Epithelial Tissues

Nestor T. Hilvano, M.D., M.P.H.

Learning Objectives You should be able to: 1. List the embryonic germ layers and some adult

tissues derived from each.

2. Describe the important characteristics (traits or features) and functions of epithelial tissues.

3. Describe the intercellular connections of epithelia.

4. Distinguish the form and function for each epithelial type and state where each type of epithelium can be found in the body.

5. Describe the different types of glands according to presence or absence of ducts, modes of glandular secretion, and types of secretion.

Tissues derived from Embryonic (germ) layers

Tissues are group of ___.a.organs b. cells c. organelles d. molecules

• 4 main types of tissues: epithelial, connective, muscular, and nervous tissues• 3 Germ layers and its derivatives: a) Ectoderm – epidermis, nervous systemb) Mesoderm – connective tissues, bones, muscles, ovaries, testes, kidneysc) Endoderm – epithelium of respiratory tract, digestive tract, and glands.

Functions of Epithelial Tissue

• Protection• Control permeability – absorption,

excretion, filtration• Provide sensation (neuroepithelium)

• Produced specialized secretions

Properties of Epithelial Tissue

* Common traits (properties or characteristics) of epithelium:

1. Cellularity 2. Polarity (apical vs basal surfaces)

3. Attachment (basement membrane)

4. Avascularity 5. Regeneration

Intercellular connections • Tight junction

- or occluding junction; prevents passage of water or solutes bet. cells; in gastrointestinal and urinary tracts

• Desmosome - or macula adherens; resist stretching and twisting; in uterus and

epidermis of skin (causing dead cells to shed in thick sheets) • Gap junction - or nexus; forms a narrow passage bet. cells; in cardiac and smooth

muscle tissues (allow ions and small molecules to pass from one cell to another)

• Intermediate junction

- or fascia adherens; held together by thick layer of proteoglycans

Classification of Epithelia• Simple

- squamous

- cuboidal

- columnar

• Stratified

• Pseudostratified

• Transitional

What epitheliium is composed of:

a) one layer of cells?

b) two or more layers of cells?

c) false-layers of cells?

d) cell layers varies depending on distension?

Simple Squamous Epithelium

• Functions: Permits diffusion(osmosis) of substances• Locations = ________________________________

Simple Cuboidal Epithelium

• Functions: Absorption and secretion• Locations = ___________________

Simple Columnar Epithelium

• Functions: Protection, absorption and secretion• Locations = ____________________________

Pseudostratified Epithelium

• Functions: Protection and secretion; secretes and propel respiratory mucus • Locations = _________________________

Stratified Squamous Keratinized

• Surface cells are non-nucleated, squamous cells with keratins (dead cells) • Functions: Protection and barrier against abrasion, organisms and chemical attack, retards water loss• Locations = ____________________________

Stratified Squamous Nonkeratinized

• Epithelium forming moist, slippery layer; cells are squamous, nucleated (living cells) • Functions: Protection/barrier• Locations = ______________________________

Stratified Cuboidal Epithelium

• rare in the body• Locations = sweat gland ducts; growing ovarian follicles and seminiferous tubules of testes

Transitional Epithelium

• Number of cell layers varies depending on function (distension) • Functions: permits expansion and recoil after stretching• Locations = __________________________________

Glandular Epithelium• Secrete substances• Presence/absence of ducts

1.) Exocrine glands: ___ 2.) Endocrine glands: ___

a. ductless b. with ducts

• Number of cells1.) Unicellular glands: ___2.) multicellular glands: ___a. salivary glands b. goblet cells

• Types of secretions1.) Serous glands: ___2.) Mucous glands: ___3.) Mixed glands: ___a. thick, viscous b. thin, watery c. both d. neither

Modes of Glandular Secretiona. Merocrine = released from secretory vesicles by

exocytosis; gland intact

b. Apocrine = apical portion shed with secretion; partial glandular destruction

c. Holocrine = whole gland shed with secetion; total destruction

• Classify the following glands:

___ - sebaceous gland

___ - sweat (eccrine) gland

___ - mammary gland

Homework (Self-review) 1. Discuss common characteristics of epithelial

tissues. 2. Compare and contrast simple squamous and

stratified squamous as to structure, functions, and locations (examples).

3. Identify the lining epithelium of: trachea, alveoli of lungs, esophagus, small and large intestines, stomach, mesothelium of body cavities, endothelium of blood vessels, thyroid gland, proximal convoluted tubules (PCT) of kidney, urinary bladder, epidermis of skin.

4. Describe briefly merocrine, apocrine, and holocrine glands.

5. Differentiate exocrine gland from endocrine gland.