The Tissue Level of Organization Chapter 4 Anatomy and Physiology

Types of Tissue Four Primary Types I. Epithelial II. Connective III. Nervous IV. Muscle

Epithelial Covers body surfaces e.g. skin, but also “internal” body surfaces: Lines the internal passageways and body cavities: Digestive system Respiratory system Reproductive system Urinary system Cells are in layers: one layer or multiple layers. Always have a “free surface” exposed to the environment or internal chamber or passageway.

Epithelial Tissue Epithelial tissue: Avascular: (does not contain blood vessels) the cells of the epithelium obtain nutrients by diffusion or absorption from deeper tissues or exposed surfaces. Network of protein fibers called the BASEMENT MEMBRANE connects the epithelium to the rest of the body.

Epithelium Functions 1. Physical protection: 2. Permeability control: From abrasion, dehydration, chemical agents, biological agents. 2. Permeability control: Some are impermeable others allow movement of molecules as large as proteins 3. Provision of sensation- touch, smell taste. 4. Provision of specialized secretions Digestive enzymes, perspiration, milk, hormones

Types of Epithelial Tissues Classified according to: A. Number of cell layers B. Cell Shape

A) Number of Cell Layers Simple Epithelium Are thin Are relatively fragile Line internal passageways: Chambers of heart, blood vessels Line regions where secretions or absorption occurs Short amount of time for materials to pass Stratified Epithelium Have several layers Cover areas which are exposed to mechanical stress. e.g. Skin Lining of mouth

Simple Stratified

B. Cell Shape Squamous: Cuboidal Columnar Thin flat cells Nucleus is the thickest portion Viewed form the surface they look like “fried eggs” Cuboidal Hexagonal cells of equal height In sectional view they appear square with the nuclei near the center of each cell Columnar Similar to cuboidal Taller and more slender Nuclei closer to basment membrane

Squamous Cell Cuboidal Cell Columnar Cell

Types of Epithelial Tissue Simple Squamous- Consists of flat irregularly shaped cells Is the most delicate epithelium Covers the heart and lungs where it secretes lubricating fluids which reduce friction in the operation of these organs Found in blood vessels and aveoli ANATOMICAL TERMINOLOGY Mesothelium- simple squamous epithelial tissue that lines the pleura, peritoneum and pericardial cavities. Endothelium- simple squamous epithelial tissue that lines the heart and blood vessels.

Simple Squamous

Types of Epithelial Tissue Stratified Squamous Epithelium- The squamous type cells form several layers Is found in lining of mouth and esophagus Surface of skin Protect against mechanical injury Outer layers may become non-living and fall off.

Stratified Squamous

Types of Epithelial Tissue Simple Cuboidal Epithelium Are hexagonal cells of equal height and width In cross section they appear square Provides limited protection where secretion and absorption take pace Tubules of kidneys Salivary glands May secrete enzymes and buffers

Simple Cuboidal

Types of Epithelial Tissue 4. Stratified Cuboidal Epithelium 1. Are rare 2. Found along ducts of sweat glands and mammary glands 3. Provide protection, secretion, absorption of various biochemicals

Stratified Cuboidal

Types of Epithelial Tissue 5. Transitional Epithelium Unusual epithelium that lines urinary bladder where large changes in volume take place Appearance changes as stretching occurs. In empty bladder the epithelium seems to have many layers and the outermost cells look like plump cuboidal cells. Layered appearances is due to overcrowding of cells Actual structure can be seen in the full urinary bladder (few 1-2 layers)

Transitional

Types of Epithelial Tissue 6. Simple Columnar Epithelium Are similar to cuboidal epithelium but they are taller and more slender Is found in the small intestine, stomach and large intestine This is the epithelium that provides protection from the chemical stress of the digestive system.

Simple Columnar

Types of Epithelial Tissue Pseudostratified Is a mixture of epithelial cell types The cells appear to be in layers due to the various shapes of the cells and the apparent location of the nuclei However…all cells are in contact with the basement membrane Actually is a simple epithelium Found lining trachea, nasal cavities, bronchi, and parts of the male reproductive tract. Always possess cillia They provide protection and secrete protective fluids

Pseudostratified

Types of Epithelial Tissue Stratified Columnar Epithelium Are rare Occur in large salivary gland ducts and in small areas of the pharynx, anus, mammary glands, and urethra Their function is to provide protection

Stratified Columnar

Glandular Epithelia Produce exocrine or endocrine secretions. Exocrine Secretions: produced by exocrine glands that discharge their secretions through a duct, tube, or onto some external surface. Endocrine Secretions (hormones): produced by ductless glands and released into blood or tissue fluids

Mode of Secretion Merocrine Secretion: product released through exocytosis (leaves cell intact) e.g. mucus in digestive and respiratory tracts Apocrine Secretion: involves loss of both cytoplasm and secretory product (leaves cell intact) e.g. Mammary gland milk, perspiration Holocrine Secretion: entire cell becomes packed with secretion and bursts (cell is no longer intact) e.g. skin oils and waxy coating of hair