fluid shift across the capillary wall Flashcards
Interstitial fluid:
bathes the body cells, acting as the go-between blood and body cells
describe the capillaries
- Single layer of endothelial cells
- Allow rapid exchange of gases, water and solutes with interstitial fluid
- Delivery of nutrients and O2 to cells
- Removal of metabolites from cells
- Blood flow in capillaries depends on contractile state of arterioles
Terminal arterioles
- Regulate regional blood flow to capillary bed (CB) in most tissues
Precapillary sphincters
Regulate regional blood flow to CB in few tissues
Fluid movement follows its
pressure gradient
Movement of gases and solutes follows
Fick’s Law of Diffusion (against concentration gradient)
Lipid soluble substances go through the
endothelial cells
Water soluble (hydrophilic) substances go through
the water-filled pores
can Large molecules generally cross the capillary wall
no
Transcapillary fluid flow is
Passively driven by pressure gradients across the capillary wall (Starling forces)
Capillary hydrostatic pressure:
pressure exerted by blood in capillaries against the capillary wall, forces fluid OUT of capillary (favours filtration)
Capillary osmotic pressure:
pressure exerted by proteins in the blood (albumin), in the capillaries, pulls fluid INTO blood (opposes filtration)
Interstitial fluid hydrostatic pressure:
pressure of the fluid in the interstitium, forces fluid back INTO capillary (opposes filtration)
Interstitial fluid osmotic pressure:
the pressure of the proteins in the interstitium, pulls fluid OUT the capillary (favours filtration)
ultrafiltration -
exchange across the capillary wall of essentially protein-free plasma
Starling forces favour —— and ——
filtration at arteriolar end,
reabsorption at venular end
Filtration of fluid out of thecapillaryusually occurs on
the arterial side of thecapillary bed, mostly because of pressure from the arterial circulation (increased Pc) and high plasma fluid levels (decreased πc)
Absorption of fluid into the capillary usually occurs on
the venous side of thecapillary bed, mostly because ofcapillary flow resistance (decreased Pc) and higher relativeplasma proteinlevels following water filtration into theinterstitium(increased πc)
what percentage of Pulmonary resistance is that of systemic circulation
10%
describe pulmonary capillary hydrostatic pressure
low compared to capillary osmotic pressure (25 mmHg) - favours filtration
what does Lymphatic drainage do
removes any filtered fluid, preventing the accumulation of interstitial fluid
what is oedema
Accumulation of fluid in intersitital space
Pulmonary oedema:
diffusion distance increased - gas exchange comprimised as O2 and CO2 have to dissue through wide layer of interstital fluid
causes of oedema 1
Raised capillary hydrostatic pressure
- arteriolar dilation
- raised venous pressure
- Left venticular faliure (pulmonary oedema)
- Right venticular faliure (peripheral oedema (ankle, sacral)
- Polonged standing (swollen ankles)
describe pulmonary oedema
- accumulation of fluid in the interstitial and intraalveolar lung spaces
- manifested clinically by varying degrees of shortness of breath
- crepitations in auscultation of lung bases
- Chest X-ray shows haziness in perihilar region
all causes of oedema
- Raised capillary hydrostatic pressure
- Reduced plasma osmotic pressure
- Lymphatic insufficiency
- Changes in capillary permeability
cause of oedema 2
- Reduced plasma osmotic pressure
normal [plasma protein]p is 65-80g/l
Oedema if <30g/l due to:
- malnutrition
- protein malabsorption
- excessive renal excretion of protein
- hepatic faliure
cause of oedema 3
Lymphatic insufficiency
- lymph node damage
- filariasis (a tropical disease caused by the presence of filarial worms, especially in the lymph vessels where heavy infestation can result in elephantiasis)
cause of oedema 4
- Changes in capillary permeability
inflammation
histamine increases leakage of protein
what is RAAS
Renin-Angiotensin-Aldosterone System (RAAS) is upregulated in heart failure resulting in more fluid retention
