1. Chapter 19 The Cardiovascular System: Blood Vessels G. R. Pitts, J. R
Chapter 19 The Cardiovascular System: Blood Vessels G.R. Pitts, J.R. Schiller, and J. F. Thompson
Use the video clip: CH 19 - Anatomy of the Blood Vessels for a review of vessel structure

2. Vessel Structure
Structure/function relationships change as one moves through the cardiovascular tree
Tunic thickness and composition of the three layers are variable

3. Capillary Beds Flow regulated by smooth muscle “valves” Metarterioles
from arterioles to venules through capillary bed
allows flow through capillary bed w/out flow through caps
True capillaries
pre-capillary sphincter
ring of smooth muscle
open/close to control flow
regulated by chemicals
intermittent vasomotion, open for flow 5-10 times each minute

4. Capillaries
Allow exchange of nutrients and wastes between the blood and the tissue cells
Capillary structure – simple squamous epithelium
basal lamina - connective tissue
endothelial cells
Details of structure determine specific functions
3 types: continuous, fenestrated, sinusoidal

5. Vascular Anastomoses Arterial Anastomoses Arteriovenous Anastomoses
- provide collateral supply to some organs and tissues, e.g., skeletal muscles
Arteriovenous Anastomoses
- thoroughfare channels
Venous Anastomoses
- most common, e.g., deep and superficial veins in limbs and head

6. Vessel Structure - Histology
Vein Artery
Vein Artery

7. Varicose Veins

8. Vessel Structure/Function
At rest
60% of blood volume is located in veins and venules
venous system serves as reservoirs for blood
particularly veins of the abdominal organs and the skin
ANS regulates volume distribution
vasoconstriction
vasodilation
diverts blood to areas with increased metabolic needs
Spleen ~1L
Compare to Cardiac Output figures

9. Blood Distribution at Rest
 0.75 L/min
Rest
CO = 5 L/min

10. Blood Distribution -- Exercise
Using cardiac reserve
CO = 25 L/min
Heavy
Exercise
 20 L/min
 0.75 L/min
Rest
CO = 5 L/min

11. Physiology of Circulation
Flow = ΔP/R
or CO = MAP/R
MAP = mean arterial pressure
higher pressure to lower pressure with decreasing resistance (R)
Blood pressure
pressure of the blood on the vessel wall
measure the pressure of a volume in a space
systole/diastole - 120/80 (mm Hg)
BP falls progressively from the aorta to essentially 0.0 mm Hg at the right atrium (RA)

12. Physiology of Circulation
Resistance - opposes blood flow because of the friction produced by the vessel walls
Factors that affect resistance (R)
(1) resistance (R) is proportional to viscosity: V  R
“thickness” of the blood
e.g., dehydration, elevated plasma proteins, polycythemia (RBCs), leukemias (WBCs)
(2) resistance (R) is proportional to vessel length
obesity increases the route lengths within connective tissue
(3) resistance (R) is inversely proport. to vessel width
decrease the radius by 1/2 and R increases by 16X
most important in vessels that can change their size actively
changes in diameter affect flow
vessel wall drag – blood cells dragging against the wall
laminar flow – layers of flow

13. Physiology of Circulation
Systemic Vascular Resistance (SVR) =Total Peripheral Resistance (TPR)
all vascular resistance is offered by the systemic vessels
which vessels change size?
resistance is highest in arterioles
largest pressure drop is in the arterioles
Relationship of the radius to resistance in the arterioles is due to smooth muscle contraction/relaxation

14. Systemic Blood Pressure
4/16/2017
Arterial Blood Pressure
Pulsatile in arteries due to the pumping of the heart
Systolic/diastolic values
Pulse pressure = systolic (minus) diastolic
Q- What does the Windkessel effect have on pulse pressure?
Q- What is the effect of hardening of the arteries on pulse pressure?
A- Decreases pulse pressure
A- Increases pulse pressure

15. Systemic Blood Pressure
Capillary Blood Pressure
relatively low blood pressure
low pressure is good design for capillaries because:
capillaries are fragile - high pressure would tears them
capillaries are very permeable - high pressure forces a lot of fluid out

16. Systemic Blood Pressure
Venous return
the volume of blood flowing back to heart from systemic veins
depends on pressure difference from beginning of venules (16 mmHg) to heart (0 mmHg)
any change in right atrial (RA) pressure changes venous return

17. Venous Return/Valves Assistance for venous return
skeletal muscles act as pumps
contracting muscles squeeze veins
force blood back to the heart
valves prevent back flow
respiratory pump
inhaling causes a lowered pressure in the thoracic cavity
primarily to pull air into the lungs
helps to draw blood into thorax via pulmonary circulation

18. Velocity of Blood Flow
Velocity of blood flow - inversely proportional to the total cross sectional area (CSA) of vessels
Aorta
total CSA = 3-5 cm2
velocity = 40 cm/sec
Capillaries
total CSA = cm2
velocity = 0.1 cm/sec
Vena Cava
total CSA = 14 cm2
velocity = 5-20 cm/sec

19. Capillary Function Capillary Function Mechanisms of nutrient exchange
site of exchange between blood and tissues
delivery of nutrients and removal of wastes
slow flow allows time for molecules to diffuse
Mechanisms of nutrient exchange
diffusion - O2, CO2, glucose, AA's, hormones, electrolytes -- diffuse down [ ] gradients
lipid soluble molecules can pass through cell membrane easily
water soluble molecules generally require transport mechanisms to enter/exit cells

20. Capillary Function Fluid movement Forces driving the movement of fluid
Fluid diffuses out and is reabsorbed across the capillary walls
Starling’s law of the capillaries
Forces driving the movement of fluid
Hydrostatic pressure capillary (HPc)
Hydrostatic pressure interstitial fluid (HPif)
Osmotic pressure capillary (OPc)
Osmotic pressure interstitial fluid (OPif)
Net filtration pressure (NFP) is the net effect of all four forces at any point along the capillary

21. Net Filtration Pressure (NFP)
NFP = (HPC - HPIF) - (OPC - OPIF)
       = Pushing forces - Pulling forces
On average, 85% of fluid entering the tissues on the arteriole side is reabsorbed on venous end

22. Maintaining Blood Pressure: Short Term Mechanisms - CNS
Neural Control - Cardiac Centers in medulla
Vasomotor center
medullary area dedicated to control of blood vessels
sends sympathetic output to blood vessels
Vasoconstricts or vasodilates as needed
Vasomotor tone - normal amount of vasoconstriction or vasodilation
ANS can vary the vasomotor tone which varies the delivery of blood to particular regional capillary beds
receives sensory input from different sources
baroreceptors (blood pressure)
chemoreceptors (O2, CO2, H+, HCO3-)

23. Maintaining Blood Pressure: Short Term Mechanisms - CNS
Baroreceptor initiated reflex
located at carotid sinuses and aortic arch
monitors blood pressure
regulates the activity of the sympathetic nervous system (vascular tone)

24. Maintaining Blood Pressure: Short Term Mechanisms - CNS
Chemoreceptor initiated reflexes
Carotid bodies, aortic bodies
Monitor changes in indicator chemicals (O2, CO2, H+, HCO3-)
 CO2,  H+,  O2 (stresses) result in  sympathetic activity and  BP

25. Maintaining Blood Pressure: Short Term Mechanisms - CNS
Influence of higher brain centers (areas above medulla) - cortex and hypothalamus
not involved in minute-to-minute regulation
influence vasomotor center depending on conditions
temperature changes
stressful emotional situations

26. Maintaining Blood Pressure: Short Term Mechanisms - Chemicals
Renin - Angiotensin - Aldosterone
Renin/ACE
enzymes from kidney/lung
catalyze formation of Angiotensin I/II
Angiotensin II
vasoconstrictor
stimulates ADH, thirst
stimulates aldosterone release for Na+ & H2O reabsorption
why/how would these things affect blood pressure?

27. Maintaining Blood Pressure: Short Term Mechanisms - Chemicals
diverts blood from the skin and abdominal organs to the skeletal muscles
increases heart rate, stroke volume and, therefore, cardiac output & blood pressure
Adrenal medulla releases epinephrine and norepinephrine in coordination with activity from the Sympathetic Division of the ANS

28. Maintaining Blood Pressure: Short Term Mechanisms - Chemicals
Antidiuretic Hormone (ADH) or Vasopressin
osmoreceptors in hypothalamus trigger release from the neurohypophysis
ADH targets kidneys to retain water (ADH action is inhibited by alcohol)
ADH also stimulates vasoconstriction at high levels
why/how would this affect blood volume and pressure?

29. Maintaining Blood Pressure: Short Term Mechanisms - Chemicals
Atrial Natriuretic Peptide (ANP)
released from atrial cells in response to blood vol &  BP
stimulates vasodilation, Na+ and water loss, antagonizes Aldosterone, inhibits thirst
why/how would this affect blood volume and pressure?

30. Maintaining Blood Pressure: Long Term Regulation
Renal mechanism
control blood volume
nervous control - ANS
hormones
regulation in the short term by adjusting blood pressure and adjusting blood flow to different capillary beds
regulation in the long term by adjusting blood volume
target the kidneys
 BP,  urine flow to  BP
 BP,  urine flow to  BP

31. Control of Blood Flow
Autoregulation (local control) - local automatic adjustment of blood flow to match specific local tissue metabolic needs
Physical changes
Warming -  vasodilation
Cooling -  vasoconstriction
Chemical changes in local tissues generate metabolic byproducts
vasodilators or vasoconstrictors
Myogenic control
smooth muscle controls resistance
 stretch  contraction;  stretch  contraction

32. Blood Flow in Special Areas
Skeletal Muscle
fine tuned control with wide variation in rate of flow
brain directs the sympathetic division for NE release in response to the degree of muscular activity
α receptors - vasoconstriction
β receptors - vasodilation
metabolic regulation in tissue
low O2 causes vasodilation, increasing flow
high O2 cause vasoconstriction, decreasing flow
Brain
minimal variation in rate of flow
minimal nutrient storage, so adequate flow must be maintained!
local metabolic changes adjust local autoregulation

33. Blood Flow in Special Areas
Skin
adjusting rate of flow aids in temperature regulation
controls skin’s capacity as a blood reservoir
sympathetic and local metabolic regulation
Lungs
low pressure (25/10 mm Hg), low resistance system
flow regulated by O2 availability in the lungs
high O2  vasodilation to increase flow – opposite of muscle
low O2  vasoconstriction to decrease flow – opposite of muscle
Heart
variable flow depending on metabolic/pumping activity

34. Regulation of Blood Pressure
CO = MABP/R
MABP = CO x R

35. The Circulation Learn specific vessels and routes in lab

36. The Circulation Learn specific vessels and routes in lab

37. Hepatic Portal System
a portal system transfers venous blood from one capillary bed to another capillary bed before the blood is returned to the heart
HPS collects venous blood from five abdominal organs and routes the blood to the liver for specific processing of transported molecules
- stomach: toxins (ethanol)
- small intestine: nutrients, toxins
- large intestine: nutrients, toxins
- pancreas: insulin, glucagon
- spleen: RBC breakdown products

38. Fetal Circulation
Umbilical veins bring oxygen and nutrients from the placenta to the liver and then to the heart of the fetus

39. Fetal Circulation ductus venosus bypasses liver 3 Right  Left shunts
because oxygenated blood is derived from the placenta
ductus arterious  ligametum arteriosum
foramen ovale  fossa ovalis
interventricular shunt  no remnant

40. Circulatory Shock sudden dramatic loss in blood pressure or sudden decrease in circulatory flow
Hypovolemic Shock
Acute hemorrhage (or other sudden fluid loss as from vomiting or diarrhea)
Vascular Shock
Loss of vasomotor tone as from anaphylaxis, neural malfunction, or poisons (septicemia)
Cardiogenic Shock
Loss of cardiac output due to heart failure

41. End Chapter 19