Alimentary System 12 - Appetite Regulation Flashcards
When does an individual percieve thirst?
- When blood fluid osmolarity is increased (most potent)
- When blood volume is reduced
- When blood pressure is reduced
Compare the change in plasma osmolarity required to cause a strong desire to drink to the change in blood volume or arterial pressure required
- Plasma osmolarity requires change of 2-3%
- Blood volume or arterial pressure need to decrease by 10-15%
Where are osmoreceptors found?
In the hypothalamus, organum vasculosum laminae terminalis and the subfornical organ
How do osmoreceptors respond to changes in osmolarity?
- Shrink or swell in response to plasma changes
- Stimulate alteration of ADH release and regulate thirst
How does thirst cessation occur?
- Thirst is decreased by drinking even before the water has been absorbed to correct plasma osmolarity
- Receptors in the mouth, pharynx and oesophagus are involved
- Relief of thirst via these receptors is short lived, thirst is satisfied once plasma osmolarity is decreased or blood volume or arterial pressure corrected
List the hormones involved in body weight homeostasis
- Ghrelin, PYY and other gut hormones
- Leptin
- Neural input
List the functions of the arcuate nucleus, and describe how its structure allows it to perform its function
- Involved in regulation of food intake
- Incomplete blood brain barrier to access peripheral hormones
- Contains stimulatory (NPY/Agrp) and inhibitory (POMC) neurones
- Communicate with the whole brain and paraventricular nucleus
Describe how POMC regulates food intake
- POMC is converted to a-MSH which has a postitive effect on melanocortin 4 receptor in the hypothalamus.
- Stimulated to suppress food intake
Describe how Agrp regulates food intake in humans
Agrp acts as an antagonist of the melanocortin 4 receptor, which makes you feel hungry
List the human CNS mutations affecting appetite
- No NPY or Agrp mutations discovered in himans
- POMC deficiency and MC4-R mutations cause morbid obesity
What other brain regions, than the arcuate nucleus affect hunger?
- Higher centres
- Amygdala (emotion and memory)
- Other parts of the hypothalamus like the lateral hypothalamus
- Vagus nerve to brain stem to hypothalamus
Describe the process of the adipostatic mechanism
- Circulating hormone produced by fat, such as leptin made in white adipose tissue
- Hypothalamus senses the concentration of hormone
- Hypothalamus alters neuropeptides to increase or decrease food intake
What was missing in the ob/ob mouse?
Leptin, therefore he felt like he was starving and kept eating
List the functions of leptin
- Low when low body fat
- High when high body fat
- Replacement when there is a mutation decreases weight
- Hormone that decreases food intake and increases thermogenesis
- Long term regulator
How does the leptin regulatory loop lead to obesity in most people?
- They become desensitised to high levels of leptin, or already have leptin resistance - which came first?
- Some cases of leptin deficiency
