Homeostasis

Question 1

What is homeostasis

Answer 1

the maintenance of an internal environment within and organism that maintains the chemical make-up, volume and other features of the blood and tissue fluid within restricted limits

Question 2

Whats the control mechanism in homeostasis

Answer 2

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

• receptor, which detects any deviation from optimal and informs the,
• coordinator, which coordinates the information from the receptor to the appropriate,
• effector, often a muscle or a gland that makes the changes needed to return system back to optimal, the return to normality is a feedback mechanism

Question 3

What are negative and positive feedback control mechanisms of coordination

Answer 3

negative feed back - when the change produced by the control system leads to a change in the stimulus detected by the receptor and turns the system off

positive feedback - when the deviation from an optimum causes changes that result in an even greater deviation from the normal

Question 4

Why is it important that solute concentrations are maintained across the body

Answer 4

so that water potential across cells is not affected thus no loss/gain of water via osmosis

Question 5

How do poikilothermic (cold blooded) organisms maintain body temperature

Answer 5

behavioural changes:

• bask in the sun
• migration

Question 6

How do homeothermic (warm blooded) organisms maintain body temperature

Answer 6

thermoregulation keeping body temperature ±37.5°C
hypothermia - low body temperature
hyperthermia - high body temperature

Question 7

What are average blood glucose levels

Answer 7

4-6mmol/L
hypoglycemia - low glucose levels
hyperglycemia - high glucose levels

Question 8

What is osmoregulation

Answer 8

maintaining water potential and electrolyte balance

Question 9

What hormones exert control over blood glucose concentration

Answer 9

• insulin

- glucagon

Question 10

What is the Islets of Langerhans

Answer 10

tiny clusters of cells scattered throughout the pancreas that contain several types of cells, including alpha and beta cells, that produce the hormones glucagon and insulin

Question 11

What are the 2 states of nutrient usage

Answer 11

absorptive - nutrients absorbed by the intestine into cells

post-absorptive -

Question 12

What is the role of insulin

Answer 12

• controls entry of glucose into cells

- released from beta cells in the Islets of Langerhans

Question 13

What is the role of insulin in muscles

Answer 13

increase glucose and amino acid uptake

Question 14

What is the role of insulin in the liver

Answer 14

• stimulate enzymes that hydrolyse glucose into glycogen (glycogenesis)
• inhibit enzymes that breakdown glycogen
• stimulate enzymes that synthesise fats

Question 15

What is the role of glucagon

Answer 15

• acts in post-absorptive (catabolic) state
• released from alpha cells in the Islets of Langerhans
• stimulates the breakdown of glycogen in the liver into glucose

Question 16

What are the causes of the release of insulin

Answer 16

• high carbohydrate diets increase blood glucose, amino acid concentration and the density of insulin receptors on the beta cells making them more sensitive to change and release insulin from pancreas
• the hormone CCK and parasympathetic nervous system also stimulates the release of insulin

Question 17

Why is the control of body temperature advantageous

Answer 17

body temperature can be actively increased or decreased depending on the conditions and allows response to environment

Question 18

Explain how the negative feedback mechanism takes place in the liver cells (hepatocytes) to maintain control of blood glucose concentration

Answer 18

• removes glucose from the blood when levels are high through glycogenesis
• when blood glucose levels are low the liver breaks down glycogen to release glucose through glycogenolysis
• converts fats and proteins into glucose via gluconeogenesis

Question 19

What is Glycogenesis (glycogen-esis)

Answer 19

making of glycogen from glucose in the liver/muscle cells

Question 20

What is Glycogenolysis (glycogen-olysis)

Answer 20

the hydrolysis of glycogen into glucose in the liver

Question 21

What is Gluconeogenesis (gluco-neo-genesis)

Answer 21

the formation of glucose from non-carbohydrates (fatty acids and amino acids)

Question 22

How does insulin decrease the level of blood glucose

Answer 22

• binds to receptors on liver and muscle cells
• increases membrane permeability to glucose so more glucose is taken up by cells
• activates enzymes that convert glucose to glycogen by glycogenesis

Question 23

What is type 1 diabetes

Answer 23

• insulin dependent, onset in childhood
• beta cells get destroyed thus don’t produce any insulin
• glucose cannot be absorbed into the cells after eating
• carefully controlled by insulin injections

Question 24

What is type 2 diabetes

Answer 24

non-insulin dependent, onset in adulthood

• caused by lifestyle and diet (obesity)
• cells don’t respond to insulin because the receptors do not work
• controlled through diet changes and increased exercise

Question 25

How does the binding of adrenaline and glucagon to receptors in the plasma membrane of liver cells cause increase of blood glucose concentration

Answer 25

• it activates adenylate cyclase
• this converts ATP into a ‘second messenger’ called cyclic AMP (cAMP)
• cAMP activates a chain of reactions that cause glycogenolysis