6.5 - Homeostasis and controlling blood glucose concentration Flashcards
Define homeostasis
maintenance of a constant internal environment
Define glycogen
stored form of glucose
Define glucagon
hormone that increases blood glucose concentration
Define insulin
hormone that decreases blood glucose concentration
Define glycogenesis
forming glycogen from glucose
Define glycogenolysis
hydrolysis of glycogen to glucose
Define gluconeogenesis
glucose formed from non-carbohydrates: glycerol and amino acids
Define hyperglycaemia
blood glucose concentration too high
Define hypoglycaemia
blood glucose concentration too low
Define negative feedback
responds to change in internal conditions and returns them to original level
Define positive feedback
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
Discuss the negative feedback loop for body temperature increasing
- 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
Discuss the negative feedback loop for body temperature decreasing
- 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
Describe the importance of maintaining body temperature
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
Describe the importance of maintaining blood pH
too high/low: enzymes denature due to H bonds breaking so shape of active site changes
Describe the importance of maintaining blood glucose concentration
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; insufficient glucose for respiration to produce ATP to release energy
Outline the negative feedback loop
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
Compare and contrast the nervous and endocrine systems
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
Explain what happens when blood glucose concentration is too high
- 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 in membrane
- 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)
Explain what happens when blood glucose concentration is too low
- 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 (cells use fatty acids + amino acids instead)
Feature of liver cells
act as both receptors and effectors (glucagon)
Describe the effect of adrenaline (or glucagon)
- 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 gluconeogenesis (and glycogenolysis for glucagon ONLY)
What can cause hyper and hypoglycaemia?
hyper: too much carbohydrate, too little insulin
hypo: meal skipping, strenuous exercise
Describe type 1 diabetes
- 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
Describe type 2 diabetes
- 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
