Homeostasis and hormones

Question 1

What is homeostasis

Answer 1

The maintenance of an internal environment within restricted limits in organisms.

Question 2

What is the environment surrounding cells

Answer 2

Tissue fluid

Question 3

How do humans maintain a stable internal environment for the body cells

Answer 3

• Maintaining the features of tissue fluid at optimum levels to protect the cells from changes in the external environment.
• This involves features such as chemical make-up, volume and others.

Question 4

Describe three key reasons why homeostasis is essential for the proper functioning of organisms

Answer 4

1) The enzymes that control the biochemical reactions within cells, and other proteins such as channel proteins, are sensitive to changes in pH and temperature.Any change to these factors could slow the action of these enzymes our denature them.
2) Changes to the blood water potential of the blood and tissue fluids may cause cells to shrink and expand as a result of the movement of water by osmosis which stops the cells from operating normally- so blood water potential and glucose concentration must be controlled.
3) Organisms with the ability to maintain a constant internal environment are more independent to changes in the external environment so may have a greater geographical range (to find food,water etc).

Question 5

List the stages that the control of any self-regulating system involves

Answer 5

1) The optimum point: the point at which the system operates best. This is monitored by a receptor.
2) Receptor: this dates any deviation from the optimum point (stimulus) and informs the coordinator
3) Coordinator: Coordinates information from receptors and sends instructions to an appropriate effector.
4) Effector: A muscle or gland which brings about the changes needed to return the system to the optimum point. This return to normality creates a feedback mechanism.
5) Feedback mechanism: the mechanism by which a receptor responds to a stimulus created by the change to the system brought about by the effector.

Question 6

What control mechanism do most organisms use

Answer 6

Negative feedback

Question 7

Describe simply what negative feedback is

Answer 7

When the change produced by the control system leads to a change in the stimulus detected by the receptor and turns the system off.

Question 8

What is positive feedback

Answer 8

Positive feedback occurs when a deviation from an optimum causes changes that result in even greater deviation from the normal.

Question 9

What is an example of positive feedback

Answer 9

• In neurones when a stimulus leads to a small influx of sodium ions.
• This influx increases the permeability of the neurone membrane to sodium ions, so more ions enter, causing a further increase in permeability and even more rapid entry of ions.

Question 10

Why is it important that control systems have many receptors and effectors, allowing them to have separate mechanisms that each produce a movement towards an optimum

Answer 10

• This allows the body a greater degree of control over the factor being regulated.
• It is important to ensure that the information provided by receptors is analysed by the coordinator before action is taken.

Question 11

Why is it important that the negative feedback mechanism for the control of blood glucose concentration has separate feedback mechanisms

Answer 11

• Glucagon needs to be secreted if blood glucose concentration is low
• Insulin needs to be secreted if blood glucose concentration is high.

Question 12

What is an example of when positive feedback is harmful

Answer 12

Hyperthermia

Question 13

What are three characteristics universal to all hormones

Answer 13

• they are produced in (endocrine) glands which secrete the hormone directly into the blood.
• they are carried in the blood plasma to the cells on which they act- known as target cells- which have specific receptors on their cell-surface membranes that are complementary to a specific hormone.
• they are effective in very low concentrations, but often have widespread and long-lasting effects.

Question 14

What mechanism of hormone action do you need to know

Answer 14

The second messenger model

Question 15

What two hormones involved in the regulation of blood glucose concentration use the second messenger model of hormone action

Answer 15

Adrenaline and glucagon

Question 16

Describe the mechanism for adrenaline action by the second messenger model of hormone action

Answer 16

• Adrenaline binds to a transmembrane protein receptor within the cell surface membrane of a liver cell.
• The binding of adrenaline causes the protein to change shape on the inside of the membrane.
• This change of protein shape leads to the activation of an enzyme called adenyl cyclase.
• The activated adenyl cyclase converts ATP to cyclic AMP (cAMP).
• The cAMP acts as second messenger that binds to a protein kinase enzyme, changing its shape and therefore activating it.
• The active protein kinase enzyme catalyses the conversion of glycogen to glucose which moves out of the liver cells by facilitated diffusion and into the blood, through channel proteins.