| Understanding the basic anatomy and physiology of the human body | The organisation of the body | The cardiovascular system | The respiratory system | The musculoskeletal system | The nervous system | The sensory organs | Integumentary system | Digestive system | The urinary system | The reproductive system | Endocrine system | The immune and the lymphatic system | Resources |  

Understanding the basic anatomy and physiology of the human body

The organisation of the body

The human body is organised into various levels that begin at the very small and basic and come together to form the complete body whose different parts work in unison. This can be seen as a kind of ‘ladder’ going from the basic to the very complex.

At the simplest level, the body is comprised of atoms.

Atoms combine to form molecules to form cells, to form tissues, to form organs, to form body systems, to form the human body

Atoms to the human body

Activity 1

In this activity you will learn about the organisation of the body. Click here to begin.

Internal cavities

The body has two (2) sets of internal cavities that provide different degrees of protection to the organs that lie within them. These are the:

  1. Dorsal cavity that encases the brain and the spine.
  2. Ventral cavity which comprises the thorax (chest) – this encases the heart and the lungs and the abdominopelvic cavity which encases our abdominal organs and those of our reproductive system.


The body is also divided into regions. Examples of these include the:

Cells, tissues, organs and systems

The cell

The basic unit of body structure is the cell. All cells need food, water, and oxygen to live and function. As cells use or metabolise food and oxygen they give off carbon dioxide and other wastes. The cell is comprised of the cell membrane, which is the outer covering; it encloses the cell and helps it hold its shape.

The nucleus is the control centre; it directs the cell’s activities. Cytoplasm surrounds the nucleus. Organelles are structures that are suspended in the cytoplasm. The protoplasm refers to all structures, substances and water within the cell.

Chromosomes are threadlike structures within the nucleus. Each cell has 46 chromosomes. Chromosomes contain genes, which determine our physical and chemical makeup. (Sorrentino, 1997)

To review some the most common parts of the cell, click here and then roll you mouse over the image

Cell qualities

Although cells may be very different and highly specialised, they all have the same basic structure. They all have:

The cell membrane protects the cell and regulates the passage of materials into and out of the cell.

The nucleus is the control centre of the cell. DNA, which makes up the genes, is found within the chromatin granules and within the nucleolus is the RNA.

Organelles, which are structures found in the cytoplasm, are the:

Functions of the cell

  1. Respiration — all cells require oxygen to metabolise food.
  2. Ingestion and assimilation — cells are able to select chemicals from the surrounding fluid for their structure.
  3. Growth and repair — cells can synthesise new cytoplasm so that growth can occur and repair worn out parts.
  4. Excretion — waste products are eliminated into surrounding tissue to be transported by the blood for elimination via organs.
  5. Irritability and activity — cells are able to respond to stimuli. For example a stimulus causes a muscle to contract or relax.
  6. Metabolism — cells are able to break down and use substances from food as fuel.
  7. Reproduction — cells reproduce by simple division but some cells can never be replaced once destroyed. For example, central nervous system cells.

Activity 2

In this activity you will learn about the structure and function of cells. Click here


Groups of cells form tissues and there are four main types. The structure of tissues reflects their function.

Types Function Example













Epithelial tissue

This tissue covers the body surfaces and lines its cavities. Some specialise to form glands.

The functions of epithelial tissue include:

A gland is one or more epithelial cells specialised to produce and discharge substances.

Endocrine glands secrete have no ducts and secrete hormones directly into the bloodstream, for example pituitary gland.

Exocrine glands release their secretions through ducts, for example salivary and sweat glands.

Connective tissue

This tissue joins other tissues of the body together, supports the body and protects underlying organs.

Some main types are:

Muscular tissue

Muscle is composed of cells specialised to contract.

Skeletal muscle is striated (striped) and is under voluntary control.

Cardiac muscle is present only in the walls of the heart, is striated and is controlled by involuntary nerve messages from the brain.

Smooth muscle, also involuntary, is responsible for movement of food through the digestive tract, and changing the diameter of blood vessels.

Nervous tissue

Nervous tissue forms the brain, spinal cord and the nerves. The basic cell is called the neuron.

Specialised to receive stimuli and send impulses from one part of the body to another.


Groups of tissues come together to form organs. For example the heart is made up of cardiac muscle and nervous tissues, held together with connective tissues and lined with epithelium. Each organ has a specific function.

Organ Function










Several organs working together form a system. For example the urinary system is made up of the kidneys, bladder and ureters.

System Organs


Heart, blood, vessels


Nose, pharynx, trachea, bronchus, bronchiole, lungs, alveoli


Muscles, joints, bones




Brain, spinal chord, nerves


Tongue, oesophagus, stomach, liver, pancreas, gall bladder, small intestine, large intestine, rectum, anus


Kidneys, ureters, bladder, urethra


Male: Testes, scrotum, vas deferens, seminal vesicle, prostate, ejaculatory duct, urethra, penis, glans, perineum

Female: Ovaries, fallopian tubes, uterus, cervix, vagina, labia, urethra, clitoris, perineum


Glands: pituitary, hypothalamus, pineal, parathyroid, thyroid, adrenals, pancreas, gonads: ovaries ♀; testes ♂, and their hormones.


Lymph glands and vessels, lymph, lymphocytes, T and B cells.

Activity 3

In this activity you will learn the functions of the different body systems. Click here