Microcirculation Flashcards
What is microcirculation?
Blood flow through the smallest vessels involves capillaries and lymphatic vessels
Transport of nutrients and removal of waste
What are the blood vessels involved in microcirculation from the smallest to the largest?
Vena cava Aorta small veins small arteries arterioles venules capillaries
What is the structure of capillaries?
single layer of highly permeable endothelial cells
has pores that allow diffusion
SA= 500-700m2
Thin walls
Modest volume- 5% of body’s blood
Large cross sectional area amongst all the vessels
Slowest flow velocity- 2cm/min or 0.3mm/s
Why is blood flow slowest in capillaries?
so more time for gas and nutrient exchange
What is the role of the capillaries?
allow exchanging of solutes and fluid between plasma and interstitial fluid
What is starling’s law of filtration?
A law that governs the flow of filtration across the capillaries
What 4 parameters are in the starling equation?
Pc= capillary hydrostatic pressure
Pi= interstitial fluid hydrostatic pressure
Pi c= capillary plasma oncotic pressure
Pi i= interstitial fluid oncotic pressure
What does the K in Starling’s equation represent?
Filtration coefficient
What is the movement of H2O from plasma to interstitial space called?
filtration
What is the movement of H20 from interstitial space to plasma called?
absorption
What determines the net flow of fluid across a capillary?
The balance of the 4 starling forces
Why is the osmotic effect of capillary fluid greater than the osmotic effect of the interstitial fluid?
the capillary fluid/plasma contains more proteins which generates a higher colloid osmotic pressure and attracts more water via osmosis
What is colloid osmotic pressure?
osmotic pressure by proteins in blood plasma or interstitial fluid
What solutes move across capillary wall by simple diffusion?
O2, CO2, nutrients and metabolites
What 2 pathways do the solutes use to move between blood and interstitial fluid?
transcellular
paracellular
What is transcellular movement?
simple diffusion through endothelial cells
What is paracellular movement?
simple diffusion through tight junctions or gaps of endothelial cells
What are the types of transcellular movement?
simple diffusion
facilitated diffusion
transcytosis
What are the 3 types of capillary structures?
continuous
fenestrated
discontinuous/sinusoid
Describe the structure of a continuous capillary?
endothelial cells tightly held together
tight junctions between cells
continuous basement membrane
presence of intracellular clefts
What types of molecules pass through continuous capillary and what route do they use?
small molecules- water, ions
use paracellular route via intercellular clefts
Describe the structure of a fenestrated capillary?
small openings in the cells
leaky
What route is used to cross fenestrated capillaries?
use fenestrations and intracellular cleft
Describe the structure of a discontinuous/sinusoid capillary?
very leaky endothelial cells held very loosely large gaps between cells holes in the basement membrane large intracellular gaps
What route is used to cross discontinuous/sinusoid capillaries?
cross through the holes in membrane and intracellular gasp
What is the lymphatic systems role?
scavenger system
Drains excess fluid, water, ions, glucose, lipid, WBC, protein, large particles and debris from interstitial space back into blood
What is the fluid collected from interstitial space called?
lymph
What are lymphatic vessels?
smooth muscle
What is the role of the lymph nodes surrounding the lymphatic vessels?
immune function- they have lymphocytes which destroy foreign particles and bacteria present in the lymph
What allows the one way flow of lymph from tissues to veins?
lymphatic valves
Where is lymph collected from?
All body tissue except brain
What are lymphatic ducts?
sites at which lymph empties into large veins
What is oedema?
- Swelling caused by excess fluid in tissues/interstitial space
- Swelling of skin after damage to local capillaries
What causes oedema?
High hydrostatic capillary pressure due to HF, blood clot, cardiac failure, deep vein thrombosis
imbalance of starling forces
Low blood/plasma protein due to liver failure, poor nutrition and burns
Lymphatic failure due to damaged lymphatic vessels, infected lymph nodes, protein accumulated in undrained fluid?
What is lymphoedema?
accumulation of lymph which obstructs lymph system
What cause can lead to peripheral and pulmonary oedema?
HF
Describe the MOA of peripheral oedema?
- Left ventricle dysfunction= abnormal CO
- MAP falls due to small CO
- Reflexes triggered to restore MAP- baroreceptors, salt and water retention by kidneys
- Salt and water retained
- Plasma vol increases
- Venous pressure increases
- Capillary pressure increases
- Filtration increases
- Fluid lot from capillaries to tissue= swelling
Describe the MOA of pulmonary oedema?
- Left ventricular dysfunction
- Reduced ejection which means reduced SV and CO- so blood is left behind instead of ejected
- Blood backed up into left atrium
- Blood build up in pul veins which return blood to heart
- Pul veins are engorged and swell due to lots of blood and hydrostatic pressure increases
- Pul capillary pressure increases
- Increased filtration
- Fluid leaves capillaries and accumulates in interstitial space of lungs
