Chpater 16: Homeostasis Flashcards
Where is insulin secreted from?
insulin is secreted by ß cells
Where is glucagon secreted from?
glucagon is secreted by alpha cells
Where are the beta-cells and alpha-cells found?
Insulin and glucagon are secreted from beta-cells and alpha-cells which are clusters of cells in the islets of Langerhans which are found in the pancreas
What are the effects of insulin?
Insulin has 3 effects:
- increases the cell-membrane permeability of muscles cells to glucose
- stimulates glycogenesis
- increases rate of respiration
What are the effects of glucagon?
Glucagon has 3 effects: 1. stimulates glycogenolysis 2. stimulates gluconeogenesis 3. decreases rate of respiration
When is insulin secreted?
When blood glucose concentrations are too high such as after eating a meal high in carbs
When is glucagon secreted?
When blood glucose concentrations are too low such as after exercising or sleeping
When is adrenalin secreted?
When blood glucose concentrations are too low, when stressed and when exercising
What are the effects of adrenaline?
Adrenaline has 4 effects: 1. activates glycogenolysis 2. inhibits glycogenesis 3. activates glucagon secretion 4. inhibits insulin secretion
Explain the role of glucagon in the control of blood glucose concentration.
Glucagon is all about trying to get more glucose into the bloodstream because blood glucose conc. are too low. So it breaks down glycogen into glucose (glycogen-o-lysis) but it decreases the rate of respiration in liver cells so that more glucose is available for other cells. Same thing with adrenaline, which gets the body ready for action by providing muscles with more glucose for respiration.
How does insulin increase the permeability of muscle cell-membranes to glucose?
Insulin activates GLUT4 which is a protein channel in cardiac and skeletal muscle cells that transports glucose, by binding to receptors and triggering the movement of vesicles containing GLUT4 to the cell-membrane, where it fuses and where it is able to aid in the transport of glucose down its conc. gradient by facilitated diffusion
What type of feedback mechanism is involved in the control of blood glucose concentration? Give a reason for your answer.
Negative feedback. Because when BGC is too high, insulin is secreted to decrease it and bring it back to normal (90 mg per 100 cm 3) and when BGC is too low glucagon is secreted to increase it and bring it back to normal. Shorter: Because when BGC is too high or too low, hormones are secreted to bring it back to normal (90 mg per 100 cm 3).
Explain how adrenaline and glucagon act via a second messenger.
Adrenaline and glucagon act via a second messenger:
initial hormone-receptor complex
activates an enzyme
enzyme makes a secondary messenger
secondary messenger activates another enzyme
this enzyme carries out glycogenolysis
Explain how insulin works
1.
binds to specific receptors on liver cells and muscle cells
increases the number of channel proteins in cell memebranes
increasing the permeability to glucose
the cells take up more glucose
2
insulin activates enzymes in liver and muscle cells
enzymes carry out glyco-gen-esis - the making of glycogen
convert glucose to glycogen
cells able to store glycogen in cytoplasm
3.
insulin increases rate of respiration
esp. in muscle cells
Explain how glucagon works.
1.
glucagon binds to specific receptors on liver cells
activates enzymes to carry out
glycogen-o-lysis
break down of glycogen into glucose
2.
activates enzymes involved in carrying out
gluco-neo-genesis
forming glucose from non-carbohydrates
3
glucagon decreases the rate of respiration in cells
