Hunger and feeding

Question 1

What controls our hunger and tells us to stop eating when we have had enough?

Answer 1

Brain receptors
Liver
Stomach and intestines
Small intestine
Fatty tissue 
External cues

Question 2

3 main fates of nutrients

Answer 2

Supply energy e.g. for muscle contraction, body T, active transport, DNA replication etc.
Provide building blocks e.g. for complex molecules such as muscle proteins, cell membranes, DNA, hormones, enzymes etc
Stored for the future - glucogen in muscle and liver, triglyceride in adipose tissue
(evolutionary advantage vs obesity epidemic)

Question 3

Main dietary constituents

Answer 3

Proteins
Fats
Carbohydrates
Minerals
Vitamins
Water
-failure to meet minimum nutritional requirement threatens physical fitness and general health

Question 4

Proteins

Answer 4

Essential for growth and repair of body tissues and cells, especially muscle

Question 5

Fats

Answer 5

An energy source and valuable source of fat soluble vitamins, brain and cell wall construction

Question 6

Carbohydrates

Answer 6

Our bodies’ main source of energy essential for brain metabolism

Question 7

Minerals

Answer 7

Inorganic elements necessary to normal body processes

Question 8

Vitamins

Answer 8

Play an important part in many chemical processes in the body

Question 9

Water

Answer 9

Essential to our normal body function

60% of human body made up of water

Question 10

Essential dietary constituents

Answer 10

No single food can supply all our anabolic needs
Essential fatty acids cannot be synthesised and must be obtained from diet
Amino acids - 22 required for protein synthesis (9 can only be obtained from diet)

Question 11

Essential fatty acids exmaples

Answer 11

Linoleic acid
Linolenic acid
Arachidonic acid

Question 12

Amino acids

Answer 12

We can synthesise 11 of the amino acids from carbohydrate precursors
9 essential amino acids can only be obtained from diet

Question 13

Essential amino acids

Answer 13

Any Help in Learning These Little Molecules Proves Truly Valuable
(Arginine), histidine, isoleucine, leucine, tryptophan, lysine, methionine, phenylalanine, threonine, valine

Question 14

Daily calorific intake

Answer 14

57% carbs (4kcal/g)
30% fats (9kcal/g)
13% protein (4kcal/g)

Question 15

Liver

Answer 15

Glucose –> glycogen
Glycogen –(glucogon)–> glucosee
Liver monitors blood glucose and as it begins to drop, it converts stored glycogen into usable glucose

Question 16

Brain receptors

Answer 16

Hypothalamic cells sensitive to dropping blood glucose - ‘glucoreceptors’

Question 17

Stomach

Answer 17

Stretch receptors in wall of stomach - say when approaching being full
Chemoreceptors sensitive to small amounts of food dissolved in fluid in stomach - send signals to brain saying ‘filling up’

Question 18

Duodenum

Answer 18

Small intestine
Hormone cholecystokinin - CCK released from mucousal cell layer of duodenum
-says ‘stop eating’

Question 19

Fat cells compared to glycogen

Answer 19

1. Fat is longer term energy store
2. Slower to use (cf glycogen)
3. More energy per unit mass than glycogen

Question 20

Fat cells and leptin

Answer 20

Not just an inert store
Adipose tissue (‘brown fat’) releases leptin into bloodstream
Hypothalamic receptors detect leptin which may be message ‘plenty of fat in storage - dont eat anymore’
Unsure of its role in humans - no miracle cure for obesity yet

Question 21

Dual centres for feeding

Answer 21

Hypothalamus contains ‘on’ and ‘off’ switch for feeding
On = lateral region of hypothalamus
Off = ventromedial region of hypothalamus
Evidence from ‘lesioning’ experiments

Question 22

Dual centre hypothesis

Answer 22

Theory has fallen out of favour over last few decades - far too simplistic
Neuropeptide Y - potent stimulator of appetite - but actions are outside hypothalamus
Thus hypothalamus can’t be ‘centre’ of appetite control

Question 23

Viscious circle - insulin

Answer 23

Ventromedial lesions to hypothalamus - damage to parasympathetic system
Animal eats more and gets fatter and fatter –> thus more insulin secreted –> blood glucose falls so animal eats more –> food converted into adipose tissue rather than glucose - animal stays hungry –> animal eats more…etc.

Question 24

Average person calorie excess

Answer 24

15/day

adds up to 5475 calories per year = 1.56 pounds

Question 25

What explains loss of appetite after a meal?

Answer 25

Could be nerve signals from gut to brain
Or hormone, secreted by gut, that reaches brain via blood stream
-Ghrelin (>food intake) - peptide made by stomach cells in stomach wall
-PYY (

Question 26

Ghrelin

Answer 26

Hormone of hunger
Levels are high when one is fasting and fall after eating
When volunteers were given ghrelin, they ate more than on days when they received a placebo

Question 27

PYY(3-36)

Answer 27

Produced by cells in small and large intestines
Potent inhibitor of appetite
Selectively inhibits appetite - stimulating neurones by binding to receptors called NPY Y2.PYY
Thus hormone of satiety - makes you feel satisfied with amount you’ve eaten so you stop
Effects last for 24hr (don’t want breakfast after big meal night before)
more you eat, bigger rise in PYY
Slowly digested food (fat and high fibre foods) give bigger rise

Question 28

Obesity theory PYY

Answer 28

Reduced sensitivity to PYY?
Refined carb diet reducing rise in PYY levels after a meal?
Since PYY and ghrelin are hormones they have no side effects - synthetic forms being produced and clinically assessed