homeostasis Flashcards
homeostasis
Maintenance of constant internal environment via physiological control systems
control temperature, blood pH,
blood glucose concentration
and water potential within limits
negative feedback
When there is a deviation from
normal values and restorative
systems are put in place to
return this back to the original level
involves the nervous system
and hormones
islets of langerhans
Region in the pancreas containing cells involved in detecting changes in blood glucose levels
contains endocrine cells (alpha
cells and beta cells) which release hormones to restore blood glucose levels
alpha cells
Located in the islets of Langerhans
release glucagon
when detect blood glucose
concentration is too low
beta cells
Located in the islets of Langerhans
release insulin
when detect blood glucose
concentration is too high
factors affecting blood glucose concentration
Eating food containing
carbohydrates -> glucose
absorbed from the intestine to
the blood
exercise -> increases rate of
respiration, using glucose
action of insulin
Binds to specific receptors on
membranes of liver cells
increases permeability of cell
membrane (GLUT-4 channels
fuse with membrane)
glucose can enter from blood by
facilitated diffusion
activation of enzymes in liver
for glycogenesis
rate of respiration increases
action of glucagon
Binds to specific receptors on membranes of liver cells
activates enzymes for glycogenolysis
activates enzymes for
gluconeogenesis
rate of respiration decreases
blood glucose concentration
increases
role of adrenaline
Secreted by adrenal glands above the kidney when glucose
concentration is too low (exercising)
activates secretion of glucagon
glycogenolysis and gluconeogenesis
works via secondary messenger
model
gluconeogenesis
Creating glucose from non-carbohydrate stores in the liver e.g.
amino acids -> glucose
occurs when all glycogen has
been hydrolysed and the body
requires more glucose
initiate by glucagon when blood
glucose concentrations are low
glycogenolysis
Hydrolysis of glycogen back into
glucose
occurs due to the action of
glucagon to increase blood
glucose concentration
glycogenesis
Process of glucose being converted to glycogen when blood glucose is higher than normal
caused by insulin to lower blood
glucose concentration
what is a second messenger model
Stimulation of a molecule
(usually an enzyme) which can
then stimulate more molecules
to bring about desired response
adrenaline and glucagon
demonstrate this because they
cause glycogenolysis to occur
inside the cell when binding to
receptors on the outside
second messenger model process
Adrenaline/glucagon bind to
specific complementary
receptors on the cell membrane
activate adenylate cyclase
converts ATP to cyclic AMP
(secondary messenger)
cAMP activates protein kinase A
(enzyme)
protein kinase A activates a
cascade to break down glycogen
to glucose (glycogenolysis)
diabetes
A disease when blood glucose
concentration cannot be
controlled naturally
type 1 diabetes
Due to the body being unable to
produce insulin
starts in childhood autoimmune disease where beta cells attacked
treated using insulin injections
type 2 diabetes
Due to receptors in target cells
losing responsiveness to insulin
usually develops due to obesity
and poor diet
treated by controlling diet and
increasing exercise with insulin
injections
osmoregulation
Process of controlling the water
potential of the blood
controlled by hormones e.g.,
antidiuretic hormone (affects
distal convoluted tubule and
collecting duct)
nephron
The structure in the kidney
where blood is filtered, and
useful substances are
reabsorbed into the blood
formation of glomerular filtrate
Diameter of efferent arteriole is
smaller than afferent arteriole
build-up of hydrostatic pressure
water/glucose / ions squeezed
out capillary into Bowman’s
capsule through pores in
capillary endothelium,
basement membrane and
podocytes
large proteins too large to pass
reabsorption of glucose by PCT
Co-transport mechanism
walls made of microvilli
epithelial cells to provide large
surface area for diffusion of
glucose into cells from PCT
sodium actively transported out
cells into intercellular space to
create a concentration gradient
glucose can diffuse into the
blood again
counter current multiplier mechanism
Describes how to maintain a
gradient of Na+ in medulla by
the loop of Henle.
Na+ actively transported out
ascending limb to medulla to
lower water potential
water moves out descending
limb + DCT + collecting duct by
osmosis due to this water
potential gradient
reabsorption of water by DCT/ collecting duct
Water moves out of DCT and
collecting duct by osmosis
down a water potential gradient
controlled by ADH which
changes the permeability of
membranes to water
role of hypothalamus in osmoregulation
Contains osmoreceptors which
detect changes in water potential
produces ADH
when blood has low water
potential, osmoreceptors shrink
and stimulate more ADH to be
made so more released from the
pituitary gland
anti-diuretic hormone
Produced by hypothalamus,
released by pituitary gland
affects permeability of walls of
collecting duct & DCT to water
more ADH means more
aquaporins fuse with walls so
more water is reabsorbed back
to blood- urine more
concentrated.
role of the pituitary gland in osmoregulation
ADH moves to the pituitary
gland from the hypothalamus
releases ADH into capillaries
travels through blood -> kidney
