Biology- Communication and Homeostasis

> Normal blood glucose conc. is 90mg/ 100cm-3.

If the blood glucose level rises too high:

> Detected by beta cells in the Islets of Langerhans, which then secrete insulin into the blood.

> The target cells are hepatocytes (liver cells) and muscle cells.

> When blood passes insulin binds to the receptors, activating adenyl cyclase inside the cell to turn ATP to cAMP inside the cell, triggering a series of enzyme-controlled reactions.

> Concentrations are lowered by:

- More glucose channels placed on cell surface membranes. - More glucose used in respiration.  - More glucose converted into fats.  - Glycogenesis = glucose converted to glycogen in cells for storage. 

If the blood glucose level drops too low:

> Detected by alpha cells in the Islets of Langerhans, which secrete glucagon into the blood. 

> The target cells are hepatocytes (liver cells), which possess the specific receptor for glucagon.

> Concentrations are increased by:

- Glycogenolysis = glycogen converted to glucose in cells.      - Use of more fatty acids in respiration.                   - Gluconeogenesis = the production of glucose by conversion from amino acids and fats.

Fall in core temperature (37 C):

> Thermoregulatory centre in hypothalamus detects change

> Nervous system and hormonal system carry signals to the skin, liver and muscles

> More heat generated and less heat lost

> Responses include: 

- Increased rate of metabolism in order to release more heat.  - Release of heat through extra muscle contraction.  - Decreased loss of heat to the environment. 

Rise in core temperature (37 C):

> Thermoregulatory centre in hypothalamus detects change

> Nervous system and hormonal system carry signals to the skin, liver and muscles

> Less heat generated and more heat lost

> Responses are the opposite to above