Anatomy Lecture 2

What is histology?

The study of tissues

Define tissue

A group of similar cells and extracellular products that perform a common function

Describe the extracellular matrix

Produced by the cells and surrounds them

What is the extracellular matrix composed of?

Water, protein fibers, dissolved molecules

What differs in the extracellular matrix across tissues?

Composition, volume, and consistency

What are the four types of tissues in the body?

* Epithelial tissue
* Connective tissue
* Muscle tissue
* Nervous tissue

What are the two types of epithelial tissue?

Simple and stratified

How many layers are in simple epithelial tissue?

1

How many layers are in stratified epithelial tissue?

2 or more

What are the types of simple epithelial tissue?

1. Simple squamous epithelial tissue
2. Simple cuboidal epithelial tissue
3. Simple columnar epithelial tissue
4. Pseudostratified columnar epithelial tissue

What are the types of stratified epithelial tissue?

1. Keratinized stratified squamous epithelial tissue
2. Non-keratinized stratified squamous epithelial tissue
3. Stratified cuboidal epithelial tissue
4. Stratified columnar epithelial tissue
5. Transitional epithelial tissue

What are the types of muscle tissue?

1. Smooth muscle
2. Cardiac muscle
3. Skeletal muscle

Which type of muscle tissue is voluntary?

Skeletal

What are the types of nervous tissue?

1. Neuron
2. Glial cells

What are the types of connective tissue?

1. Connective tissue proper
2. Supporting connective tissue
3. Fluid connective tissue

What are the types of proper connective tissue?

Loose and dense

What is the difference between loose and dense connective tissue?

Loose connective tissue is low in protein fibers and dense connective tissue is high in protein fibers

What are the types of loose proper connective tissue?

* Areolar connective tissue
* Adipose connective tissue
* Reticular connective tissue

What are the types of dense proper connective tissue?

* Dense regular connective tissue
* Dense irregular connective tissue
* Elastic connective tissue

What are the types of supporting connective tissue?

Cartilage and bone

What are the types of cartilage supporting connective tissue?

* Hyaline
* Elastic cartilage
* Fibrocartilage

What are the types of bone supporting connective tissue?

* Compact bone
* Spongy bone

What are the types of fluid connective tissue?

Blood and Lymph

Where is epithelial tissue?

Lines every body surface (epidermis) and all body cavities

What is derived from epithelial tissue?

A majority of glands

Does epithelial tissue have blood vessels?

No. It is avascular

Is the extracellular matrix present in epithelial tissue?

No. It possesses little to no extracellular matrix

What are the characteristics of epithelial tissue?

* Cellularity
* Polarity
* Attachment to a basement membrane
* Avascularity
* Innervation
* High regeneration capacity

Describe how epithelial tissue possesses cellularity

* Composed almost entirely of cells bound by intercellular junctions
* Little extracellular matrix between cells

Describe how epithelial tissue possesses polarity

Epithelia have an apical surface, lateral surface, and basal surface

Define the apical surface

It is exposed and may have modifications like microvilli and cilia

Describe microvilli

Increase surface area for absorption of nutrients

Describe cilia

Help move particles

Define the lateral surfaces

Have intercellular junctions

Define the basal surface

Attached to connective tissue underneath it

Define attachment to a basement membrane as a characteristic of epithelial tissue

Basal surface attaches to a basement membrane, which is a structure produced by both epithelial and neighboring connective tissues

Define avascularity as a characteristic of epithelial tissue

Epithelial tissues lack blood cells. They receive nutrients by diffusion from underlying tissues

Define innervation as a characteristic of epithelial tissue

Epithelia are richly innervated to detect changes in the environment

Define high regeneration capacity as a characteristic of epithelial tissue

Epithelial cells are quickly replaced because the exposed apical surface is frequently damaged

What are the functions of epithelial tissue?

* Physical protection
* Selective permeability
* Secretion
* Sensation

Describe how epithelial tissue is used for physical protection

It defends against dehydration and abrasion as well as physical, chemical, and biological agents

Describe how epithelial tissue is used for selective permeability

It regulates the passage of molecules in or out of certain regions of the body

Describe how epithelial tissue is used for secretion

It secretes substances for use in the body or for elimination from the body

Describe how epithelial tissue is used for sensation

The tissue possesses nerve endings that can detect light, taste, sound, smell, and hearing

Where is the basement membrane?

Between epithelium and underlying connective tissue

What makes up the basement membrane?

Proteins and carbohydrates into discrete layers

What are the layers that make up the basement membrane?

* Lamina lucida
* Lamina densa
* Reticular lamina

What produces the lamina lucida and laminda densa?

Epithelial cells produce the components for the two laminae

What produces the reticular lamina?

Connective tissue

What are the functions of the basement membrane?

* Provides physical support
* Anchors epithelial tissue
* Acts as a barrier regulating passage of large molecules between epithelium and connective tissue

What are the different types of intercellular junctions?

* Tight junctions
* Adhering junctions
* Desmosomes
* Gap junctions

Describe tight junctions

* Encircle epithelial cells near apical surface and attach each cell to its neighbor
* Prevent molecules from traveling between epithelial cells

Describe adhering junctions

Formed around the cell deep to the tight junction and help stabilize the apical surface of the epithelial cell

Describe desmosomes

* Junctions that appear at locations of mechanical stress between cells
* Some basal epithelial cells have hemidesmosomes anchoring them to basement membrane

Describe gap junctions

Allow adjacent cells to communicate with each other by the flow of ions and small molecules

What are the different classifications of the epithelium by layer?

1. Simple epithelium
2. Stratified epithelium
3. Pseudostratified epithelium

How many layers does the simple epithelium have?

One layer of cells

How many layers does the stratified epithelium have?

Two or more layers of cells

How many layers does the pseudostratified epithelium have?

Appears to have multiple layers, but all cells attach to the basement membrane

Describe the simple epithelium

All cells have an apical surface and attach to the basement membrane

Describe the stratified epithelium

Not all cells have an apical surface nor do all cells attach to the basement membrane

Pseudostratified epithelium is a subtype of what

Simple epithelium

What are the different classifications of epithelial tissue by shape?

* Squamous
* Cuboidal
* Columnar
* Transitional

Describe squamous epithelial tissue

Flat, wide, and somewhat irregular in shape

Describe cuboidal epithelial tissue

About the same size on all sides; nucleus is usually centrally located

Describe columnar epithelial tissue

Taller than they are wide, nucleus is oval, and located in basal region of cell

Describe transitional epithelial tissue

Cells change shape depending on degree of stretch

* Polyhedral in a relaxed state
* Squamous when stretched

Where is transitional epithelial tissue found?

The lining of the urinary bladder

Describe simple squamous epithelium

Single layer of flat cells with a flat nucleus that allows for rapid change

What are examples of simple squamous epithelium?

Lining of alveoli and lining of blood vessels

Define endothelium

What epithelium is called when lining blood and lymphatic vessels

Define mesothelium

The simple squamous epithelium of a serous membrane

Describe simple cuboidal epithelium

Single layer of cells as tall as they are wide with a round or spherical nucleus

Which epithelium tissues allow for absorption and secretion?

Simple columnar and simple cuboidal

What are some examples of the simple cuboidal epithelium?

Kidney tubules and ducts of exocrine glands

Describe simple columnar epithelium

Single layer of tall, narrow cells with an oval nucleus near the bottom third of the cell

What are the forms of the simple columnar epithelium

Ciliated and nonciliated

What could nonciliated forms of simple columnar epithelium have?

Microvilli and goblet cells which secrete mucin

What are examples of nonciliated simple columnar epithelium?

Most of the digestive tract (stomach to anal canal)

What is a ciliated example of simple columnar epithelium?

Uterine tube

Describe pseudostratified columnar epithelium

Single layer of narrow cells with varying heights and both ciliated and nonciliated forms

* Appears stratified but is simple
* All cells touch basement membrane but not all reach apical surface

What is the function of pseudostratified columnar epithelium

Protection

What is the function of ciliated pseudostratified columnar epithelium

Secretes mucin and moves mucus

What is an example of pseudostratified columnar epithelium

Respiratory tract lining

Describe stratified squamous epithelium

Multiple layers with only the deepest layer of cells contacting the basement membrane

What are the shapes of the various cells in the stratified squamous epithelium?

* Apical cells are squamous
* Deeper cells are cuboidal or polyhedral

What is the function of stratified squamous epithelium?

Protection

What are the types of stratified squamous epithelium?

Keratinized and nonkeratinized

Describe keratinized stratified squamous epithelium

Apical cells are dead, flat, and filled with the tough protein keratin. Dry

Where is keratinized stratified squamous epithelium found?

In the epidermis of the skin

Describe nonkeratinized stratified squamous epithelium

Apical cells are flat, moist, and alive. Wet

Where is nonkeratinized stratified squamous epithelium found?

The esophagus and vagina

What is rare epithelial tissue?

Stratified cuboidal epithelium and stratified columnar epithelium

Describe stratified cuboidal epithelium

* Multiple layers of cells
* Apical cells are as tall as they are wide

What is the function of stratified cuboidal epithelium?

Protection, secretion, support the walls of some ducts

Where are stratified cuboidal epithelium found?

Lining of sweat gland duct

Describe stratified columnar epithelium

Multiple layers of cells with elongated apical cells

What is the function of stratified columnar epithelium?

Protection, support, and secretion

Where is stratified columnar epithelium found?

Part of male urethra, ducts of some salivary glands

What is the general purpose of stratified epithelial tissues?

Protection