6.4 homeostasis Flashcards
Homeostasis in mammals
Maintenance of a stable internal environment within restricted limits
By physiological control systems (normally involving negative feedback)
Importance of maintaining core temperature
Too high: hydrogen bonds in tertiary structure break
-enzymes denature, active site changes shape + substrates cannot bind
- fewer E-S complex’s
Too low: not enough KE
- fewer ES complexes
Importance of maintaining blood pH
Above or below optimum pH
Ionic/hydrogen bonds in tertiary structure break
Enzymes denature; active changes shape so substrate cannot bind
Fewer es complexes
Importance of maintaining stable blood glucose conc
Too low (hypoglycaemia)
- not enough glucose for respiration
- less ATP produced
-active transport cannot happen > cell death
Too high (hyperglycaemia)
- water potential of blood decreases
- water lost from tissue to blood via osmosis
- kidneys cannot absorb all glucose > more water lost in urine causing dehydration
Negative feedback
Receptors detect change from optimum
Effectors respond to counteract change
Returning levels to optimum
E.g. control of blood glucose conc
Positive feedback
Receptors detect change from normal
Effectors respond to amplify change
Producing greater deviation from normal
E.g. contractions in childbirth
Importance of conditions being controlled by separate mechanisms involving negative feedback
Departures in different directions from original state can all be controlled/reversed
Giving a greater degree of control (over changes in internal environment)
Factors influencing blood glucose conc
Consumption of carbohydrates - glucose absorbed from intestine to blood
Rate of respiration of glucose - e.g. increases during exercise due to muscle contraction
Glycogenesis
Glucose > glycogen
Glycogenolysis
Glycogen > glucose
Gluconeogenesis
Converting amino acids and/or glycerol > glucose
Beta cells
In islets of langerhans in pancreas detect blood glucose conc
If too high > secrete insulin
Insulin (to decrease blood glucose conc)
Attaches to specific receptors on cell surface membrane of target cells
Causes more glucose channel proteins to join cell surface membrane
- increases permeability to glucose > more glucose enters cell by facilitated diffusion
Activating enzymes involved in conversion of glucose to glycogen (glycogenesis)
- lowers glucose conc in cells > glucose enters cells by facilitated diffusion down conc gradient
Action of glucagon (Increase blood glucose conc )
Alpha cells in islets of langerhans in pancreas detect blood glucose conc too low > secrete glucagon
Attaches to specific receptors on cell surface membrane of target cells e.g. liver
Activates enzymes involved in hydrolysis of glycogen to glucose (glycogenolysis)
Activates enzymes involved in conversion of glycerol/amino acids to glucose (gluconeogenesis)
Establishes conc gradient > glucose leaves cells and enters blood via facilitated diffusion
Role of adrenaline (increase blood glucose conc)
Fear/stress/exercise > adrenal glands secrete adrenaline
Attaches to specific receptors on cell surface membranes of target cells
Activates enzymes involved in hydrolysis of glycogen to glucose (glycogenolysis)
Establishes conc gradient > glucose leaves cells and enters blood by facilitated diffusion
Second messenger model of adrenaline and glucagon action
Attach to specific receptors on cell membrane which:
Activates enzyme adenylate cyclase (changes shape)
Converts many ATP to many cyclic AMP (cAMP)
CAMP acts as second messenger > activates protein kinase enzymes
Protein kinases activates enzymes to break down glycogen to glucose
Type 1 diabetes
B cells in islets of langerhans in pancreas produce insufficient insulin
Controlled by injection of insulin
- blood glucose conc monitored, dose of insulin matched to glucose intake
Eating regularly, control carb intake e.g. those that are absorbed slower to avoid sudden rise in glucose
Type 2
Faulty receptor loses sensitivity to insulin
So fewer glucose transport proteins > less uptake of glucose > less conversion of glucose to glycogen
Type 2 control by insulin
May use drugs which target insulin receptors to increase their sensitivity > more glucose uptake by cells
Type 2 control by diet
Reduced sugar intake (carbs) > less absorbed
Reduced fat intake > less glycerol converted to glucose
More regular exercise > uses glucose for respiration
Lose weight > increased sensitivity of receptors to insulin
