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Thursday, April 10, 2008

article : Animal tissue review

A review of the structure of animal tissue (connective, nervous, epithelial, and muscle) and how it is directly related to its function.

The structure of animal tissue is directly related to its function. Animals have groups of cells in the tissue, which are combined together to perform as an organ. Tissues are groups of cells with a basic structure and function. There are four major types of tissues: epithelial tissue, connective tissue, nervous tissue, and muscle tissue. Tissues are woven together with a sticky extra cellular matrix.

Epithelial tissue is a tissue that is made up of tightly packed cells that line organs and body cavities. The cells contained in the epithelium are closely joined without much material between them. Inside the epithelia the cells are locked together by tight junctions. The reasons for the tightly packed cells are to act as a barrier against mechanical injury, invading microorganisms, and fluid loss. The base of the barrier cells are attached to the basement membrane, which is a dense extracellular matrix. The basement membrane has many functions, some of which are filtering waste from the blood in the kidney, providing routes of migration for the cells during their development, and organizing sequential events in the cellular metabolism.

When defining epithelial consider two criteria, one, the number of cell layers and two, the shape of the cells on the free surface. When an epithelium has a single layer of cells, it is called a simple epithelium, whereas multiple tiers of cells are known as stratified epithelium. There are pseudostratified epithelium, which is single layered but appears to be stratified because the cells vary in length. The free surface of epithelium cells are shaped as cubiodal, columnar, or squamous. As well as keeping the organs in line, epithelia absorb or secrete chemical solutions.

Connective tissue is animal tissue that functions mainly to bind and support other tissues. They have sparse populations of cells scattered through an extracellular matrix. This extracellular matrix is a web of fibers that is woven in a homogeneous ground substance that can be liquid, solid or jellylike. The matrix of the cells is usually secreted by the connective tissue. There are a few major types of connective tissue. A few of these are loose connective tissue, adipose tissue, and fibrous connective tissue has a specific function that is correlated to its structure.

The most abundant tissue is the loose connective tissue in the vertebrate. This acts with the underlying tissue and functions as packaging material which holds the organs in place. The fibers are made of protein and there are three kinds: collagenous fibers, elastic fibers, and reticular fibers. The most abundant fibers are the collagenous made of collagen, the greatest strength and do not tear easily. The elastic fibers are made of a protein called elastin. These fibers are strong yet they allow the skin to return to its original shape, if it has been stretched. Then the last kind are the reticular fibers that are very thinly branched. The reticular fibers are made of collagen and are continuous with collagenous fibers joining the connective tissue to the adjacent tissue.

Another loose form of connective tissue is the adipose tissue that stores fat in adipose cells that is distributed throughout the matrix. These tissues are key in storing fuel molecules and insulating and padding the body. The adipose cells store fat and swell when fat is stored and shrink when the fat is used as fuel.

Fibrous connective tissue is enriched in collagenous fibers. These fibers are bundled in an arrangement that maximizes tensile strength. The fibrous connective tissue makes up ligaments which attach bones and joints together and tendons which attaches muscles and bones together.

The nervous tissue is the tissue that senses stimuli and then transmits the signal from one part of the animal to another. The neuron is the functional unit of the nervous tissue or the nerve cell which is specialized in transmitting signals called nerve impulses. This consist of the cell body and two or more extensions that are called dendrites and axons. The dendrites transmit an impulse that is sent towards the cell body, and the axons transmit impulses away from the cell body.

Muscle tissue is made up of long, excitable cells that are capable of considerable contraction. These are arranged in a parallel pattern within the cytoplasm of the muscle cells. There are a large number of microfilaments that are made of contractile proteins actin and myosin. Since this is needed for movement it is one of the most abundant tissues in most animals.

The vertebrate body there are three types of muscle tissue. The first is skeletal muscle, which is normally responsible for the voluntary movement in the body. The second is the cardiac muscle that forms the wall of the heart. This muscle relays signals from cell to cell during a heartbeat. The third type is the smooth muscle which is found in the digestive track, bladder, arteries, and other internal organs.

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