17b. Food Intake & Weight Loss Flashcards
What are energy intake and body weight thought to be regulated by?
Homeostatic mechanisms
What has challenged the theory that homeostatic mechanisms regulate energy intake and body weight?
Obesity epidemic
How do we get a feeling of satiety when food and drink are in the stomach?
Causes stomach to distend
Activates mechanoreceptors in the stomach
How do we get a feeling of satiety when food and drink are in the duodenum?
CCK is released
How do we get a feeling of satiety when food and drink are digested?
Carbs turn to glucose
Fats turn to fatty acids
Proteins turn to amino acids
The presence of these nutrients makes the liver send signals to the brain via the Vagus nerve
Which elements in the nervous system and digestion control appetite?
Hypothalamus/arcuate nucleus
Gut hormones
Neurotransmitters
How does the arcuate nucleus control appetite?
Neurons stimulate or inhibit food intake
Neurons influence energy homeostasis
How do gut hormones regulate appetite?
Act peripherally to modulate digestion and absorption of nutrients
Reach the hypothalamus from the circulation or via vagus nerve
Examples of neurotransmitters that control appetite
Neuropeptide Y Cholecystokinin (CCK) Insulin Glucagon Glucagon-like peptide 1 Bombesin Ghrelin Leptin
Which neurotransmitters increase appetite?
Neuropeptide Y
Ghrelin
What does neuropeptide Y do to appetite?
Increases it
What does cholecystokinin do to appetite?
Promotes satiety
reduces appetite
What does insulin do to appetite?
Increases satiating effect of CCK
What does glucagon do to appetite?
Glucose metabolism
Reduces appetite
What does glucagon-like peptide 1 do to appetite?
Promotes satiety
What does bombesin do to appetite?
Acts in similar way to CCK
peptide found in the brain
What does ghrelin do to appetite?
Increases with food deprivation
May trigger hunger
What does leptin do to appetite?
Promotes satiety
Stops feeding behaviour
When is CCK released?
When food is present in the duodenum
What functions does CCK have?
Bile release
Pancreatic juice release
Delays gastric emptying
Promotes satiety
What kind of meals stimulate CCK more?
Protein and fat rich foods
Where is insulin released from?
Beta cells of pancreas
When is insulin released?
In response to elevated blood glucose
What is the role of insulin?
To lower blood glucose
Control the storage and release of fatty acids in/out of adipose tissue
How does insulin lower blood glucose?
By storing it in liver and muscle tissue as glycogen
How does insulin store glucose and fat?
Activates glucose transport into the fat cells by recruiting glucose-transport protein 4 (GLUT4)
Regulating several lipase enzymes
What are the metabolic actions of insulin?
Stimulates synthesis of triglycerides from free fatty acids
Inhibits release of free fatty acids from triglycerides
Increases synthesis of liver glycogen
Inhibits gluconeogenesis
Stimulates glucose uptake in skeletal muscle
Reduces hunger
What leads to excess amounts of insulin?
Chronic excess energy intake
Sedentary lifestyle
What does increased insulin levels do to lipolysis?
Inhibits lipolysis (so fat isn't broken down from adipose tissue)
What happens to lipolysis during insulin resistance?
Lipolysis not inhibited
Leads to visceral fat deposition
What happens as visceral fat increases?
Adiponectin production decreases
What is adiponectin?
Protein hormone that increases the oxidation of fatty acids
Promotes clearance of excess fat in tissues
Improves insulin sensitivity
What implications does increased carbs have on lipolysis and weight?
Increased carbs = increased insulin production = decreased lipolysis/weight gain
Which cytokines can adipose tissue increase?
Inflammatory ones
IL-6
TNF-a
What is visceral fat a constant source of?
Excess free fatty acids
Where do excess free fatty acids go?
Blood to the liver