Introduction to Introduction to HistologyHistology

Cell StructuresCell Structures

Dr. Rebecca A. CodeDr. Rebecca A. Code

Summer Scholars 2007Summer Scholars 2007

Histology – the study of Histology – the study of cellular structures of the cellular structures of the

bodybody Anatomy at the microscopic level Anatomy at the microscopic level

(microanatomy)(microanatomy) Cells---tissues---organs---organ Cells---tissues---organs---organ

systemssystems 10101515 cells in the human body cells in the human body 200+ cell types in the body200+ cell types in the body

Observation – the key to identifying cell types

Nucleus – present in almost Nucleus – present in almost all cells, stains well with all cells, stains well with

hematoxylin.hematoxylin.• SizeSize• ShapeShape• LocationLocation• NumberNumber• Nucleolus – site of rRNA Nucleolus – site of rRNA

synthesissynthesis• DensityDensity

• Euchromatic – light staining Euchromatic – light staining nucleus due to regions of nucleus due to regions of chromosomes that are less chromosomes that are less coiled, indicating that the DNA coiled, indicating that the DNA is actively transcribing mRNA.is actively transcribing mRNA.

• Heterochromatic – dense, darkly Heterochromatic – dense, darkly staining nucleus due to tightly staining nucleus due to tightly coiled chromatin, presumably coiled chromatin, presumably not transcriptionally active.not transcriptionally active.

Cytoplasmic organelles – Cytoplasmic organelles – other clues to differentiate other clues to differentiate

cell types and functioncell types and function RibosomesRibosomes MitochondriaMitochondria Golgi apparatusGolgi apparatus Endoplasmic Endoplasmic

reticulumreticulum MicrofilamentsMicrofilaments Secretory Secretory

vesiclesvesicles Pigment granulesPigment granules Lipid dropletsLipid droplets

Cell SpecializationsCell Specializations

Microvilli – found on many epithelial cells; 1-2 Microvilli – found on many epithelial cells; 1-2 m long extensions of cell membrane; m long extensions of cell membrane; increase surface area (15-20X) for increase surface area (15-20X) for absorption;absorption; lots of microvilli = brush borderlots of microvilli = brush border

Cilia – 7-10 Cilia – 7-10 m long; m long; motilemotile structures structures stabilized by microtubules; function to move stabilized by microtubules; function to move fluid over cells; found in trachea, bronchi, fluid over cells; found in trachea, bronchi, oviducts, flagella of sperm.oviducts, flagella of sperm.

Stereocilia –very long microvilli, non-motile; Stereocilia –very long microvilli, non-motile; for absorption; in epidydimus and on hair cells for absorption; in epidydimus and on hair cells of inner ear.of inner ear.

Microvillus Cilium

Cell Adhesions/JunctionsCell Adhesions/Junctions

Nearly all cells are connected to Nearly all cells are connected to neighboring cells by cell junctionsneighboring cells by cell junctions

Occluding junctions join cells together to Occluding junctions join cells together to form impermeable barrierform impermeable barrier

Adhering junctions provide mechanical Adhering junctions provide mechanical attachment between cells.attachment between cells.

Communicating junctions permit Communicating junctions permit movement of ions or molecules between movement of ions or molecules between cellscells

Cell Cell JunctionsJunctions

Occluding – the most Occluding – the most apical junctionapical junction Zonula occludens, tight Zonula occludens, tight

junctionsjunctions

Adhering – 2 types:Adhering – 2 types: Zonula adherentesZonula adherentes Macula adherens = Macula adherens =

desmosomesdesmosomes

CommunicatingCommunicating Gap junctionsGap junctions

Histology = 2 dimensional Histology = 2 dimensional imageimage

A section is a slice of tissueA section is a slice of tissue Orientation when sectioned affects Orientation when sectioned affects

what you see.what you see.

Section of Round Solid Section of Round Solid ObjectObject

AB

AB

Sections cut through a Sections cut through a curved tubecurved tube

Light Microscope = tool of Light Microscope = tool of the histologistthe histologist

Oculars Oculars (eyepieces)(eyepieces)

StageStage Objective LensObjective Lens CondenserCondenser Light sourceLight source Focus knobsFocus knobs

Specimen PreparationSpecimen Preparation

Fixation, dehydration, embeddingFixation, dehydration, embedding SectioningSectioning Staining: most common is H&EStaining: most common is H&E

Hematoxylin: cationic dye (+ charge) that Hematoxylin: cationic dye (+ charge) that binds to negatively charged (acidic) binds to negatively charged (acidic) structures in the cell. Example: nucleus = structures in the cell. Example: nucleus = blueblue

Eosin: anionic dye (- charge) adheres to Eosin: anionic dye (- charge) adheres to basic structures in the cell. Example: basic structures in the cell. Example: amine groups (NHamine groups (NH33

++) on proteins make ) on proteins make cytoplasm pink.cytoplasm pink.

Kidney cellsKidney cells

Heterochromatic and Euchromatic Heterochromatic and Euchromatic NucleiNuclei

Golgi Apparatus in Nerve Golgi Apparatus in Nerve CellsCells

Mitochondria and Mitochondria and MyofibrilsMyofibrils

Microvilli of Intestinal Epithelial Microvilli of Intestinal Epithelial CellsCells

Cilia of Tracheal Epithelial CellsCilia of Tracheal Epithelial Cells

False Intercellular Bridges False Intercellular Bridges (Desmosomes)(Desmosomes)