General Physiology MBBS 1st Year One Shot

General Physiology is one of the most important subjects in the first year of MBBS. It builds the base for understanding how the human body works. Many clinical subjects later depend on these concepts. So, a clear understanding at this stage is very important.

This one shot revision helps you revise key topics. It focuses on important areas that are often asked in exams. The aim is to help you understand concepts and not just memorize them.

Introduction to General Physiology

General Physiology explains how cells, tissues, and organs function. It also explains how different systems work together to maintain balance in the body.

The subject mainly focuses on:

• Body fluid compartments

• Cell membrane structure

• Transport mechanisms

• Homeostasis

These topics are important for both theory and clinical understanding.

Body Fluid Compartments

The human body contains a large amount of water. This is called Total Body Water (TBW). In a normal adult male, it is about 60% of body weight.

Distribution of Body Fluids

Total body water is divided into two main parts:

• Intracellular Fluid (ICF): This is the fluid inside the cells. It forms about two-thirds of total body water.

• Extracellular Fluid (ECF): This is the fluid outside the cells. It forms about one-third of total body water.

Subdivisions of ECF

Extracellular fluid is further divided into:

• Interstitial Fluid: Present between cells

• Plasma: Present in blood

There is also a small amount of fluid called transcellular fluid. It is found in body cavities like:

• Pleural cavity

• Pericardial cavity

• Synovial joints

Variation in Body Fluids

Body fluid distribution changes with age and gender.

• Women have slightly less water than men due to higher fat content

• Children have more extracellular fluid than adults

Because of this, children lose water faster and are more prone to dehydration.

Measurement of Body Fluid Volume

Body fluid volumes are measured using the Indicator Dilution Method.

Here:

• V = Volume

• I = Amount of indicator

• C = Concentration

Different indicators are used for different compartments:

• Total body water → Heavy water

• ECF → Inulin

• Plasma → Evans blue dye

Disturbances in Body Fluids

Fluid imbalance can disturb normal body function. It is mainly of two types:

Dehydration

Loss of water from the body.

Types:

• Isotonic dehydration → Equal loss of water and sodium

• Hypertonic dehydration → More water loss than sodium

• Hypotonic dehydration → More sodium loss than water

Overhydration

Excess water in the body.

Types:

• Isotonic overhydration

• Hypertonic overhydration

• Hypotonic overhydration

Water moves between compartments to maintain balance. This movement depends on an osmotic gradient.

Homeostasis

Homeostasis means maintaining a stable internal environment. It mainly refers to the stability of extracellular fluid.

All body systems help in maintaining homeostasis:

• The heart and lungs control oxygen and carbon dioxide

• Kidneys remove waste

• The digestive system provides nutrients

• The nervous and endocrine systems regulate functions

Control Mechanisms

Homeostasis works through control systems.

Each system has:

• Controlled variable

• Sensor

• Controller

• Effector

Types of Control

1. Feedback Control

This is the most common type.

• Negative Feedback
  It reduces change and brings the system back to normal

Higher gain means better control.

• Positive Feedback
  It increases change
  It continues until a specific event stops it

Examples:

• Childbirth

• Blood clotting

Cell Membrane Structure

The cell membrane controls the movement of substances.

It follows the Fluid Mosaic Model.

Main components:

• Lipids

• Proteins

• Carbohydrates

Lipids

• Form a bilayer

• Provide structure

• Cholesterol controls fluidity

Proteins

Two types:

• Integral proteins

• Peripheral proteins

They help in transport and communication.

Carbohydrates

• Present on the surface

• Help in cell recognition

Junctional Complexes

Cells are connected by special junctions:

• Desmosomes → Provide strength

• Gap junctions → Allow passage of ions

• Tight junctions → Prevent leakage

Transport Mechanisms

Substances move across the cell membrane in different ways.

1. Passive Transport

No energy is required.

Diffusion

Movement from high concentration to low concentration.

Types:

• Simple diffusion

• Facilitated diffusion

Factors affecting diffusion:

• Concentration gradient

• Temperature

• Surface area

• Membrane thickness

2. Facilitated Diffusion

• Uses carrier proteins

• Shows saturation

Example:

• Glucose transport

Active Transport

Requires energy (ATP).

Moves substances against the concentration gradient.

Types:

• Primary active transport

• Secondary active transport

Sodium-Potassium Pump

This is a very important concept.

Functions:

• Maintains ion balance

• Prevents cell swelling

• Helps in nerve impulse transmission

It works continuously in all cells.

Vesicular Transport

This involves movement using vesicles.

Endocytosis

• Substance enters the cell

Types:

• Phagocytosis

• Pinocytosis

Exocytosis

• Substance leaves the cell

Examples:

• Hormone release

• Neurotransmitter release

Important Exam Points

• Focus on understanding concepts

• Practice diagrams and flowcharts

• Revise short notes regularly

• Link theory with clinical examples

Concept clarity is more important than writing long answers.

General Physiology forms the base of medical science. It explains how the body maintains balance and performs functions. Topics like body fluids, membrane structure, and transport systems are very important.

A clear understanding of these concepts helps in exams and clinical practice. Regular revision and simple understanding can improve performance and confidence.