Jul 10, 2023
The epithelium tissue is a type of human tissue that borders hollow organs and body cavities and covers all internal and exterior body surfaces, making up the majority of glandular tissue. Epithelial tissue performs a variety of functions in many parts of the body, including absorption, secretion, and defense.
The four tissue types that make up your body's organs are as follows:
Epithelial tissue is made up of epithelial cells. The cells can take on a variety of shapes and can be arranged in a single layer or multiple layers depending on where they are located in your body and the functions they carry out.
|Types of Simple Epithelium||General Description|
|Simple squamous epithelium:||Single layer on the basement membraneIt has flat cellsNucleus: FlatSometimes nucleus can be globularMinimal cytoplasmResting thyroid follicle (less secretion)|
|Simple cuboidal epithelium:||Nucleus: Spherical-shaped (central) height is equal to the breadthThe cytoplasm of the nucleus is moderateOval thyroid follicle|
|Simple columnar epithelium:||Height is greater than breadthNucleus: Oval and basalCytoplasm is largeIt has increased the endoplasmic reticulum to secrete the thyroxine (secreting active thyroid follicles)In order to store the ER these cells increased their heights|
Q. Thyroid follicles are lined by which type of epithelium
Thyroid follicles are lined by the central spherical nucleus. The height of the cells is equal to the breadth. The type depends on the release of thyroxine. If the thyroid hormone is scanty then it is Squamous epithelium. If Medium level of thyroid hormone then it is Cuboidal and if High levels of thyroid hormone then it is Columnar epithelium.
Q. Secreting active thyroid follicles are lined by which type of epithelium
If active thyroid follicles secrete, it may increase the amount of endoplasmic reticulum and there is an increase in the height of the cell. Oval basal nucleus and Increased secretions of thyroxine hormone suggest that it is the simple columnar epithelium.
Location where simple squamous epithelium is present:
In this the nucleus is flat and globular and Cytoplasm is scanty.
In this the height is equal to breadth and there is a Central spherical nucleus. Location where simple cuboidal epithelium is present is:
Functions of simple cuboidal epithelium:
In this Height of the cells is greater than breadth and there is a present Oval basal nucleus. Height is more due to increased cytoplasm above the nucleus.
Location where simple columnar epithelium is present:
It is Multi-layered and is Present in the areas where cells need protection from abrasions. It has Transitional Epithelium that means It is not exactly stratified because each cell is touching the basement membrane so they are not qualified as stratified. This type of epithelium is present in renal tube (Urothelium)
It is present in the regions which need protection. It is of two types:
Q. Epithelium lining of lingual surface of epiglottis is
It is present in the laryngeal surface (respiratory tube). Location where pseudostratified ciliated columnar
Cilia is present to move the mucus. It is pseudostratified because every cell is touching the basement membrane but nuclei are in various levels
It is not exactly stratified. It is present in the respiratory tube. Posterior or laryngeal surface of epiglottis will have pseudostratified ciliated columnar epithelium with goblet cells
It is a stretchable epithelium. In this the cells towards the lumen are very large called umbrella shaped cells. If urine is stored, then the epithelium will get stretched and there is Relaxation of the epithelium, if no urine is present.
Sometimes it appears as 8 to 10 layers when it is in Relaxation phase Whereas, sometimes it appears as 2-3 layers when it is Stretched. Each cell is attached to the basement membrane by a cytoplasmic extension. So, they are not qualified as stratified epithelium
|Identification of Images|
|Pseudostratified columnar epithelium||Pseudostratification with cilia (respiratory epithelium)|
|Keratinized stratified squamous epithelium||Flat cells towards the surfaceBasement membrane not straight, having papillary appearanceLocated in skin|
|Transitional epithelium (Urothelium)||Cells towards the lumen are umbrella shaped (Globular)Basement membrane is straightFound in urinary bladder|
Any external opening of the body is always lined by the stratified squamous epithelium. Embryology describes an external opening lined by surface ectoderm (rule of embryology). Surface ectoderm is considered as stratified squamous epithelium. Stratified squamous epithelium is not only present on surface ectoderm, it can be present on the mesoderm and endoderm. For example Vagina (Upper part- mesoderm, lower part- endoderm), But the entire epithelium is stratified squamous epithelium. Labia majora and minora lined by surface ectoderm
It may also be present in the internal opening for example Vocal cord. Abrasions of the vocal cord are caused due to the fast moving of air in and out during sneezing or coughing. So, in order to prevent this type of damage, it is made of stratified squamous epithelium.
Larynx is lined by respiratory epithelium (pseudostratified ciliated epithelium). Vocal cords don't have the pseudostratified ciliated epithelium.
There are seven openings that are divided into two categories:
“The above all are lined by stratified squamous epithelium because they are prone to abrasions”.
|Openings on the face||Description|
|Lined by stratified squamous epithelium.Middle ear cavity and the external ear cavity are separated by the tympanic membrane.External ear cavity is lined by stratified squamous epitheliumMiddle ear cavity, lined by stratified cuboidal epithelium This tympanic membrane has two epitheliumsInner layer: Stratified cuboidal epitheliumOuter layer: Stratified squamous epitheliumIt is lined by the skin (sweat and sebaceous gland)Sweat gland in the ear: Ceruminous gland (Wax gland)It is a modified apocrine sweat gland|
|Lined by Stratified squamous epitheliumFirst layer of cornea is lined by stratified squamous epithelium|
|Lined by Stratified squamous epitheliumIt is lined by skinNasal vestibule is lined by the skin with hair: Stratified squamous epithelium|
|Lined by stratified squamous epitheliumIt is discussed in two partsTongue, hard palateThese are keratinised called as orthokeratinization and parakeratinizationTonsils, epiglottis (lingual cavity- non keratinized)|
|It is found in the hard palate, tongue (Oral cavity)||It is found on the skin|
|Nucleus is present in the superficial layers||Superficial cells of a keratinized epithelium has no nuclei|
|Openings of Perineum||Description|
|Urethra||It is present at the anterior regionIt is 4 cm in length (In female)Entirely, lined by stratified squamous epithelium It is 20 cm length in maleTip of the male urethra is made by stratified squamous epithelium|
|Vagina||It is present at the middle portionEntire vaginal epithelium is made of stratified squamous epithelium|
|Anal canal||It is present at the posterior regionLocated below the pectinate line (Dentate line) is made of stratified squamous epithelium|
These junctions are prone to metaplasia, dysplasia and it finally leads to cancer. It includes different type of cancer:
Due to GERD the cells of epithelium are moved back from the stomach into the lower esophagus by changing the epithelium that is from normal squamous epitheliumIt is replaced into the columnar epithelium. It is dangerous because there is metaplasia that can further lead to dysplasia. This metaplasia is called Barrett's Esophagus, Finally, causing the cancer (adenocarcinoma) to the lower esophagus.
In this esophagus there is a squamo-columnar junction known as the Z line. It is a zig zag line found in the lower end of the esophagus. Lower 2 cm of the esophagus is lined by columnar epithelium (like the stomach). Whitish mucosa is the stratified squamous epithelium.
Histologically, at the upper mucosa whitish epithelium is Squamous and Lower pinkish mucosa is columnar epithelium.This squamo-columnar junction is prone to metaplasia, dysplasia, and cancer. It can occur in the uterine cervix and anal canal as well.
Z-line is 2 cm above the gastroesophageal junction. But in some patients it is 5 cm above as it is becoming more proximal. It is dangerous, because cancer may be developed.
Upper part of the gut tube is the oral cavity, Then it will continue as the pharynx. Further continues as the esophagus Oesophagus further continues as the stomach. Stomach forms small intestine (Proximal duodenum). Gastroesophageal junction is present between the distal Oesophagus and proximal duodenum. 2 cm above the GEJ has SCJ (Squamo-columnar junction).It is a Z-line or zig zag line. Epithelium of the oral cavity is stratified Squamous epithelium.
It is encroaching into the pharynx, esophagus (but not entirely). It moves up to the lower esophagus. The lower most esophagus is made of columnar epithelium (lower 2 cm). Stomach and duodenum are lined by columnar epithelium, So it is called Squamo columnar junction present 2 cm above the GEJ. In the case of GERD, acid is moved back into the lower esophagus. Now this acid will burn the epithelium, so the epithelium will be replaced by columnar epithelium causing metaplasia
In Barrett's Oesophagus, we will find that squamous cells are replaced with columnar cells (in biopsy). In this condition, we will also find goblet cells. As it has columnar epithelium with goblet cells, it is called intestinal metaplasia. Hence Barrett's metaplasia is an intestinal metaplasia.
According to the Pathology Robbins, it is called a misnomer because columnar epithelium is not for absorption. As columnar epithelium is not involved in absorption, it is not called intestinal metaplasia. But Harrison, Bailey, Robinson, and pathology call it as intestinal metaplasia.Gray's anatomy describes it as gastric metaplasia because during biopsy, he found parietal cells. Calling Barrett's metaplasia as gastric metaplasia is a misnomer Because stomach doesn't contain goblet cells. So the best answer is Barrett's metaplasia is intestinal metaplasia.
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