Control of food intake Flashcards
What is the stomach volume when fasting and during food accommodation?
Fasting: 50ml
During food accommodation: 1.5L
Define hunger.
Discomfort caused by lack of food and the desire to eat - a strong physiological craving/drive for food/sensation of emptiness in the stomach due to the increase in ghrelin hormone.
Define appetite.
The physiological desire/drive to satisfy the body’s need for food; hunger a stimulated response.
Define satiety.
state of being full after eating food (joyous moments – no longer need to continue eating).
Define aphagia.
The inability or refusal to swallow.
Define Hyperphagia/polyphagia.
An abnormal desire for food (extreme unsatisfied drive to eat).
What happens during accommodation of food?
Inhibitory NANC neurotransmitters VIP and NO enlarge and expand the fundus area of the stomach.
PYY (Peptide YY) also released, providing a satiety feeling and also decreases gut motility.
What are the 3 types of relaxation of the gastric reservoir?
- Receptive
- Adaptive
- Feedback
What is receptive relaxation?
Vagovagal reflex that is stimulated by chewing and swallowing, causing relaxation of smooth muscle of stomach.
Mechanoreceptors are involved.
What is adaptive relaxation?
Stomach stretches when food enters, causing an increase in intragastric pressure, causing relaxation of gastric reservoir through NANC inhibition.
Mechano and/or chemoreceptors involved
What is feedback relaxation?
Presence of nutrients, particularly lipids in the small intestine, and CCK trigger relaxation of the gastric reservoir.
What are receptive, adaptive and feedback relaxation mediated by?
NANC inhibition as well as reflex chains involving release of Noradrenaline (NA) from sympathetic fibres.
What is the role of NANC inhibitors in relaxation of gastric reservoir?
In order for relaxation of gastric reservoir, inhibitory vagal pathways innervate inhibitory enteric pathways that release NO, VIP, PACAP and/or ATP.
What mediates contraction of the stomach?
Excitatory vagal pathways which innervate excitatory enteric pathways that release acetylecholine (Ach).
What is the control centre for appetite, food intake, hunger and thirst?
Hypothalmus
How does the hypothalamus control appetite, food intake, hunger and thirst?
The base of the hypothalamus contains several nuclei that regulate energy homeostasis (energy inflow and energy expenditure).
What is are the roles of Orexigenic and Anorexigenic Neurotransmitters in Hypothalamus?
Orexigenic Neurotransmitters increase appetite
Anorexigenic Neurotransmitters decrease appetite
What is the role of the Pre-frontal cortex in controlling food intake?
Pre frontal cortex involved in FOOD-SEEKING:
- integrate sensory information from inside and outside the body
- receives emotional and cognitive information from limbic system
- translates this homeostatic and environmental information into adaptive behavioural responses (e.g. eating).
What is the role of the limbic system in controlling food intake?
System of nerves and networks in areas of the brain concerned with instinct and mood, and may control emotions e.g. pleasure, fear, anger, HUNGER etc.
What is the role of lateral hypothalamus?
Hunger/thirst centre
What is the role of the ventromedial nucleus (VMN)
Satiety centre
What is the role of the Dorsomedial Nucleus (DMN).
Hunger centre (release of NPY into DMN increases feeding).
What is the role of the Paraventricular Nucleus (PVN).
Modulates feeding behaviour.
Release of NPY, opioids, GABA into PVN increasing feeding.
Release of leptin into PVN decreases feeding.
What is the role of the arcuate nucleus?
Modulates feeding behaviour
Release of orexigenic signals into arcuate nucleus (NPY, opioids, dynorphin, β-endorphin, POMC, galanin, amino acids, GABA and glutamate) increase feeding.
What is the role of Suprachiasmatic Nucleus (SCN)?
Controls circadian rhythms, which could affect mood/drive to eat
Located on either side of hypothalamus, directly above optic chiasm.
What is the role of Medial-Amygdaloid Nucleus?
Regulates appetite and food intake as 5HT binds to receptors (5-HT2C and 5HT1A) decreasing appetite.
Describe The Appetite Suppressing Pathway.
- 5HT2C agonist e.g. mcPP binds to 5HT2C receptors on POMC neurones (appetite suppressing neurones)
- POMC neurones activated and POMC precursor (pro-opiomelanocortin) is broken down into ⍺-MSH
- ⍺-MSH released by POMC neurones and bind to MC4R receptors, causing suppression of appetite.
What are the Anorexigenic factors that suppress appetite?
5HT (by binding to 5HT2C and 5HT1A)
Dopamine
GABA
Insulin
Describe the Appetite Stimulating Pathway.
Agouti Related peptide (AgRP) and Neuropeptide Y (NPY) released by AgRP/NPY neurone, which is the appetite stimulating neurone.
Appetite suppressing neurone POMC doesn’t release ⍺-MSH hormone, therefore MCR4 receptors not occupied, causing for stimulation of appetite.
What are the Orexigenic factors stimulating appetite?
Opioids
What does the stimulation of VMN cause(satiety centre)?
Aphagia
What do the lesions of VMN cause?
Hyperphagia
What do Lesions of Lateral Hypothalamus cause?
Aphagia
What us the role of Zimelidine?
inhibits reuptake of 5HT from synaptic cleft, causing for suppression of appetite.
When are carbohydrates and fats metabolised?
Carbohydrates - During the day
Fat - all night
Give 4 different signals that affect apetite.
1) Concentration of glucose in the blood will stimulate glucoreceptors in the hypothalamus.
- Decreased glucose up-regulated hunger
- Increased glucose up-regulates feeling of satiety.
2) Cold environments stimulate feeding while hot environments inhibit feeding. This is useful as allows to put fat on when cold.
3) Afferent inputs to stomach:
- Distension of full stomach inhibits appetite
- Contraction of empty stomach stimulates appetite
4) Deposition of fat (which releases leptin) may also control appetite
What is the role of gut hormones?
Released with a meal
Fat ingestion causes CCK release and slowing of gastric emptying
CCK (from I cells in the intestine or nerve endings) and somatostatin inhibit further food intake
Injection of CCK in the brain could reduce appetite
What is the role of pancreatic hormones (isulin, glucagon and amylin)
Insulin acts on insulin receptors in arcuate nucleus of hypothalamus with either net catabolic or anabolic effect, influencing homeostasis.
- Catabolic effect: insulin inhibits NPY and AgRP synthesis, causes for increased food intake and increased body fat
- Anabolic effect: insulin stimulates POMC and CART neurones, causes for decreased food intake and decreased body fat
Glucagon acts at the liver where it increases glucose production while generating a signal to reduce energy intake that is relayed to the hindbrain.
Amylin acts directly at the hindbrain to reduce energy intake.
What is the Area postrema (AP)?
A medullary structure in the brain that controls vomiting
What is leptin?
A hormone produced by white adipose (fat) cells that acts as a satiety factor in regulating appetite.
Increases expression of anorexigenic factors POMC, CART, CRH and neurotensin.
Inhibits NPY which generally stimulates feeding. Also inhibits ghrelin
Stimulates metabolic rate
What is ghrelin?
Appetite inducing hormone produced by P/D1 Cells and stimulates hunger.
Can be released by pancreas and adrenals.
Stimulates food intake:
- increases expression of orexigenic factors NPY and AgRP
- suppresses the ability of leptin to stimulate anorexigenic factors
Secretion of ghrelin can be inhibited by leptin.
What is obestsatin?
Hormone produced by epithelial cells of the stomach which suppresses appetite and reduces body weight gain.
