Histological Features of Cells and Identifying Epithelia What well - - PowerPoint PPT Presentation

Histological Features of Cells and Identifying Epithelia

What we’ll talk about…

• Preparation of samples for histological analysis
• Identifying key cellular features and structures
• Classification of epithelia
• Identifying features of epithelia

Preparation of samples

Samples for histological analysis are often obtained by biopsy.

Kidney Ultrasound Probe Needle Biopsy

Fixation of sample prevents degradation and preserves structure of cells and tissues.

Protein 1

NH2

Protein 2

N H CH2OH

Protein 1

N CH2 NH C

Protein 2

H

+

C H H

Formaldehyde

Tissue sample are embedded in wax and sliced into thin sections.

Sample embedded in paraffin Sample Paraffin

Samples mounted on slides and then stained with specific dyes.

Sample

Hematoxylin and eosin are the dyes most commonly used in histology.

Hematoxylin stains acidic structures blue Eosin stains basic structures pink Nucleus

Feature you can see in most histological images

Nuclei are often the most visible and easily recognizable structure.

Nuclei

Nuclei can have different shapes and localize to different regions of cells.

Oval nucleus Lobed nucleus

The amount of heterchromatin and euchromatin indicate the transcriptional activity of a cell.

Heterochromatin Euchromatin H&E EM

The number of mitotic cells indicates the rate of cell division.

Dividing cells

The number of nuclei indicate the density of cells in a tissue.

Few cells Many cells

Other organelles visible in histological samples

A prominent nucleolus indicates a cell synthesizing a lot protein.

Nucleus Nucleolus

A lot of rough ER indicates a cell that is actively secreting protein.

Nuclei Rough ER

Secretory granules indicate a cell that participates in regulated secretion of material.

Nucleus Secretory granules

Red blood cells provide a convenient cellular ruler to measure the size of objects.

Red blood cell is 7 microns wide

Classify epithelia in histological images

An epithelium is a sheet of polarized cells that rests

• n a basement membrane.

Epithelia Basement Membrane Connective Tissue Apical Basal

Epithelia are classified based on the shape of its cells and the number of layers of cells.

Simple Squamous Simple Cuboidal Simple Columnar Stratified Squamous Stratified Cuboidal Pseudo-stratified Basement Membrane

Microvilli Cilia

Simple squamous epithelia contain a single layer of flat cells.

Nucleus Apical Basal

Simple cuboidal epithelia contain a single layer of squarish cells.

Height Width Nucleus Apical Basal

Simple columnar epithelia contain a single layer of tall cells.

Width Height Nucleus Apical Basal

Microvilli are short, finger-like extensions of the apical membrane supported by actin filaments.

Nucleus Microvilli Microvilli Actin Filaments Apical Basal

Stratified squamous epithelia contain multiple layers of cells with outer layer having flat cells.

Basal Layer: Cuboidal Apical Layer: Squamous

Some stratified squamous epithelia contain a layer

• f keratin on their apical surface.

Basal Layer Apical Layer Keratin

Cilia are long extensions of the apical cell membrane that generate wave-like motion.

Cilia Microtubule Epithelia

Pseudostratified epithelia appear stratified but every cell contacts the basement membrane.

Nuclei at different levels Apical Basal

Stereocilia are long, branched extensions of the apical cell membrane and are supported by actin.

Stereocilia Epithelia Apical Basal

Transitional epithelia change appearance when stretched.

Epithelia Relaxed Distended

Apical Basal Apical Basal

All epithelia attach to a basement membrane via interactions along their basal surface

Epithelia Basement Membrane Apical Basal