TISSUES

Animal Tissues

1. A tissue is a group of similar cells and their intercellular substance specialized for a particular function. Depending on their function and structure, the various tissues of the body are classified into four principal types: epithelia], connective. muscular. and nervous.
   
2. Epithelium has many cells, little intracellular material, and no blood vessels (avascular). It is attached to connective tissue by a basement membrane. It can replace itself. The subtypes of epithelium include covering and lining epithelium and glandular epithelium. Layers are arranged as simple (one layer), stratified (several layers), and pseudostratifled (one layer that appears as several); cell shapes include squamous (flat), cuboidal (cubelike), columnar (rectangular), and transitional (variable). Glandular Epithelium - A gland is a single cell or a mass of epithelial cells adapted for secretion. Exocrine glands (sweat, oil, and digestive glands) secrete into ducts or directly onto a free surface. Endocrine glands secrete hormones directly into the blood.
   
3. Connective tissue is the most abundant body tissue. It has few cells, an extensive intercellular substance, and a rich blood supply (vascular), except for cartilage. It does not occur on free surfaces. The intercellular substance determines the tissue's qualities. Connective tissue protects, supports, and binds organs together. Connective tissue is classified into two principal types: embryonic and adult. Adult connective tissue is connective tissue that exists in the newborn and that does not change after birth. It is subdivided into several kinds: connective tissue proper, cartilage, bone tissue, and vascular tissue. Five examples of such tissues may be distinguished: Loose, Adipose, Dense, Elastic, and Reticular. Cartilage has a jellylike matrix containing collagenous and elastic fibers and chondrocytes. Hyaline cartilage is found in the embryonic skeleton, at the ends of bones, in the nose, and in respiratory structures. Fibrocartilage connects the pelvic bones and the vertebrae. It provides strength. Elastic cartilage maintains the shape of organs such as the larynx, auditory tubes, and external ear.
   
4. Muscle tissue performs one major function: contraction. Three main types of muscle tissue are: Skeletal (Striated), Cardiac, and Viscera; (Smooth). Muscle tissue either allows for the organism to move through the environment or provides for motion of materials within the organism.
   
5. Nervous tissue is specialized to conduct electrical impulses. The principle cell type is the neuron. Two general nerve cell types are recognized: Motor and Sensory. The nervous system is divided into two major functioning parts: Central and peripheral.

Plant Tissues

1. Tissues that give rise to growth in length are termed Primary Tissues. These tissues are often termed meristems: Apical and Root. Tissues that cause growth in diameter are termed Secondary Tissues: Cambium.

2. Examples of a few simple plant tissues are: Parenchyma - food storage, Collenchyma - support for young tissues, Sclerenchyma - support for mature tissues.

3. Complex tissues include: Vascular Tissues (Xylem and phloem). Xylem transports water and other
nutrients up from the roots into the stems and leaves. Phloem transports water and newly manufactured food down the plant to be stored in the roots, etc..

4. Dermal Tissues include the epidermis and associated structures.