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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