Introduction to Histology
What is histology? HISTOLOGY histo = tissue ogy = study So HISTOLOGY = the study of tissues!
What is a TISSUE? Tissues are groups of cells with specialized structural and functional roles. Intercellular materials, varying from solid to liquid, separate cells. (also known as MATRIX)
Four Main Kinds of Tissue: -Epithelial -Connective -Muscle -Nervous
EPITHELIAL TISSUE: *General Characteristics: covers all free body surfaces (outer and inner surfaces of organs) major tissue of glands
EPITHELIAL TISSUE: anchored to connective tissue by a BASEMENT MEMBRANE lack blood vessels
EPITHELIAL TISSUE: nutrients get to the epithelial tissue by diffusion from the connective tissue below
EPITHELIAL TISSUE: readily divide; so injured areas heal quickly as new cells replace lost or damaged ones
EPITHELIAL TISSUE: cells are tightly packed form effective protective barriers
EPITHELIAL TISSUE: functions include: protection secretion absorption excretion
EPITHELIAL TISSUE: cells are classified according to shape and number of layers of cells -simple = single layer of cells -stratified = two or more layers of cells -squamous = thin, flattened cells -cuboidal = cube-shaped cells -columnar = elongated cells
EPITHELIAL TISSUE: free surface cells may have modifications suited to their function (i.e. cilia, microvilli, mucus-secreting cells)
Connective, Muscle and Nervous Tissues
General Characteristics: Functions include: Support Provide framework Protect Fill space Store fat Produce blood cells Connect Protect against infection Repair damaged tissue
Connective Tissue: Considerable amount of intercellular material (MATRIX) between cells *Matrix consists of fibers and ground substance
Connective Tissue: Major Cell Types: 1) Fibroblasts: produce collagenous & elastic fibers 2) Macrophages: phagocytes (engulf pathogens) 3) Mast cells: usually near blood vessels; release heparin and histamine
Connective Tissue Fibers may be: 1) Collagenous fibers: composed of collagen; have great tensile strength 2) Elastic Fibers: composed of microfibrils embedded in elastin; are very elastic 3) Reticular fibers: very fine, collagenous fibers
Categories of connective tissue: Loose (Areolar) Connective Tissue: -forms thin membranes between organs and binds them -beneath the skin and between muscles Adipose tissue: -stores fat -found beneath the skin, around kidneys, heart and joints
Categories of connective tissue: Dense connective tissue: -composed of strong, collagenous fibers -found in tendons, ligaments, white portion of eyes, deep layer of skin
Categories of connective tissue: Cartilage: -provides a supportive framework for various structures -intercellular material made of fibers and gel-like ground substance -cartilaginous structures enclosed in a perichondrium -cartilage lacks a direct blood supply and is slow to heal -major types are: hyaline, elastic, and fibrocartilage
Fibrocartilage Elastic cartilage Hyaline cartilage
Categories of connective tissue: Bone: -intercellular matrix contains mineral salts and collagen -cells are organized in concentric circles around central canals -an active tissue that heals rapidly
Categories of connective tissue: -transports substances; helps maintain a stable internal environment -composed of: red blood cells (RBCs, WBCs, and platelets in plasma. -blood develops in red marrow in the hollow parts of long bones.
MUSCLE TISSUES General Characteristics: muscle tissues contract, moving structures that are attached to them three types are: SKELETAL, SMOOTH, and CARDIAC
Skeletal Muscle Tissue: usually attached to BONES and controlled by conscious effort cells, or muscle fibers, are long and threadlike muscle fibers contract when stimulated by nerve impulses, then immediately relax
Smooth Muscle Tissue: in the walls of hollow internal organs and blood vessels usually it is involuntarily controlled
Cardiac Muscle Tissue: found only in the heart cells are joined by intercalated discs and form branched networks
NERVOUS TISSUES in the brain, spinal cord, and peripheral nerves
Neurons (Nerve Cells): sense changes and respond by transmitting nerve impulses to other neurons or muscles or glands coordinate, regulate, and integrate body activities
functions include: (Nervous Tissue) Supporting Cells: -bind and support nervous tissue -phagocytosis -connect neurons to blood vessels