1. Ch 15: Blood Flow and the Control of Blood Pressure, Part 2
Keypoints
Blood pressure (BP) and Regulation
Exchange at capillaries
Lymphatic system
Cardio-vascular diseases

2. Review: R = 8L  r4 R = Resistance L = Length of “pipe” = viscosity
r = radius

3. Control of Blood Flow 1. Local control: By paracrines
O2 CO2 NO (in erection)
In the heart, adenosine serves as a paracrine to dilate coronary arteries
Others: histamine,
↓ O2 and ↑ CO2  arteriolar dilation
The ↑ flow is hyperemia

4. Control of blood flow, cont’d
2. Endocrine:
ANP and Angiotensin II (Chapt 20)
3. ANS (mostly sympathetic):
NE on α receptors  vasoconstriction
E on β2 receptors  vasodilation (F or F)

5. Distribution of Blood

6. Exchange at the Capillaries
Capillaries are anatomically designed for exchange
Continuous (leaky junctions)
Fenestrated (kidney and intestine)
Sinusoids in liver, bone marrow and kidney
Capillaries in the brain are less leaky and are surrounded by astrocytes and pericytes  BBB
Fig 15-16

7. Exchange at the Capillaries
Capillary blood flow: Greatest total cross sectional area  Lowest Velocity
Most cells within 0.1mm of capillary – why?
Direct correlation between # of caps and metabolic needs of tissue
Three types of exchange of molecules across the barrier:

9. Methods of Capillary Exchange
Paracellular diffusion – between the cells
Leaky cell-cell junctions
Transendothelial transport (transcytosis) through the cells
Endo- and exocytosis, diffusion through the endothelial cell
Bulk flow: mass movement of H2O and dissolved solutes as result of hydrostatic or osmotic pressure
Filtration – flow direction out of capillaries
Absorption – flow direction into capillaries

10. Two Forces Regulate Capillary Bulk Flow
Hydrostatic P: lateral component of fluid flow
Colloid Osmotic P: due to solute difference (main solute difference due to proteins inside the capillary)
Mostly:
Net filtration at arterial end
Net re-absorption at venous end
Fig 15-18

11. Lymphatic System Close functional association with three other systems
Cardiovascular
Digestive
Immune

12. Lymphatic System Functions
Return filtered fluid & proteins to circulatory system (anatomical design!)
Transfer fat from small intestine to circulatory system (lacteals)
Trap and deal with pathogens

13. Edema Blockage of lymph drainage Capillary filtration > absorption
Due to disruption of capillary exchange
2 major causes:
Blockage of lymph drainage
Cancer & fibrotic growth
Pathogens
Pregnancy
Capillary filtration > absorption
Venous pressure  due to right / left heart failure, backs up in to capillaries
Plasma protein concentration  due to liver failure or severe malnutrition (Kwashiorkor) reduces colloid osmotic pressure
 in interstitial protein

14. Regulation of Blood Pressure
Reflex control: Baroreceptor Reflex = 1o homeostatic control for BP; adjustments for standing
Medullary cerebrovascular control center (CVCC) integrates neural control (fig 15-23)
Baroreceptors = stretch sensitive receptors in aorta and carotid artery
Fig 15-21
Cardiovascular System: Blood Pressure Regulation

15. Regulation of Blood Pressure, cont’d
Arterial chemoreceptors activated by O2
Cerebral cortex
emotional responses such as blushing & fainting  vasovagal response
Integration with Kidney function
Orthostatic hypotension normally triggers Baroreceptor reflex
Hormones from heart affect kidney function and vice versa.

16. Cardiovascular Diseases
Account for ~ 1/2 of deaths in US – most common: CAD
Uncontrollable & controllable risk factors
Gender, age, genetics
Cigarette smoking, obesity, high BP, high cholesterol, DM

17. Cigarette Smoking: Vasoconstriction & BP  Risk for atherosclerosis 
Nicotinic cholinergic receptors stimulate sympathetic neurons at precapillary sphincters
Vasoconstriction & BP 
Risk for atherosclerosis 
Carbon monoxide (myocardium extracts most of O2 brought to it under resting conditions)

18. Atherosclerosis Fig 15-24 Common to several cardiovascular diseases
Changes in artery walls start with extracellular lipid deposits
Macrophages ingest the EC LDL-cholesterol
Called foam cells
Fatty streaks just under endothelial lining of larger arteries
Macrophage paracrines ↑ smooth muscle cells
Smooth muscle cells proliferate  stable plaques vs. vulnerable (easy to rupture) plaques  platelet activation  thrombus
Cerebral and coronary thrombi and emboli  Stroke or MI
Fig 15-24

19. Role of Hypertension Essential HT = idiopathic and/or hereditary
Creates damage to endothelium
Plaques form and occlude lumina
↑ BP  ↑ afterload (R)  cardiac hypertrophy
CHF
Ca2+ channel blockers hyperpolarize smooth muscle cells  less likely to contract
ACE inhibitors block ACE-I → ACE II
Vasodilation
Diuretics  blood volume
β-blockers  catecholamine effects

20. Running Problem: Essential Hypertension