6.4 homeostasis

Question 1

Homeostasis in mammals

Answer 1

Maintenance of a stable internal environment within restricted limits

By physiological control systems (normally involving negative feedback)

Question 2

Importance of maintaining core temperature

Answer 2

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

Question 3

Importance of maintaining blood pH

Answer 3

Above or below optimum pH

Ionic/hydrogen bonds in tertiary structure break

Enzymes denature; active changes shape so substrate cannot bind

Fewer es complexes

Question 4

Importance of maintaining stable blood glucose conc

Answer 4

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

Question 5

Negative feedback

Answer 5

Receptors detect change from optimum

Effectors respond to counteract change

Returning levels to optimum

E.g. control of blood glucose conc

Question 6

Positive feedback

Answer 6

Receptors detect change from normal

Effectors respond to amplify change

Producing greater deviation from normal

E.g. contractions in childbirth

Question 7

Importance of conditions being controlled by separate mechanisms involving negative feedback

Answer 7

Departures in different directions from original state can all be controlled/reversed

Giving a greater degree of control (over changes in internal environment)

Question 8

Factors influencing blood glucose conc

Answer 8

Consumption of carbohydrates - glucose absorbed from intestine to blood

Rate of respiration of glucose - e.g. increases during exercise due to muscle contraction

Question 9

Glycogenesis

Answer 9

Glucose > glycogen

Question 10

Glycogenolysis

Answer 10

Glycogen > glucose

Question 11

Gluconeogenesis

Answer 11

Converting amino acids and/or glycerol > glucose

Question 12

Beta cells

Answer 12

In islets of langerhans in pancreas detect blood glucose conc

If too high > secrete insulin

Question 13

Insulin (to decrease blood glucose conc)

Answer 13

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

Question 14

Action of glucagon (Increase blood glucose conc )

Answer 14

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

Question 15

Role of adrenaline (increase blood glucose conc)

Answer 15

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

Question 16

Second messenger model of adrenaline and glucagon action

Answer 16

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

Question 17

Type 1 diabetes

Answer 17

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

Question 18

Type 2

Answer 18

Faulty receptor loses sensitivity to insulin

So fewer glucose transport proteins > less uptake of glucose > less conversion of glucose to glycogen

Question 19

Type 2 control by insulin

Answer 19

May use drugs which target insulin receptors to increase their sensitivity > more glucose uptake by cells

Question 20

Type 2 control by diet

Answer 20

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