HISTOLOGYHISTOLOGY

THE STUDY OF THE STUDY OF TISSUESTISSUES

TISSUESTISSUES A tissue is a A tissue is a

functional collection of functional collection of cells and associated cells and associated intercellular material intercellular material that is specialized to that is specialized to carry out a specific carry out a specific role.role.

Technique of Tissue

Sectioning1. Tissue is preserved in a fixative (chemical)2. Cut into very thin slices by a special

machine- slices are called histological sections

3. Sections are mounted on microscope slides4. Sections on slides are stained

-helps make cells and other structures easier to distinguish under the microscope

Classification of the FOUR basic Classification of the FOUR basic tissuestissues

1- Epithelial1- Epithelial 2- Connective (CT)2- Connective (CT) 3- Muscular 3- Muscular 4- Nervous4- Nervous

Connective vs EpithelialConnective vs Epithelial Lots of extra-cellular Lots of extra-cellular

material, material, few cellsfew cells Lots of Lots of blood vesselsblood vessels Covered by other Covered by other

tissuestissues

Little extra cellular Little extra cellular material, material, lots of cellslots of cells

No blood vesselsNo blood vessels Usually form surface Usually form surface

layers and are NOT layers and are NOT covered by another covered by another tissue (*except blood tissue (*except blood vessels)vessels)

Epithelial tissue

Connective tissue

Epithelial TissuesEpithelial Tissues

Flat sheet of cells with upper surface exposed to Flat sheet of cells with upper surface exposed to environment or internal space. environment or internal space. (Barriers! (Barriers! Protection!)Protection!)

Covers body surface & lines body cavitiesCovers body surface & lines body cavities Forms external & internal lining of organsForms external & internal lining of organs Constitutes most gland tissues Constitutes most gland tissues (Secretion!)(Secretion!) Little extra cellular materialLittle extra cellular material No room for blood vessels (No room for blood vessels (avascularavascular) so ) so

depends on blood vessels in CT for food and depends on blood vessels in CT for food and waste movementwaste movement

Epithelial Tissue SpecificsEpithelial Tissue Specifics Basement membraneBasement membrane:

Anchors epith to CT Made of proteins,

acellular Basal surface Basal surface - epith

surface that sits on basement membrane

Apical surface Apical surface - epith surface that faces away from basement. “Free Surface”

Apical Surface- faces surface, may havecilia, microtubules

Basal Surface-Adheres to Basementmembrane

Connect cells to basement membrane

A thickening of the basement membrane is a contributing cause of blindness and kidney in diabetes.

Basement Membrane

Classification of Epithelial TissuesClassification of Epithelial Tissues Arrangement of CellsArrangement of Cells

Simple (single layer)Simple (single layer) Stratified (multiple layers)Stratified (multiple layers) Pseudostratified (single Pseudostratified (single

layer, but looks multilayeredlayer, but looks multilayered

Shape of CellsShape of Cells SquamousSquamous CuboidalCuboidal ColumnarColumnar

Simple Squamous (“fried eggs”)Simple Squamous (“fried eggs”) Flat & thin, form liningsFlat & thin, form linings Location:Location:

MesotheliumMesothelium EndotheliumEndothelium Bronchioles and alveoli Bronchioles and alveoli

of lungs, kidney, tympanic of lungs, kidney, tympanic membranemembrane

Function:Function: FiltrationFiltration DiffusionDiffusion SecretionSecretion

Mesothelium is the simple squamous Mesothelium is the simple squamous epithelium lining body cavities.epithelium lining body cavities.

Endothelium is the simple squamous Endothelium is the simple squamous epithelium lining blood vesselsepithelium lining blood vessels

Two blood vessels seen in cross section

13. Identify the tissue. 14. Identify the structure.15. What tissue makes up this (#14) structure?16. Identify the cellular structure.

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13. Simple Cuboidal Epithelium14. Blood Vessel15. Simple Squamous epithelium16. Nucleus

Stratified Squamous EpithelialStratified Squamous Epithelial Characteristics:Characteristics:

Many layers becoming Many layers becoming flatter from basal to flatter from basal to apical surfacesapical surfaces

Basal cells are mitoticBasal cells are mitotic Apical cells are deadApical cells are dead

LOCATIONS: LOCATIONS:  KeritanizedKeritanized

• skin skin NonkeritanizedNonkeritanized

• Mouth, esophagus, Mouth, esophagus, pharynx, vagina pharynx, vagina

FUNCTION:FUNCTION: protectionprotection

Stratified layersof epithelial cells

Apical cells will be sloughed off and replaced by cells in layer below.

Basal cells Mitotic areaCells are rounder

Stratified layers

Simple Cuboidal EpitheliumSimple Cuboidal Epithelium Characteristics: single layer, square or Characteristics: single layer, square or

roundishroundish LocationLocation: Ducts of many : Ducts of many glandsglands, lines , lines

kidney tubules, surface of ovarykidney tubules, surface of ovary FunctionFunction: : secretion and absorptionsecretion and absorption

Simple cuboidal epithelium lining a Simple cuboidal epithelium lining a tubule (longitudinal cut). tubule (longitudinal cut).

Simple Columnar EpitheliumSimple Columnar Epithelium Characteristics: tall, narrow cells

• May contain brush borders (microvilli) & goblet cells

Location: lines the gastrointestinal tract from stomach to anus, ducts of glands, gallbladder

Function: secretion and absorption

Nucleus

Simple columnar epithelium with very Simple columnar epithelium with very

regular line-up of nucleiregular line-up of nuclei. .

Pseudostratified Ciliated Columnar Pseudostratified Ciliated Columnar EpitheliumEpithelium

LocationLocation: Respiratory tract: Respiratory tract FunctionFunction: secrete mucous to trap foreign particles: secrete mucous to trap foreign particles Not all cells reach apical layer BUT all cells are connected to basement membrane!Not all cells reach apical layer BUT all cells are connected to basement membrane! Cilia (sweep), Goblet cell (secrete mucous)Cilia (sweep), Goblet cell (secrete mucous)

Cilia

Goblet CellMicrovilli

Basement Membrane