Discovery Science: Earth Biology – Humans Anatomy
The form, location, and structure of cells, tissues, organs, and whole body parts is nearly identical in all human beings.
The spine and the bones give the body its stability, muscles and joints provide for its flexibility, and the blood circulation supplies all the tissues and internal organs with vital substances.
Earth Science: Biology – Humans – Tissues and Organs
There are specialized cells within the human body that organize themselves into tissues and organs. These cells are replaced continuously in a process that slows down with age.
Tissues are groups of cells with a unified structure and function held together by fibers or an outer body of cells. Organs consist of four basic types of cell tissues: epithelial, connective, nerve, and muscular.
Epithelial, connective, and nerve tissue
Epithelial tissues obstruct infectious organ- isms, protect against injury, and prevent loss of fluids. They are closely layered together. They cover body surfaces and organs and line cavities. Epithelial cells lining the lungs and intestines are in a single layer. Inside the nose, they are in multiple layers and combined with nasal hairs.
The epithelial tissues of the skin can regrow rapidly to repair cuts and injuries. Connective tissues support and bind other tissues. They can be liquid (blood), jellylike (tendons), and rigid (cartilage and bone). The loose connective (areolar) tissues are the most common in humans,
These tissues, which connect the skin and organs and hold them in place, are highly flexible and tear-resistant. Dense connective tissue is found in the ligaments and tendons, which attach muscles to bones. Cartilage and bone constitute special connective tissues that support the body.
Bone tissue is hardened by deposits of calcium phosphate, but is not brittle, and serves to protect the body as well as provide support. Nerve tissues in the spine, brain, and nervous system send electrical and chemical signals throughout the body.
These tissues include nerve cells and the surrounding neuroglial cells.
Muscle tissue
The elongated cells of muscle tissue can contract in response to a nerve impulse to cause movement. There are about 650 muscles in the body, making this the most common human tissue by volume.
The muscles can be divided into three types: skeletal, smooth, and cardiac. Skeletal muscles are attached to bones by tendons and permit the body to move. Smooth muscles contract involuntarily and are found in the walls of the digestive tract, internal organs, and blood vessels.
While they contract more slowly than skeletal muscles, the contraction persists for a longer period of time. Cardiac muscle, also involuntary, is resistant to fatigue allowing for continuous, rhythmic heart contractions.