1. The Cardiovascular System: Blood Vessels and Circulation
Chapter 16

2. Blood Vessels Arteries- from heart
Elastic => large
Muscular => distribution to organs
Arterioles => distribution to capillaries- mostly muscle
Capillaries- thin walled for diffusion
Veins- to heart
Venules => from capillaries
Veins from tissue to vena cavae to heart

3. Figure 16.1ab

4. Figure 16.1c

5. Blood Vessel Structure
Three layers
Arteries-> thicker tunica media
Elastic tissue and/or muscle
As they get smaller-> more muscle
Arterioles-> very muscular- control
Veins- bigger lumen and thinner walls
Veins-> valves to prevent backflow
Venules very thin, no valves

6. Vessel Functions Muscular arteries & arterioles regulate flow
Sympathetic activity to smooth muscle vasoconstriction (narrowing)
Decreased sympathetic activity or NO causes relaxation or dilation
Arterioles adjust flow into capillaries
Systemic veins & venules serve as blood reservoirs (~64% total blood volume)

7. Capillary Details Capillaries only have endothelium
Very thin cells & cell nuclei protrude into lumen- easy diffusion
Connected from arterioles to venules in networks
Sometimes direct route from arteriole to venule
Filling controlled by small arterioles & precapillary sphincters

8. Figure 16.2a

9. Figure 16.2b

10. Capillary Exchange Slow flow through capillaries
Allows time for exchange through wall
Blood pressure 
filtration of fluid out of capillary
Mostly in first ½ of vessel length
Osmosis (protein concentration)
Reabsorption of fluid from outside to inside
Mostly in last ½ of vessel length
Balance determines fluid in circulation
Excess fluid returned via lymphatic system
Local signals can adjust capillary flow

11. Figure 16.3

12. Venous Return Blood enters veins at very low pressure.
Needs more pumping to get back to heart
= action of heart; muscle pumps; respiratory pump
Some pressure from heart action
Not enough to overcome gravity

13. Muscle & Respiratory Pumps
Contracting skeletal muscles squeeze veins emptying them
Because of venous valves flow is toward heart
Respiratory pump has similar action
Inhalation decreased thoracic pressure & increased abdominal pressure
Blood flows toward heart
Exhalation allows refilling of abdominal veins

14. Figure 16.4

15. Blood Flow Resistance= opposition to flow
from high pressure area to lower pressure area, i.e. down pressure gradient
Greater gradient greater flow
Ventricular contraction blood pressure (BP)
Highest in aorta and declines as flows through vessels
mmHg in aorta ~16 mmHg at venules
 0 at R. Atrium
Resistance= opposition to flow
depends on lumen diameter & length & blood viscosity
Smaller lumen  greater resistance
Higher viscosity greater resistance
viscosity of blood depends on Hct

16. Resistance Depends on vessel lumen diameter And blood viscosity
Smaller lumen  greater resistance
And blood viscosity
Higher viscosity greater resistance
viscosity of blood depends on Hct
And total vessel length
Longer the length of flow the more friction with wall
Total body resistance increases with growth and addition of tissue

17. Anatomical Design Length and pressure
Design and local flow control- central pressure

18. Pressure Gradients Adult anatomy gives constant length
If central blood pressure is controlled it is constant
Only variable is radius of the arterioles
Each tissue can do it separately
Review design in picture below
All tissues have the same pressure gradient

19. Pressure Gradients (Cont.)
Note pulse in aorta & large arteries
MAP
pressure fall related to resistance
Note role of arterioles
Note low venous pressures
can’t get back to the heart!

20. Figure 16.5

21. Regulation of Blood Pressure & Flow
Fast responses: e.g. standing up
Slower responses: e.g. blood volume
Distribution: e.g. to working muscles
Balance of CO with flow to body
Interacts with many other control systems
Cardiovascular (CV) Center major regulator

22. Inputs Higher centers: Sensory receptor input: cerebral cortex,
limbic system,
hypothalamus
HR increases before race;
flow adjusted for body temperature
Sensory receptor input:
proprioceptors,
baroreceptors
chemoreceptors

23. Inputs (Cont.) Proprioceptors: Baroreceptors: in aorta & carotid
Start HR change as activity starts
Baroreceptors: in aorta & carotid
pressure   parasympathetic &
 sympathetic stimulation  CO
Chemoreceptors: in aorta & carotid
Low O2, high H+, CO2   vasoconstriction  BP

24. Figure 16.6

25. Output ANS to heart Vasomotor
 Sympathetic  HR &  force of contraction
 Parasympathetic  HR
Vasomotor
to arterioles  vasomotor tone
To veins move blood to heart  BP

26. Hormone regulation Renin-Angiotensin system
Angiotensin II  vasoconstriction+ thirst
 aldosterone   Na+ & water loss in urine on
Epinephrine & Norepinephrine  CO
ADH = Vasopressin
constriction   BP
Thirst & water retention in kidney BP
ANP- from cells in atria
Vasodilation & loss of salt & water in urine BP

27. Figure 16.7

28. Checking Circulation- Pulse
Pulse in arteries = HR
Use radial artery at wrist,
carotid artery,
brachial artery
Tachycardia = rapid rest rate (>100 bpm)
Bradycardia= slow rest rate (<50 bpm)

29. Blood Pressure Use sphygmomanometer Raise pressure above systolic-
Usually on brachial artery
Raise pressure above systolic-
stop flow
Lower pressure in cuff until flow just starts
first sound  Systolic Pressure
Lower until sound suddenly gets faint
Diastolic pressure
Normal values <120 mmHg for systolic & < 80 mmHg for diastolic

30. Circulatory Routes Two parts: Systemic & Pulmonary
Systemic circulation- throughout body
Oxygenated blood deoxygenated as it goes
All systemic arteries branch from aorta
All systemic veins empty into Superior Vena Cava, Inferior Vena Cava or the Coronary Sinus
Carry deoxygenated blood to heart

31. Figure 16.8

32. Figure 16.9

33. Figure 16.10a

34. Figure 16.10b

35. Figure 16.10c

36. Figure 16.11

37. Figure 16.12

38. Figure 16.13

39. Figure 16.14a

40. Figure 16.14b

41. Figure 16.14c

42. Figure 16.15

43. Pulmonary Circulation
From right ventricle pulmonary trunk
R. & L. pulmonary arteries
Carry deoxygenated blood
 R. & L. lungs
Gas exchange occurs
 2 R. & 2 L. pulmonary veins
Carry oxygenated blood
 L. atrium

44. Hepatic Petal Circulation
Portal vein transports blood from one capillary bed to another
GI organs
 Splenic & superior mesenteric veins
 hepatic portal vein
sinusoids in liver
Mixes with oxygenated blood
 hepatic vein inferior Vena Cava

45. Figure 16.16a

46. Figure 16.16b

47. Fetal Circulation
Specialized for exchange of materials with maternal blood and bypass of lungs
Exchange in placenta umbilical vein
 liver ductus venosus
 inferior vena cava  R. atrium
Mixes with deoxygenated blood from lower body
 foramen ovale L. Atrium
Or  R. Ventricle Pulmonary trunk  ductus arteriosus  aorta
 internal iliacs  umbilical arteries Placenta

48. Figure 16.17

49. At Birth Umbilical arteries medial umbilical ligaments
Umbilical vein  ligamentum teres
Ductus venosus  ligamentum venosum
Placenta expelled
Foramen ovalis closes fossa ovale
Ductus arteriosus  ligamentum arteriosum

50. Aging Stiffening of aortae Loss of cardiac muscle strength
Reduced CO & increased systolic pressure
Coronary artery disease
Congestive heart failure
atherosclerosis