TISSUES

Body Tissues Cells are specialized for particular functions Tissues - groups of cells with similar structure and function Histology - study of the organization of cells and extracellular material into tissues and organs Four primary tissue types 1) Epithelium 2) Connective tissue 3)Nervous tissue 4) Muscle

Epithelial Tissues Found in different areas 1) Body coverings 2 ) Body linings 3) Glandular tissue Functions 1) Protection 2) Absorption 3) Filtration 4) Secretion

Epithelium Characteristics 1) Cells fit close together – Desmosomes and Tight junctions 2) Apical Surface - Tissue layer always has one free surface (unattached) exposed to the body’s surface or the cavity of an internal organ 3) The lower surface is bound by a basement membrane 4) Avascular (have no blood supply) so they depend on diffusion for food and oxygen 5) Regenerate easily if well nourished

Classification of Epithelium Each Epithelium is given 2 names: First name indicates the Number of cell layers Simple – one layer Stratified – more than one layer Figure 3.17a

Classification of Epithelium Second name indicates the Shape of cells Squamous – flattened Cuboidal – cube-shaped Columnar – column-like Figure 3.17b

Simple Epithelium Simple squamous Single layer of flat cells resting on a basement membrane Cells fit closely together. Forms membranes where filtration or exchange of substances through rapid diffusion occurs Ex: Serous membranes that line organs and air sacs in lungs Figure 3.18a

Simple Epithelium Simple cuboidal Single layer of cube-like cells on basement membrane Common in glands and their ducts Forms walls of kidney tubules and covers the ovaries Figure 3.18b

Simple Epithelium Simple columnar Single layer of tall cells that fit closely together Often includes goblet cells, which produce mucus Lines entire digestive tract Functions in absorption and secretion Figure 3.18c

Simple Epithelium Pseudostratified Columnar Single layer, but some cells are shorter than others ALL cells touch basement membrane Often looks like a double cell layer Sometimes ciliated, such as in the respiratory tract May function in absorption or secretion Also has goblet cells to produce mucous Figure 3.18d

Stratified Epithelium Stratified squamous Cells at the free edge are flattened; cells near the basement membrane are cube or column shaped Found as a protective covering where friction is common Figure 3.18e

Stratified Epithelium Stratified squamous (continued) Two types: 1) SS Keratinized – all extenal skin Keratin is a protein that makes skin dry and rough and keeps water out and things like bacteria and viruses. Keratin doesn’t allow you to see the nucleus and it will be flaky 2) SS Non-Keratinized – all internal skin Mouth, tongue, vagina No keratin so the nucleus can be seen to surface layer; still able to resist penetration of organisms but skin is moist & slippery (resists wear & tear) Figure 3.18e

Stratified Epithelium Stratified cuboidal and columnar 1) Rare in human body 2) Found mainly in ducts of large glands

Stratified Epithelium Transitional epithelium - Highly modified, stratified squamous epithelium Shape of cells depends upon the amount of stretching 1) Basal layer cells (bottom) are cuboidal or columnar 2) Free (apical) surface cells are rounded and dome like if not stretched but squamous like (flat) when full of urine Lines organs of the urinary system (Ureters and Bladder) Figure 3.18f

Glandular Epithelium Gland – one or more cells that secretes a particular product Two major gland types Endocrine gland – Ductless and the secretions are hormones Exocrine gland - Empty through ducts to the epithelial surface. Include sweat and oil glands

Connective Tissue Found everywhere in the body Includes the most abundant and widely distributed tissues Functions: 1) Binds body tissues together 2) Supports the body 3) Provides protection

Connective Tissue Characteristics Variations in blood supply Some tissue types are well vascularized (much blood supply) Ex: bone Some have poor blood supply (tendons or ligaments) or are avascular (no blood) (cartilage) Extracellular matrix – main difference between other tissue types Non-living material that surrounds living cells