14 - Feeding and body weight

Question 1

4 components of energy exposure (4)

Answer 1

1. basal metabolic rate
2. thermic effect of food
3. non-exercise activity thermogenesis
4. exercise activity thermogenesis

Question 2

basal metabolic rate (2)

Answer 2

1. energy required to maintain body
2. BMR = 50-80%

Question 3

thermic effect of food (2)

Answer 3

1. heat generated in digestion, absorbing and storing nutrients from food
2. TEF = 10%

Question 4

non-exercise activity thermogenesis (2)

Answer 4

1. energy required for daily activities
2. NEAT = 15%

Question 5

exercise activity thermogenesis

Answer 5

EAT = 5%

Question 6

metabolic rates of liver, brain and heart/kidneys (3)

Answer 6

1. liver = 200 kcal/kg/day
2. brain = 240 kcal/kg/day
3. heart & kidneys = 400 kcal/kg/day

Question 7

short term energy store

Answer 7

glycogen, stored mainly in liver and muscles

Question 8

long term energy store

Answer 8

fats, in adipose tissue

Question 9

energy storage

Answer 9

= energy intake - energy expenditure

Question 10

adipose tissue (2)

Answer 10

1. fat = 25% of body weight in healthy adults
2. white adipocytes store high-energy fats (triglycerides)

Question 11

high-energy fats (2)

Answer 11

1. triglycerides
2. stored in white adipocytes in adipose tissue

Question 12

white adipocyte functions (3)

Answer 12

1. insulin sensitive - energy production/storage
2. lipid storage - triglycerides (homeostasis between lipolysis and lipogenesis)
3. secretory functions - endocrine hormones (e.g. leptin)

Question 13

how is body composition estimated?

Answer 13

dual-energy X-ray absorption (DXA) - two different energy X-ray beams to estimate 2 components of body composition

Question 14

2 components of body composition (2)

Answer 14

1. fat mass - adipose tissue, stores energy as fats
2. lean mass - everything else, including internal organs, muscle, body fluids and bond

Question 15

how is adiposity measured

Answer 15

BMI (body mass index) = weight/height (squared)

Question 16

obesity

Answer 16

excessive weight gain due to greater energy intake than energy expenditure (BMI>30)

Question 17

how much do gene variants contribute to majority of observed obesity phenotypes?

Answer 17

50-80%

Question 18

ob gene (2)

Answer 18

1. ob gene expressed in adipose tissue
2. codes for protein leptin

Question 19

leptin (3)

Answer 19

1. acts as hormone on leptin receivers in brain
2. communicates status of energy sources
3. mutation in leptin receptor (dp gene) produces similar phenotype to ob gene)

Question 20

how does the hypothalamus regulate body weight?

Answer 20

controls appetite and food-seeking behaviour

Question 21

satiety cascade

Answer 21

series of psychological, behavioural and physiological events leading from hunger to feeding to satiety

Question 22

what triggers food-seeking behaviour and initiation of feeding?

Answer 22

blood glucose levels dip a few minutes before food-seeking behaviour begins

Question 23

metabolism during feeding/fasting? (3)

Answer 23

1. rapid response after meal to take up nutrients and energy during absorptive phase
2. gradual switch to fasting phase (nutrients in food depleted)
3. glycogen acts as short term energy store and fat in adipose tissue as longer term storage

Question 24

what should feeding behaviour be sensitive to?

Answer 24

stores of glycogen and fat within adipose tissue

Question 25

signals of satiety following meal initiation (2)

Answer 25

1. insulin - short term signal 2. leptin - long term signal

Question 26

peptides released after meal to decrease appetite and feeding behaviours (4)

Answer 26

1. leptin 2. insulin 3. cholecystokinin (CCK) 4. glucagon-like peptide-1 (GLP-1)

Question 27

where is leptin secreted?

Answer 27

white adipose tissue

Question 28

where is insulin secreted?

Answer 28

B-cells in pancreas

Question 29

where is cholecystokinin (CCK) secreted?

Answer 29

cells in lining of small intestine

Question 30

where is glucagon-like peptide-1 secreted?

Answer 30

cells in lining of small and large intestines (and other organs)

Question 31

autonomic satiety signals to brain (2)

Answer 31

1. Cholecystokinin (CCK) 2. glucagon-like peptide-1

Question 32

endocrine satiety signals to brain (3)

Answer 32

1. leptin 2. insulin 3. glucagon-like peptide-1

Question 33

how are endocrine satiety signals sent to the brain?

Answer 33

bind to receptors on neurons in hypothalamus (GLP-1, leptin, insulin)

Question 34

how are autonomic satiety signals sent to the brain?

Answer 34

Act via intestinal vagal afferents to signal satiety to neurons in brain stem (vagus nerve also signals gut digestion (fullness) via stretch receptors in gut wall (GLP-1, CCK)

Question 35

neural control of feeding (3)

Answer 35

1. leptin 2. insulin 3. glucagon-like peptide-1 - act via hypothalamus

Question 36

how does neural control of feeding occur?

Answer 36

bind to receptors on neurons in arcuate nucleus (ARC) to signal satiety. these neurons signal to paraventricular nucleus (PVN) to regulate feeding behaviour

Question 37

2 key neuron types in arcuate nucleus (2)

Answer 37

1. POMC neurons (proopiomelanocortin) (protein precursor used to synthesise MSH (agonist of MC4R)) 2. NPY/AgRP neurons (neuropeptide Y/ agouti-related protein)

Question 38

role of POMC (proopiomelanocortin) neurons in arcuate nucleus

Answer 38

(activated by leptin, GLP-1 and insulin) releases melanocyte stimulating hormone (MSH) to increase satiety signal

Question 39

role of NPY (neuropeptide Y)/AgRP (agouti-related protein) neurons in arcuate nucleus

Answer 39

(activated by hormone ghrelin from the stomach) released to increase hunger signal. NPY also inhibits POMC neurons to decrease satiety signal

Question 40

MC4R+ neurons: decrease in feeding

Answer 40

if satiety signal (MSH - melanocyte stimulating hormone) > hunger signal (AgRP - agouti-related protein), signal to other brain regions to cease feeding behaviours and release further anorexigenic (appetite suppressing) hormones

Question 41

MC4R+ neurons: increase in feeding (2)

Answer 41

1. inhibited by AgRP (agouti-related protein) -> block of feeding behaviours reduced. 2. AgRP and NPY also activate other neurons in PVN to signal to other brain regions to stimulate feeding behaviours (increase release of further orexigenic (appetite stimulating) hormones

Question 42

Ghrelin

Answer 42

produced in stomach, stimulates hunger and food intake via vagal afferents to brainstem and as hormone to activate NPY/AgRP neurons in arcuate nucleus of hypothalamus