PHYSIOL A Flashcards
what are the targets of homeostatic control?
- conc. of O2 & CO2, nutrients, salts & electrolytes, waste products
- temp
- volume and pressure of extracellular fluid
- pH of internal environment
define homeostasis:
regulation of internal environment so as to maintiain appropriate life sustaining conditions to cells and tissues of the body
what is the concept of positive feedback?
amplifies initial change by amplifying signal indefinitely - ended by a separate mechanism
allows large response to develop from small initial signal
describe blood clotting as a positive feedback mechanism:
- tear in vessel wall
- stimulates platelet aggregation
- platelets release chemicals to attract other platelets
- newly attracted platelets further release chemicals to attract other platelets
- clot formation complete other inhibitory processes prevent further aggregation
simply describe Ferguson reflex:
fetus’ head stretches isthmus - stimulates stretch receptor neurons
- signals to brain relayed to pituitary stimulates release of oxytocin from posterior pituitary …oxytocin stimulates contraction
- fetus’ head pushes against isthmus more => more oxytocin produced and released
what is the homeostatic control of blood pressure?
- haemorrhage reduced BP
- stretch of baroreceptors decreases
- info sent afferent path to brain
- info through efferent to heart and vessels
- response = heart beats faster and blood vessels constrict to raise blood press to normal level (“homeostatic” level)
effects of excessively low blood glucose(Hypoglycaemia)?
<4mmol/L
- CNS dysfunction
- dysfunction/damage to retina, germinal epithelium and RBCs
cells almost exclusively glucose for energy
what do endocrine cells release?
hormones
which can be either paracrine or autocrine
what do nerve cells release in terms of homeostasis regulation?
neurotransmitters - physical connections through synapses
what do chemical signals act on?
receptors at target site, on membrane or within cell
in terms of thermoregulation what happens when the environmental temperature is higher than body temperature?
- vasodilatation, moving blood away from skin surface
- sweating
- hair follicles relax, air flow next to skin increases heat loss by convention
in terms of thermoregulation what happens when body temp is higher than environmental temperature?
- reduced sweating
- piloerection(hairs erect due to pilorum muscles) goose bumps!
- constriction of skin arterioles
- shivering(muscles)
- metabolic changes(brown fat mitochondrion)
describe the blood glucose feedback loop in steps:
- eating increases blood glucose
- this change in blood glucose is detected by beta cells in pancreas
- causes insulin release into blood stream
- insulin acts on target tissues(liver/muscles)
- response of target tissues will result in removal of glucose from circulation - due to the increased uptake by liver & muscle
- blood glucose levels decrease, restoring homeostasis
when blood glucose rises, cells increase their uptake but what do they do with the glucose?
- used for metabolic energy
- fat synthesis (storage)
- glycogen synthesis (storage)
in periods of fasting describe the feedback mechanism that brings blood glucose back to homeostatic levels:
- low blood glucose is recognised by beta cells in pancreas
- pancreas is stimulated to secrete glucagon
- increase of circulating glucagon(but cannot be used yet)
- glycogen broken down in liver
- released into blood stream for use
what goes wrong in type 1 diabetes?
beta cells fail to detect blood glucose, therefore failure to release insulin into blood stream to stimulate uptake of increased blood glucose
what goes wrong in type 2 diabetes?
tissue cells are desensitised to insulin,
what are 5 important roles of calcium in homeostasis?
- neurotransmitter and hormone release mechanism
- muscle contraction
- hardening of teeth and skeleton
- blood clotting
- cell devision and excitability
describe blood calcium regulation:
- decrease in plasma calcium concentration
- decrease detected by CHEMOreceptors in PARATHYROID gland
- this stimulates release of ParaThyroid Hormone(PTH) release into blood stream
- PTH acts on target tissues (bone, kidney, gut)
- response= increase REsorption FROM bone, BY kidney, TO gut(where it is absorbed)
some potential consequences of diabetes mellitus?
- CVD
- retinopathy/neuropathy (think glucose only energy supply)
in terms of feedback mechanisms what is the cause of rickets?
rickets is a disease surround calcium levels in the blood
When one has rickets, low blood causes PTH hormone release and increased resorbtion of Calcium from bone BUT vitamin D3 is needed for this, its not there so, calcium isn’t resorbed meaning it cannot be absorbed in gut
what are the communication types in the endocrine system?
- gap junctions(cell to cell)
- contact-dependent signals(interaction between membrane molecules)
- local communication(paracrine/autocrine)
- long-distance communication(through blood=endocrine)
what are the major endocrine glands(top to bottom)?
- pituitary gland
- thyroid gland
- parathyroid gland
- adrenal glands(on tops of kidneys
roles of endocrine system?
4 x regulation of metabolism
H2O and electrolytes
growth and development
responding to stress
3 x controlling wake-sleep patterns
temperature
repoduction