1b Appetite Flashcards
What are the three things which stimulate thirst?
- Body fluid osmolality
- Blood Volume lowers
- Blood Pressure lowers
Which of the three stimuli for thirst is the most potent?
An INCREASE in plasma osmolality
Which hormone is the main regulator for osmolality?
ADH or Vasopressin
Where does ADH act?
Via the aqua porin 2 channel in the kidneys - renal collecting duct
When ADH is low, what volume of water is lost and what is this called?
Large volumes of urine is lost - diuresis
When ADH is high, what volume of water is lost and what is this called?
Small volume - anti-diuresis
Where is ADH stored
posterior pituitary gland
ADH is secreted through neurons in what region of the brain?
Hypothalamus
What regions are the sensory osmoreceptors found in the hypothalamus?
Organum vasculosum of the lamina terminalis (OVLT)
Subfornical Organ (SFO)
- Describe the process that leads to production of AVP and its subsequent function.
- When plasma is more concentrated, water moves out the osmoreceptors, causing them to SHRINK
- This means the PROPORTION OF CATION channels in the membrane increases
- This causes the membrane to depolarise
- Send signals to the ADH producing cells to increase ADH → Fluid retention, Invokes drinking
When is thirst completely satisfied?
Thirst is only completely satisfied once plasma osmolality is decreased or blood volume or arterial pressure corrected.
Which receptors are involved in the sensation of thirst?
Receptors in mouth, pharynx, oesophagus are involved - relief of thirst via these is short lived
What can excess excretion of water by kidneys lead to?
Waste of energy and can interfere with nutrient absorption which has a strong sodium dependence and is sodium driven
How does the renin-angiotensin system REACT to a decrease in blood pressure?
- Juxtaglomerular cells of renal afferent arteriole, once the decreased blood pressure here is detected, will release renin
- cleaves angiotensinogen in the liver to release angiotensin I
- Angiotensin I is converted into Angiotensin II in the lungs
- Angiotenin II Binds to receptors on the intraglomerular messenger cells
- This binding causes these cells to contract along with the blood vessels surrounding them, which then leads to release of aldosterone in the zona glomerulosa of the adrenal cortex
This increases blood pressure
What are the three functions of angiotensin II?
Induces thirst - ADH secretion as well
Vasoconstriction, increase in sympathetic activity
Increase in enzyme activity of those involved in aldosterone release
How does aldosterone work in terms of water retention?
H20 retention via Na+Cl- absorption and K+ excretion
What 2 types of drugs that affect the RAAS are known to treat high blood pressure?
ACEi
Direct Renin Inhibitors
A reduction in body fat…
increases food intake and reduces energy expenditure
An expansion of adipose tissue…
reduces food intake and increases energy expenditure
In which state is there activation of the sympathetic nervous system?
Overfed state - adaptive physiological response used to stimulate thermogenesis and stabilise body weight during periods of over eating
How does reduced adipose tissue lead to weight regain?
Increased hunger and food intake
Decreased energy expenditure
Decreased sympathetic nervous system activity
Decreased thyroid function
How does increased adipose tissue lead to weight loss?
Decreased hunger and food intake
Increased energy expenditure
Increased sympathetic nervous system activity
Leads to weight loss
What is the significant hormone involved in the central circuit defense against reduction of body fat?
Leptin
Where does the most important regulation of appetite occur?
Hypothalamus
What are the two main gut hormones involved in the regulation of appetite?
GHRELIN, PYY & other gut hormones
Which nerve do signals from Ghrelin and PYY travel to the brainstem via?
Vagus nerve
Other than the gut hormones through vagus nerve, how else does the hypothalamus receive input about appetite regulation?
Neural input from the periphery and other brain regions
Leptin
What is the part of the hyopthalamus which is an aggregation of neurones in the medial basal part and it is the most important site in hypothalamic integration of energy balance called?
Arcuate nucleus