Basic Body Structure and Organization

 

Organ Systems and Organs

Before one can understand how xenobiotics affect these different body components, it's important to understand normal body components and how they function. For this reason, this section provides a basic overview of anatomy and physiology as it relates to toxicity mechanisms.

xenobiotics : General term for a foreign substance taken into the body. It derived from the Greek term 'xeno' which means 'foreigner'.

toxicity : The quality or degree of being toxic or poisonous.

Basic Body Structure and Organization

We can think of the basic structure and functional organization of the human body as a pyramid or hierarchical arrangement in which the lowest level of organization (the foundation) consists of cells and chemicals. Organs and organ systems represent the highest levels of the body's organization (Figure 1).

Figure 1. Pyramid represents a hierarchical organization of human body components
(Image Source: NLM)

Simplified definitions of the various levels of organization within the body are:

• Organ system — a group of organs that contribute to specific functions within the body. Examples include:
  • Gastrointestinal system
  • Nervous system
• Organ — a group of tissues precisely arranged so that they can work together to perform specific functions. Examples include:
  • Liver
  • Brain
• Tissue — a group of cells with similar structure and function. There are only four types of tissues:
  1. Epithelial
  2. Connective
  3. Muscle
  4. Nerve
• Cell — the smallest living units in the body. Examples include:
  • Hepatocyte
  • Neuron
• Chemicals — atoms or molecules that are the building blocks of all matter. Examples include:
  • Oxygen
  • Protein

 

Levels of Structural Organization of the Body - No Sound

 

In the animation, an image of each level of structural organization of the body is displayed, beginning with chemicals, then cells, then tissues, then organs, then organ systems, and finally, the organism.

Animation 1. Levels of structural organization of the body
(this video has no sound)

Organ Systems of the Human Body

The human body consists of eleven organ systems, each of which contains several specific organs. An organ is a unique anatomic structure consisting of groups of tissues that work in concert to perform specific functions. Table 1 includes the structures and functions of these eleven organ systems.

Organ System	Functions	Organs
Integumentary	Barrier to invading organisms and chemicals Temperature control	Skin Hair Subcutaneous tissue
Skeletal	Supports and moves body Protects internal organs Mineral storage Blood formation	Bones Cartilage Ligaments Bone marrow
Muscular	Locomotion Heat production	Muscles Tendons
Nervous	Coordinates activities of other organ systems Responds to sensations	Brain Spinal cord Nerves Eyes Ears
Endocrine	Regulates body functions by chemicals (hormones)	Pituitary gland Parathyroid gland Thyroid gland Adrenal gland Thymus Pancreas Gonads
Cardiovascular	Transports oxygen and nutrients to tissues Removes waste products	Heart Blood Blood vessels
Lymphatic	Returns tissue fluid to blood Defends against foreign organisms	Spleen Lymph nodes Thymus Lymphatic vessels
Respiratory	Oxygen/carbon dioxide exchange	Lungs Trachea Larynx Nasal cavities Pharynx
Digestive	Processes foods Absorption of nutrients into body	Stomach Intestinal tract Liver Pancreas Esophagus Salivary glands
Urinary	Elimination of wastes Regulates pH and volume of blood	Kidneys Urinary bladder Urethra
Reproductive	Produces germ cells (eggs and sperm) Environment for growth of fetus (female)	Ovaries Uterus Mammary glands Testes Prostate gland External genitalia

Table 1. Organ systems of the human body

Knowledge Check

Groups of cells with similar structure and function are known as:

Tissues

Organs

Organ systems

The organ system that transports oxygen and nutrients to tissues and removes waste products is the:

Urinary system

Integumentary system

Cardiovascular system

The organ system that regulates body functions by chemicals (hormones) is known as the:

Nervous system

Reproductive system

Endocrine system