Appetite Flashcards
What 3 factors cause thirst?
Body fluid osmolality
Blood volume is reduced
Blood pressure is reduced
What is the most potent stimulant of thirst?
Plasma osmolality increase is the more potent stimulus – change of 2-3% induces strong desire to drink. Decrease of 10-15% in blood volume or arterial pressure is required to produce the same response.
What are osmoreceptors and where are they found?
Sensory receptors responsible for osmoregulation. Found in the hypothalamus - Organum vasculosum of the lamina terminalis and subfornical organ.
How do osmoreceptors control ADH?
- 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 does the sensation of thirst change?
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.
What 2 findings underlie the body weight homeostasis hypothesis?
Neuman 1902 – his weight was stable for a long time despite no conscious effort to balance out intake and expenditure
Passmore 1971 – most individual adults maintain a relatively stable weight over long periods
How is body weight homeostasis maintained?
A reduction in fat mass increases food intake and reduces energy expenditure.
Adipose tissue expansion reduces food intake and increases energy expenditure.
How does dysfunction of weight homeostasis occur?
In an overfed state, increase in sympathetic nervous system activity and energy expenditure reduces hunger and food intake causing weight loss. In an underfed state, decrease in thyroid function, energy expenditure and sympathetic nervous system activity results in weight regain.
What is involved in appetite regulation?
Inputs include ghrelin, PYY, leptin and other gut hormones as well as neural input from the periphery and other brain regions which travel through vagus nerve to the brainstem. Brainstem communicates with hypothalamus which communicates with high brain centres like amygdala. Hypothalamus then coordinates and synthesises responses by increasing/decreasing energy expenditure and need for food intake.
What are the words for appetite stimulant and depressant?
Orexigenic – appetite stimulant
Anorectic – appetite suppressive
What is the role of the paraventricular nucleus?
Paraventricular nucleus lies adjacent to the third ventricle and projects neurons to the posterior pituitary. Also where ADH is stored which affects osmoregulation, appetite and stress reaction of the body.
What is the role of the lateral hypothalamus?
Lateral hypothalamus only produces orexigenic peptides.
What is the role of the ventromedial hypothalamus?
Ventromedial hypothalamus is associated with satiety and lesions in this region in rats lead to severe obesity. Debate as to extent of relation but most recent studies show that the melanocortins found in the ventromedial hypothalamus regulate feeding behaviour.
What other hypothalamic factors influence appetite?
Food intake decreases when arcuate nucleus POMC neurons activate (ACTH precursor). Other hypothalamic factors implicated in appetite regulation include endocannabinoids, AMP activated protein kinase and protein tyrosine phosphatase.
What is the arcuate nucleus and what are its roles?
Brain area involved in the regulation of food intake. Incomplete blood brain barrier, allows access to peripheral hormones. Integrates peripheral and central feeding signals. Has 2 neuronal populations: Stimulatory (Neuropeptide Y and Agouti-Related Protein) and Inhibitory (POMC neuron).
