Lecture 08 - Glomerular Filtration

Lecture 08 - Glomerular Filtration - Renal Blood Flow To...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
Renal Blood Flow To provide the student with a working knowledge of how renal blood flow is dictated by kidney vascular resistance and where this resistance resides as well as factors that may modify or affect the vascular resistance. To provide the student with a working knowledge of how renal blood flow autoregulation is mediated and the contribution of local hormones and tubuloglomerular feedback systems in the regulation of renal blood flow. - Blood flow to the kidney is highest per gram tissue of any organ o Approximately 20% of cardiac output at rest Renal blood flow is around 1200 ml/min and renal plasma flow is approximately 650 ml/min in a 70 kg human. Glomerular filtration rate is approximately 100-200 ml/min or 150-180 liters/day. This is a protein free ultrafiltrate formed from renal plasma flow. Filtration fraction is GFR/RPF and is high at 15-20%, the highest achievable in any capillary bed. Renal vascular resistance – why is it so low – dilated vessels or multiple resistors (glomeruli) in parallel? Renal oxygen requirements – very low A-V oxygen difference implying low nutrient needs. However, local oxygen tension in kidney is actually low, implying preglomerular shunting of oxygen between arterial and venous systems. If no GFR and tubular reabsorption, nutrient requirement is only approximately 5% of renal blood flow. o Purpose of elevated blood flow to kidney Interesting contrast to the heart, where increased blood flow is usually of benefit. Major requirement for elevated renal plasma flow is high level of GFR. Increased blood flow leads to increased GFR, increased renal transport requirements, and increased nutrient and oxygen needs. The kidney not uncommonly fails with reduction in blood flow in spite of low nutrient needs. Oxygen tension is approximately 45 mmHg in cortex and 30 mmHg in medulla. Increased aortic oxygen tension does not lead to increased oxygen tension in kidney due to the countercurrent exchange of oxygen in kidney (and the saturability of Hgb)
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
- Regulation of renal blood flow with changes in blood pressure o Anatomical relations within the renal vasculature. Approximately 50% of vascular resistance resides proximal to the glomerulus. Glomerulus is an array of parallel capillaries with cross communications and no smooth muscle. Mesangial cells tether the glomerular capillary loops. Glomerular capillary hydrostatic pressure is about 50 mmHg and is remarkably constant along capillary length. Urinary space pressure is about 15 mmHg providing a glomerular hydrostatic pressure difference of approximately 35 mmHg. Second major resistance is at the efferent arteriole which constitutes 30-35% of total renal vascular resistance. Peritubuar pressures are lower, close to tubular pressures.
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 09/14/2011 for the course PHARM rs taught by Professor Staff during the Spring '11 term at UCSD.

Page1 / 5

Lecture 08 - Glomerular Filtration - Renal Blood Flow To...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online