The glomerulus is the primary site of filtration. Blood enters the glomerulus through the afferent arteriole, passes through bowman's capsule surrounding the glomerulus, enters the nephron and leaves it through the efferent arteriole. The glomerular filtration barrier consists of fenestrated capillary endothelium, visceral epithelial layer, and basement membrane with type IV collagen and heparan sulfate.
Glomerular filtration rate is defined as the volume of plasma that is filtered by the glomeruli per unit of time. Creatinine clearance is frequently used to estimate GFR, but because creatinine is secreted by the proximal tubule, the clearance of creatinine frequently overestimates GFR. Inulin clearance is the best estimate of GFR because Inulin is freely filtered and is neither reabsorbed nor secreted. Inulin clearance can be calculated by the formula U x V/P where U represents urine concentration of Inulin (mg/mL), V represents urine flow rate (mL/min), and P represents plasma concentration of Inulin (mg/mL).
Filtration fraction represents the fraction of renal plasma flow that is filtered via the glomerular capillaries and can be calculated by the ratio of glomerular filtration rate and renal plasma flow (FF=GFR/RPF).
The fractional excretion of sodium is the percentage of the sodium filtered by the kidney, which is excreted in the urine. Fractional excretion of sodium is decreased when the perfusion of kidneys is decreased due to a compensatory increase in the reabsorption of sodium.
Glomerular filtration rate (GFR) is an estimate of how much blood passes through the glomeruli each minute. GFR is frequently used to assess the function of kidneys.
Prostaglandins dilate the afferent arteriole and increase the blood flow to the glomerulus. This increases renal plasma flow (RPF) and glomerular filtration rate (GFR) proportionally. Thus, filtration fraction (FF) isn't affected.
Renin-angiotensin-aldosterone system regulates the process of filtration. Angiotensin II has effects on afferent and efferent arterioles and regulates glomerular filtration rate (GFR). Preferential constriction of the efferent arteriole induced by angiotensin II increases GFR.
Tubuloglomerular feedback is one of the mechanisms that regulates glomerular filtration rate (GFR). Increased GFR can result in increased distal tubular sodium chloride concentration, which leads to a release of adenosine from the macula densa cells. Adenosine constricts the afferent arteriole and reduces glomerular filtration rate.
Atrial natriuretic peptide (ANP) is released in response to the distension of the atria of the heart (e.g., volume overload) while brain natriuretic peptide (BNP) is released in response to ventricular distension. These hormones increase renal sodium excretion (natriuresis) and inhibit renin secretion.
Antidiuretic hormone promotes the insertion of aquaporins in the collecting duct and induces reabsorption of the free water.
Norepinephrine acts on alpha 1 receptors, which causes constriction of renal arteries, decreased blood flow to the afferent arterioles and decreased filtration. This can result in renal failure.
Dopamine causes renal artery dilation, resulting in increased renal blood flow and increased filtration.
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