Lecture 14 - Capillary exchange Flashcards
How are capillaries suited to their function?
Extremely small distance for substances to diffuse across (thin walls and cells in close prximity)
Blood flows slowly through a large surface area for exchange to occur (10+ billion capillaries = 600m²)
Three capillary types: what are they and where are they prevalent?
Continuous (main capillary type)
Fenestrated (endocrine, intestines, kidneys)
Sinusoidal (liver, endocrine, bone marrow, spleen)
Transport mechanisms in capillary exchange
Diffusion: substances will move from an area of high concentration to low concentration - lipids, small soluble molecules, ions through channels
Bulk transport: mass movement through clefts/pores down a concentration gradient - larger molecules
Transcytosis: vesicular transport - macromolecules (glycoproteins)
Four forces in capillaries that cause fluid to move
Net filtration pressure in capillaries determine the movement of fluid, the NFP is dependent on:
- Capillary hydrostatic pressure: the blood pressure exerted on walls that pushes fluid out
- Interstitial fluid hydrostatic pressure: the fluid exerted on the walls by the intersttitial fluid which pulls fluid back into the capillaries
- Blood colloid osmotic pressure: The plasma osmotic pressure pulling fluid in
- Interstitial fluid colloid osmotic pressure: The interstitial fluid pressure pulling fluid out
Net filtration pressure equations
Net filtration pressure = hydrostatic pressure - osmotic pressure
NHP = CHP (decreases) - IHP (negligible)
NOP = BCOP (blood volume) - IHP (negligible)
Effect of positive and negative NFP
NHP > NOP = positive NFP = filtration
NHP < NOP = negative NFP = reabsorption
When is NHP/NOP more significant
NHP (CHP) decreases along a capillary but NOP (BCOP) remains constant so, at the beginning of the capillary, fluid is moved out and, nearer the end of the capillary, fluid is pulled back in
When NFP changes: hypertension, hemorrhage, dehydration, and tissue damage
Hypertension: more fluid is filtered than normal, build-up of fluid in tissues, systemic oedema (swelling)
Hemorrhage: more fluid is reabsorbed than normal, fluid recalled from tissues to bloodstream, increasing cardiac output and blood pressure
Dehydration: more fluid is reabsorbed than normal, fluid recalled from tissues to bloodstream, delaying symptoms of dehydration
Tissue damage: more fluid is filtered than normal, plasma proteins leak into interstitial fluid, oedema
Pulmonary circulation: ensuring blood oxygen levels are high
Arterioles in lungs will constrict in regions of low oxygen levels, sending blood to oxygen richer areas, enhancing oxygen absorption
In other organs, blood will dilate if oyxgen is in low levels, increasing oxygen delivery
Feautures allowing efficient exchange in lungs
Difference in CHP is significant, lungs is significantly lower to absorb more oxygen and to also prevent oedema in the lungs from interstitial fluid
Arteries are more distensible, can accomodate increased CO without significant pressure increase
Low vascular resistance
Feautures allowing efficient exchange in coronary circulation
Coronary flow increases when vasoconstriction occurs within the body and adrenaline causes coronoary vasodilartion
As left artery is compressed during systole, coronary flow is restricted and coronary flow is highest during diastole, enabled by arterial elastic recoil
To ensure coronary supply, cardiomyocytes have high oxygen reserves, the myocardium has high capillary density (to extract oxygen),
Artery collaterals
research
Cerebral circulation: key features
Consumes 12% CO for 2% body mass
Flow rate = 750 ml/min
Neurons have poor metabolic reserves
4 arteries used to supply the brain which anastomose inside cranium
Flow can be maintained if there is a disruption
