Posterior Pituitary Flashcards
What does the posterior piruitary originate from?
Neuro tissue - large numbers of glial-type cells
What are 2 hormones that the posterior pituitary secretes?
Vasopressin (ADH, primarily from supraoptic nuclei)
Oxytocin (expression of milk from glands of breasts to nipples, promotes onset of labour. Primarily paraventricular nuclei)
What happens when you have a water deficit?
The plasma osmolality increases (less water so increased conc of solutes)
Therefore, cellular hydration decreases (water moves into plasma)
You become thirsty and vasopressin is released
Renal water excretion decreases due to vasopressin and you drink water
Total body water increases
Mechanism of vasopressin
1) ADH binds to membrane receptor of collecting duct cell
2) Receptor activate cAMP second messenger system
3) Cell inserts AQP2 water pores into apical membrane (collecting tubule lumen side)
4) Water is absorbed by osmosis into the blood
What type of cells are responsible for regulating ADH release?
Osmoreceptors and baroreceptors
What is ANP?
Atrial-natriuretic peptide
In the kidney, ANP _____ diuresis and natriureis
stimulates
True or false - ANP causes vasodilation of the afferent arteriole and contraction of the efferent arteriole so increases GFR.
True
ANP is made and secreted in the cardiac ___ cells in the walls of the ___ in the heart which contain volume receptors.
muscle
atria
What is osmolality
Concentration of particles per kilogram of fluid.
(Size of particle doesn’t matter just number of particles)
T or F - drinking rapidly suppresses vasopressin release and thirst
True
T or F - in pregnancy osmotic threshold for VP release and thirst is increased
False
It is decreased
T or F - plasma VP concentration increase with age
True
Diabetes insipidus
Syndrome of inappropriate antidiuretic hormone secretion - SIADH
What does polyuria mean?
Large volume of urine
What does polydypsia mean?
Large volume of drinking
What happens in Diabetes insipidus?
Patient is drinking loads (polydypsia) but also has large volume of water (polyuria) without any glucose and potassium present.
The urine is too dilute for the osmolality of the water. Not reabsorbing enough water.
Inability to concentrate urine.
Hyponatraemia
Plasma hypo-osmolality
Urine osmolality
The 2 types of Diabetes Insipidus
Cranial DI - lack of ADH (therefore low levels in plasma)
Nephrogenic DI - resistance to ADH (therefore higher levels in plasma)
Causes of Cranial DI (lack of ADH)
Destruction of hypothalamus
Interruption of connection between hypothalamus and pituitary
eg tumours, trauma, infections, granuloma (small area of inflammation)
Causes of Nephrogenic Diabetes insipidus (resistance to ADH)
Osmotic diuresis (diabetes mellitus)
drugs
Chronic renal failure
Metabolic
How can a water deprivation test differentiate cranial DI to nephrogenic DI?
When desmopressin is give:
CDI - plasma osmolality starts decreasing. Urine osmolality starts increasing.
NDI - plasma osmolality keeps increasing
Urine osmolality remains low
Management of Cranial DI
desmopressin
(for nephrogenic DI needed very high dose desmopressin)
