Posterior pituitary Flashcards
What is the origin of the two parts of the pituitary?
Embryonic
Anterior pituitary - originates from the upwards invagination of the roof of the oral cavity
Posterior pituitary - made from the downward extension of the floor of the brain
What is the name of the upwards invagination of the oral cavity?
Rathke’s pouch
What is the name of the downward extension of the floor of the brain?
Infundibulum
What is Rathke’s pouch made of?
Endocrine glands
What is the Infundibulum made of?
Extension of the CNS
What is another name for the posterior pituitary?
Neurohypophysis
What two hormones are secreted by the posterior pituitary?
ADH
Oxytocin
What two nuclei make up the cells of the posterior pituitary?
Paraventricular nucleus
Supraoptic/ Suprachiasmatic nuclei
How are the hormones released from the posterior pituitary?
- ADH and oxytocin are made in the hypothalamus
- Trasport along the hypothalamic-pituitary tract to the posterior pituitary
- Released into the blood when hypothalamic neurons fire
What is the most important hormone released by the posterior pituitary?
ADH
Structural properties of ADH
Loop of 9 amino acids
Connected by disulphide bonds
What are the receptors for ADH?
V1 and V2
Both are G-protein coupled receptors
What type of receptors are V1 and V2?
G-protein coupled receptors
Where are V1 receptors found?
In the smooth muscle
Causes vasoconstriction upon activation
Where are V2 receptors found?
In nephrons
Enhances water reabsorption via translocation of aquaporins
What is the main function of ADH?
To control plasma osmolality
What is osmolality?
Concentration of a solution expressed as the total number of solute particles per kilogram
What does hyposmolality cause?
Cerebral oedema
Serious consequences in the brain since it is entrapped by skull
Increased pressure reduces the blood flow to the brain and causes ischaemia
What two mechanisms reduce osmolality if high?
Stimulate thirst - drinking water maintains healthy osmolality
Stimulate secretion of ADH
Describe how the body responds to hyperosmolality
- Osmotic sensors in the brain detect high plasma osmolality
- Send impulses to the supraoptic nucleus of the hypothalamus
- Firing of neurons releases ADH from the posterior pituitary
- Nephrons reabsorb more water by insertion of aquaporins
- This corrects plasma osmolality
Describe how the body responds to hyposmolality
- Less ADH is formed
- Less aquaporin translocation in the nephrons
- More water is lost in the urine - less resorption of water
What does diabetes insipidus mean in Greek?
Much tasteless urine - blood glucose is not high
What causes diabetes insipidus?
Low ADH secretion - damaged posterior pituitary due to injury/ operation/ tumour
Impaired ADH receptor function - nephrogenic diabetes insipidus
What are the symptoms of diabetes insipidus?
Polyuria
Polydypsia
What is polyuria?
Urinary loss of water due to less water reabsorption
Low renal aquaporin
Increased desire to urinate
What is polydipsia?
Urinary loss of water leads to hyperosmolarity
Stimulates thirst - drink water to regulate plasma concentration
If asleep = die from hyperosmolarity since can’t drink
What nucleus in the posterior pituitary releases ADH?
Suprachiasmatic nucleus
What nucelus in the posterior pituitary releases oxytocin?
Paraventricular nucleus
Why can high levels of oxytocin mimic ADH effects?
They are structurally similar
Due to its simple structure, oxytocin can be synthesised artificially
TRUE or FALSE
True
What is a use for synthetically manufactured oxytocin?
Induce labour
When is oxytocin released?
In response to stretching of the cervix during labour
Stimulation of nipples from feeding
What does oxytocin do?
Helps with birth and milk ejection
Released in both males and females - used in social bonding
Increases trust between people, increases generosity and involved in romantic attraction and monogamous pair bonding
What is the normal range of plasma osmolality?
275 - 295 mosmol/kg
