Antidiuretic Hormone(Vasopressin) – Posterior Pituitary Hormones
Free Biochemistry lectures for Medical students by Biochemistry Club
Its main action is to prevent diuresis.
- The ADH acts on the distal convoluted tubules of the kidney, producing reabsorption of water, which results in decreased urinary output.
- K+ is excreted.
- The ADH binds to membrane receptors and activates Adenylate cyclase.
- This results in production of cyclic AMP which will activate the Protein kinase.
- The Protein kinase phosphorylates proteins of the microtubules & microfilaments.
- The net effect is the reabsorption of water.
Regulation
- The regulation of ADH secretion is through the osmolality of blood.
- Decreased osmolality (hemodilution) leads to decreased ADH secretion.
- Conversely, increase in osmolality (hemoconcentration or dehydration) leads to stimulation of the secretion of ADH.
Deficiency of ADH
Diabetes insipidus
It may be
- Central or
- Nephrogenic
- It is characterized by excretion of large volumes of dilute urine.
- Hypernatremia and hypertonic contraction of extracellular fluid volume.
- Very rare condition.
Syndrome of Inappropriate Secretion of ADH (SIADH)
- Excess ADH secretion from ectopic production of ADH by malignant tumors elsewhere.
- ADH is continuously secreted.
- There are NO control mechanisms.
- Generally, there is hypotonic expansion of extracellular volume, but sometimes there is Euvolemia associated with hyponatremia.
- It has Slow onset and is mostly asymptomatic.
- Acute onset will manifest the symptomatology of water intoxication.
Water Intoxication
- Headache
- Confusion
- Anorexia
- Nausea
- Vomiting
- Hyponatremia & impaired urinary dilution
- Coma & Convulsions
All these lectures are organized and listed in detail in their proper sections. To view these lessons please visit the Hormones & Signal Transduction Section. This can be approached by directly clicking the Biochemistry II button or it can also be approached from the drop down menu in Biochemistry II tab. Once you reach the section click the curriculum tab to view the full list in the section.
Any further questions or inquiries are welcome.