Homeostasis

1. Homeostasis Prof. K. Sivapalan

2. Environment. • Unicellular organisms exchang nutrients and wastes with the environment. • They moved in the environment towards nutrients and away from wastes and poisons • Multicellular organisms also must exchange the same with environment. • But the functional unit of the body is the cell. • Each cell cannot exchange with environment directly. • The space surrounding each cell is the internal environment. • This space is named extra cellular space.

3. Internal environment. • It is a potential space with extra cellular fluid and inter-cellular substance. • The cells are kept in place by the intercellular substance and specific unions or junctions between cells. • Intercellular substance contains mainly hyaluronic acid which is a ‘gel’. • It allows free movement of water as in space. • This space contains a fluid which simulates the sea in which unicellular organisms evolved. • This fluid, known as extra cellular fluid [ECF], fills the internal environment. • As the cells cannot move, the fluid must be in constant motion to bring nutrients to the cells and take the wastes away.

4. Maintaining the constancy • The cells take all nutrients for their needs from ECF. • All wastes from the cells go into this fluid. • Nutrients taken must be replaced and wastes removed from this fluid. • Otherwise the amount of nutrients can be depleted and the wastes can accumulate to toxic levels leading to death. • Maintaining the constancy of the internal environment [maintaining constant conditions in the internal environment] is known as ‘Homeostasis’.

5. Systems for homeostasis. • The body has several systems to provide nutrients and to remove wastes and control mechanisms to regulate their activity. • Lungs provide oxygen and excrete carbon dioxide. • Gastrointestinal tract provides nutrients for growth and energy. • Kidneys remove water soluble wastes from the body. • Liver removes fat soluble wastes, poisons and toxins. • Skin excretes excess heat. • Musculo-skeletal systems provide mobility to obtain nutrients and physical protection. • Immune system provides protection from micro-organisms.

6. Transport within the body • All these organs are placed in various parts of the body and the substances had to be transported from place to place. • Blood is the medium of transport and the circulatory system keeps the blood flowing. • The internal environment exchanges the nutrients, wastes, electrolytes and water with blood as it moves through the tissues.

7. Regulation and coordination • Many internal external factors influence the functions of the systems and the constituents of the body and body fluids. • The amounts of these substances in the blood and the functional status of the systems are monitored by specific receptors. • These receptors provide necessary input to the control centers in the nervous system and endocrine system. • The efferents from the nervous system and the hormones from endocrine glands regulate the effectors and coordinate them to maintain the constancy of the internal environment.

8. Neurological Control Receptor Afferent Centre Parameter Efferent Response Gland Muscle

9. Hormonal Control. - Secretion of hormone. + Positive Feed Back Metabolite Negative feed back. + + Response.

10. Continuity of the community. • All the above systems ensure healthy life of the individual. • However, aging and death are inevitable. • Reproductive system ensures the continuity of the life of the community.