Chapter 20– Blood Vessels & Circulation

Chapter 20–

• Chapter 20–

• Blood Vessels & Circulation

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.

• 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.

• Comprehend Terminology (those in bold)

• Study-- Figure questions, Think About It questions, and Before You Go On (section-ending) questions

• Do Testing Your Recall— 1-8, 10-12, 14-16, 18

• Do True or False– 1-2, 4-5, 8-9

• Do Testing Your Comprehension-- #5

§ 20.1—General Anatomy of Blood Vessels

• § 20.1—General Anatomy of Blood Vessels

1A. Closed circulatory system– Def. Blood flows in a continuous circuit through the body under pressure generated by the heart.

• 1A. 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

1. Innermost layer (tunica interna/intima)

• 1. 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

2. Middle layer (tunica media)—thickest layer

• 2. Middle layer (tunica media)—thickest layer

• Structures:

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

• B. Functions of this layer:

• Strengthen the vessel
• Provide vasomotion--?

3. Outermost layer (tunica externa or advertitia)—

• 3. 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. 20.2

More muscular

• More muscular

• Able to resist high blood pressure

• Thus called resistance vessels

• Retain their round shape even when empty

• Divided into three categories by size (next slide)

1. Conducting (elastic/large) arteries - largest

• 1. 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)

Def.– a balloon-like outpocketing of an artery wall (Fig. Y)

• Def.– a balloon-like outpocketing of an artery wall (Fig. Y)

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

• Causes– OFTEN chronic hypertension or atherosclerosis

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

• Fig. Y

2. Distributing (muscular, medium) arteries

• 2. 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

3. Resistance (small) arteries

• 3. 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

Where– structures in major arteries above heart

• Where– structures in major arteries above heart

• Function– to monitor blood pressure/chemistry

• Three kinds (2 categories): Fig. 20.4

• Carotid sinuses (Baroreceptors)—Details next

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

• Carotid bodies (Chemoreceptors)

• Location-- oval bodies near carotids
• monitor blood chemistry
• adjust respiratory rate to stabilize pH, CO2, and O2

• Aortic bodies (Chemoreceptors)

• Location-- in walls of aortic arch
• same function as carotid bodies

Material exchanges– between blood and tissue fluids

• Material exchanges– between blood and tissue fluids

• Locations-- _____________ and smallest of the venules

• Structure– endothelium + ____________

• Fig. X next

• Close vicinity to all cells— Exceptions

• Scarce in: tendons, ligaments, & cartilage
• Absent from (3 locations): -__________________________(Epi. & Eyes)

1. Continuous capillaries- occur in most tissues, ex. Skeletal muscle

• 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

2. Fenestrated capillaries

• 2. 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

3. Sinusoids (discontinuous) capillaries-

• 3. 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

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

• b/c Greater capacity for blood containment than arteries do (Fig. 20.8)
• thinner walls—due to less muscular and elastic tissue; why?
• lower blood pressure: 10 mm Hg with little fluctuation
• ____________ aid skeletal muscles in upward blood flow

Postcapillary venules-- only tunica intima

• Postcapillary venules-- only tunica intima

• Receive blood from capillaries
• more porous than capillaries

• Muscular venules-- receive blood from #1

• have tunica media (1-2 layers of smooth muscle) + thin tunica externa

• Medium veins–

• Most have individual names, Examples-- radius or ulna veins
• Many have venous valves

Venous sinuses--

• 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

• Large veins--

• Greater than 10 mm (diameters)
• Venae cavae, pulmonary veins, internal jugular veins

Most common route

• Most common route

• heart  arteries  arterioles  capillaries  venules  veins

• Portal system

• blood flows through two consecutive capillary networks before returning to heart
• 3 places in human body–

Def. Point where 2 blood vessels merge

• Def. Point where 2 blood vessels merge

• Arteriovenous shunt

• artery flows directly into vein; fingers etc.

• Venous anastomosis

• most common type
• alternate drainage of organs; Fig. 20.33

• Arterial anastomosis

• Two arteries merge
• collateral circulation (coronary); Fig. 20.31

§ 20.2— Blood Pressure, Resistance, and Flow

• § 20.2— Blood Pressure, Resistance, and Flow

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

• 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

Blood pressure (BP)– Def. the force per unit area exerted by the blood against a vessel wall

• Blood pressure (BP)– Def. the force per unit area exerted by the blood against a vessel wall
• In what vessels can you find BP?
• Figure 20.10 has the answer

BP is understood to mean the pressure in the _________________

• BP is understood to mean the pressure in the _________________
• BP rises and falls in a pulsatile fashion in the arteries and arterioles
• Figure Z (what BP do we measure?)

Systolic P.– the maximum p. exerted in the arteries when blood is ejected into them during ventricular ejection, averages 120 mm Hg (Mercury)

• 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)

Diastolic P.– the arterial p. when blood is draining off into the arterioles during diastole, averages ________ Hg. Lowest during cardiac cycle.

• 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?

Pulse P.– is the difference between systolic and diastolic pressure

• Pulse P.– is the difference between systolic and diastolic pressure
• 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

Def.– high blood pressure; a chronic resting blood pressure higher than 140/90-- (hypertension)

• Def.– 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

Resistance depends on three variables below: (Note: Blood Flow = ΔP/Resistance)

• Resistance depends on three variables below: (Note: Blood Flow = ΔP/Resistance)

• Blood viscosity inversely relates to blood flow—

• Anemia & hypoproteinemia -- ___ blood flow
• Polycythemia & dehydration -- ___ blood flow
• Vessel length– pressure and flow decline with distance (farther end of the vessel)
• The above two variables usually quite stable
• Vessel radius on blood flow— proportional to the fourth power of radius
• Blood Flow α radius4
• Table 20.2

Neural control–

• 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

Hormonal control--

• Hormonal control--

• Angiotensin II-- ↑ BP
• Aldosterone– ↑ BP
• Atrial natriuretic peptide-- ↓ BP
• Antidiruetic hormone-- ↑ BP
• Epinephrine and Norepinephrine-- ↑ BP

Blood flow= Δ Blood Pressure/Resistance

• Blood flow= Δ Blood Pressure/Resistance

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

• Why vasodilation causes resistance to decrease?

• 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

Diffusion: (1a, 1b, and 1c of Fig. 20.16)

• Diffusion: (1a, 1b, and 1c of Fig. 20.16)

• From high to low conc. areas
• Via endothelial cells, intercellular clefts, and filtration pores

• Transcytosis: (2 of Fig. 20.16)

• Pinocytosis/endocytosis then exocytosis
• Fatty acids, albumin, insulin etc.

• Fig. 20.16

Hydrostatic pressure– due to liquid

• 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

• Colloid osmotic pressure– due to protein

• Mostly by albumin etc.

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

• Fig. 20.17

Def.– accumulation of fluid in a tissue.

• Def.– accumulation of fluid in a tissue.

• Three causes:

• Increased capillary filtration: hypertension etc.
• Reduced capillary reabsorption: due to albumin-- hypoproteinemia
• Obstructed lymphatic drainage

• Edema’s consequences:

• Oxygen delivery/waste removal are impaired
• Tissue death (necrosis)

Watch a video— Baroreceptor reflex control of blood pressure

• Watch a video— Baroreceptor reflex control of blood pressure

• Watch a video— Fluid exchange across the capillary