1. Objective 7 Velocity of Blood Flow
The rate (velocity, speed) of blood flow in different portions of systemic circulation varies. The velocity of blood flow is inversely related to the total cross sectional area of the blood vessels that it is flowing through:
velocity 
total cross sectional area
So, as cross sectional area increases, velocity decreases.
Where is cross sectional area the greatest?
Vessel Cross Sectional Area (cm2) Velocity (cm/sec)
Aorta
Arteries
Arterioles < 20
Capillaries 4,
Venules 4,
Veins Vena Cavae

2. Objective 8 Autoregulation
Autoregulation refers to the automatic adjustment of blood flow to tissues based on their changing needs.
Autoregulation:
 is controlled by local, not systemic factors (What are the systemic factors?)
 is altered by changing arteriolar diameter and by opening and closing precapillary sphincters (How does flow change when arteriolar diameter increases? Decreases?)

3. Myogenic Controls Autoregulation involves three mechanisms:
metabolic controls
angiogenesis (long terms control)
Myogenic Controls
Reduced arteriolar pressure leads to arteriole vasodilation to ensure tissue perfusion
reduced arteriolar pressure arteriolar dilation
Increased arteriolar pressure leads to arteriole vasoconstriction to reduce blood flow and to protect arteriolar walls from pressure induced damage
increased arteriolar pressure arteriole constriction

4. 2. Metabolic Controls - responds to changes in tissue metabolic rate
Elevated MR leads to arteriolar dilation and relaxation of precapillary sphincters
Thus, blood flow into tissues is increased
Increased tissue metabolism

5. Factors that cause arteriolar dilation/sphincter relaxation
Decreased tissue O2
Increased tissue CO2
Decreased tissue pH
Increased adenosine
Increased extracellular K+
Increased histamine, kinin
Decreased endothelin
Increased osmolarity
Increased tissue temperature

6. Reduced MR leads to arteriolar constriction and contraction of precapillary sphincters
Thus, blood flow into tissues is decreased
Decreased tissue metabolism

7. Factors that cause arteriolar constriction/sphincter constriction:
Increased tissue O2
Decreased tissue CO2
Increased tissue pH
Decreased adenosine
Decreased extracellular K+
Decreased histamine, kinin
Increased endothelin
Decreased osmolarity
Decreased tissue temperature

8. Some definitions:
Reactive hyperemia:
increased blood flow in response to ischemia
Active hyperemia:
increased blood flow in response to elevated MR

9. Vasomotion: the intermittent, slow flow of blood through capillaries based on the opening/closing of precapillary sphincters

10. 3. Angiogenesis:  the growth of new blood vessels into an area
 stimulated by periods of hypoxia, or by growth factors, interleukins or colony stimulating factors (CSF’s)

11. Objective 9 Blood Flow To Special Areas
The cardiac output can be distributed to organs differentially based on their needs:
Organ Flow At rest (ml/min) Flow During Strenuous Exercise (ml/min)
Brain
Heart
Muscle , ,000
Skin ,900
Kidney ,
Abdomen ,
Other
Total , ,000

13. Objective 10 Capillary Dynamics
How Materials Move Through Capillary Walls
Movement Through Lipid Bilayers
Lipids and lipid soluble substances can diffuse through the bilayers (O2, CO2, ethanol)
Movement Between Endothelial Cells
A 40A pore is large enough to permit diffusion of water and small water soluble substances

14. Fluid Movements
Fluids and dissolved substances move through capillary walls by bulk flow, governed by the following forces:
Hydrostatic Pressure (HP): the pressure exerted by a fluid in an enclosed space
fluids and dissolved substances move from areas of high to areas of low hydrostatic pressure
When fluid is in a space, it exerts pressure on its surroundings
The amount of pressure depends on the amount of fluid and the size of the space

15. Osmotic Pressure (OP):. the “pulling pressure” that a hypertonic
Osmotic Pressure (OP): the “pulling pressure” that a hypertonic solution exerts on a hypotonic solution
Hypertonic Hypotonic

16. HPc:. capillary hydrostatic pressure (favors fluid out of capillary,
HPc: capillary hydrostatic pressure (favors fluid out of capillary, filtration)
the pressure that blood exerts on the wall of a capillary; note that HPc is different at the arterial end and at the venous end of the capillary
Hpif: interstitial fluid hydrostatic pressure (opposes filtration, favors reabsorption
the hydrostatic pressure of the interstitial fluid; ranges from slightly positive to slightly negative (effectively zero)

17. OPc: capillary osmotic pressure: (favors reabsoption)
the presence of large, non diffusible proteins in blood plasma exerts an osmotic pressure on tissue fluid; averages 26 mmHg
Opif: interstitial fluid osmotic pressure: (favors filtration)
proteins in the interstitial fluid exert osmotic pressure on the plasma; averages 1 mmHg

18. Net Filtration Pressure (NFP): = Net Pressure Out - Net Pressure In
Forces favor filtration
Forces favor reabsorption
Net Filtration Pressure (NFP):
= Net Pressure Out - Net Pressure In

19. Net Filtration Pressure (NFP): = Net Pressure Out - Net Pressure In
For the arterial end:
NFP = [HPc + Opif] - [Opc + Hpif]
= (35 mmHg mmHg) - (26 mmHg + 0 mmHg)
= 10 mmHg

20. For the venous end:
NFP = (17 mmHg mmHg) – (26 mmHg + O mmHg)
= -8 mmHg
What is the only value that changes in the 2 equations?
Hydrostatic pressure
Note:
If NFP is a positive number there is a net movement out of the capillary (arteriolar end)
If NFP is negative there is net reabsorption into the capillary (venule end, usually)

21. Lets try these:
Your patient suffers from hypertension. Based on the following values predict the outcome at the capillary end of things.
Here are the values:
Arterial end: Venous end:
HPc = 45mmHg HPc = 20mmHg
Opif = 1mmHg Opif = 1mmHg
Opc = 26mmHg Opc = 26mmHg
Hpif = 0mmHg Hpif = 0mmHg

22. Your patient suffers from liver disease
Your patient suffers from liver disease. Based on the following values predict the outcome at the capillary end of things.
Here are the values:
Arterial end: Venous end:
HPc = 35mmHg HPc = 17mmHg
Opif = 1mmHg Opif = 1mmHg
Opc = 10mmHg Opc = 10mmHg
Hpif = 0mmHg Hpif = 0mmHg

23. Your patient suffers from severe dehydration
Your patient suffers from severe dehydration. Based on the following values predict the outcome at the capillary end of things.
Here are the values:
Arterial end: Venous end:
HPc = 35mmHg HPc = 17mmHg
Opif = 1mmHg Opif = 1mmHg
Opc = 37mmHg Opc = 37mmHg
Hpif = 0mmHg Hpif = 0mmHg

24. Objective 11 Edema/Circulatory Shock
Definition: increased fluid in interstitial fluid spaces
Causes: increased HPc: hypertension, venous congestion, increased blood volume
Decreased Opc: reduced albumin synthesis, loss of albumin from the body
Increased Opif: increased tissue protein levels, such as in myxedema associated with adult hypothyroidism

25. Lymphatic Obstruction
Lymphedema, left leg
Myxedema, reversible with thyroid hormone
Filariasis

26. Circulatory Shock (Cardiovascular Collapse)
 systemic hypoperfusion due to either reduced CO or reductions in the effective circulating blood volume
cardiogenic shock: heart failure
hypovolumetric shock: blood volume reduction
neurogenic (vascular) shock extreme vasodilation
anaphylactic shock extreme vasodilation and blood volume reduction due to an allergic reaction