16 homeostasis

Question 1

what is homeostasis?

Answer 1

the maintenance of an internal environment within restricted limits in an organism

Question 2

why is homeostasis essential for the proper functioning of organism?

Answer 2

• enzymes that control biochemical reactions are sensitive to changes in temperature and pH, changes to these may reduce their rate of reaction or prevent them from working altogether
• changes to water potential may cause cells to shrink or expand meaning they cannot operate normally, important for maintenance of blood glucose conc
• organisms that can maintain a constant internal temp are more independent of changes in external environment, wider geographical range so find food and shelter

Question 3

what is the optimum point?

Answer 3

the point at which the system operates best, monitored by a receptor

Question 4

what is negative feedback?

Answer 4

occurs when the stimulus causes the corrective measures to be turned off, in doing so this returns the system to its original (optimum) level

e.g. control of blood glucose

Question 5

what is positive feedback?

Answer 5

occurs when the feedback causes the corrective measures to remain turned on, causes the system to deviate even more from the original level

e.g. stimulus in neurones, influx of sodium ions

Question 6

characteristics of hormones

Answer 6

• produced in glands, which secrete hormone directly int blood
• carried in blood plasm to target cells which have receptors complementary to hormones on surface
• effective in very low concentrations, widespread and long-lasting effects

Question 7

what hormones are involved in the secondary messenger model?

Answer 7

adrenaline and glucagon

Question 8

stages of the secondary messenger model involving glucagon

Answer 8

-glucagon binds to protein receptor

Question 9

where is glucagon produced

Answer 9

alpha cells (larger)

Question 10

where is insulin produced?

Answer 10

beta cells (smaller)

Question 11

where are alpha and beta cells located?

Answer 11

islets of langerhans

Question 12

what are three important processes that take place in the liver?

Answer 12

glycogenesis
glycogenolysis
gluconeogenesis

Question 13

what is glycogenesis?

Answer 13

conversion of glucose to glycogen

high blood concentration, liver removed glucose from the blood and converts it to glycogen

Question 14

what is glycogenolysis

Answer 14

breakdown of glycogen to glucose

blood concentration high, liver converts stored glycogen back into glucose which diffuses into the blood

Question 15

what is gluconeogenesis?

Answer 15

production of glucose from non-carbohydrates

when supply of glycogen is exhausted, liver can produce glucose from non-carbohydrates sources e.g. glycerol and amino acids

Question 16

what are the sources of blood glucose?

Answer 16

• directly from the diet (glucose absorbed following hydrolysis of carbohydrates)
• glycogenolysis
• gluconeogenesis

Question 17

what hormones operate to maintain a constant blood glucose concentration?

Answer 17

insulin
glucagon
adrenaline