19 16-17 Flashcards
tissue perfusion, why?
Blood flow involved in: The delivery of o2/nutrients and the removal of wastes from tissue cells. Gas exchange in the lungs. Absorption of nutrients in the digestive tract. Urine formation in the kidneys.
Velocity of blood flow
Fastest in the aorta, declines as vessel diameter decreases.
Autoregulation (blood flow)
The automatic adjustment of blood flow to each tissue in proportion to the tissue’s requirements at any instant.
How is blood flow autoregulated in the body?
Intrinsically by local conditions by adjusting diameter of local arterioles. Organs regulate their own blood flow by varying the resistance of their arterioles. Metabolic or myogenic.
Metabolic control of autoregulation
Response to Ph, O2, Co2, adenosine, NO, postaglandins, ect. Most strongly stimulated by a shortage of O2 in tissue. Nitric Oxide is a vasodilator (more blood flow), Endothelins are vasoconstrictors (less blood flow).
Myogenic control of autoregulation
Stretch constricts. Respond directly to passive stretch with increased tone which resists stretch and causes vasoconstriction. Also responds to reduced stretch with vasodilation/increased blood flow.
Long-term autoregulation (ANGIOGENESIS)
Develops over weeks or months by ↑ size of existing vessel and ↑ number of vessels in a specific area
Types of transport in capillaries
Diffusion thru membrane (O2, hormones, nutrients, CO2, waste), pinocytosis (liquid-insulin/fatty acid), bulk flow (large amounts of fluid), vesicles
Vasomotion
Flow of blood through the capillaries reflects the action of the precapillary sphincters in response to local autoregulatory controls
Hydrostatic pressure
HP “pusher” Force of fluid against a membrane. Hydrostatic pressure in the cap can push fluid out - if pressure is higher in interstitial fluid then fluid will get pushed in. ARTERIAL - 35mmHg VENOUS - 17mmHG
Colloid osmotic pressure
OP “sucker” The force opposing hydrostatic pressure. Due to non-diffusible solutes (rbc, proteins) that draw water. 26mmHg inside cap, 1 outside
NFP
Net filtration pressure. Pos number means fluid is moving out of cap, neg number means its moving in. NFP = (HPc +OPif) - (HPif + OPc) Outward pressures minus inward pressures.
For every 20l of blood going thru capillaries how much comes back in? And the rest?
17l. 3l removed by lymphatic sys (the 10-15% that is not reabsorbed into the caps)
Frank Starling law of capillaries
What goes out must come in
How can this get messed up?
High BP (too fast of flow/also may burst cap), liver problems (not enough albumin, OpC is down, can’t pull water in)
