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Human Anatomy and

Physiology ILaboratory

Histology:

Epithelial and Connective Tissue

The Histology lab involves study of the appropriate laboratory exercise, completing the Review Sheet for the exercise, and taking the relevant quiz. Look also at the online histology sites mentioned in the introduction. Alternately, your instructor may have you turn in drawings of the tissues in lieu of the Review Sheets. Use the Virtual Microscope or other histology sites for good images of epithelial and connective tissue.Click on the sound icon for the audio file (mp3 format) for each slide. There is also a link to a dowloadable mp4 video which can be played on an iPod.

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Four Basic Tissue Types:

Epithelial – lining and secretory tissue

Connective – supportive and nutritive tissue

Muscular – contracts to produce movement

Nervous – integration and control

All specific tissues fall into one of the four basic types. In this section we look at epithelial and connective tissues. We will look at nerve and muscle tissues when we cover those topics.

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Characteristics of Epithelial Tissue• Closely packed cells of a mostly uniform type

• Cells attached to a basement membrane

• Cells are joined by a junctional complex

•Tight junctions

• Desmosomes

• Gap junctions

These are the characteristics common to all epithelial tissues.

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Epithelium is named according to shape, structure, and arrangement of cells.

Shapes of Epithelium•squamous - thin and flat cells

•cuboidal - cube shaped cells

•columnar - column shaped cells

One of the major characteristics of epithelial cells is that they come in somewhat standard shapes, which is the basis for naming them. There are occassional variations, for example a "short columnar" which is shorter than regular columnar and taller than cuboidal.

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Epithelial Shapes

Here are the basic shapes of epithelial cells. Note that the shape and position of the nucleus is a distinguishing characteristic for each shape, and can be diagnostic for epithelial types.

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Arrangement and Structureof Epithelial Cells

•simple - single layer of cells

•stratified - multilayered cells

•pseudostratified - false stratified

•transitional - stretchable

•ciliated - cells possess cilia

Arrangement and structural characteristics also distinguish different types of epithelial tissue.

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Simple vs. Stratified

Single Layer

Multi-layered

Epithelial tissue is called simple if it is one layer thick, stratified if it is multilayered. The apical surface is the free surface in both cases, i.e. the surface toward the lumen of an enclosed tubule or duct, or the surface of the body in the case of the skin. The basal surface is the surface opposite to the apical surface and is attached to a basement membrane.

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Basement Membrane Tissue wraps to form capillaries, alveoli of lungs, etc.

Tissue wraps to form capillaries, alveoli of lungs, etc.

Simple Squamous Epithelium

Simple squamous epithelial cells, attached to a basement membrane, wrap around to form tubes and cavities. The basement membrane is on the outside of these tubes (the basal surface), while the apical surface is toward the inside. Capillary walls for instance and the alveoli of the lungs are formed of this very thin tissue. Thinness is the hallmark of simple squamous epithelium, which allows diffusion of substances across the epithelial membrane.

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Functions of Simple Squamous Epithelium

• The thinnest tissue of the body.

• Allows transport across membranes in lungs and capillaries.

• Secretes fluid in serous membranes (e.g. pericardial and pleural membranes, mesenteries).

• Lines cardiovascular system, covers organs, forms glomerular capsules in kidney.

Simple squamous epithelium functions to produce the thinnest membranes of the body such as capillary walls and alveoli of the lungs. This thinness allows for transport of substances across the membranes. Simple squamous epithelium is also secretes serous fluid in mesenteries, and lines the cardiovascular system.

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Mesothelial Lining of Peritoneal Cavity

nucleus

cytoplasm

Plasma membrane

The lining of the peritoneal cavity (roughly the abdominal cavity) is formed of a serous membrane composed primarily of simple squamous epithelium. You are looking at the epithelium from above and can see the cells‘ nuclei and plasma membranes.

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Nucleus of simple squamous cell

Edgewise view of simple squamous cell

Bowman’s Capsule in the Kidney

Cuboidal epithelium also wraps to form tubules and alveoli. These cells are the primary secretory cells in the body's glands.

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Simple Cuboidal Epithelium

Tissue wraps to form tubules and ducts of glands.

Tissue wraps to form tubules and ducts of glands.

Forms ducts, tubules and secretory cells in exocrine glands and in organs such as the kidney.

Basement membrane

Cuboidal epithelium also wraps to form tubules and alveoli. These cells are the primary secretory cells in the body's glands.

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Convoluted Tubules of the Kidney

Nucleus of cuboidal cell

Lumen of tubule

Cuboidal epithelial cells

The secretory cells of most of the body's glands, as well as other organs such as the liver, kidney, and spleen are cuboidal epithelial cells, arranged into tubules, alveoli, or acini.

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Simple Columnar Epithelium

•Non-ciliated in the GI tract, e.g. stomach and intestinal lining.

•Ciliated in portions of the respiratory and genitourinary tracts.

Apical surface may have microvilli or cilia

Apical surface may have microvilli or cilia

Cell nuclei lie toward basal surface

Simple columnar epithelium is a lining tissue found where secretion and absorption occur, as in the GI tract, or kidney. They may have microvilli to provide extra surface area, or cilia where mucus movement along their apical surface occurs, such as in the large bronchioles of the respiratory tract. In the GI and respiratory tracts the tissue incorporates goblet cells which secrete mucus.

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Simple Columnar Epithelium

nucleus

Tubule lumenbasement membrane

This is a longitudinal section of a kidney tubule in which the simple columnar epithelial cells are of the "short columnar" variety, with nuclei which are ovoid and more centered in the cell. These tubules reabsorb substances and secrete substances in producing urine.

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Simple Columnar Epitheliumin the Gastrointestinal Tract

Goblet cells secrete mucus

Basement membrane

Goblet cells are specialized epithelial cells which secrete mucus. Mucus helps protect the GI tract lining and traps particulates in the respiratory tract.

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Lining in the Small Intestine

simple columnar cellsConnective tissue (lamina propria)

villus

Goblet cell

The lining of the small intestine has several surface modifications to increase its surface area. One is the finger-like villi seen here. The villi are then covered (or lined as you prefer) with columnar epithelial cells. Notice the goblet cells which secrete mucus, so called because of their characteristic goblet shape, narrow at the base and expanded at the apical end. They often give the appearance of holes punched in the lining tissue.

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Ciliated Simple Columnar Epithelium

Ciliated simple columnar is found in large bronchioles of the respiratory tract and in the genitourinary tract.

In the respiratory tract the lining is mostly ciliated, with the mucus produced by goblet cells helping to trap particulates. Ciliary action then moves this mucus up the respiratory passages until it reaches the throat where it is swallowed.

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Ciliated Simple Columnar of Fallopian Tube

cilia

Ciliated simple columnar cells

lumen

nucleus

connective tissue

Ciliated simple columnar epithelium is also found in the fallopian tube, where the cilia help in the movement of an oocyte and zygote down the tube toward the uterus. The center of a tube is known as the lumen.

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Pseudostratified Ciliated Columnar Epithelium (PCCE)

A non-ciliated pseudostratified epithelium is found in large

glands and parts of male urethra.

A non-ciliated pseudostratified epithelium is found in large

glands and parts of male urethra.

cilia

Nuclei at different levels are diagnostic for pseudostratified epithelium.

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Pseudostratified Ciliated Columnar Epithelium in the Respiratory Tract

Cilia beat in wave-like fashion to move mucus along the lining surface, carrying dust and particulates up and out of the respiratory tract.

Cilia

Goblet cells secrete mucus

Pseudostratified epithelial cells

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P.C.C.E. in the Trachea

P.C.C.E.

Lumen of Trachea

nucleuscilia

Goblet cell

Basal cell

As in most all epithelia, basal cells undergo mitosis to produce new cells so that the epithelium constantly exfoliates and is renewed.

This shows P.C.C.E. found in the trachea and bronchi of the respiratory tract. In addition to the pseudostratified epithelial cells, there are also goblet cells which secrete mucus, and basal cells which undergo mitosis to replace pseudostratified cells which die.

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Transitional Epithelium

Transitional epithelium lines the urinary tract where it provides stretchability.

4-5 cells non-distended, 3 cells stretched.

superficial cells

basement membrane

Transitional epithelium is found only in the urinary tract, in the urinary bladder and ureter. There it stretches to allow filling of the bladder and to damp the back-pressure in the ureter during micturition(urination) which might otherwise damage the kidney.

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Transitional EpitheliumWall of the urinary bladder

Non-distended transitional epithelium. Distension reduces the number of cell layers.

Transitional epithelium lines the renal calyces, the ureters, the urinary bladder, and a portion of the urethra.

basement membrane

This is transitional epithelium in its unstretched form, when the bladder is empty for example. It is usually 5 layers thick. Imagine as this tissue stretches and the cells slide against one another, the number of layers shrinks to 3 or 4. What junctional structures keep the cells from actually pulling apart?

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Stratified Squamous

Basal layerundergoesmitosis

old cells exfoliate from surface

cells moveup frombelow

Stratified squamous epithelium forms the outer layer or epidermis of the skin. Skin is found as the organ of the integument and also as the lining of mucous membranes in the oral cavity, esophagus, anus and vagina.

When an epithelial tissue has more than one layer it is stratified. Stratified squamous epitheliumconsists of squamous cells in many layers, and is found as the epidermis, or outer layer, of the body's skin. Cells in the epidermis are constantly being replaced as new cells are produced by mitosis in the basal layer and old cells are exfoliated from the apical surface. Humans exfoliate about 90 pounds of cells in the course of a lifetime, and this process keeps the cells of the epidermis constantly renewed.

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Stratified Squamous in the Epidermis of the Skin

Flattened, cornified cells cover the surface as the stratum corneum.

epidermis of stratified squamous epithelium Stratum basale cells constantly

undergo mitosis.

dermis

In the outer skin of the body the cells die and become impregnated with keratin and keratohyalinebefore exfoliating. This produces a protective layer of dead cells called the cornified layer or stratum corneum.

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Non-keratinized Stratified Squamous Epithelium

Section of vaginal wall.

squamous surface cell

Stratified squamous epithelium

Connective submucosa

Notice how the cells of the intermediate layers of the stratified squamous epithelium do not flatten and loose their nucleus as they do in keratinized epithelium (previous slide).

In the body's internal skin found in the anus, vagina, oral cavity and esophagus, the cells do not become keratinized and exfoliate while still intact. This is the basis for the ability to identify cancerous cells which have exfoliated from the cervix of the uterus using a “Pap Smear”.

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Characteristics of Connective Tissues

Cells of connective tissues are widely spaced within an intercellular matrix which determines the characteristics of each specific tissue.

Intercellular matrix components:� fibers - may be collagen (inelastic), elastin (elastic), or reticular.

� loose or dense structure

� ground substance - a semisolid gel containing water, glycoproteins, and other substances

* Used here the term refers to tissues classified as connective tissue proper as well as cartilage and bone tissue.

*

Connective tissue has characteristics which are almost the opposite of those of epithelial tissue. It has cells which are widely spaced apart within an intercellular matrix, and the cells may be of several different types. The matrix may have various combinations of ingredients, which determines the type of connective tissue.

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Cells Found in Connective Tissues

� fibrocytes, or other generic cell for each tissue: osteocytes for bone, chondrocytes for cartilage, adipocytes for adipose, etc.

� macrophages and other phagocytic cells.

� mast cells - like basophils in the blood, these cells secrete histamine and heparin which mediate inflammatory responses.

� plasma cells - a type of lymphocyte, they secrete antibodies. These cells, along with other white blood cells migrate into connective tissues from the circulation.

There will always be one cell type which identifies the specific connective tissue, such as fibrocytesfor the fibrous tissues, osteocytes for bone, chondrocytes for chartilage, and adipocytes for adipose tissue. These cells may be called -blasts (e.g. fibroblasts) if they are actively producing new tissue, -clasts if they are breaking down tissue for rebuilding (e.g. osteoclasts), or -cytes (e.g. osteocytes) if they are mature cells. The other cells are defense cells, very similar to white blood cells found in the circulation.

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Areolar Tissuethe Prototype Connective Tissue

Areolar tissue is called the prototype connective tissue because it has all the aforementioned components: three types of fibers, all types of cells, in a loose, fluid-filled intercellular matrix. It is the most abundant connective tissue, found associated with most epithelial tissues.

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Collagen fibers

Elastic fibers

Fibroblast

Mast cell

Reticular fibers

Found in outer dermis of skin, interstitial tissue, mesenteries and serous membranes.

Found in outer dermis of skin, interstitial tissue, mesenteries and serous membranes.

Areolar Tissue

Areolar tissue is found in the outer dermis of the skin beneath the epidermis, in serous membranes of the body, and is the major interstitial tissue, the tissue which binds cells together. Its intercellular matrix contains most of the body's water.

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Adipose TissueLow Power

arteriole

Adipocytes

Connective matrix

Insulation and shock absorption; fatty pads around organs, subcutaneous fat.

Insulation and shock absorption; fatty pads around organs, subcutaneous fat.

Adipose tissue is a tissue which doesn't match the characteristics of other connective tissues. Its cells are close together, and its matrix is sparse. Fat cells (adipocytes) are filled with a lipid vacuole which almost completely occupies their cytoplasm. It is found in fat pads and in subcutaneous fat which function as insulation and shock absorption, as well as nutritional storage.

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Adipose Tissuehigh power

nucleus of adipocyte

capillary

venule

nucleus of adjacent

fibroblast

Adipose tissue is found in large amounts beneath the skin (subcutaneous) and in serous membranes throughout the body. It is rich in blood vessels as seen in this highly magnified view.

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Dense Irregular Connective Tissue

Nuclei of fibroblasts

Collagen fibers

High power

Low power

Found in the deep dermis of the skin and in the submucosa of the hollow organs.

Found in the deep dermis of the skin and in the submucosa of the hollow organs.

Dense regular is also known as fibrous connective tissue, or inelastic tissue. It has bundles of inelastic collagen fibers, seen in the high power view above. It is found in the inner dermis of the skin as well as tendons, ligaments, and connective fascia.

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Dense Regular(Fibrous Connective Tissue)

collagen fibers

nuclei of fibroblasts

Found in tendons, ligaments, and fascialcoverings.

Found in tendons, ligaments, and fascialcoverings.

Tendon, l.s.Tendon, l.s.

Dense regular tissue is found where tensile strength is important, such as tendons and ligaments. There are few fibroblasts and many dense bundles of inelastic collagen fibers.

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Elastic Connective Tissue

elastic fibers fibroblasts

Found in the stroma of the lungs and in the walls of the large arteries.

Found in the stroma of the lungs and in the walls of the large arteries.

The wall of the aortaThe wall of the aorta

Elastic connective tissue has elastic fibers which are flexible. It is found where flexibility and recoil are important, such as in the walls of arteries (for the expansion and contraction with the pulse) and the stroma or internal support of the lungs (for recoil during expiration).

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Reticular Connective Tissue

High power

fibroblast

lymphocyte

reticular fibers

Forms the internal stroma of the soft organs such as the spleen and lymph nodes.

Forms the internal stroma of the soft organs such as the spleen and lymph nodes.

Section of

lymph node

Section of

lymph node

Reticular connective tissue forms the internal support of most of the soft epithelial organs, glands, etc.

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Lab Protocol1. Identify characteristics, functions and locations of tissues

observed. Suggestion: make a chart showing these things for the major epithelial and connective tissues.

2. Complete the Review Sheet for the Classification of Tissues exercise in the lab manual.

3. Take the Histology online quiz.