Chapter 03

You look at a tissue under a microscope and see a simple squamous epithelium. Can it be a sample of the skin surface? Why or why not?

No. A simple squamous epithelium does not provide enough protection against infection, abrasion, and dehydration and is not found in the skin surface.

ZS: I looked it up and should be stratified squamous for the skin

Which of the following is an example of a connective tissue:

A. Adipose

B. Nerves

C. Muscles

D. All of the above

A

There are three main types of connective tissue: loose, dense, and adipose. Specialized connective tissue includes bones, blood, and cartilage

Which of the following statements is true regarding the intestinal mucous membrane:

A. It is composed of smooth muscle cells organized as two or more sublayers

B. It consists of an epithelial lining with an underlying connective tissue rich in blood vessels, lymphatics, and small glands

C. It is a thin layer of loose connective tissue covered with mesothelium

D. All of the above

B

What is a tissue?

A group of specialized cells and cell products that work together to perform specific functions

What is histology?

The study of tissues

What are the four primary tissue types?

Epithelial tissue, connective tissue, muscle tissue, and nervous (or neural) tissue

Why can the appearance of a tissue vary markedly in histological preparations?

Depending on the plane of section

Can the internal organization of a cell or tissue vary even within a single plane of section?

Yes, even within a single plane of section, the internal organization of a cell or tissue may vary as the level of section changes

What is scoliosis?

Spinal curvature

What is a cardiac arrhythmia?

An abnormal heart rhythm

What does AED stand for?

Automated external defibrillator

What is the key point of section 3.1 Epithelial Tissue?

Epithelial tissue is composed of tightly bound, avascular sheets of cells that cover exposed surfaces and line internal cavities and passageways

What are epithelia?

Sheets of cells that cover every exposed body surface and line internal cavities and passageways; epithelial tissue includes epithelia and glands

Give an example of an exposed surface covered by epithelia.

The surface of the skin

Give examples of internal passageways lined by epithelia.

The digestive, respiratory, reproductive, and urinary tracts, as well as the inner surfaces of the blood vessels and heart

What does cellularity mean as a characteristic of epithelia?

Epithelia are composed of cells bound tightly together by specialized junctions; there is little or no intercellular space between these cells

What is polarity in an epithelium?

A property in which an epithelium's exposed apical surface and its attached basal surface differ in plasma membrane structure and function; polarity occurs whether the epithelium has a single layer or multiple layers of cells

What does avascularity mean for epithelia?

Epithelia do not contain blood vessels and are therefore avascular; because of this, epithelial cells must obtain nutrients by diffusion across the basal surface

What does the sheets or layers characteristic of epithelia mean?

All epithelial tissue is composed of a sheet of cells one or more layers thick

What does regeneration mean as a characteristic of epithelia?

Stem cells located within the epithelium divide to continually replace surface epithelial cells that are damaged or lost

What is the key point about the functions of epithelial tissue?

Epithelial tissues protect surfaces, control permeability, provide sensation, or produce secretions

How do epithelia protect surfaces?

They protect exposed and internal surfaces from abrasion, dehydration, and destruction by chemical or biological agents

How do epithelia control permeability?

Any substance that enters or leaves the body has to cross an epithelium; some epithelia are relatively impermeable, whereas others are permeable to substances as large as proteins

What molecular machinery do many epithelia contain related to permeability?

Machinery needed for selective absorption or secretion; the epithelial barrier can be regulated and modified in response to various stimuli

Can physical stress alter the structure and properties of an epithelium?

Yes, even physical stress can alter the structure and properties of epithelia, such as the calluses that form on your hands and feet

How do epithelia provide sensation?

Sensory nerves innervate most epithelia; specialized epithelial cells can detect changes in the environment and convey information about such changes to the nervous system

How do touch receptors provide sensation in epithelia?

By stimulating adjacent sensory nerves

What are neuroepithelia?

Specialized sensory epithelia found in special sense organs that provide the sensations of smell, taste, sight, balance, and hearing

How do epithelia produce specialized secretions?

Gland cells are epithelial cells that produce secretions, substances produced and discharged from a cell

What are unicellular glands?

Individual gland cells scattered among other cell types in an epithelium

What is a glandular epithelium?

An epithelium in which most or all of the epithelial cells produce secretions

What is the key point about specializations of epithelial cells?

The apical and lateral surfaces of epithelial cells are specialized in a variety of ways to perform cellular functions

Along what axis do many epithelial cells show a definite polarity?

An axis that extends from the apical surface to the basolateral surfaces

What is the basolateral surface of an epithelial cell?

Where the cell is exposed to an internal or external environment, contacts the basement membrane and neighboring epithelial cells

Does the arrangement of organelles vary among epithelial cells?

Yes, the actual arrangement of organelles varies depending on the cell's associated proteins and functions

What projections are found on the apical surface of many epithelial cells?

Microvilli

Where are microvilli especially abundant on epithelial surfaces?

Where absorption and secretion occur, such as in the digestive and urinary tracts

What is stereocilia?

Very long microvilli found in the epididymis of the male reproductive tract; unlike cilia, stereocilia cannot move

What is a ciliated epithelium?

An epithelium that has cilia on its apical surface that beat together in a coordinated fashion

Give an example of a ciliated epithelium and its function.

The ciliated epithelium lining the trachea, which moves mucus toward the throat, carrying trapped dust and pathogens away from the lungs

What three factors interact to keep epithelial tissues intact and healthy?

Intercellular connections, attachment to the basement membrane, and epithelial maintenance and renewal

What binds adjacent epithelial cell membranes together?

A variety of cell junctions

What does extensive infolding of adjacent cell membranes do?

Interlocks the cells and increases the surface area of the cell junctions

What do intercellular connections prevent?

Chemicals or pathogens from entering the epithelium

What gives an epithelium its strength and stability?

The combination of cell junctions and physical interlocking, along with cell adhesion molecules (CAMs) and intercellular cement

What does the basal surface of a typical epithelium attach to?

The basement membrane, a complex structure produced by the epithelium and cells of the underlying connective tissue

What is the superficial portion of the basement membrane called?

The basal lamina

What secretes the basal lamina?

Epithelial cells

What does the basal lamina contain?

A network of fine protein filaments

What is one function of the basal lamina?

Restricting the movement of proteins and other large molecules from the underlying connective tissue into the epithelium

What lies deep to the basal lamina?

The second layer of the basement membrane, called the reticular lamina

What secretes the reticular lamina?

The underlying connective tissue

What does the reticular lamina contain?

Bundles of coarse protein fibers

What does the reticular lamina do?

Anchors the basement membrane to the underlying connective tissue

Why must epithelial cells continually repair and renew themselves?

Because exposure to enzymes, toxic chemicals, pathogens, and abrasion damages epithelial cells, so the faster tissues have to be replaced

How quickly are the fastest epithelial cells replaced, such as those lining the small intestine?

They may survive only a day or two

How can an epithelium maintain itself if the underlying connective tissue is severely damaged?

Only through continual division of stem cells, which are usually found close to the basal lamina

What is the key point about classification of epithelia?

Epithelial tissue is classified according to the number of cell layers and the shape of the cells at the exposed surface

What are the two types of layering in epithelium classification?

Simple and stratified

What are the three cell shapes used in epithelium classification?

Squamous, cuboidal, and columnar

What is a simple epithelium?

An epithelium that has only one layer of cells covering the basement membrane

What is true of the polarity and nuclei of all cells in a simple epithelium?

All the cells have the same polarity, so their nuclei are located at the same distance from the basement membrane

Why are simple epithelia thin and fragile?

Because a single layer of cells cannot provide much protection

Where are simple epithelia found in the body?

Only in protected areas inside the body, such as the thoracic, abdominal, and pelvic cavities, the chambers of the heart, and the lining of blood vessels

Where else are simple epithelia found, and why?

Where secretion, absorption, or filtration occurs, such as in the lining of the intestines and the gas exchange surfaces of the lungs

Why does a thin single layer provide an advantage where secretion, absorption, or filtration occur?

By decreasing the diffusion distance and the time needed for materials to pass through the epithelial layer

What is a stratified epithelium?

An epithelium that has two or more layers of cells

Why do we use the shape of the most superficial cells to classify a stratified epithelium?

Because the height and shape of the cells in a stratified epithelium differ from layer to layer

Why are stratified epithelia thicker and stronger than simple epithelia?

Because multiple layers of cells make stratified epithelia thicker and sturdier

Where do stratified epithelia typically occur?

Where mechanical or chemical stresses are severe, such as the surface of the skin and the lining of the oral cavity

Where are stem cells located in a simple epithelium?

At or near the basement membrane

Where are stem cells found in a stratified epithelium?

In the deeper layers of the epithelium

What do cells of a squamous epithelium look like?

Thin, flat, and irregular in shape, like flat pieces of a puzzle

What is a simple squamous epithelium?

The most delicate epithelium in the body

Where is simple squamous epithelium found?

In protected regions where diffusion or other transport occurs, or where a slippery surface reduces friction, such as the respiratory exchange surfaces (alveoli) of the lungs and the lining of blood vessels

What is mesothelium?

The simple squamous epithelium that lines the ventral body cavities

What is endothelium?

The simple squamous epithelium that lines the heart and blood vessels

What is stratified squamous epithelium, and where does it occur?

An epithelium formed of a series of layers, occurring where mechanical stresses are severe, such as the surface of the skin and the lining of the oral cavity, throat, esophagus, rectum, vagina, and anus

What is keratin?

A protein that makes the superficial layers of a stratified squamous epithelium tough and water resistant

Where is keratinized stratified squamous epithelium found?

In the hair, nails, and calloused skin

What is a nonkeratinized stratified squamous epithelium, and where does it occur?

A stratified squamous epithelium, also called mucosal, that must stay moist or it will dry out and deteriorate; it occurs in the oral cavity, pharynx, esophagus, rectum, anus, and vagina

What do the cells of a cuboidal epithelium look like?

Like hexagonal boxes and appear square in typical sectional views, with each nucleus centrally located

What is simple cuboidal epithelium?

An epithelium that provides limited protection and occurs in regions where secretion or absorption takes place

Give an example of a location with simple cuboidal epithelium.

The kidney tubules, which are lined with simple cuboidal epithelium

What is stratified cuboidal epithelium, and where is it found?

A rare epithelium found lining the ducts of sweat glands and mammary glands

What do the cells of a columnar epithelium look like?

Hexagonal in cross section, but their height is much greater than their width

Where are the nuclei of columnar cells typically located?

Within the basal portion of the cell

What is a simple columnar epithelium, and where is it found?

An epithelium found in areas where absorption or secretion occurs, such as the lining of the stomach, intestinal tract, and many excretory ducts

What is stratified columnar epithelium, and where is it found?

A rare epithelium that occurs in the pharynx, epiglottis, anus, and a few large excretory ducts; it usually has only two layers, though it may have more

What two specialized epithelia line the respiratory system and hollow conducting organs of the urinary system?

Pseudostratified ciliated columnar epithelium and transitional epithelium

What does pseudostratified ciliated columnar epithelium contain?

A mixture of cell types

Why does pseudostratified ciliated columnar epithelium look stratified?

Because the cells' nuclei are located at varying distances from the surface

Why is pseudostratified ciliated columnar epithelium actually a simple epithelium, despite its appearance?

Because all the cells rest on the basement membrane, so it is actually a simple epithelium

What surface feature does pseudostratified ciliated columnar epithelium possess?

Cilia

Where does pseudostratified ciliated columnar epithelium line?

Most of the nasal cavity, trachea, and bronchi, and also portions of the male reproductive tract

Where is transitional epithelium found?

It lines the renal pelvis, ureters, and urinary bladder

What is unique about transitional epithelium?

It is a stratified epithelium that can stretch without damaging the epithelial cells

What do the cells of transitional epithelium look like in an empty urinary bladder?

The epithelium has many layers, and its outermost cells are rounded or balloon-shaped cuboidal cells

What happens to transitional epithelium as the bladder fills and stretches?

It resembles a stratified, nonkeratinized squamous epithelium with two or three layers

What is the key point about glandular epithelia?

We classify glandular epithelia based on the glands' secretions, structure, and mechanism of secretion