Homeostasis

Homeo = Same, Stasis = standing. It refers to the maintenance of constant internal environment of the body.

• Claude Bernard (French physiologist) first proposed the idea as “milieu interieur” (internal environment).
• Walter B. Cannon (American physiologist) gave the term homeostasis in 1930.

Internal environment in the body is the extracellular fluid (ECF). It is the fluid outside the cell and in which the cells live. ECF includes blood plasma, interstitial fluid and transcellular fluid.

• Blood plasma is the liquid portion of blood.
• Interstitial fluid is the fluid present between tissue cells.
• Transcellular fluid is the fluid secreted by epithelial cells and stored in body cavities. Examples: CSF, Synovial fluid, Aqueous and vitreous humour, Pleural, pericardial, peritoneal fluid, digestive juices, urine withinR kidney tubules etc.
• ECF contains nutrients, ions and all other substances necessary for the survival of the cells.

Homeostasis forms basis of physiology because the body works properly only when all functions stay within a normal range. If any function goes above or below this range, the body automatically tries to bring it back to normal. Doctors also use this concept to understand diseases by identify deviation in homeostasis.

Components of Homeostatic System

Homeostatic system in the body acts through self-regulating devices. It operates in a cyclic manner. This cycle includes four components:

1. Sensors or detectors, which recognize the deviation.
2. Transmission of this message to a control center.
3. Transmission of information from the control center to the effectors for correcting the deviation.
4. Effectors, which correct the deviation.

Role of Various Systems of The Body in Homeostasis

Homeostasis is maintained by the coordinated action of several body systems. Some of the major functions where homeostatic mechanism are clearly established are:

1. Regulation of pH

• The pH of ECF must be maintained at 7.4.
• Any decrease (Acidosis) or increase (Alkalosis) severely affect tissues.
• System involved:
  • Respiratory System: Regulates CO₂ (major acid).
  • Blood Buffers: Immediate Regulation.
  • Kidneys: Long term acid base balance.

2. Regulation of Body Temperature

• Normal body temperature is 37.5^oC.
• Any change affects metabolic activities.
• Systems involved:
  • Skin (Sweating, vasodilation, vasoconstriction)
  • Respiratory System (Heat loss during breathing)
  • Digestive System
  • Excretory System
  • Skeletal Muscles (Shivering generates heat)
  • Nervous System (Hypothalamus as temperature-regulating center).

3. Regulation of Nutrient Supply

• Cells require nutrients for energy, growth, and metabolism.
• Nutrients must be digested, absorbed, transported, and supplied to tissues.
• Systems involved:
  • Digestive System: Digestion and absorption.
  • Circulatory System: Transport of nutrients to cells.

4. Regulation of Oxygen Supply and Waste Removal

• Cells need a continuous supply of oxygen for metabolism.
• Carbon dioxide and other metabolic wastes must be removed.
• Systems involved:
  • Respiratory System: Exchange of O₂ and CO₂.
  • Kidneys and Other Excretory Organs: Remove nitrogenous wastes and toxins.

5. Hormonal Regulation

• Hormones control metabolism, growth, electrolyte balance, reproduction, etc.
• Proper synthesis, releases, and action of hormones are essential.
• System involved:
  • Endocrine system

6. Water and Electrolyte Balance

• Maintaining proper water level and electrolyte concentration prevents:
  • Dehydration
  • Water toxicity
  • Changes in osmolality
• System involved:
  • Kidneys: Major regulator
  • Skin: Sweating
  • Salivary Glands
  • Gastrointestinal Tract

7. Role of Blood

• Blood forms a major part of the internal environment.
• It must contain:
  • Normal RBC count
  • Adequate plasma with normal composition
• Functions:
  • Trnasport of nutrients
  • Transport of gases (O₂/CO₂)
  • Carrying metabolic wastes
  • Maintaining internal consistency.

8. Role of Skeletal Muscles

• Help the organism move to obtain food and escape harmful conditions.
• Generate heat during activity and shivering.
• Protect the body from injury.

9. Role of the Central Nervous System (CNS)

• CNS = Brain + Spinal Cord
• Functions:
  • Sensory system detects changes in internal and external environment.
  • Brain integrates information and makes decisions.
  • Motor system executes responses to avoid damage and maintain stability.

10. Role of the Autonomic Nervous System (ANS)

• Regulates involuntary and vegetative functions, including:
  • Heart rate
  • Blood pressure
  • Respiration
  • Digestion
  • Temperature regulation
• Essential for moment-to-moment homeostasis.