Introduction to Histology (Epithelial Tissue)

Basic Science Core - Histology Exam 1

Structural Hierarchy of the Human Body

1) Atoms

2) Molecules

3) Macromolecules

4) Organelles

5) Cells

6) Tissues

7) Organs

8) Organ systems

9) Human body

Four Basic Tissue Types

1) Epithelial tissue

2) Connective tissue

3) Muscle tissue

4) Nervous tissue

Epithelial tissue

• Refered to as Epithelium

• Likes to form layers (Like a sheet)

• Covers body surfaces

• Lines body cavities

• Prominent in glandular tissue

Epithelial tissue function

• Protection, secretion, absorption, excretion

• Lacks blood vessels (avascular)

• Rests on a basement membrane

• Part of the MUCOSA of many organ wall

Types of Epithelium (7)

Simple vs Stratified

• Simple is 1 layer

• Stratified is multiple layers

Pseudostratified vs transitional

• Pseudostratified → Looks like any cells but it is not

• Transitional →

Connective Tissue (Function)

Supports other tissues

.

• Mechanical reinforcement (tendons, ligaments), protection & support (bone, cartilage), immune surveillance (blood), transport of nutrients/wastes (blood), energy storage (adipose)

Types of Connective Tissue (4 Big Types

1) Blood

2) Bone

3) Cartlidge

4) Connective Tissue Proper

Muscle Tissue (And Function)

Consists of excitable, contractile cells

• Movement, motility

• Heat production

• Skeletal, cardiac and smooth

Types of Muscle (3)

Nervous Tissue

Consists of excitable cells capable of

electrical transmission (conduction)

as a communication tool

• Brain, spinal cord, nerves, sensory organs

• Neurons, neuroglia

Epithelial Tissue Functions (5)

Secretion

Mechanical protection

Absorption / Reabsorption

Receptor transduction

Transportation

Secretion

hormones, gastric juice, pancreatic juice, saliva, bile

Mechanical protection

skin (epidermis), linings of GI tract

Absorption / Reabsorption

nutrients, electrolytes, vitamins, water

Receptor transduction

taste buds, hair cells, photoreceptors (rods & cones)

Transportation

cilia (oviducts, certain airways)

Surface Domains of Epithelial Cell (3)

Apical surface

Lateral surface

Basolateral (Basal) surface

Apical surface

faces lumen,

may have specialized features

(cilia, microvilli, stereocilia)

Lateral surface

may form

“tight junctions”

Basolateral (Basal) surface

attaches to the BASEMENT

MEMBRANE

Epithelial Cell Turnover / Renewal (4)

• Rate of turnover is specific to the type

  of epithelium

• Replenished by a “stem cell” population

\

• 1) Surface epithelial cells in the stomach every 1-2 days

• 2) Enterocytes in the small intestine every 4-6 days

• 3) Oral epithelial cells every 14-21 days

• 4) Liver hepatocytes every 200-300 days

Apical Surface Variations

MICROVILLI

CILIA

STEREOCILIA

MICROVILLI

finger-like projections

that increase surface area and facilitate

absorption; found in the small intestine

and kidneys

CILIA

hair-like structures that can

move in a coordinated manner to propel

substances along a surface; only found in

the oviducts and certain airways

(trachea, bronchi, non-respiratory

bronchioles)

STEREOCILIA

long, non-motile

structures that are thicker than cilia and

involved in sensory transduction

Simple Squamous Epithelium

Single layer of flat, thin cells

Allows for rapid, efficient

movement of substances by

diffusion

Simple Squamous Epithelium (Where in the body)

• Lung alveoli

• Endothelium

• Lining of lymphatic vessels

Alveoli

• Overwhelming major of gas exchange occurs within the alveoli -- smaller amount occurs with respiratory bronchioles

.

• Alveoli are richly surrounded by pulmonary capillaries

.

• Each lung has a total of approx. 300 million alveoli

Alveolar-Pulmonary Capillary Interface

• Physiological significance lies with the interface’s THINNESS & small amount of interstitial fluid

Non-Keratinized Stratified Squamous Epithelium

Multiple layers of flat, thin cells

Provides a barrier against mechanical stress and abrasion

Lubrication (due to mucus production) – helps to

maintain moisture, preventing drying and cracking

Non-Keratinized Stratified Squamous Epithelium Examples

Examples:

• Esophagus

• Oral cavity (buccal lining, inside of the lips, soft

palate, floor of the mouth, some parts of the tongue)

• Cornea

• Vagina

• Anus

Keratinized Stratified Squamous Epithelium

• Multiple layers of flat, thin cells BUT with a layer of KERATIN on top

.

• Provides a barrier against mechanical stress and abrasion

Keratinized Stratified Squamous Epithelium in Oral Health Care

The gingiva, hard palate and parts

of the tongue (especially the dorsal

surface) have this type of

epithelium, which helps them

withstand the forces of chewing

and the tongue’s movements

Keratinized Stratified Squamous Epithelium Examples

Epidermis of the skin

• Oral cavity (hard palate,

gingiva)

• Some parts of the tongue

Two Types of Stratified Squamous Epithelium

• Keratinized Stratified Squamous Epithelium

• Non-Keratinized Stratified Squamous Epithelium

Oral Cavity Epithelium

Basal Cell Layer

The Basal Layer in the cell:

• Site for normal cytosis for cell replenishment in the oral cavity

Epithelial Dysplasia

• Pre Cancerous Condition

• Occurs if cell growth is occurring above the cell layer

Where are the Keratinized vs Non Keratinized Sites in the Oral Cavity

Simple Cuboidal Epithelium

• Single layer of square (cube-shaped) cells

• Allows for secretion and absorption (or reabsorption)

• Forms protective linings

Simple Cuboidal Epithelium Examples (3)

Examples:

• Thyroid follicles

• Kidney tubules (within nephrons)

• Ducts draining salivary glands (smaller ducts)

Thyroid Gland Diagram

Gross Anatomy of the Thyroid Gland

• The thyroid gland is located anterior and lateral to the trachea, just below the thyroid cartilage (Adam's apple).

• It consists of two (sometimes three) lobes (one on each side of the trachea).

• The lobes are connected by a bridge of thyroid tissue called the isthmus, which is located just below the cricoid cartilage.

• The thyroid gland is barely palpable.

• The thyroid gland weighs 10 to 20 grams in normal adults.

Microanatomy of the Thyroid Gland

Microscopically, the thyroid is composed of spherical follicles, each composed of a single layer of follicular cells surrounding a lumen filled with colloid

Thyroid follicles are the sites of

• THYROID HORMONE (T3 and T4) SYNTHESIS

Nephrons

• The functional units of the kidney are the NEPHRONS

• Each kidney contain approximately 1 million nephrons

• Nephrons themselves are NOT cells……but rather they are made up of different types of cells

Nephron Diagram

Nephron Structure

PCT – Tubular reabsorption:

• putting a filtered substance back into the blood

.

• Notice the MICROVILLI on the cells lining the PCT

.

• DCT – Tubular secretion:

  • Removing a substance from the blood and putting into the kidney tubule

Nephron Structure Diagram

Simple Cuboidal Epithelium in Nephron Tissue Photo

Salivary Gland Histology (3)

Acini are classified as:

• serous

• mucous

• mixed

Salivary Gland Diagram

Stratified Cuboidal Epithelium

Multiple layers of square (cube- shaped) cells

• Forms protective linings

Stratified Cuboidal Epithelium (3)

Examples:

• Parts of the male urethra

(penile urethra)

• Ducts draining sweat glands

• Ducts draining salivary glands

(larger ducts)

Male Urinary Tract Cellular Photo (Stratified Cuboidal Epithelium)

Simple Columnar Epithelium

• Single layer of tall cells

• Allows for secretion and absorption; forms protective linings; sensory transduction

• May contain GOBLET CELLS and may have MICROVILLI

Simple Columnar Epithelium Examples

Examples:

• Linings of stomach, small intestine, large

intestine, gall bladder

• Hair cells in the cochlea

Lining of Small Intestine

Lining of Large Intestine

Anatomy of the Inner Ear

Inner ear:

• Cochlea

• Spiral organ of Corti

• Semicircular canals

• Vestibule (utricle and saccule)

• CN VIII (dgagTrachol Nerve)

Anatomy of the Ear Diagram

3 spiral ducts of the Cochlea

3 Spiral Ducts:

• Scala vestibuli

• Scala tympani

• Scala media or cochlear duct

Anatomy of the Cochlea

The cochlear duct is separated from the scala vestibuli by the:

vestibular membrane and

from the scala tympani by the basilar membrane.

The cochlea is filled with 2 types of fluid:

• Perilymph

• Endolymph.

Perilymph

Scala vestibuli and scala typmani; similar to ECF

Endolymph

Scala media; high in [K+] and low in [Na+] compared to ECF

Organ of Corti → Unique property

• Only cells with the long hair cili (Put right name)

• Resting on the basilar membrane is the spiral organ of

  Corti which consists of many supporting cells and hair

  cells.

Physiology of Hearing Step 1

When sound waves strike the eardrum, it vibrates back & Forth

• This rocking motion is transferred to the ossicles, which in turn vibrate.

• As the stapes rocks back & forth against the oval window

  • Its sets the perilymph in the scala vestibuli into a similar back & forth motion

Physiology of Hearing Step 2

Pressure waves descend through the flexible vestibular membrane, then through the endolymph of the cochlear duct, and finally through the basilar membrane.

Physiology of Hearing Step 3

Back to spiral organ

• The tips of the hairs are embedded within and firmly bound to the tectorial membrane above the spiral organ of Corti

Physiology of Hearing Step 4

As the basilar membrane

vibrates, the bending of the

hair cells is transduced into

electrical signals that travel via

CN VIII.

Mechanism of Auditory Transduction

Hair Cell Damage Diagram

Pseudostratified Columnar Epithelium

Single layer of cells that appears to be stratified due to the varying heights of the cells and placement of their nuclei

.

• Allows for secretion, forms protective linings

• Usually contains CILIA and GOBLET CELLS

Pseudostratified Columnar Epithelium Examples

Examples:

• Linings of trachea, bronchi, non-

respiratory bronchioles

CONDUCTION ZONE

moves air

• warms air

• moistens air

• filters air

• airway resistance

RESPIRATORY ZONE

gas exchange

Conduction Zone vs. Respiratory Zone

Conduction Zone vs. Respiratory Zone (Smooth Muscle, Cilia and Cartilage)

Goes Aways

• Cartilage → After Bronchi

• Cilia → After Respiratory Bronchioles

• Smooth Muscle → After Alveolar Ducts

Respiratory Epithelium or Mucosa

From the trachea down to the non- respiratory bronchioles

Transitional Epithelium

• Multiple layer of cells that have different shapes with great distensibility

• Characterized by its ability to change shape and thickness depending on the degree of distention

Transitional Epithelium Examples

Examples:

• Linings of ureters and urinary bladder (urothelium)

Myoepithelium (Myoepithelial Cells)

Myoepithelial cells are found in various glands – mammary, lacrimal, salivary and sweat

• Hybrid of epithelial and smooth muscle cells

.

• Have the ability to contract and promote glandular secretion in response to hormones and neurotransmitters

Myoepithelium Diagram

Posterior Pituitary Hormones (2)

• Oxytocin

• Lactation

Process of Milk Ejection

• 1) Stimulation of the nipple through suckling produces a neurohumoral reflex that causes secretion of oxytocin.

.

• 2) In turn, oxytocin causes contraction of the myoepithelial cells of the mammary alveoli & ducts and the ejection of milk.

Diagram of Milk Ejection