Chapter 20 Lecture PowerPoint

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Blood Vessels and Circulation

• General Anatomy of Blood Vessels • Blood Pressure • Capillary Exchange • Venous Return and Circulatory Shock

20-2

Anatomy of Blood Vessels

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Capillaries Artery: Tunica interna Tunica media Tunica externa Nerve Vein

• • • Figure 20.1a

(a) 1 mm

© The McGraw-Hill Companies, Inc./Dennis Strete, photographer

arteries

carry blood away from heart

veins

carry blood back to heart

capillaries

connect smallest arteries to veins

20-3

Vessel Wall

•

tunica interna

(tunica intima) – lines the blood vessel and is exposed to blood –

endothelium

basement membrane and a sparse layer of loose connective tissue • • – simple squamous epithelium overlying a

selectively permeable barrier secretes chemicals

that stimulate dilation or constriction of the vessel • normally

repels blood cells and platelets

(prevents clots)

20-4

Vessel Wall

•

tunica media

– middle layer –

smooth muscle

, collagen, and elastic tissue – strengthens vessel and prevents blood pressure from rupturing them –

vasomotion

– changes in diameter of the blood vessel brought about by smooth muscle

20-5

Vessel Wall

•

tunica externa

(tunica adventitia) – outermost layer – loose connective tissue that often merges with that of neighboring blood vessels, nerves, or other organs – anchors the vessel and provides passage for small nerves, lymphatic vessels

20-6

Figure 20.2

20-7

Arteries

•

arteries

- sometimes called

resistance vessels

because they have strong, resilient tissue structure that resists blood pressure – small arteries are called arterioles – carry blood away from heart

20-8

•

Aneurysm

aneurysm

- weak point in an artery or heart wall – forms thin-walled, bulging sac that pulses with each heartbeat • may rupture at any time, causing hemorrhage –

dissecting aneurysm -

blood accumulates between the tunics of the artery and separates them – can cause pain by putting pressure on other structures – result from congenital weakness of the blood vessels or result of trauma or bacterial infections such as syphilis • most common cause is atherosclerosis and hypertension

20-9

Arterial Sense Organs

• sensory structures in the walls of certain vessels that monitor blood pressure and chemistry – send info to brainstem that serves to regulate heart rate, vasomotion, and respiration –

carotid sinuses –

baroreceptors (pressure sensors) • in walls of internal carotid artery • monitor blood pressure –

carotid bodies

- chemoreceptors (monitor blood chemistry) • oval bodies near branch of common carotids • adjust respiratory rate to stabilize pH, CO 2 , and O 2 –

aortic bodies -

chemoreceptors • one to three in walls of aortic arch • same function as carotid bodies

20-10

Capillaries

•

capillaries

- site where nutrients, wastes, and hormones are exchanged between the blood and tissue fluid (exchange vessels) – the ‘business end’ of the cardiovascular system – absent or scarce in tendons, ligaments, epithelia, cornea and lens of the eye •

three capillary types

distinguished by structural differences that account for their greater or lesser permeability

20-11

Three Types of Capillaries

1. continuous capillaries

- occur in most tissues –

endothelial cells

have

tight junctions

forming a continuous tube with

intercellular clefts

• allow passage of solutes such as glucose –

pericytes

wrap around the capillaries and contain the same contractile protein as muscle • contract and regulate blood flow

20-12

Continuous Capillary

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Pericyte Basal lamina Intercellular cleft Pinocytotic vesicle Endothelial cell Erythrocyte

Figure 20.5

Tight junction 20-13

Three Types of Capillaries

2. fenestrated capillaries

- kidneys, small intestine – organs that require rapid absorption or filtration – endothelial cells riddled with holes called

filtration pores (fenestrations)

• spanned by very thin glycoprotein layer • allows passage of only small molecules

20-14

(a)

Fenestrated Capillary

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Endothelial cells Erythrocyte Nonfenestrated area Filtration pores (fenestrations) Basal lamina Intercellular cleft (b)

b: Courtesy of S. McNutt

400 µm

Figure 20.6a

Figure 20.6b

20-15

Three Types of Capillaries

3. sinusoids (discontinuous capillaries)

- liver, bone marrow, spleen – irregular blood-filled spaces with large fenestrations – allow proteins (albumin), clotting factors, and new blood cells to enter the circulation

20-16

Sinusoid in Liver

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Macrophage Endothelial cells Erythrocytes in sinusoid Liver cell (hepatocyte) Microvilli Sinusoid

Figure 20.7

20-17

Capillary Beds

• capillaries organized into networks called

capillary beds

– usually supplied by a single

metarteriole

•

thoroughfare channel

- metarteriole that continues through capillary bed to venule •

precapillary sphincters

control which beds are well perfused –

when sphincters open

• capillaries perfused with blood and exchange substances with tissue fluid –

when sphincters closed

• blood bypasses the capillaries • flows through thoroughfare channel to venule • 3/4 of the body’s capillaries are shut down at a given time

20-18

Capillary Bed Sphincters Open

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Precapillary sphincters Thoroughfare channel Metarteriole Capillaries Venule

Figure 20.3a

Arteriole (a) Sphincters open

when sphincters are open, the capillaries are well perfused

20-19

Capillary Bed Sphincters Closed

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Figure 20.3b

Arteriole (b) Sphincters closed Venule

when the sphincters are closed, little to no blood flow occurs (skeletal muscles at rest)

20-20

Veins (Capacitance Vessels)

• greater capacity for blood containment than arteries • thinner walls, flaccid, less muscule and elastic tissue • collapse when empty, expand easily • have steady blood flow • merge to form larger veins • subjected to relatively low blood pressure Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Distribution of Blood Veins 54% Systemic circuit 70% Pulmonary circuit 18% Heart 12% Capillaries 5% Arteries 11%

Figure 20.8

20-21

•

Veins

postcapillary venules

– smallest veins – even more porous than capillaries so also exchange fluid with surrounding tissues • •

medium veins

have

venous valves

– skeletal muscle pump propels venous blood back towards heart

venous sinuses

– veins with especially thin walls, large lumens, and no smooth muscle

20-22

Varicose Veins

• blood pools in the lower legs in people who stand for long periods, stretching the veins – cusps of the valves pull apart in enlarged superficial veins further weakening vessels – blood backflows and further distends the vessels, their walls grow weak and develop into

varicose veins

• hereditary weakness, obesity, and pregnancy also contribute •

hemorrhoids

canal are varicose veins of the anal

20-23

?

20-24

Blood Pressure

• blood pressure (bp) – the force that blood exerts against a vessel wall • measured at

brachial artery

of arm using

sphygmomanometer

• two pressures are recorded: –

systolic pressure

: peak arterial BP taken during ventricular contraction (ventricular systole) –

diastolic pressure

: minimum arterial BP taken during ventricular relaxation (diastole) between heart beats • normal value, young adult:

120/75 mm Hg 20-25

Abnormalities of Blood Pressure

•

hypertension

– high blood pressure

– chronic is resting BP > 140/90 – consequences • can weaken small arteries and cause aneurysms

•

hypotension

– chronic low resting BP

– caused by blood loss, dehydration, anemia

20-26

Blood Pressure

• one of the body’s chief mechanisms in preventing excessive blood pressure is the ability of the arteries to

stretch and recoil

during the cardiac cycle • importance of arterial elasticity – expansion and recoil maintains steady flow of blood throughout cardiac cycle, smoothes out pressure fluctuations and decreases stress on small arteries • BP rises with age – arteries less elastic and absorb less systolic force • BP determined by

cardiac output, blood volume

and

peripheral resistance 20-27

BP Changes With Distance

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

120 100 80 60 40 20 0 Diastolic pressure Systolic pressure

Figure 20.10

Increasing distance from left ventricle 20-28

Two Purposes of Vasomotion

• general method of

raising or lowering BP throughout the whole body

– important in supporting brain during hemorrhage or dehydration • method of

rerouting blood

from one region to another for perfusion of individual organs – either centrally or locally controlled • during exercise, blood flow reduced to kidneys and digestive tract and increased to skeletal muscles • metabolite accumulation in a tissue affects local circulation without affecting circulation elsewhere in the body

20-29

Blood Flow in Response to Needs

Aorta Superior mesenteric artery Dilated Increased flow to intestines Common iliac arteries Constricted Reduced flow to legs (a) Constricted Reduced flow to intestines Dilated Increased flow to legs (b) Figure 20.14

arterioles shift blood flow with changing priorities

20-30

Blood Flow Comparison

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

At rest Total cardiac output 5 L/min Moderate exercise Total cardiac output 17.5 L/min Coronary 200 mL/min (4.0%) Other 350 mL/min (7.0%) Cutaneous 300 mL/min (6.0%) Muscular 1,000 mL/min (20.0%) Cerebral 700 mL/min (14.0%) Renal 1,100 mL/min (22.0%) Digestive 1,350 mL/min (27.0%) Coronary 750 mL/min Cutaneous 1,900 mL/min (4.3%) (10.9%) Other 400 mL/min (2.3%) Cerebral 750 mL/min (4.3%) Renal 600 mL/min (3.4%) Digestive 600 mL/min (3.4%) Muscular 12,500 mL/min (71.4%)

Figure 20.15

during exercise – increased perfusion of lungs, myocardium, skeletal muscles – decreased perfusion of kidneys and digestive tract

20-31

Capillary Exchange

• only through capillary walls are exchanges made between the blood and surrounding tissues •

capillary exchange

– two way movement of fluid across capillary walls – water, oxygen, glucose, amino acids, lipids, minerals, antibodies, hormones, wastes, carbon dioxide, ammonia • chemicals pass through the capillary wall by

three routes

–

through endothelial cell cytoplasm

– –

intercellular clefts between endothelial cells filtration pores (fenestrations) of the fenestrated capillaries 20-32

Capillary Exchange - Diffusion

•

diffusion

is the most important form of capillary exchange – glucose and oxygen diffuse out of the blood – carbon dioxide and other waste diffuse into the blood

Always down conc. gradient

• capillary diffusion can only occur if: – the solute can permeate the plasma membranes of the endothelial cell, or •

lipid soluble substances

diffuse easily through plasma membranes – can find passages large enough to pass through •

water soluble substance

must pass through filtration pores and intercellular clefts • large particles like proteins are held back

20-33

Capillary Exchange - Transcytosis

• endothelial cells 1. pick up material on one side of the plasma membrane by pinocytosis or receptor-mediated endocytosis, 2. transport vesicles across cell, and 3. discharge material on other side by exocytosis • important for fatty acids, albumin and some hormones (insulin) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Filtration pores Transcytosis Diffusion through endothelial cells Intercellular clefts

Figure 20.16

20-34

Filtration and Reabsorption

• fluid filters out of the arterial end of the capillary and osmotically reenters at the venous end – delivers materials to the cell and removes metabolic wastes • opposing forces –

blood hydrostatic pressure

(physical) drives fluid out of capillary • high on arterial end of capillary, low on venous end –

colloid osmotic pressure

• • results from plasma proteins (albumin)- more in blood

oncotic pressure

(COP) draws fluid into capillary = net COP (blood COP - tissue COP) • capillaries reabsorb about

85%

of the fluid they filter

20-35

Capillary Filtration and Reabsorption

•

capillary filtration

at arterial end •

capillary reabsorption

at venous end Figure 20.17

20-36

Capillary Filtration and Reabsorption

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Figure 20.17

20-37

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Edema

•

edema

– the accumulation of excess fluid in a tissue – occurs when fluid filters into a tissue faster than it is absorbed

• three primary causes

–

increased capillary filtration

• kidney failure, histamine release, old age, poor venous return –

reduced capillary absorption

• hypoproteinemia, liver disease, dietary protein deficiency –

obstructed lymphatic drainage

• surgical removal of lymph nodes

20-39

Consequences of Edema

• tissue necrosis – oxygen delivery and waste removal impaired • pulmonary edema – suffocation threat • cerebral edema – headaches, nausea, seizures, and coma • severe edema - circulatory shock – excess fluid in tissue spaces causes low blood volume and low blood pressure

20-40

?

20-41

Mechanisms of Venous Return

•

venous return

– the flow of blood back to the heart –

pressure gradient

• blood pressure is the most important force in venous return –

gravity

drains blood from head and neck –

skeletal muscle pump

in the limbs –

thoracic (respiratory) pump

• inhalation - thoracic cavity expands and thoracic pressure decreases, abdominal pressure increases forcing blood upward –

cardiac suction

of expanding atrial space

20-42

Skeletal Muscle Pump

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To heart Valve open Venous blood Valve closed (a) Contracted skeletal muscles (b) Relaxed skeletal muscles

Figure 20.19 a-b

20-43

Venous Return and Physical Activity

• •

exercise increases venous return

in many ways: – heart beats faster, harder increasing CO and BP – vessels of skeletal muscles, lungs, and heart dilate – increased respiratory rate, increased action of thoracic pump – increased skeletal muscle pump

venous pooling

occurs with inactivity – venous pressure not enough force blood upward – with prolonged standing, CO may be low enough to cause dizziness • prevented by tensing leg muscles, activate skeletal muscle pump – jet pilots wear pressure suits

20-44

• –

Circulatory Shock

–

circulatory shock

– cardiac output is insufficient to meet the body’s metabolic needs

cardiogenic shock

- inadequate pumping of heart (MI)

low venous return (LVR)

– cardiac output is low because too little blood is returning to the heart

1. hypovolemic shock

- most common -loss of blood volume: trauma, burns, dehydration

2. obstructed venous return shock

-tumor or aneurysm compresses a vein

3. venous pooling (vascular) shock

-next slide

20-45

Vascular Shock and Others

• • –

venous pooling (vascular) shock

• • long periods of standing, sitting or widespread vasodilation

neurogenic shock

- loss of vasomotor tone, vasodilation – emotional shock, brainstem injury

septic shock

– bacterial toxins trigger vasodilation and increased capillary permeability

anaphylactic shock

– severe immune reaction to antigen, histamine release, generalized vasodilation, increased capillary permeability

20-46

TIAs and CVAs

•

transient ischemic attacks (TIAs )

– brief episodes of cerebral ischemia – caused by spasms of diseased cerebral arteries – dizziness, loss of vision, weakness, paralysis, headache or aphasia – lasts from a moment to a few hours – often early warning of impending stroke •

stroke - cerebral vascular accident (CVA)

– sudden death of brain tissue caused by ischemia • atherosclerosis, thrombosis, ruptured aneurysm – effects range from unnoticeable to fatal • blindness, paralysis, loss of sensation, loss of speech common

20-47

•

Hypertension

hypertension

– most common cardiovascular disease affecting about 30% of Americans over 50 •

“the silent killer”

– major cause of heart failure, stroke, and kidney failure • damages heart by increasing afterload – myocardium enlarges until overstretched and inefficient • renal arterioles thicken in response to stress – drop in renal BP leads to salt retention (aldosterone) and worsens the overall hypertension •

primary hypertension

– obesity, sedentary behavior, diet, nicotine •

secondary hypertension

– secondary to other disease – kidney disease, hyperthyroidism

20-48

END 20-49