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structure of animal tissues
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.
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 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.


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