Human Body Tissues

The structure and function of an organ are dependent on the tissues that make it up. A tissue is a group or layer of cells with similar structures, plus the intercellular substances, the material packaged between them, all of which function together for the same specialized purpose. The four basic types of tissue in the human body are epithelial, connective, muscle, and nervous.

Epithelial Tissue

The epithelial tissue in the human, also called epithelium, covers body surfaces and lines internal body cavities. A type of epithelial tissue makes up the outer layer of the skin, called the epidermis. Epithelium provides protection. For a substance to enter or exit the body at the digestive tract, the genital tract, or the lungs, it must cross epithelial tissue. Epithelial tissues have a nerve supply, but no direct blood supply. Cells in epithelial tissue are packed so closely together there is virtually no room between them for any extra material.

  • Squamous epithelium, such as that lining the air spaces of the lungs and blood vessels, is composed of flattened scale-shaped cells. Squamous epithelial tissue that lines the sacs of the lungs allows for the diffusion of oxygen and carbon dioxide across its surface.
  • Cuboidal epithelium, is made up of cube-shaped cells. Cuboidal epithelial tissue lines the inside of the kidney tubules.
  • Columnar epithelium has cells resembling tiny columns, or rectangular pillars. The nuclei in columnar epithelial cells are usually located near the bottom of each cell. This type of tissue lines the cavity (lumen) of the digestive track.
  • Stratified (layered) epithelium, such as makes up the epidermis, the outer layer of the skin, contains cells reinforced by keratin, a fibrous protein that provides strength. The skin's stratified epithelium provides protection from injury and possible pathogen (virus and bacterium) invasion, as well as protects the underlying tissues from drying out. Stratified epithelial tissues also covers the tongue.
  • Transitional epithelium, found for example in the lining of the urinary bladder, stretches and contracts, having a structure that suits function.

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Connective Tissue

Connective tissue provides support and protection, as well as binds organs together. Connective tissue also functions to divide and compartmentalize other tissues and organ structures inside the body. The five main types of connective tissue in the human body: 1. loose fibrous, 2. dense fibrous, 3. cartilage, 4. bone, and 5. blood. Loose connective tissue includes adipose (fatty) tissue, which is specialized for fat storage.

  • Loose fibrous connective tissue forms a protective covering for many internal organs, such as muscles, blood vessels, and nerves. Loose fibrous connective tissue in the walls of lungs and arteries allows those organs to expand.
  • Adipose tissue is a specialized type of loose connective tissue. Its cells, fibroblasts, enlarge for storing fat. Adipose tissue is located beneath the skin and around organs such as the heart and kidneys.
  • Dense fibrous connective tissue contains more collagen fibers than loose fibrous tissue and has more specific functions. Tendons, which connect muscles to bones, is made up of dense fibrous connective tissue, as is ligaments, which connect bones or cartilage to bones at the joints. One type of dense fibrous connective tissue is found in the vocal chords.
  • Cartilage is a tough connective tissue in which the cells lie in small chambers called lacunae. Hyaline cartilage, the most common type, is found in the nose and at ends of the long bones and the ribs, and it forms rings in the walls of respiratory passages and provides flexibility. The human fetal skeleton is also made of this type of cartilage, which is later replaced by bone during growth.
  • Bone the most rigid connective tissue and major component of the skeletal system, providing a framework and support for the body as a whole.
  • Blood is sometimes classified as connective tissue or by itself as vascular tissue.

Muscle tissue

Muscle or muscular tissue, built for repeated contraction and relaxation, permits animals to move and stabilizes posture. Accounting for up to 50 percent of body weight in healthy humans, muscle tissue produces the majority of body heat.

Three main types of muscle tissue: 1. skeletal, 2. cardiac, and 3. smooth contractile tissue, muscle tissue is sometimes called contractile tissue, because it contains contractile protein filaments that interact to produce movement.

  • Skeletal or striated muscle tissue is under voluntary control and is attached by tendons to the bones of the skeleton
  • Cardiac muscle tissue is found only in the walls of the heart. As a result of its contraction blood is pumped through the heart. Cardiac muscle tissue is involuntary.
  • Smooth muscle is so named because its cells lack bands or striations. Smooth muscle tissue is involuntary and is found in the walls of blood vessels, air passages of the lungs and inside the eye.
  • Visceral muscle is smooth muscle, called visceral because it is found in the walls of the viscera, internal organs such as intestines and abdomen. Contractions of visceral (smooth) muscle in the intestine moves food along the digestive tract.

Nerve Tissue

Nerve, or nervous tissue coordinates body parts and allows an animal to respond to the environment. It functions to transfer information from one part of the body to another by sensing both internal and external stimuli and initiating a response.


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