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Body fluid Homeostasis and related disorders
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hypothalamic role in body fluid homeostasis, role of vasopressin, factors affecting its release and its affects in detail and disorders related to vasopressin
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Body Fluid Homeostasis &Related Disorders
Friday, 24 September 2021 10:17 AM
Ionic composition of body fluid compartments
- Sodium concentration always higher OUTSIDE the cell
- Potassium concentration always higher INSIDE the cell
- Change in body fluid first buffered by plasma then sequentially dampened
by interstitial fluid then by intracellular fluid
- Ultimate target of body homeostasis is maintenance of a stable
intracellular environment
- Responses
○ Physiological changes
§ Brainstem, lamina terminalis and the hypothalamic-pituitary
axis
□ 3 regions of the brain
§ Vasopressin - ADH
§ Renin-angiotensin-aldosterone system
□ Regulates sodium and potassium concentration
○ Behavioral changes
§ Circumventricular organs
□ Region of the brain next to the ventricle
® Area containing cerebrospinal fluid that has
continuous exchange with the blood
® So can easily sense the change in osmolarity in
body fluids
□ Lack blood brain barrier
® Allows hormones in circulation to act on this part
of the brain
§ Renin-angiotensin system
□ Drinking / thirst
The hypothalamo-pituitary axis
- Hypothalamus contains many neuronal populations
- Vp is synthesized in the magnocellular neurons of the Paraventricular
nucleus (PVN) and supraoptic nucleus (SON)
○ Large in size neurons
○ Cell body of magnocellular neurons located in PVN and SON
- Vp transported through the long axon to the axon terminals in posterior
pituitary gland
, nucleus (PVN) and supraoptic nucleus (SON)
○ Large in size neurons
○ Cell body of magnocellular neurons located in PVN and SON
- Vp transported through the long axon to the axon terminals in posterior
pituitary gland
- Storage of Vp
○ Vp is a peptide hormone so water soluble and cannot pass
membrane
§ Should be stored in endoplasmic reticulum and packed into
vesicles
○ In posterior pituitary
○ Stored in secretory granules (Herring bodies) within the axon and
axon terminals of magnocellular neurons until mobilized for
secretion
§ Herring bodies
□ Bulky regions
- Stimuli induced Vp secretion into circulation
○ Vp released in response to stimuli detected at cell body in SON and
PVN
○ In response to a correct stimuli
§ depolarization of magnocellular neurons
§ Propagation of an AP down their axon to the axon terminal
(Herring bodies)
§ opening of calcium channels in axonal terminal
□ Trigger exocytosis of vesicles causing Vp release into
circulation
§ fenestrated capillaries absorb Vp
Factors affecting Vp release from posterior pituitary gland
1. Osmolality of body fluid
a. Osmolality controlled by modulating the amount of free water in our
body
b. Osmoreceptor - cation channel
i. Senses small changes in plasma osmolality
ii. Mechano-sensitive receptor
1) Sensitive to stretching / shrinking of cell membrane
iii. Transient receptor potential vanilloid - TRPV
1) Converts changes in plasma osmolality to electrical
signals
iv. 6 transmembrane domains
v. Between 5th and 6th transmembrane domain
1) Pore loop segment
a) Cation conducting pore
b) When activated allows cations to rush into cell
c) Depolarization occurs
d) Allows AP to fire
vi. Located in
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