beats too rapidly?
The heart pumps in proportion to the amount of blood that enters. A heart that beats too rapidly does not have sufficient time to fill completely between beats. Thus, when the heart beats too fast, very little blood leaves the ventricles and enters the circulation, so tissues suffer damage from inadequate blood supply.
60
What effect would stimulating the acetylcholine receptors of the heart have on cardiac output?
Stimulating the acetylcholine receptors of the heart would slow the heart rate (parasympathetic neurons release acetylcholine). Since cardiac output is the product of stroke volume and heart rate, a reduction in heart rate will lower the cardiac output (assuming that the stroke volume remains the same or doesn’t increase).
61
What effect would an increase in venous return have on the stroke volume?
The venous return fills the heart with blood, stretching the heart muscle. According to the Frank–Starling principle, the more the heart muscle is stretched, the more forcefully it will contract (to a point). The more forceful the contraction, the more blood the heart will eject with each beat (stroke volume). Therefore, increased venous return would increase the stroke volume (if all other factors are constant).
62
Joe’s end-systolic volume is 40 mL, and his end-diastolic volume is 125 mL. What is Joe’s stroke volume?
SV = EDV − ESV, so SV = 125 mL − 40 mL = 85 mL
63
Oxygen-rich blood is delivered to the heart muscle by the (a) aorta, (b) aortic sinuses, (c) great cardiac vein, (d) coronary arteries.
d
64
The conducting system of the heart consists of all of the following structures except the (a) sinoatrial node, (b) atrioventricular node, (c) fossa ovalis, (d) atrioventricular bundle
c
65
The serous membrane covering the outer surface of the heart is the (a) parietal layer of the serous pericardium, (b) endocardium, (c) myocardium, (d) visceral layer of the serous pericardium.
d
66
The simple squamous epithelium covering the heart valves is the (a) epicardium, (b) endocardium, (c) myocardium, (d) endothelium.
d
67
The heart is surrounded by the (a) pleural cavity, (b) peritoneal cavity, (c) abdominopelvic cavity, (d) mediastinum, (e) abdominal cavity.
d
68
The cardiac skeleton of the heart has which two of the following functions? (a) It physically isolates the muscle fibers of the atria from those of the ventricles. (b) It maintains the normal shape of the heart. (c) It helps distribute the forces of cardiac contraction. (d) It allows more rapid contraction of the ventricles. (e) It strengthens and helps prevent overexpansion of the heart.
a and b
69
Cardiac output is equal to the (a) difference between the end-diastolic volume and the end-systolic volume, (b) product of heart rate and stroke volume, (c) difference between the stroke volume at rest and the stroke volume during exercise, (d) stroke volume less the end-systolic volume, (e) product of heart rate and blood pressure.
b
70
The first heart sound that you hear when listening to your heart accompanies the closing of (a) only the bicuspid valve, (b) both the semilunar valves, (c) only the tricuspid valve, (d) both the atrioventricular valves.
d
71
Examples of positively inotropic factors are (a) beta-blocking drugs, (b) drugs mimicking epinephrine, (c) calcium-channel blockers, (d) low doses of dopamine.
b
72
What role do the chordae tendineae and papillary muscles play in the normal function of the AV valves?
During ventricular contraction, tension in the papillary muscles pulls against the chordae tendineae, which keep the cusps of the AV valve from swinging into the atrium. This action prevents the backflow, or regurgitation, of blood into the atrium as the ventricle contracts.
73
Describe the three distinct layers that make up the heart wall.
(1) The epicardium is the visceral layer of the serous pericardium, which covers the outer surface of the heart. (2) The myocardium is the muscular wall of the heart, which forms both atria and ventricles. It contains cardiac muscle tissue and associated connective tissues, blood vessels, and nerves. (3) The endocardium is made up of a simple squamous epithelium and an areolar layer that covers the inner surfaces of the heart, including the valves.
74
What are the valves in the heart, and what is the function of each?
The tricuspid valve (right atrioventricular valve) and the mitral valve (left atrioventricular valve) prevent the backflow of blood from the ventricles into the atria. The pulmonary and aortic semilunar valves prevent the backflow of blood from the pulmonary trunk and aorta into the right and left ventricles.
75
Where are the Purkinje fibers located, and what is their function?
The Purkinje fibers radiate from the apex toward the base of the heart. They conduct action potentials very rapidly to all the ventricular cardiac contractile cells in order to start ventricular contraction.
76
What is the cardiac cycle? What phases and events are necessary to complete a cardiac cycle?
The cardiac cycle comprises the events in a complete heartbeat, including a contraction–relaxation period for both atria and ventricles. The cycle begins with atrial systole as the atria contract and push blood into the relaxed ventricles. As the atria relax (atrial diastole), the ventricles contract (ventricular systole), forcing blood through the semilunar valves into the pulmonary trunk and aorta. The ventricles then relax (ventricular diastole). For the rest of the cardiac cycle, both the atria and ventricles are in diastole; passive filling occurs.
77
What three factors regulate stroke volume to ensure that the left and right ventricles pump equal volumes of blood?
The factors that regulate stroke volume are (1) preload, the stretch on the heart before it contracts; (2) contractility, the force of contraction of individual ventricular contractile cells; and (3) afterload, the pressure that must be exceeded before blood can be ejected from the ventricles.
78
The cells of the conducting system differ from the contractile cells of the heart in that (a) conducting cells are larger and contain more myofibrils, (b) contractile cells exhibit pacemaker potentials, (c) contractile cells do not normally exhibit autorhythmicity, (d) both a and b are correct.
c
79
In an adult who is standing at rest, which of the following is larger? (a) the end-systolic volume, (b) the end-diastolic volume.
b
80
If the papillary muscles fail to contract, (a) the ventricles will not pump blood, (b) the atria will not pump blood, (c) the semilunar valves will not open, (d) the AV valves will not close properly, (e) none of these happen.
d
81
Cardiac output cannot increase indefinitely because (a) the available filling time becomes shorter as the heart rate increases, (b) the cardiovascular centers adjust the heart rate, (c) the rate of spontaneous depolarization decreases, (d) the ion concentrations of pacemaker plasma membranes decrease.
a
82
Can a myocardial infarction be diagnosed through blood tests? Explain.
Yes, there are blood tests that can help diagnose a myocardial infarction. Damaged myocardial cells release enzymes into the circulation, and these elevated enzymes can be measured in blood tests. These enzymes include cardiac troponin T, cardiac troponin I, and a special form of creatinine phosphokinase, CK-MB.
83
How is a constant blood supply to the heart muscle ensured?
The coronary arteries provide a constant blood supply to the heart muscle. The interconnections between the arteries, called arterial anastomoses, ensure constant blood supply to all parts of the myocardium, despite pressure fluctuations in the left and right coronary arteries as the heart beats.
84
What is cardiac reserve? What effect does exercise have on it?
Cardiac reserve is the difference between resting and maximal cardiac outputs. Exercise increases cardiac output significantly.
85
What factors influence cardiac output?
Stroke volume and heart rate influence cardiac output.
86
What effect does sympathetic stimulation have on the heart? What effect does parasympathetic stimulation have on the heart?
Sympathetic activation increases the heart rate and the force of contractions; parasympathetic stimulation decreases the heart rate and the force of contractions.
87
Why are compounds such as propranolol, metoprolol, atenolol, and labetalol useful in treating hypertension?
These drugs lower blood pressure as they block beta receptors, alpha receptors, or both, and prevent sympathetic stimulation of the heart.
88
Vern is suffering from cardiac arrhythmias and is brought into the emergency room of a hospital. In the emergency room he begins to exhibit tachycardia and as a result loses consciousness. Explain why Vern lost consciousness.
During tachycardia (an abnormally fast heart rate), there is less time between contractions for the heart to fill with blood again. Thus, over time the heart fills with less and less blood, and pumps less blood out. As the stroke volume decreases, the cardiac output decreases. When cardiac output decreases to the point where not enough blood reaches the brain, loss of consciousness occurs.
89
Harvey has a heart murmur in his left ventricle that produces a loud “gurgling” sound at the beginning of systole. Which valve is probably faulty?
Harvey probably has a regurgitating mitral valve, or left atrioventricular (AV) valve. When an AV valve fails to close properly, blood flowing back into the atrium produces a murmur. A murmur at the beginning of systole implicates the AV valve because this is the period when the valve has just closed and the blood in the ventricle is under increasing pressure; thus the likelihood of backflow is the greatest. A sound heard at the end of systole or the beginning of diastole would implicate a regurgitating semilunar valve—in this case, the aortic valve.
90
The following measurements were made on two individuals (the values recorded remained stable for 1 hour): Person 1: heart rate, 75 bpm; stroke volume, 60 mL Person 2: heart rate, 90 bpm; stroke volume, 95 mL Which person has the greater venous return? Which person has the longer ventricular filling time?
Using CO = HR × SV, person 1 has a cardiac output of 4500 mL, and person 2 has a cardiac output of 8550 mL. According to the Frank–Starling principle, in a normal heart the cardiac output is directly proportional to the venous return. Thus, person 2 has the greater venous return. Ventricular filling decreases with increased heart rate; person 1 has the lower heart rate and therefore the longer ventricular filling time.
91
Karen is taking the medication verapamil, a drug that blocks the calcium channels in cardiac muscle cells. What effect should this medication have on Karen’s stroke volume?
By blocking calcium channels, verapamil will decrease the force of cardiac contraction, which directly lowers Karen’s stroke volume.
92
Identify the layers of the epidermis.
The layers of the epidermis are the stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum.
93
Dandruff is caused by excessive shedding of cells from the outer layer of skin on the scalp. So dandruff is composed of cells from which epidermal layer?
Dandruff consists of cells from the stratum corneum.
94
A splinter that penetrates to the third layer of the epidermis of the palm is lodged in which layer?
This splinter is lodged in the stratum granulosum.
95
Why does taking a bath cause wrinkly fingertips and toes?
Wrinkles in the tips of the fingers (and toes) are due to the constriction of blood vessels in the underlying skin, which causes the skin to shrink. This effect is controlled by the autonomic nervous system, a division of the nervous system that acts outside our awareness.
96
Some criminals sand the tips of their fingers so as not to leave recognizable fingerprints. Would this practice permanently remove fingerprints? Why or why not?
Sanding the tips of the fingers will not permanently remove fingerprints. The ridges of the fingerprints are formed in layers of the skin that are constantly regenerated, so these ridges will eventually reappear. The pattern of the ridges is determined by the arrangement of tissue in the dermis, which is not affected by sanding.
97
Name the sources of epidermal growth factor in the body.
Salivary glands and duodenal glands (glands of the duodenum) produce epidermal growth factor (EGF).
98
Identify some roles of epidermal growth factor related to the epidermis.
Epidermal growth factor (EGF) promotes the divisions of basal cells in the stratum basale and stratum spinosum, accelerates the production of keratin in differentiating keratinocytes, stimulates epidermal development and epidermal repair after injury, and stimulates synthetic activity and secretion by epithelial glands.
99
Describe the location of the dermis.
The dermis (a connective tissue layer) is located between the epidermis and the subcutaneous layer (hypodermis).
100
Where are the capillaries and sensory nerve fibers that supply the epidermis located?
The capillaries and sensory nerve fibers that supply the epidermis are located in the papillary layer of the dermis.
101
What accounts for the ability of the dermis to undergo repeated stretching?
The presence of elastic fibers and the flexibility and resilience of skin turgor allow the dermis to undergo repeated cycles of stretching and recoiling (returning to its original shape).
102
List the two terms for the tissue that connects the dermis to underlying tissues.
The tissue that connects the dermis to underlying tissues is the subcutaneous layer or hypodermis.
103
Describe the subcutaneous layer.
The subcutaneous layer is a layer of loose connective tissue (areolar tissue) and adipose tissue below (deep to) the dermis. The subcutaneous layer is not considered a part of the integument, but it is important in stabilizing the position of the skin in relation to underlying tissues.
104
Identify several functions of subcutaneous fat.
Subcutaneous fat provides insulation to help reduce heat loss, serves as an energy reserve, and acts as a shock absorber for the body.
105
Name the two major pigments in the epidermis.
The two major pigments in the epidermis are melanin, which ranges in color from red-yellow (pheomelanin) to brown-black (eumelanin), and carotene, an orange-yellow pigment.
106
Why does exposure to sunlight darken skin?
When exposed to the ultraviolet (UV) radiation in sunlight, melanocytes in the epidermis and dermis synthesize the pigment melanin, darkening the skin.
107
Why does the skin of a fair-skinned person appear red during exercise in hot weather?
When skin gets warm, arriving oxygenated blood is diverted to the superficial dermis for the purpose of eliminating heat. The oxygenated blood gives a reddish coloration to the skin.
108
Explain the relationship between sunlight exposure and vitamin D3 synthesis.
In the presence of ultraviolet radiation in sunlight, epidermal cells in the stratum spinosum and stratum basale convert a cholesterol-related steroid compound into cholecalciferol, or vitamin D3.
109
In some cultures, women must be covered completely, except for their eyes, when they go out in public. Explain why these women may develop bone problems later in life.
Cholecalciferol (vitamin D3) is needed to form strong bones and teeth. When the body surface is covered, UV light cannot penetrate to the stratum basale in the skin to begin vitamin D3 production, resulting in fragile bones.
110
Describe a typical strand of hair.
A typical hair is a keratinous strand produced by epithelial cells of the hair follicle.
111
What happens when the arrector pili muscle contracts?
The contraction of the arrector pili muscle pulls the hair follicle erect. The result is known as “goose bumps.”
112
Once a burn on the forearm that destroys the epidermis and extensive areas of the deep dermis heals, will hair grow again in the affected area?
Even though hair is a derivative of the epidermis, the hair follicles are in the dermis. Where the epidermis and deep dermis are destroyed, new hair will not grow.
113
Identify two types of exocrine glands found in the skin.
Two types of exocrine glands found in the skin are sebaceous (oil) glands and sweat glands.
114
What are the functions of sebaceous secretions?
The functions of sebaceous secretions (called sebum) are to lubricate and protect the keratin of the hair shaft, lubricate and condition the surrounding skin, and inhibit the growth of bacteria.
115
Deodorants are used to mask the effects of secretions from which type of skin gland?
Deodorants are used to mask the odor of apocrine sweat gland secretions, which contain several kinds of organic compounds. Some of these compounds have an odor, and others produce an odor when metabolized by skin bacteria.
116
Which type of skin gland is most affected by the hormonal changes that occur during puberty?
Apocrine sweat glands enlarge and increase secretory activity in response to the increase in sex hormones that occurs at puberty.
117
What substance makes fingernails hard?
Keratin is the substance that makes fingernails hard.
118
What term is used to describe the thickened stratum corneum underlying the free edge of a nail?
The area of thickened stratum corneum under the free edge of a nail is called the hyponychium
119
Where does nail growth occur?
Nail growth occurs at the nail root, an epidermal fold that is not visible from the surface.
120
What term describes the combination of fibrin clots, fibroblasts, and the extensive network of capillaries in healing tissue?
The combination of fibrin clots, fibroblasts, and the extensive network of capillaries in tissue that is healing is called granulation tissue.
121
Why can skin regenerate effectively even after considerable damage?
Skin can regenerate effectively even after considerable damage because stem cells persist in both the epithelial and connective tissue components of skin. When injury occurs, cells of the stratum basale replace epithelial cells, and mesenchymal cells replace cells lost from the dermis.
122
Older people do not tolerate the summer heat as well as they did when they were young, and they are more prone to heat-related illnesses. What accounts for these changes?
As a person ages, the blood supply to the dermis decreases and eccrine sweat glands become less active. These changes make it more difficult for older individuals to cool themselves in hot weather.
123
Why does hair turn white or gray with age?
With advancing age, melanocyte activity decreases, leading to gray or white hair.
124
The two major components of the integumentary system are (a) the cutaneous membrane and the accessory structures, (b) the epidermis and the subcutaneous layer, (c) the hair and the nails, (d) the dermis and the subcutaneous layer.
a
125
Beginning at the basement membrane and traveling toward the free surface, the epidermis includes the following strata: (a) corneum, lucidum, granulosum, spinosum, basale, (b) granulosum, lucidum, spinosum, basale, corneum, (c) basale, spinosum, granulosum, lucidum, corneum, (d) lucidum, granulosum, spinosum, basale, corneum.
c
126
A glassy layer present only in thick skin is the (a) stratum corneum, (b) stratum lucidum, (c) stratum granulosum, (d) stratum spinosum, (e) stratum basale.
b
127
Exposure of the skin to ultraviolet (UV) radiation (a) can result in increased numbers of melanocytes forming in the skin, (b) can result in decreased melanin production in melanocytes, (c) can cause destruction of vitamin D3, (d) can result in damage to the DNA of cells in the stratum basale, (e) has no effect on the skin cells.
d
128
Which layer of the dermis is involved in dermatitis? (a) the subcutaneous layer, (b) the superficial fascia, (c) the reticular layer, (d) the papillary layer.
d
129
The lamellar corpuscles in the reticular layer of the dermis are specialized in sensing (a) pain, (b) deep pressure and vibration, (c) temperature, (d) light touch.
b
130
The accessory structures of the integument include the (a) blood vessels, glands, muscles, and nerves, (b) tactile discs, lamellar corpuscles, and tactile corpuscles, (c) hair, skin, and nails, (d) hair follicles, nails, sebaceous glands, and sweat glands.
d
131
Each of the following is a part of the hair follicle, except the (a) glassy membrane, (b) external root sheath, (c) internal root sheath, (d) eponychium.
d
132
The two types of exocrine glands in the skin are (a) eccrine and sweat glands, (b) sebaceous and sweat glands, (c) apocrine and sweat glands, (d) sebaceous and eccrine glands.
b
133
Sebaceous follicles are large sebaceous glands found on all the following body parts except the (a) face, (b) external genitalia, (c) arms, (d) nipples.
c
134
An important example of a specialized gland in the skin is the (a) mammary gland, (b) mucous gland, (c) apocrine sweat gland, (d) eccrine sweat gland.
a
135
The cells that create scar tissue during the repair of an injury are (a) mast cells, (b) macrophages, (c) fibroblasts, (d) melanocytes.
c
136
Muscle weakness and a reduction in bone strength in the elderly result from decreased (a) vitamin D3 production, (b) melanin production, (c) sebum production, (d) dermal blood supply.
a
137
In which layer(s) of the epidermis does cell division occur?
Epidermal cell division occurs in the stratum basale.
138
What is the function of the arrector pili muscles?
These smooth muscles cause hairs to stand erect when stimulated.
139
What widespread effects does epidermal growth factor (EGF) have on the integument?
Epidermal growth factor promotes the divisions of basal cells in the stratum basale and stratum spinosum, accelerates the production of keratin in differentiating epidermal cells, stimulates both epidermal development and epidermal repair after injury, and stimulates secretory product synthesis and secretion by epithelial glands.
140
What two major layers constitute the dermis, and what components are in each layer?
The dermis is made up of (1) the papillary layer, which consists of areolar connective tissue and contains capillaries and sensory nerve fibers and receptors, and (2) the reticular layer, which consists of dense irregular connective tissue and bundles of collagen fibers. Both layers contain networks of blood vessels, lymphatic vessels, and nerve fibers.
141
List the four phases in the regeneration of the skin after an injury.
Regeneration of injured skin involves (1) bleeding and inflammation (inflammation phase), (2) scab and granulation tissue formation (migration phase), (3) loss of granulation and undermining of the scab (proliferation phase), and (4) scarring (scarring phase).
142
How is thin skin different from thick skin?
Thin skin contains four layers of keratinocytes, whereas thick skin contains five layers.
143
In clinical practice, drugs can be delivered by diffusion across the skin. This delivery method is called transdermal administration. Why are fat-soluble drugs more suitable for transdermal administration than drugs that are water soluble?
The integument is the first barrier to substances entering the body. This method of delivering drugs requires the substance to move across the epidermal plasma membranes. The lipid bilayer of the plasma membranes creates a barrier that prevents water from rapidly entering or leaving the cells. Fatsoluble (lipophilic) substances, such as oil containing a dissolved drug, can easily pass through this barrier to underlying connective tissue and enter the circulation. Water-soluble drugs are lipophobic and thus do not readily penetrate the integument.
144
In evaluating burns, it is important to determine the depth of the burn correctly. How would you differentiate among a first-degree burn, a second-degree burn, and a third-degree burn?
In a first degree burn, only the surface of the epidermis is damaged. The skin reddens and can be painful. In a second-degree burn, the entire epidermis and some of the dermis are damaged. Hair follicles and glands are usually not affected, but blistering, pain, and swelling occur. Third-degree burns destroy the epidermis and dermis, extending into the subcutaneous layer. Despite swelling, these burns are less painful than second-degree burns, because sensory nerves are destroyed.
145
Why is it important for a surgeon to choose—when possible—an incision pattern according to the skin’s tension lines?
Incisions along tension lines—which represent the orientation of dermal collagen and elastin fibers—are more likely to remain closed, and thus heal more quickly, than incisions that cut across tension lines.
146
The fibrous protein that is responsible for the strength and water resistance of the skin surface is (a) collagen, (b) eleidin, (c) keratin, (d) elastin, (e) keratohyalin.
c
147
The darker a person’s skin color, (a) the more melanocytes she has in her skin, (b) the more layers she has in her epidermis, (c) the more melanin her melanocytes produce, (d) the more superficial her blood vessels.
c
148
In order for bacteria on the skin to cause an infection in the skin, they must accomplish all of the following, except (a) survive the bactericidal components of sebum, (b) avoid being flushed from the surface of the skin by sweat, (c) penetrate the stratum corneum, (d) penetrate to the level of the capillaries, (e) escape the dendritic cells.
d
149
In an elderly person, blood supply to the dermis is reduced and sweat glands are less active. This combination of factors would most affect (a) the ability to thermoregulate, (b) the ability to heal injured skin, (c) the ease with which the skin is injured, (d) the physical characteristics of the skin, (e) the ability to grow hair.
a
150
Lisa is unhappy about the presence of white patches on several parts of her body. These patches do not cause pain or discomfort, but Lisa considers them disfiguring. Identify Lisa’s condition, and explain what has caused it.
Lisa has vitiligo. The white patches on her skin are the result of the loss of melanocytes in those areas. This condition develops when the body’s immune defenses malfunction and antibodies attack normal melanocytes.
151
Exposure to optimum amounts of sunlight is necessary for proper bone maintenance and growth in children. (a) What does sunlight do to promote bone maintenance and growth? (b) If a child lives in an area where exposure to sunlight is rare because of pollution or overcast skies, what can be done to minimize impaired maintenance and growth of bone?
(a) Ultraviolet radiation in sunlight converts a cholesterol-related steroid compound into vitamin D3, or cholecalciferol. This compound is then converted to the hormone calcitriol, which is essential for absorbing the calcium and phosphate ions by the small intestine that is necessary for normal bone maintenance and growth. (b) The child can drink more milk. Milk is routinely fortified with cholecalciferol, normally identified as “vitamin D,” which is easily absorbed by the intestines.
152
One of the factors to which lie detectors respond is an increase in electrical skin conductance due to the presence of moisture. Explain the physiological basis for the use of this indicator.
Sweating from eccrine sweat glands is precisely regulated, and one influencing factor is emotional state. Presumably, a person who is lying is nervous and sweats profusely; the lie detector machine detects a change in electrical skin conductance caused by this sweating.
153
Many people change the natural appearance of their hair, either by coloring it or by altering the degree of curl in it. Which layers of the hair do you suppose are affected by the chemicals added during these procedures? Why are the effects of the procedures not permanent?
The chemicals in hair dyes break the protective covering of the cortex, allowing the dyes to stain the medulla of the shaft. Dying is not permanent because the cortex remains damaged, allowing shampoo and UV rays from the sun to enter the medulla and affect the color. Also, the living portion of the hair remains unaffected, so that when the shaft is replaced the color will be lost.
154
List the five general classes of blood vessels.
The five general classes of blood vessels are arteries, arterioles, capillaries, venules, and veins.
155
Which type of vessel is characterized by thin walls with very little smooth muscle tissue in the tunica media?
Blood vessels with thin walls and very little smooth muscle tissue in the tunica media are veins. Arteries and arterioles have a large amount of smooth muscle tissue in a thick, well-developed tunica media.
156
Why are valves located in veins but not in arteries?
In the arterial system, pressures are high enough to keep the blood moving forward. In the venous system, blood pressure is too low to keep the blood moving on toward the heart. Valves in veins prevent blood from flowing back toward the capillaries whenever the venous pressure drops.
157
Where in the body would you find fenestrated capillaries?
Fenestrated capillaries are located where fluids and small solutes move freely into and out of the blood, including endocrine glands, the choroid plexus of the brain, absorptive areas of the intestine, and filtration areas of the kidneys.
158
Identify the factors that contribute to total peripheral resistance.
The factors that contribute to total peripheral resistance are vascular resistance, vessel length, vessel luminal diameter, blood viscosity, and turbulence.
159
In a healthy person, where is blood pressure greater: at the aorta or at the inferior vena cava? Explain.
In a healthy person, blood pressure is greater at the aorta than at the inferior vena cava. Blood, like other fluids, moves along a pressure gradient from areas of high pressure to areas of low pressure. If the pressure were higher in the inferior vena cava than in the aorta, the blood would flow backward.
160
While standing in the hot sun, Lailah begins to feel lightheaded and faints. Explain what happened.
While Lailah was standing for a period of time, blood pooled in her lower limbs, which decreased venous return to her heart. In turn, cardiac output decreased, so less blood reached her brain, causing light-headedness and fainting. A hot day adds to this effect, because the loss of body water through sweating reduces blood volume.
161
Mike’s blood pressure is 125/70. What is his mean arterial pressure (MAP)?
Mike’s mean arterial pressure (MAP) is approximately 88.3 mm Hg; 70 + (125 − 70)/3 = 70 + 18.3 = 88.3.
162
Describe the actions of vasodilators and local vasodilators.
Vasodilators promote the dilation of precapillary sphincters. Local vasodilators, such as decreased O2 level or increased CO2 level, act on tissues to accelerate blood flow.
163
How would applying slight pressure to the common carotid artery affect your heart rate?
Pressure on the common carotid artery would decrease blood pressure at the baroreceptors in the carotid sinus. This decrease would lower the frequency of action potentials along the glossopharyngeal nerve (IX) to the medulla oblongata, and more sympathetic impulses would be sent to the heart. The net result would be an increase in the heart rate.
164
What effect would vasoconstriction of the renal artery have on blood pressure and blood volume?
Vasoconstriction of the renal artery would decrease both blood flow and blood pressure at the kidney. In response, the kidney would increase the amount of renin it releases, which in turn would lead to an increase in the level of angiotensin II. The angiotensin II would bring about increased blood pressure and increased blood volume.
165
Why does blood pressure increase during exercise?
Blood pressure increases during exercise because (1) cardiac output increases and (2) resistance in visceral tissues increases.
166
Name the immediate and long-term problems related to the cardiovascular response to hemorrhaging.
The immediate problem during hemorrhaging is maintaining adequate blood pressure and peripheral blood flow; the long-term problem is restoring normal blood volume
167
Explain the role of aldosterone and ADH in long-term restoration of blood volume.
Both aldosterone and ADH promote fluid retention and reabsorption at the kidneys, preventing further reductions in blood volume.
168
Identify the two circuits of the cardiovascular system.
The two circuits of the cardiovascular system are the pulmonary circuit and the systemic circuit.
169
Identify the major patterns of blood vessel organization seen in the pulmonary and systemic circuits of the cardiovascular system.
The major patterns are as follows: (1) The peripheral distributions of arteries and veins on the body’s left and right sides are generally identical, except near the heart, where the largest vessels connect to the atria or ventricles; (2) a single vessel may have several names as it crosses specific anatomical boundaries, making accurate anatomical descriptions possible; and (3) tissues and organs are usually serviced by several arteries and veins.
170
Name the blood vessels that enter and exit the lungs, and whether they contain primarily oxygenated or deoxygenated blood.
The pulmonary arteries enter the lungs carrying deoxygenated blood, and the pulmonary veins leave the lungs carrying oxygenated blood.
171
Trace the path of a drop of blood through the lungs, beginning at the right ventricle and ending at the left atrium.
The path of blood through the lungs is right ventricle → pulmonary trunk → left and right pulmonary arteries → pulmonary arterioles → alveolar capillary network → pulmonary venules → pulmonary veins → left atrium.
172
A blockage of which branch from the aortic arch would interfere with blood flow to the left arm?
A blockage of the left subclavian artery would interfere with blood flow to the left arm.
173
Why would compression of the common carotid arteries cause a person to lose consciousness?
Compression of the common carotid arteries would decrease blood pressure at the carotid sinus and cause a rapid reduction in blood flow to the brain, resulting in a loss of consciousness. An immediate reflexive increase in heart rate and blood pressure would follow.
174
Isabella is in an automobile accident, and her celiac trunk is ruptured. Which organs will be affected most directly by this injury?
Rupture of the celiac trunk would most directly affect the stomach, spleen, liver, and pancreas.
175
Whenever Noah gets angry, a large vein bulges in the lateral region of his neck. Which vein is this?
The vein that is bulging in Noah’s neck is the external jugular vein.
176
A thrombus that blocks the popliteal vein would interfere with blood flow in which other veins?
A blockage of the popliteal vein would interfere with blood flow in the tibial and fibular veins (which form the popliteal vein) and the small saphenous vein (which joins the popliteal vein).
177
Name the three vessels that carry blood to and from the placenta.
Two umbilical arteries supply blood to the placenta, and one umbilical vein returns blood from the placenta. The umbilical vein then drains into the ductus venosus within the fetal liver. (Remember, arteries carry blood away from the heart, and veins carry blood to the heart.)
178
A blood sample taken from an umbilical cord contains high levels of oxygen and nutrients, and low levels of carbon dioxide and waste products. Is this sample from an umbilical artery or the umbilical vein? Explain.
This blood sample was taken from the umbilical vein, which carries oxygenated, nutrient-rich blood from the placenta to the fetus.
179
Name the structures in the fetal circulation that stop functioning at birth. What becomes of these structures?
Structures specific to the fetal circulation include two umbilical arteries, an umbilical vein, the ductus venosus, the foramen ovale, and the ductus arteriosus. In the newborn, the foramen ovale closes and persists as the fossa ovalis, a shallow depression
179
Identify components of the cardiovascular system that are affected by age.
Components of the cardiovascular system affected by age include the blood, heart, and blood vessels.
180
Define thrombus.
A thrombus is a stationary blood clot within the lumen of a blood vessel.
181
Define aneurysm.
An aneurysm is the ballooning out of a weakened arterial wall resulting from sudden pressure increases.
182
Describe what the cardiovascular system provides for all other body systems.
The cardiovascular system provides other body systems with oxygen, hormones, nutrients, and white blood cells in blood, while removing carbon dioxide and metabolic wastes; it also transfers heat to body tissues.
183
What is the relationship between the skeletal system and the cardiovascular system?
The skeletal system provides calcium needed for normal cardiac muscle contraction, and it protects developing blood cells in the red bone marrow. The cardiovascular system provides calcium and phosphate for bone deposition, delivers erythropoietin to red bone marrow, and transports parathyroid hormone and calcitonin to osteoblasts and osteoclasts.
184
The blood vessels that play the most important role in regulating blood pressure and blood flow to a tissue are the (a) arteries, (b) arterioles, (c) veins, (d) venules, (e) capillaries.
b
185
Cardiovascular function is regulated by all of the following except (a) local factors, (b) neural factors, (c) endocrine factors, (d) venous return, (e) conscious control.
e
186
Chemoreceptors that respond to changes in carbon dioxide and oxygen levels in blood are located in the (a) aortic sinuses, (b) aortic bodies, (c) right atrium, (d) brainstem, (e) atrioventricular node.
b
187
The two-way exchange of substances between blood and body cells occurs only through (a) arterioles, (b) capillaries, (c) venules, (d) all of these.
b
188
Large molecules such as peptides and proteins move into and out of the bloodstream by way of (a) continuous capillaries, (b) fenestrated capillaries, (c) thoroughfare channels, (d) venules.
b
189
The local control of blood flow due to the action of precapillary sphincters is (a) vasomotion, (b) autoregulation, (c) selective resistance, (d) turbulence.
b
190
Blood is transported through the venous system by means of (a) skeletal muscle contractions, (b) decreasing blood pressure, (c) the respiratory pump, (d) a and c.
d
191
The most important factor in vascular resistance is (a) the viscosity of the blood, (b) the diameter of the lumen of blood vessels, (c) turbulence due to irregular surfaces of blood vessels, (d) the length of the blood vessels.
b
192
Net hydrostatic pressure forces water ______ a capillary; net osmotic pressure reabsorbs water _______ a capillary. (a) into, out of, (b) out of, into, (c) out of, out of, (d) into, into.
b
193
The three arteries formed by the branching of the celiac trunk are the (a) common hepatic, left gastric, and splenic, (b) left colic, sigmoid, and rectal, (c) middle colic, right colic, and ileocolic, (d) gastroduodenal, cystic, and right gastric.
a
194
The unpaired arteries supplying blood to the visceral organs include (a) the adrenal, renal, and lumbar arteries, (b) the iliac, gonadal, and femoral arteries, (c) the celiac and superior and inferior mesenteric arteries, (d) all of these
c
195
The paired arteries supplying blood to the body wall and other structures outside the abdominopelvic cavity include the (a) left gastric, hepatic, splenic, and phrenic arteries, (b) adrenal, colic, lumbar, and gonadal arteries, (c) iliac, femoral, and lumbar arteries, (d) celiac, left gastric, and superior and inferior mesenteric arteries
c
196
Peripheral distributions of arteries and veins are identical on the left and right sides of the body, except near the (a) gonads, (b) heart, (c) kidneys, (d) lower limbs.
b
197
The vessel that transports venous blood from organs in the peritoneal cavity to the liver is the (a) inferior vena cava, (b) hepatic vein, (c) cystic vein, (d) hepatic portal vein.
d
198
What are the primary forces that cause fluid to move (a) out of a capillary at its arterial end and into the interstitial fluid, (b) into a capillary at its venous end from the interstitial fluid?
(a) Capillary hydrostatic pressure forces fluid out of a capillary at the arterial end. (b) Blood colloid osmotic pressure causes the movement of fluid back into a capillary at its venous end.
199
What cardiovascular changes occur at birth?
When an infant takes its first breath, the lungs expand and pulmonary vessels dilate. The smooth muscles in the ductus arteriosus contract, due to increased venous return from the lungs, isolating the pulmonary and aortic trunks, and blood begins flowing through the pulmonary circuit. As pressure increases in the left atrium, the valvular flap closes the foramen ovale, completing the vascular remodeling.
200
A major difference between the arterial and venous systems is that (a) arteries are usually more superficial than veins, (b) in the limbs there is dual venous drainage, (c) veins are usually less branched compared to arteries, (d) veins exhibit a much more orderly pattern of branching in the limbs, (e) veins are not found in the abdominal cavity.
b
201
Which of the following conditions would have the greatest effect on peripheral resistance? (a) doubling the length of a vessel, (b) doubling the diameter of a vessel, (c) doubling the viscosity of the blood, (d) doubling the turbulence of the blood, (e) doubling the number of white cells in the blood.
b
202
Baroreceptors stimulated by increased blood pressure (a) induce vasoconstriction and cause an increase in cardiac output, (b) induce vasodilation and cause a decrease in cardiac output, (c) do none of these.
b
203
Relate the anatomical differences between arteries and veins to their functions.
Artery walls are generally thicker and contain more smooth muscle and elastic fibers, enabling them to resist and adjust to the pressure generated by the heart. Venous walls are thinner; the pressure in veins is less than that in arteries. Arteries constrict more than veins do when not expanded by blood pressure, due to a greater degree of elastic tissue. Finally, the endothelial lining of an artery has a pleated appearance because it cannot contract and so forms folds. The lining of a vein looks like a typical endothelial layer.
204
How is arterial blood flow to the tissues controlled by the capillaries?
Bands of smooth muscles, called precapillary sphincters, are present at the entrances of the capillaries. Their contraction and relaxation control blood flow to the tissues. Contraction of the sphincters narrows the capillary entrances, reducing or stopping the flow of blood. When the sphincters relax, the entrances dilate, and blood flows into the capillaries. The central passageway in the arteriole system acts as a thoroughfare channel. Blood flow through this channel is controlled by the sphincter effect of the arteriole.
205
How is blood pressure maintained in veins to counter the force of gravity?
Contraction of the surrounding skeletal muscles squeezes venous blood toward the heart. This mechanism, the muscular pump, is assisted by the presence of valves in the veins, which prevent backflow of the blood. The respiratory pump, which results from the increase in internal pressure of the thoracic cavity during exhalation, pushes venous blood into the right atrium.
206
Compare hypertension and hypotension.
Abnormally high blood pressure is termed hypertension, whereas abnormally low blood pressure is called hypotension. Of the two, hypertension is more common. Many cases of hypotension result from aggressive drug treatment for hypertension. Smoking, stress, and obesity are some of the factors that lead to hypertension.
207
Why is blood flow to the brain relatively continuous and constant?
The brain receives arterial blood from four arteries that form anastomoses within the cranium. An interruption of any one vessel will not compromise the blood flow to the brain.
208
Compare the effects of the cardioacceleratory and cardioinhibitory centers on cardiac output and blood pressure.
The cardioacceleratory and vasomotor centers are stimulated when general sympathetic activation occurs. The result is an increase in cardiac output and blood pressure. When the parasympathetic division is activated, the cardioinhibitory center is stimulated, reducing cardiac output.
209
Bob is sitting outside on a warm day and is sweating profusely. Mary wants to practice taking blood pressures, and he agrees to play the patient. Mary finds that Bob’s blood pressure is elevated, even though he is resting and has lost fluid from sweating. (She reasons that fluid loss should lower blood volume and, thus, blood pressure.) Why is Bob’s blood pressure high instead of low?
Fluid loss lowers blood volume, leading to sympathetic stimulation, which elevates blood pressure. So, Bob’s blood pressure is high instead of low.
210
People with allergies commonly take antihistamines with decongestants to relieve their symptoms. The container warns that individuals who are being treated for high blood pressure should not take the medication. Why not?
Antihistamines and decongestants are sympathomimetic drugs; they have the same effects on the body as does stimulation of the sympathetic nervous system. In addition to the desired effects of counteracting the symptoms of the allergy, these medications can produce an increased heart rate, increased stroke volume, and increased peripheral resistance, all of which will contribute to elevating blood pressure. In a person with hypertension (high blood pressure), these drugs would aggravate this condition, with potentially hazardous consequences.
211
Jolene awakens suddenly to the sound of her alarm clock. Realizing that she is late for class, she jumps to her feet, feels light-headed, and falls back on her bed. What probably caused this reaction? Why doesn’t this happen all the time?
When Jolene stood up rapidly, gravity caused her blood volume to move to the lower parts of her body away from the heart, decreasing venous return. The decreased venous return resulted in a decreased end-diastolic volume (EDV), leading to a decreased stroke volume and cardiac output. In turn, blood flow to the brain decreased, so the diminished oxygen supply caused her to be light-headed and feel faint. This reaction doesn’t happen all the time because as soon as the pressure drops due to inferior movement of blood, baroreceptors in the aortic arch and carotid sinuses trigger the baroreceptor reflex. Action potentials are carried to the medulla oblongata, where appropriate responses are integrated. In this case, we would expect an increase in peripheral resistance to compensate for the decreased blood pressure. If this doesn’t compensate enough for the drop, then an increase in heart rate and force of contraction would occur. Normally, these responses occur so quickly that changes in pressure following changes in body position go unnoticed.
