TISSUES CH. 4 August 30th, 2007

What is a Tissue? Tissue are a collection of cells associated by intercellular materials specialized for a particular function.

4 Types of Tissues Epithelial: characterized by a virtual lack of intercellular substances between adjacent cells; forms skin and lines interior surfaces of body (gut, peritoneum, etc.) 2. Connective Tissue: cells usually are widely separated by an abundant intercellular matrix; includes blood, cartilage, bone, tendons, adipose (fat). 3. Muscle Tissue: elongate cells separated by fine, vascular connective tissue. Three types occur: skeletal, cardiac, and smooth. 4. Nervous Tissue: cells are grouped into masses or bundles, many with long processes; specialized for sensory reception and transmission of impulse functions.

Epithelial Tissue Characteristics 1) Closely packed cellular arrangement 2) Covers or lines surfaces (interior and/or exterior) 3) Form ducts and secretory portions of glands 4)All epithelia are anchored to underlying tissues by a basement membrane composed of an upper basal lamina and a lower layer of reticular fibers 5) Avascular tissues- no blood vessels in epithelial tissues, cells derive nutrients by diffusion from blood vessels in surrounding connective tissue.

Epithelial Functions: 1. Protective = prevents desiccation (skin), abrasion 2. Absorption = digestive and excretory tracts 3) Secretory = oils, water, enzymes, hormones, salts (in some animals) 4) Excretion = removal of harmful wastes

Epithelial Classification: 1. Cell Shape a) flat = squamous b) square = cuboidal c) elongate = columnar 2. Layering or Stratification a) Simple - 1 cell-layer thick b) Stratified = > 2 cell-layers thick

Simple Epithelial Type ( 1 layer) 1) Simple Squamous = flat or spindle-shaped in cross-section. In surface view gives appearance of "tiled floor" so it is also named "pavement epithelium." Found in thin Loop of Henle (kidney medulla), endothelial vessel walls, lining of body cavity (mesothelium), pulmonary alveoli, etc. 2) Simple Cuboidal = square cells found in covering of ovaries, convoluted and collecting tubules in kidney, ducts of most glands. 3) Simple Columnar = column-shaped cells found in absorptive/secretory lining of digestive tract, larger ducts, lining of uterine cervix, etc. Many have microvilli (brush border in intestinal lining) on apical surface, some have cilia (e.g., fallopian tubes). 4) Goblet Cells = mucus-secreting cells within simple secretory epithelium, mucus aids passage of contents down digestive tract, out of respiratory tract.

Pseudostratified Columnar Epithelium All cells are in contact with basement membrane, but not all cells reach epithelial surface, and nuclei reside at more than 1 level. This gives the appearance of >1 layer, when in fact only one layer is present. PSC occurs lining larger excretory ducts, larger ducts of male reproductive system, and respiratory tract. PSC lining respiratory tract has numerous goblet cells and is ciliated.

Stratified Epithelium (classify by the outer layer of cells) 1) Stratified Squamous = thick membrane, only the outer layer(s) is squamous. Basal layers often demonstrate considerable irregularity. This epithelium usually becomes keratinized to decrease water loss and protect from abrasion (skin). -> Keratinized = surface cells die and transform into soft scales of keratin, but remain strongly adherent to live cells below. ->Nonkeratinized = fairly rare, lines mouth, esophagus, and vagina.

Stratified Epithelium (cont.) 2) Stratified Cuboidal/Columnar = usually only two layers thick. ->Cuboidal is present only in the ducts of sweat glands in humans and skin of aquatic vertebrates. ->Columnar found in parts of male urethra, larger excretory ducts, and conjunctiva of eye.

Stratified Epithelium (cont.) 3) Transitional Epithelium = composed of several layers of cells, thickness influenced(as is cell shape) by the state of the organs which it lines. Present only in distensible surfaces of excretory tract (bladder, ureters, pelvis of kidney). -> In contracted state, it is many layers thick. The basal layer is cuboidal to columnar, intermediates layers are polyhedral, surface layer with large rounded cells. ->In distended state, upper cells become flat and the entire epithelium appears as a thin (2-5 layers thick) stratified squamous epithelium. - Rounded surface cells may be binucleate.

Connective Tissues Binds structures, provides support and protection, fills spaces, produces blood cells, and store fat. Tissues are widely separated by a matrix or covering. Types: 1. Areolor tissue 2. Adipose 3. Dense Connective 4. Hyaline Cartilage 5. Compact Bone 6. Spongy Bone 7. Blood

Types of Connective Tissue 1. Areolor tissue – Between bones and beneath the skin. It bind organs together. 2. Adipose – Beneath the skin, around heart, and in breasts. It insulates and fat storage. 3. Dense Connective – Tendons and Ligaments. It binds organ together. 4. Hyaline Cartilage – Ends of long bones, nose, anterior ribs. It supports and protects.

Types of Conn. Tissue (cont.) 5. Compact Bone – Shafts of bones. It supports and protects. 6. Spongy Bone – Ends of bones. It supports and protects. 7. Blood – In the vessels. It supplies cells with nutrients and oxygen.

Muscle Tissue Composed of muscle fibers that contain actin and myosin that account for movement. Types: Skeletal Smooth Cardiac

Skeletal Muscle Voluntary Attach to bones by tendons. Cylindrical shaped, but long. Have striations, which are light and dark bands.

Smooth Muscle Spindled shaped cells with irregular pattern of nuclei. Involuntary Found in hollow viscera; intestines, stomach, etc.

Cardiac Muscle Involuntary Has striations and is branched Located only in the walls of the heart.

Nervous Tissue Found in the brain and spinal cord Composed of neurons. Conduct impulses from sensory organs to the spinal cord and brain. Also conduct from the brain to the muscles.