L5. Food Intake Flashcards
Energy sources of the body?
- Triglycerides (fatty acids)
- Carbohydrates (glucose and others)
- Protein (amino acids)
Glucose?
- Glucose is the principal circulating sugar in the blood a major energy source of the body
- It is the ONLY source of energy that the brain can use (ketones)
- Glucose metabolism maintains blood glucose levels at 4-6mM
- Other sugars include fructose and galactose
Storing glucose?
- Shortly after we have eaten food glucose is readily available in the blood
- Excess glucose is stored as glycogen in the body (lots of glucose molecules joined together into a giant branching molecule)
- When blood glucose levels drop, glycogen is broken down to release glucose
Free fatty acids?
- Fatty acids are the other major energy source of the body
- Slower source of ATP production than glucose
BUT - Each fatty acid molecule generates a lot more ATP
Storing free fatty acids?
- Shortly after we have eaten food, fatty acids are readily available in the blood
- Excess fatty acids are stored as triglycerides, mostly in adipose tissue (three fatty acid molecules and one glycerol molecule joined together to become a triglyceride molecule)
- Stored triglycerides are broken down into 3 free fatty acids and one glycerol molecule when in need of energy and haven’t eaten recently
Amino acids?
- 3rd energy source of the body
BUT - In a normal, well-fed state, amino acids are mostly used to make new body proteins, like muscle tissue
- Any excess will be made into fatty acids for storage in adipose tissue
- In a state of starvation, the body can break down body proteins into amino acids
- Amino acids can be used for gluconeogenesis
Absorptive vs post-absorptive states?
Absorptive = high insulin and high anabolic processes for storage of energy
Post-absorptive = low insulin so high catabolic processes for getting glucose
Pancreas?
- Key endocrine organ which controls glucose homeostasis
- Exocrine (98%): which secretes digestive enzymes and bicarbonate into the small intestine via a duct
- Endocrine (2%): secretes hormones into the blood
- Endocrine portion consists of 1-3 million Islets of Langerhans (pancreatic islets)
- Within islets:
A (alpha) cells secrete glucagon
B (beta) cells secrete insulin - 60-80% of cells within Islets are B cells
Insulin?
Insulin is a peptide hormone so it can be made and stored in vesicles within the beta cells of the pancreas
- Secreted as a prohormone
- Cleaved to form the active hormone
- Composed of two short peptide chains which are joined together; A peptide and B peptide
Insulin receptor?
- Insulin receptor is a receptor tyrosine kinase
- Autophosphorylates its own tyrosine residues
- Phosphorylates ‘insulin receptor substrates’
Insulin effects?
Insulin triggers cellular uptake of glucose:
- Insertion of glucose transporters (GLUT4) via exocytosis into the cellular membrane
- Transporters are constantly recycled back into the endosome: endocytosis
- Then reformed into vesicles, and inserted into the membrane
- This cycle continues while insulin is present
Note: Cells in the brain have a different type of glucose transporter that is not insulin sensitive
- When insulin isn’t present anymore:
- When blood glucose levels drop, insulin secretion stops, and insulin concentration drops
- Glucose transporters are no longer inserted into the membrane but they continue to be removed by endocytosis
- Glucose uptake stops
Glucagon?
Acts to increase blood glucose levels to within the homeostatic range (4-6mM)
- If blood glucose levels drop too low glucagon acts on the liver to:
1. Increase glycogenolysis (glycogen breakdown), releasing glucose
2. Increasing gluconeogenesis (synthesising new glucose)
Which will increase blood glucose concentration
Satiety signals?
Anorexigenic signal: a signal that promotes satiety (fullness) and the cessation of food intake
- These signals act in the brain to decrease our feelings in hunger
- Done by leptin
Leptin?
- Is a peptide hormone
- Secreted by fat (adipose tissue), the amount of leptin secreted is proportional to the amount of body fat
- Leptin secretion also increases after a meal
- It changes the activity of neurons in the hypothalamus resulting in reduced hunger/increased metabolic rate: anorexigenic
- Obesity is associated with leptin resistance
Hunger signals?
Orexigenic signal: a signal that stimulates hunger and food intake
- These signals act in the brain to increase our feeling of hunger
- Done by ghrelin
Ghrelin?
- Is a peptide hormone
- Secreted by endocrine cells in the oxyntic glands of stomach
- Ghrelin changes the activity of neurons in hypothalamus resulting in increased hunger: orexigenic
- Stimulates: hunger, food intake, and gastric emptying
- Suppresses fat utilisation in adipose tissue
True or false?
Orexigenic signals stimulate hunger
True
Choose the CORRECT statement
A. Leptin is secreted by fatty acids
B. The amount of leptin secreted by the body is proportional to the amount of adipose tissue
C. Leptin decreases energy expenditure
D. Leptin secretion decreases after a meal
B
Ghrelin is released by endocrine cells in the stomach BECAUSE ghrelin is a peptide hormone
A. If both statements are true, and the second causes the first
B. If both statements are true, but the second does not cause the first
C. If the first is true and the second is false
D. If the first is false and the second is true
E. Both statements are false
B
Gluconeogenesis increases in response to glucagon secretion BECAUSE glucose transporters (GLUT 4) are constantly recycled
A. If both statements are true, and the second causes the first
B. If both statements are true, but the second does not cause the first
C. If the first is true and the second is false
D. If the first is false and the second is true
E. Both statements are false
B
