Appetite Flashcards
What factors can control thirst?
- body fluid osmolality
- reduced blood volume
- reduced blood pressure
What is the most potent stimulus of thirst?
plasma osmolality increase more potent stimulus (change of 2 - 3%) induces strong desire to drink
Hormone that helps regulate osmolality?
ADH / vasopressin
What does ADH act on?
collecting duct aquaporin 2 channel, acts on kidneys to regulate volume and osmolality of urine
When plasma ADH is low?
large volume of urine excreted
When plasma ADH is high?
small volume of urine excreted
Where are osmoreceptors found?
in hypothalamus (organum vasculosum of lamina terminalis (OVLT) and subfornical organ (SFO))
How do osmoreceptors lead to ADH release?
- cells shrink when plasma more conc.
- higher proportion of cations so membrane depolarizes
- send signals to ADH producing cells to increase ADH
- fluid retention, invokes drinking
Describe the sensation of thirst?
- sensation decreased by drinking even before sufficient water absorbed by GI tract to correct osmolality
- receptors in mouth, pharynx and oesophagus involved
- relief of thirst sensation by these receptors is short lives
- thirst only completely satisfied once plasma osmolality decreased or blood volume or arterial pressure corrected
What cells in the renal afferent arteriole respond to a drop in blood pressure?
juxtaglomerular cells respond by releasing angiotensinogen
Where is angiotensinogen converted into angiotensin I?
in the liver
How is angiotensin I converted into angiotensin II?
using ACE in the lungs
What are some effects of angiotensin II?
- thirst
- acting on zona glomerulosa
- water retention
- ADH secretion
- vasoconstriction, increasing sympathetic activity
What stimulus does the zona glomerulosa of the adrenal cortex respond to?
high potassium, low sodium and angiotensin II
What does aldosterone and angiotensin II lead to?
water retention via Na+Cl- absorption and K+ excretion
Outline body weight homeostasis
reduction in fat mass increases food intake and reduces energy expenditure whilst adipose tissue expansion reduces food intake and increases energy expenditure.
What signals act on the hypothalamus to regulate appetite?
- Ghrelin, PYY and other hormones
- neural input from periphery and other brain regions
- leptin
What is the role of the arcuate nucleus?
brain area involved in regulation of food intake
What kind of barrier does the arcuate nucleus have?
incomplete BBB allowing access to peripheral hormones - integrates peripheral and central feeding signals
What are the 2 neuronal populations of the arcuate nucleus?
stimulatory i.e. increases feeding (NPY/Agrp neuron) or inhibitory i.e. decreases feeding (POMC neuron)
Which nucleus controls appetite and energy expenditure?
paraventricular nucleus
