what two words are used to classify epithelium in terms of the number of cell layers

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Surface Epithelium: Histology

The epithelium is a complex of specialized cellular organizations arranged into sheets and lining cavities and roofing the surfaces of the torso. The cells exhibit polarity, having an apical and a basal pole. Structures important for the epithelial integrity and part involve the basement membrane, the semipermeable canvass on which the cells rest, and interdigitations, too equally cellular junctions. The epithelium is classified according to the cells (squamous, cuboidal, columnar), the number of layers, and other unique characteristics either due to function (transitional epithelium allowing distention) or appearance (pseudostratified epithelium giving a fake impression of multiple layers). The surface epithelium has multiple functions, which include protection, secretion, filtration, and sensory reception.

October 28, 2021
one:15 pm

Epithelial Tissue

Surface epithelium

A complex of specialized cellular organizations arranged into sheets and lining cavities and roofing the surfaces of the body:

Derived from all 3 germ layers:
- Ectoderm (e.g., epidermis)
- Mesoderm (e.1000., GI tract lining)
- Endoderm (e.m., linings of body cavities)
One of 4 major bones tissue types (the other 3 include nervous, muscular, and connective tissues)

These cells exhibit polarity:

Apical/luminal pole: derived from the apex, faces the surface/lumen
Basal pole: derived from the base, fastened to the connective tissue located below the epithelium

The surface epithelium does not possess blood vessels; therefore, nutrients and oxygen are received from side by side connective tissue.

Functions

Protection (provides roofing surface or lining)
Secretion (release of hormones, sweat, mucus, and enzymes) equally found in glands
Absorption (substance intake equally seen in the intestinal lining)
Excretion and filtration of substances
Sensory reception (detection of awareness) equally found in olfactory epithelium

Related structures

Intercellular junctions:
- Adhesion of cells is facilitated by cadherins (calcium-dependent adhesion molecules).
- At the apical finish, structures encircle the area (like a band around the prison cell):
  - Tight or occluding junctions (zonulae occludens): have tight ridges, preventing passive flow of substances between cells
  - Adherent junctions (zonulae adherens): assistance stabilize both junctions and hold cells together.
- Desmosomes (macula adherens) and gap junctions (communicating junctions):
  - Structures bound to intracellular intermediate filaments, aiding the zonulae adherens
  - Additionally, gap junctions permit flow of molecules.
- Hemidesmosomes: anchor epithelial cells to the basal lamina (of the basement membrane)
Interdigitations: prison cell membrane foldings that increase the surface area (east.g., for ion or water transport)
Basement membrane:
- Thin semipermeable sheet on which the basal surface of epithelia rests
- Attachment of cells achieved with laminin and integrin
- Parts:
  - Basal lamina: thin, sheetlike layer of fine fibrils found nearest the epithelial cells
  - Reticular lamina: thicker and more than fibrous
- Function:
  - Zipper to underlying tissue
  - Separation of tissues
  - Filtration
  - Scaffold and guidance (repair)
  - Cell signaling

Characteristics of the epithelium — Epithelia have an apex, lateral borders, and a surface sitting on a basement membrane:
Equally seen in the image, these cells exhibit polarity (accept apical domains and basal/basolateral domains). At the upmost end, structures encircle the expanse (like a band around the cell) facilitating cell-to-prison cell adhesion (tight junctions and adherent junctions). Most the basement membrane, hemidesmosomes anchor the epithelia to the basal lamina. On the correct is shown the histology of the intestinal epithelial lining with corresponding structures. On the apical domain, microvilli are seen.
Paradigm by Lecturio.

Classification

By number of layers

Simple epithelium:
- Consists of a single layer
- Typically found where absorption, secretion, and filtration occur
Stratified epithelium:
- Composed of ≥ 2 layers
- Found in high-abrasion areas (skin and lining of the mouth)
- Name of cells in stratified epithelia based on shape of cells in apical layer
Pseudostratified epithelium:
- All cells are attached to the basement membrane, but not all cells extend to the free surface.
- The nuclei, being at dissimilar levels, give the epithelia a stratified appearance.

By shape of the cells

Squamous cells: thin or flattened cells
Cuboidal cells: cell width and thickness mostly like (cube-shaped)
Columnar cells: cells are taller than wide (column-shaped).
Transitional: shape of cells "goes through a transition":
- When the organ (e.yard., bladder) is relaxed, cells announced cuboidal.
- When the organ is distended, cells flatten.

By function

Note that there are tissues that have both:

Covering epithelium: line the cavities or organs
Glandular epithelium: secretory

The types of epithelia:
The differentiation and classification of the types are based on the shape of the cell and the layers. Simple epithelium indicates 1 layer of cells. Stratified epithelium indicates multiple layers. Pseudostratified epithelium gives a false impression of > 1 layer attributable to unlike nuclei levels. Transitional epithelium is a type in which the shape of cells "go into transition" depending on the organ function (distention versus relaxation, equally seen in the urinary bladder).
Paradigm: "Types of epithelium" by U.S. National Cancer Establish'due south Surveillance. License: Public Domain, edited by Lecturio.

Simple Epithelium

Uncomplicated squamous epithelium

Characteristics:
- Single layer of flattened cells
- Disc-shaped nuclei (most prominent structure)
- Sparse cytoplasm
Typically plant in lining of vessels, regulating passing substances to the tissue(south)
Located in:
- Air sacs/alveoli of lungs
- Lining of the heart
- Claret vessels and lymphatic vessels
- Renal loops of Henle
- Cornea
Special naming:
- Endothelium: uncomplicated squamous epithelium lining blood vessels and lymphatic vessels
- Mesothelium: uncomplicated squamous epithelium establish in big torso cavities (secreting serous fluid)

Structure noted in simple squamous epithelium (single layer of flattened cells)
Image: "Simple squamous epithelium" by Phil Schatz. License: CC Past 4.0

Epithelial tissues simple squamous epithelium — A whole mount of simple squamous epithelium
Image: "Epithelial Tissues Simple Squamous Epithelium" by Berkshire Customs Higher Bioscience Paradigm Library. License: CC0 i.0

Simple cuboidal epithelium

Single layer of cube-like cells
Cuboidal shape allows increased mitochondria and other organelles needed for functions such as agile send, secretion, and absorption.
Found in:
- Ducts and secretory portions of glands
- Kidney tubules

Simple columnar epithelium

Single-layer tall cells
Oftentimes with cilia or microvilli
Mostly involved in assimilation and secretion
Plant in:
- Ciliated epithelium in the bronchi, fallopian tubes, and uterus
- Smooth (nonciliated) epithelium in the digestive tract
- Lining of the gallbladder

Pseudostratified, Stratified, and Transitional Epithelia

Pseudostratified columnar epithelium

Characteristics:
- Cells vary in height, with all cells resting on the basement membrane only but some reaching all the mode to the upmost surface.
- Nuclei placed at different heights
- Some accept cilia.
Functions in secretion and absorption
Establish in:
- Ciliated epithelium of the trachea
- Part of the upper digestive tract

Pseudostratified epithelium:
Shown is a single layer of columnar cells, with varying levels of nuclei
Paradigm: "Pseudostratified epithelium" by Phil Schatz. License: CC By iv.0

Cross-section of pseudostratified columnar epithelium — Pseudostratified columnar epithelium found in the trachea
Prototype: "Cross-department of pseudostratified columnar epithelium" past OpenStax Higher. License: CC BY three.0

Stratified squamous epithelium

About widespread of the stratified epithelia
Composed of several layers, providing protective function
Free surface cells are squamous.
Deeper layer cells are cuboidal or columnar.
Establish in areas subjected to article of clothing and tear
Found in:
- Skin, which is keratinized or filled with keratin:
  - These cells will lose the organelles and nuclei as they flatten and accumulate keratin.
  - Cells move toward the surface, becoming metabolically inactive and are sloughed off.
- Esophagus, mouth, vagina, which accept nonkeratinized cells (retain the nuclei)

Epithelial tissues stratified squamous epithelium — Histologic picture of stratified squamous epithelium
Image: "Epithelial Tissues Stratified Squamous Epithelium" by Berkshire Community College Bioscience Image Library. License: CC0 ane.0

Stratified columnar epithelium and stratified cuboidal epithelium

Both are rare and have limited distribution.
Stratified columnar epithelium:
- Secretory and protective function
- Found in:
  - Male person urethra
  - Some glandular ducts
Stratified cuboidal epithelium is institute in ducts of large glands (e.g., sweat glands, mammary glands).

Stratified cuboidal epithelium — Stratified columnar epithelium
Image: "Stratified columnar epithelium" by Phil Schatz. License: CC By 4.0

Parotid gland — Stratified cuboidal epithelium (seen on the left) is visible in a duct surrounded past connective tissue in the parotid gland.
Epitome: "WVSOM Parotid Gland1" past Wbensmith. License: CC By iii.0

Transitional epithelium

Characteristics:
- Surface layer of umbrella cells (dome-like cells)
- Allows for stretching of the organs as they distend
- Urothelium: transitional epithelium in the urinary tract
Establish in:
- Urinary bladder
- Urethra
- Ureters

Clinical Relevance

Ichthyosis: dermatologic disease in which aberrant keratinization occurs. Ichthyosis is caused by an autosomal dominant mutation in the filaggrin gene, which results in pare bulwark dysfunction. Clinical presentation features rough, dry, and scaly peel, with symptoms worsening during cold, dry months. The diagnosis is normally clinical simply ofttimes aided with a skin biopsy showing hyperkeratosis and a diminished stratum granulosum.
Transitional prison cell carcinoma: malignancy affecting the urinary float. Transitional prison cell carcinoma is the most common cancer involving the urinary organisation. The predominant histologic type is urothelial (transitional prison cell) carcinoma in the United states and Europe. Take chances factors include genetics, smoking, opium employ, and occupational carcinogen exposure. Presentation is unremarkably with painless hematuria, and the diagnostic approach includes cystoscopy, urine cytology, and biopsies. Transurethral resection of bladder tumor, radical cystectomy, and chemotherapy are amongst the handling options, which depend on the phase.
Barrett's esophagus: replacement of stratified squamous epithelium with gastric columnar epithelium in the esophagus caused by chronic GERD. This is associated with an increased risk of esophageal adenocarcinoma. Esophagogastroduodenoscopy would show proximal displacement of the squamocolumnar junction (Z-line) from the gastroesophageal junction (GEJ). Biopsies reveal columnar epithelium and goblet cells in the distal esophagus. Treatment is with proton pump inhibitors and lifestyle modifications.
Cervical cancer: very common cancer affecting women. Nigh cases of cervical cancer are due to HPV. The region around the external os is lined by nonkeratinized stratified squamous epithelium continuous with that of the vagina. This area meets the mucus-secreting columnar epithelium of the endocervix in the transformation zone. Exposure of the transformation zone to HPV can pb to squamous differentiation into squamous intraepithelial lesion (leading to squamous jail cell carcinoma). The endocervical columnar epithelium tin can develop into glandular intraepithelial lesions (which tin progress to adenocarcinoma).

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Source: https://www.lecturio.com/concepts/surface-epithelium/