University:
Western Sydney University
Course:
MEDI 2003 | Clinical Sciences 2
Academic year:

2024
Views:

96

Pages:

3
Author:

Mariam A. A.

• • • • • • Microcirculation Arteries entering an organ branch 6-7 times → arterioles (10-15 μm in diameter) Arterioles branch 2-5 times → capillaries (5-9 μm) 10 billion capillaries Total surface area ~ 500-700m2 Individual cells are rarely more than 20-30μm from a capillary Capillaries → venules → veins Capillary structure • Precapillary sphincters: small cuffs of smooth muscle positioned at the arterial end of the capillary o Flow through capillaries requires pressure difference and an open precapillary sphincter • Metarterioles o Short vessels that link arterioles and capillaries o Provide nutrient flow i.e. exchange of nutrients and metabolites • Arteriovenous shunts o Non-nutrient blood flow (heat exchange/ temp regulation in skin) bypasses the nutrient capillary bed, moving through an arteriovenous shunt Intercellular clefts (pores) • Liver: wide open → leaky o All dissolved substance including plasma proteins pass from the blood into the liver tissues • • Renal/glomerular: small oval windows (fenestrae) allow the passage of very small molecules and ions Brain: tight junctions allow only extremely small molecules i.e. water, O2, CO2 Interstium • ~1/6th of the body volume • Supported by collagen and elastin fibers • Filled with proteoglycan (sugar-protein) o 98% hyaluronic acid and 2% protein • Proteoglycan + water → tissue gel (sponge) → entraps interstitial fluid and ensures even distribution • Small ‘trickles’ of free fluid develop between proteoglycan molecules • Oedema = excess fluid is present in the interstitial spaces Lymphatic system • 2-3L/day of fluid moves from interstitial space into circulation (L + R subclavian arteries) via lymph system • Removes excess: fluid, osmotically active proteins, large particles o Size: particles are too big to be reabsorbed into venous capillaries o Removal of proteins from the interstitial spaces is an essential function, without which death would occur in approximately 24 hours o Move via slit-like valves between adjacent endothelial cells o Valves ensure one-way drainage