task 7 - homeostasis Flashcards
regulatory mechanisms
maintain the organisms homeostasis in the face of variability environment
4 parts of the system
system variable, set point, detector, correctional mechanism/effect
system variable
the characteristic that is regulated by the mechanism
set point
the optimal value of the system variable
detector
an entity that monitors the value of the system variable
correctional mechanism/effect
an entity that restores the system variable to the set point
negative feedback
a process whereby the effect produced by an action serves to diminish/terminate the action, regulates the regulatory system
ingestive behaviors
eating and drinking) to replenish the body’s depleted stores of water in nutrients
satiety mechanism
physiological mechanisms that reduce hunger/thirst and thus produce the motivation to stop eating/drinking. makes for adequate intake of nutrients
- delay the ingestion and replenishment of depleted stores. they are NOT detectors
osmosis
low to high concentration movement
osmometric thirst
→ motivation to drink caused by loss of water from the intracellular fluid (fluid in the cell)
→ caused by the increase of solutes (makes the cells smaller and draws liquid out the cells)
osmoreceptors
neurons whose firing rate is affected by their level of hydration. they detect change in the cell’s volume and transform those changes into membrane potentials
activation of the osmoreceptors
- activation in the anterior cingulate cortexand hypothalamus corresponding to a sensation of thirst
- activation in the lamina terminals (location of the osmoreceptors)
- the median preoptic nucleus of the lamina terminalis receives input from both OVLT and SFO. integrates info. and control drinking in the brain through connections to other brain parts
osmotic thrist: correctional devices
cortex, vasopressin
osmotic thrist: what do the correctional devices do?
- create thirst
- constrict vessels
- conserve water
osmotic thrist: system variable? set point?
osmotic pressure
0
osmotic thrist: is positive or negative feedback?
decreased osmotic pressure post the correctional devices work
negative feedback
volumetric thirst
motivation to drink caused by reduction of the volume of the blood plasma
- leads to a salt appetite because of loss of sodium from hypovolemia (causes loss of blood volume without depleting the intracellular fluid)
- the atria of the heart contains baroreceptor cells; a second set of receptors for volumetric thirst, produces volumetric thirst after a reduction in blood flow to the heart
hypovolemic thirst: correctional devices?
baroreceptor reflex
vasopressin
RA system
hypovolemic thirst: what do the correctional devices do?
- create thirst
- constrict vessels
- conserve water
- conserve salt
hypovolemic thirst: system variable? set point?
blood pressure
120/80
hypovolemic thirst: positive or negative feedback?
increased blood volume
negative feedback
angiotensin
a hormone produced at the kidneys when cells inside them detect releases in blood flow - initiates volumetric thirst which in turn causes the kidneys to conserve water and salt, and increases blood pressure
- doesn’t cross blood barrier
digestion
the gastrointestinal process of breaking down food and absorbing its constituents into the body
energy delievered?
- lipids from fat
- amino acids from proteins
- glucose from complex carbohydrates
energy stored?
- triglycerides, glycerol and 3 fatty acids (FATS)
- glycogen; complex insoluble carbohydrate
- proteins (chain of amino acids)
phases of energy metabolism
- cephalic phase
- absorptive phase
- fasting phase
cephalic phase
the preparatory phase that begins with the sight/smell/thought of food and ends when the food starts being absorbed in the bloodstream
absorptive phase
the period during which the energy absorbed into the bloodstream from the meal is meeting the bodys immediate energy needs
fasting phase
the period during which all of the non-stored energy from the previous meal has been used and the body is withdrawing energy from its reserves to meet its immediate energy requirements lasts till next cephalic phase
the flow of energy in the metabolic phase is controlled by 2 pancreatic hormones?
isulin and glucagon
insulin functions
- promotes the use of glucose as the primary source of energy. since glucose can’t pass through cell membrane it needs to be taken in the cell by glucose transporters
- promotes the conversion of bloodborne fuels (carried by the blood) to forms that can be stored
- promotes the storage of glycogen in the liver, muscle and fats in adipose tissue and proteins in muscle
set-point assumption
hunger is caused by the presence of an energy deficit, and eating is the means by which the energy resources of the body are returned to their optimal level (energy set point)
- all set-point systems are negative feedback systems
glucostatic theory
the set point is defined by a specific level of blood glucose levels
lipostatic theory
the set point is defined by a specific level of body fat
glucoprivic hunger
hunger that is provoked by glucose deprived cells
lipoprivic hunger
hunger that is provoked by lipid deprivation of cells
the brain receives signals through the vagus nerve from the liver receptors that detect lipid and glucose deprivation of cells and this causes?
cause immediate eating
cutting the vagus abolishes the two types of hunger
problems with the set-point theories?
the set point theories are inconsistent with evolutionary pressures. ancestors needed to eat large quantities when it was available
they also do not recognize major influences such as taste, learning and societal influences
positive-incentive theory
animals are not normally driven to eat by internal energy deficits but by the anticipated pleasure of eating (the anticipated pleasure of a behavior is called its positive-incentive value)
- formed from the evolutionary pressures of unexpected food shortages have shaped warm-blooded animals to take advantage of food when it is present and eat it
- the degree of hunger felt depends on the interaction of all the factors that influence the positive-incentive value of eating
blood glucose levels
the intention to start eating triggers a decline in blood glucose (the glucostatic theory)
brain stem
the area postrema and the nucleus of the solitary tract (AP/NST) located in the dorsal medulla receive taste information from the tongue and a variety of sensory information from internal organs
hypothalamus
melanin-concentrating hormone (MCH) and orexin are neuropeptides that are produced by neurons in the lateral hypothalamus
- activity of these neurons increases food intake and decreases metabolic rate
- the axons of these neurons travel to many brain structures that are involved in motivation and movement
vasopressin
- constricts blood vessels
- conserves water
serotonin and satiety
→ serotonin agonists reduce hunger and eating in some people who overeat under some conditions
→ serotonin agonists seem to increase short-term satiety signals associated with the consumption of a meal unlike the signals from leptin and insulin which produce long-term satiety signals based on fat stores
cholecystokinin (CCK)
produced in the gastrointestinal system, suppression of eating
secreted when fat or protein is detected by receptors mainly in walls of duodenum
peptide YY (PYY)
secreted proportional to amount of calories consumed, mainly in the ileum and colon
insulin
→ serves as a negative feedback signal in the regulation of body fat
- positively correlated with levels of bodyfat
- correlated with visceral fat (stored around the internal organs of the body cavity
leptin
fat releases this peptide hormone. it is believed to be a negative feedback signal normally released from fat stores to decrease appetite and increase fat metabolism
- levels of leptin are correlated with subcutaneous fat (stored under the skin)
- have an inhibitory effect on the NPY/ARGP neurons when activation of leptin on the receptors occur
more fat > higher leptin > higher satiety > less food intake > reduction of fat mass
ghrelin
a peptide hormone that is released from the gastrointestinal system when a person is in the fasting phase and the digestive system is empty, binds to receptors in the hypothalamus to help stimulate eating behavior
- reduced after a meal and increase with fasting
- blocking the signal inhibits eating
- increasing the levels can cause weight gain by increasing food intake and decreasing metabolism of fats
neurons of the arcuate nucleus
- neuropeptide Y (NPY); stimulates food intake
- agouti-related protein (AGRP); released by NPY and also acts together with it
