UNIT 3: HISTOLOGY

ANATOMY AND PHYSIOLOGY

OBJECTIVES Define tissue Describe the germ tissue layers, their location, and

what tissues they produce in eucoelomate animals (humans).

List the 4 major types of tissues of the human body.

Describe the characteristics, cell types, function, and the location of epithelial tissues.

Describe the characteristics, cell types, functions, and the location of connective tissues.

Describe the characteristics, cell types, functions, and the location of muscle tissues.

Describe the characteristics, cell types, functions, and the location of nervous tissues.

HISTOLOGY Histology is defined as the study of the

microanatomy of animal and plant tissues

A tissue is a group of like cells of similar specialized structure which carry out similar specific functions.

GERM TISSUE LAYERS We all start as a single cell called a

zygote. This cell begins to divide, and gives rise

to germ cells or stem cells that eventually form the developing embryo.

Because humans are eucoelomate (true body cavity) animals, like earthworms, we have three germ tissue layers:

A. EndodermB. MesodermC. Ectoderm

GERM TISSUE LAYERS: A. ENDODERM

The endoderm layer is the innermost layer, which forms the epithelial lining in our digestive tract from mouth to rectum.

The endoderm also forms many organs: the stomach, the liver, the pancreas, the urinary bladder, the epithelial parts of trachea, the lungs, and the intestines

GERM TISSUE LAYERS:B. MESODERM

The mesoderm layer is the middle layer.

It surrounds the endoderm layer develops into our large body cavities.

The mesoderm also gives rise to: muscle, bone, connective tissue, adipose tissue, the circulatory system, the kidneys, the dermis

GERM TISSUE LAYERS:C. ECTODERM The ectoderm

layer is the outermost layer.

It is the tissue layer which gives rise to our skin, hair, nails, eyes and nervous tissue (brain, spinal chord, nerves).

4 TYPES OF TISSUES A tissue is a group of cells with

similar specialized structure which carry out specific functions.

Groups of tissues compose and work together to form organs.

All organs are composed of two or more types of tissues.

There are four major tissue types:1. Epithelial2. Connective3. Muscle4. Nervous

1. EPITHELIAL TISSUES

1. EPITHELIAL TISSUE:A. LOCATIONS

General LocationsBody coveringsBody liningsGlandular tissue

Including:Skin, lining of trachea, esophagus, urinary bladder, and digestive tract, sweat glands, kidneys

1. EPITHELIAL TISSUE:B. FUNCTIONS

General Functionsa. Protectionb. Absorptionc. Filtrationd. Secretion

1. EPITHELIAL TISSUE:B. FUNCTIONS

Functions (continued):e. These cells are rapidly dividing

because they are constantly being sloughed away or rubbed off.

f. Therefore they must constantly be replaced.

1. EPITHELIAL TISSUE: C. CHARACTERISTICS

General Characteristics:a. Cells fit closely together and often form

sheetsb. The apical (top) surface is the free

surface of the tissuei. They face the air (skin, lungs) or a

fluid-filled organ cavity (the lumen of the gut).

ii. Apical ends may have cilia or be highly folded to increase surface area (microvilli).

1. EPITHELIAL TISSUE:C. CHARACTERISTICS

Characteristics (cont’d):d. The basal (lower layer) consists of

germ cells, which are constantly dividing to produce new cells.

e. The basal surface of the epithelium rests on a basement membrane.

i. Basement membrane: a layer of extracellular matrix and proteins (desmosomes) anchoring the epithelium to the connective tissue underneath

Apical surface of simple cuboidal epithelial withmicrovilli present.

Basement membrane where the cellsare attached to the non-living basal lamina.

Nucleus

Microvilli

1. EPITHELIAL TISSUE: C. CHARACTERISTICS

1. EPITHELIAL TISSUE:C. CHARACTERISTICS

Characteristics (cont’d):e. Epithelial are avascular (no direct

blood supply)f. Regenerate easily if well nourished

(by diffusion through other cells)

Apical surface

Basalsurface

Simple

Apical surface

Basalsurface Stratified

(a) Classification based on number of cell layersFigure 3.17a

1. EPITHELIAL TISSUE:D. CLASSIFICATION

Epithelial tissues are classified in two ways:A. Number of cell

layersB. Shape of cells

1. EPITHELIAL TISSUE:D. CLASSIFICATION

A. Number of cell Layers:i. Simple epithelial tissues are only

one cell layer thick.ii. Stratified epithelial tissues are

several layers thick.iii. Pseudostratified epithelial tissues

looks like multiple layers, but on close examination are actually only one cell layer thick.

GENERAL STRUCTURAL CHARACTERISTICS OF EPITHELIAL TISSUES:

c. Pseudostratified epithelial tissues appear to be composed of multiple layers but on close examination are actually only one cell layer thick.

1. EPITHELIAL TISSUE:D. CLASSIFICATION

Classification by shape – three basic shapes:a. Squamousb. Cuboidalc. Columnar

1. EPITHELIAL TISSUE:D. CLASSIFICATION

a. Squamous - flattened cells, fried egg shape in appearance.

1. EPITHELIAL TISSUE:D. CLASSIFICATION

b. Cuboidal - square or cubed shaped. Cells are as wide as they are tall.

1. EPITHELIAL TISSUE:D. CLASSIFICATION

c. Columnar - cells are taller than they are wide. Shaped like columns or rectangles.

1. EPITHELIAL TISSUE:E. NAMING EPITHELIAL TISSUES

Epithelial tissues are named in the following manner:1. First word: Number of layers

(simple, stratified, pseudostratified)

2. Second word: Shape of cell (squamous, cuboidal, columnar)

3. Third word: Describes the apical surface; if there are structures (cilia or microvilli) or materials present (keratin).

1. EPITHELIAL TISSUE:E. NAMING EPITHELIAL TISSUES

You can tell a lot about a tissue from its name For example: pseudostratified

columnar ciliated epithelium What can you tell from the name

about the tissue?1. It is one cell-layer thick2. It is column shaped.3. It has cilia on its apical surface

EXAMPLES OF EPITHELIAL TISSUES

1. EPITHELIAL TISSUE:F. EXAMPLE TYPESI. Simple SquamousII. Simple cuboidalIII. Simple ColumnarIV. Stratified Squamous

I. Non-keratinized II. Keratinized

V. Pseudostratified columnarVI. Stratified transitionalVII. Glandular

1. EPITHELIAL TISSUE: EXAMPLESI. SIMPLE SQUAMOUS

a. Name: Simple squamous epithelium

Single layer of flat cellsb. Location: usually forms

membranesLines body cavitiesLines lungs and capillaries

c. Function: diffusion, filtration, or secretion in membranes

d. Unique Facts:Found lining blood

vessels and is called endothelium.

Found in alveoli (or “air sacks”) of the lungs.

Allows the rapid exchange of materials by diffusion and osmosis from cell to cell.

1. EPITHELIAL TISSUE:EXAMPLES – I. SIMPLE SQUAMOUS

Figure 3.18a

Nucleus ofsquamousepithelial cell

Basementmembrane

(a) Diagram: Simple squamous

Photomicrograph: Simplesquamous epithelium forming partof the alveolar (air sac) walls (185×).

Nuclei ofsquamousepithelialcells

Air sacs oflungs

1. EPITHELIAL TISSUE:EXAMPLES – I. SIMPLE SQUAMOUS

1. EPITHELIAL TISSUE:EXAMPLES – II. SIMPLE CUBOIDAL

a. Name: Simple cuboidal epitheliumSingle layer of cube-like cells

b. Locations: Common in glands and their ductsForm walls of kidney tubulesCovers the ovaries

c. Functions: secretion and absorption; ciliated types propel mucus or propel reproductive cells

1. EPITHELIAL TISSUE:EXAMPLES – II. SIMPLE CUBOIDAL

d. Unique Facts: Simple cuboidal cells are common in secretory glands and ducts

Found in the walls of kidney tubules where they are involved with reabsorption of materials as urine is being produced

Found on the surface of mammalian ovaries, where their ciliated surfaces move the ovum (egg cell) from the co

Figure 3.18b

(b) Diagram: Simple cuboidal

Nucleus ofsimplecuboidalepithelialcell

Photomicrograph: Simple cuboidalepithelium in kidney tubules (250×).

Basementmembrane

Connectivetissue

Basementmembrane

Simplecuboidalepithelialcells

1. EPITHELIAL TISSUE:EXAMPLES – II. SIMPLE CUBOIDAL

1. EPITHELIAL TISSUE:EXAMPLES – II. SIMPLE CUBOIDAL

1. EPITHELIAL TISSUE:EXAMPLES – III. SIMPLE COLUMNAR

a. Name: Simple columnar epithelium

Single layer of tall cellsOften includes mucus-producing goblet cells

b. Location: lines digestive tractc. Functions: in secretion and

absorption; ciliated types propel mucus or reproductive cells; microvillate types absorb nutrients

1. EPITHELIAL TISSUE:EXAMPLES – III. SIMPLE COLUMNAR

d. Unique Facts:Commonly found in the lining of the small and large intestine where it is involved with absorption of molecules from digested food and re-absorption of water.

Some are microvillate (have microvilli on their apical surface)

microvilli on apical surface

1. EPITHELIAL TISSUE:EXAMPLES – III. SIMPLE COLUMNAR

Microvillate epithelium: In the small intestine the apical surface of these cells have microvilli present on their surface and specialized gland cells called goblet cells which produce and secrete mucus.

microvilli on apical surface

1. EPITHELIAL TISSUE:EXAMPLES – III. SIMPLE COLUMNAR

1. EPITHELIAL TISSUE: EXAMPLESSTRATIFIED EPITHELIA

Stratified cuboidal and columnar epithelia:Rare in human bodyFound mainly in ducts of large glands

Stratified cuboidal — two layers of cuboidal cells; functions in protection

Stratified columnar — surface cells are columnar, cells underneath vary in size and shape; functions in protection

1. EPITHELIAL TISSUE:EXAMPLES – IV. STRATIFIED SQUAMOUS

a. Name: Stratified squamous epithelium

Cells at the apical surface are flattened

b. Functions: as a protective covering where friction is common

c. Locations: linings of the…i. Skinii. Mouthiii. Esophagus

Figure 3.18e

Stratifiedsquamousepithelium

Basementmembrane

(e) Diagram: Stratified squamous

Photomicrograph: Stratifiedsquamous epithelium lining ofthe esophagus (140×).

Connectivetissue

Stratifiedsquamousepithelium

Nuclei

Basementmembrane

1. EPITHELIAL TISSUE:EXAMPLES – IV. STRATIFIED SQUAMOUS

1. EPITHELIAL TISSUE:EXAMPLES – IV. STRATIFIED SQUAMOUS

d. Unique Facts:Present in areas where there is wear and tear on the tissue, where cells are continually being sloughed away, (or rubbed off) by abrasion.

Two types of stratified squamous epithelial tissue: Keratinized and Non-keratinized.

1. EPITHELIAL TISSUE:EXAMPLES – IV. STRATIFIED SQUAMOUS

e. Stratified squamous non-keratinized epithelium:

Lines the oral cavity and the esophagus and the vagina of the female reproductive system.

The surface of these epithelia are moist and protected by mucosa

1. EPITHELIAL TISSUE:EXAMPLES – IV. STRATIFIED SQUAMOUS

f. Stratified squamous keratinized epithelium

Keratin is a layer a waterproof protein Produced on the apical surface of these

epithelia

1. EPITHELIAL TISSUE: EXAMPLESV. PSEUDOSTRATIFIED COLUMNAR

a. Name: Pseudostratified columnarSingle layer, but some cells are shorter than others

Often looks like a double layer of cells but all cells rest on the basement membrane

b. Location: respiratory tract, where it is ciliated

c. Functions: in absorption or secretion

1. EPITHELIAL TISSUE: EXAMPLESV. PSEUDOSTRATIFIED COLUMNAR

d. Unique Facts:Can be ciliated:

The apical surface of these cells have tiny, hair-like projections called cilia, which are involved with the movement across the surface of the cells.

Figure 3.18d

Pseudo-stratifiedepitheliallayer

Basementmembrane

(d) Diagram: Pseudostratified (ciliated) columnar

Photomicrograph: Pseudostratifiedciliated columnar epithelium liningthe human trachea (430×).

Pseudo-stratifiedepitheliallayer

BasementmembraneConnectivetissue

Cilia

1. EPITHELIAL TISSUE: EXAMPLESV. PSEUDOSTRATIFIED COLUMNAR

1. EPITHELIAL TISSUE: EXAMPLESVI. STRATIFIED TRANSITIONAL

a. Name: Transitional epitheliumComposed of modified stratified squamous epithelium

Shape of cells depends upon the amount of stretching

b. Location: lines organs of the urinary system

c. Functions: stretching and the ability to return to normal shape

1. EPITHELIAL TISSUE: EXAMPLESVI. STRATIFIED TRANSITIONAL

d. Unique Facts: This epithelium is unique to the urinary bladder and a small portion of the ureters.

It has the unique property of expansion and contraction.

This allows the tissue to adjust to the urinary bladder’s expansion and contraction when it is full or empty.

1. EPITHELIAL TISSUE: EXAMPLESVI. STRATIFIED TRANSITIONAL

Figure 3.18f

Transi-tionalepithelium

Basementmembrane

Photomicrograph: Transitional epithelium lining ofthe bladder, relaxed state (215×); surface roundedcells flatten and elongate when the bladder fillswith urine.(f) Diagram: Transitional

Connectivetissue

Transitionalepithelium

Basementmembrane

1. EPITHELIAL TISSUE: EXAMPLESVI. STRATIFIED TRANSITIONAL

1. EPITHELIAL TISSUE: EXAMPLESVII. GLANDULAR EPITHELIUM

GlandsOne or more cells responsible for secreting a particular product

Secretions contain protein molecules in an aqueous (water-based) fluid

1. EPITHELIAL TISSUE: EXAMPLESVII. GLANDULAR EPITHELIUM

Two major gland types:1. Endocrine gland

Ductless since secretions diffuse into blood vessels

All secretions are hormones2. Exocrine gland

Secretions empty through ducts to the epithelial surface

Include sweat and oil glands