Endocrine function of the kidney
Erythropoietin has the effect of stimulating progenitor cells of erythropoiesis, erythroid stem cells, converting to proerythroblasts, proerythroblast, and increasing erythropoiesis.
Overview of kidney functions
Production of urine – removal of waste products and excess substances from the blood; this is the major function of the kidneys…by doing this the volume and composition of blood plasma stays within normal limits
Secretion of the renin – when systemic blood pressure decreases, the kidneys secrete an enzyme called renin. Renin triggers the angiotensin mechanism which increases blood pressure (defined later)
Secretion of erythropoietin – when oxygen levels fall below normal, the kidneys release erythropoietin, which stimulates hematopoiesis in the red bone marrow. More RBCs means more oxygen
Regulating Blood Pressure: The Renin-Angiotensin-Aldosterone System
Kidneys secrete renin to regulate blood pressure
The kidneys participate in the regulation of blood pressure through the RAA (Renin - Angiotensin - Aldosterone) system according to the following mechanism:
When blood flow to the kidney decreases or blood Na+ decreases, it has the effect of stimulating the Para glomerular organization to secrete a hormone called renin. Under the action of renin, a protein in the blood called angiotensinogen is converted into angiotensin I. Angiotensin I reaches the lungs, due to the action of converting enzyme (converting enzyme), converted into angiotensin II.
Angiotensin II has a strong effect on increasing blood pressure by the following mechanism:
Angiotensin II causes vasoconstriction leading to an increase in blood pressure (vasoconstriction is strongest in the arterioles). Strong vasoconstrictor effect in normal people. The vasoconstrictor effect is reduced in patients with decreased Na+, cirrhosis, heart failure, and steatosis because in these patients, Angiotensin II receptors in vascular smooth muscle are reduced.
Make you feel thirsty
Angiotensin II stimulates the thirst center in the hypothalamus to cause thirst to replenish the body.
Increased secretion of ADH
Angiotensin II stimulates the supraoptic nucleus to increase secretion of ADH to increase water reabsorption in the distal and collecting tubules.
Increased secretion of aldosterone
Angiotensin II stimulates the adrenal cortex to secrete aldosterone to increase Na+ and water reabsorption in the distal and collecting tubules.
Thus, angiotensin II causes vasoconstriction and increases blood volume, thus increasing blood pressure. Increased blood pressure affects the kidneys to reduce renin secretion. The kidney's blood pressure regulation mechanism follows the principle: cause causes the effect, consequences create a cause.
Kidneys excrete erythropoietin to increase red blood cell production
Effect of Erythropoietin on RBC Numbers
The kidneys are involved in the regulation of red blood cell production by the hormone erythropoietin.
When there is blood loss, anaemia, or O2 deficiency, the kidneys produce the hormone erythropoietin. Erythropoietin stimulates erythroid stem cells to convert to proerythroblasts and increase erythropoiesis. Therefore, erythropoietin is used to treat anaemia.
Kidneys participate in the formation of the active form of vitamin D
Diagram: Formation of the active form of vitamin D.
From a new perspective, vitamin D is considered a hormone. In the process of forming the active form of vitamin D, the kidneys are involved by the following mechanism (diagram):
Both 25-Hydroxycholecalciferol and 1,25-Dihydroxycholecalciferonl are biologically active, but 1,25-Dihydroxycholecalciferol is 100 times more potent than 25-Hydroxycholecalciferol.
They have the following effects:
In bone: increase bone-forming cells, increase bone-forming activity, increase calcium and phosphorus absorption and mobilization in bone.
In the intestine: increased absorption of Calcium and Phosphorus.
In the kidney: increased calcium reabsorption in the renal tubules.