when does an individual perceive thirst?
- Body fluid osmolality is increased.
- Blood volume is reduced.
- Blood pressure is reduced
what is the most potent signal?
Plasma osmolality increased is the more potent stimulus
how does ADH act?
Acts on the kidneys to regulate the volume and osmolality of urine
- when ADH is low a large amount of urine is made
- when ADH is high a small amount of urine is made
where are osmoreceptors and ADH released from?
- Found in the hypothalamus, OVLT, and SFO
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what do osmoreceptors do?
- Sense changes in body fluid osmolality
- Cells shrink or swell in response
- ## Send signals to the ADH producing cells in the hypothalamus to alter ADH release.
what does increased plasma osmolarity result in?
- Invokes drinking and ADH release
- Increased ADH stimulates kidney to conserve water.
what does decreased plasma osmolarity result in?
- Thirst is suppressed and ADH release decreased
- Absence of ADH the kidney excretes more water.
what is the sensation of thirst?
- Receptors in mouth, pharynx, oesophagus seem to be involved.
- Relief of thirst sensation via these receptors is short lived
how is thirst satisfied?
once plasma osmolality is decreased or blood volume or arterial pressure corrected.
how is angiotensin ii involved in sensation of thirst?
- Evokes the sensation of thirst
- angiotensin ii is increased when blood volume and pressure are reduced.
- Activates SFO neurons
- all contributes to homeostasis
what is the function of the hypothalamus in terms of body weight ?
- its part of homeostasis
- the hypothalamus decides the food intake you need and the energy expenditure
why are there so many different hormones that make you hungry or full?
- different reasons for being hungry result in different hunger
eg. being hungry for 2 hours compared to being hungry for 2 years
what is the hypothalamus made out of?
LATERAL HYPO
PARAVENTRICULAR NUCLEUS
VENTROMEDIAL HYPO
what is the arcuate nucleus?
- brain area involved in the regulation of food intake.
- Incomplete blood brain barrier, allows access to peripheral hormones
- Integrates peripheral and central feeding signals.
what are the two neural populations?
Stimulatory (NPY/Agrp neuron)
Inhibitory (POMC neuron)
how does the melanocortin system work?
- exists in the para ventricular nucleus and when stimulates decreases the food intake
- So POMC stimulates MC4R to REDUCE feeding.
- POMC is broken down to a-MSH which acts on MC4R.
what mutations might affect appetite?
- POMC deficiency and MC4R mutations cause MORBID OBESITY.
- as there is no limit on food intake
what are other signals from other brain regions?
Amygdala- emotion, memory
Vagus to brain stem to hypothalamus.
how does the adipostat mechanism work?
- Circulating hormone produced by fat
- Hypothalamus senses the concentration of hormone.
- Hypothalamus then alters neuropeptides to increase or decrease food intake.
what is leptin made by?
where does it circulate?
what does it do?
Made by adipocytes in white adipose tissue.
circulates in plasma
Acts upon the hypothalamus regulating appetite (intake) and thermogenesis (expenditure).
what are leptin levels depending on body fat?
- low for low body fat
- high when high body fat
what happens when you are obese?
people who are obese have high leptin but the leptin receptors are resistant to it
for kids with a missing leptin gene who are fat what happens?
injecting leptin can cause loss of weight
why do we feel less hungry after we have eaten a meal?
- hormones released from the gut are very important
- ghrelin and PYY
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The Oesophagus and Stomach43
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The Liver - (1)33
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The small intestine43
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The pancreas26
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The large intestine29
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ions vitamins and minerals40
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jaundice and liver failure46
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immunology and infection of the gut:24
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obesity8
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regulation of the gut :39
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appetite regulation :28
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GI cancer :23
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pain and appendicitis :13
