Homeostasis + negative feedback Flashcards
Homeostasis
Involves physiological control systems that maintain the internal environment within restricted limits
Important in maintaining:
- A stable core temperature
- A stable blood pH
- Stable blood glucose concentration
Why is it important that core temperature remains stable?
To maintain a stable rate of enzyme-controlled reactions + prevent damage to membranes
Temp too low- enzyme + substrate molecules have insufficient kinetic energy
Temp too high- enzymes denature
Why is it important that blood pH remains stable?
To maintain a stable rate of enzyme-controlled reactions
Acidic pH- H+ ions interact with hydrogen bonds and ionic bonds in tertiary structure of enzymes, shape of active site changes so no ES complexes form
Why is it important that blood glucose concentration remains stable?
- Maintain constant blood water potential to prevent osmotic lysis/ crenation of cells
- Maintain constant conc of respiratory substrate
Negative feedback
When any deviation from normal values are restored to their normal level. Involves nervous system + often hormones too
Suggest why separate negative feedback mechanisms control fluctuations in different directions
Provides more control, especially in case of overcorrection, which would lead to a deviation in the opposite direction from the original one
Factors that influence blood glucose concentration
- Amount of carbohydrate ingested from diet
- Rate of glycogenolysis
- Rate of gluconeogenesis
Define glycogenesis, glycogenolysis, gluconeogenesis
Glycogenesis- Liver converts glucose into glycogen
Glycogenolysis- Liver hydrolyses glycogen into glucose which can diffuse into blood
Gluconeogenesis- Liver converts glycerol + amino acids into glucose
Explain the action of insulin
Beta cells in islets of langerhans (in pancreas) detect when blood glucose levels are too high + secrete insulin
Insulin decreases blood glucose levels in following ways:
- Attaching to receptors on surfaces of target cells which changes the tertiary structure of channel proteins so more glucose is absorbed by facilitated diffusion
- Vesicles in cytoplasm fuse with cell surface membrane forming glucose channel proteins so more glucose is absorbed from blood into cells
- Activating enzymes involved in conversion of glucose to glycogen - results in glycogenesis in the liver
Explain the action of glucagon
Alpha cells in the islets of Langerhans (in pancreas) detect when blood glucose is too low
Glucagon increases blood glucose in the following ways:
- Attaching to receptors on surface of target cells (liver)
- When glucagon binds it causes a protein to be activated into adenylate cyclase + to convert ATP into cyclic AMP (cAMP). cAMP activates an enzyme, protein kinase, that can hydrolyse glycogen into glucose
- Activating enzymes involved in conversion of glycerol + amino acids into glucose (gluconeogenesis)
Explain the action of adrenaline
If blood glucose is too low, the adrenal glands will also secrete adrenaline
Adrenaline will increase blood glucose in the following ways:
- Adrenaline attaches to receptors on target cells (liver) causing a protein to change shape.
- This leads to the activation of adenyl cyclase which converts ATP to cyclic AMP (cAMP)
- cAMP acts as the second messenger + activates enzyme protein kinase can hydrolyse glycogen into glucose
Type 1 and type 2 diabetes
Type 1- Unable to produce insulin. Usually starts in childhood + could be the result of an autoimmune disease where beta cells are attacked. Treatment involves injections of insulin
Type 2- Receptors on target cells lose their responsiveness to insulin. Usually develops in adults due to obesity + poor diet. Controlled by regulating intake of carbohydrates, increasing exercise + sometimes insulin injections
