Introduction To Human Body

Human body or human beings are the complex organisms on this planet. Human body is consisting of billions of microscopic parts and each having its own identity, working together in an organized and systematic manner for the benefit of total being. Human body is a single structure but made up of billions of smaller structures from which the four major are- cells, tissue, organ and system.


Anatomy is defined as the study of structure of the body and their physical relationship.


Physiology is defined as the study of how the body work and how they cooperate together to maintain life and health of the individual.

Levels of structural Organization and body systems

Within the body there are different levels of structural organizations like;

  • Cell
  • Tissue
  • Organs
  • System


Cells are the smallest functional units of the body. Human body develops from single cell called zygote. Individual cells are too small to be seen with the naked eye. A cell is made up of plasma membrane which contains a number of organelles floating inside it in a watery fluid called as cytosol.

These organelles are very small in size with highly specialized functions. Some examples of these organelles include; nucleus, mitochondria, ribosomes, Golgi complex, lysosomes, endoplasmic reticulum, microfilaments and microtubules.


The tissues of the body are made up of large number of cells and they are classified according to the size, shape and functions of these cells.

There are four main types of tissue; epithelial tissue, connective tissue, muscle tissue and nervous tissue.


The organs of the body are consisting of different types of tissues which are made up of different types of cells. Some examples of the organs; liver, heart, eyes etc.

introduction to human body
introduction to human body


Body systems can define as group of organs and tissues that works together to perform important functions for the body. There are some organs in the body which are the part of more than one body system. There are total eleven body systems in human body.

Integumentary system, Respiratory system, Excretory system, Circulatory system, Urinary system, Endocrine system, Nervous system, Exocrine system, Musculoskeletal system, Lymphatic system, Reproductive system.

Basic life processes

The all living organisms have some characteristics that differs them from non-living organisms. The basic process of life includes organization, metabolism, responsiveness, movements and reproduction.

In humans basic life process is more complex than other living organisms, which includes growth, differentiation, respiration, digestion and excretion. All body cells, organs and systems work together and all of these processes are related to each other.

Brief description of life process

  • Organization

As the name suggest organization means getting coordinated with each other. Each component has its own duty to perform in an organization system. If single cell loses its integrity or organization, it will die.

  • Metabolism

Metabolism is defined as the total of the chemical reactions that occur in the body which is mainly due to the group of processes of which, first is anabolism and second is catabolism.

Anabolism– It refers to building or synthesizing large complex substances.

Catabolism– It refers to breaking down complex substances to simpler building blocks which releases the energy. These substances act as raw material for anabolism.

  • Responsiveness

When the change occurs in the external and internal environment, the identification and reaction to that change is called responsiveness. It is also called as the act of sensing a stimulus and responding to it.

  • Movement

There are many types of movements within the body. Movement of the whole body or any part of it is very important for obtaining food, avoiding injury and reproduction. Some of the body movement is under voluntary control and most of under involuntary control.

  • Reproduction

Reproduction refers to the formation of new person or organism. Successful reproduction is essential to ensure the continuation of a species from one generation to the next.

Sexual and Asexual are the two main types of reproduction.

  • Growth

Growth can be identified by the increase in size either through an increase in the number of cells or through an increase in the size of each individual cell. At cellular level in order for growth to occur, anabolic processes must occur at faster rate than catabolic processes.

  • Differentiation

It is a developmental process through which unspecialized cells change into specialized cells with special structural and functional characteristics. By this process cells develop into tissues and organs.

  • Respiration

Respiration is defined as the exchange of gases mainly oxygen and carbon dioxide between the cells and the external environment. Respiration is very important part of the body system. Cellular respiration deals with the cell’s utilization of oxygen and release of carbon dioxide in its metabolism.

  • Digestion

Digestion is the process that breaks down chemically complex ingested food into simple molecules that can be absorbed into the circulation and then used by the body cells.

  • Excretion

It is the process of removal of waste products of digestion and metabolism from the body. The waste products from digestive system are excreted through faeces. Many excreted products are toxic and harmful to life.


Homeostasis is defined as the state of steady internal, physical chemical and social conditions maintained by living systems.

Homeostasis is a self-regulating internal process by which an organism tends to maintain stability while adjusting to conditions that are best for its survival. When this balance is lost there is a serious risk to the well-being of the individual. Homeostasis is maintained by control systems which detect and responds to changes in the internal environment.

Control system has three basic components; detector, control centre and effector. The control centre determines the limits within which the variable factor should be maintained. It receives an input from the detector or sensor, and combines the incoming information.

When the incoming signal indicates that an adjustment is needed the control centre responds and its output to the effector is changed. This is the whole dynamic process that maintains homeostasis. Most of the homeostasis controls in the body use negative feedback mechanism to prevent sudden and serious changes in the internal environment.

Basic anatomical terminology

Before learning in more detailed about the topics of different human body systems, it is necessary to know about same basic useful terms to describe body structure.

  1. Directional terms
  2. Planes of the body
  3. Body cavities

1. Directional terms

It describes the positions of structures relative to structures or locations in the body.

  • Superior or cranial– It means towards the head of the body or upper. Ex-hand
  • Inferior or caudal– It means away from head or lower. Ex- foot
  • Anterior or ventral– front part. Ex – kneecap
  • Posterior or dorsal– back part. Ex – shoulder blades
  • Medial – towards the midline of the body. Ex –middle toe
  • Lateral– away from the midline of the body. Ex –little toe
  • Proximal – towards or nearest to the trunk. Ex- the proximal end of the femur joins with the pelvic bone.
  • Distal – away or farthest from the trunk. Ex – the hand is located at the distal end of the forearm.

 2. Planes of the body

  • Coronal plane or frontal plane– A vertical plane running from side to side; divides the body or any of its parts into anterior and posterior portions.
  • Sagittal plane or lateral pane– A vertical plane running from front to back; divides the body or any its parts into right and left sides.
  • Axial plane or transverse plane– A horizontal plane; divides the body or any its parts into upper and lower parts.
  • Median plane– Sagittal plane through the midline of the body; divides the body or any of its parts into right and left halves.

3. Body cavities

The cavities of the body contain organs or some organs contains cavities. There are two main body cavities namely ventral and dorsal body cavities. The ventral is larger cavity whereas dorsal is smaller cavity.

Ventral cavity

It is subdivided into two parts by the diaphragm namely thoracic cavity and abdominopelvic cavity.

  • Thoracic Cavity– It also called as upper central, thoracic or chest cavity contains the heart, lungs, trachea, esophagus, large blood vessels and nerves. Thoracic cavity bound laterally by the ribs and diaphragm.
  • Abdominal and pelvic cavity– The lower part of the ventral abdominopelvic cavity can be divided into two portions; abdominal portion and pelvic portion.

Abdominal cavity contains most of the gastrointestinal tract, kidneys and adrenal glands. The abdominal cavity bound cranially by the diaphragm, laterally by the body wall and caudally by the pelvic cavity.

Pelvic cavity contains most of the urogenital system a rectum. The pelvic cavity is bounded cranially by the abdomen cavity, dorsally by the sacrum and. Laterally by the pelvis.

Dorsal cavity

Dorsal cavity contains organs lying more posterior in the again can be divided into two portions. The upper portion and lower portion. Upper portion contains the brain whole lower portion contains spinal cord.

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