HISTOLOGY THE STUDY OF TISSUES

GENERAL Tissue = Cells with similar structure & function organized into groups or layers Four major types: Epithelial (Covers or lines surfaces, found in glands) Connective (Binds & supports body parts) Muscle (Movement) Nervous (Detects changes & transmits info.)

CHARACTERISTICS OF EPITHELIAL TISSUE Covers all body surfaces inside & out Many tightly packed cells, usually arranged into layers Free surface & basement membrane Functions: protection, absorption, sensation, secretion High rate of cell division (healing) Avascular (rely on diffusion)

Epithelial Cell Surface - May be variously modified Cilia move substances across the free surface. Microvilli increase surface area for absorption. Stereocilia vibrate in response to sound waves. Apical cells may be keratinized for protection.

CLASSIFICATION OF EPITHELIAL TISSUE Layers Simple (one layer) Stratified (>1 layer; Note: only cells at surface have characteristic shape) Shapes Squamous (thinnest, if simple) Cuboidal Columnar Transitional (changes shape)

CONNECTIVE TISSUE - GENERAL Few cells widely spaced in non-living matrix Matrix may be fibrous, solid, semi-solid, fluid Largest % of tissue by weight; found in all body parts Binds, protects, supports, transports, storage, insulation May be vascular

CONNECTIVE TISSUE - GENERAL Fibroblast Most common cell Secretes fibers Collagen – strong, flexible, structural Elastic – stretch & recoil Reticular – highly branched, supportive Differs in type, amount, and arrangement of fibers in matrix Loose or dense; regular or irregular

MUSCLE TISSUE Contract, provide movement 3 types based on location, morphology, & function: Skeletal (attached to bones; voluntary movement) Smooth (moves substances through hollow organs) Cardiac (heart; moves blood)

NERVOUS TISSUE Rapidly regulates & coordinates body functions Brain, spinal cord, nerves 2 types of cells: Neuron (nerve cell) Most specialized cell in body Generates & transmits nerve impulses Neuroglia (“nerve glue”) Assist neurons (bind, protect, supply)

Hollow Organs Substances pass through Wall is composed of 3-4 layers Lumen is term for inner space Septum (internal wall) may subdivide lumen E.g. digestive organs, urinary tract, heart, blood vessels, ducts

Solid Organs Outer Cortex Deeper Medulla May require internal support Parenchyma is functional tissue; stroma is supportive/filler tissue (usually deeper) E.g. brain, spleen, kidney