Homeostasis Flashcards
What is homeostasis
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
Whats the control mechanism in homeostasis
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
What are negative and positive feedback control mechanisms of coordination
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
Why is it important that solute concentrations are maintained across the body
so that water potential across cells is not affected thus no loss/gain of water via osmosis
How do poikilothermic (cold blooded) organisms maintain body temperature
behavioural changes:
- bask in the sun
- migration
How do homeothermic (warm blooded) organisms maintain body temperature
thermoregulation keeping body temperature ±37.5°C
hypothermia - low body temperature
hyperthermia - high body temperature
What are average blood glucose levels
4-6mmol/L
hypoglycemia - low glucose levels
hyperglycemia - high glucose levels
What is osmoregulation
maintaining water potential and electrolyte balance
What hormones exert control over blood glucose concentration
- insulin
- glucagon
What is the Islets of Langerhans
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
What are the 2 states of nutrient usage
absorptive - nutrients absorbed by the intestine into cells
post-absorptive -
What is the role of insulin
- controls entry of glucose into cells
- released from beta cells in the Islets of Langerhans
What is the role of insulin in muscles
increase glucose and amino acid uptake
What is the role of insulin in the liver
- stimulate enzymes that hydrolyse glucose into glycogen (glycogenesis)
- inhibit enzymes that breakdown glycogen
- stimulate enzymes that synthesise fats
What is the role of glucagon
- 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
What are the causes of the release of insulin
- 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
Why is the control of body temperature advantageous
body temperature can be actively increased or decreased depending on the conditions and allows response to environment
Explain how the negative feedback mechanism takes place in the liver cells (hepatocytes) to maintain control of blood glucose concentration
- 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
What is Glycogenesis (glycogen-esis)
making of glycogen from glucose in the liver/muscle cells
What is Glycogenolysis (glycogen-olysis)
the hydrolysis of glycogen into glucose in the liver
What is Gluconeogenesis (gluco-neo-genesis)
the formation of glucose from non-carbohydrates (fatty acids and amino acids)
How does insulin decrease the level of blood glucose
- 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
What is type 1 diabetes
- 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
What is type 2 diabetes
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
How does the binding of adrenaline and glucagon to receptors in the plasma membrane of liver cells cause increase of blood glucose concentration
- it activates adenylate cyclase
- this converts ATP into a ‘second messenger’ called cyclic AMP (cAMP)
- cAMP activates a chain of reactions that cause glycogenolysis
