Homeostasis Flashcards
what is meant by homeostasis?
the process of maintaining a constant internal environment, despite external changes
what are 3 examples of homeostasis?
-control of blood pH
-control of core temperature
-control of blood glucose
why does blood pH have to be controlled?
enzymes have an optimum pH and above and below this, the distribution of hydrogen and ionic bonds in the 3D tertiary structure start to change, making the active site no longer complementary to the substrate and decreasing rate of metabolism. enzymes then denature at extremes, so they can no longer function.
how do you calculate pH?
pH=-log10[H+]
why does core temperature have to be controlled?
enzymes have an optimum temperature. as temperature increases, kinetic energy increases, so there are more successful collisions between the active site and the substrate, causing an increased rate of metabolism. however, hydrogen bonds begin to break as temperature increases, so tertiary structure changes. enzymes then denature and stop functioning.
why does control of blood glucose concentration have to be controlled?
if blood glucose concentration falls too low, rate of respiration falls too low and the cell can’t make enough ATP to stay alive
if blood glucose concentration is too high, the water potential of the blood falls so low that water leaves cells by osmosis, down the water potential gradient. if too much water leaves, they shrivel up (crenate) and die.
what is negative feedback?
a mechanism that reverses a change to restore a level back to normal.
what happens when there is a rise in temperature?
-the thermoregulatory centre in the hypothalamus detects the change
-the nervous and hormonal system and carry signals to the skin, liver, and muscles.
-less heat is then generated and more heat is lost
-temperature then falls
what happens when blood glucose concentration becomes higher than normal?
-the pancreas detects the change and secretes insulin
-this travels in the blood and binds to receptors on the liver and muscle cells
-these respond by bringing about changes which increase glucose uptake by the cells so blood glucose concentration falls back to normal
what are the advantages of multiple negative feedback systems and what is an example of this?
-more rapid response to changes
-more control over changes in the internal environment
an example is the body reducing blood glucose by secreting more insulin AND by secreting less glucagon.
what is positive feedback?
a mechanism that amplifies a change away from the normal level
is positive feedback involved in homeostasis?
no
why is positive feedback not involved in homeostasis?
because it doesn’t keep internal environment constant
what is positive feedback useful for?
rapid activation of a process (e.g. in labour)
when does positive feedback also occur (other than for rapid activation of a process)?
when homeostasis systems break down, like in hyperthermia
what cells detect an increase in blood glucose and what do they do?
by beta cells in the pancreas (at islets of langerhans), which secrete insulin to decrease blood glucose
what cells detect an decrease in blood glucose and what do they do?
alpha cells in the pancreas (at islets of langerhans), which secrete glucagon to increase blood glucose
glucose is a _______________ substrate
respiratory
describe the process when blood glucose rises above normal
-insulin is secreted, which binds to insulin receptors on the plasma membrane of liver cells and muscle cells
-insulin decreases blood glucose by:
*causing vesicles storing glucose carrier proteins to fuse with the plasma membrane, so there are more glucose carriers, so increased permeability to glucose, so more glucose enters the cell
*activating enzymes for glycogenesis (converting glucose to glycogen)
*increasing rate of respiration of glucose
why is glycogen a good storage molecule?
it is insoluble
describe the process when blood glucose falls below normal
-glucagon is secreted, which binds to glucagon receptors on the plasma membrane of liver cells
-glucagon increases blood glucose by:
*activating enzymes for gluconeogenesis (conversion of amino acids and glycerol to glucose)
*activating enzymes for glycogenolysis (conversion of glycogen to glucose)
*decreasing rate of respiration of glucose
what is glycogenesis?
condensation of glucose to glycogen
what is gluconeogenesis?
conversion of amino acids and glycerol to glucose
what is glycogenolysis?
hydrolysis of glycogen to glucose
explain two advantages of having two opposing hormones to regulate blood glucose concentration rather than having just one
-more controlled response to blood glucose control being out of the optimum range
-more rapid response, so there is less change from the optimum range
describe and explain 3 ways insulin will result in increased uptake of glucose by binding to insulin receptors on plasma membranes, with reference to glucose carriers and diffusion gradients
-more glucose carriers join the plasma membrane from the fusing vesicles, so the membrane is more permeable to glucose
-insulin activates the enzymes for glycogenesis, turning glucose to glycogen. this decreases the concentration of glucose inside the cell, making a steeper concentration gradient
-insulin increases the rate of respiration of glucose, decreasing the concentration of glucose inside the cell, so facilitated diffusion occurs into the cell
can insulin be made in type 1 diabetes? why?
no- the body is unable to produce its own insulin, usually due to beta cell damage in the islets of langerhans
can insulin be made in type 2 diabetes? why?
yes- however the body becomes insensitive to this due to loss of functioning insulin receptors on the liver and muscle cells
when does type 1 diabetes occur?
quickly during childhood
when does type 2 diabetes occur?
slowly at 40+ years, or earlier if obese
what are the risk factors for type 1 diabetes?
diseases
genetics
what are the risk factors for type 2 diabetes?
age
obesity
diet high in refined sugars
family history
ethnicity (african/asian)
