Histological Techniques, Epithelium, And Glands

Microscopy

Freeze fracture: Tissue is frozen and split into inner and outer leaflets. Can be used to see proteins embedded in the membrane.

Preparation

Preparation steps:

1. Fix the tissue to stabilize it
2. Dehydrate
3. Embed it into a hardening material
4. Section into thin slices
5. Mount on slide and stain

Common stains

Hematoxylin and Eosin

Hematoxylin stain nucleus blue, eosin stains cytoplasm pink

Silver

Stains golgi (below), reticular fibers (type III collagen)

Other stains

• Periodic acid schiff: Mitochondria, glycogen, glycoproteins stained red
• Aldehyde fuchsin: Elastic fibers stain red/deep purple
• Orcein: Elastic fibers, collagen fibers, cytoplasmic counterstain stain brown

Epithelium

How to identify epithelium:

• Found on all body surfaces
• Covers all passage which connect to exterior
• Makes up secretory cells of glands
• No blood supply (avascular)
• Lies on basement membrane or basal lamina

Epithelium is either glandular or surface. It is classified by:

• The number of cells: Simple or stratified. Simple is when cells rest directly on basement membrane. Stratified is stacked layers.
• The height/shape of the surface layer: Squamous, cuboidal, or columnar. Squamous is flat (squat).

Other layer types:

• Pseudostratified: Not stratified, one layer but looks like several because nuclei are in different parts of the cell
• Transitional: Multiple variations in one tissue

Note: if a cell is binucleated and stratified, it is BLADDER tissue

Type	Diagram	Locations
Simple squamous		Endothelium, mesothelium, parietal layer of Bowman's capsule, thin segment of loop of Henle, rete testis, pulmonary alveoli
Simple cuboidal		Thyroid, choroid plexus, ducts of glands, inner surface of lens, covering of ovary
Simple columnar		Surface stomach, small/large intestine, gallbladder, excretory ducts of glands, uterus oviducts, small bronchi of lungs
Stratified squamous		Tympanic cavity, buccal surface, esophagus, epiglottis, conjunctiva, cornea, vagina, skin epidermis, gingiva, hard palate
Stratified columnal		Male urethra, fornix of conjunctiva, large duct execretory glands
Stratified cuboidal		Sweat ducts
Pseudostratified		Large excretory ducts of glands, parts of male urethra, epididymis, trachea, bronchi, eustachian tube
Transitional		Bladders, ureters, prostatic urethra

Glands

Definitions

Glandular epithelia are groups of cells which secrete things. Exocrine glands have an acinus (secretory portion) and a duct (conducting portion).

• Parenchyma: secretory cells
• Strome: Connective tissue between parenchyma
• Exocrine glands: Surface or cavity secretions via ducts
• Endocrine glands: Blood stream secretion

Modes of Secretion

1. Merocrine (most common): Vesicular release
2. Apocrine: When vesicles are so large, a portion of the cell is released (e.g. mammary glands)
3. Holocrine: Whole cell is shed (e.g. sebaceous glands)

Classification

1. Number of ducts
   1. Simple (one)
   2. Compound (multiple)
2. Shape of secretory portion
   1. Tubular
   2. Branched tubular
   3. Acinar (grape shaped)
   4. Branched acinar
   5. Tubuloacinar
3. Secretion type
   1. Serous (aqueous)
   2. Mucous (mucinous glycoproteins)

Cell surface specializations

Microvilli

Filled with actin connected to terminal web, surrounded by glycocalyx containing glycosylated products

Cilia

More brush like or fibrous than microvilli. Made of 9 + 2 microtubule axoneme structures. Embedded in basal bodies, which are centrioles that nucleate axonemes of cilia

An example of an axoneme

Stereocilia

Very thin microvilli found in male reproductive tract (epididymis) and vestibular apparatus of inner ear.

Microplicae

Folds that can appear on the surface of cells, especially the GI