Four Primary Tissue Types Found in Adults
In the adult human body, "tissue" is the scientific name for cell groups with a uniform structure or form that perform a similar function or job. Epithelium, nerve, muscle and connective tissue comprise an interconnected, elaborate system that, when properly functioning, allows adults to operate and, when malfunctioning, creates problems in the body's function that can spread to the other tissue elements.
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Epithelium
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Epithelium type (or "epithelial") tissues are intimately connected tissues that together form a protective barrier for the adult. They always have a fixed, basal segment that is merged with underlying connective tissue and a free, apical area that serves as an inside cavity or internal organ. They are usually full of lots of nerves and have no blood cells, but are capable of soaking up nutrients from those underlying connective tissues. The primarily example is the skin, which protects from the negative effects of extra-bodily stimuli. Epithelium tissue can also filter out materials, such as the kidneys; secrete, such as the glands and absorb, like with the gut, stomach and intestinal lining. Epithelium tissue is adept at regenerating, such as the healing of a skinned knee. They are often classified by cellular shape: squamous epithelium tissue is flat and scaly, cuboidal tissue is evenly tall and wide and columnar tissue is tall. They can be either simple, having a single layer of cells, or stratified, with stacked cells designed to protect from abrasion.
Muscle
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Muscle tissue in adults functions to aid bodily movement, digestion and the movement of blood, food and waste through the organs. These tissues can be spindled organ and blood vessel walls that transfer things through organs (smooth muscle tissue), large body muscles connected to bones to allow movement (skeletal muscle) or interconnected cells in the heart wall that synchronize heartbeat movement (the cardiac muscle).
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Connective
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Connective tissue describes a wide variety of tissues in the adult human body that serve to support and compose the body's structure, usually through fibrous strands of the protein collagen. Such tissue is comprised of both fibers that allow elasticity and support as well as ground substance, the gel-like non-cellular components that case the fibers. They store nutrients and provide internal organ support. Connective tissue can be inner layers of skin, bone, fat tissue, cartilage, tendons and ligaments that attach bones to muscle and, categorically speaking, blood. Some connective tissue is classified as loose, such as the areolar, adipose and reticular connective tissues, while others are known as dense regular and irregular connective tissue.
Nervous
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Nervous tissue includes the brain, spinal cord and nerves; it is are made up of neurons and glial cells. Nervous tissue in adults includes the conductors signaling and transferring impulses and commands to the rest of the body's organs through neurons and electrical signals. The electric signals are transmitted from the brain, through the spinal cord, and down to the other parts of the body.
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