4A - Phys of Microcirculation / Pathophys of Edema

Question 1

What is the major function of the capillary network?

Answer 1

To facilitate exchange of nutrients and waste with tissue - They have very thin vessel walls with fenestrations

Question 2

How do we normally exchange things between vasculature & interstitium?

Answer 2

1. Diffusion across endothelial cell membranes (via gradients)
2. Movement through fenestrations
3. Transport via small vesicles (pinocytosis) - (not focused on for this exam)

Question 3

What are the forces that drive fluid movement through capillary walls and fenestrations?

Answer 3

Starling forces/pressures

Question 4

What are the two main Starling forces?

- Two minor ones?

Answer 4

Two main ones

1. Pc : Capillary hydrostatic pressure (blood pressure in the capillaries)
2. πc : Capillary oncotic pressure (force due to proteins)

Two minor ones

3. Pi : Interstitial hydrostatic pressure (interstitial fluid surrounding cells)
4. πi : Interstitial oncotic pressure

Question 5

What four things are too big to pass through capillary fenestrations?

Answer 5

1. RBC
2. WBC
3. Platelets
4. BIG CHUNKY PROTEINS (Generating the oncotic pressure!)

Question 6

Which of the Starling forces is responsible for the net excretion out of the circulation at the arterial end?

Answer 6

Pc : Capillary hydrostatic pressure (blood pressure in the capillaries)

Items such as: glucose, amino acids, fatty acids, gases, hormones, etc

Question 7

Which of the Starling forces is responsible for net absorption into the arterial circulation at the venous end?

Answer 7

πc : Capillary oncotic pressure (force due to proteins)

Items such as: glucose, amino acids, fatty acids, gases, hormones, etc

Question 8

Compare Pc and πc levels

• at the arterial end
• at the venous end

Answer 8

Pc: Higher at arterial end, lower at venous end

πc: Lower at arterial end, higher at venous end

Question 9

Why is Pc higher at the arterial end and lower at the venous end?

Answer 9

It is high initially, but by the time it reaches the venous end:

1. A decrease in fluid levels
2. Further distance from the heart

Question 10

Why is πc lower at the venous end and higherat the arterial end?

Answer 10

It is low initially, but by the time it reaches the venous end:
- Decreased fluid levels mean increased concentration of proteins - higher oncotic pressure

Question 11

At the arterial end, which Starling force is higher: Pc or πc?

Is there net filtration or absorption?

Answer 11

Pc > πc

Net filtration (i.e. fluid leaving the capillary)

Question 12

At the venous end, which Starling force is higher: Pc or πc?

Is there net filtration or absorption?

Answer 12

Pc < πc

Net absorption (i.e. fluid enters the capillary)

Question 13

Is the amount of fluid that leaves the capillary on the arterial end equal to the amount of fluid that enters the capillary on the venous end?

Answer 13

No, this is why the lymphatic vessel system is critical in picking up the excess fluid. Lymph activity prevents fluid buildup and edema.

Question 14

Order these lymphatic vessels in terms of farthest from the vena cava to closest to the vena cava.

A. Lymphatic venules & veins
B. Lymphatic ducts (right lymphatic duct & thoracic duct)
C. Lymphatic capillaries

Answer 14

1. Lymphatic capillaries
2. Lymphatic venules and veins
3. Lymphatic ducts (right lymphatic duct & thoracic duct)

(Farthest to closest to vena cava)

Question 15

Which lymphatic vessel collects lymph from most of the body regions?

To which vein does this vessel drain into?

Answer 15

The thoracic duct

Drains into the right subclavian vein

Question 16

Which lymphatic vessel receives lymph from the right side of the head, neck, trunk, and right upper extremity?

To which vein does this vessel drain into?

Answer 16

The right lymphatic duct

Drains into the right subclavian vein

Question 17

What are lymph nodes?

Answer 17

Lymph nodes are beads or swellings along certain lymphatic vessels - essentially filters

Question 18

Where are lymph nodes most extensively found?

Answer 18

Axillary region, breast, neck, abdomen, thorax, pelvis, and groin

Question 19

What is edema?

What are the two forms?

Answer 19

Palpable swelling due to expansion of extracellular fluid
- Excess fluid in the interstitium becomes infiltrated with protein or other material so that it cannot move freely within the tissue spaces.

Pitting and non-pitting

Question 20

When does edema occur?

Answer 20

When the volume of interstitial fluid exceeds the capacity of the lymphatics to return it to the circulation.

Question 21

What are the four causes of edema?

Answer 21

1. Excess filtration (typically due to increased Pc)
2. Decreased absorption (typically due to decreased πc)
3. Increased capillary permeability
4. Blocked lymphatics