Homeostasis Flashcards
define homeostasis
maintaining a constant internal environment
define set point
level at which a variable is maintained in a steady state control system
define tolerance levels
upper and lower limits around the set point, if the variable exceeds or goes below tolerance levels, negative feedback occurs
define feedback system
circular situation in which the body responds to a stimulus with a response that alters the original stimulus, hence providing feedback
positive feedback
feedback system where response reinforces or intensifies original stimulus
negative feedback
feedback system where response reduces or eliminates original stimulus
steady state control system
negative feedback system that maintains homeostasis
modulator
control centre responsible for processing information received from receptors and sending information to effectors
why is positive feedback not involved in homeostasis?
when a variable exceeds or goes below tolerance level, a feedback system is required to make the variable within tolerance levels again and achieve steady state. positive feedback causes responses which reinforce or intensify the original stimulus, which will not achieve steady state
things that happen in the liver
- respiration
- glycogenesis - converting glucose into glycogen
- glycogenolysis - break down glycogen into glucose
- gluconeogenesis - converting other substrates like fats or amino acids into glucose
blood glucose levels increase above tolerance levels
stimulus: blood glucose levels increase above tolerance levels
receptors: beta cells in pancreatic islets
modulator: beta cells secrete insulin
effector: insulin
response: blood glucose levels decrease
feedback: negative feedback occurs, blood glucose levels within tolerance levels, beta cells no longer stimulated to release insulin
what does insulin do
- increases amount of glucose taken up by body cells, mainly liver and skeletal muscles
- glycogenesis
- convert glucose to fat to be stored in adipose tissue
- convert glucose into proteins (protein synthesis)
blood glucose levels decrease below tolerance levels
stimulus: blood glucose levels decrease below tolerance levels
receptors: alpha cells in pancreatic islets
modulator: alpha cells secrete glucagon
effector: glucagon causes glycogenolysis and gluconeogenesis in liver
response: blood glucose levels increase
feedback: negative feedback occurs, when blood glucose levels have reached within tolerance levels again, alpha cells are no longer stimulated to release glucagon
adrenaline and glucose
increases glycogenolysis in liver
inhibits the effects of insulin
cortisol and glucose
released by adrenal cortex, glucocorticoid, adrenocorticotropic hormone (ACTH) from ALPG
stimulates gluconeogenesis and glycogenolysis
increases rate at which amino acids are removed from cells and transported to liver
type 1 vs type 2 diabetes
juvenile onset/adult onset
beta cells produce little to no insulin/receptors on membranes of target cells less sensitive to insulin
insulin pump or injections/reduced sugar and fat
exercise regularly
define thermoregulation
balance of heat gain and heat loss to maintain a constant internal environment independent of environmental temperature
too hot
stimulus: body temperature increases above tolerance levels
receptors: peripheral thermoreceptors in skin and mucous membranes, central thermoreceptors in thermoregulatory centre of hypothalamus
modulators: electrical impulses via hypothalamus stimulating nerves through sympathetic nervous system
effector:
response: body temperature decreases
feedback: negative feedback occurs, reducing or eliminating original stimulus, body temp within tolerance levels, no more nervous stimulation
effector for too hot
- blood vessels in the skin vasodilate, increase heat loss from blood through skin via CCR
- increase sweating from sweat glands, evaporation of sweat has a cooling effect
- behavioural responses
too cold
stimulus: body temperature drops below tolerance levels
receptors: peripheral thermoreceptors in skin and mucous membranes, central thermoreceptors in thermoregulatory centre of hypothalamus
modulator: electrical impulses via nerves stimulated by hypothalamus through sympathetic nervous system
effectors:
response: body temperature increases
feedback: negative feedback occurs, reduce or eliminate original stimulus, body temp returns within tolerance levels, no more nervous stimulation from hypothalamus
effector for too cold
- vasoconstriction of blood vessels in skin, decrease heat lost from blood through skin via CCR
- shivering occurs, rhythmic muscular contractions generating heat
- adrenal medulla stimulated to release adrenaline and noradrenaline, increase metabolism
- behavioural responses
effect of increasing/decreasing thyroxine on heat produced
increase/decrease secretion of thyroid stimulating hormone releasing factor (TSHrF) from hypothalamus
increase/decrease secretion of TSH from ALPG
increase/decrease secretion of T3 and T4 from thyroid gland
increase/decrease BMR
increase/decrease amount of heat produced by body
heat stroke
failure of person’s thermoregulation mechanisms when exposed to excess heat, >42
heat exhaustion
collapse of a person after exposure to heat, mechanisms for thermoregulation still function normally (exessive sweating, vasodilation, increase water loss, decrease blood plasma volume, decrease resistance to blood flow, decrease blood pressure, collapse)
hypothermia
abnormally low body temperature below level required to maintain body functions, <33, death at <32, metabolic activity decreases, heat production decreases, normal body temp 37
hyper/hypothyroidism
hyperthyroidism/hypothyroidism
eg: graves disease - enlargement of thyroid gland caused by immune system reaction, genetically predisposed/ Hashimoto’s disease - attack on thyroid gland by patient’s immune system
cause: too much/too little T3 T4
treatment: surgery, taking radioactive iodine, drugs that block thyroid gland’s use of iodine/ iodine supplements, oral or injected synthetic thyroxine
symptoms of hyper/hypothyroidism
hot flushes and sweating/intolerance to cold
unexplained weight gain/loss
fatigue
more rapid heartbeat, bulging eyeballs/ goitre - swelling of the neck due to enlargement of thyroid gland
increase/decrease appetite
fluids in body
intracellular
extracellular
- intravascular (blood plasma)
- interstitial
- transcellular (fluid in specific organs)
osmotic pressure
pressure caused due to the difference in osmotic concentrations between 2 solutions
water intake and loss
food, drink, metabolic water
lungs, kidney, skin(sweat glands), alimentary canal
too high osmotic pressure
stimulus: increase in osmotic pressure of blood above tolerance levels due to decrease in concentration of water in blood
receptor: osmoreceptors in osmoregulatory centre in hypothalamus
modulator: hypothalamus stimulates PLPG via nervous stimulation to release more ADH
effector: increase permeability of DCTs and collecting ducts in nephrons in kidneys, more water reabsorbed into blood, smaller volume and more concentrated urine
response: osmotic pressure decreases
feedback: negative feedback occurs, osmotic pressure of blood within tolerance levels, ADH not released
too low osmotic pressure
stimulus: decrease in osmotic pressure of blood below tolerance levels due to increase in concentration of water in blood
receptors: osmoreceptors in osmoregulatory centre in hypothalamus
modulator: hypothalamus stimulates PLPG less through less nervous stimulation, causing PLPG to release less ADH
effectors: decrease permeability of DCTs and collecting ducts in nephrons in kidneys, less water reabsorbed into blood, larger volume, more diluted urine produced
response: osmotic pressure increases
feedback: negative feedback occurs, osmotic pressure of blood within tolerance levels, no ADH released
too high osmotic pressure (thirst)
stimulus: osmotic pressure of blood increases above tolerance levels due to decrease in concentration of water in blood
receptors: osmoreceptors in thirst centre of the hypothalamus
modulator: stimulation of hypothalamus causes conscious sensation which leads to feeling thirsty
effector - person drinks water, water absorbed by colon in alimentary canal
response - osmotic pressure of blood decreases
feedback: negative feedback occurs, osmotic pressure of blood within tolerance levels, thirst centre of hypothalamus no longer stimulated, sensation of feeling thirsty stops
aldosterone
increase reabsorption of sodium, excretion of potassium in nephrons, done by a NaK pump with active transport
net movement of ions into blood, water enters blood from nephron via osmosis
released when too little Na too much K too little blood volume and too little blood pressure
dehydration
water loss exceeds water intake, not enough water in the body to carry out normal functions
severe thirst, low bp, dizzy, headache, delirious, death
water intoxication
body fluids become diluted, cells take in extra water via osmosis
person loses a lot of water and salts when sweating and replacing loss with plain water
lightheadedness, headache, vomiting, collapse, death
mechanism of breathing
inspiratory centre of medulla oblongata sends an impulse to the phrenic nerve, stimulating diaphragm muscle to contract and flatten, and intercostal nerve, stimulating intercostal muscles to contract, ribcage swings upwards and outwards, air rushes into lungs - inhalation
stretch receptors in pleural membranes of lungs are stimulated, sends impulse through vagus nerve to expiratory centre of hypothalamus, prevents further stimulation of inspiratory centre
diaphragm muscles relaxes and arches upwards, intercostal muscles relax, ribcage swings downwards and inwards, air rushes out of lungs, exhalation
too much CO2
stimulus - increased CO2 conc of blood and decrease in blood pH above and below tolerance levels (reaction of CO2 and pH)
receptors - central chemoreceptors in medulla oblongata (CO2) and aortic and carotid bodies (pH)
modulator - chemoreceptors send impulses to the inspiratory centre of the medulla oblongata
effector - rate and depth of breathing increases
response - CO2 conc of blood decreases, blood pH increases
feedback - negative feedback occurs, CO2 concentration returns within tolerance levels, blood pH returns within tolerance levels, rate and depth of breathing return back to normal
oxygen and carbon dioxide affecting rate of breathing
O2 - very large decrease in oxygen concentration (stimulates peripheral)
CO2 - small increase able to cause large marked increase in rate and depth of breathing
voluntary control of breathing
connections from cerebral cortex to descending tracts of spinal cord bypasses respiratory cnetre of medulla oblongata
hyperventilation
extremely rapid or deep breathing, more air is exhaled than inhaled, loss of CO2 from blood
voluntary/physical stress
usually corrects itself
why shouldnt you hyperventilate before swimming
decrease CO2 in blood, narrow blood vessels to brain, decrease O2 to brain, faint, respiratory centre of medulla oblongata maintains rate and depth of normal breathing, no voluntary holding breath, inhale water
