TissuesTissuesTissue = a group of cells (and their extracellular Tissue = a group of cells (and their extracellular

products) that share a similar structure or function.products) that share a similar structure or function.

Each organ is made up of Each organ is made up of severalseveral tissue tissue typestypes..

Main Tissue TypesMain Tissue Types

1.1. EpitheliumEpithelium

2. Connective (bone cartilage, tendons, 2. Connective (bone cartilage, tendons, ligaments ligaments AND blood)AND blood)

3. Muscle3. Muscle

4. Nervous 4. Nervous

Epithelial TissuesEpithelial Tissues Cover surfaces of the body.Cover surfaces of the body.

Line tubes and hollow organsLine tubes and hollow organs

within the body.within the body.

Form various glands.Form various glands.

Common characteristics shared by all Common characteristics shared by all epitheliaepithelia

1. Form continuous sheets or tubes, 1 to many cells thick.1. Form continuous sheets or tubes, 1 to many cells thick.

2. Consist of closely packed cells with very little intercellular 2. Consist of closely packed cells with very little intercellular matrix.matrix.

Common characteristics shared by all Common characteristics shared by all epithelia:epithelia:

3. Extensively interconnected by cell-cell junctions.3. Extensively interconnected by cell-cell junctions.

Terminal bars represent cell-to-cell attachment sites.

Common epithelial characteristics:Common epithelial characteristics:

4. Cells are 4. Cells are polarpolar with with

structurally and functionally structurally and functionally

distinct surface domains: distinct surface domains:

apical, basal, lateral.apical, basal, lateral.

5. Supported by a basal lamina (in red), 5. Supported by a basal lamina (in red),

a basement membrane that cells a basement membrane that cells

use for structural support and attachment.use for structural support and attachment.

lumen

apical portionof a cell basal

portionof a cell

Common characteristics of Common characteristics of epithelium:epithelium:

6. Avascular6. Avascular

7. Dependent on diffusion of dissolved 7. Dependent on diffusion of dissolved gases and metabolites.gases and metabolites.

8. Continually renewed by mitosis.8. Continually renewed by mitosis.– Intestinal epithelium half-life = 4-6 daysIntestinal epithelium half-life = 4-6 days– Skin epidermis half-life = 2-4 weeksSkin epidermis half-life = 2-4 weeks

Classification of Epithelia must be in this Classification of Epithelia must be in this order:order:

1. Number of cell layers1. Number of cell layers– Simple – one cell layer resting on the basal laminaSimple – one cell layer resting on the basal lamina– Stratified – >1 cell layer thick, only basal layer rests on Stratified – >1 cell layer thick, only basal layer rests on

basal laminabasal lamina– Pseudostratified – looks stratified, but all cells are Pseudostratified – looks stratified, but all cells are

actually in contact with BL.actually in contact with BL.

2. Shape of the most superficial layer of cells2. Shape of the most superficial layer of cells– Squamous – flattened in shapeSquamous – flattened in shape– Cuboidal – cube-shaped or squareCuboidal – cube-shaped or square– Columnar – rectangular or elongated with respect to the Columnar – rectangular or elongated with respect to the

basal laminabasal lamina

3. Surface specializations3. Surface specializations– Ciliated or non-ciliatedCiliated or non-ciliated– Keratinized or non-keratinizedKeratinized or non-keratinized– Brush border (microvilli) or stereociliaBrush border (microvilli) or stereocilia– Goblet cellsGoblet cells

Simple squamous epithelium of capillaries

kidney tubuleskidney tubules

Human kidneyHuman kidney

DuodenumDuodenum

Gobletcell

Microvilli(striated border)

Slide 53a

EsophagusEsophagus

classify thisepithelium

Thick skin

keratin

StratifiedSquamous Epithelium

TracheaTrachea Epididymis

Pseudostratified Epithelium

cilia stereocilia

Transitional EpitheliumTransitional Epithelium lining the Bladder lining the Bladder

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

Structure and Function are Structure and Function are Connected!Connected!

Simple squamous epithelium Simple squamous epithelium indicates lots of transport across it.indicates lots of transport across it.

Stratified epithelium suggests Stratified epithelium suggests protection.protection.

Simple columnar epithelium indicates Simple columnar epithelium indicates secretion and/or absorptionsecretion and/or absorption