Circulation and Hemokdynamics II

Question 1

where are the smooth muscle locations found in the capillary bed

Answer 1

Arterioles will contain smooth muscle in the walls

Metarterioles will contain some smooth walls

the capillaries will contain pre-capillary sphincters which will be important in shunting the blood or increasing flow into the bed

Question 2

how are substances able to cross the capillary wall

Answer 2

Clefts allow for passage of water soluble substances such as glucose and electrolytes

• small in brain
• large in liver and gut

Lipid soluble substances such as O2 and CO2 can pass through the cell wall

some larger molecules may pass through in vesicles

Question 3

what is the starling equation

Answer 3

flow = kf (Pc-Pi) - (hc-hi) or flow = kf (forces moving fluid out) - (forces moving fluid in)

flow = (Pc + hi) - (Pi + hc)

net driving pressure determines rate of fluid exit from or entry into the capillary

the net exchange is a gradual leakage of fluid out of capillary and into the interstitium which must be gathered up by the lymphatic system and returned to venous circulation

Question 4

what are the two pressures that play a factor in the movement of water in and out of the capillary

Answer 4

(-) drawing it into the capillary
(+) drawing out of the capillary

Hydrostatic pressure (blood pressure)(P)

Osmotic pressure (solute sucking pressure) (pi symbol)

both sides of the capillary wall will have a intervascular and extravascular component to each of these pressures

Pc = hydrostatic pressure pushing out of the capillary (+)
hc = hydrostatic pressure pushing into the capillary (-)

pi = osmotic pressure pulling into the capillary (-)
hi = osmotic pressure pulling into the intersitial space (+)

Question 5

what is a net positive starling equation

Answer 5

net movement of fluid out of the capillary

Question 6

what is a net negative starling equation

Answer 6

net movement of fluid into the capillary

Question 7

what can elevate Pc, Pi, hc,hi?

Answer 7

Pc = elevated venous pressure (heart failure)

Pi = restricted lymphatic flow or increased driving force out of capillary

hc = decrease in albumin (starvatio or liver failure)

hi = restricted lymph flow or inflammation

edema!

Question 8

what is the typical net pressure at the arterial end and at the venous end

Answer 8

arterial = positive (flow out of capillaries)

venous = negative (flow into capillaries)

Question 9

how does lymph impact the flow?

Answer 9

excess fluid and proteins and other substances enter lymphatics via valved channels

muscle pumps push lymph through lymph node scrubbers

about 2 to 3 liters a day re enter at subclavian vein

Question 10

what is the metabolic control of the capillary bed: Active hyperemia

Answer 10

Active hyperemia is increasing interstitial concentration of metabolites such as CO2, H+, K+, lactate and adenosine or reduction of O2 due to increasing metabolic rate

this causes smooth muscle of arterioles, metaarterioles, and pre-capillary sphinctors to relax and increase flow through the area

Question 11

what is the metabolic control of the capillary bed: reactive hyperemia

Answer 11

reactive hyperemia is when a vascular obstruction causes build up of metabolites leading to a vasodilation

therefore if the obstruction is removed the area is flooded with blood

i.e: sitting on hand

Question 12

Method of local control: Shear

Answer 12

if a vascular bed dilates due to metabolic demand, the flow through upstream arterioles and small arteries would increase

this would increase the shear or wall friction leading to the release of NO which would cause vasodilation and augment the downstream metabolic effect.

Question 13

how does Histamine and Bradykinin affect blood flow

Answer 13

lead to arteriolar vasodilation

increases capillary porosity (Kf) allowing escape of large molecules

can cause edema in response to tissue damage

Question 14

How does serotonin affect blood flow

Answer 14

can cause vasoconstriction in response to tissue damage

Question 15

how does prostaglandin affect blood flow

Answer 15

can cause mixed signals of both vasoconstriction and vasodilation

Question 16

what controls Coronary circulation

Answer 16

Largely under metabolic control

sympathetic innervation of vasculature but usually ignored

ventricular contraction (especially on left side) causes constriction of vasculature most notably near the endocardial surface

Question 17

what controls cerebral circulation

Answer 17

largely metabolic control

Question 18

where is the highest pressure of the pulmonary vascular system found?

Answer 18

in the right ventricle and pulmonary artery at about 24 to 0 mmHg

Question 19

why is the pressure in the Pulmonary circulation much lower than in the systematic circulation

Answer 19

it is because there is a much lower resistance in the pulmonary circulation

Question 20

how does the body regulate the pulmonary blood flow

Answer 20

Vasoconstriction to alveolar hypoxia (hypoxic vasoconstriction) to move blood to more oxygenated regions of the lung

little sympathetic influence

Arterial system in Pulmonary is much more compliant than in the systemic arteries: therefore, relatively small changes in mean pressure will significantly dilate arteries and reduce resistance and help maintain pressure low in the fact of large changes to flow

Question 21

how is skeletal muscle controlled at rest and during flight response

Answer 21

at rest: central, baroreceptor control

• norepinephrine to alpha receptors
• when active it comes under local control via metabolic dilation buts some sympathetics to keep CO up via the potential dilation from metabolic control

During flight response: adrenal glands secret epinephrine which bind to B2 receptors and cause vasodilation

Question 22

how is the skin blood flow regulated

Answer 22

sympathetic vasoconstriction to baroreceopter reflex

sympathetic inhibition and dilation of shunt pathways to excessive body temperature to help cool down

Question 23

what are the two types of shunts

Answer 23

Right to left shunt: blood passing from systemetic veins to systemic arteries without passing through functional lung tissue

left to right shunt: Blood passing from systemic arteries to systemic veins without passing through a capillary bed for substance exchange

Question 24

central vs local control for skin and gut, heart, brains, muscle, and pulmonary

Answer 24

skin: more central control than local
heart: way more local control than central
brain: way more local than central control
muscle: much more local control when active than central control when active

Pulmonary: some central control, and hypoxic vasoconstriction to alveolar gasses for local control