Microcirculation and Lymphatics

Question 1

What are the pre capillary resistance vessels?

Answer 1

Arterioles

Metarterioles (precapillary sphincters)

Question 2

What are the post capillary resistance vessels?

Answer 2

Venules

Question 3

Where is most of the resistance in the microcirculation?

Answer 3

In the pre capillary vessels

Question 4

What is the structure of the metarterioles and how does this contribute to the resistance?

Answer 4

The metarterioles are vessels that link the arterioles and the venules and they have discontinuous smooth muscles that form pre capillary sphincters along the length of the metarterioles that can reduce or shut off blood flow.

Question 5

What is the velocity of capillary blood flow?

Answer 5

Low velocity

Question 6

What is the direction of capillary blood flow?

Answer 6

High to low pressure from the arterioles to the venules

Question 7

How would you describe the flow of blood in capillaries?

Answer 7

Not uniform and intermittent. It is not continuous.

Question 8

What is the Rouleaux Formation?

Answer 8

RBCs touch and stack in the tight vessel of the capillaries because they must squeeze through.

Question 9

Is there more pre or post capillary resistance? How much more?

Answer 9

Precapillary. There is about a 4:1 ratio of pre to post capillary resistance.

Question 10

What is the importance of the Rouleaux Formation in capillaries?

Answer 10

It allows the membranes of the RBCs and the capillaries to be in close contact and allows for good gas exchange.

Question 11

What is transcapillary fluid exchange?

Answer 11

It is the movement of fluid or the exchange of nutrients in and out of the capillary.

Question 12

What is the plasma oncotic pressure?

Answer 12

Osmotic pressure exerted by contents of the plasma, mainly proteins.

Question 13

What is the capillary hydrostatic pressure?

Answer 13

Mean capillary blood pressure

Question 14

What is the tissue oncotic pressure?

Answer 14

Osmotic pressure of the substances in the interstitial area, like proteins. It is the counterpart of the plasma osmotic pressure.

Question 15

What is the interstitial hydrostatic pressure?

Answer 15

Hydrostatic pressure caused from the volume of fluid in the interstitial area

Question 16

How is transcapillary exchange controlled in terms of the oncotic and hydrostatic pressure?

Answer 16

The capillary hydrostatic pressure will overcome the interstitial hydrostatic pressure and will cause a net movement of fluid from the capillary. However the oncotic pressure will hold fluid in the capillaries due to the proteins present.

Question 17

What is the main protein determining the plasma oncotic pressure?

Answer 17

Albumin

Question 18

How does albumin increase the oncotic pressure to retain fluid in the capillaries?

Answer 18

Albumin interacts with Cl- and leads to the retention of more Na in the capillaries, which exerts an oncotic pressure to uptake fluid from the interstitial area.

Question 19

How does RV failure affect TCF exchange?

Answer 19

RV failure will lead to increased blood in the vena cava which will go to the liver and can cause cirrhosis and portal hypertension.

Question 20

How does LV failure affect TCF exchange?

Answer 20

LV failure will cause backups in the pulmonary vein, which can lead to filtration and cause a pulmonary edema due to the high venous pressure.

Question 21

Which system has a larger effect on the hydrostatic pressure?

Answer 21

Venous system

Question 22

How does liver disease affect TCF?

Answer 22

It can cause a loss of the protein albumin, which will lead to fluid loss in the capillaries and result in fluid accumulation in the interstitial space.

Question 23

What is the pre capillary resistance?

Answer 23

It determines the arterial blood flow into the capillary

Question 24

What is the post capillary resistance?

Answer 24

It determines the flow of blood into the veins from the capillary

Question 25

Why does the venous system have a larger effect on the hydrostatic pressure?

Answer 25

The venous system has less post capillary pressure so the hydrostatic pressure is nearly entirely determined by the post capillary pressure

Question 26

If the pre and post capillary pressure both increase, what happens to the hydrostatic pressure?

Answer 26

Increases the capillary hydrostatic pressure

Question 27

If the pre and post capillary pressure both decrease, what happens to the hydrostatic pressure?

Answer 27

Decreases the capillary hydrostatic pressure

Question 28

What do prostacyclins result in?

Answer 28

Vasodilation via cAMP

Question 29

What do Endothelium-Derived Relaxing Factor (EDRF) result in?

Answer 29

Vasodilation via NO

Question 30

What does nitric oxide result in?

Answer 30

Vasodilation via cGMP

Question 31

What does endothelin result in?

Answer 31

Vasoconstriction via IP3

Question 32

What does metabolites like K+/H+/CO2/adenosine cause?

Answer 32

Vasodilation

Question 33

Describe the structure of the lymphatics.

Answer 33

• Unidirectional blood flow as they have valves
• Non fenestrated endothelium and no smooth muscle
• Large vessels return fluid to the subclavian vein

Question 34

What is an edema? What symptoms do they show?

Answer 34

It is excess fluid in the interstitial space. They show as swelling of the ankles and ascites.

Question 35

What can cause edemas?

Answer 35

• Reduction in albumin concentration
• Increase in hydrostatic pressure of the capillaries
• Increased capillary permeability
• Lymphatic obstruction