Topic 6 - Response to environmental changes Flashcards
What is meant by the optimum point?
The desired level at which the system operates
What is meant by a feedback mechanism?
Where a receptor detects a stimulus created by a change to the system and the effector brings about the appropriate response.
List the characteristics which all hormones share:
- produced in glands, which secrete the hormone directly into the blood
- carried in the blood plasma to the cells on which they act (target cells)
- effective in very low concentrations, but often have widespread and long-lasting effects
Outline the second messenger model used by adrenaline and glucagon
- Adrenaline binds to transmembrane protein receptor within liver cell membrane
- This causes the protein to change shape
- Leads to the activation of adenyl cyclase enzyme, which converts ATP to cyclic AMP (cAMP)
- cAMP acts as a second messenger that binds to protein kinase enzyme to activate it
- Active protein kinase enzyme converts glycogen to glucose, which moves from liver cell to blood via facilitated diffusion
List features of the pancreas
- Large pale-coloured gland
- Situated in the upper abdomen behind stomach
- Produces enzymes for digestion and hormones for regulating blood glucose
What are the groups of hormone-producing cells in the pancreas called and what do these include?
They are called islets of Langerhans and include:
- alpha cells - larger and produce glucagon
- beta cells - smaller and produce insulin
What are liver cells called?
Hepatocytes
What is glycogenesis?
The conversion of glucose into glycogen by the liver, which can store 75-100g of glycogen
What is glycogenolysis?
The breakdown of glycogen to glucose by the liver. The glucose diffuses into the blood to restore normal blood glucose concentration.
What is gluconeogenesis?
The production of glucose from sources other than carbohydrate when glycogen supply is exhausted e.g. glycerol and amino acids
Name the three sources of blood glucose
- Directly from the diet absorbed following carbohydrate hydrolysis
- Hydrolysis in the small intestine of glycogen (glycogenolysis) stored in the liver and muscle cells
- Gluconeogenesis
How do beta (B) cells work and what does insulin bring about?
B-cells detect rise in blood glucose so secrete insulin into blood plasma. The insulin bind to glycoprotein receptors, which causes:
1. a change in the tertiary structure of glucose transport carrier proteins, which allows move glucose into cells by facilitated diffusion
2. an increase in the number of carrier proteins which transport glucose in the plasma membrane by fusing the protein-containing vesicles with the plasma membrane
3. activation of enzymes to convert glucose to glycogen and fat
In what 4 ways is blood glucose concentration lowered?
- By increasing the rate of absorption of glucose into cells, especially muscle cells
- By increasing the respiratory rate of cells
- By increasing the rate of glycogenesis
- By increasing the rate of conversion of glucose to fat
Describe the role of glucagon and the alpha (a) cells of the pancreas
Alpha cells detect fall in blood glucose, which triggers secretion of glucagon into the blood plasma. Glucagon:
1. Attaches to protein receptors on liver cell membrane
2. Activates enzymes that convert glycogen to glucose
3. Activates enzymes for gluconeogenesis
This will increase the glucose concentration and cause the alpha cells to reduce glucagon secretion (negative feedback)
Outline the role of adrenaline in blood glucose regulation
At times of excitement or stress, adrenaline is produced by the adrenal glands, which raises the blood concentration by:
1. Attaching to protein receptors on the target cell membrane
2. Activating enzymes which breakdown glycogen into glucose
