Tissues Tissue = a group of cells (and their extracellular products) that share a similar structure or function. Each organ is made up of several tissue types.

Main Tissue Types 1. Epithelium 2. Connective (bone cartilage, tendons, ligaments AND blood) 3. Muscle 4. Nervous

Epithelial Tissues Cover surfaces of the body. Cover surfaces of the body. Line tubes and hollow organs Line tubes and hollow organs within the body. within the body. Form various glands. Form various glands.

Common characteristics shared by all epithelia 1. Form continuous sheets or tubes, 1 to many cells thick. 2. Consist of closely packed cells with very little intercellular matrix.

Common characteristics shared by all epithelia: 3. Extensively interconnected by cell-cell junctions. Terminal bars represent cell-to-cell attachment sites.

Common epithelial characteristics: 4. Cells are polar with structurally and functionally distinct surface domains: apical, basal, lateral. 5. Supported by a basal lamina (in red), a basement membrane that cells use for structural support and attachment. lumen apical portion of a cell basal portion of a cell

Common characteristics of epithelium: 6. Avascular 7. Dependent on diffusion of dissolved gases and metabolites. 8. Continually renewed by mitosis. –Intestinal epithelium half-life = 4-6 days –Skin epidermis half-life = 2-4 weeks

Classification of Epithelia must be in this order: 1. Number of cell layers –Simple – one cell layer resting on the basal lamina –Stratified – >1 cell layer thick, only basal layer rests on basal lamina –Pseudostratified – looks stratified, but all cells are actually in contact with BL. 2. Shape of the most superficial layer of cells –Squamous – flattened in shape –Cuboidal – cube-shaped or square –Columnar – rectangular or elongated with respect to the basal lamina 3. Surface specializations –Ciliated or non-ciliated –Keratinized or non-keratinized –Brush border (microvilli) or stereocilia –Goblet cells

Simple squamous epithelium of capillaries

kidney tubules

Human kidney

Duodenum Goblet cell Microvilli (striated border) Slide 53a

Esophagus classify this epithelium Thick skin keratin Stratified Squamous Epithelium

Trachea Epididymis Pseudostratified Epithelium cilia stereocilia

Transitional Epithelium lining the Bladder

1. a. Name the space at the pointer. 1.b. Identify the tissue lining that space. (Be specific.)

2.a. Identify the structure at the pointer. b. What is its main function?

Structure and Function are Connected! Simple squamous epithelium indicates lots of transport across it. Simple squamous epithelium indicates lots of transport across it. Stratified epithelium suggests protection. Stratified epithelium suggests protection. Simple columnar epithelium indicates secretion and/or absorption Simple columnar epithelium indicates secretion and/or absorption