Appetite Flashcards
what is thirst controlled by?
- Body fluid osmolality – this is the most potent stimulus
- Blood volume is reduced
- Blood pressure is reduced
what hormone regulates osmolality?
- Antidiuretic hormone (ADH) or vasopressin- water reabsorption
- Acts on the kidneys to regulate the volume & osmolality of urine
- Collecting duct - Aquaporin 2 channel
- When plasma ADH is low a large volume of urine is excreted (water diuresis)
- When plasma ADH is high a small volume of urine is excreted (anti diuresis).
ADH is stored in the posterior pituitary
where are osmoreceptors located?
in hypothalamus
- Sensory receptors (osmoreceptors)
- In organum vasculosum of lamina terminalis (OVLT) and sub fornical organ (SFO)
how do osmoreceptors affect ADH release?
- Cells shrink when plasma more concentrated
- Proportion of cation channels increases – membrane depolarizes
- Send signals to the ADH producing cells to increase ADH
- Fluid retention
- Invokes drinking
how is sensation of thirst decreased?
- Thirst is decreased by drinking even before sufficient water has been absorbed by the GI tract to correct plasma osmolality
- Receptors in mouth, pharynx, oesophagus are involved
- Relief of thirst sensation via these receptors is short lived.
Thirst is only completely satisfied once plasma osmolality is decreased or blood volume or arterial pressure corrected
describe the renin-angiotensin-aldosterone system and its effects
what types of medication is used to treat high BP?
ACEi and renin inhibitors
how is bodyweight homeostasis maintain?
- The central circuit defend against reduction of body fat was revealed
- A reduction in fat mass increases food intake and reduces energy expenditure
- Adipose tissue expansion reduces food intake and increases energy expenditure
- System against rapid expansion is yet to be discovered
how is appetite regulated?
- Largely regulated in hypothalamus
- Provides link between peripheral stimulus/hormones and upper control
- Peripheral stimulus via vagus nerve to brain stem which communicates with hypothalamus
- Hypothalamus communicates with other systems such as amygdala
how does the hypothalamus regulate appetite?
- Signals can be orexigenic (stimulating) or anorexigenic (suppressing)
- Arcuate nucleus= aggregation of neurons in medial basal part, adjacent to 3rd ventricle
- Causes orexigenic and anorectic
- Paraventricular nucleus
- adjacent to 3rd ventricle
- Neurons project to posterior pituitary (ADH storage)
- Orexigenic and anorectic
- Lateral hypothalamus = orexigenic peptides
- Ventromedial hypothalamus= satiety (anorectic)
how does the arcuate nucleus control appetite and energy expenditure?
- Brain area involved in the regulation of food intake
- Incomplete blood brain barrier, allows access to peripheral hormones.
- Integrates peripheral and central feeding signals
- Two neuronal populations:
- Stimulatory (NPY/Agrp neuron)
- Inhibitory (POMC neuron)
what is the melanocortin system activated by?
products of POMC (& MSH)
- MC4R are expressed in paraventricular nucleus
what mutations affect appetite?
- No NPY or Agrp mutations associated with appetite discovered in humans.
- POMC deficiency and MC4-R mutations cause morbid obesity.
- Mutations not responsible for the prevalence of obesity - but useful to explain signaling.
what does leptin hormone do?
- Decreases appetite (inhibitory)
- Made by adipocytes in white tissue and enterocytes in small intestine
- Circulates in plasma
- Acts upon the hypothalamus decreasing appetite (intake) and increasing thermogenesis (expenditure)
- It also in development of atherosclerosis through innate immune system
- Low levels in Alzheimer’s and depression
what happens when leptin is missing?
missing in ob/ob mouse–> obesity
replacement decreases weight
- increased food intake
- energy expenditure
- fat and glucose metabolism
what are the different hormones released from the GI tract?
what are the comorbidities of obesity?
