|
|
Line 2: |
Line 2: |
| | | |
| | | |
− | ==Aldosterone== | + | ==[[Aldosterone]]== |
| | | |
− | Aldosterone is a steroid hormone which is secreted from the zona glomerulosa of the adrenal gland. It has a mineralocorticoid activity and is the most important regulator of plasma potassium. When plasma potassium increases increased stimulation of aldosterone occurs directly and as a result of Renin-Angiotensin-Aldosterone System (RAAS). It is also the most important regulator of sodium excretion.
| |
− |
| |
− | ===Release===
| |
− |
| |
− | * Release is stimulated by 3 things
| |
− | # Corticotropin (ACTH)
| |
− | # Angiotensin 2
| |
− | # K<sup>+</sup>
| |
− | * Its release is inhibited by Atrial Natriuretic Peptide
| |
− |
| |
− | * Most increases in the concentration of aldosterone however can be explained by increases in the '''Renin-Angiotensin-Aldosterone System''' and therefore angiotensin 2 and/or by increases in K<sup>+</sup> concentration
| |
− | * Only in severe fluid loss does ACTH significantly stimulate the release of aldosterone
| |
− | * ANP is secreted in response to sodium/water loading and therefore inhibits aldosterone secretion
| |
− |
| |
− | ===Action===
| |
− |
| |
− | * Diffuses across the cell membrane - lipophillic (essentially steroidal)
| |
− | * Of the principal cells of [[Reabsorption and Secretion Along the Distal Tubule and Collecting Duct - Anatomy & Physiology#Distal Tubule| distal tubule]] and [[Reabsorption and Secretion Along the Distal Tubule and Collecting Duct - Anatomy & Physiology#Collecting Duct| collecting duct]]
| |
− | * Binds to cytoplasmic receptors
| |
− | * Works by altering gene transcription and increases synthesis of proteins
| |
− | ** Affects ATP levels
| |
− |
| |
− | =====Sodium=====
| |
− |
| |
− | * Affects sodium entry and transport
| |
− | * Increases number of apical sodium channels, NaCl co-transporters and Na<sup>+</sup>K<sup>+</sup>ATPase
| |
− | * Increases activity of the hydrogen sodium exchanger in the apical membrane
| |
− | * Increases membrane permeability
| |
− | * Increases sodium pump activity
| |
− | * Total quantity of sodium is conserved not the actual plasma concentration
| |
− | ** When sodium is reabsorbed water follows it so the volume of the plasma is altered rather than the concentration of sodium changing
| |
− | ** '''Angiotensin 2''' and '''Aldosterone''' affect sodium but they also affect ECF volume so only quantity affected not concentration
| |
− | ** [[Pituitary Gland - Anatomy & Physiology #Posterior Pituitary Gland | ADH]] and thirst response also work together to dilute the ECF if concentrations of sodium are high so although there is more NaCl the actual concentration is not really changed.
| |
− | * If there was no secretion of aldosterone a 20kg dog would excrete 15g per 24 hours
| |
− | * At maximal secretion no significant amount of sodium would be excreted
| |
− |
| |
− | =====Potassium=====
| |
− |
| |
− | * In cases of increased K<sup>+</sup>
| |
− | * Increased Na<sup>+</sup> / K<sup>+</sup> ATPase pump activity increases the amount of K<sup>+</sup> in cells to reduce plasma K<sup>+</sup>
| |
− | * Generally not excreted
| |
− | * However if plasma K<sup>+</sup> is still high aldosterone is stimulated
| |
− | * Causes potassium secretion
| |
− | ** Stimulates Na<sup>+</sup> / K<sup>+</sup> ATPases in the basolateral membrane of the principal cells
| |
− | ** Increased potassium in the cells
| |
− | ** Potassium leaves via apical leak channels
| |
− | ** Thanks to electro-chemical gradient
| |
− | * Very tightly regulated system
| |
− | ** Allows large increase in K<sup>+</sup> to have a miniscule effect on plasma K<sup>+</sup>
| |
− |
| |
− | =====Hydrogen=====
| |
− |
| |
− | * Increases hydrogen secretion by increasing Hydrogen ATPases in the apical membrane of the intercalated cells
| |
− | * Increases hydrogen secretion by increasing sodium hydrogen exchanger in the apical membrane of the principal cells
| |
− |
| |
− | ==Revision==
| |
− |
| |
− | Use the [[Important Hormonal Regulators of the Kidney - Renal Flash Cards - Anatomy & Physiology|flash card revision resource]] for this section to test yourself.
| |
− |
| |
− | [[Category:Urinary System - Anatomy & Physiology]][[Category:Endocrine System - Anatomy & Physiology]]
| |
| | | |
| | | |