Feeding and Satiety

Question 1

what is energy homeostasis

Answer 1

physiological process whereby energy intake is matched to energy expenditure over time via feedback loop - promoting body fuel stability (energy stored as fat)

Question 2

what is obesity in terms of BMI

Answer 2

small constant mismatch between energy intake and energy expenditure;
>30 - obese
>40 - morbidly obese

Question 3

factors influencing obesity

Answer 3

genetics - susceptibility genes, increasing the risk of developing disease
environmental

Question 4

consequences of obesity

Answer 4

stroke (hypertension)
respiratory disease - sleep apnea
heart disease
gallbladder disease
osteoarthritis 
dementia - alzheimer's
NAFLD 
diabetes
cancer

Question 5

obesity’s affect on the brain

Answer 5

alters brain function/brain re-programming - brain views extra weight as normal and dieting as a threat to body survival

Question 6

how does the CNS influence energy body balance and body weight

Answer 6

behaviour - feeding and physical activity
ANS activity - regulates energy expenditure
neuroendocrine system - secretion of hormones

Question 7

control centre of the brain for feeding behaviour

Answer 7

hypothalamus;
lesioning ventromedial hypothalamus - obesity
lesioning lateral hypothalamus - leanness

Question 8

concepts underlying the hypothalamus

Answer 8

satiety signalling - feeling full
adiposity negative feedback signalling - state of being obese
food reward

Question 9

what are satiation signals

Answer 9

short term processes regulating meal initiation, termination and inter-meal frequency (increase to limit meal size)

Question 10

different types of satitation signals

Answer 10

cholecystokinin (CCK)
peptide YY
glucagon-like peptide
oxyntomodulin (OXM)
obestatin

Question 11

describe cholecystokinin

Answer 11

secreted from enteroendocrine cells in duodenum and jejunum
Released in proportion to lipids and proteins in meal
Signals via sensory nerves to hindbrain and stimulates hindbrain directly (nucleus of solitary tract (NTS)

Question 12

describe peptide YY

Answer 12

secreted from endocrine mucosal L-cells of G-I tract
Levels increase rapidly post-prandially
Inhibits gastric motility, slows emptying and reduces food intake (Hypo)

Question 13

describe glucagon-like peptide (GLP-1)

Answer 13

product of pro-glucagon gene.
released from L cells in response to food ingestion
Inhibits gastric emptying and reduces food intake (Hypo, NTS)

Question 14

describe oxyntomodulin

Answer 14

from pro-glucagon gene and released from oxyntic cells and L-cells of small intestine after meal.
Acts to suppress appetite – mechanism and site unclear.

Question 15

describe obestatin

Answer 15

peptide produced from gene that encodes ghrelin and released from cells lining stomach/small intestine.
Suggested to reduce food intake – may act to antagonise the actions of ghrelin – actions unclear at present.

Question 16

what is ghrelin

Answer 16

a hunger signal
octanoylated peptide produced and secreted by oxyntic cells in stomach
there are ghrelin-containing neurones in the hypothalamus

Question 17

ghrelin function

Answer 17

levels increases before meals and decreases after meals

levels are raised by fasting and hypoglycaemia

Question 18

ghrelin in the hypothalamus

Answer 18

control fat metabolism
increase lipogenesis
decreases lipid oxidation (liver and adipose)

Question 19

peripheral ghrelin

Answer 19

stimulates food intake;

decreasing energy expenditure and fat utilisation –> increasing body weight

Question 20

central appetite controllers

Answer 20

glutamate, gaba and opiods

monoamines

Question 21

function of flutamate, gaba and opiods

Answer 21

increase food intake when injected into hypothalamic centres - effects modest/short lasting

Question 22

function of monamines

Answer 22

suppress food intake - many drugs developed to act on these system (many are withdrawn)

Question 23

hormones reporting fat stores to the brain

Answer 23

adiposity signals - levels will increase in blood as more fat is stored;
leptin (from fat cells)
insulin (pancreatic beta-cells)

Question 24

function of the hormones reporting fat stores to the brian

Answer 24

inform the hypothalamus to alter energy balance - eat less and increase energy burn
this malfunctions in obese state

Question 25

mutation in leptin gene

Answer 25

a reduced leptin will mimic starvation, causing an unrestrained appetite and obesity

Question 26

biological roles of leptin

Answer 26

food intake.energy expenditure/fat disposition
peripheral glucose homeostasis/insulin sensitivity
maintaince of immune system
maintenance of reproductive system
angiogenesis
tumourigenesis
bone formation

Question 27

describe the food reward effect on the brain

Answer 27

dopamine pathway activated in foods strongly linked to sugar and fat

Question 28

describe leptin therapy in obesity

Answer 28

limited by severe leptin resistance present in most obese individuals

Question 29

how does diet-induced obesity result in leptin resistance

Answer 29

defective leptin transport into brain

altered signal transduction following leptin binding to its receptor

Question 30

describe adaptive thermogenesis

Answer 30

Thermogenic adipocytes – increase energy expenditure uncoupling of oxidative metabolism from ATP production