negative feedbsck

Question 1

what is homeostasis?

Answer 1

maintenance of a constant internal environment

Question 2

what does homeostasis ensure?

Answer 2

it ensures the cells are in an environment which allows them to carry out their function

Question 3

what does homeostasis act to do?

Answer 3

bring any fluctuations in line with the set point

Question 4

why is homeostasis important?

Answer 4

-to ensure enzymes which control metabolic reactions are working at their optimum rate

-to ensure a constant blood glucose concentration

-if organisms can resist fluctuations in their internal environments, they are less reliable on their external
environment

Question 5

what is negative feedback?

Answer 5

the condition being regulated is brought back to a set value as soon as
it is detected to have parted from it

Question 6

negative feedback flow diagram:

Answer 6

input → detector → control unit → effector → output

Question 7

steps of negative feedback:

Answer 7

1) stress or disturbance changes the internal environment

2) change is detected by receptors

3) corrective measures are activated

4) corrective measures counteract the change back toward set point

Question 8

what is positive feedback?

Answer 8

the deviation from the predetermined state is enhanced

Question 9

examples of positive feedback:

Answer 9

-the entry of sodium ions into the axon after an action potential is reached

Question 10

where is glucose carried?

Answer 10

-it is carried around the body in solution in the blood plasma
-it’s a small molecule so can easily move out of the blood capillaries into the tissue fluid

Question 11

glucose in a healthy person:

Answer 11

around 800mg per dm³

Question 12

hypoglycaemia

Answer 12

-if a person’s blood glucose concentration drops below about 600mg dm³ they can rapidly lose consciousness

-the brain is very sensitive to drops in the amount of glucose in the blood as they can only respire glucose

-cells need a constant supply of glucose as it is the main respiratory substance

Question 13

hyperglycaemia

Answer 13

-very high concentrations of glucose in the blood → drop in the water potential (more negative) in the blood
-water then moves out of cells causing dehydration → the cells will start to shrivel and die

Question 14

when does blood glucose increase?

Answer 14

following ingestion of food or drink containing carbohydrates

Question 15

when does blood glucose fall?

Answer 15

after exercise / if you have not eaten

Question 16

which organ is key in blood glucose control?

Answer 16

the pancreas, it detects changes in the blood glucose level
-it contains endocrine tissue made of a group of cells called the islets of langerhans

Question 17

what do the islets of langerhan do?

Answer 17

secrete the two hormones that control blood glucose concentration
(insulin & glucagon)

Question 18

what other hormone is important for blood glucose concentration?

Answer 18

adrenaline, which is released by the adrenal glands

Question 19

what do the islets of langerhan contain?

Answer 19

two cell types:
α cells that secrete the hormone glucagon
β cells that secrete the hormone insulin

Question 20

what do α and β cells act as?

Answer 20

the receptors that initiate the response for controlling blood glucose concentration

Question 21

steps of an increase in blood glucose concentration:

Answer 21

1) blood glucose levels increase

2) β cells detect a rise in blood glucose concentration

3) β cells release the hormone insulin

4) insulin makes the liver cells more permeable to glucose & enzymes are activated to convert glucose to glycogen

5) glucose is removed from the blood and stored as glycogen in cells

Question 22

the action of insulin

Answer 22

insulin travels in the bloodstream and binds to glycoprotein receptors on the cell surface membrane of target cells

binding causes…
a change in the tertiary structure of glucose transport proteins (they open)

-an increase in the number of glucose carrier molecules in the cell surface membrane
↳ an increase in glucose uptake

-activates an enzyme that converts glucose into glycogen or fat

Question 23

glycogenesis:

Answer 23

-once glucose has entered a liver cell an enzyme rapidly converts it to glucose phosphate

-different enzymes then convert glucose phosphate into glycogen

(this helps to lower glucose concentration within the liver cells, a steep diffusion gradient is maintained between the blood in the capillaries and the liver cells)

Question 24

why is an increase in glucose carrier proteins important?

Answer 24

increased respiration → lowered blood glucose concentration

Question 25

what happens when a low blood glucose level is detected?

Answer 25

-if a decrease in blood glucose concentration occurs, it is detected by the α and β cells in the pancreas:

the α cells respond by secreting glucagon
the β cells respond by stopping the secretion of insulin

Question 26

steps of low blood glucose levels

Answer 26

1) a cells detect lower blood glucose levels and secrete glucagon

2) glucagon binds to glucagon receptors on the surface of target cells

3) the binding causes a protein to be activated into adenylate cyclase, ATP gets converted into cAMP

4) cAMP activates protein kinase, which hydrolyse glycogen into glucose

5) enzymes that control the conversion of glycerol and amino acids into glucose are also activated

Question 27

the second messenger model:

Answer 27

1) glucagon binds to glucagon receptors

2) once bound, it causes a change in shape in the enzyme adenyl cyclase (activated)

3) activated adenyl cyclase enzymes convert ATP into cAMP (the second messenger - next molecule that causes activation)

4) cAMP activates the enzyme kinase which catalyses the hydrolysis of glycogen to glucose

Question 28

role of adrenaline
(second messenger model)

Answer 28

adrenaline will increase blood glucose in the following ways:

1) adrenaline attaches to receptors on the surfaces of target cells, this causes G protein to be activated and to convert ATP into cAMP

2) cAMP activates an enzyme that can hydrolyse glycogen into glucose

Question 29

glycogenolysis

Answer 29

rhe hydrolysis of glycogen back into glucose in the liver

Question 30

glyconeogenesis

Answer 30

-glucose is created from non-carbohydrate stores in the liver
-this occurs if all glycogen has been hydrolysed into glucose and your body still needs more glucose

(glycerol + amino acids → glucose)