Microcirculation

Question 1

microciculation

Answer 1

diameters less than 100 micrometers

Question 2

arterioles

Answer 2

5-100 micrometers

thick layer of smooth muscle

Question 3

terminal arterioles

Answer 3

arterioles that end in capillaries

Question 4

metarterioles

Answer 4

thinner and less well-developed layer of muscle
allow blood to pass around capillary bed
diameter can be varied, thus their resistance can be varied (Poiseuille)

Question 5

capillaries

Answer 5

4-8 micrometers
single layer of endothelial cells
lack muscle
nutrient excahnge

Question 6

precapillary sphincter

Answer 6

band of smooth mm before individual capillaries

on/off switch

Question 7

postcapillary venules

venules

Answer 7

15-20 micrometers & 35-45 micrometers
thin walled, highly compliant, lack mm
capacitance vessels - stretch!

Question 8

arteriovenous anastomosis / av shunt

Answer 8

highly muscular
blood flow directly from arterial to venous system w/o entering capillaries
not in all tissues

Question 9

4 ways substances cross the endothelium of a capillary

Answer 9

1) diffusion - ie O2 and CO2
2) bulk flow - driven by P generated by heart pumping
3) pinocytosis - for lrg proteins
4) active transport - into and out of the endothelial layer

• most occurs by diffusion created by concentration gradient
  enormous surface area of capillaries = slow mvmt

Question 10

hydrostatic presure

Answer 10

created by hearts pumping and applying pressure to the blood

drives fluid across capillaries

Question 11

osmotic (oncotic) pressure

Answer 11

generated by concentration of impermeable solutes (water follows these solutes)
salts, albumin

Question 12

hydrostatic pressure w/in capillary

Answer 12

35 at arterial end
15 at venous end
main force to move stuff OUT
pressure diff drives the flow

Question 13

osmotic (oncotic) pressure

Answer 13

main force to move stuff IN
albumin, globulins and fibrinogen (25mmHg pressure)
Note: capillaries filter only 1% of fluid so loss of plasma doesn’t raise oncotic pressure

Question 14

tissue hydrostatic pressure

Answer 14

maybe 0 or less due to sucking action of lymphatics

Question 15

tissue osmotic pressure

Answer 15

small amt of protein can get through capillary wall and cause an osmotic gradient, however most is returned to blood via lymphatics
1-2mmHg

Question 16

starlings law of the capillary

Answer 16

Q (fluid that leaves) =
k((Pc+Oncotic i) - (Pi +Oncotic capillary))

OUT - IN
k- tissue specific constant

Question 17

renal system; filtration/absorption

Answer 17

blood enters at high pressure (45mmHg) so large amts of fluids filtered out, some components are recovered by the kidney the rest makes urine

Question 18

pulmonary circ; filtration/absorption

Answer 18

blood enters at Pressure < plasma oncotic pressure

pulmonary capillaries absorb fluid (pulmonary secretions

Question 19

nutritional edema

Answer 19

plasma protein conc drops = >
plasma osmotic pressure falls 
(main force keeping fluid in capillaries)
arterial pressure remains normal
ascites

Question 20

local control of blood flow

Answer 20

1) metabolic; Inc levels of metabolic wastes -> vasodilation -> Inc blood flow
wastes; adenosine, lactic acid, K, H, CO2
Lack of O2 also initiates this too

2) myogenic - smooth mm response
inc P -> mm contract -> Inc R
dec P -> mm relax -> dec R
imp in standing up, keeps Q similar over a lrg range of BPs (preventing damage, allowing adequate Q), auto reg, no need for CNS imput

Question 21

central control of blood flow

Answer 21

CNS - urgent situations
1) humoral - peptides released into blood plasma
(atrial natriuretic peptide, angiotensin II, epinephrine, nitric oxide, endothelin)
2) neural mech - direct innervation
innervation of small art and ven by SNS
NT - NE, ACh, Sub P, Neuropeptide Y
main mech - regulate blood flow to diff regions of the body

Question 22

atrial natriuretic peptide (ANP)

Answer 22

causes excretion of Na and water, also causes vasodilation to decrease TPR
humoral mech of central control

Question 23

angiotensin II

Answer 23

potent vasoconstrictor

stimulates aldosterone synthesis and release for retention of Na (and thus water)

Question 24

epinephrine

Answer 24

released from adrenals vis SNS
vasodilation in liver and skel mm
increases heart rate

Question 25

nitric oxide (NO)

Answer 25

gas produced by endothelium
short half-life
causes vascular relaxation

Question 26

endothelin (ET-1)

Answer 26

potent vasoconstrictor from endothelium