Transcript High blood pressure

Chapter Goals
After studying this chapter, students should be able to . . .
1. describe the general functions of the major components of the circulatory
system.
2. describe the structures and pathways of the pulmonary and systemic
circulations.
3. compare the structure of an artery and vein, and explain how the structure of
each type of vessel relates to its function.
4. describe the structure of capillaries and explain the physiological significance
of this structure.
5. explain how atherosclerosis may develop and comment on the significance
of this condition.
6. describe the components and functions of the lymphatic system.
7. define cardiac output and describe how it is affected by cardiac rate and
stroke volume
8. explain how autonomic nerves regulate the cardiac rate and the strength of
ventricular contraction
Chapter Goals
After studying this chapter, students should be able to . . .
9. explain the intrinsic regulation of stroke volume (the Frank-Starling law of the
heart)
10. list the factors that affect the venous return of blood to the heart
11. explain how tissue fluid is formed and how it is returned to the capillary
blood
12. explain how edema may be produced
13. explain how antidiuretic hormone helps to regulate the blood volume,
plasma osmolality, and the blood pressure
14. explain the role of aldosterone in the regulation of blood volume and
pressure
15. describe the renin-angiotensin system and its significance in cardiovascular
regulation
16. use Poiseuille's law to explain how blood flow is regulated
17. define total peripheral resistance, and explain how vascular resistance is
regulated by extrinsic control mechanisms
Chapter Goals
18. describe the intrinsic mechanisms involved in the autoregulation of blood
flow
19. explain the mechanisms by which blood flow to the heart and skeletal
muscles is regulated
20. describe the changes that occur in the cardiac output and in the distribution
of blood flow in the body during exercise
21. describe the factors that regulate the arterial blood pressure
22. describe the baroreceptor reflex and explain its significance in blood
pressure regulation
23. explain how the sounds of Korotkoff are produced and how these sounds
are used to measure blood pressure
24. describe how the pulse pressure and mean arterial pressure are calculated
and explain the significance of these measurements
25. explain the mechanisms that contribute to and that help compensate for the
conditions of hypertension, circulatory shock, and congestive heart failure
IV. CIRCULATION
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Hemodynamics
Capillary Dynamics
Lymphatics
Special Areas
Hemodynamics
• Cardiac output
• Venous return
• Circulation
Cardiac Output
• Cardiac Output = Heart Rate X Stroke Volume
• a. If HR = 70 b/m and SV = 70 mL/b, then
CO = 70 x 70
= 4,900 mL/m
• b. If CO = 4,900 mL/m and SV = 100 mL/b, then
HR = 4,900/100
= 49 b/m
Cardiac Output (cont’d)
• c. Since physical conditioning results in a greater
SV, then HR is less for any given CO. The only
time the heart muscle itself receives blood and
nourishment is during diastole, and the slower HR
the more time the heart spends in diastole. So
physical conditioning allows a longer time for the
heart to receive nourishment with each cardiac
cycle.
Cardiac Output (cont’d)
• d. Starling's Law -- The force with which a muscle
contracts is proportional to the initial length of the
contracting fibers.
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Venous Return
a. Valves
b. “Skeletal Muscle Pump”
c. Low peripheral resistance
d. "Thoracic pump"
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Circulation
• Volume of Flow
– Effect of Pressure and Resistance on Flow
F(vol) = rP/R
10-2
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Circulation
• Volume of Flow
– Poiseuille's Law
F(vol) = prP(r)4/8hL
Where h = Viscosity
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10-9
Cardiac Control (cont’d)
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Circulation (cont’d)
• Velocity of Flow
F(vel) = 1/cross-sectional area
– i.
– ii.
Aorta = 50 cm/sec
Capillaries = 0.06 cm/sec
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10-18a
10-18b
Circulation (cont’d)
• Regulation of Flow
– Chemical
 Metabolites (CO2 & Lactic Acid —>dilation)
 Tissue hypoxia —> adenosine —> dilation
– Neural : epinephrine —> vasoconstriction
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Circulation (cont’d)
• Blood Pressure
– Types
• Pulse Pressure = Systolic Pressure - Diastolic
Pressure
• Mean Pressure - Average during one cardiac cycle =
D + 1/3(S - D) or D + 1/3 Pulse pressure
• Arterial Blood Pressure - Pressure in a large artery
– Regulation
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Capillary Dynamics
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Lymphatics
• Since there is normally a net filtration
pressure in capillaries, the lymphatic vessels
return the fluid filtered to the blood stream.
Vessels begin as blind capillaries, which
eventually empty into the subclavian veins.
Lymph is propelled by the same factors that
aid venous return
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10-25b
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Special Areas
1. Coronary - Heart receives only during diastole
2. Pulmonary - Low resistance results in low
pressure, so there is a net reabsorption pressure in
pulmonary capillaries, which keeps the pulmonary
membrane thin and, thus, aids gas exchange.
3. Cerebral - Circle of Willis maintains blood flow to
both sides of the brain, even if a blood vessel
proximal to the circle is blocked
Chapter Summary
Blood Vessels
I. Arteries contain three layers, or tunics: the interna, media, and externa.
A. The tunica interna consists of a layer of endothelium, which is separated from the
tunica media by a band of elastin fibers.
B. The tunica media consists of smooth muscle.
C. The tunica externa is the outermost layer.
D. Large arteries, containing many layers of elastin can expand and recoil with
rising and falling blood pressure. Medium and small arteries and arterioles are
less distensible, and thus provide greater resistance to blood flow.
II. Capillaries are the narrowest but the most numerous of the blood vessels.
A. Capillary walls consist of just one layer of endothelial cells. They provide for the
exchange of molecules between the blood and the surrounding tissues.
B. The flow of blood from arterioles to capillaries is regulated by precapillary
sphincter muscles.
C. The capillary wall may be continuous, fenestrated, or discontinuous.
Chapter Summary
III. Veins have the same three tunics as arteries, but they generally have a
thinner muscular layer than comparably sized arteries.
A. Veins are more distensible than arteries and can expand to hold a larger
quantity of blood.
B. Many veins have venous valves that ensure a one-way flow of blood to
the heart.
C. The flow of blood back to the heart is aided by contraction of the skeletal
muscles that surround veins. The effects of this action is called the
skeletal muscle pump.
Chapter Summary
Atherosclerosis and Cardiac Arrhythmias
I. Atherosclerosis of arteries can occlude blood flow to the heart and brain,
causing up to 50% of all mortality in the United States, Europe, and Japan.
A. Atherosclerosis begins with injury to the endothelium, the movement of
monocytes and lymphocytes into the tunica interna, and the conversion of
monocytes into macrophages that engulf lipids. Smooth muscle cells then
proliferate and secrete extracellular matrix.
B. Atherosclerosis is promoted by smoking, hypertension, and high plasma
cholesterol concentration, among other risk factors; low-density lipoproteins
(LDL), which carry cholesterol into the artery wall, is oxidized by the endothelium
and is a major contributor to atherosclerosis.
II. Occlusion of blood flow in the coronary arteries by atherosclerosis may
produce ischemia of the heart muscle and angina pectoris, which may lead
to myocardial infarction.
III. The ECG can be used to detect abnormal cardiac rates, abnormal
conduction between the atria and ventricles, and other abnormal patterns of
electrical conduction in the heart.
Chapter Summary
Lymphatic System
I. Lymphatic capillaries are blind-ended but highly permeable. They drain
excess tissue fluid into lymph ducts.
II. Lymph passes through lymph nodes and is returned by way of the lymph
ducts to the venous blood.
Chapter Summary
Cardiac Output
I. Cardiac rate is increased by sympathoadrenal stimulation and decreased by
the effects of parasympathetic fibers that innervate the SA node.
II. Stroke volume is regulated both extrinsically and intrinsically.
A. The Frank-Starling law of the heart describes the way the end-diastolic volume,
through various degrees of myocardial stretching, influences the contraction
strength of the myocardium and thus the stroke volume.
B. The end-diastolic volume is called the preload. The total peripheral resistance,
through its effect on arterial blood pressure, provides an afterload that acts to
reduce the stroke volume.
C. At a given end-diastolic volume, the amount of blood ejected depends on
contractility. Strength of contraction is increased by sympathoadrenal stimulation.
III. The venous return of blood to the heart is dependent largely on the total
blood volume and mechanisms that improve the flow of blood in the veins.
A. The total blood volume is regulated by the kidneys.
B. The venous flow of blood to the heart is aided by the action of skeletal muscle
pumps and the effects of breathing.
Chapter Summary
Blood Volume
I. Tissue fluid is formed from and returns to the blood.
A. The hydrostatic pressure of the blood forces fluid from the arteriolar ends of
capillaries into the interstitial spaces of the tissues.
B. Since the colloid osmotic pressure of plasma is greater than tissue fluid, water
returns by osmosis to the venular ends of capillaries.
C. Excess tissue fluid is returned to the venous system by lymphatic vessels.
D. Edema occurs when there is an accumulation of tissue fluid.
II. The kidneys control the blood volume by regulating the amount of filtered
fluid that will be reabsorbed.
A. Antidiuretic hormone stimulates reabsorption of water from the kidney filtrate and
thus acts to maintain the blood volume.
B. A decrease in blood flow through the kidneys activates the renin-angiotensin
system.
C. Angiotensin II stimulates vasoconstriction and the secretion of aldosterone by the
adrenal cortex.
D. Aldosterone acts on the kidneys to promote the retention of salt and water.
Chapter Summary
Vascular Resistance and Blood Flow
I. According to Poiseuille's law, blood flow is directly related to the pressure
difference between the two ends of a vessel and is inversely related to the
resistance to blood flow through the vessel.
II. Extrinsic regulation of vascular resistance is provided mainly by the
sympathetic nervous system, which stimulates vasoconstriction of arterioles
in the viscera and skin.
III. Intrinsic control of vascular resistance allows organs to autoregulate their
own blood flow rates.
A. Myogenic regulation occurs when vessels constrict or dilate as a direct
response to a rise or fall in blood pressure.
B. Metabolic regulation occurs when vessels dilate in response to the local
chemical environment within the organ.
Chapter Summary
Blood Flow to the Heart and Skeletal Muscles
I. The heart normally respires aerobically because of its high capillary supply,
myoglobin content, and enzyme content.
II. During exercise, when the heart's metabolism increases, intrinsic metabolic
mechanisms stimulate vasodilation of the coronary vessels and thus
increase coronary blood flow.
III. Just prior to exercise and at the start of exercise, blood flow through skeletal
muscles increases due to vasodilation caused by cholinergic sympathetic
nerve fibers. During exercise, intrinsic metabolic vasodilation occurs.
IV. Since cardiac output can increase by a factor of five or more during
exercise, the heart and skeletal muscles receive an increased proportion of
a higher total blood flow.
A. The cardiac rate increases due to lower activity of the vagus nerve and higher
activity of the sympathetic nerve.
B. The venous return is greater because of higher activity of the skeletal muscle
pumps and increased breathing.
C. Increased contractility of the heart, combined with a decrease in total peripheral
resistance, can result in a higher stroke volume.
Chapter Summary
Blood Flow to the Brain and Skin
I. Cerebral blood flow is regulated both myogenically and metabolically.
A. Cerebral vessels automatically constrict if the systemic blood pressure
rises too high.
B. Metabolic products cause local vessels to dilate and supply more active
areas with more blood.
II. The skin has unique arteriovenous anastomoses, which can shunt the blood
away from surface capillary loops when body temperature rises.
A. The activity of sympathetic nerve fibers causes constriction of cutaneous
arterioles.
B. As a thermoregulatory response, there is increased cutaneous blood
flow and increased flow through surface capillary loops when the body
temperature rises.
Chapter Summary
Blood Pressure
I. Baroreceptors in the aortic arch and carotid sinuses affect, via the
sympathetic nervous system, the cardiac rate and the total peripheral
resistance.
A. The baroreceptor reflex causes pressure to be maintained when an upright
posture is assumed. This reflex can cause a lowered pressure when the carotid
sinuses are massaged.
B. Other mechanisms that affect blood volume help to regulate blood pressure.
II. Blood pressure is commonly measured indirectly by auscultation of the
brachial artery when a pressure cuff is inflated and deflated.
A. The first sound of Korotkoff, caused by turbulent flow of blood through a
constriction in the artery, occurs when the cuff pressure equals the systolic
pressure.
B. The last sound of Korotkoff is heard when the cuff pressure equals the diastolic
blood pressure.
III. The mean arterial pressure represents the driving force for blood flow
through the arterial system.
Chapter Summary
Hypertension, Shock, and Congestive Heart Failure
I. Hypertension, or high blood pressure, is classified as either primary or
secondary.
A. Primary hypertension, also called essential hypertension, may be the result of the
interaction of many mechanisms that raise the blood volume, cardiac output,
and/or peripheral resistance.
B. Secondary hypertension is the direct result of known, specific diseases.
II. Circulatory shock occurs when there is inadequate delivery of oxygen to the
organs of the body.
A. In hypovolemic shock, low blood volume causes low blood pressure that may
progress to an irreversible state.
B. The fall in blood volume and pressure stimulates various reflexes that produce a
rise in cardiac rate, shift of fluid from the tissues into the vascular system,
decrease in urine volume, and vasoconstriction.
III. Congestive heart failure occurs when the cardiac output is insufficient to
supply the blood flow required by the body. The term congestive is used to
describe the increased venous volume and pressure that results.