BIOSCI 107 EPITHELIAL TISSUE

Epithelial Tissue location

Body surface, lines hollow organs and forms glands

The four junctions?

tight, adherens and gap junctions, desmosomes and hemidesmosomes

Key functions of Epithelia

- Selective Barrier

- Secretory

- Protective

In the cytoskeleton

- Micro filaments e.g. actin

- Intermediate filaments e.g. keratin

Function of Microfilaments

Provides strength, alters cell shape and links the cytoplasm to the membrane.

- Bundles beneath the cell membrane and cytoplasm

Function of Intermediate filaments

Provides strength, and moves materials through the cytoplasm

Different surfaces of cell junctions? (3)

Apical, Lateral or Basal

Which junction is only found in epithelial tissue?

Tight junctions are only found in this type of tissue

Tight Junction

- Joins cytoskeleton of adjacent cells via ZO-1 (protein) to actin

- Keeps cell polarities

- Prevents diffusion across the junction

- Regulate transport through the ECM

- Claudins and Occludins

Adherens Junctions

- Belt-like structure

- Cadherins span the gap between adjacent cells

Catenins link cadherin to actin

Desmosome

- Cadherins span the intercellular space

- Joins to intermediate filaments, e.g. keratin

- Contributes to stability of C&T, resists shearing

Gap Junction

- Direct communication between cells

- 6 connexins make a connexon a.k.a. hemichannel

- 2 hemichannels make a gap junction

Hemidesmosome

- Connects epithelia to basement membrane

- Integrin span the gap, and binds to laminin (basal) and keratin (apical)

Junctional complex

The combination of tight junctions, adherens junctions and desmosomes

Basal Lamina

Secreted by epithelial cells - contains collagen, laminin, glycoproteins and proteoglycans

Reticular lamina

Produced by cells of underlying connective tissue (fibroblasts) - contains proteins such as fibronectin, collagen etc.

Functions of basement membrane

- Supports overlying epithelium

- Provides surface for epithelial cell migrating

- Physical barrier e.g. to invasion such as melanoma

the two types of epithelial tissue? where are they located?

- Covering and Lining: Skin and internal organs, blood vessels, ducts and body cavities

- Glandular Epithelia: secretory portion of glands

Arrangement types of covering & lining epithelia

- Simple

- Stratified

- Pseudostratified

Shapes of covering & lining epithelia

- Squamous

- Cuboidal

- Columnar

- Transitional

Subtypes of Simple squamous epithelium (2)

Mesothelium: lines cavities

Endothelium: Lines inside of heart and blood vessels

Appearance of Simple squamous epithelium

Flat and irregular

Functions of Simple squamous epithelium (3)

- Most delicate epithelium

- Filters and diffuses

- Not present in areas subject to mechanical stress

Location of Simple squamous epithelium (3)

- Inside eye

- Alveoli

- Linings of cavities and blood vessels

Appearance of simple cuboidal epithelium

Cuboidal, round, centrally located nucleus

Functions of simple cuboidal epithelium (1)

Secretion and absorption

Location of simple cuboidal epithelium (4)

- Surface of ovaries

- Capsule of lens of eye

- Kidney tubules

- Ducts of many glands

Appearance of Non-cilliated simple columnar epithelium (2)

- Columnar like with nuclei near base of cells

- has micro villi

Functions of Non-cilliated simple columnar epithelium (3)

- Contain microvilli at apical surface and goblet cells

- Secrete and absorb (has large columnar cells and thus higher level of secretion and absorption compared to cuboidal)

- Microvilli increase S.A. of the plasma membrane (incr. absorption)

Location of Non-cilliated simple columnar epithelium (3)

- Lines gastrointestingal tract (stomach to anus)

- Ducts of many glands

- Gall bladder

Appearance of Cilliated simple columnar epithelium

Nuclei near the base of cells - goblet cells are scattered

Function of Cilliated simple columnar epithelium

- moves mucus (via cilia) up the throat

- Dispels oocytes through fallopian tubes to uterus

Location of Cilliated simple columnar epithelium (6)

- Lines bronchioles, fallopian tubes, uterus, paranasal sinuses, spinal cord and brain

Function of Stratified squamous epitheliums (5)

- Protects against abrasion, water loss, ultraviolet radiation and foreign invasions

- both types form first line of defence against microbes

subtypes of stratified squamous epithelium

Keratinized: Has keratin in the apical layer

Non-keratinized: no keratin abundance and is moistened instead, by mucus

Appearance of stratified squamous epithelium

- 2 or more layers of cells in which the apical layers are squamous and deeper are cuboidal or columnar

Location of Stratified squamous epithelium (6)

Keratinized: Forms superficial layer of skin

Non-keratinized: lines wet surfaces (lining of mouth, oesophagus, pharynx, vagina) and covers tongue

Subtypes of Pseudostratified columnar epithelium (2)

Cilliated: contains goblet cells or cilia

Non-Ciliated: lack both

Appearance of Pseudostratified columnar epithelium

All cells reach the basement membrane, not all reach the apical layer; hence there is only one layer

Functions of Pseudostratified columnar epithelium (2)

Ciliated: Secretes mucus and traps foreign particles

Non-Ciliated: Absorbs and protects (NC is rarer)

Location of Pseudostratified columnar epithelium (4)

Ciliated: Lines airways, most of the upper respiratory tract

Non-Ciliated: Lines larger ducts of many glands, epididymis and part of the male urethra

Appearance of Stratified cuboidal epithelium

2 or more layers of cube-shaped cells (fairly rare)

Function of Stratified cuboidal epithelium (3)

Protection, limited secretion and absorption

Location of Stratified cuboidal epithelium (3)

- Sweat and esophageal glands

- Male urethra

Appearance of Stratified columnar epithelium

- 2 layers of cells; only apical layer has columnar cells (uncommon)

Function of Stratified columnar epithelium (2)

Protection and secretion

Location of Stratified columnar epithelium (4)

- Lines part of the urethra, excretory ducts of glands (e.g. esophageal glands), anal mucous membrane, conjunctiva of eye

Appearance of stratified transitional epithelium (2)

Relaxed: similar to cuboidal epithelium

Stretched: Squamous appearance

Function of Stratified transitional epithelium (2)

- Allows urinary organs to stretch while maintaining protective lining without rupture

Location of stratified transitional epithelium (3)

- Lines urinary bladder and portions of ureters and urethra

Subtypes of Glandular epithelia

Endocrine: Diffuses into the bloodstream via traversing interstitual fluid

Exocrine: Secretes into ducts that empty onto the surface of epithelium i.e. skin or lumen

Appearance of Glandular epithelia

Appearance is dependent on where the substance is secreted

Functions of Glandular epithelia

Endocrine: Hormones regulate metabolic and physiological activities - maintains homeostasis

Exocrine: Produces substances (e.g. sweat) to lower body temp, oil, earwax, saliva or digestive enzymes

Locations of Glandular epithelia (9)

Endocrine: Pituitary, pineal, thyroid and parathyroid glands

Exocrine: Sweat and salivary glands, oil and wax glands, and the pancreas

Simple glands

There is a single gland that does not divide on its way to the gland cells

Compound glands

Has more than one duct

Types of Simple glands (5)

- Simple Tubular

- Simple coiled tubular

- Simple branched tubular

- Simple alveolar

- Simple branched alveolar

Types of Compound glands

- Compound tubular

- Compound alveolar

- Compound tubuloalveolar