Renal Physiology.docx

Glomerate filtration rate GFR= how much blood can be filtered from glomerulus into tubule Passive process due to fluid dynamics Glomerular capillaries are far more permeable than other capillaries. 3 forces that determines GFR. Glomerular capillary blood pressure due to larger afferent compared to e...

Glomerate filtration rate GFR= how much blood can be filtered from glomerulus into tubule Passive process due to fluid dynamics Glomerular capillaries are far more permeable than other capillaries. 3 forces that determines GFR. Glomerular capillary blood pressure due to larger afferent compared to efferent arteriole- favours filtration. Plasma- colloid osmotic pressure (mixture of proteins)- opposes filtration. Bowmans’s capsule hydrostatic pressure (physical pressure exerted by liquid)- opposes filtration. = Net filtration pressure- favours filtration. Intrinsic and extrinsic control. - blood pressure is determined by GFR. Blood pressure in the kidney is subject to intrinsic and extrinsic control. Intrinsic= from within the kidneys Extrinsic= external to the kidneys Intrinsic control (autoregulation) Myogenic mechanism Baroreceptor in arteriole- contract or dilates. Tubuloglomerula feedback Specialised cells called Juxtaglomerular apparatus Specialised collection of cells in DCT and afferent arteriole. Granular cells in the efferent arteriole Macula densa cells in the DCT monitors NaCl: High BP= high blood flow Increased BP= increased in blood flow therefore more filtrate so more NaCl More NaCl= macula densa cells send out a paracrine message to arteriole cells by releasing ATP and adenosine. Arteriole cells constrict and release blood flow. Another level of control by the tubuloglomular feedback is when macula densa cells secrete nitric oxide (vasodilator). This stops the action of ATP + adenosine. Extrinsic control Overrides intrinsic control. Dehydration Purposely want to regulate GFR. Example of dehydration Reduce blood volume= reduced arteriole blood pressure Detected by aortic arch or carotid sinus by the baroreceptors. Increases sympathetic activity= BP increases Arteriole vasoconstriction. Acts on glomerular capillaries Decreases GFR Decreases amount of filtrate Decreased amount of urine More fluid absorbed back. RAAS – Renin angiotensin aldosterone system Granular cells in the arteriole release renin due to: Baroceptors activity Macula densa cells detect decrease in NaCl. Innervated by SNS Renin ultimately causes the release of angiotensin II Angiotensin II causes: Arteriolar vasoconstriction Vasopressin release Aldosterone release Thirst All the above counteract the stimuli which led to renin release. Counter current multiplication and loop diuretics Loop diuretics is used to treat oedema associated with heart, liver, and renal failure. Treats hypertension- decrease blood volume= decrease BP Helps to urinate more frequently. Works by NKCC2 cotransporters. Counter current is the descending and ascending limb being next to each other meaning fluid goes in opposite directions. Loop diuretics block the NKCC2 cotransporter.