Hunger And Thirst Flashcards
(23 cards)
What is Osmometric & Volumetric thirst?
Volumetric thirst
▪ Caused by low extracellular fluid volume
(hypovolemia – low blood flow).
▪ Signalled by renin (hormone released by kidney).
▪ Renin causes the release of Angiotensinogen
Angiotensin I and Angiotensin II
Osmometric thirst
▪ Keep track of intracellular fluid volume. Induced
by increase in solute outside cell.
▪ Signalled by osmoreceptors (detect changes in cell size)
How do we induce thirst and satiate thirst?
▪ Neurons in the AV3V region of the hypothalamus can be sensitive to angiotensin/osmoreceptors/both
▪ Drinking hypertonic saline (inducing thirst) => activate AV3V + anterior cingulate cortex
▪ Anterior cingulate cortex + cold sensors in mouth and stomach => rapid mechanism, responsible for the conscious sensation of thirst
What is our short term reservoir of energy?
Glucose
▪ Simple sugar
▪ Fuel for cells
▪ In Blood
High glucose level
➡️ use insulin to put glucose in storage
Glycogen
▪ Polysaccharide (chains of sugar)
▪ stored in liver and muscles
▪ short term storage of energy
What happens when you have a low glucose level?
increase glucose levels by turning the Glucagonin storage back to glucose!
Does the CNS use the same glucose as the rest of the body?
CNS+ cells outside CNS can use glucose:
-Cells outside the CNS can only use glucose transporter when insulin is present (meaning when there is excess glucose)
CNS only can use glucose
-When glucose is rare (there is no insulin), glucose goes in priority to the brain
What does the body do with High glucose level?
put glucose in storage
▪ Pancreas releases insulin
▪ Insulin transforms glucose into glycogen to be stored in liver and muscles
▪ The excess glucose can be used to both cells in the CNS and outside of the CNS
What does the body do with Low glucose level?
increase glucose levels
▪ Pancreas releases glucagon
▪ Glucagon transforms glycogen
into glucose
▪ Glucose can only be used by cells in the CNS
What happens to the fat you eat?
When you eat food
▪ Fat is stored in adipose tissues in the shape of triglycerides.
▪ Fatty acids are transformed into triglycerides by insulin
What happens when When digestive system is empty (low blood glucose level)?
Pancreas releases glucagon => glucagon breaks triglycerides into fatty acids => fatty acids are used by the cells outside the CNS
Livers breaks triglycerides into glycerol => glycerol is transformed into glucose => glucose is used by cells inside the CNS
What happens when food is in the digestive system
▪ High blood glucose = release of insulin by pancreas
▪ Glucose is stored as glycogen in the livers by insulin
▪ Fatty acids are stored in adipose tissue as triglycerides
▪ Glucose is used as a source of energy by the brain + cells outside CNS
What happens when empty digestive system?
Empty digestive system
▪ Low blood glucose = release of glucagon by pancreas
▪ Glycogen is transformed into glucose by glucagon and used as a source of energy by the brain
▪ Triglycerides are broken down into glycerol and fatty acids. Glycerol are transformed into glucose which is used by the brain only. Fatty Acids are used as a source of energy for cells outside the CNS
How does the empty Empty Duodenum (tummy) cause hunger? (Chemical)
Ghrelin
What does the Duodenum(tummy) do Post-Eating?
Cholecystokinin (CCK) GLP-1 to make you feel satisfied and full.
▪ CCK and PYY are anticipatory (happens after you eat, but before food is digested)
▪ Increasing CCK does not lead to weight loss -> will reduce meal length but people compensate by eating more often
▪ GLP-1 agonist can lead to weight loss
What happens when High blood-glucose level?
• Pancreas release insulin.
• Insulin crosses the blood/brain barrier
• Neurons in the hypothalamus detects it and
inhibits hunger
What happens when High levels of glucose and fatty acids?
liver signals satiety through the 10th cranial nerve (vagus nerve)
People tend to think animals have a set weight, why?
The body weight of most people and animals is regulated over a long-term basis
▪ If an animal is force-fed, it will reduce its food intake once it is permitted to choose how much to eat to go back to a set point
▪ This indicates the presence of a long-term satiety mechanism
What does leptin do?
Decrease hunger
Increase sensitivity of hypothalamic neurons to
short term satiety signals
What happens when Leptin Deficiency?
• Cannot produce leptin => body think it’s starving
• Leads to obesity
• Treated with Leptin injection
What does Ghrelin do?
stimulates ARGP/NPY Neurons in the arcuate nucleus of the hypothalamus -> inhibit oxytocin neurons in the paraventricular nucleus of the hypothalamus -> signals hunger
What is Prader Willi Syndrome?
Loss of PVN Oxytocin neurons due to deletion of genes on chromosomes 15 => no sensation
of satiety
▪ Born without interest in eating, low muscle mass
▪ Between 2-8 years old: permanent sensation of starving to death
▪ Have no satiety signal to stop eating/throw up => eat until they rupture their stomach
• Average life expectancy = 30 yrs
What is Hypoglycaemia
Lack of sugar, excess insulin, drugs that inhibit glucose metabolism ➡️ Low Glucose Level
Hyperglycaemia
Caused by problem in insulin signalling
▪ Glucose is not taken from blood to fat cells/muscle
▪ Lead to a loss of fat -> decrease in leptin signalling -> intense
hunger (even if there is high glucose levels !)
High glucose but can’t use it!
How does obesity happen using the previously discussed concepts?
▪ Elevated levels of fat
▪ Leptin resistance
▪ Reduction in leptin’s ability to cross the blood/brain barrier
▪ Reduction in neuronal response to leptin
▪ Reduction in the downstream consequences of leptin-signalling neuron
▪ Harder to feel satiated -> need more leptin (meaning more fat cells) to be satiated
