This region of the nephron is under the control of two hormones: aldosterone and antidiuretic hormone (ADH). Potassium, acid-base, and water balance are controlled here.
This type cell is found in the late distal tubule and is represented by the IC box. Its main function is acid-base balance.
The basolateral border of this cell is freely permeable to hydrogen and potassium. As blood becomes more acidic, hydrogen ions (H+) equilibrate with this cell and electrostatically send potassium ions (K+) from it into the blood as indicated by the block arrows. The hydrogen ions are secreted into the filtrate by hydrogen/potassium exchange pumps in its luminal border(*).
'New' bicarbonate ions (HCO3-) are formed within this cell by the action of carbonic anhydrase. Only the basolateral border is permeable to these ions and they diffuse into the blood as indicated by the block arrow.
This common type of cell is represented by the two PC boxes. It is the major type of cell in the late distal tubule and the collecting duct. Its main function is to regulate potassium and water balance.
The hormone aldosterone affects this cell by stimulating (solid arrow) it to produce additional sodium/potassium pumps in its basolateral border(*). This pump moves 3 sodium ions (Na+) from the filtrate into the peritubular capillaries in exchange for 2 potassium ions (K+) as indicated by the curved block arrows. The hormone also increases the number of potassium channels in the luminal border (**) to facilitate the diffusion of this ion from the cell and into the filtrate.
The hormone ADH also affects this cell by stimulating it to produce water channels in its otherwise impermeable luminal border; this is indicated by the thick broken wall in this region of the nephron. In the late distal tubule the simultaneous presence of both hormones allows water to 'follow salt' into the peritubular capillaries (not indicated in the mind map). In the collecting duct ADH allows water to diffuse (block arrow) from the filtrate into the hypertonic blood in the ascending vasa recta.
Two conditions stimulate the adrenal cortex (AC) to secrete (solid-head dashed arrow) this hormone.
An increase in blood potassium (K+) stimulates (solid arrow) the adrenal cortex (AC) to secrete (solid-headed dashed arrow) aldosterone. The result will be to lower blood potassium due to increased activity of the principal cells.
This hormone is formed when the enzyme renin (R) is present in the blood. Renin converts the inactive compound angiotensinogen (A) into angiotensin I (A1) as indicated by the reaction arrow. The enzyme angiotensin converting enzyme (ACE), bound to the walls of pulmonary capillaries, catalyzes the conversion of A1 into the more potent compound angiotensin II (A2) as indicated by the second reaction arrow. This hormone stimulates the adrenal cortex (AC) to secrete (solid-headed dashed arrow) aldosterone. It also causes (solid arrow) generalized vasoconstriction (VCN) which increases (solid arrow) blood pressure (BP).
This hormone is secreted by the posterior pituitary (PP) as indicated by the solid-headed dashed arrow. ADH affects the principal cells by increasing their permeability to water as indicated by the thick broken walls of the late distal convoluted tubule and the collecting duct. This permits the reabsorption of water (block arrow) into the vasa recta. The secretion of this hormone is controlled by two mechanisms.
Renin (R) is released when blood pressure is low. As a result angiotensin II (A2) is formed as discussed above. This hormone stimulates the release of ADH as indicated by the solid-headed dashed arrow.
When the osmotic pressure (OP) of the blood is high the central nervous system will stimulate (solid arrow) the posterior pituitary (PP) to release ADH. The blunt headed line represents this neural connection. The effect will be to increase water reabsorption thus reducing blood osmotic pressure.
High blood pressure (BP) will inhibit (dashed arrow) the central nervous system from signaling the posterior pituitary to release ADH. The effect will be to reduce water reabsorption, reduce blood volume and reduce blood pressure.
Last Updated: 7/19/2005