TISSUES Tissues - cells working together to perform a common function Histology - Study of tissues

4 BASIC TYPES Epithelial - covers & lines surfaces, forms glands Connective - connects tissues, provides support, stores energy reserves Muscle - Contracts for movement, generates heat Neural - Carries information from one part of body to another in the form of electrical impulses

Epithelial Tissue - layer of cells that forms a barrier Functions: –provides physical protection –controls permeability –provides sensations –produces secretions Characteristics: –consists mainly of cells –consists of single layer or multiple layers –always has a free surface exposed to the environment –avascular –mitotic rate can be very high

Intercellular Connections Tight Junction - formed by fusion of cell membranes Desmosome - thin proteoglycan layer between opposing cell membranes Gap Junction - binding of membrane proteins

Shapes: Squamous - flat Cuboidal - cubed Columnar - higher than wide CLASSIFICATION Subdivided according to shape & arrangement of cells in each type Arrangements: Simple - single layer of same shape Stratified - many layers of same shape Transitional - several layers of differing shapes

SIMPLE SQUAMOUS (most delicate) Locations –Alveoli in lungs –blood & lymphatic vessels Functions –Reduce friction –Diffusion of gases –Controls permeability

STRATIFIED SQUAMOUS (tough) Locations –Surface of skin –Lining of mouth, throat, esophagus, rectum, vagina Functions –Protection against abrasion, pathogens, and chemicals

SIMPLE CUBOIDAL Locations - –glands, ducts, kidney tubules, thyroid gland Functions - –protection, secretion, and/or absorption

STRATIFIED CUBOIDAL (RARE) Locations - –lining of some ducts like sweat glands Functions - –Protection, secretion, absorption

TRANSITIONAL EPITHELIUM (STRETCHY) Locations - –Urinary bladder, ureters Functions - –Permits expansion & recoil after stretching

SIMPLE COLUMNAR Locations- –Lining of stomach, intestine, gallbladder, uterine tubes, collecting ducts of kidneys Functions - –Protection, secretion, absorption

PSEUDOSTRATIFIED COLUMNAR EPITHELIUM Locations - –lining of nasal cavity, bronchi, trachea Functions - –protection, secretion –Nuclei are located at varying distances from surface

STRATIFIED COLUMNAR Relatively Rare Locations - –pharynx, epiglottis, anus, mammary ducts, urethra Functions - –Protection

Glandular epithelium Cells that make up glands are specialized to produce and secrete substances Types of secretions from cells –1. endocrine Glands that secrete their products into tissues or blood Ex: Pituitary and sex glands –2. exocrine a.Merocrine: release products by exocytosis Ex: salivary glands/ pancreas b.Apocrine: Lose small portions of glandular bodies during secretion ex: mammary glands: fat droplets/sweat glands a.Holocrine: entire cell disintegrates Ex: sebaceous glands of skin (fatty mixture called sebum)