Hunger and Thirst Flashcards
What is an injestive behavior?
eating or drinking
What is homeostasis?
Process by which substances in the body and characteristics of the body are maintained at an optimal level.
What are predictive patterns? How are they useful for homeostasis?
- The body will turn hunger “on” before we reach starvation and turn it “off” before we feel satiation because it takes time for nutrients to get to the cells
What is a system variable?
A variable that is controlled by a regulatory system
What is a set point?
Optimal value of the system variable
What is a regulatory system?
System/dispositive that aims to keep a variable near, above, or below a set point
What is a correctional mechanism?
Mechanism of a regulatory system that can control the regulated system variable
What is a negative feedback in a regulatory system?
process by which the effect of a correctional mechanism diminishes or terminates further corrective action
What type of feedback is involved in the satiety mechanism?
negative feedback mechanism
What is the satiety mechanism?
- negative feedback brain mechanism
- causes cessation of hunger or thirst
What is the satiety mechanism associated with?
- adequate supply of readily available food and water
- adequate long-term supply of fat
When is the satiety mechanism activated?
- when food and water are ingested
- before most cells in the body have access to the ingested substances
What are the two tpes of thirst?
- osmometric thirst
- volumetric thirst
What are the steps of the physiological regulatory mechanism of thirst?
1) Body loses water
2) Detectors signal loss of water
3) Drinking occurs
4) Stomach fills with water
5) Stomach sends signals to brain
6) Satiety mechanism inhibits further drinking
7) Water is absorbed: body fluid levels go back to normal
What occurs when a person ingests salt?
- the interstitial fluid becomes very salty
- cells lose water to the hypertonic interstitial solution
- cells shrink in size
What is tonicity?
relative concentration of dissolved solutes on either side of a membrane that is permeable to water, that allows you to describe the direction and amount of water flow across the membrane
What is an isotonic solution?
- similar concentration of solutes on either side of a membrane
What is the movement of water in a case where you have an isotonic solution?
- No movement of water
What is the movement of water in a hypotonic solution?
- Water enters the cell
What is a hypertonic solution?
- solute is more concentrated insed the cell than out
What is a hypertonic solution?
- solute more concentrated outside the cell than in
What is the movement of water in a hypertonic solution?
- water exits the cell, which shrinks the size of the cell
What is osmometric thirst?
- thirst caused by the shrinking of cells that dehydrate due to a hypertonic interstitial fluid
What are osmoreceptors?
neurons that detect changes in cell size and react to them
What is the reaction of osmoreceptors to changes in cell size?
- change in membrane potential
- release of neurotransmitters
What is volumetric thirst?
thirst that occurs in cases of hypovolemia
What is hypovolemia?
There is not enough blood circulating through the body
What hormone is released when there is not enough blood in the body?
renin
What signaling molecule tells the brain that there is not enough blood in the body?
angiostensin
What organ is responsible for monitoring the amount of blood in the body?
the kidneys
What is the difference between the signaling of osmometric thirst and volumetric thirst?
Osmometric thirst is linked to the firing of action potentials through neurons, whilst volumetric thirst is linked to a hormonal cascade initiated by the kidneys
What region of the brain is activated to signal volumetric thirst? What activates this region of the brain?
- activation of hypothalamic neurons near the anteroventral tip of the third ventricle
- angiotensin
What region of the brain is linked to osmometric and volumetric thirst?
The AV3V region
What are the two regions of the brain that show activation in cases of thirst?
- AV3V
- Anterior cingulate cortex
how are nutrients made accessible to the body?
- interstitial fluid
Where are situated osmoreceptors?
AV3V region of the brain
What composes the rapid feedback drinking mechanism?
- cold sensors in the mouth
- sensory fibers in the stomach
What is the effect of the rapid feedback drinking mechanism?
Reduces activity in the anterior cingulate cortex
What does the pancreas detect?
blood glucose levels
What happens when blood glucose levels are high?
pancreas releases insulin
What occurs after the pancreas releases insulin?
the liver and muscles store glucose as glycogen
What happens when blood sugar levels are low?
pancreas releases gluagon
What happens when the pancreas releases glucagon?
Liver and muscles convert glycogen back into glucose
What is glycogen broken down into?
- triglicerids
- fatty acids
What is the difference between the glucose consumption of cells outside the brain and cells inside the brain?
- cells outside the brain have a glucose transporter that is only functional in the presence of insuline, so they can only use glucose in the blood if it is in excess levels
- cells within the brain have a glucose transporter that works in the absence of insulin
When is glucagon released?
Low blood sugar levels
When is insulin released?
high blood sugar levels
What is the animal short-term soure of nutrients?
glycogen
Where is glycogen stored?
- liver
- muscle cells
What are the functions of insulin?
- facilitates entry of glucose in cells for immediate use
- facilitates conversion of glucose into glycogen for short-term storage
- facilitates the storage of fatty acids in adipose tissue for long-term storage
What are the two pancreatic hormones?
- glucagon
- insuline
What are the functions of glucagon?
- promotes conversion of liver glycogen into sugar for immediate use
- promotes conversion of adipose triglycerides into fatty acids
What is the difference between glycogen and adipose tissues?
- glycogen is for short-term storage and made of glucose
- adipose tissue is for long-term storage and made from fatty acids
What are triglycerides?
- form of fat storage in adipose cells that constitute our long-term store of nutrients
What is the composition of a triglyceride molecule?
1 glycerol + 3 fatty acids
What is the role of the anterior cingulate cortex?
The anterior cingulate cortex receives information from the cold sensors as well as the fibers in the stomach, which then determines the presence of water and creates a preventive reaction and stops thirst before water actually penetrates the cells
What induces hunger?
- ghrelin
- duodenum
What is ghrelin?
- peptide hormone
- indicates hunger
When is ghrelin released?
- a little before the body runs out of nutrients
OR - at a learned meal time
What is the duodenum?
first portion of the small intestine
What is the role of the duodenum in hunger regulation?
the presence or absence of food in the duodenum regulates the release of ghrelin from the stimach
When are the long term satiety signals released?
directly after the ingestion of food
What are the short term satiety signals sent by the stomach?
- CCK
- GLP-1
What is the impact of the injection of CCK?
People eat less at a time, but more meals
What is the impact of the injection of GLP-1?
long term weight loss and decreased appetite
Other than the regulation of satiety, what is the role of CCK?
causes the gallbladder to release enzymes in the duodenum
Other than the regulation of satiety, what is the role of GLP-1
Causes the secretion of insulin from the pancreas
Is the release of satiety signaling hormones an anticiaptory process?
Yes, digestion is a long process
How do we come to feel satiety from hunger?
- two wave process
- includes an anticipatory and a post-digestion mechanism
What is the first portion of the satiety feedback mechanism
- CCK
- GLP-1
What is the post-digestion mechanism?
- includes liver and pancreas
What is the role of the liver in the signaling of satiety?
- measures glucose and free fatty acid levels in the blood
- sends signaling through the 10th cranial nerve
What is the role of the pancreas in the signaling of satiety?
- secretes insuline
What is the role of insuline in the sentiment of satiety?
- detected by neurons in the hypothalamus that reduce the feeling of hunger
What is the long-term satiety mechanism?
homeostatic regulation of feeding
What is the homeostatic regulation of feeding?
- leptin is secreted by adipocytes
What are the effects of leptin?
- negative feedback signaling that reduces hunger
- increases the sensitivity of hypothalamic neurons to short-term satiety signals
What is congenital leptin deficiency?
the body cannot produce leptin, so it constantly thinks it is starving
When are the emergency hunger circuits activated?
when there is a specific critical need to either eat or not eat
What are the two types of emergency hunger circuits?
- glucoprivation
- lipoprivation
What causes glucoprivation?
- very low blood sugar levels
What detects glucoprivation?
- liver
- pancreas
- brainstem
What detects lipoprivation?
- Hypothalamus (lack of leptin)
- liver
What causes lipoprivation?
- dangerously low levels of fatty acids
What are the effects of hypoglycemia?
- suppresses insulin secretion
- triggers glucose production in the liver
- slows down basal metabolic rate
- intense and sustained feeling of hunger
What are the effects of lipoprivation?
same as for low blood sugar
What causes hyperglycemia?
disruption in insulin signaling that prevents the body from storing glucose as glycogen
What are the effects of hyperglycemia?
- high blood sugar
- weight loss => low leptin => extreme hunger
- dehydration (hypertonic interstitial solution
What area of the brain is associated with hunger and satiety?
Arcuate nucleus of the hypothalamus
What neurons are associated with promoting hunger?
AGRP neurons
What neurons are associated with inhibiting hunger?
POMC neurons
What neurons does leptin inhibit?
AGRP neurons
What neurons does leptin promote?
POMC neurons
What neurons does ghrelin promote?
AGRP neurons
What neurons does ghrelin inhibit?
POMC neurons
Where do AGRP and POMC neurons fire?
Paraventricular nucleus of the hypothalamus
What is the main role of the paraventricular nucleus of the hypothalamus?
signaling intense hunger due to a lack of leptin signaling
What causes the Prader-Willis syndrome?
insufficient presence of oxytocin neurons in the paraventricular nucleus of the hypothalamus, which prevents from ever feeling satiated
Why does hunger have a hedonistic aspect?
neurons in the medulla and hypothalamus release neuropeptides throughout the brain that influence dopamine neuronal activity
What is particular about obese person’s sensitivity to leptin?
- they are less sensitive, as it seems that they have a more elevated leptin set point
- reduced ability for leptin to cross the blood-brain barrier
- reduced response from hypothalamic neurons to leptin signaling
What is the observed difference in brain anatomy in obese animals?
inflammation in the hypothalamic arcuate nucleus
What is the purpose of bariatric surgery?
reduce the amount of food that can be eaten during a meal
What is the most common method of performing bariatric surgery?
severing of the jujenum
What are the effects of bariatric surgery?
reduction of hunger (alters the release of gastric hunger and satiety signals)
