1 . Homeostasis is the maintenance of a constant internal environment.
2 . For any homeostatic control to occur there must be:
- a stimulus which is a change in the internal environment,
- a receptor which can detect the stimulus,
- an automatic or self-regulatory corrective mechanism, which bring about a negative feedback.
3 . Homeostasis may include the regulation of the following:
- Blood glucose level,
- Blood water potential,
10.2 Blood glucose regulation.
1 . The regulation of blood glucose level is done by the pancreas.
2 . Homeostatic control of blood glucose level:
Fig.10.1 Homeostatic control of blood glucose level.
3 . The two hormones, insulin and glucagon have different effects on the glucose level in the blood. They are produced by the same region of the pancreas, the islets of Langerhans, but by different cells. Their secretion into the blood is controlled by the negative feedback mechanism depicted in Figure 10.1.
4 . Insulin converts glucose to glycogen which reduces the blood glucose level.
5 . Glucagon converts glycogen to glucose which increases the blood glucose level.
10.3 Regulation of blood water potential.
1 . The regulation of blood water potential is done by the kidneys.
2 . Homeostatic control of water potential:
Fig.10.2 Homeostatic control of water potential.
3 . On a cold day, if you don’t sweat, you’ll produce more urine which will be pale and dilute.
4 . On a hot day, you sweat a lot, your urine will be dark-coloured, concentrated and little of it.
10.4 Temperature regulation.
1 . The regulation of temperature is done by the skin.
2 . The skin:
Fig.10.3 The structure of the skin.
3 . When the body is exercising vigorously or when the surrounding is hot:
- Thermoreceptors in the skin detect an increase in environmental temperature or heat sensors in the hypothalamus detect a rise in the temperature of the blood.
- The sweat glands increase the production of sweat.
- Vasodilation, increases the internal diameter of blood vessels so that more blood is brought to the capillaries.
- Body loses heat as sweat evaporates.
- Body loses heat as more blood is brought to the skin surface, leading to increased heat loss by conduction, convection and radiation.
- Metabolic rate is lowered leading to the decreased heat production by cells.
- Body temperature is lowered.
4 . When the body is at rest or when the surrounding is cold:
- Thermoreceptors in the skin detect decrease in the environmental temperature or heat sensors in the hypothalamus detect drop in temperature of blood.
- The sweat glands stop production of sweat.
- Vasoconstriction, reduces the internal diameter of blood vessels so that less blood is brought to the capillaries.
- Body gains heat as erector muscles in the skin contract causing the hairs to stand up, creating a layer of air which will act as insulation.
- Skeletal muscles contract and relax repeatedly; this shivering resulting in production of heat.
- Less blood is brought to the skin surface so that less heat will be lost.
- Metabolic rate is raised leading to increased heat production by cells.
- Body temperature is raised
5 . The skin is:
- A waterproof structure;
- One of the organs of the sense of touch.
6 . The skin has three parts:
- I. Cornified layer;
- II. Granular Layer;
- III. Malphigian Layer.