The human body contains about 100,000,000,000,000 (100 Trillion) cells.

The adult human body contains approximately 60% water, and so makes up a significant proportion of the body, both in terms of weight and volume. Water content can vary from a high 75% in a newborn infant to a lower 45% in an obese person.

The vast majority of cells in the human body are not human at all; rather they are of bacteria, archaea

Human Body Systems

Tissues: (From PhysiologyProject - Cells to Systems)

  • Epithelial tissue is tissue that lines the organs and blood vessels. Epithelial tissue forms a barrier for the specific body surface that they need to protect.
  • Connective tissue is tissue throughout the body that connects, provides structure and support, and aides in transporting molecules.
    • Loose connective tissue (fascia) has many cells in it, but not very many fibers.
    • Dense connective tissue (tendons, ligaments, etc.) only has a few cells but has many, dense fibers.
    • Adipose (fat) tissue
    • Cartilage
    • Bone
    • Blood
  • Muscle tissue are cells designed for contraction, movement, and heat production.
  • Nerve tissue makes up the body's communication network. Neurons are the functional cells in nerve tissues that are designed to send and receive information and neuroglia are the cells that make sure neurons get nutrients, lay down more blood vessels near the neurons, and clean up dead cells.
See also:
An Introduction to Physiology (
Human Anatomy and Tissues Help |
Organ Systems:
Organs are composed of two or more of the four kinds of tissue.
  • Skeletal System (bones) [Structure]
  • Muscular System (muscles) [Movement]
  • Nervous System [Communication]
  • Endocrine System [Communication]
    Adrenal gland, Corpus luteum, Hypothalamus, Kidney, Ovaries, Pancreas, Parathyroid gland, Pineal gland, Pituitary gland, Testes, Thyroid gland
  • Circulatory (Cardiovascular)
  • Respiratory System
  • Digestive and Excretory Systems
  • Reproductive System
  • Integumentary system -
    skin, hair, nails, skin glands and their products (sweat).
  • Other:
    Immune System
    Lymphatic System
Note: There are a variety of ways to classify human anatomy. The above includes the major systems in most of them. Some combine Muscular and Skeletal and Cardiovascular and Respiratory.
From the earliest days of physiology - at least as early as the time of Aristotle- physicians recognized that good health was somehow associated with a balance among the multiple life-sustaining forces ("humors") in the body.
Homeostasis is a state of dynamic consistency. In such a state, a given variable like blod glucose may vary in the short term but is stable and predictable when averaged over the long term.
Senses - part of Nerve system:
Sight, Sound, Smell, Taste, and Touch

Aristotle might consider this evidence for the hierarchy of senses he proposed in the fourth century B.C. His rankings were based on which senses were most important for us to experience and survive in the world. The top sense was sight, followed by hearing, smell, taste and then touch. Sight and hearing allow us to sense things from a distance and so were deemed critical for survival, whereas taste and touch require contact. Smell fell somewhere in the middle.

The Five Senses |

Human Anatomy & Physiology: Table of Contents
Human Anatomy Model, Anatomy Chart, Anatomical Chart | InnerBody

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last updated 2 Aug 2014