K + A Na + KEY Leak channel Countertransport Exchange pump Diffusion Reabsorption Secretion Cotransport K + Aldosterone- regulated pump Aldosterone-regulated reabsorption of sodium ions, linked to the passive loss of potassium ions. A b Na + Aldosterone • Hormone produced by adrenal cortex • Stimulates synthesis and incorporation of Na + pumps and channels (In plasma membranes along DCT and collecting duct) • Reduces Na + lost in urine Variable reabsorption of water, sodium ions, and calcium ions (under hormonal control) Atrial natriuretic peptide (ANP) opposes secretion of aldosterone and its actions on DCT and Collecting System Variable reabsorption of water, sodium ions, and calcium ions (under hormonal control) à Parathyroid hormone Regulates calcium ion reabsorption at DCT Parathyroid Glands Parathyroid hormone (PTH) is secreted by the Parathyroid glands in response to low concentrations of Ca 2+ in blood
37 Secretion at DCT – Blood entering peritubular capillaries still contains undesirable substances that did not cross filtration membrane at glomerulus – Rate of K + and H + secretion rises or falls according to concentrations in peritubular fluid • Higher concentrations lead to higher rates of secretion Figure 26–13c Tubular Secretion and Solute Reabsorption by the DCT. Tubular fluid CO 2 Cl – H + NH 4 + Cl – Cl – Na + Na + NH 4 + CO 2 H 2 O H 2 CO 3 HCO 3 – H + Amino acid deamination HCO 3 – Cl – Cl – H + HCO 3 – HCO 3 – KEY Leak channel Countertransport Exchange pump Diffusion Reabsorption Secretion Cotransport Na + HCO 3 – Na + H + HCO 3 – Aldosterone- regulated pump A Hydrogen ion secretion in response to acidosis – Hydrogen ions generated by dissociation of carbonic acid – Bicarbonate ions diffuse into bloodstream This system helps prevent changes in plasma pH: - Respiratory acidosis - Ketoacidosis - Lactic acidosis … à Aldosterone stimulates H + secretion Prolonged aldosterone stimulation can cause alkalosis
38 Figure 26–9 An Overview of Urine Formation. Proximal Convoluted Tubule • Reabsorption of water, ions, and all organic nutrients Distal Convoluted Tubule • Secretion of ions, acids, drugs, toxins • Variable reabsorption of water, sodium ions, and calcium ions (under hormonal control) Renal Corpuscle • Production of filtrate Glomerulus Glomerular capsule Collecting duct Nephron Loop Descending thin limb • Further reabsorption of water Thick ascending limb • Reabsorption of sodium and chloride ions KEY Filtration occurs exclusively in the renal corpuscle, across the filtration membrane. Water reabsorption occurs primarily along the PCT and the descending thin limb of the nephron loop, but also to a variable degree in the DCT and collecting system. Variable water reabsorption occurs in the DCT and collecting system. Solute reabsorption occurs along the PCT, the thick ascending limb of the nephron loop, the DCT, and the collecting system.
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- Fall '18