3.1.3 Microcirculation

Question 1

How can reprofusion cause damage following ischemia?

Answer 1

Reprofusion following an ischemic episode can lead to the generation of ROS. These will inactivate NO and promote microvascular injury.

Question 2

What is the difference between capillaries and post endothelial venules?

Answer 2

Capillaries - Site for exchange of nutrients. Filtration/ reabsorption is determined by capillary pressure and oncotic pressure respectfully.

Post-capillary venules - Important site of inflammation-induced leukocyte trafficking and increased vascular permeability

Question 3

What are and what is the role of precapillary sphincters?

Answer 3

These are bands of smooth muscle at the end of arterioles and in front of capillaries. They are either open or closed, and the number of them that are open determines the number of perfused capillaries. This will determine total surface area for exchange.

Question 4

Are changes in cytosolic calcium more dependent on an influx of calcium or intracellular store of calcium?

Answer 4

Changes in cytosolic Ca++ are more dependent on influx than a release from intracellular stores. This is why physicians treat hypertension with Ca++ channel antagonists

Question 5

Answer 5

A

Question 6

Describe the lymphatics and it flow.

Answer 6

Question 7

What is the role of Endothelin-1?

Answer 7

Endothelin-1 is a peptide that causes vascular smooth contraction and vasoconstriction by a release of intracellular Ca++ and an influx of Ca++.

The unusual characteristic is that ET-1 produces a sustained vasoconstriction.

Question 8

Answer 8

Question 9

What are arteriovenous shunts?

Answer 9

These direct blood flow from an arteriole directly to a venular. These have non nutritional blood flow since no exchange of nutrients occurs

Question 10

What is filtration?

Answer 10

Fluid movement out of a vessel

Question 11

How can vasomotion of precapillary sphincters affect filtration when organ blood flow is decreased?

Answer 11

The opening and closing of these determines number of perfused capillaries, and therefore total surface area for exchange. These open in response to locally produced dilators which accumulate in tissue when blood flow is not enough.

Question 12

Under normal conditions what is the biggest determining factor for filtration and reabsorption?

Answer 12

Filtration is largely dependent on Pc

Reabsorption is largely dependent on plasma oncotic pressure

This is because interstitial pressure and interstitial protein concentration are almost zero

Question 13

What is the process of hyperpolarization mediated vasodilation?

Answer 13

Activation of K_ATP channels increases organ blood flow when ATP generation is impaired (hypoxia or ischemia). Decreased ATP levels lead to K+ increasing efflux. This causes hyperpolarization of vascular smooth muscle and decreases Ca++ influx, ultimately leading to relaxation of vascular smooth muscle and increased blood flow.

Question 14

Answer 14

C

Question 15

How are the effects of increased cytosolic calcium different between endothelial cells and smooth muscle cells?

Answer 15

Question 16

How will increasing venous pressure raise capillary pressure?

Answer 16

When venous pressure is increased, the rate of blood out of a capillary will decrease. This increase of volume in the capillary will increase capillary pressure. As a result there will be increased filtration of fluid out of the capillary into the tissue. Possibly leading to edema

Question 17

What is reabsorption?

Answer 17

Fluid movement into a vessel

Question 18

What is the pathway by which an allergen can increase filtration?

Answer 18

Question 19

What can happen when inhibition of NO production occurs?

Answer 19

This can lead to decreased NO production and thus decreased blood flow to an organ

Question 20

How does decreased NO production lead to increased vascular permeability?

Answer 20

Adhesion molecules are upregulated. Leading to leukocyte adherence. These release proteolytic enzymes that damage endothelium and increases VP

Question 21

Answer 21

D

Question 22

Answer 22

D

Question 23

What are some complications associated with edema?

Answer 23

Impaired exchange of metabolites between blood and tissue. Increased interstitial pressure leading to decreased blood flow.

Question 24

What is the process by which epinephrine can cause vascular smooth muscle relaxation?

Answer 24

Vascular smooth in some organs have beta-2 adrenergic receptors (primarily skeletal muscle). These respond to circulating epinephrine and lower cytosolic Ca++ levels

Question 25

What are lymphatics?

Answer 25

Lymphatics remove excess fluid that is caused by filtration exceeding reabsorption under normal conditions. This also removes a small amount of plasma proteins that enters tissue.

Question 26

How can arterioles have a role in altering filtration of capillaries? How can increasing radius of an arteriole affect capillaries?

Answer 26

Arterioles are the main character in vascular resistance. When arteriolar radius increases, this will decrease vascular resistance within an organ. Decreased vascular resistance will then increase blood flow to the organ and increases capillary pressure. Increased capillary pressure will increase filtration across the capillary.

Question 27

What is the role of nitric oxide production in endothelial cells?

Answer 27

Question 28

How does the rate of cross-bridge cycling differ in smooth muscle as compared to cardiac or skeletal muscle? What does this effect?

Answer 28

The rate of cross-bridge cycling is much slower in smooth muscle than in skeletal or cardiac muscle. This allows vascular smooth muscle to maintain sustained tension.

Question 29

What is the difference between diffusion and bulk flow?

Answer 29

Question 30

What is the equation for net filtration force?

Answer 30

Question 31

How does cytosolic calcium regulate the contractile activity of smooth muscle?

Answer 31

Increasing the cytosolic calcium concentration will increase the number of cross bridges that causes contraction.

Question 32

What will cause a net filtration to occur in the first half of the capillary? What is causing the net reabsorption on the second half of the capillary?

Answer 32

Capillary pressure (P_c) is greater than interstitial pressure on the first half causing net filtration.

Interstitial pressure is greater than Pc so there is a net reabsorption on the second half.

Question 33

In general, how can liver disease, kidney disease, and protein malnutrition effect oncotic pressure?

Answer 33

These can decrease protein levels. The decreased protein levels would decrease the force for reabsorption of fluid into capillaries. This can lead to increased interstitial fluid volume and edema.

Question 34

How does vascular permeability affect filtration?

Answer 34

Increasing vascular permeability can increase filtration into interstitial tissue

Question 35

How can filaria lead to severe edema?

Answer 35

Question 36

How can NO inhibition lead to platelet aggregation?

Answer 36

When endothelial cells are damaged, NO production is decreased. This allows adherence and aggregation of platelets to the damaged area.

Question 37

What is the process by which lymph obstruction can lead to edema?

Answer 37

If lymphatics are obstructed then protein will accumulate in the interstitial space, this will decrease oncotic force for reabsorption

Question 38

Answer 38

E

Question 39

What is the process by which NE can cause contraction of vascular smooth muscle?

Answer 39

Activation of alpha-1 receptors which opens Ca++ channels.