1 (b.b.) Muscle and Skin
The muscles in your arm do their work by contracting, becoming shorter and thicker. Because muscle cells can only contract, not extend, skeletal muscles must work in pairs. While one muscle contracts, the other muscle in the pair relaxes to its original length. First, the biceps muscle on the front of the upper arm contracts to bend the elbow, lifting the forearm and hand. As the biceps contracts, the triceps on the back of the upper arm relaxes and returns to its original length. Then, to straighten the elbow, the triceps muscle contracts. As the triceps contracts to extend the arm, the biceps relaxes and returns to its original length. Like the muscle cells that form it, muscle tissue can contract, or shorten. By doing this, muscle tissue makes parts of your body move.
The surfaces of your body, inside and out, are covered by epithelial tissue (ep uh thee lee ul). Some epithelial tissue, such as your skin, protects the delicate structures that lie beneath it. The skin covers and protects the body from injury, infection, and water loss. The skin protects the body by forming a barrier that keeps disease-causing microorganisms and harmful substances outside the body.
The levels of organization in the human body consist of cells, tissues, organs, organ systems and finally the organism. The smallest unit of organization is the cell. The next largest unit is tissue; then, organs, then the organ system. Finally the organism, is the largest unit of organization.
The surfaces of your body, inside and out, are covered by epithelial tissue (ep uh thee lee ul). Some epithelial tissue, such as your skin, protects the delicate structures that lie beneath it. The skin covers and protects the body from injury, infection, and water loss. The skin protects the body by forming a barrier that keeps disease-causing microorganisms and harmful substances outside the body.
The levels of organization in the human body consist of cells, tissues, organs, organ systems and finally the organism. The smallest unit of organization is the cell. The next largest unit is tissue; then, organs, then the organ system. Finally the organism, is the largest unit of organization.
