ANIMAL TISSUES

• Nervous tissue is responsible for transmitting electrical signals and coordinating the activities of the body.
• As the walls of the heart contract, cardiac muscle tissue propels blood into the circulation; involuntary control.
• In an animal, individual cells differentiate during development to perform special functions as aggregates called tissues.
• A tissue is a group of similar cells specialized for the performance of a common function.
• The study of tissues is called histology (Gr histos, tissue + logos, discourse).
• Animal tissues are classified as epithelial, connective, muscle, or nervous.
• Epithelial tissue exists in many structural forms.
• Epithelial tissue either covers or lines something and typically consists of renewable sheets of cells that have surface specializations adapted for their specific roles.
• A basement membrane separates epithelial tissues from underlying, adjacent tissues.
• Epithelial tissues absorb, transport, excrete, protect, and contain nerve cells for sensory reception.
• The size, shape, and arrangement of epithelial cells are directly related to these specific functions.
• Epithelial tissues are classified on the basis of shape and the number of layers present.
• Epithelium can be simple, consisting of only one layer of cells, or stratified, consisting of two or more stacked layers.
• Individual epithelial cells can be flat (squamous epithelium), cube shaped (cuboidal epithelium), or columnlike (columnar epithelium).
• The cells of pseudostratified ciliated columnar epithelium possess cilia and appear stratified or layered, but they are not, hence the prefix pseudo.
• Pseudostratified ciliated columnar epithelium lines the bronchi, uterine tubes, and some regions of the uterus.
• Pseudostratified ciliated columnar epithelium propels mucus or reproductive cells by ciliary action.
• Stratified squamous epithelium consists of many layers of cells.
• Stratified squamous epithelium lines the esophagus, mouth, and vagina.
• Keratinized variety lines the surface of the skin.
• Stratified squamous epithelium protects underlying tissues in areas subject to abrasion.
• Elastic cartilage is located in the external ear and epiglottis, maintaining a structure's shape while allowing great flexibility.
• Blood is located within blood vessels, transporting oxygen, carbon dioxide, nutrients, wastes, hormones, minerals, vitamins, and other substances.
• Muscle tissue allows movement, with the three kinds of muscle tissue being skeletal, smooth, and cardiac.
• Smooth muscle tissue is formed of spindle-shaped cells, each containing a single centrally located nucleus, located mostly in the walls of hollow organs, and its function is to move substances or objects (foodstuffs, urine, a baby) along internal passageways and for involuntary control.
• Cardiac muscle tissue consists of branched striated cells, each containing a single nucleus and specialized cell junctions called intercalated disks that allow ions (action potentials) to move quickly from cell to cell, located in the walls of the heart.
• Bone (osseous) tissue is composed of blank bone matrix deposited in concentric layers around osteonic canals.
• Fibrocartilage contains many large, collagenous fibers in its intercellular material.
• Nervous tissue is composed of several different types of cells: Impulse-conducting cells are called neurons, cells involved with protection, support, and nourishment are called neuroglia, and cells that form sheaths and help protect, nourish, and maintain cells of the peripheral nervous system are called peripheral glial cells.
• Elastic cartilage contains fine collagenous fibers and many elastic fibers in its intercellular material.
• Nervous tissue transmits electrical signals from sensory receptors to the spinal cord or brain, and from the spinal cord or brain to effectors (muscles and glands).
• Bone tissue is located in bones, supporting, protecting, providing a lever system for muscles to act on, storing calcium and fat, and forming blood cells.
• Skeletal muscle tissue is composed of striated muscle fibers (cells) that are long and cylindrical and contain many peripheral nuclei, located in skeletal muscles attached to bones, and its function is voluntary movement and locomotion.
• Fibrocartilage is located in intervertebral disks, pubic symphysis, and disks of knee joint, absorbing compression shock.
• Blood is a type of connective tissue, consisting of red blood cells, white blood cells, and platelets suspended in an intercellular fluid (plasma).
• Blood transports various substances throughout the bodies of animals.
• Bone cells (osteocytes) also lie within lacunae, but the matrix around them is heavily impregnated with calcium phosphate and calcium carbonate, making this kind of tissue hard and ideally suited for its functions of support and protection.
• In fibrous connective tissue, the collagen fibers are densely packed and may lie parallel to one another, creating very strong cords, such as tendons and ligaments.
• Connective tissues have two general types of fiber arrangement: loose connective tissue and fibrous connective tissue.
• Adipose tissue cells (adipocytes) contain large fat droplets that push the nuclei close to the plasma membrane.