Tissue and Skin

Tissues Tissues are layers or groups of similar cells with a common function 4 types of tissues include: Epithelial Connective Muscle Nervous

Epithelial Tissue Epithelial tissue covers all free body surfaces, forms the inner lining of body cavities, lines hollow organs, and is the major tissue of glands. A basement membrane anchors epithelium to connective tissue. Epithelial tissue lacks blood vessels, has cells that are tightly packed, and is continuously replaced. It functions in protection, secretion, absorption, and excretion.

Epithelial Tissue Apical Surface Basal Surface A free surface or edge exposed to the body’s exterior or to the cavity/lumen of an internal organ. Basement membrane Lower surface of epithelium Structureless material secreted by the cells.

Types of Epithelial Tissue Simple Squamous Cuboidal Columnar Pseudostratified Stratified Squamous Cuboidal Columnar Transitional

Simple Squamous Epithelial This tissue consists of a single layer of thin, flattened cells through which substances pass easily. It functions in the exchange of gases in the lungs and lines blood vessels, lymph vessels, and membranes within the thorax and abdomen.

Simple Cuboidal Epithelium This tissue consists of a single layer of cube shaped cells. It carries on secretion and absorption in the kidneys and various glands.

Simple Columnar Epithelium This tissue is composed of elongated cells whose nuclei are near the basement membrane. It lines the uterus and digestive tract, where it functions in protection, secretion and absorption.

Pseudostratified Columnar This tissue appears stratified because the nuclei are at two or more levels. Its cells may have cilia that move mucus over the surface of the tissue. It lines tubes if the respiratory system.

Stratified Squamous Epithelium This tissue is composed of many layers of cells; the top layers are flattened. It protects underlying cells from harmful environmental effects. It covers the skin and lines the oral cavity, esophagus, vagina and anal canal.

Stratified Cuboidal Epithelium This tissue is composed of two or three layers of cube-shaped cells. It lines the larger ducts of the sweat gland, salivary glands and pancreas. It functions in protection.

Stratified Columnar Epithelium The top layer of cells in this tissue contains elongated columns. Cube-shaped cells make up the bottom layers. It is in part of the male urethra and parts of the pharynx Functions in protection and secretion.

Transitional Epithelium Specialized to become distended. It is in the walls of organs of the urinary tract. It helps prevent the contents of the urinary passageways from diffusing out.

Connective Tissue Connects, supports, protects, fills spaces, stores fat, produces blood cells, protects against infections, and helps repair damage tissues Most are well vascularized except tendons, ligaments and cartilage Fibers—made by CT cells and secreted Collagen fibers (white) Elastic fibers (yellow) Reticular fibers (fine collagen)

Types of Connective tissue From most rigid to softest: Bone Cartilage Dense connective tissue Loose connective tissue Blood

Major Cell types Fibroblasts produce collagenous and elastic fibers Macrophages are phagocytes Mass cells release heparin and histamine and usually are near blood vessels

Bone The extracellular matrix of bone contains mineral salts and collagen Its cells usually form concentric circles around osteonic canals Active tissue that heals rapidly Osseus tissue Most rigid connective tissue, with deposits of mineral salts and collagen within the matrix. Bone cells, called osteocytes, lie within lacunae and are arranged in concentric circles Good blood supply, enabling rapid recovery after an injury. Rocklike hardness allows protection and support of other body organs

Cartilage Provides a supportive framework for various structures. Cartilage cells (chondrocytes) lie within lacunae in the gel-like fluid matrix.

Types of Cartilage Hyaline cartilage is white with abundant fine collagen fibers, is found at the ends of bones, and supports respiratory passages. Elastic cartilage, with elastic fibers, provides a framework for the external ears and parts of the larynx. Fibrocartilage is a tough tissue that provides a shock-absorbing function in intervertebral disks and in the knees and pelvic girdle.

Dense Connective Tissue This tissue consists of densely packed collagenous fibers and is very strong but lacks a good blood supply. Fibroblasts—cells that make fibers It is found as part of tendons and ligaments.

Loose Connective Tissue This type of tissue forms delicate, thin membranes throughout the body that bind body parts together. Fibroblasts are separated by a gel-like ground substance that contains collagenous and elastic fibers. It binds the skin to underlying organs and fills spaces within muscle.

Areolar Tissue Most widely distributed connective tissue in the body Cusions and protects body organs it wraps “Glue” that holds internal organs together

Adipose Tissue Fat storing connective tissue Found beneath the skin (insulates the body), around joints, padding the kidneys and other internal organs, and in certain abdominal membranes.

Reticular Connective Tissue Network of interwoven reticular fibers associated with reticular cells Internal supporting framework

Blood Blood is composed of cells (red and white) suspended in a fluid matrix (plasma). It is formed in the blood-forming tissues inside red bone marrow and functions to transport substances throughout the body.

The Integumentary System The skin and its accessory structures make up the integumentary system. Five major functions Serving as a barrier against infection and disease Helping to regulate body temperature Removing waste products from the body Providing protection against Ultraviolet radiation from the sun Producing vitamin D

Layers of Skin Epidermis Dermis Subcutaneous layer beneath dermis not part of skin

Subcutaneous Layer Hypodermis Loose Connective Tissue Adipose Tissue Major Blood Vessels

Epidermis Layer of stratified squamos epithelium that lacks blood vessels Thickest on Palms Keratonized Outermost Layer Its layers are made of Mostly DEAD CELLS. Most of the cells of the epidermis undergo rapid cell division (MITOSIS). As new cells are produced, they push older cells to the surface of the skin.  The older cells become flattened, lose their cellular contents and begin  making KERATIN.

Dermis Composed of irregular dense connective tissue that binds the epidermis to underlying layer Contains blood vessels Nerve tissue is scattered through the dermis