Problem 7 Flashcards
Hunger & Thirst
System Variable
Characteristic/ Thing to be regulated
ex.: Thirst
Set Point
Optimal value of the system variable
ex.: not being thirsty
Detector
monitors the value of the system variabel
Correctional mechanism
restores the system variable to set point
ex.: water (eating, drinking)
Negative feedback
Process whereby the effect produced by an action serves to diminish /terminate the action
ex.: Blood sugar regulation –> insulin lowers blood glucose when levels are high ; glucagon raises blood glucose when levels are low
What are Satiety mechanisms ?
brain-based mechanisms that reduce hunger + thirst by making sure there is an adequate intake of nutrients
e.g.: water or food
Intracellular fluid
fluid portion of the cytoplasm of the cells
–> 2/3 of the body water is contained here
Intravascular fluid
extracellular fluid, found within blood vessels
--> must be closely regulated because it manages the heart
Osmometric thirst
Occurs when the solute concentration of interstitial fluid increases
--> interstitial fluid draws water out of the cell which causes the cells to shrink in volume
Solute
substances dissolved in solution
ex.: salt
Osmoreceptors
- located in lamina terminalis
- responsible for osmometric thirst
Lamina terminalis
reflects the activity/concentration of solutes
- -> contains the OVLT + SFO which are circumventricular organs - these organs are located outside the blood brain barrier
Anterior cingulate cortex
Activation of this region reflects a persons thirst
Volumetric/Hypovolemic Thirst
occurs when the volume of the blood plasma decreases
--> leads to salt appetite
Angiotensin
hormone, initiates drinking and salt appetite
--> causes kidneys to retain salt and water when there is reduced blood flow to kidneys
Correctional devices for Volumetric thirst
- Baroreceptor reflex
- Vasopressin
- RA System
Correctional device for Osmometric thirst
- Cortex
- Vasopressin
Baroreceptors
detect when the blood volume in the heart falls
=> correctional device for volumetric thirst
Subfornical organ
SFO
- low doses of angiotensin in the SFO cause drinking
- destruction of the SFO or injection of a drug that blocks angiotensin abolishes drinking
Median preoptic nucleus
Integrating system for most stimuli of osmometric and volumetric thirst
Function of the Short term reservoir
Sustains fuel need for several hours between meals
--> stores carbohydrates
- located in liver and muscle cells
- filled with glycogen
Short term reservoir
Procedure
- Food is absorbed from digestive tract
- Presence of insulin causes the conversion of glucose - glycogen
- Level of glucose falls
- Fall in level of glucose is detected by cells in pancreas + brain
- Pancreas stops secretion of insulin + starts secretion of glucagon
- Presence of glucagon causes the conversion of glycogen - glucose
Process continues for hours until reservoir is used up
–> we usually eat before its empty, if not - long term
Function of the Long term reservoir
keeps us alive when we are fasting
--> stores fat, consist of adipose tissue
Adipose tissue
located beneath skin
Triglyceride
molecules that contain glycerine + fatty acids
--> size of fat cells is determined by the amount triglycerides
Long term reservoir
Procedure
- Usage of the contents of the short term reservoir
- Fat cells start converting triglycerides into fuels which are then released into bloodstream
- Triglycerides are broken down into their constituents
- -> glycerol
- -> fatty acids
- Fatty acids are directly metabolized by all cells of the body except the brain
- Liver takes up the glycerol and converts it to glucose
- Glucose is taken into cells and brain
Cephalic Phase
Preparatory Phase of metabolism
- -> begins with sight, smell or thought of food - -> ends with food entering the digestive system
- insulin is released by pancreas in anticipation of arrival of glucose
Absorptive Phase
Digestive phase of metabolism
- -> carbohydrates - glucose - -> proteins - amino acids - -> fats = fats
Glucose
- level rises when eating
- pancreas stops secreting glucagon + begins secreting insulin so that glucose can be turned into glycogen
Ghrelin
Peptide hormone, initiates eating
- -> released from gastrointestinal system when digestive system is empty - -> binds to receptors in hypothalamus
Fasting Phase
Period where all the unstored energy from previous meal has been used
–> body withdraws energy from its reserves (Longterm reservoir) to meet immediate energy requirements
Glucodeprivation
stimulates eating
Short term satiety signals
come from immediate effects of eating a particular meal
–> long before food is fully digested
Food digestion
Procedure
- Food reaches stomach + mixed with hydrochloric acid and pepsin
- Food reaches duodenum + mixed with bile and pancreatic enzymes
- Duodenum secretes CKK due to the presence of fats/nutrients
- CKK inhibits gastric contractions/ delays gastric emptying
- -> stops stomach from giving the duodenum more food
- Signals from the CKK receptors are transmitted to the brain via the vagus nerve
Hydrochcloric acid and pepsin
Enzymes that break proteins into their constituent amino acids
Long term satiety signals
Signals arising from here alter the sensitivity of the brain to hunger or short term satiety
Leptin
- peptide hormone, increases metabolic rate
- released by fat cells (obese people have become resistant to effects of leptin)
–> suppresses eating
The role of the Brainstem in Food intake
- Brainstem contains neural circuits that can detect hunger + satiety signals
- controls some aspect of food intake
Ventromedial Hyptohalamus
involved in regulating eating
Lateral Hypothalamus
- involved in initiating eating
- secretes peptides
- -> orexin
- -> MCH
The role of Orexin in Hunger and Satiety
- projects to regions in the brain involved in metabolism, motivation
–> level is increases when hungry
PYY-Peptide
Provides rapid signal that food has been consumed
- is released proportional to amount of calories consumed
- -> satiety signal by delaying gastric emptying
- -> tells the arcuate nucleus to suppress appetite
Vasopressin
- Peptide hormone that promotes water conservation
- slows down urine production and prevents dehydration.
Renin-Angiotensin System
regulates blood pressure and fluid balance
=> correctional device/mechanism of volumetric thirst
Renin
- secreted by kidneys
- “Angiotensinogenase” –> decomposes angiotensin
- causes an increase in blood pressure, leading to restoration of perfusion pressure in the kidneys
Interstitial fluid
fluid filling the space between the cells of the body
Gluconeogenesis
conversion of proteins to glucose
Pancreas
secretes Insulin and Glucagon
a-MSH
inhibits eating
NPY Neurons
- promote eating and weight gain
- excitatory connections with orexin + MCH
- secreted by CART
