Homeostasis Flashcards
(78 cards)
What is homeostasis?
the maintenance of a stable internal environment
Why is it important to maintain the right core body temp?
- optimum temp for enzyme activity is about 37°C in humans
- if body temp is too high, enzymes may become denatured. enzyme’s molecules vibrate too much, which breaks hydrogen bonds holding them in their 3D shape. shape of active site changes and it no longer works as a catalyst, so metabolic reactions are less efficient
- if body temp is too low, enzyme activity is reduced, slowing rate of metabolic reactions
Why is it important to maintain the right blood pH?
- optimum pH for enzyme activity is around pH 7, but some enzymes work best at other pHs, e.g. enzymes in stomach work best at a low pH
- if blood pH is too high or too low, enzymes become denatured. hydrogen bonds that hold them in their 3D shape are broken, so shape of active site is changed an dit no longer works as a catalyst, so metabolic reactions are less efficient
Why is it important to maintain the right blood glucose concentration?
- too high
- too low
cells need glucose for energy and blood glucose conc also affects WP of blood
- too high = WP of blood is reduced to a point where water molecules diffuse out of cells into blood by osmosis, can cause cells to shrivel up and die
- too low = cells are unable to carry out normal activities because there isn’t enough glucose for respiration to provide energy
How do homeostatic systems work?
homeostatic systems detect a change and respond by negative feedback
- receptors detect when a level is too high or too low
- info is communicated via the nervous system or hormonal system to effectors
- effectors respond to counteract the change - bringing the level back to normal
What is negative feedback?
-example?
the mechanism that restores the level to normal
-body temp
When might negative feedback not work?
if a change is too big, then effectors may not be able to counteract it, e.g. a huge drop in body temp
Why does the body require multiple negative feedback mechanisms?
having more than one mechanism gives more control over changes in the internal environment - means you can actively increase OR decrease a levels it returns to normal
What is positive feedback?
-examples?
positive feedback mechanisms amplify a change from the normal level
- blood clot after an injury
- hypothermia
Explain the positive feedback mechanism that involves blood clotting after an injury.
- platelets become activated and release an chemical - this triggered more platelets to be activated, and so on
- platelets very quickly form a blood clot at the injury site
- process ends with negative feedback, when the body detect the blood clot has been formed
Explain the positive feedback mechanism that is involved in hypothermia.
- hypothermia is low body temp, below 35°C
- it happens when heat is lost from the body quicker than it can be produced
- as body temp falls, the brain doesn’t work properly and. shivering stops - making body temp fall even more
- positive feedback takes body temp further away from the normal level, and it continues to decrease unless action is taken
Why is positive feedback not involved in homeostasis?
it doesn’t keep the internal environment stable
Why must blood glucose concentration be carefully controlled?
all cells need a constant energy supply to work
What is the normal blood glucose concentration?
around 90 mg per 100cm3 of blood
How is blood glucose concentration monitored?
by cells in pancreas
What causes concentration of glucose in the blood to change?
- blood glucose concentration rises after eating food containing carbohydrate
- blood glucose concentration falls after exercise, as more glucose is used in respiration to release energy
How does the hormonal system control blood glucose concentration?
uses two hormones - insulin and glucagon
How do hormones travel?
in the blood to their target cells (effectors)
Where are insulin and glucagon produced?
they’re secreted by clusters of cells in the pancreas called islets of Langerhans:
- beta cells secrete insulin
- alpha cells secrete glucagon
Explain how insulin lowers blood glucose conc when its too high.
- insulin binds to specific receptors on cell membranes of liver cells and muscle cells
- it increases permeability of muscle-cell membranes to glucose, so cells take up more glucose. this involves increasing the number of channel proteins in cell membrane
- insulin also activates enzymes in liver and muscle cells that convert glucose into glycogen (glycogenesis)
- cells store glycogen in cytoplasm, as an energy store
- insulin also increases rate of respiration of glucose, especially in muscle cells
What are liver cells also called?
hepatocytes
What is glycogenesis?
formation of glycogen from glucose
Explain how glucagon raises blood glucose conc when its too low.
- glucagon binds to specific receptors on cell membranes of liver cells
- glucagon activates enzymes in liver cells that break down glycogen into glucose (glycogenolysis)
- glucagon activates enzymes involved in the formation of glucose from glycerol and amino acids (gluconeogenesis)
- glucagon decreases rate of respiration of glucose in cells
Compare the responses produced by the hormonal system and the nervous system.
- because they travel in the blood to their target cells, responses produced by hormones are slower than those produced by nervous impulses, which are very quick
- hormones are not broken down as quickly as neurotransmitters though, so there effects last longer