Anatomy Chapter 3 Part II: Body Tissues

Part II: Body Tissues The human body starts out as a single cell, a fertilized egg, then divides repeatedly. There is a division of labor in the body (cell differentiation), as certain groups of specialized cells perform functions that benefit the organism as a whole. Specialization carries hazards – small groups of cells become indispensible, loss could disable or destroy the body (heart, brain). Groups of cells with similar structure and function makeup tissues. Four primary tissue types: epithelium (covering), connective (support), nervous (control), and muscle (movement). Most organs contain several tissue types; arrangement determines the organs structure and function.

I. Epithelial tissue Epithelial tissue or epithelium – lining, covering, and glandular tissue Covering and lining epithelium cover all free body surfaces, lines body cavities, forms boundaries from outside; nearly all substances given off or received must pass through epithelium (bacteria) Epithelial functions include protection, absorption, filtration, and secretion Glandular epithelium forms various glands in the body (perspiration, oil, digestive enzymes, mucus)

Special characteristics: Apical surface – free surface or edge Basement membrane – lower surface, epithelium rests on Avascular – no blood supply: diffusion

Classification of Epithelium: Simple squamous epithelium: rapid diffusion Air sacs Walls of capillaries Basale layer of skin Simple epithelia – one layer thick; absorption, secretion, filtration

Simple cuboidal epithelia – glands and their ducts Salivary glands Pancreas Kidney tubules Surface of ovaries

Simple columnar epithelia – single layer of tall cells that fit closely together. Mucous membranes or mucosa if lining opens to the outside of the body. Lining of digestive tract and Respiratory tract

Pseudostratified columnar epithelia– nuclei appear at different heights above basement membrane, giving a false stratified look. Tissue lines the respiratory tract. Mucous is produced by Goblet cells to trap dust and debris, cilia propel upward and out from the lungs.

Stratified epithelia – consists of two or more cell layers, durable, function primarily to protect. Stratified squamous epithelium – most common stratified epithelium; several layers of cells; found at sites that receive abuse or friction: skin.

Transitional epithelia – modified to line a few organs; urinary bladder, ureters, part of urethra. Subject to considerable stretching.

Classification of Connective Tissue Connective tissue connects body parts – found every where in the body; most abundant and widely distributed of tissue types; function in protection, supporting, binding together body tissues Most are vascularized – have a good blood supply; tendons and ligaments have poor blood supply and cartilage is avascular causing these tissue to heal very slowly when injured Extracellular matrix – outside the cell, produced by the cells and secreted; structureless ground substance (water, adhesion proteins {glue}, large charged polysaccharide molecules {trap water – reservoir} and fibers (collagen {white}, elastic {yellow}, reticular fibers Forms soft packing tissue around organs, bear weight, withstand stretching and other abuses (abrasions)

Bone – osseous tissue; cavities called lacunae are surrounded by a hard matrix; protect and support

Cartilage – less hard, more flexible, found in few places in the body; most abundant is hyaline cartilage Hyaline cartilage – larynx (voice box), attach ribs to breastbone, covers ends of bones that form joints, makes up fetal skeleton Fibrocartilage – cushion disks between vertebrae of spinal column Elastic cartilage – supports external ear

Dense connective tissue – collagen fibers are main matrix; form strong, ropelike structures such as tendons (attach skeletal muscles to bones) and ligaments (connect bones to bones at joints); makes up lower layers of skin (dermis) arranged in sheets Loose connective tissue – softer, have more cells, fewer fibers

Areolar tissue – most widely distributed connective tissue, soft pliable; cushions and protects organs; universal packing tissue – helps hold internal organs together. Reservoir of water and salts for surrounding tissue. Edema – areolar tissue soaks up excess fluid and area swells and becomes puffy; phagocytes enter swollen area. Adipose tissue – fat, droplet of stored oil occupies most of fat cell’s volume; forms subcutaneous tissue beneath skin, insulates body, protects it from extremes of heat and cold; protects some organs; fat deposits in hips, breasts; stored fuel

Blood or vascular tissue – considered connective tissue because it consists of blood cells, surrounded by nonliving, fluid matrix called blood plasma Blood is atypical. Blood is a transport vehicle for the cardiovascular system, carrying nutrients, wastes, and other substances

Muscle Tissue Tissues highly specialized to contract, or shorten, to produce movement. Three types of muscle tissue: skeletal, cardiac, and smooth muscle. Skeletal muscle tissue – attached to skeleton, controlled voluntarily, form flesh of the body, called the muscular system. Cells are long, cylindrical, multinucleate, with obvious striations (stripes). Cells often called muscle fibers.

Cardiac muscle tissue– found only in the heart; contracts to propel blood through the blood vessels. Has striations, is uninucleate, relatively short, branching cells fit tightly together at junctions called intercalated disks. Involuntary control.

Smooth muscle tissue – no striations, single nucleus, spindle-shaped Smooth muscle tissue – no striations, single nucleus, spindle-shaped. Found in walls of hollow organs (stomach, bladder, uterus, blood vessels). Can enlarge or contract cavity of organ as things are propelled through a specific pathway. Involuntary. Peristalsis – wavelike motion that keeps food moving through digestive tract.

Nervous Tissue Neurons – receive and conduct electrochemical impulses from one part of the body to another. Two major functional characteristics: irritability and conductivity. Axons are long processes of the cell that conduct impulses over long distances in the body. Supporting cells insulate, support, and protect neurons. Brain Spinal cord Nerves

Tissue Repair Tissue injury stimulates body’s inflammatory and immune response and the healing process begins. Repair occurs in two major ways: Regeneration – replacement of destroyed tissue by the same kind of cells Fibrosis – repair by dense connective tissue, by formation of scar tissue Injury sets series of events into motion: The capillaries become very permeable Granulation tissue forms The surface epithelium regenerates Regeneration differs in tissue type: epithelial tissue and mucous membranes regenerate easily; as do fibrous connective tissue and bone; skeletal tissue regenerates poorly if at all, cardiac and nervous tissue is replaced largely by scar tissue.

Developmental Aspects of Cells and Tissues Cell division is critical during growth periods Amitotic cells have become handicapped by injury and cannot be replaced by the same type of cells (heart muscle – myocardial infarction) Neoplasm is a failure of cells to follow the normal controls of cell division; causes tumors. Benign tumors are usually not harmful, not invasive Malignant tumors are cancerous, invasive, tissue destroying Hyperplasia is the result of certain body tissues (organs) enlarging because of a local irritant or condition that stimulates cells Atrophy is a decrease in size or an organ of body area that loses its normal stimulation (sessile people – couch potatoes, aged people)