Fluid exchange Flashcards
Why is fluid exchange important?
Fluid exchange is important for normal physiological function, we need water for chemical reactions
What can fluid re-absorption maintain?
Fluid re-absorption from tissues to blood can maintain circulation during haemorrhage
What can abnormalities in fluid exchange lead to?
Abnormalities in fluid exchange can lead to oedema/tissue swelling
What type of membrane is a capillary wall?
Capillary wall is a semi-permeable membrane
What does fluid move across and into where and what does this exert?
Fluid moves across the membrane into interstitial space due to blood flow which exerts a hydraulic pressure
What can large molecules not pass through and exert what?
Large molecules (e.g. plasma proteins) cannot pass through the membrane so they exert an osmotic pressure termed oncotic pressure
What does oncotic pressure create?
The oncotic pressure creates a suction force to move fluid into the capillary
What does fluid movement across capillary walls depend on?
Fluid movement across capillary walls depends on the balance between hydraulic and oncotic pressures across the capillary wall.
What are the four pressures which determine filtration rate?
Pc-Capillary blood pressure
PI-Interstitial fluid pressure
np-Plasma proteins
nI-Interstitial proteins
What do well perfused capillaries do?
Well Perfused Capillaries Filter Along Their Entire Length
What does the lymphatic circulation return?
Lymphatic circulation returns excess tissue fluid/solutes back to the CVS
How many litres per day are filtered in lymphatic circulation?
About 8 litres per day are filtered
What do lymph vessels have?
Lymph vessels have valves and smooth muscle
What contributes to lymph flow?
Spontaneous contractions of the smooth muscle contributes to lymph flow
What also contributes to lymph flow?
Surrounding skeletal muscle contractions and relaxation also contributes to lymph flow
What does lymph also contain, especially at the lymph nodes?
Lymph also contains immune cells, especially at the lymph nodes
What does overall control of extracellular fluid balance depends on?
Capillary filtration
Capillary reabsorption
Lymphatic system
What are starling’s factors determine changes in fluid balance?
Circulation
Interstitial fluid
Lymphatic system
What happens in hypovolemia?
A bit of filtration to begin with but then reabsorption
The osmotic pressure is now able to overcome the hydraulic pressure
Why is hypovolemia useful?
It is a useful self correcting mechanism during low blood pressure
More fluid is absorbed back into the circulation, thus increasing the blood volume
What does increased Pc give?
Gives Oedema
What is an oedema?
Excess of fluid within interstitial space
Imbalance between filtration, reabsorption, lymph function
Causes of Oedema
Increased capillary pressure (Pc)
Decreased plasma protein oncotic pressure (πP)
Inflammatory response
Lymphatic problems
What are clinical scenarios of increased capillary pressure?
Dependent (gravitational) oedema – standing up for long periods
What steps are involved in the formation of oedema?
Reduced plasma protein concentration–>Reduced plasma oncotic pressure–>Fluid efflux from capillaries into the interstitial fluid–>Oedema
What swelling triggered by and cause?
Swelling is triggered by local chemical mediators of inflammation
Large increase in capillary permeability
What does inflammation cause?
Increased LP
Increased protein permeability (↑ πi), ↓σ
Chemicals/Insect Bite/Nettle Sting
Infection/Physical Trauma/Autoimmune disease
Lymphatic obstruction
Filariasis/Elephantitis Nematode infestation Larvae migrate to lymphatic system They can grow/mate/form nests Thus, block lymph drainage
When is lymphatic removal required?
Lymphoedema
What is lymphoedema caused by?
Causes by surgery to treat testicular cancer
