Capillaries Flashcards
capillaries are made up of what type of cells?
single layer endothelial cells 0.5μm thick resting on basement membrane
– no smooth muscle but contractile elements in cells allow shape change
what are the different kinds of capillary beds?
»Continuous: least permeable in skin, muscle, lungs,
cerebral circulation (allows for the blodo brain barrier)
» Fenestrated: commonest type & more permeable eg
in glomeruli, intestinal villi
» Discontinuous: most permeable - in bone marrow,
liver, spleen- facilitates the passing of large proteins)
what is the function of the capillaries?
exchange of the gases (lipid soluble molecules like anaesthetic agents)
Lipid insouble molecules pass through pores (glucose, amino acids and drugs)
structure of capillaries restricts permeability to large lipid insoluble molecules particularly when protein is bound
what do we call it when we have an increase of fluid in the interstitial space?
oedema
how much water moves from capillaries into the interstitial space per day?
8L/day
what structures are responsible for moving the interstitial fluid away from the interstial space and back into circulation?
filtration = reabsorption + lymph flow
what controls the movement of fluid out of capillaries and into the interstitium?
water moves by osmosis (dilute to salty area)
- depends on the number of particles in the solution and obviously the colloid osmotic pressure
what is the ‘colloid pressure’? (or oncotic pressure)
pressure exerted by big bulky proteins
What is Starling’s Hypothesis?
capillary walls are leaky to water but impermeable to proteins -
what did Startling’s Hypothesis determine?
it determined the forces determining capillary exchange
what is the filtration coefficient?
it is the coefficient related to density and permeability of the capillaries
if the pressure in your vessel increases, where does the fluid move?
into the interstitium
if the pressure in your intersitial fluid increases - where does the fluid move?
into the vessel
if you increase the colloid osmotic pressure in the vessel, where will the fluid move?
(colloid osmotic pressure = sucking force) - therefore the fluid will move into the vessel
the natural gradiant of the vessels filters filtration?
yes - but it’s not uniform throughout
b/c the pressure at the arteriole end coming fromt he aorta is much higher
how does the startling forces change in skeletal muscle, alveoli and glomeruli?
in skeletal muscle = gradient favoring filtration
the more the role of the organ is towards filtration, the higher the net gradient - so the alveoli we need to have stuff back in force all the time (gas exchange) so we really need filtration, and in the kidneys the same - so they have a higher net favoring filtration
what is oedema?
• Increase in interstitial fluid volume due to alteration in one or
more of the Starling forces
• Pulmonary
- Leakage of fluid from pulmonary capillaries
– Breakthrough to alveoli
• Systemic
– Localised / generalised
– Sacral / ankle oedema
– Ascites or pleural effusion
why do you get swollen ankles after a flight?
venous pooling in your ankles-leads to increased hydrostatic pressure in your vessels and a net transfusion of fluid across the wall and into the interstitial space
what are the causes of oedema?
- Lymphatic Blockage eg by fliaria nematodes
After radical mastectomy
- Increased capillary hydrostatic pressure
Eg excessive kidney retention of salt & water
3.High venous pressure & venous constriction
Heart Failure
- Decreased plasma proteins
Nephrotic Syndrome (plasma protein conc ( <2.5g/100ml)
Loss of proteins from denuded skin (burns)
Failure to produce proteins eg. Liver cirrhosis
- Increased capillary permeablity
Immune reactions that cause relase of histamine & other immune products
Bacterial infections
Burns
what happens in elephantiasis?
worms block the lymphatics after being transmitted by mosquito bite - and you can treat it with a metabolic inhibitor
why does a radical mastectomy lead to a swollen arm?
b/c of damage to the axillary lymph nodes
why do you see oedema in heart failure?
due to high venous pressure and venous constriction - attempt to profuse all organs
