Paper 2 - Homeostatis Flashcards
What is homeostasis
Maintenance of a constant internal environment, via physiological mechanisms in mammals
Ensures internal cells of the body are in an environment that meets their needs and allows them to function normally despite internal/ external changes
What does a change in temperature effect
- enzymes sensitive to changes in temp and ph
- changes away from optimum result in enzyme losing its tertiary structure so it’s active site is not longer complementary to substrate and rate of reaction slows or stops
Mammals maintains a steady core temp and blood ph to maintain optimum conditions for enzymes
What are the different control mechanisms that help homeostasis
- receptors detect stimuli around the body
- effectors carry out corrective measures in response to change
- there is often a coordinator which is the brain
- the brain acts as a control centre
What is a feedback loop
A receptor detects any deviation from the set point and informs the controller, which co ordinates info sends instructions to an appropriate effector which brings about response which is the changes needed to return the system to a set point
What is negative feedback
- restores systems to their original level
- when something changes the opposite effect occurs - a movement away from the norm produces a response that returns the value to the norm
- e.g. water balance, temp and blood glucose concentration
What is positive feedback
- amplify the change
- e.g. blood clotting and labour contractions
What is the control of blood glucose
- involves negative feedback mechanism via endocrine system
- blood glucose levels controlled by pancreas
- pancreas had a glucose receptor cells which monitor concentration of glucose in the blood
- pancreas also has endocrine cells ( islets of langerhans ) which secrete hormones
- alpha cells secrete glucagon while the b cells secrete insulin
Role of insulin in control of glucose concentration
- high level ( hyperglycaemia )
- attaches to complementary receptors on the cell surface membrane of target cells ( liver or muscle )
- controls uptake of glucose causing addition of channel protiens in the cell surface membrane of target cells
- insulin also activates enzymes that are involved in the conversion of glucose to glycogen ( glycogenesis)
- this decreases blood glucose concentration
Role of glucagon in control of blood glucose
- too little ( hypoglycaemia)
- binds to receptor protiens on cell surface membrane of target cells
- activates enzymes involved in the hydrolysis of glycogen to glucose ( glycogenolysis )
- activates enzymes involved in conversion of glycerol and amino acids into glucose ( gluconeogenesis )
What happens after a meal
- glucose absorbed for, gut into hepatic portal vein
- blood glucose conc. increases which is detected by the pancreas
- pancreas secretes insulin from its b cells
- insulin causes glucose to be taken up by the liver and converted to glycogen by glycogenesis
- reduces blood glucose which causes the pancreas to stop secreting insulin
- if glucose levels falls to far this is detected by the pancreas
- pancreas now secretes glucagon from its a cells
- glucagon causes liver to hyrdrolyse some of its glycogen store to glucose, which diffuses into the blood ( glycogenolysis )
- this increases blood glucose which causes the pancreas to stop producing glucagon
- these negative feedback loops continue all day as shown in the graph
What is glucagon
Hormone that causes hydrolysis of glucogen to glucose
What is glycogen
Energy storage carbohydrate found in liver and muscle cells
What is glycogenolysis
Glycogen hydrolysed to glucose
What is glycogenesis
Glucose converted to glycogen ( condensation )
What is gluconeogenesis
Glucose generated from amino acids and glycerol
what hormone increases blood glucose levels
adrenaline
what is the second messenger model of hormone action
- adrenaline and glucagon both attacthes to receptors on the outside of the cell surface membrane of target cells - they are the first messengers
- they activate enzymes involved in the conversion of glycogen to glucose
- hormone receptor complex is formed
- this activates an enzyme inside the cell that results in the production of a chemical that acts as a second messenger
- adenylate cyclase activated which converts ATP to cyclic AMP
- cAMP is the second messenger and actiavtes protien kinase, a phosphorylation enzyme that speeds up the break down of glycogen to glucose
second messenger model of hormone action condensed
1) adenylate cyclase activated
2) cAMP produced / 2cnd messenger produced
3) activates protien kinase
4) so glycogenolysis / gluconeogenesis occurs and glycogenesis inhibited
what is type 1 diabetes
- insulin dependant
- severe insulin deficiency due to autoimmune destruction of b cells, due to virus or faulty gene
what is type 2 diabetes
- non insulin dependant
- insulin is produced but the insulin receptors in the target cells dont work, so insulin has no effect
what causes the symptoms of diabetes
- high blood glucose concentration after a meal
- active transport pumps in the proximal convuluted tubule of the kidney cant reasbsorb all the glucose from the kidney filtrate so some glucose is excreted as urine
what are the symptoms of diabetes
- high thirst - water leaves cells by osmosis due to low water potential of the blood
- large vol of urine - due to excess water in the blood
- poor vision due to osmotic loss of water from the eye lens
- tirdness due to loss of glucose in urine and poor uptake of glucose by liver and muscle cells
- muscle wasting due to gluconeogenesis caused by increased glucagon
what are the treatments for diabetes
- type 1 - treated with insulin injections as it provides the insulin that is lacking
- type 2 - insulin is injected so that any receptors that are not faulty definatley receive insulin so that sugar can be stored in cells
- diet
