Homeostasis (Homeo-Sameness, stasis – standing still). Homeostasis is the situation (condition) of equilibrium or balance inside the environment of the body due to the constant interaction of many regulatory processes.
It is a dynamic condition because when the body undergoes in a changing state, the equilibrium can shift points in a narrow range that is compatible with maintaining life.
(i) The level of glucose in our blood normally stays between 70gm and 110 mg per 100 ml of blood.
(ii)Every organ or structure of our body from the cellular level to the systematic level plays a vital role in keeping the internal environment normal.
Homeostasis and body fluids
An important function of homeostasis is maintaining the volume and composition of body fluids that are dilute, watery solution containing dissolved chemicals that are found inside that cell as well as outside the cell.
The fluids which are present inside the cells are called intracellular fluid (ICF), and the fluids present outside of the cells are called extracellular fluid.
The ECF (extracellular fluid) that fills the narrow space between cells and tissues is known as interstitial fluid.
ECF present within the blood vessels is known as blood plasma within lymphatic vessels it is termed as lymph, in the brain and spinal cord it is known as cerebrospinal fluid, in joint it is synovial fluid. The ECF (extracellular fluid) of the eyes is called aqueous humor and vitreous body.
The proper functioning of the cells depends upon the fluids which are surrounding them. Because of these, interstitial fluid is often called the body’s internal environment. The composition or distribution of interstitial fluid changes as substances moves back and forth between it and blood plasma.
This exchange of material takes place across the thin wall of the smallest blood vessels called the blood capillaries.
The exchange of material in both directions across blood capillaries provides needed materials such as glucose, oxygen ions, and so on to tissue cells, it also removes wastes, such as carbon dioxide, from interstitial fluid.
Control of Homeostasis
Homeostasis in the human body is always disturbed due to some external environmental factors (like intense heat during summer or lack of enough oxygen after 2 miles of running) and for some internal environmental factors (like high or low glucose level).
In some cases, the homeostasis imbalance is also due to our social environment like stress, work pressure, etc.
In most of the cases, the imbalance of homeostasis is mild and temporary. In some cases, it is intense as the body has many regulating systems that can usually balance the internal environment. The nervous system regulates homeostasis by sending an electrical signal known as nerve impulses to organ (work immediately). The endocrine system consists of many glands that secrete messenger molecules called hormones into the blood (work slowly). Both the nerve system and endocrine system work for the same, usually through a negative feedback system.
A feedback system (feedback loop) is a cycle of an event in which the status of a body condition is monitored, changed, evaluated, re-evaluate, and so on.
A feedback system includes three basic components-:
- Control center, and
Each monitored variable, such as blood pressure, body temperature, or blood glucose level, is known as a controlled condition. Any disturbance that changes a controlled condition is termed as a stimulus.
A receptor may be a structure that advises or monitors changes during a controlled condition and sends input to a control center within the form of nerve impulses or chemical signals.
(ii) Control center
A control center in the body, e.g., the brain sets the range of values within which a control condition should be maintained and evaluates the input it receives from receptors and generates output commands when they are needed .output from the control center typically occurs as nerve impulses, or as hormones or other chemical signals.
(iii) An effecter
An effecter is a structure that receives output from the control center and produces or releases a response or effect that changes the balanced condition. Nearly about every tissue or organ in the body can act as an effecter.
Example of Feedback System
When your body temperature drops continuously, your brain (control center) sends nerve impulse (output) to your skeletal muscle (effecter) after that body generates a balanced heat and raises your body temperature.
A group of receptors and effectors communicating with their control center from a feedback system that can maintain the internal environment of our body.
In the feedback system, the imbalance of the internal environment can control either by negating it (negative feedback) or enhancing it (positive feedback).
A negative feedback system reverses a change in a very controlled condition.
For example, blood pressure (BP) Blood pressure is the force exerted by blood as it presses against the walls of blood vessels.
If some internal or external stimulus cause BP to rise following events occurs
Baroreceptors (the receptors ) pressure-sensitive nerve cell located within walls of blood vessels detect the higher pressure(BP) the baroreceptor send a nerve impulse to the brain (control center), which interprets the impulses and responds by sending nerve impulses to heart and blood vessels (the effecter). Heart rate decreases and blood vessels widen, which causes BP to decrease. This sequence of events quickly returns the controlled condition blood pressure to normal, and homeostasis is restored.
Positive feedback system
A feedback system tends to strengthen or reinforce a change in one of the body controlled conditions. It is similar to a negative feedback system, except for the way the response affects the controlled condition.
The control center still provides commands to an effector, but this time the effectors produce a physiological response that adds to or reinforces the initial change in the controlled condition.
The action or activity of a positive feedback system continues until it is interrupted by some mechanism.
Example – Blood lost from the body.
Importance of homeostasis
- The term homeostasis coined by Walter cannon
- Hemostats help to maintain our internal body environment.
- It helps to remove body waste.