Capillaries pt 2 Flashcards
Explain the importance of fluid exchange
1) fluid exchange is important as we need water for chemical reactions
2) fluid reabsorption from tissues to blood can maintain circulation during a haemorrhage
3) abnormalities in fluid exchange can lead to oedema/tissue swelling
Briefly describe the basement membrane
the basement membrane contains cells to prevent the movement of large proteins and blood cells.
Explain fluid movement at the capillary wall
The capillary wall is a semi permeable membrane
-fluid moves across membrane into interstitial space due to blood flow which exerts hydraulic pressure (pressure exerted by a fluid in a closed system)
-large molecules cannot pass through membrane so they exert osmotic pressure. This creates enough force to move fluid into capillary
What are the 4 pressures that determine filtration rate
Osmotic pressures:
-Pi p- plasma proteins
-Pi i- interstitial proteins
Hydrostatic pressure:
Pc= capillary blood pressure
Pi=3.142 interstitial fluid pressure
What is the equation for Jv according to starlings principle of fluid exchange
Jv= Lp A { (Pc - Pi) - o ( 3.14 x p - 3.14 x i)}
Jv= movement of fluid
Lp= hydraulic conductance of endothelium
O= reflection coefficient
A= wall area
3.14 x p= plasma proteins
3.14 x i= interstitial proteins
What is the equation for effective osmotic pressure
Effective osmotic pressure= reflection coeffient x potential osmotic pressure
Reflection coeffient for plasma protein is 0.9
what do starlings forces normally favour
starlings forces normally filter filtration in comparison to absorption
explain filtration in the arterial end
The pressure drops as you move down the capillary so the filtration is less by the time you get to the venous end.
What is the difference between Pc and Pi p?
Pc but not Pi p alters along end of capillary
what is the equation for net filtration
net filtration (P) = (Pc - Pi) - o (reflection coefficient) (Pi x p - Pi x i)
Explain what lymphatic circulation does
Lymphatic circulation returns excess tissue fluid/solutes back into the cardio vascular system
Lymph vessels have valves and smooth muscles, the surrounding skeletal muscle contractions and relaxations all contribute to lymph flow
what does overall control of extracellular fluid balance depend on?
Overall control of extracellular fluid balance depends on:
-capillary filtration
-capillary re absorption
-lymphatic system
List starling’s factors that determine changes in fluid balance
1) Circulation
2) Interstitial fluid
3) Lymphatic system
Explain low capillary pressure (hypovolemia) in the arterial end
-Firstly filtration occurs followed by reabsorption.
-the osmotic pressure can now overcome the hydraulic pressure.
-useful self correcting mechanism during low BP so more fluid is reabsorbed back into circulation
-increases blood volume
What does a drop in CO ultimately lead to in terms of Pc
Drop in CO leads to drop in BP (BP = CO x TPR) so Pc is reduced
What does increased Pc give
Increased Pc gives oedema
Explain what oedema is
Excess of fluid within the interstitial space.
Imbalance between filtration, reabsorption and lymph function
What does oedema cause
oedema causes:
-increased capillary pressure
-decreased plasma protein oncotic pressure
-inflammatory response
-lymphatic problems
Explain what can occur due to increased capillary pressure
1) dependent oedema- standing up for long periods
2) deep vein thrombosis
3) cardiac failure
What are the causes of low protein oedema
low protein oedema:
1) malnutrition/malabsorption- not enough protein intake to make plasma proteins
2) nephrotic syndrome- urinary protein loss
3) liver disease- not enough endogenous albumin produced
What is the effect of low protein oedema on the body
-reduced plasma protein concentration
-reduced plasma oncotic pressure ( greater influence of Pc and 3.14 x i)
-fluid efflux from capillaries into the interstitial fluid
Explain what does inflammation cause
-increased Lp
-increased protein permeability
-chemicals/insect bite/nettle sting
-infection/trauma etc
Explain lymphatic problems
Lymphatic obstruction:
-filariasis/elephantitis- larvae migrate to lymphatic system and grow by mating to form nests which block lymph drainage
Lymphatic removal:
-lymphoedema- caused by surgery to treat testicular cancer
-removal of lymphatics
What is the mechanism for both solute exchange and fluid exchange
solute exchange mechanism is through diffusion
Fluid exchange mechanism is through bulk flow (all molecules together)
Explain the function of both solute exchange and fluid exchange
Solute exchange- nutrition of tissue, hormone and drug delivery
Fluid exchange- regulation of plasma and interstitial fluid volumes
