Renal mechanism of urine formation and Permeability of the tubules Renal mechanism of urine formation Renal mechanism of concentrated and dilute urine formation- Concentrated urine is formed by passive water reabsorption from the tubules while many solutes in the tubular fluid are absorbed by active process. Dilute urine is formed by absorption of solutes alone […]

Renal function tests Renal clearance is the measurement of the kidney’s ability to remove substances from the plasma. Clearance measurements are used to determine Renal Blood Flow (RBF),  Renal Plasma Flow (RPF), Glomerular Filtration Rate (GFR), Filtration Fraction (FF) and how different substances are handled by the kidney tubules (reabsorbed or secreted) and to compare

Uremia or Azotemia Uremia or azotemia, is the elevated level of waste products in the blood, particularly nitrogen-containing compounds like urea and creatinine. Urea is the chief nitrogenous end product of protein metabolism and is excreted by the kidneys in the urine of mammals. It is also found in the blood and lymph. Uremia is

Functions of the urinary bladder Urinary bladder provides an expandable reservoir for urine, which is continuously flowing from pelvis of the kidney through ureters. Micturition Micturition is the process in which the urinary bladder empties when it becomes filled with urine. Passage of Urine from the kidney to the bladder Urine is secreted continuously though

Reabsorption and secretion in different regions of tubules Water transport is by osmotic diffusion. Proximal tubule: 65% reabsorption. Loop of Henle: 15%. Distal tubule: 10%. Collecting duct: 9.3%. Urine: 0.7%. Glucose, proteins, amino acids, vitamins and acetoacetate ions are completely reabsorbed by active process in proximal tubule. 50% of urea is reabsorbed. Creatinine is not reabsorbed

Absorptive capabilities of different tubular segments Proximal tubule 65 % of the reabsorption and secretion take place. Only 35% of the GF leaves the proximal tubule. Thin segment of Loop of Henle Permeability of the epithetical cells of descending limb of Loop of Henle is great and occurs by simple diffusion. It is highly permeable

Tubular secretion Several substances are transported from the peritubular capillaries into the interstitial fluid and then to the tubular lumen via the tubular epithelial cells. Antiport of H+ along with Na2+ reabsorption in the proximal tubule and distal tubule. H­+ is secreted throughout the nephron. K+ transport is unique, in that it is reabsorbed in some parts of the tubule

Tubular reabsorption Reabsorption plays a major role than the secretion in the formation of urine. More than 90% of the water in the GF is reabsorbed as it passes through the tubules. Some substances such as sodium, glucose and amino acids are almost completely reabsorbed so that their concentration decreases almost to zero before the fluid becomes

Glomerular filtration Glomerular filtrate is the fluid that is filtered through the glomerular membrane into the Bowman’s capsule. Glomerular capillary membrane Glomerular capillaries are relatively impermeable to proteins so that the filtered fluid, glomerular fluid (GF) is essentially protein free and devoid of cellular elements. The glomerular capillary membrane has three layers: Endothelium of the capillary Basement

Formation of urine in the nephrons Three processes are involved in the formation of urine in the nephrons- Glomerular filtration, Tubular reabsorption, Tubular secretion.