Fluid exchange

Question 1

Why is fluid exchange important?

Answer 1

Fluid exchange is important for normal physiological function, we need water for chemical reactions

Question 2

What can fluid re-absorption maintain?

Answer 2

Fluid re-absorption from tissues to blood can maintain circulation during haemorrhage

Question 3

What can abnormalities in fluid exchange lead to?

Answer 3

Abnormalities in fluid exchange can lead to oedema/tissue swelling

Question 4

What type of membrane is a capillary wall?

Answer 4

Capillary wall is a semi-permeable membrane

Question 5

What does fluid move across and into where and what does this exert?

Answer 5

Fluid moves across the membrane into interstitial space due to blood flow which exerts a hydraulic pressure

Question 6

What can large molecules not pass through and exert what?

Answer 6

Large molecules (e.g. plasma proteins) cannot pass through the membrane so they exert an osmotic pressure termed oncotic pressure

Question 7

What does oncotic pressure create?

Answer 7

The oncotic pressure creates a suction force to move fluid into the capillary

Question 8

What does fluid movement across capillary walls depend on?

Answer 8

Fluid movement across capillary walls depends on the balance between hydraulic and oncotic pressures across the capillary wall.

Question 9

What are the four pressures which determine filtration rate?

Answer 9

Pc-Capillary blood pressure
PI-Interstitial fluid pressure
np-Plasma proteins
nI-Interstitial proteins

Question 10

What do well perfused capillaries do?

Answer 10

Well Perfused Capillaries Filter Along Their Entire Length

Question 11

What does the lymphatic circulation return?

Answer 11

Lymphatic circulation returns excess tissue fluid/solutes back to the CVS

Question 12

How many litres per day are filtered in lymphatic circulation?

Answer 12

About 8 litres per day are filtered

Question 13

What do lymph vessels have?

Answer 13

Lymph vessels have valves and smooth muscle

Question 14

What contributes to lymph flow?

Answer 14

Spontaneous contractions of the smooth muscle contributes to lymph flow

Question 15

What also contributes to lymph flow?

Answer 15

Surrounding skeletal muscle contractions and relaxation also contributes to lymph flow

Question 16

What does lymph also contain, especially at the lymph nodes?

Answer 16

Lymph also contains immune cells, especially at the lymph nodes

Question 17

What does overall control of extracellular fluid balance depends on?

Answer 17

Capillary filtration
Capillary reabsorption
Lymphatic system

Question 18

What are starling’s factors determine changes in fluid balance?

Answer 18

Circulation
Interstitial fluid
Lymphatic system

Question 19

What happens in hypovolemia?

Answer 19

A bit of filtration to begin with but then reabsorption

The osmotic pressure is now able to overcome the hydraulic pressure

Question 20

Why is hypovolemia useful?

Answer 20

It is a useful self correcting mechanism during low blood pressure
More fluid is absorbed back into the circulation, thus increasing the blood volume

Question 21

What does increased Pc give?

Answer 21

Gives Oedema

Question 22

What is an oedema?

Answer 22

Excess of fluid within interstitial space

Imbalance between filtration, reabsorption, lymph function

Question 23

Causes of Oedema

Answer 23

Increased capillary pressure (Pc)

Decreased plasma protein oncotic pressure (πP)

Inflammatory response

Lymphatic problems

Question 24

What are clinical scenarios of increased capillary pressure?

Answer 24

Dependent (gravitational) oedema – standing up for long periods

Question 25

What steps are involved in the formation of oedema?

Answer 25

Reduced plasma protein concentration–>Reduced plasma oncotic pressure–>Fluid efflux from capillaries into the interstitial fluid–>Oedema

Question 26

What swelling triggered by and cause?

Answer 26

Swelling is triggered by local chemical mediators of inflammation
Large increase in capillary permeability

Question 27

What does inflammation cause?

Answer 27

Increased LP
Increased protein permeability (↑ πi), ↓σ
Chemicals/Insect Bite/Nettle Sting
Infection/Physical Trauma/Autoimmune disease

Question 28

Lymphatic obstruction

Answer 28

Filariasis/Elephantitis
Nematode infestation
Larvae migrate to lymphatic system
They can grow/mate/form nests
Thus, block lymph drainage

Question 29

When is lymphatic removal required?

Answer 29

Lymphoedema

Question 30

What is lymphoedema caused by?

Answer 30

Causes by surgery to treat testicular cancer