HUMAN ANATOMY LECTURE THREE TISSUES (Part 1)

TISSUES Classification based on structure of the cells, cell function, and composition of the extracellular matrix (binding material) 4 tissues types: (1) Epithelial (2) Connective (3) Muscle (4) Nervous Histology – microscopic study of tissues - Biopsy: removal of tissues for diagnostic purposes - Autopsy: examination of organs to determine cause of death

EPITHELIAL TISSUE Covers body surfaces, body cavities and forms glands - skin - lining of digestive tract, respiratory passage, urogenital systems - heart and blood vessels Consists mainly of cells with little extracellular matrix inbetween Free/apical surface – not in contact with other cells Basement membrane/basal surface – attaches to underlying tissues Avascular Cell surface modifications – microvilli (increase surface area) and cilia (movement of particles across surface)

FUNCTIONS OF EPITHELIUM Protecting underlying structures eg: lining of mouth prevents abrasion Acting as barriers eg: skin prevents H 2 O loss and toxins from entering Permitting passage of substances eg: diffusion of O 2 and CO 2 in lungs, nephrons in kidney Secreting substances eg: sweat gland, mucous glands, pancreas enzymes Absorbing substances eg: lining of small intestine Provide sensation

EPITHELIAL CHARACTERISTICS Classified by: Number of cell layers Simple: one layer from free surface to basement membrane Stratified: several layers Pseudostratified: modified simple, looks stratified but actually only one layer of cells Shape of cells Squamous: flat, scale-like Cuboidal: equal in height and width (cube) – round nucleus Columnar: taller than wide – long nucleus * Usually named after both cell layers and shape*

FUNCTIONAL CHARACTERISTICS Simple - allows diffusion of gases, filtration of blood, secretion, absorption Stratified - protection against abrasion Squamous - allow diffusion or act as filters Cuboidal and Columnar - secretion or absorption

SIMPLE SQUAMOUS EPITHELIUM STRUCTURE: single layer of flat, thin cells, fragile so protected LOCATION: alveoli, nephrons of kidneys, inner ear, lining blood and lymphatic vessels FUNCTION: diffusion, filtration, absorption, secretion, some protection against friction

SIMPLE CUBOIDAL EPITHELIUM STRUCTURE: single layer cube-shaped cells, some have microvilli or cilia LOCATION: kidney tubules, glands and ducts, terminal bronchioles of lungs, surface of ovaries FUNCTION: absorption and secretion in the kidney, secretion in glands, movement of mucus out of bronchioles

SIMPLE COLUMNAR EPITHELIUM STRUCTURE: single layer of tall, narrow cells, some have microvilli and cilia LOCATION: glands and some ducts, bronchioles, auditory tube, uterus, stomach, intestines, gallbladder, bile ducts, ventricles of brain FUNCTION: movement of particles, secretion of glands, absorption

STRATIFIED SQUAMOUS EPITHELIUM STUCTURE: many layers of cells that are cuboidal in lowers layers and progressively flatten as near surface. In moist areas, surface cells retain a nucleus and cytoplasm. In keratinized, surface cells are dead. LOCATION: Moist – oral cavity, esophagus, anus, vagina, urethra, cornea Keratinized – skin FUNCTION: protect against abrasion, barrier against infection and chemicals, prevents water loss

STRATIFIED CUBOIDAL EPITHELIUM STRUCTURE: many layers of cube-shaped cells LOCATION: sweat glands, salivary gland ducts FUNCTION: secretion, absorption, protection against infection

STRATIFIED COLUMNAR EPITHELIUM STRUCTURE: many layers of tall, thin cells LOCATION: mammary gland ducts, larynx, male urethra FUNCTION: protection

PSEUDOSTRATIFIED COLUMNAR EPITHELIUM STRUCTURE: appears stratified but actually one layer of tall and short cells – only some cells reach the free surface but all reach basement membrane (nuclei at various levels). Usually ciliated and associated with goblet cells (mucus producing) LOCATION: nasal cavity and sinuses, pharynx, trachea, bronchi, auditory tubes FUNCTION: synthesis and secrete mucus, moves mucus over free surface

TRANSITIONAL EPITHELIUM STRUCTURE: specialized stratified epithelium. Cells can change shape when stretched. Unstretched – layers of cuboidal or columnar cells with dome-shaped free surface. Stretched – low cuboidal or squamous shaped with fewer cell layers. LOCATION: lining of bladder, ureters, urethra FUNCTION: accommodates fluctuation in fluid volume, protection against acidity of urine

CELLULAR CONNECTIONS Epithelial cells connect to one another in various ways - found on lateral and basal cell surfaces FUNCTIONS: Form permeability barrier Binds cells together Provides mechanism for intercellular communication TYPES: Desmosomes Tight Junctions Gap Junctions

DESMOSOMES Found in areas subjected to high stress Disc-shaped areas with glycoproteins and intermediate filaments connecting the two cells Button Desmosomes – 2 small discs - connects cell to cell Hemidesmosomes – ½ a desmosome - connect cell to basal lamina

TIGHT JUNCTIONS Binds cells together Formed by interlocking membrane proteins Zona adherens – between adjacent cells - weak glue holding cells together Zona occludens – permeability barrier (nothing gets through) eg: in stomach, urinary bladder so chemicals cannot pass

GAP JUNCTIONS Protein channels allowing small substances to pass between cells (intercellular communication)

GLANDULAR EPITHELIUM Specialized epithelium for secretion Two types: Endocrine - no opening to exterior, no ducts - produce hormones released into tissue - within epithelial tissue or specialized organs Exocrine - ducts open to epithelial surface - classified by structure and method of secretion

GLAND STRUCTURE Unicellular Glands Goblet Cells - secrete mucus - scattered among epithelial cells eg: trachea and intestinal cells

Multicellular Glands Classified by type of duct: Simple - single duct that doesn’t divide or branch off Compound - duct divides into many branches - ducts end in straight or coiled tubules - ducts ending in blind sacs are called alveolar or acinar - ducts may be both tubular and sac-like, called tubuloalveolar or tubuloacinar

METHODS OF SECRETION Merocrine Product released by exocytosis No loss of cytoplasm eg: sweat glands secrete mucin (mucus and water) Apocrine Cytoplasm lost with product - part of cell pinched off and released eg: mammary glands (combo of merocrine and apocrine secretions) Holocrine Product accumulates in cell, cells ruptures, dies and all is released eg: sebaceous (oil) glands of hair and skin