1. Chapter 20–
Blood Vessels & Circulation

2. Ch. 20 (Blood vessels) Study Guide
Critically read Chapter 20 pp 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 2 2

3. § 20.1—General Anatomy of Blood Vessels

4. § Introduction of Blood Vessels
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

6. § Vessel wall of arteries/veins-1
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

7. The vessel wall 1 2
Next slide 3

8. § Vessel wall of arteries/veins-2
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--?

9. § Vessel wall of arteries/veins-3
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

10. Conducting (large) artery
Lumen
Tunica interna:
Endothelium
Basement
membrane
Tunica media
Tunica externa
Vasa
vasorum
Nerve

11. § Arteries 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)

12. § Categories of Arteries-1
1. Conducting (elastic/large) arteries - largest
Ex. aorta, common carotid, subclavian, common iliac, and pulmonary trunk (Fig )
Structure– (Slide #10)
tunica media 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)

13. ID—A--The aorta and its major branches (Table 20.3)

14. 20-14 R. common L. common carotid a. carotid a. R. subclavian a.
L. subclavian a.
Brachiocephalic trunk
Aortic arch
Ascending
aorta
Descending
aorta, thoracic
(posterior to
heart)
Diaphragm
Aortic hiatus
Descending
aorta,
abdominal
20-14

15. Aneurysm (read p. 758 box)
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

17. § Categories of Arteries-2
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 , 29, 30, 36

18. § Categories of Arteries-3
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

19. 1 2 2a 3 4

20. § Arterial Sense Organs (3 kinds)
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

21. Figure 20.4  2
To brain 1C 
To the face 3
1A+B

22. § Capillaries 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)

24. § 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

25. Continuous capillary

26. § 3 Types of 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 a and b

27. Fenestrated Capillary

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

29. § 3 Types of 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

30. Sinusoid in Liver

31. § Veins (capacitance vessels; why?)
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

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

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

35. § Circulatory Routes Most common route Portal system
heart  arteries  arterioles  capillaries  venules  veins
Portal system
blood flows through two consecutive capillary networks before returning to heart
3 places in human body–

36. B. Hepatic portal sys. (p.797)
Figure 20.38b 4 3 5 2 1

37. § 3 Anastomoses 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
Arterial anastomosis
Two arteries merge
collateral circulation (coronary); Fig

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

39. § 20.2— Blood Pressure, Resistance, and Flow

40. § 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

41. § Blood Pressure
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 has the answer

42. Why ?
Why?

43. § Blood Pressure
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?)

44. Four different kinds of arterial BP--C.
D. Mean arterial
pressure
B--?

45. § Blood Pressure
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)

46. § Blood Pressure
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?

47. § Blood 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

48. Fig.-- Aortic pressure throughout the cardiac cycle
Systolic pressure
Mean arterial
pressure A.
Diastolic pressure

49. 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?

50. § Hypertension/hypotension
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

51. § Peripheral 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

52. Table 20.2
Blood Flow

53. § Blood pressure regulation (A)
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

54. Figure 20.13
Brain stem

55. § Blood pressure regulation (B)
Hormonal control--
Angiotensin II-- ↑ BP
Aldosterone– ↑ BP
Atrial natriuretic peptide-- ↓ BP
Antidiruetic hormone-- ↑ BP
Epinephrine and Norepinephrine-- ↑ BP

56. Understanding blood pressure
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 again

57. Figure 20.13  
Brain stem

58. § 20.3 Capillary exchange routes
Diffusion: (1a, 1b, and 1c of Fig )
From high to low conc. areas
Via endothelial cells, intercellular clefts, and filtration pores
Transcytosis: (2 of Fig )
Pinocytosis/endocytosis then exocytosis
Fatty acids, albumin, insulin etc.
Fig

59. 1c 2 1a 1b Fatty acids, albumin, insulin Albumin O2, CO2, steroids
Glucose ions 1b

60. Hydrostatic pressure– due to liquid
§ Filtration (arterial end) and Reabsorption (venous end) of the capillary
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

61. Net filtration p.
Net reabsorption p.

62. § Edema (pulmonary, cerebral, etc.)
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)

63. When available and time allows
Watch a video— Baroreceptor reflex control of blood pressure
Watch a video— Fluid exchange across the capillary