Capillaries II: Fluid exchange

Question 1

Describe the importance of fluid exchange? (3ptS)

Answer 1

1. Fluid exchange is important for normal physiological function. We need H20 for chemical reactions
2. Fluid reabsorption from the tissues to the blood can maintain circulation during hemorrhage.
3. Abnormalities in food exchange can lead to oedema/ tissue swelling.

Question 2

Describe fluid movement across the capillary wall?

Answer 2

1. Capillary wall is a semi-permeable membrane
2. Fluid moves across the membrane into the interstitial space due to blood flow which exerts a hydraulic pressure.
3. Fluid movement across capillary walls depends on the balance between hydraulic and oncotic pressures across the capillary wall.
4. Large molecules such as plasma proteins cannot pass through the capillary membrane so they exert oncotic pressure which creates suction force to move the fluid into the capillary.

Question 3

Name the 4 pressures which determine filtration rate? (4pts)

Answer 3

1. P1- interstitial fluid pressure which favours the movement of fluid into the capillary
2. PC= capillary blood pressure which favours the movement of fluid out of the capillary
3. NP= plasma porteins
4. NI= intersiital proteins

Question 4

Describe well perfused capillaries

Answer 4

Well perfused capillaries filter along their entire length- there will be a build up extracellular fluid and this will drain into the lymphatic system and be returned into the circulation.

Question 5

Describe lymphatic circulation? (4pts)

Answer 5

1. Lymphatic circulation returns excess tissue fluid/ solute back to the cardio-vascular system
2. Lymph vessels have valves and smooth muscle which aids in maintaining the direction of flow
3. Spontaneous contractions of the smooth muscle contributes to lymph flow and venous return
4. Surrounding skeletal muscle contractions/ relaxation contributes to lymph flow.

Question 6

Describe Hypovolemia

Answer 6

Hypovolemia is low extracellular fluid volume and low capillary pressure

Question 7

How many litres is blood volume

Answer 7

Blood volume is usually 5L of which 3L is plasma

Question 8

What happens when an individual looses a large quantity of blood? (8pts)

Answer 8

1. Individual looses a large quantity of blood volume
2. Blood volume drops
3. Venous return drops
4. There is less filling of the ventricles and less stretch of the heart
5. By starlings law, there is less contractile force generated in the ventricular contraction. This means there is less stroke volume.
6. A a result cardiac output falls
7. Blood pressure falls
8. Net filtration pressure decreases, hydrostatic pressure falls. As we progress along the length of the capillary there is a net shift in the starlings forces so the overall balance no longer favours filtration.

Question 9

What happens when an individual looses a large quantity of blood? (8pts)

Answer 9

1. Individual looses a large quantity of blood volume
2. Blood volume drops
3. Venous return drops
4. There is less filling of the ventricles and less stretch of the heart
5. By starlings law, there is less contractile force generated in the ventricular contraction. This means there is less stroke volume.
6. A a result cardiac output falls
7. Blood pressure falls
8. Net filtration pressure decreases, hydrostatic pressure falls. As we progress along the length of the capillary there is a net shift in the starlings forces so the overall balance no longer favours filtration.

Question 10

What is the solution after a haemorrhage ?

Answer 10

1. 500ml intersisital fluid is internally transfused into the blood over 0.5 h after a haemorrhage
2. This is life-preserving
3. This supports CVP
4. This increases cardiac output
5. This causes a rise in blood pressure
6. This causes a greater BF
7. This is caused by sympathetic nerve-induced vasoconstriction of nerve-induced capillary arterioles leading to a drop in downstream capillary pressure.

Question 11

What happens when capillary pressure increases?

Answer 11

There is increased venous pressure

Question 12

Describe how a blood pressure machine works? ( 3pts)

Answer 12

1. Machine is on
2. There is a rise in the volume of the forearm
3. When the machine shuts the forearm volume returns to normal

Question 13

Describe Oedema?

Answer 13

1. Oedema= Excess of fluid within the interstitial fluid. It is the imbalance between filtration, reabsorption and lymph function
2. Oedema is caused by:
3. Increased capillary pressure
4. Decreased plasma protein oncotic pressure
5. Inflamattory response- increases gaps within the capillary membrane which makes it more prone to leakage. This causes the loss of plasma proteins which leads to the loss of the oncotic pressure gradient. This favours filtration which causes Oedema and swelling
6. Lymphatic problems

Question 14

Describe what happens in increased capillary pressure?

Answer 14

1. Dependant ( gravitational oedema)= caused by standing up for long periods of time
2. Deep vein thrombosis- blocks a deep vein which impedes venous return in the heart. This creates the pooling of blood upstream from there.
3. Cardiac failure- as the heart weakens it gradually looses its ability to effectively perfuse a system.

Question 15

What is low protein oedema caused by?

Answer 15

1. Malnutrition/ malabsorption= this means there is not enough protein intake to make plasma proteins
2. Nephrotic syndrome- causes urine protein loss which is replaced by liver production
3. Liver disease- not enough endogenous albumin is produced.

Question 16

What does low protein oedma do?

Answer 16

1. Reduced plasma protein concentration
2. This leads to reduced plasma concentration
3. This leads to reduced plasma oncotic pressure which means there is less of a reabsorption force to counter the filtration force that is due mainly to the plasma hydrostatic pressure
4. As a result there is a net increase in fluid efflux from capillaries into the interstitial fluid
5. This leads to Oedema

Question 17

Describe inflamatory medicated oedema?

Answer 17

1. Swelling is triggered by local chemical mediators of inflammation
2. This causes a large increase in capillary permeability. This means the capillary membrane is more prone to leakages hence allowing greater filtration of fluid due to large gaps. This cases the loss of proteins which causes the decrease of plasma oncotic pressure and increase in interstitial fluid oncotic pressure. Thos will reduce the forces for reabsorption and increases the forces for filtration.