The Tissue Level of Organization

Four main types of tissueEpithelial tissue

Four Tissue Types• Epithelial (epithelium)• Connective• Muscle• Nervous

Function of Epithelial tissue• Covers body surfaces• Lines body cavities and ducts• Forms glands

Functions of Connective Tissue • Protects and supports body and organs• Binds organs together• Storage of energy reserve

Function of Muscular Tissue• Generate force for movement• Body temperature maintenance

Functions of Nervous Tissue• Initiates nerve impulses• Body coordination

Epithelium• Two types of epithelium– Covering and lining– Glandular

Covering and lining epithelium• Characterized by– cell arrangement – cell shape

Epithelial cell arrangements• Simple– One layer of cells

• Stratified– Two or more layers of cells

• Pseudostratified– One layer of cells; appears to have multiple layers

Epithelial cell shapes• Squamous– Flat, thin, arranged like floor tiles.• Shape allows for rapid transport

• Cuboidal– Shaped like cubes (or hexagons)• Secretion and absorption

Epithelial cell shapes• Columnar– Tall and cylindrical

• Protect underlying layers of tissue• May also have cilia, may also secrete and absorb materials

• Transitional– Shape can change (from columnar to flat)

• Allows body parts to stretch or expand or move

Simple squamous epithelium

Simple cuboidal epithelium

Simple columnar epithelium

Pseudostratified columnar epithelium

Transitional epithelium

Stratified squamous epithelium

Stratified cuboidal epithelium• Rare• Found in ducts of some glands (mammary,

sweat, salivary, pancreas)

Stratified columnar epithelium• Rare• Found only in male urethra and lactiferous

ducts

Epithelial structure• Little or no space between cells• Cells meet at “junctions”.• Avascular

Epithelial structure• Held in place by underlying connective tissue• Nutrients supplied by underlying tissue

Glandular epithelium• Has cells that are specialized to produce and

secrete substances into ducts or into body fluids• gland = 1 or more cuboidal or columnar cell• secretion• salivary glands, sweat glands, endocrine glands

Exocrine and Endocrine gland• Endocrine – ductless – secrete products

directly into blood.– Pituitary, thyroid, adrenal glands

• Exocrine – secretions sent into ducts at skin surface or organ.

Types of ducts

Exocrine glands classified by function• Holocrine– Cell dies as it secretes; replaced by new cell

• Merocrine– Cell secretes via exocytosis Golgi produced secretory

vesicles• Apocrine– Part of cell pinches off and becomes secretion. Cell repair

itself and repeats