Endocrine functions of the
Kidneys, Heart and Pineal Gland
The kidneys produce 3 hormones.
• 1,25 DHC
• Renin
• Erythropoietin.
• The heart produces ANP although also
produced by other tissues. Acts to
increase excretion of Na by the kidneys.
• The pineal gland secretes melatonin.
Renin
• Renin is an enzyme that acts together with
Angiotensin converting enzyme to form
angiotensin II.
• Is a product primarily from the Kidneys.
• Formed in the secretory granules of the
JG cells.
• Its only function is to split angiotensin I
from angiotensinogen.
Glomerulus
Angiotensinogen
• Found in the α globulin fraction of the
plasma.
• Circulating levels is increased by
glucocorticoids, thyroid hormones,
estrogens and angiotensin II.
Angiotensin converting Enzyme
• Forms angiotensin II from angiotensin I
• Some conversion occurs in other parts of
the body.
Actions of Angiotensins
• Angiotensin I functions solely as the precursor
for Angiotensin II.
• Angiotensin II causes arteriolar constriction and
causes a rise in systolic and diastolic blood
pressure.
• One of the most potent vasoconstrictors known.
• Acts directly on the adrenal cortex to increase
aldosterone and the R-A-S system is a major
regulator of aldosterone secretion.
Angiotensin II
• Is one of the most potent vasoconstrictors
known.
• Acts directly on the adrenal cortex to
increase secretion of aldosterone.
• Acts on the post ganglionic sympathetic
neurons to release norepinephrine.
• Acts on the brain to increase water intake
and increase secretion of vasopressin and
ACTH.
The R-A-A-S
Tissue R-A-S
• In addition to the system generating circulating
angiotensin II, many tissues contain
independent R-A-S that genarate angiotensin
II…for local use.
• Blood vessels, uterus, placenta, eyes, exocrine
portion of the pancreas, heart, adrenal cortex,
testis, ovary, anterior and intermediate lobe of
the pituitary .
• Their function is unsettled.
• Contributes very little to the circulating renin
pool.
The JGA
• Renin is produced by the JG cells
• Located in the media of the afferent
arterioles as they enter the glomeruli
Regulation of Renin Secretion
• Increased renin secretion depends on the
following: Sodium Depletion
Diuretics
Hypotension
Hemorrhage
Dehydration
Heart failure
cirrhosis
Constriction of renal artery
• Angiotensin II feeds back to inhibit renin
secretion by a direct action on the JG cells.
• Increased activity of the sympathetic nervous
system increases renin secretion.
Erythropoietin
• Regulate the level of RBC in the blood by
enhancing bone marrow activity.
• Increased if RBCs are reduced, and reduced if
the RBCs are increased.
• Its blood levels are increased in anemia.
• Mostly from the kidneys and some from the liver.
• During fetal life, erythropoiesis takes place
majorly in the liver. Liver also produces
erythropoietin (15 % )
• Then erythropoiesis taken over by bone marrow,
and erythropoietin produced by the kidneys.
Regulation of Erythropoietin
• The usual stimulus for erythropoietin
secretion is hypoxia.
• Also stimulated by androgens.
• Secretion is also facilitated by alkalosis
that develops at high altitudes also by
catecholamines
Hormones of the Heart and other
natriuretic peptides.
natriuretic peptides are secreted by the heart.
• Atrial natriuretic peptide is a polypeptide
• Also there is the brain natriuretic peptide
• ANP and BNP act on the kidneys to increase Na
excretion
• Act on the renal tubules to inhibit Na
reabsorption.
• They relax vascular smooth muscles in arterioles
and venules.
• They inhibit renin secretion and counteract the
pressor effect of catecholamines and
angiotensin II.
Pineal Gland
• Known to secrete melatonin.
• Functions as a timing device to regulate
internal events with the light - dark cycle in
the environment.
• Arises from the roof of the third ventricle.
• Has concretions which are radiopaque.
Melatonin
• No role in regulation of skin colour.
• Synthesis and secretion is increased in the
dark period
• Low levels during the day.