circulation 6

Question 1

RBC velocity in capillaries

Answer 1

=1/total cap cross-sectional area

-capillary branching reduces rbc velocity AND vascular resistance

Question 2

benefits of closed circ system

Answer 2

-fast circulation time and strong control of bp and blood flow

Question 3

capillary roles

Answer 3

diffusion of gases
rbc and large proteins exchange don’t nomrally move across endothelium
wbc exchange
fluid pressure gradient to cross endothelium
(capillary bp tends to force fluid out of capillaries)

Question 4

capillary variation

Answer 4

• tight intercell junctions: most caps, specialized for blood-brain barrier and histamine response of wbc
• intracell fenestrations for plasma filtration in kidney glomeruli
• intercellular sinusoids for large molecule movement in liver and rbc in spleen

Question 5

blood filtrations in caps

Answer 5

endothelial permeability sets limits to filtration
-capillary bp P cap drives filtration
-plasma osmotic pressure (picap) opposes filtration; picap set by concentrations of plasma ions and proteins
NET PRESSURE DRIVING FILTRATION=Pcap-picap

Question 6

lymphatic system

Answer 6

mostly at capillaries

• takes interstitial fluid as lymph, which is returned to venous system after lymph nodes
• lymph flow is slow due to low pressure, but skeletal muscles compress vessels and they are valved to compensate

Question 7

plasma filtration at capillaries

Answer 7

net pressure driving filtration is primarily Pcap>picap

• Pcap changes along capillary, picap is stationary
• at Pcap>picap, net filtration, at Pcap<picap, net reabsorption into caps

Question 8

MAP and kidneys

Answer 8

glomerular filtration=MAP
renin-angiotensin system (RAS) constricts glomerular efferent arterioles
antidiuretic hormone/aka vasopressin stimulates H2O reabsorption and decreases excretion (-ve feedback)
+ve feedback:atrial natriueretic peptide ANP released by atrial stretch, causes increased excretion of Na+ and H2O

Question 9

gravity and hydrostatic pressure in veins

Answer 9

hydrostatic pressure acts on vessel wall in addition to bp:

vessel transmural pressure (TP)=MAP+hydrostatic pressure (HP)

Question 10

transmural pressure and veins

Answer 10

=MAP+hydrostatic pressure
-no flow means TP=HP
veins are thin walled, compliant, and sweel with hydrostatic pressure
-can cause potential problems in hot tubs or longs flight because blood can pool in your legs