Physiology of feeding and satiety Flashcards
What is energy homeostasis?
Physiological process whereby energy intake is matched to energy expenditure over time
How is energy primarily stored?
Promotes body fuel stability
What leads to obesity
Accessible, tasty calorie dense food and sedentary lifestyle. This is due to a small constant mismatch between energy intake and energy expenditure
What are some consequences of metabolic stress?
Metabolic syndrome central obesity dyslipidemia insulin resistance type 2 diabetes cardiovascular disease
At what BMI is a someone classified as overweight and then obese and morbidly obese?
Overweight = 25-29.9
Obese is 30-39.9
Morbidly obese is more than 40
What has a dramatic increase in obesity caused?
A global epidemic
Describe obesity as a general disorder
Not a single disorder, but a heterogeneous group of conditions with multiple causes
What are the major influencing factors on obesity
Genetics (fatness through susceptible genes) and environment (compare food in USA to Africa)
What are some of the consequences of obesity?
Stroke respiratory disease (sleep apnoea) Heart disease (lipids, diabetes, hypertension) Gallbladder disease Osteoarthritis Dementia NAFLD (fatty liver) Diabetes Cancer (uterus, breast, prostate, colon)
Name 3 reasons of why we need fat?
Energy storage
Prevention of starvation
Energy buffer during prolonged illness
why is obesity described as a disease of the brain?
Difficult to lose weight once gained
Increased body fat alters the brain function
Long term obesity induces brain re-programming
Your brain biews the extra weight (fat) as normal and dieting as a threat to the body’s survival
How does the CNS influence energy balance and body weight?
Behaviour - feeding and physical activity
ANS activity - regulates energy expenditure
Neuroendocrine system - secretion of hormones
Where is the site of integration
The brain
What is the area responsible for control of energy intake and body weight?
Hypothalamus
Lesioning ventromedial hypothalamus causes what?
Obesity
Lesioning lateral hypothalamus causes what?
Leanness
What 3 basic concepts underlie the control of energy intake and body weight?
Satiety signalling (sensation of fullness generated during a meal between termination of one meal and the initiation of the next)
Adiposity negative feedback signalling (state of being obese)
Food reward
What happens to the satiation signals during a meal
They increase to limit the meal size
Where is Cholecystokinin (CCK) secreted?
From enteroendocrine cells in the duodenum and jejunum
How is the volume of CCK regulated?
It is released in proportion to lipids and proteins in a meal
Where is Peptide YY (PYY3-36) secreted?
From endocrine mucosal L cells of GI tract.
How are the levels of PYY3-36 monitored?
They increase rapidly pst prandially
What is the role of PYY
To inhibit gastric motility, slow emptying and reduce food intake
What is glucagon-like peptide 1 (GLP-1)
Product of pro-glucagon gene.
Where is GLP-1 released from?
L cells in response to food ingestion
What does GLP-1 do?
Inhibits gastric emptying and reduces food intake
Where is Oxyntomodulin (OXM) released from?
Oxyntic cells of the small intestine after a meal
How does OXM act?
Acts to suppress appetite - although the mechanism is unnclear
What is OXM
A product of pro-glucagon gene
What is obestatin
Peptide produced from the gene that encodes ghrelin
Where is obestatin released from?
cells lining the stomach and the small intestin
What is the roll of obestatin?
To reduce food intake or to antagonise the actions of ghrelin (this remains unclear)
What is Ghrelin?
A hunger signal
Octanoylated peptide
Where is Ghrelin secreted?
Oxyntic cells in the stomach
What happens to ghrelin levels?
They increase before meals and decrease after meals. Levels are raised by fasting and hypoglycaemia
What do feedback loops(s) do?
Act to maintain constancy of total body energy stores
To control amount of body fat, what occurs?
status of fat stores must be communicated to the brain
What 2 hormones report fat status to the brain?
Leptin (made and released from fat cells)
Insulin *made and released from pancreatic cells
The levels of these in blood increase as more fat is stored
What is the function of insulin and leptin?
To inform the brain (hypothalamus) to alter energy balance
Eat less and increase energy burn
This malfunctions in the obese state
what are some of the roles of leptin?
Food intake / energy expenditure / fat deposition
Peripheral glucose homeostasis / insulin sensitivity
Maintenance of the immune system
Maintenance of the reproductive system
Angiogenesis
Tumourigenesis
Bone formation
What are some of the rolls of insulin
Circulates in proportion to body adiposity
Transport system for insulin to enter brain
High levels of insulin receptors in hypothalamus
Intracerebroventricular (ICV) insulin inhibits food intake and decreases body weight of rodents
Neurone specific deletion of the insulin receptor results in obesity
Peripheral actions of insulin are opposite = anabolic
Describe the food reward
Pleasure derived from eating - chocolate makes us feel good
What is a treatment for leptin resistant obese individuals
Leptin therapy
What does diet-induced obesity result in?
Leptin resistance
Why does diet-induced obesity result in leptin resistance?
Defective leptin transport into brain
Altered signal transduction following leptin binding to its receptor
Name 2 types of drugs that have previously been used for obesity?
Noradrenergics (appetite suppressors - inhibit noradrenaline uptake)
Serotonergic (appetite suppressors acting on 5-HT system)
What is the main type of drug used for obesity currently?
Orlistat (Xenical or Alli)
How does orlistat work?
Inhibits pancreatic lipase decreasing triglyceride absorption
Reduces efficiency of fat absorption in small intestine
Can cause cramping and severe diarrhoea
Need to take vitamin supplements
What type of surgery can be done for obese individuals?
Gastric by-pass
What are the benefits of fastric by-pass surgery?
produces substantial weight loss in one year that is sustainable
Induces high level of complete resolution of Type 2 diabetes
Restricts calorie intake and induces malabsorption of nutrients
