homoestasis Flashcards
Describe homeostasis in mammals
● Maintenance of a stable internal environment within restricted limits
● By physiological control systems (normally involve negative feedback)
Explain the importance of maintaining stable core temperature
● If temperature is too high:
○ Hydrogen bonds in tertiary structure of enzymes break
○ Enzymes denature; active sites change shape and substrates can’t bind
○ So fewer enzyme-substrate complexes
● If temperature is too low:
○ Not enough kinetic energy so fewer enzyme-substrate complexes
Explain the importance of maintaining stable blood pH
● Above or below optimal pH, ionic / hydrogen bonds in tertiary structure break
● Enzymes denature; active sites change shape and substrates can’t bind
● So fewer enzyme substrate complexes
Too low blood glucose concentration (hypoglycaemia)
● Not enough glucose (respiratory substrate) for
respiration
● So less ATP produced
● Active transport etc. can’t happen → cell death
Too high (hyperglycaemia)
● Water potential of blood decreases
● Water lost from tissue to blood via osmosis
● Kidneys can’t absorb all glucose → more water
lost in urine causing dehydration
Describe the role of negative feedback in homeostasis
- Receptors detect change from optimum
- Effectors respond to counteract change
- Returning levels to optimum / normal
Examples: control of blood glucose
concentration, blood pH, core
temperature.
Explain the importance of conditions being controlled by separate mechanisms involving negative feedback
● Departures in different directions from the original state can all be controlled / reversed
● Giving a greater degree of control (over changes in internal environment)
Describe positive feedback
- Receptors detect change from normal
- Effectors respond to amplify change
- Producing a greater deviation from normal
Describe the factors that influence blood glucose concentration
● Consumption of carbohydrates → glucose absorbed into blood
● Rate of respiration of glucose eg. increases during exercise due to muscle contraction
Describe the role of the liver in glycogenesis, glycogenolysis and gluconeogenesis
Glycogenesis- glucose → glycogen
Glycogenolysis- glycogen → glucose
Gluconeogenesis- amino acids and/or
glycerol → glucose
Explain the action of insulin in decreasing blood glucose concentration
*Beta cells in islets of Langerhans in pancreas detect blood glucose conc→ secrete insulin:
● attach to specific receptors on cell surface membranes of target cells eg. liver / muscles
*causes more glucose channel proteins to join cell surface membrane
- Increasing permeability to glucose
-more glucose can enter cell by facilitated diffusion
*activates enzymes involved in conversion of glu to gly (glycogenesis)
-Lowering glucose concentration in cells, creating a concentration gradient so cells dont burst
-So glucose enters cell by facilitated diffusion
Explain the action of glucagon in increasing blood glucose concentration
Alpha cells in islets of Langerhans in pancreas detect blood glucose too low → secrete glucagon:
● Attaches to specific receptors on cell surface membranes of target cells eg. liver
1. Activates enzymes involved in hydrolysis of glycogen to glucose (glycogenolysis)
2. Activates enzymes involved in conversion of glycerol / amino acids to glucose (gluconeogenesis)
● This establishes a concentration gradient → glucose enters blood by facilitated diffusion
Explain the role of adrenaline in increasing blood glucose concentration
*Fear / stress / exercise → adrenal glands secrete adrenaline:
● Attaches to specific receptors on cell surface membranes of target cells eg. liver
● Activates enzymes involved in hydrolysis of glycogen to glucose (glycogenolysis)
● This establishes a concentration gradient → glucose enters blood by facilitated diffusion
Describe the second messenger model of adrenaline and glucagon action
Adrenaline / glucagon (‘first messengers’) attach to specific receptors on cell membrane which:
1. Activates enzyme adenylate cyclase (changes shape)
2. Which converts many ATP to many cyclic AMP (cAMP)
3. cAMP acts as the second messenger → activates protein kinase enzymes
4. Protein kinases activate enzymes to break down glycogen to glucose
Suggest an advantage of the second messenger model
● Amplifies signal from hormone
● As each hormone can stimulate production of many molecules of second messenger (cAMP)
● Which can in turn activate many enzymes for rapid increase in glucose
Type 1 diabetes
● β cells in islets of langerhans
in pancreas produce insufficient insulin
● Normally develops in childhood due to
an autoimmune response destroying β
cells of Islets of Langerhans
Type 2 diabetes
*receptor (faulty) loses responsiveness /
sensitivity to insulin (but insulin still produced)
● So fewer glucose transport proteins → less uptake of glucose → less conversion of glucose to glycogen
● Risk factor = obesity
Describe how of type I diabetes can be controlled
● Injections of insulin
● Blood glucose concentration monitored with biosensors; dose of insulin matched to glucose intake
● Eat regularly and control carbohydrate intake eg. those that are broken down / absorbed slower
○ To avoid sudden rise in glucose
Describe how of type II diabetes can be controlled
● may use drugs which target insulin receptors to increase their sensitivity
○ To increase glucose uptake by cells / tissues
● Reduce sugar intake (carbohydrates) / low glycaemic index → less absorbed
● Reduce fat intake → less glycerol converted to glucose
● More (regular) exercise → uses glucose / fats by increasing respiration
● Lose weight → increased sensitivity of receptors to insulin
Describe how you can evaluate the positions of health advisers and the food
industry in relation to the increased incidence of type II diabetes
● Health advisers aim - reduce risk of type II diabetes due to health problems caused (eg. kidney failure)
○ So need to reduce obesity as it is a risk factor
● Food industry aim - maximise profit
Role of glycogen
form of energy storage
