Epithelial Tissues, Chapter 5

Microanatomy

These are tissues are sheets of cells that cover or line all body surfaces, cavities, and tubes (glands)

Epithelial tissues

A single layer of epithelium cells is:

Simple epithelium

Multiple layers or cells of epithelium is:

Stratified epithelium

Squamous is

flattened cells

Cuboidal is

cube-shaped cells

Columbar is

Tall, rectangular cells

The basal surface faces:

the basement membrane

The apical surface faces:

outwards

What are cell junctions and what do they do?

Bind epithelial cells to adjacent cells, providing physical strength and mediate the exchange of information and metabolites.

Epithelium that is primary involved in secretion is arranged into structures called:

glands

These glands are connected to the surface epithelium of the GI tract by branching system of ducts

Exocrine glands

These glands are lost connection to the epithelial surface, which they developed, releasing their secretions directly into the blood

Endocrine glands

Simple epithelia are almost always found at interfaces involved in:

Selective diffusion, absorption and secretion

What are some examples where simple epithelia can be found?

Bowmans capsule

Loop of Henle

Simple epithelia may exhibit surface specializations, such as:

microvilli

cilia

Composed of flattened, irregularly shaped cells, forming a continuous surface (pavemented epithelium)

Simple squamous epithelium

“Squamous is derived from the comparison of the cells to the:

scales of a fish

Single layer of cube-like cells with spherical nuclei

Simple cuboidal epithelium

What are the functions of simple cuboidal epithelium?

Excretion, secretion and absorption (microvilli)

Where are some areas simple cuboidal epithelium can be found?

Kidney tubules

Small ducts of exocrine glands

Rete testis

Surface of ovary

What are some locations of simple columnar epithelium?

Small intestine

Stomach lining

Gallbladder

Collecting ducts of kidney

What are the differences between simple columnar epithelium and simple cuboidal?

Cells are taller

Appear more columnar in sections, perpendicular to the basement membrane

What is larger, cilia or microvili?

Cilia

visible with light microscope

Where can simple columnar ciliated epithelium be found?

In the female reproductive tract

This appears stratified but is a single layer of cells.

Psuedostratified columnar epithelium

Where are pseudostratified epithelium located?

respiratory tract

Stratified epithelium consists of:

two or more layers of cells

How is stratified epithelia classified?

Based on the shape and structure of the surface cells

Transitional epithelium is what kind of epithelium?

Stratified epithelium

Where can transitional epithelium be found?

Only in the urinary outflow tract

(waterproof, expansile)

Surface cells are tough, non-living and filled with keratin:

keratinized type, stratified squamous epithelium

Surface cells are alive and moist from glandular secretions

Non-keratinized type, stratified squamous epithelium

Where can keratinized stratified squamous epithelium be found?

Epidermis of skin (stratum corneum)

Where can non-keratinized stratified squamous epithelium be found?

Lining of oral cavity

Epiglottis

Esophagus

Anus

Cervix

Vagina

Glans penis

cornea

Thin stratified epithelium, usually only two or three layers of cube-like cells

Stratified cuboidal epithelium

Where can stratified cuboidal epithelium be found?

Large ducts of exocrine glands, lining

(salivary glands)

Several layers of cells that can change shape, allowing for distension

Transitional epithelium

What is the main function of transitional epithelium?

Permits expansion and recoil after stretching

(can withstand toxicity of urine)

What are the 5 main functions of epithelial tissues?

1. Protection (skin, lining of organs)

2. Absorption (intestines)

3. Filtration (kidney)

4. Excretion (sweat glands)

5. Secretion (hormone release)

What are the three types of surfaces of epithelia?

Intercellular surfaces

Luminal surfaces

Basal surfaces

The basal surfaces are like the basement membranes, which are:

Interface between all epithelia and underlying supporting tissues

These bind base of the cell to the underlying basement membrane

Hemidesmosomes

Luminal surfaces may incorporate three main types of specializations:

Cilia

Microvilli

Stereocilia

These link adjacent or lateral surfaces of epithelial cells to form a continuous, cohesive layer

Cell junctions

Where do tight junctions occur?

Luminal end of lateral cell membrane

What are the functions of the tight junctions?

Control the paracellular diffusion

Prevents the exchange of intrinsic proteins and lipids between apical and basolateral plasma membrane

Adhering junctions provide:

Anchorage points for cytoskeletal elements

What are the 3 types of adhering junctions?

Adhesion belt

Desmosome

Hemidesmosome

Where are adhering junctions located?

Lateral plasma membrane, immediately deep to tight junction

What are the 3 polarity domains of epithelial cells?

Apical domain

Lateral domain

Basal domain

Kartagener syndrome is a genetic disorder that has abnormalities from inherited abnormalities in cilia. Symptoms include brochiectasis and sinusitis, situs inversus, male infertility. This syndrome is from what kind of dysfunciton?

Ciliary dysfunction

What are 3 additional cilary disorders?

Hydrocephalus

Bardet-Biedl syndrome

Cystic disease of the kidneys

Stereocilia are:

Very long microvilli

Where are stereocilia located?

Epididymis

Inner ear

These are modified columnar epithelial cells that synthesize and secrete mucus. They are terminally differentiated and DO NOT DIVIDE.

Goblet cells

A composed mixture of neutral and acidic glycoproteins (mucopolysaccharides)

Mucigen

Where are mucigen granules located?

Apical cytoplasm

What are 3 types of exocrine glands?

Liver

Large bowel

Goblet cells (simple)

the morphology of the gland can be divided into 2 components:

Duct

Secretory component

What are the two duct systems in exocrine glands?

Unbranched (simple)

Branched (compound)

What are the 2 secretory components of the exocrine glands?

Tubular

Acinar

What are the 3 means of secretions of exocrine glands?

merocrine (eccrine)

Apocrine

Holocrine

This secretion involves the process of exocytosis, most common (proteins)

Merocrine

This secretion involves the discharge of free, unbroken, membrane-bound vesicles containing a secretory product

Apocrine secretion

This secretion involves the discharge of whole secretory cells, with subsequent disintegration of cells to release the secretory product

Holocrine secretion

The sebaceous glands are what type of secretion?

Holocrine

Lipid secretory products of the breasts and some sweat glands are what type of secretion?

Apocrine secretion

this type of gland has a simple, straight tubular lumen.

Simple tubular glands

Simple tubular glands can be found in:

Large intestines, goblet cells

A single tube that is tightly coiled in three dimensions

Simple coiled tubular glands

What is an example of a simple coiled tubular gland?

Sweat glands

This tubular gland has a terminal secretory portion S.

Simple coiled tubular gland

Where are simple branched tubular glands located?

Found mainly in the stomach

a single, unbranched duct connected to multiple branching, tube-like secretory units

Simple branched tubular glands

This gland consists of several tubular secretory portions T

Simple branched tubular glands

Where do simple acinar glands occur?

Penis urethra

These glands occur in the form of pockets of epithelial surfaces, lined by secretory cells

Simple acinar glands

This can be used to describe any rounded exocrine secretory unit

Acinus

an exocrine gland with multiple round, grape-like secretory sacs (acini) that empty into a single, unbranched duct

Simple branched acinar gland

These glands consists of numerous acini, each of which drain into a minute duct

Compound acinar gland

Where are compound acinar glands located?

Pancreas

These glands have three types of secretory units, branched tubular, branched acinar, branched tubular with acinar end-pieces called demilunes

Compound tubulo-acinar glands

What is the mechanism of epithelial cell renewal?

Cells at the basal layer divide and differentiate, replacing damaged or dead cells

Why is epithelial cell renewal important?

Constant renewal maintains the integrity of epithelial surfaces, especially in high-wear areas

What are three common pathologies of epithelial tissues?

Carcinomas

Metaplasia

Dysplasia

this is abnormal development or growth of epithelial tissue

Dysplasia

Malignancy arising from epithelial cells

Carcinoma

Replacement of one mature differentiated cell type with another mature differentiated cell type

Metaplasia

Metaplasia is triggered by:

chronic irritation of cells

How can you reverse metaplasia?

Remove stimulus (medication for reflux, vaccines for HPV)

What are 2 examples of metaplasia?

Intestinal metaplasia

Squamous metaplasia

What is an example of intestinal metaplasia?

Barrett’s Esophagus

What is an example of squamous metaplasia?

Cervical metaplasia

The ectocervix has what kind of cells:

Stratified squamous epithlieum

The endocervix has what kind of cells:

Simple columbar epithelium

What are some histological features of squamous cell carcinoma?

large pleomorphic cells

invasion of the basement membrane

The epithelial tissues have roles in what 3 organ systems?

Respiratory (move mucus, ciliated epithelium)

Digestive (absorbs nutrients, columnar epithelium)

Integumentary (protection, stratified squamous epithelium)

The secretion of hormones are controlled by what three components?

1. Metabolic factors (blood glucose)

2. Secretion of other hormones (TSH controls secretion of thyroxine)

3. Nervous system (secretion of adrenaline by the adrenal medulla)