NEUROHYPOPHYSIS

ADH(Antidiuretic

Hormone)

General Characteristics

Synonim – Pressophysin, Ariginine vasopressin,

Synthesis - Supraoptic Nucleus of Hypothalamus, - magnocellular neurosecretory neurons, - Herring bodies (coarse granules),

Strored - Neurohypophysis

Physiologic Carrier - Neurophysin II

Polypeptide - MW 1000 - 9 amino acids

Half Life - 16-20 min - metabolized rapidly in Liver &

Kidney

Receptors - V1A, V1B & V2

Mode of Action - G protein coupled receptors (cAMP

mediated).

prepropressorophysin

Transport & Secretion

CONTROL OF SECRETION OF ADH

Osmotic stimuli Non-osmotic stimuli Osmotic inhibitor Non-osmotic inhibitor

Osmotic stimuli

Hyperosomolality

- primitive determinant - osmoreceptors -located in ant. Hypothalamus (OVLT)

- impermeable solutes - Na+, Sucrose & Mannitol, cross BBB

slowly (Na+ potent stimulators) - Hyperglycemia or Uremia less potent

Water Deficit Extracellular

Osmolarity

H2O excreted

ADH Secretion

Plasma ADH

H2O reabsorption

H2O permeablity in Distal tubules,Collecting duct

Non osmotic stimuli

Hypovolemia Pain, emotion, stress Nausea, vomiting Pulmonary disease- pneumonia, TB CNS disease- stroke, meningitis,

subdural hematoma Geriatric hyponatremic patient Cirrhosis of Liver & Nephrosis

INHIBITOR OSMOTIC INHIBITOR - increase water intake or hyposmolality

NON-OSMOTIC INHIBITOR - arterial B.P or blood volume,

- drugs – anticholinergics, atropine, ethanol, phenytoin, lithium & caffeine,

- Inhalation of CO2

Regulation of ADH Secretion

Increased ADH - Plasma

Osmolarity - Blood Volume - Blood Pressure - Nausea - HypoxiaDrugs - Morphine - Nicotine - Cyclophosphamide

Decreased ADH - Plasma

Osmolarity - Blood Volume - Blood Pressure

Drugs - Alcohol - Clonidine - Haloperidol

PHYSIOLOGICAL ACTION OF ADH

1.Antidiuretic2.Vasoconstricton3.Glycogenolysis4.Act as Neurotransmitter5.ACTH secretion

Applied

SIADH ( Syndrome of Inappropriate ADH secretion)

DI (Diabetes Insipidus)

SIADH (Syndrome of InappropriateADH secretion)

Cause - inappropriate secretion - ectopic source – Carcinoma

Characteristic Features - water retention - hypernatriurea, - hyponatremia

T/t - Demiclocycline

DI (Diabetes Insipidus)

Cause

- Central or Neurogenic DI - complete or partial failure of ADH

secretion

- Nephrogenic - complete or partial failure of response of CT

Features – polyurea, polydypsia

If thirst mechanism is absent - severe dehydration

T/t - Desmopressin

OXYTOCIN

General Characteristics

Synthesis - Paraventricular Nuclei - magnocellular neurosecretory system

Strored - Neurohypophysis

Physiologic Carrier - Neurophysin I

Polypeptide – 9 amino acids

prepro-oxyphysin

Control of secretion of oxytocin

Stimulators Inhibitors

Milk ejection reflex

Genital tract stimulation

Cholinergic neuron stimulation

Activation of sympathetic neuron

Emotional stress

Psychic factor Ethanol,

Enkephalin

Milk ejection reflexor

Milk Let-Down Reflex

Physiological action of oxytocin

1. In Mammary gland – Milk Ejection

2. In Pregnant uterus – Induction of Labour

3. In Non pregnant uterus - facilitates passage of sperms

from female genital tract to Uterine tube

4. In Blood vessel -High doses – relaxatation of

blood vessels, leads to fall in BP

5. In Male - facilitates the transport of sperms

THANK YOU