6.4 - Homeostasis

Question 1

define homeostasis

Answer 1

maintenance of a constant internal environment

Question 2

define glucose

Answer 2

monosaccharide

Question 3

define glycogen

Answer 3

stored form of glucose

Question 4

define glucagon

Answer 4

hormone that increases blood glucose concentration

Question 5

define insulin

Answer 5

hormone that decreases blood glucose concentration

Question 6

define glycogenesis

Answer 6

forming glycogen from glucose

Question 7

define glycogenolysis

Answer 7

hydrolysis of glycogen to glucose

Question 8

define gluconeogenesis

Answer 8

glucose formed from non-carbohydrates: glycerol and amino acids

Question 9

define hyperglycaemia

Answer 9

blood glucose concentration is too high

Question 10

define hypoglycaemia

Answer 10

blood glucose concentration is too low

Question 11

define negative feedback

Answer 11

responds to change in internal conditions and returns them to optimum

Question 12

define positive feedback

Answer 12

amplifies a change from the normal level
e.g hypothermia, cervix dilation in childbirth
- not involved in homeostasis as doesn’t keep internal environment stable, effectors respond to further increase level away from normal level

Question 13

discuss the negative feedback loop for body temperature increasing

Answer 13

• thermostat in hypothalamus activates cooling mechanisms
• sweat glands produce more sweat to increase heat loss by evaporation
• vasodilation to increase heat loss by radiation
• hairs on skin lie flat to reduce insulation and increase heat loss
• no shivering occurs
• cooling mechanisms switched off by thermostat in hypothalamus

Question 14

discuss the negative feedback loop for body temperature decreasing

Answer 14

• thermostat in hypothalamus activates warming mechanisms
• sweat glands produce less sweat to reduce heat loss by evaporation
• vasoconstriction to reduce heat loss by radiation
• hairs on skin stand up to trap air as insulation
• shivering occurs and muscle contraction generates heat
• warming mechanisms switched off by thermostat in hypothalamus

Question 15

importance of maintaining body temperature

Answer 15

too high: enzymes denature due to H bonds breaking, so shape of active site changes
too low: less kinetic energy so less frequent collisions between enzyme and substrate, so less ESCs formed and lower reaction rate

Question 16

importance of maintaining blood pH

Answer 16

too high/low: enzymes denature due to H bonds breaking so shape of active sit changes

Question 17

importance of maintaining blood glucose concentration

Answer 17

too high: blood WP decreases, water moves out of cells by osmosis, cells shrink
too low: blood WP increases, water moves into cells by osmosis, cells swell. and insufficient glucose for respiration to produce ATP to release energy

Question 18

outline the negative feedback loop

Answer 18

normal level
level changes
receptors detect level too high/low
nervous/endocrine system coordinates info from receptors to effectors
effectors respond to counteract change
normal level

Question 19

compare and contrast the nervous and endocrine systems

Answer 19

NERVOUS
- fast transmission
- chemical + electrical
- neurones and neurotransmitter
- short-lasting effect
- travel via neurones

ENDOCRINE
- slow transmission
- chemical
- hormones
- long-lasting effect
- travel via blood

neurotransmitter/hormones bind to complementary receptors

Question 20

explain what happens when blood glucose concentration is too high

Answer 20

• beta cells secrete insulin
• binds to specific receptors on liver + muscle cell membranes
• increases muscle cell membrane permeability to glucose by increasing no. of channel proteins
• activates enzymes in liver and muscle cells that in glycogenesis convert glucose -> glycogen, which is stored in cytoplasm as an energy source
• increases respiration rate (especially in muscle cells)

Question 21

explain what happens when blood glucose concentration is too low

Answer 21

• alpha cells secrete glucagon
• binds to specific receptors on liver cell membranes
• activates enzymes in liver cells which in glycogenolysis hydrolyse glycogen -> glucose
• activates enzymes involved in glucose formation from glycerol and amino acids
• glucose formed from non-carbohydrates in gluconeogenesis and diffuses out of cell via facilitated diffusion
• respiration rate decreases

Question 22

feature of liver cells

Answer 22

act as both receptors and effectors (glucagon)

Question 23

describe the effect of adrenaline (or glucagon)

Answer 23

• adrenaline binds to complementary receptors on liver cell membrane, causing them to change shape
• change on shape activates adenylate cyclase which hydrolyses ATP to cAMP (2nd messenger)
• change in shape activates enzyme protein kinase
• cascade effect until glycogen -> glucose in glycogenolysis or gluconeogenesis

Question 24

what can cause hyper and hypoglycaemia?

Answer 24

hyper: too much carbohydrate, too little insulin
hypo: meal skipping, strenuous exercise

Question 25

type 1 diabetes

Answer 25

• insufficient insulin production
• childhood autoimmune response = T-cells attack beta cells which synthesise insulin
• occurs in children/young people
• treated by regular blood tests, insulin injections, diabetes appropriate diet

Question 26

type 2 diabetes

Answer 26

• insulin still produced but less receptors/receptors no longer respond to it
• caused by obesity/poor diet
• occurs age 40+
• treated by sugar and fat controlled diet, regular exercise, can be supplemented by insulin injections, other drugs slow rate of glucose absorption

Question 27

what are ex vivo and in vivo in gene therapy?

Answer 27

ex vivo = gene inserted via virus vector into cell outside body
in vivo = gene inserted via virus vector into cell inside body

Question 28

describe how insulin is genetically engineered

Answer 28

• restriction endonuclease cut open plasmids + DNA ligase splices plasmids + human DNA together
• recombinant plasmids inserted into E.coli by transformation (bath of Ca2+ ions then heat/electric shock)
• once transgenic bacteria identified by markers, they are isolated, purified and placed into fermenters with optimal conditions
• transgenic bacteria multiply by binary fission and express human protein insulin
• insulin eventually extracted and purified