Peripheral Vascular Blood Flow Regulation

Question 1

cerebral circulation

Answer 1

brain is the most actively metablizing organ, constant intravascular volume

total flow remains relatively constant but regional distribution changes dramatically and rapidly with neuronal activity

Question 2

effect of aterial CO2 on cerebral blood flow

Answer 2

Question 3

factors affecting cerebral blood flow

Answer 3

vasoconstrictor influences - HCO₃

vasodilator influences - low O2 (below 50mmHg), adenosine, NO, low pH, K+

cerebral spinal fluid pressure

Question 4

cushing reflex

Answer 4

a reflex increase in arterial pressure (via smpathetic systemic vasoconstriction) in response to increased intracranial pressure (tumor, hemorrhage, etc.) that results in ischemia in the vasomotor areas of the brainstem

the net result is that cerebral blood flow is maintained short term

Question 5

splanchnic bed

Answer 5

major blood reservoir, holds 20% of the total blood volume

Question 6

control of the splanchnic circulation

Answer 6

neural control primarily NE - vasoconstrictor tone is present due to normal sympathetic activity

reflex control - target organs for all reflexes that change sympathetic activity

local control - locally released hormones, metabolism

Question 7

control of splancnic veins

Answer 7

large venous reservoir

sympathetic tone

mechanical influences

Question 8

effect of sympathetic nerve activity in the GI tract

Answer 8

potent vasoconstriction

shunting blood to other beds and reducing venous capacitance during exercise or hemorrhage

Question 9

Why does an obstruction of the portal vein lead to ascites?

Answer 9

70% of blood flow from the aorta that goes to the liver goes through the portal vein, so obstrucction leads to increased pressrues and edema in the peritoneal cavity

Question 10

innervation of skeletal muscle

Answer 10

sympathetic adrenergic innervation - vasoconstriction and reduced flow

symapthetic cholinergic innervation - vasodilation

tonic activity on these nervse contributes to the high basal tone of muscle vessels needed to limit flow at rest

Question 11

reflex controls of skeletal muscle

Answer 11

baroreceptors

chemoreceptors

other

exercise

Question 12

local control of skeletal muscles

Answer 12

oxygen

adenosine

others

**these are metabolic byproducts

Question 13

cerebral circulation

Answer 13

750 ml/min

14% of resting CO

50-60 ml/min/100gm

Question 14

splanchnic circulation

Answer 14

1500 ml/min

25-30% of CO

Question 15

skeletal muscle circulation

Answer 15

at rest 800-1200 ml/min

15% of CO

3 ml/min/100g of muscle

Question 16

cutaneous circulation

Answer 16

at normothermia:

200-500 ml/min

10% of CO

10 ml/min/100 gm skin

Question 17

cutaneous and venous plexuses

Answer 17

found near the surface of the skin and are important sites of heat loss due to large volume and slow blood velicty

Question 18

thermoregulation of the skin

Answer 18

temperature sensors in the skin and muscle

blood-sensitive neurons in CNS

high environmental temperatures lead to increase flow and significant vasodilation -> flow diverted form the splanchnic and renal beds

this leads to 60% of CO

low temperatures sympathetic vasoconstriction happens to decrease flow, venous return is directed through deeper veins

Question 19

pulmonary circulation

Answer 19

5000 ml/min, 100% of CO -> total flow is not strongly regulated by lungs

Question 20

functional characteristics of the pulmonary circulation

Answer 20

low pressure (MAP 14mmHg)

high flow (5L/min)

low resistance (1/7th TPR)

hydrostatic pressure

reservoir

Question 21

recruitment of closed capillaries

Answer 21

results in an increased flow with a small increase in pulmonary arterial presure

Question 22

effect of inhalation on pulmonary circulation

Answer 22

intrathoracic pressure decreases -> decreased external pressure on large pumonary blood vessels

lung inflates -> increased stretch on small pulmonary vessels

small increase in ascular resistance

Question 23

effect of expiration on pulmonary circulation

Answer 23

opposite effects of inspiration

small net increase in vascular resistance

Question 24

circulatory changes at birth

Answer 24

presence of oxygen in lungs reelaxes pulmonary precapillary vessels - causes fall in pulmonary vascular resistance and pulmonary arterial pressure

increase in pulmonary blood flow

increased blood flow through lungs causes increased left atrial pressure

when left atrial pressure exceeds the right atrial pressure, the foramen closes

when the umbilical cord is tied off, venous return and arterial pressrues decreases

when the pulmonary artery pressure falls below aortic pressure, flow is reversed in the ductus arteriosus which causes a temporary increase in both pulmonary blood flow and pressure

Question 25

Tetralogy of Fallot

Answer 25

pulmonic stenosis

VSD

tranpositioned aorta