Tubular Reabsorption and Secretion PDF

Tubular Reabsorption and Secretion Dr Pallav Sengupta Assistant Professor, Physiology www.gmu.ac.ae COLLEGE OF HEALTH SCIENCES  Tubule Substances reabsorbed Substances Secreted PCT...

Tubular Reabsorption and Secretion Dr Pallav Sengupta Assistant Professor, Physiology www.gmu.ac.ae COLLEGE OF HEALTH SCIENCES  Tubule Substances reabsorbed Substances Secreted PCT K+, Cl-, Na+, Mg2+, Uric acid, drugs, Toxins Bicarbonate, Phosphate, Amino acids, Glucose, water Descending loop of Water and Urea Henle Ascending loop of Henle K+, Cl-, Na+, urea DCT K+, Cl-, Na+, H+, Water Collecting duct K+, Cl-, Na+, Water, urea 3 Site of reabsorption Substances reabsorbed from PCT Glucose, amino acids, sodium, potassium, calcium, bicarbonate, chloride, phosphate, uric acid, water. Substances reabsorbed from loop of Henle Sodium, chloride and water. Substances reabsorbed from DCT Sodium, chloride, bicarbonate, water. 4 Sodium reabsorption in proximal tubule The sodium-potassium ATPase: major force for reabsorption of sodium, chloride and water In the first half of the proximal tubule, sodium is reabsorbed by co-transport along with glucose, amino acids, and other solutes. In the second half of the proximal tubule, sodium reabsorbed mainly with chloride ions. Na+ reabsorption in first half of PCT 5 Sodium reabsorption in proximal tubule and descending loop of Henle These parts are highly permeable to water. Water reabsorption is secondary to sodium reabsorption Known as Obligatory water reabsorption  Sodium reabsorption in distal tubule, ascending loop of Henle and collecting duct These parts are not permeable to water. Water reabsorption is dependent on ADH Known as Facultative water reabsorption 8 Glucose Reabsorption Reabsorbed totally in PCT Glucose is reabsorbed along with Na+ in the early portion of the proximal tubule. Glucose is typical of substances removed from the urine by secondary active transport. Essentially all of the glucose is reabsorbed, and no more than a few milligrams appear in the urine per 24 hours.  The renal threshold for glucose is the plasma level at which the glucose first appears in the urine. The renal threshold would be about 300 mg/dl – i.e., 375 mg/min (TmG) divided by 125 mL/min (GFR). However, the actual renal threshold is about 200 mg/dL of arterial plasma, which corresponds to a venous level of about 180 mg/dL. Potassium reabsorption and secretion 10  Factors affecting functions of kidney Antidiuretic hormone (ADH): Increases permeability of water at DCT and CD. More water reabsorption less urine Alcohol, caffeine inhibit ADH action Aldosterone: Increases reabsorption of sodium and secretion of K+ at DCT, Atrial natriuretic peptide (ANP): Decreases sodium reabsorption and increases urination Renin-angiotensin-aldosterone system: Renin converts Angiotensinogen to Angiotensin I. Ang I converts to Ang II at lung. Angiotensin II different effects: Increases thirst Increases ADH release Increases aldosterone Cause vasoconstriction Required for regulation of blood pressure  Learning Resources Text Book: Colbert BJ, Ankney J, Lee KT. Anatomy and Physiology for health professions. 2nd edition, Pearson education; 2011. ISBN-13: 978-0-13-506077-3. Chapter 16, pp. 421-422. Power-point presentation in the Moodle www.gmu.ac.ae COLLEGE OF HEALTH SCIENCES