B4.064 Prework 1: Microcirculation

Question 1

components of the microcirculation

Answer 1

arterioles
precapillary sphincters
capillaries
venules
arteriovenous shunts
lymphatics

Question 2

discuss the morphology of microcirculation vessels

Answer 2

all vessels contain a single layer of epithelial cells

smooth muscle surrounds all vessels except capillaries and post capillary venules

Question 3

effect of arteriole dilation

Answer 3

increase arteriolar radius within an organ
decrease vascular resistance in the organ
increase blood flow to the organ
increase capillary pressure
increase filtration of fluid

Question 4

what do arterioles help regulate

Answer 4

organ blood flow

filtration by altering capillary pressure

Question 5

function of precapillary sphincters

Answer 5

open and close
# open determines # of perfused capillaries
determines total surface area for exchange

Question 6

do precapillary sphincters affect vascular resistance within an organ?

Answer 6

no

determined by arterioles

Question 7

function of capillaries

Answer 7

single layer of endothelial cells with no overlying vascular smooth muscle
sit of exchange of nutrients and fluid between blood and tissue
filtration/reabsorption: capillary pressure, oncotic pressure of plasma

Question 8

function of post capillary venules

Answer 8

single layer of endothelial cells with no overlying vascular smooth muscle
important site of inflammation induced: leukocyte trafficking, increased vascular permeability

Question 9

describe arteriovenous shunts

Answer 9

blood flows from an arteriole directly to a venule, skipping capillaries
flow through AV shunts is termed non-nutritional blood flow since no exchange of nutrients occurs with the tissue

Question 10

importance of AV shunts

Answer 10

temperature regulation

primarily located in skin

Question 11

function of lymphatics

Answer 11

under normal conditions, filtration of fluid slightly exceeds reabsorption
lymphatics remove this excess fluid and also small amount of plasma proteins which enters tissue

Question 12

net filtration force

Answer 12

(Pc-Pi) - (Op-Oi)
hydrostatic pressure gradient - oncotic pressure gradient
c=capillary
i=interstitial

Question 13

pressures under normal conditions

Answer 13

interstitial pressure (Pi) about 0
interstitial protein concentration is nearly zero so the interstitial oncotic pressure (Oi) is about 0

Question 14

what controls filtration under normal conditions

Answer 14

Pc, capillary pressure

Question 15

what controls reabsorption under normal conditions

Answer 15

Op, plasma oncotic pressure

Question 16

discuss the pressure gradients along a capillary

Answer 16

in first half Pc > Op so net filtration

in second half Op > Pc so net absorption

Question 17

what is the effect of local dilation on arterioles within one organ?

Answer 17

less pressure drop across arterioles
increases rate of inflow of blood into capillaries
increases capillary blood volume
increases capillary pressure
filtration increased

Question 18

what is the effect of local constriction on arterioles within one organ?

Answer 18

greater pressure drop across arterioles
decreases rate of inflow of blood into the capillaries
decreases capillary blood volume
decreases capillary pressure
filtration decreased

Question 19

effect of venous pressure on capillary pressure

Answer 19

when venous pressure increases, rate of blood flow out of a capillary decreases
volume of blood in the capillary increases and capillary pressure increases
increased filtration of fluid out of the capillary into the tissue

Question 20

what are 3 causes of decreased oncotic pressure

Answer 20

liver disease: impaired production of plasma proteins
kidney disease: can increase excretion of plasma proteins in urine
protein malnutrition: impaired plasma protein production

Question 21

result of decreased oncotic pressure

Answer 21

force for reabsorption of fluid into capillaries is reduced

volume of interstitial fluid will be increased (edema)

Question 22

what is an example of an event that would increase vascular permeability?

Answer 22

exposure to an allergen

Question 23

what controls the opening of precapillary sphincters

Answer 23

open in response to locally produced dilators which accumulate in tissue when blood flow is not sufficient to meet metabolic demands of the organ

Question 24

what is the result of the opening of precapillary sphincters

Answer 24

increased capillaries perfused
increased total surface area for exchange
increased filtration

Question 25

give an overview of the lymphatic system

Answer 25

one way system that returns excess interstitial fluid to the cardio system all lymphatic vessels converge into larger lymphatic vessels which empty into the systemic circulation via the systemic veins

Question 26

what factors influence the contractile activity of vascular smooth muscle

Answer 26

``` stretch of vessels sympathetic vasoconstrictor nerves hormones local factors endothelin derived factors ```

Question 27

how does cytosolic calcium influence muscle activity

Answer 27

cytosolic Ca2+ concentration control cross bridging and thus vasoconstriction

Question 28

what factors regulate cytosolic Ca2+ levels

Answer 28

influx of Ca2+ through membrane channels release of Ca2+ from sarcoplasmic reticulum removal by Ca2+ ATPase pumps in sarcoplasmic reticulum and plasma membrane

Question 29

how does vascular smooth muscle differ from cardiac or skeletal muscle?

Answer 29

rate of cross bridge cycling is much slower due to a lower ATPase activity vascular smooth muscle to maintain sustained tension changes in cytosolic Ca2+ are more dependent on the influx of extracellular Ca2+ rather than release from intracellular stores

Question 30

how is NO produced in endothelial cells?

Answer 30

increases Ca2+ entry activates NO synthase | NO forms from L-arginine

Question 31

vasodilation mechanism of NO

Answer 31

highly permeable diffuses into underlying vascular smooth muscle decreases intracellular Ca2+ levels causes relaxation continuously produced in nearly all organs

Question 32

how is NO production inhibited

Answer 32

local infusion of L-name | competitive inhibitor

Question 33

functions of NO

Answer 33

vasodilator inhibits leukocyte and platelet adherence maintains normal low vascular permeability antioxidant

Question 34

what is endothelin 1

Answer 34

``` 21 AA peptide that is not stored but is synthesized in response to various stimuli slow process (1 hour) formation increased following endothelial cell damage ```

Question 35

what is the function of endothelin 1

Answer 35

acts through membrane receptors on vascular smooth muscle cells to cause vasoconstriction by: 1. release of intracellular Ca2+ 2. influx of Ca2+

Question 36

what is unusual about the effects of endothelin 1

Answer 36

prolonged vasoconstriction | significantly augments organ injury in conditions where endothelin 1 formation is increased

Question 37

what is ischemia

Answer 37

decreased blood flow

Question 38

what is reperfusion

Answer 38

restoration of blood flow after ischemic period

Question 39

what happens with reintroduction of O2 during reperfusion

Answer 39

generation of ROS inactivation of NO promotes microvascular injury

Question 40

3 primary effects of ROS

Answer 40

damage to endothelial cells > increased permeability inactivation of NO > leukocyte adherence, constriction increased endothelin formation > constriction and decreased flow