HOMEOSTASIS BASIC CONCEPTS

                                                            HOMEOSTASIS

The protection of internal environment from the harms of fluctuations in external environment & keeping internal conditions in a narrow range with various control systems is termed as homeostasis.

External Environment:

External environment (surroundings of an organism) and its components fluctuate continuously like temperature, amount of solutes and amount of water etc.

Internal environment:

Each organism of a species due to its evolutionary history has assumed, a specific set up of internal environment at various levels of organization suitable to its external environment.

Most susceptible components of internal environment that may be affected by fluctuations in external environments are water, solutes and temperature.

Mechanism of Homeostasis:

Homeostasis does not mean to keep a fixed internal environment as changes are maintained within a narrow range which is necessary for normal body functions.

Example:

 For example, water availability can fluctuate greatly for the organisms in the external environment from abundant supply to almost dry conditions, however, the quantity of water in the body (internal environment) may vary in response to abundant supply and also to dry condition, but in a narrow range. The control systems would not let the body,

·        1. Flooded with water in abundant supply

·       2.  Dehydrate in dry conditions.

Furthermore, adaptation to lower level of range in dry conditions and to higher level of range in abundant supply of water is good for the organism to feel normal within internal

fluctuations forced by drastic external fluctuations.

Types of Homeostasis:

There are three types of homeostasis;

·         Thermoregulation

·         Osmoregulation

·         Excretion

Thermoregulation:

The mechanism of regulation of internal temperature within a tolerable range is termed as thermoregulation.

Osmoregulation:

The mechanism of regulation , of solute and the gain and loss of water between organism and its environment is termed as osmoregulation.

Excretion:

The mechanism which eliminates harmful nitrogenous waste is termed as excretion.

Mechanism of excretion depends upon the availability of water.

Homeostasis at cell Level in multicellular organism:

Internal environment of an organism at cell level, with in a cell membrane also keeps fluctuating as compared to extracellular environment (vascular and other interstitial fluids). Here, in addition to solute and water various essential metabolites, hormones etc. are kept in a required range.

Inverse effector Response:

Type of feedback mechanism in which effector shows inverse response to the stimulus to protect an organism from fluctuations in external environment is called inverse effector response.

Comparison with physical system:

Living control systems work exactly on the mechanism of physical control system. It has three components:

·         Receptor

·         Control Center

·         Effector.

WORKING OF PHYSICAL SYSTEM:

In a physical control system e.g. temperature control system, there is a sensor (thermometer) that monitors temperature change from a set point and signals to control centre to take action by switching on heater or cooling units in response to drop or rise in the temperature compared to set point.

CONTROL SYSTEM IN LIVING ORGANISMS:

Similar to it in living system there is set point in temperature regulated (endothermic) animals. The receptors (sensor) detect temperature change, e.g. of increase and signal to control Center for action of cooling systems and the vice versa. Detection of change and signaling for effector’s response to control system is a feedback mechanism. In these processes there is an inverse effector’s response to the change in external environment as there is generally cooling effector’s response to warmth sensing in external environment, thus are termed as negative feedback.