Exam 3 Kirk L4: Microcirculation

Question 1

What are the precapillary resistance vessels?

Exchange vessels?

Post-capillary resistance vessels?

Answer 1

Precapillary resistance vessels: arterioles, metarterioles (bypass the capillary system) and pre-capillary sphincter

Exchange vessels: capillaries

Post capillary resistance vessels (much lower resistance, like 4:1) are the venules

Question 2

Describe Capillary Flow:

___ velocity

Intermittent

Direction

Uniform?

___ pressure

Answer 2

Capillary Flow:

Low velocity

Intermittent (pulsitility from arteries to push it through)

Direction (pressure gradients)

NOT uniform

low pressure (pressure is really low but it is still critical for function)

Question 3

Explain fick’s law of diffusion modified for capillaries

Answer 3

J = -PS (Co-Ci)

P stands for permeability

S stands for Surface Area

Question 4

Water salt, O2, and urea diffuse rapidly and move almost unrestrictred, therefore the amount delivered to tissues is dependent on ______

With larger molecules, the limiting factor is ____

(What do you have to do if you want to increase O2 to a tissue)

Answer 4

Water, salt, o2, urea are “FLOW limited”

This means that the amount of o2 you’re delivering is dependent on the amount of flow because they are delivered so effeciently (if you want to increase O2 to a tissue you have to increase blood flow to that tissue)

With larger molecules, their ability to diffuse is the limiting factor

Question 5

Factors governing Trans-capillary fluid exchange:

1.

2.

3.

4.

Answer 5

Factors governing transcapillary fliud exchange: it is the oncotic and hydrostatic pressures inside and outside of the capillaries SO
1. oncotic pressure of plasma

2. hydrostatic pressure in capillaries
3. Tissue oncotic pressure
4. Interstitial hydrostatic pressure

Question 6

What does the starling hypothesis say:

Flow of fluids between capillary walls depends on….

Answer 6

Starling Hypothesis:
flow of fluid across capillary walls depends on the balance between the osmotic forces and hydrostatic forces across the walls

Question 7

Explain the change in hydrostatic AND oncotic pressure from the arterial side of the capillaries to the venous side.

Answer 7

So, the oncotic pressure throughout the capillaries does not change much at all, and stays at 25 mmHg.

The hydrostatic pressure however, goes from 32mmHg in the capillary side to 15mmHg at the venous side. This is important because at the arteriole side you get 7 mmHg pushing water OUT of the capillaries for filtration, and by the time you reach the venous side, you get net 10mmHg into capillaries for absorption.

Question 8

Where in the body is the hydrostatic pressure in the capillaries the highest?

Where in the body is the hydrostatic pressure in the capallaries the lowest?

Answer 8

The kidneys want to be constantly filtering out blood, so they have really high hydrostatic pressures at 60mmHg.

The hydrostatic pressure in the capillary bed in the lungs is only 25mmHg, because you want to keep the lugns very dry and don’t want to push too much fluid out of the lungs.

Question 9

Define pinocytosis

Where does it happen

How much does it contribute to overall transport

Answer 9

Pinocytosis is vesicle transport of larger lipid inolsuble molecules across endothelial cells

Varies amoung tissue (lots in muscle, very little in brain)

Responsible for little overall transport

Question 10

Arterial pressure exerts a ____ effect on capillary hydrostatic pressure because of _________

Venous pressure exerts a relatively _____ effect on capillary hydrostatic pressure because of ______

Answer 10

Arterial pressure exerts SMALL effect on capillary hydrostatic pressure becaue of the significant precapillary resistance.

Venous pressure exerts relatively LARGE effect on capillary hydrostatic pressure because of little post capillary resistance.

Question 11

An increase in _____ will exert a greater increase in capillary hydrostatic pressure than an increase in ____

Answer 11

An increase in VENOUS PRESSURE will exert a greater increase in capillary hydrostatic pressure than an increase in arterial pressure.

This is due to backing up effect

Question 12

What causes an increase in venous pressure?

Answer 12

LVHF causes an increase in venous pressure

(pressure backs up into left atrium, into the pulmonary veins, edema)

Question 13

Does arterial pulmonary hypertension cause PE?

Answer 13

Arterial pulmonary hypertension does NOT cause pulmonary edema becaue the pulmary arteries are before the lungs

Question 14

What is the total osmotic pressure of plasma?

What mainly contributes to that total osmotic pressure>

Answer 14

Total osmotic pressure of plasma is 6000 mmHg.

This is due to the salts that exist in plasma

These salts RAPIDLY diffuse (almost immediately), once in the capillaries so those salts don’t affect oncotic pressure as much

Question 15

The key factor that holds fluid within the capillaries is _______.

Answer 15

Key factor that holds fluid within the capillaries is oncotic pressure

This is primarily caused by the protein albumin which stays in the blood and does not diffuse out

Question 16

hydrostatic pressure causes ______

oncotic pressure causes _______

Answer 16

Hydrostatic pressure causes filtration (blood leaving capillaries)

Oncotic pressure causes absorption (water entering the capillaries)

Question 17

In the systemic capillary system, resistance primarily arises from…..

Answer 17

Capillary system, resistance arises from pre-capillary system

Remember the resistance in precapillary side to post capillary side is 4:1

Question 18

What contributes to high osmotic pressure but not oncotic pressure in the capillaries?

Answer 18

The salts which rapidly diffuse through the capillary wall

Question 19

What would cause increased capillary absorption?

Answer 19

Remember, absorption means water entering capillaries

This is due to oncotic pressure but remember oncotic pressure does not really change (remains at 25mmHg)

What does change is hydrostatic pressure, if you can decrease hydrostatic pressure, you will get an increase in absorption

Only answer choice that reflected that fact was an increase in pre-capillary resistance (which would decrease hydrostatic pressure)

Question 20

Lymphatics

What is their function

What kind of valves do they have

what happens if you destroy the lymphatic vessels (like in cancer or surgery)

Answer 20

Lymphatics:

Function: collect and return interstitial fluid to the circulatory system

Unidirectional valves (like veins)

destroy lymphatics, you get swelling and edema/fluid buildup in the tissues

Question 21

What are the precipitating factors in peripheral edema?

What are some possible causes

Answer 21

Factors in peripheral edema: reduction in plasma protein concentration, an increase in hydrostatic pressure (due to an increase in venous pressure), increased capillary membrane permeability

Causes: CHF, renal disease, liver disease

burn (increases capillary membrane permeability)

Question 22

Where is the first place you start to see edema in people with CHF?

Answer 22

First place edema starts is where the hydrostatic pressure is the highest (in the lower extremities)