S2: Control of Food Intake

Question 1

Define satiety

Answer 1

State of being full after eating food

Question 2

Define appetite

Answer 2

Describes the desire to satisfy the body’s need of food; often a hunger stimulated response

Question 3

Define Hunger

Answer 3

Discomfort caused by lack of food and the desire to eat – a strong craving for food

Question 4

Define Aphagia

Answer 4

The inability or refusal to swallow

Question 5

Define hyperphagia/polyphagia

Answer 5

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

Question 6

What provide cues to tell use when to start and stop eating?

Answer 6

Hunger, satiation and satiety are cues that tell us when to start and stop eating.

Question 7

What controls food intake?

Answer 7

Hypothalamic control: Balance between stimulating and inhibiting forces in the hypothalamus regulates feeding

Question 8

Reasons for differences in BMI

Answer 8

• Genes - 70%

- How much we eat and its compositions

Question 9

List the factors that influence appetite

Answer 9

External e.g. food availability, variety of food, social eating

Sensory factors: The combination of taste, smell, sight and sometimes sound a food

Emotional state: stress, anxiety, depression

Social factors: e.g. in asian culture rice is a staple

Physiological regulation: Our desire for food is driven by the evolutionary need to supply our bodies with nutrients and energy so that we can survive, propagate and pass our genes onto our offsping

Question 10

What two neurotransmitters in the hypothalamus control feeding behaviour?

Answer 10

• Orexigenic neurotransmitters: ↑appetite

* Anorexigenic neurotransmitters: ↓ appetite

Question 11

What is the role of the lateral hypothalamus (LH) in the control of food intake?

Answer 11

It is the hunger centre.

LH and VMN have the ability to restrain feeding if required

• Lesion - increase appetite , with weight gain that tends to persist

Question 12

Where is the satiety centre?

Answer 12

Ventromedial nucleus (VMN)

Question 13

What is the role of the Dorsomedial Nucleus (DMN) in the control of food intake?

Answer 13

It is the hunger centre (along with the lateral hypothalamus).

It modulates energy intake and releases NPY (neuropeptide y) into DMN which increases feeding

Question 14

List anorexigenic factors that decrease appetite

Answer 14

5-HT (5-HT2C and 5-HT1A), dopamine, GABA

Question 15

What is the dinural variation in food intake?

Answer 15

• Carbohydrates metabolised during the day
• Fats metabolised at night
• Hypothalamus responds to the switch between carbohydrate and fat metabolism

Question 16

Role of the prefrontal cortex in the executive control of food intake

Answer 16

• Integration of sensory information from inside and outside the body;
• Receive emotional and cognitive information from the limbic system
• Helps one make choices by translating all of the homeostatic and environmental information into adaptive behavioural response

Question 17

Role of the limbic system in the executive control of food intake

Answer 17

Complex system of nerves and networks in the brain; areas concerned with instinct and mood. May control emotions, pleasure (fear, anger, etc.)
- So cortico-limbic mechanisms of reward appear to be under executive control

• The satiation of feeding behaviour is associated with motor planning and execution

Question 18

List various molecules that increase appetite

Answer 18

Opioids, somatostatin, growth hormone releasing hormone

Question 19

Why does the brain have a glucostat?

Answer 19

The brain has a glucostat, it can measure the amount of glucose that is reaching it because it relies on it so heavily.

the concentration of glucose in the blood will stimulate glucoreceptors in the hypothalamus. This means we have to take glucose up.
Decreased blood glucose will up-regulate hunger while increased blood glucose will up-regulate satiety.

Question 20

Why do diabetics feel hungry despite increased glucose?

Answer 20

Diabetics feel hungry despite increased glucose. This is because blood glucose is not entering the cells, so the body isn’t sensing this.

Question 21

How does the temperature of environment affect appetite?

Answer 21

Cold environments simulate feeding while hot environments inhibit appetite. This is useful as allows to put fat on when cold.

Question 22

List afferent inputs of food intake

Answer 22

• Distension of a full stomach inhibits appetite, contraction of an empty one stimulates appetite both via afferents
• Denervation of intestine and stomach seems to have no effect on food intake, tells us there are other things going on
• Deposition of fat may control appetite, as fat tissue has ability to release leptin (more fat = more leptin)

Hormones and factors are released coincident (at same time) with a meal play a role in regulating food intake.
Fat ingestion causes CCK release and slowing of gastric emptying giving a feeling of fullness.

Question 23

How does injection of CCK in the brain reduce appetite?

Answer 23

Fat ingestion causes CCK release and slowing of gastric emptying giving a feeling of fullness.

Hence CCK (from I cells in the intestine or nerve endings) inhibit further food intake; this can be described as a satiety factor

Question 24

Describe leptin

Answer 24

Comes from white adipose tissue and can be said to be a lipostat, meaning it signals fat stores in adipose tissue, in other words the more leptin you have the more fat you have hanging around.

Leptin controls fat stores by operating a feedback mechanism between adipose tissue and brain, increased adipose tissue size = increased leptin secretion

Leptin increases the expression of anorexigenic factors.

Leptin also stimulates metabolic rate and INHIBITS neuropeptide Y, neuropeptide Y is a stimulant of feeding. So inhibiting it, causes inhibition of feeding.

Question 25

What does resistance of leptin lead to?

Answer 25

Some people may become resistant to the effects of leptin, leading to binge eating despite having enough leptin around and an adequate/growing of adipose tissue (obese).

Question 26

Why is acts to counteract leptin?

Answer 26

Ghrelin

Question 27

What acts to work with leptin?

Answer 27

Synergistic Interaction between Leptin and CCK to reduce short-term food intake in lean mice

When you put leptin and CCK together you get a synergistic effect -> the effects of both agents together are much greater than either on its own.

Question 28

Describe Ghrelin

Answer 28

Ghrelin (is an orexin)
->
Is fasting acting and stimulates food intake

• It is released by the stomach, pancreas, adrenals in response to nutritional status
• Circulating levels of ghrelin will increase before meals (preprandially) and decrease after a meal

Ghrelin increases central orexins, for example neuropeptide Y and cannabinoids.
It also suppresses the ability of leptin to stimulate anorexigenic factors.

Ghrelin secretion can also be inhibited by leptin

Question 29

What does loss of ghrelin activity usually indicate?

Answer 29

A loss of ghrelin activity often demonstrates a success of gastric bypass

Question 30

Describe Obestatin

Answer 30

• Produced by epithelial cells of the stomach
• Encoded by ghrelin gene but acts in opposing direction to ghrelin

It suppresses food intake (suppresses appetite, so decreases body weight gain)
So it antagonises ghrelin induced food intake (and growth hormone secretion)

Question 31

What stimulates leptin/ghrelin release?

Answer 31

Info is sent to the hypothalamus -> stomach feels distended -> leptin/ghrelin released etc. central molecules will then influence our food intake