Physiological mechanisms Flashcards
Preoptic area (POA)
the region of the hypothalamus involved in temperature (only mammals and birds can regulate their body temperature)
Endotherms
animals that can regulate their body temperature through internal mechanism
Ectotherms (also called cold blooded animals)
animals that have no internal mechanism to regulate their body temperature
- therefore they do it by external means.
(ex: lizards warm their bodies by basking in the sun)
negative feedback
a mechanism by which a stimulus input causes a system to react by causing an opposite output to maintain a desired set point
- thermoregulation is achieved through negative feedback
Thermoregulation and negative feedback
two negative feedback loops.
- body temperature rises, stimulus is heat, then it is picked up by temperature sensitive receptors in the skin and brain, then an afferent pathway goes towards the control center, preoptic area of the hypothalamus, to affect our organs it could be sweat glands, the stimulus input
Cold defense
- output from the hypothalamus in response to potentially threatening cooling of the body
- decrease heat loss
- include the constriction of blood vessels of the skin
- results in increasing blood circulation to the core of the body preventing it from losing too much heat
Heat defense?
output from the hypothalamus in response to potentially threatening heating of the body
- increase heat loss
another way the body loses heat is by evaporative cooling, which you may know as sweating
Shivering ?
shaking of skeletal muscles that generate heat through the expenditure of energy
–> reaction automatically triggered by the hypothalamus are combined with behavioural responses such as putting a warm sweater or generating heat by moving around
Thermoregulatory circuits in the nervous system
- body temperature is detected by thermoreceptors deep in the body
& - temperature of the immediate surrounding is detected by thermoreceptors near surface of skin
Spino Thalamo Cotrical pathway (STC)
- the pathway through which body temperature is conveyed to the somatosensory cortex via the thalamus for the perception of temperature
- if you touch a hot plate and say ouch thats because you are perceiving that the object is hot, this is called the spina thalamo cortical pathway
Lateral parabrachial nucleus (LBN_
This is a pathway that runs from the lateral parabrachial nuclus - the region of the brainstem to the preoptic area of the thalamus involved in temperature regulation
LBN-POA pathway?
The pathway through which body temperature is conveyed to the LPB and POA for temperature regulation
- this pathway leads to the regulation of body temperature by producing heat defense and cold defense behaviours
Preoptic Area
was the major thermoregulatory structure in the brain in the hypothalamus
thermoregulation
thermoreceptors under skin –> process starts in the spinal cord then goes to the LBN and then gets to POA.
Energy homeostasis
- the brain consumes 20% of the body’s energy
- neurons consume twice the amount of energy as other cells in the body
two-thirds of the energy used by neurons is for neurotransmission - the process that maintains cellular metabolism depends on continuous supply of calories and oxygen
food energy comes from macronutrients: carbohydrates, fats, and proteins
Two states of energy homeostasis
Prandial state and Post-absorptive state
Prandial state
a state in which energy stores are replenished as nutrients are absorbed in the bloodstream and stored
Post-absorptive state
a state in which nutrients are no longer entering the bloodstream and when the body relies on the the release of stored energy from the lover as glucose and from fat cells and fatty acids and ketones
what are energy is used for your muscles ?
- glucose used by cells and neurons
- fatty acids and ketones used by all cells for energy
hormones
substances that can have effects on cells distant from the cells that released them
- hormones are chemical messengers
- some of them involved in satiety
hunger ?
the drive generated when energy stores are not sufficient to sustain energy balance
Satiety
refers to the state of being fed or to the feeling of satisfaction that follows a meal
arcuate nucleus
a region of the hypothalamus involved in the regulation of food intake
nucleus of the solitary tract (NST)
a bundle of nerve fibers that caries excitatory messages from the stomach to the hypothalamus
neuropeptides
- molecules that can act as neurotransmitters or hormones
hunger and Satiety depend on ?
they depend on the actions of hormones released from the gut, adipose cells (fat cells) and the hypothalamus
Hunger or what makes you start eating ? GHERLIN
Gherlin is a hormone found mainly in the stomach. It is orexigenic meaning that it is an agent such as a drug or hormone that stimulates appetite
Gherlin
- binds to receptors on neurons that contain two peptide neurotransmitters
(Neuropeptide Y, and Agouti-gene-related peptide - AgRP) - binding to these released into another regions of the hypothalamus called the paraventricular nucleus - PVN
- this also bings to receptors on the vagus nerve, which carries excitatory messages to the hypothalamus through the nucleus of the solitary tract of the brainstem
Leptin (satiety or what makes you stop eating)
- produced and released from the stomach adipose tissue (fat cells)
- receptors for leptin are found on the same cells of the accurate nucleus to which Gherlin binds, that is cells containing NPY and AgRP
- it suppresses hunger by having excitatory effects on neurons containing neuropeptides
- stimulates norcartic hormones
- secreted in response to high level son insulin and glucose
- maintaining weight
- levels increase with body mass and with the size of fat cells
Insulin
- anorexigenic
- released by cells of the pancreas
- the release of insulin is directly related to glucose levels
- it is secreted shortly after meals
- like leptin, it inhibits AgRP and NPY neurons in the arcuate nucleus and has excitatory effect on POMC and cART neurons
Cholecytokinnin (cck)
- released from the small intestine when the stomach is full
- CCK binds to receptors on the vagus nerve, which carries inhibitory messages to the hypothalamus through the NST, to suppress appetite
Peptide Tyrosine (PPY)
- released from the large intestine
- released in the circulation after meals and is reduced during fasting
- it suppresses appetite by inhibiting AgRP and NPY neurons in the arcuate nucleus but has no effect on POMC and cART neurons
Regulation of eating
- not all eating fulfills a homeostatic need
- eating is also driven by the rewarding properties of food
Incentive - Salience theory and eating
- environmental cues associated with the memory of certain food can induce a feeling of “wanting” that food
- eating the food will make you feel sated
- wanting and liking are dependent on two distinct systems
- wanting : the mesolimbic dopamine system
- liked reactions are associated with the release of endorphins in hedonic hotspots within the nucleus accumbens, ventral pallidum, parabrachial nucleus, obrifrontal cortex, insular cortex and amygdala
