Control of food intake

Question 1

What is the stomach volume when fasting and during food accommodation?

Answer 1

Fasting: 50ml

During food accommodation: 1.5L

Question 2

Define hunger.

Answer 2

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.

Question 3

Define appetite.

Answer 3

The physiological desire/drive to satisfy the body’s need for food; hunger a stimulated response.

Question 4

Define satiety.

Answer 4

state of being full after eating food (joyous moments – no longer need to continue eating).

Question 5

Define aphagia.

Answer 5

The inability or refusal to swallow.

Question 6

Define Hyperphagia/polyphagia.

Answer 6

An abnormal desire for food (extreme unsatisfied drive to eat).

Question 7

What happens during accommodation of food?

Answer 7

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.

Question 8

What are the 3 types of relaxation of the gastric reservoir?

Answer 8

• Receptive
• Adaptive
• Feedback

Question 9

What is receptive relaxation?

Answer 9

Vagovagal reflex that is stimulated by chewing and swallowing, causing relaxation of smooth muscle of stomach.
Mechanoreceptors are involved.

Question 10

What is adaptive relaxation?

Answer 10

Stomach stretches when food enters, causing an increase in intragastric pressure, causing relaxation of gastric reservoir through NANC inhibition.
Mechano and/or chemoreceptors involved

Question 11

What is feedback relaxation?

Answer 11

Presence of nutrients, particularly lipids in the small intestine, and CCK trigger relaxation of the gastric reservoir.

Question 12

What are receptive, adaptive and feedback relaxation mediated by?

Answer 12

NANC inhibition as well as reflex chains involving release of Noradrenaline (NA) from sympathetic fibres.

Question 13

What is the role of NANC inhibitors in relaxation of gastric reservoir?

Answer 13

In order for relaxation of gastric reservoir, inhibitory vagal pathways innervate inhibitory enteric pathways that release NO, VIP, PACAP and/or ATP.

Question 14

What mediates contraction of the stomach?

Answer 14

Excitatory vagal pathways which innervate excitatory enteric pathways that release acetylecholine (Ach).

Question 15

What is the control centre for appetite, food intake, hunger and thirst?

Answer 15

Hypothalmus

Question 16

How does the hypothalamus control appetite, food intake, hunger and thirst?

Answer 16

The base of the hypothalamus contains several nuclei that regulate energy homeostasis (energy inflow and energy expenditure).

Question 17

What is are the roles of Orexigenic and Anorexigenic Neurotransmitters in Hypothalamus?

Answer 17

Orexigenic Neurotransmitters increase appetite

Anorexigenic Neurotransmitters decrease appetite

Question 18

What is the role of the Pre-frontal cortex in controlling food intake?

Answer 18

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).

Question 19

What is the role of the limbic system in controlling food intake?

Answer 19

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.

Question 20

What is the role of lateral hypothalamus?

Answer 20

Hunger/thirst centre

Question 21

What is the role of the ventromedial nucleus (VMN)

Answer 21

Satiety centre

Question 22

What is the role of the Dorsomedial Nucleus (DMN).

Answer 22

Hunger centre (release of NPY into DMN increases feeding).

Question 23

What is the role of the Paraventricular Nucleus (PVN).

Answer 23

Modulates feeding behaviour.

Release of NPY, opioids, GABA into PVN increasing feeding.

Release of leptin into PVN decreases feeding.

Question 24

What is the role of the arcuate nucleus?

Answer 24

Modulates feeding behaviour

Release of orexigenic signals into arcuate nucleus (NPY, opioids, dynorphin, β-endorphin, POMC, galanin, amino acids, GABA and glutamate) increase feeding.

Question 25

What is the role of Suprachiasmatic Nucleus (SCN)?

Answer 25

Controls circadian rhythms, which could affect mood/drive to eat Located on either side of hypothalamus, directly above optic chiasm.

Question 26

What is the role of Medial-Amygdaloid Nucleus?

Answer 26

Regulates appetite and food intake as 5HT binds to receptors (5-HT2C and 5HT1A) decreasing appetite.

Question 27

Describe The Appetite Suppressing Pathway.

Answer 27

- 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.

Question 28

What are the Anorexigenic factors that suppress appetite?

Answer 28

5HT (by binding to 5HT2C and 5HT1A) Dopamine GABA Insulin

Question 29

Describe the Appetite Stimulating Pathway.

Answer 29

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.

Question 30

What are the Orexigenic factors stimulating appetite?

Answer 30

Opioids

Question 31

What does the stimulation of VMN cause(satiety centre)?

Answer 31

Aphagia

Question 32

What do the lesions of VMN cause?

Answer 32

Hyperphagia

Question 33

What do Lesions of Lateral Hypothalamus cause?

Answer 33

Aphagia

Question 34

What us the role of Zimelidine?

Answer 34

inhibits reuptake of 5HT from synaptic cleft, causing for suppression of appetite.

Question 35

When are carbohydrates and fats metabolised?

Answer 35

Carbohydrates - During the day | Fat - all night

Question 36

Give 4 different signals that affect apetite.

Answer 36

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

Question 37

What is the role of gut hormones?

Answer 37

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

Question 38

What is the role of pancreatic hormones (isulin, glucagon and amylin)

Answer 38

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.

Question 39

What is the Area postrema (AP)?

Answer 39

A medullary structure in the brain that controls vomiting

Question 40

What is leptin?

Answer 40

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

Question 41

What is ghrelin?

Answer 41

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.

Question 42

What is obestsatin?

Answer 42

Hormone produced by epithelial cells of the stomach which suppresses appetite and reduces body weight gain.