Section 6- Homeostasis Flashcards
What is homeostasis?
The regulation and maintenance of the internal environment, within restrictive limits, controlled by physiological control systems
(e.g. temperature, blood pH, blood sugar levels, water potential of blood)
Why is temperature controlled internally?
Prevents proteins denaturing and to keep enzymes at their optimum
True for endotherms (warm blooded, mammals and birds)
What is negative feedback?
A negative feedback mechanism is one where a stimulus causes a response that reverses the effect of that stimulus
What happens when we are too cold?
Goosebumps, hairs become erect: erector pili muscles cause hairs to become erect to trap a layer of insulating hair
Shivering: by repeatedly contracting muscles we increase respiration rate, which produces heat as a waste product
Vasoconstriction: More blood is diverted away from the skin surface to prevent heat loss by radiation
Will gluconeogenesis require energy, or release energy?
Require energy
Reversing glycolysis
Why are diabetics encouraged to eat starchy foods rather than sugary foods?
Fatty foods contain sucrose which hydrolyse quick
What is gluconeogenesis?
Making new glucose from pyruvate, amino acids or glycerol
What is glycogenolysis?
Hydrolysis of glycogen
What 3 hormones does the control of blood glucose depend upon?
Insulin
Glucagon
Adrenaline
What 3 factors are blood glucose levels increased by?
Diet
Gluconeogenesis
Glycogenolysis
What happens if blood glucose goes too high?
Cells in the pancreas celled Beta-cells, islets of Langerhans, detects the rise in blood glucose and secret insulin
Insulin binds to complementary receptors on the surface membranes of target cells
Binding stimulates the cells to take up more glucose by facilitated diffusion
Also stimulates the process of glycogenesis
What detects rise in blood glucose?
Beta-cells found in islets of Langerhans
What happens if blood glucose goes too low?
Alpha cells in the islets of Langerhans detect the drop and secrete glucagon
Binds to complementary receptors on the surface of liver cells, stimulating process of glycogenolysis
If glycogen stores are depleted then gluconeogenesis is stimulated
How does adrenaline stimulate glycogenolysis?
Adrenalin is secreted from the adrenal glands on top of the kidneys
Binds to complementary receptors on liver cells where it stimulates glycogenolysis
What does the second messenger model describe?
How adrenaline and glucagon can stimulate glycogenolysis without entering the cell
What is the second messenger model?
- Hormone (first messenger) binds to the complementary receptor on the surface membrane of the target cell
- This binding activates adenylate cyclase - enzymes catalyses ATP into cyclic AMP (cAMP)
- cAMP is second messenger which activates an enzymes called proteinkinase A
- Proteinkinase A starts a cascade of reactions resulting in glycogenolysis
What are 2 reasons why it was better to start with mRNA from pancreas cell rather than with the DNA from these cells?
Contains no introns
Specific mRNA is found in pancreas cells
How can the kidney be adapted to reduce the volume of urine produced in an organism that does not need to drink water?
Long loop of Henle
Very low water potential in medulla
Large number of aquaporins in the collecting duct
How does insulin increase permeability of cells to glucose?
Increases the number of carrier proteins
Triggers conformational change which opens glucose carrier proteins
How does insulin lead to a decrease in blood glucose concentration?
Increases permeability of cells to glucose
Increases glucose concentration gradient
Triggers inhibition of enzymes of glycogenolysis
How does insulin increase permeability of cells to glucose?
Increases number of glucose carrier proteins
Triggers conformational change which opens glucose carrier proteins