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Chapter 20– Blood Vessels & Circulation

Ch. 20 (Blood vessels) Study Guide 1. Critically read Chapter 20 pp. 756-774 right

before 20.4 “Venous return and circulatory shock” section. Also read Table 20.3 (p.782) and Insight 20.5 (p.808) in the textbook.

2. Comprehend Terminology (those in bold)3. Study-- Figure questions, Think About It

questions, and Before You Go On (section-ending) questions

4. Do Testing Your Recall— 1-8, 10-12, 14-16, 185. Do True or False– 1-2, 4-5, 8-96. Do Testing Your Comprehension-- #5

2

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§ 20.1—General Anatomy of Blood Vessels

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§ Introduction of Blood Vessels1A. Closed circulatory system– Def. Blood flows

in a continuous circuit through the body under pressure generated by the heart.– 1B. Open circulatory system-- In what

animals?

2. Three principal categories of blood vessels:– Arteries: efferent vessels– Capillaries:– Veins: afferent vessels

Fig. 20.x

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§ Vessel wall of arteries/veins-11. Innermost layer (tunica interna/intima)

A. Structures: lines the inside of the vessel and is exposed to the blood; consists of--• Endothelial cells– histology?• Basement membrane• Connective tissue (sparse)

B. Functions of the endothelial cells—• Selectively permeable barrier• Secrets chemicals--?• Repels blood cells and platelets

Fig. x 20-6

The vessel wall

1

2

3

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Next slide

§ Vessel wall of arteries/veins-22. Middle layer (tunica media)—

thickest layer A.Structures:

– Smooth muscle cells-- – Collagen fibers– Elastic fibers (in arteries)

B. Functions of this layer:– Strengthen the vessel– Provide vasomotion--?

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§ Vessel wall of arteries/veins-33. Outermost layer (tunica externa or

advertitia)—A. Structures:

– Largely loose connective tissue (collagen fibers)

B. Functions:– Protection & anchoring– Provide passage for--

• Vasa vasorum— vessels of the vessels

Fig. 20.220-9

Lumen

Endothelium

Nerve

Conducting (large) artery

Tunica interna:

Basementmembrane

Tunica media

Tunica externa

Vasavasorum

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§ Arteries1. More muscular2. Able to resist high blood pressure

– Thus called resistance vessels3. Retain their round shape even when

empty4. Divided into three categories by size

(next slide)

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§ Categories of Arteries-11. Conducting (elastic/large) arteries - largest

– Ex. aorta, common carotid, subclavian, common iliac, and pulmonary trunk (Fig. 20.23)

– Structure– (Slide #10)• tunica media-- 40-70 layers of smooth

muscle alternating with elastic tissue • Internal/external elastic lamina— not obvious• tunica externa– vasa vasorum

– Function--• Able to expand/recoil-- • But not so in atherosclerosis– aneurysms

and rupture (Slides #15-16)

ID—A--The aorta and its major branches

(Table 20.3)

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R. subclavian a.

L. subclavian a.

Brachiocephalic trunk

Diaphragm

Aortic hiatus

Aortic arch

R. commoncarotid a.

Descendingaorta,abdominal

Descendingaorta, thoracic(posterior to heart)

Ascendingaorta

L. commoncarotid a.

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Aneurysm (read p. 758 box)1. Def.– a balloon-like outpocketing of an

artery wall (Fig. Y)

2. Risk– for rupture, most often reflects gradual weakening of the artery

3. Causes– OFTEN chronic hypertension or atherosclerosis

4. Common sites– abdominal aorta, renal arteries, and the arterial circle at base of brain

Fig. Y20-15

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§ Categories of Arteries-22. Distributing (muscular, medium) arteries

– Distribute blood to specific organs – Ex. brachial, femoral, renal, and splenic

arteries etc.– Structure--

• tunica media– up to 40 layers of smooth muscle

• Internal/external elastic lamina— conspicuous/not conspicuous (circle one)

Fig. 20.34, 29, 30, 36

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§ Categories of Arteries-33. Resistance (small) arteries

– Up to 25 layers of smooth muscle– Elastic tissue little

– ARTERIOLES (smallest of these); 1-3 smooth m. layers• Empty blood into capillaries through

____________________• Here individual muscle cells form a

precapillary sphincter encircling the entrance to capillary; function?

Fig. 20.3

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1

3

4

2

2a

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§ Arterial Sense Organs (3 kinds)• Where– structures in major arteries above heart• Function– to monitor blood pressure/chemistryThree kinds (2 categories): Fig. 20.41.Carotid sinuses (Baroreceptors)—Details next

– Location-- in walls of ascending aorta etc.– monitors BP – a rise in BP signals brainstem . . .

2.Carotid bodies (Chemoreceptors)– Location-- oval bodies near carotids– monitor blood chemistry

• adjust respiratory rate to stabilize pH, CO2, and O2

3.Aortic bodies (Chemoreceptors)– Location-- in walls of aortic arch– same function as carotid bodies

Figure 20.4

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1C

2

3

1A+B

To brain

To the face

§ Capillaries

1. Material exchanges– between blood and tissue fluids

– Locations-- _____________ and smallest of the venules

2. Structure– endothelium + ____________– Fig. X next

3. Close vicinity to all cells— Exceptions– Scarce in: tendons, ligaments, & cartilage– Absent from (3 locations): -

__________________________(Epi. & Eyes)20-22

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§ 3 Types of Capillaries

1. Continuous capillaries- occur in most tissues, ex. Skeletal muscle – endothelial cells have tight junctions

with intercellular clefts (allow passage of solutes)

– What molecules can pass– ex. glucose – What molecules can not– protein,

formed elements of the blood– Fig. 20.5

Continuous capillary

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§ 3 Types of Capillaries2. Fenestrated capillaries

– Structure – have _____________ on endothelial cells

– filtration pores – spanned by very thin glycoprotein layer - allows passage of molecules such as _____________

– Locations-- organs that require rapid absorption or filtration - kidneys, small intestine etc.

– Fig. 20.6 a and b

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Fenestrated Capillary

20.6b--Surface view of a fenestrated endothelial cell 20-28

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§ 3 Types of Capillaries3. Sinusoids (discontinuous) capillaries-

– Structure– endothelial cells separated by wide gaps; no basal lamina

– Conform to the shape of the surrounding tissue

– Molecules can pass– proteins and blood cells

– Locations-- liver, bone marrow, spleen, lymphatic organs

– Fig. 20.7

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Sinusoid in Liver

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§ Veins (capacitance vessels; why?)

1. b/c Greater capacity for blood containment than arteries do (Fig. 20.8)

2. thinner walls—due to less muscular and elastic tissue; why?

3. lower blood pressure: 10 mm Hg with little fluctuation

4. ____________ aid skeletal muscles in upward blood flow

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§ Types of veins-- Smallest to largest vessels (A)

1. Postcapillary venules-- only tunica intima– Receive blood from capillaries– more porous than capillaries

2. Muscular venules-- receive blood from #1– have tunica media (1-2 layers of smooth

muscle) + thin tunica externa

3. Medium veins–

– Most have individual names, Examples-- radius or ulna veins

– Many have venous valves

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§ Types of veins-- Smallest to largest vessels (B)

4. Venous sinuses--– veins with thin walls, large lumens, no smooth

muscle; vasomotion– yes/no? (Circle one)– Examples– coronary sinus of the heart and the

dural sinuses of the brain

5. Large veins--– Greater than 10 mm (diameters)– Venae cavae, pulmonary veins, internal jugular

veins

§ Circulatory Routes

1. Most common route– heart arteries

arterioles capillaries

venules veins

2. Portal system– blood flows through

two consecutive capillary networks before returning to heart

– 3 places in human body–

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Figure 20.38b

1

3

2

4

5

B. Hepatic portal sys. (p.797)

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§ 3 AnastomosesDef. Point where 2 blood

vessels merge

3.Arteriovenous shunt– artery flows directly into

vein; fingers etc.

4.Venous anastomosis– most common type– alternate drainage of

organs; Fig. 20.33

5.Arterial anastomosis– Two arteries merge– collateral circulation

(coronary); Fig. 20.31

What type of circulatory route does inferior/superior mesenteric vein belong?

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§ 20.2— Blood Pressure, Resistance, and Flow

§ Blood pressure, resistance, and flow

• Importance– deliver oxygen and nutrients and to remove wastes at a rate keeps pace with tissue metabolism

• Blood flow (F)– is the amount of blood flowing through an organ, tissue, or blood vessel in a given time

• Hemodynamics: Blood Flow (F) = ΔP/R– Where ΔP is the pressure difference and R is the

resistance

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§ Blood Pressure1. Blood pressure (BP)– Def. the force

per unit area exerted by the blood against a vessel wall

2. In what vessels can you find BP?

Figure 20.10 has the answer

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Why ?

Why?

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§ Blood Pressure3.BP is understood to mean the

pressure in the _________________

4.BP rises and falls in a pulsatile fashion in the arteries and arterioles

Figure Z (what BP do we measure?)

D. Mean arterialpressure

A--?

B--?

Four different kinds of arterial BP--

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C.

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§ Blood Pressure5.Systolic P.– the maximum p.

exerted in the arteries when blood is ejected into them during ventricular ejection, averages 120 mm Hg (Mercury) • Physiology– during ventricular systole,

a volume of blood enters the arteries from the ventricle. How much actually moves to the arterioles?

• Status of the semilunar valves in this particular cardiac cycle? (open or close)

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§ Blood Pressure6.Diastolic P.– the arterial p. when blood

is draining off into the arterioles during diastole, averages ________ Hg. Lowest during cardiac cycle.

• Physiology– during ventricular diastole, the semilunar valves close, no blood enters the arteries but the arteries moves the blood forward. Why?

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§ Blood Pressure7.Pulse P.– is the difference between

systolic and diastolic pressure

8.The Mean Arterial P. (MAP)— is the average blood pressure throughout the cardiac cycle• is monitored and regulated by BP

reflexes• MAP = diastolic p. + 1/3 pulse p.

Figure Z

Systolic pressure

Mean arterialpressure

Diastolic pressure

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A.

Fig.-- Aortic pressure throughout the cardiac cycle

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Q.—Peter’s systolic pressure is 140 mm Hg and his diastolic pressure is 95 mm Hg (written 140/95). A) What is his systolic p. and diastolic p., respectively? B) His pulse pressure? C) His mean arterial pressure?

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§ Hypertension/hypotensionDef.– high blood pressure; a chronic resting

blood pressure higher than 140/90-- (hypertension)

Results– aneurysms, atherosclerosis, heart failure, stroke, etc.

Hypotension– a chronic low resting BP (90/50 or lower);

Causes– blood loss, dehydration, anemia, in people approaching death

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§ Peripheral Resistance• Resistance depends on three variables

below: (Note: Blood Flow = ΔP/Resistance)1. Blood viscosity inversely relates to blood flow—

– Anemia & hypoproteinemia -- ___ blood flow– Polycythemia & dehydration -- ___ blood flow

2. Vessel length– pressure and flow decline with distance (farther end of the vessel)

The above two variables usually quite stable

3. Vessel radius on blood flow— proportional to the fourth power of radius

– Blood Flow α radius4

Table 20.2

Table 20.2

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Blood Flow

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§ Blood pressure regulation (A)

1. Neural control– – Baroreflex autonomic regulation--

• BP increases –baroreceptors firing rate increases

• Figure 20.13

– Chemoreflex– response to changes in blood chemistry

– Medullary ischemic reflex– an automatic response to a drop in perfusion of the brain

Figure 20.13

Brain stem

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§ Blood pressure regulation (B)

2. Hormonal control--

a) Angiotensin II-- ↑ BP

b) Aldosterone– ↑ BP

c) Atrial natriuretic peptide-- ↓ BP

d) Antidiruetic hormone-- ↑ BP

e) Epinephrine and Norepinephrine-- ↑ BP

Understanding blood pressure1. Blood flow= Δ Blood Pressure/Resistance

BP = Blood Flow x Resistance (R) BP = Blood Flow x 1/(Radius)4

2. Why vasodilation causes resistance to decrease?

3. BP = Blood Flow x R = Cardiac output x R BP = Heart rate (beats/min) x stroke volume

(ml/beat) x R– Thus, heart rate and stroke volume impact BP

Fig. 20.13 again

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Figure 20.13

Brain stem

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§ 20.3 Capillary exchange routes

1. Diffusion: (1a, 1b, and 1c of Fig. 20.16)– From high to low conc. areas– Via endothelial cells, intercellular clefts, and

filtration pores

2. Transcytosis: (2 of Fig. 20.16)– Pinocytosis/endocytosis then exocytosis– Fatty acids, albumin, insulin etc.

Fig. 20.16

O2, CO2, steroids

Glucose ions

1a

2

1b

1c

Fatty acids, albumin, insulin

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Albumin

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§ Filtration (arterial end) and Reabsorption (venous end) of the capillary

1. Hydrostatic pressure– due to liquid– Mainly caused by the blood pressure– 30 mm Hg at arterial end and 10 mm Hg at the

venous end

2. Colloid osmotic pressure– due to protein

– Mostly by albumin etc.

Difference of 1-2 above is Net Filtration or Reabsorption Pressure

Fig. 20.17

Net filtration p.

Net reabsorption

p.

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§ Edema (pulmonary, cerebral, etc.)1. Def.– accumulation of fluid in a tissue.

2. Three causes: – Increased capillary filtration: hypertension

etc.– Reduced capillary reabsorption: due to

albumin-- hypoproteinemia

– Obstructed lymphatic drainage

3. Edema’s consequences:– Oxygen delivery/waste removal are impaired– Tissue death (necrosis)

When available and time allows

• Watch a video— Baroreceptor reflex control of blood pressure

• Watch a video— Fluid exchange across the capillary

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