Introduction
Epithelial tissue is a fundamental category of body tissue that is present in various organs and envelops both internal and external surfaces of the body. The anatomical component exhibits diverse morphological and physiological characteristics contingent upon its location within the organism.
The following discourse aims to define epithelial tissue.
The epithelium is a ubiquitous tissue type that envelops both internal and external surfaces of the human body, demarcates body cavities and hollow organs, and constitutes the primary tissue in glandular structures. The epithelial tissue exhibits diverse functions that are contingent upon its anatomical location within the human body, such as safeguarding, excretion, and assimilation.
The human body's organs are comprised of four fundamental categories of tissue, which are:
The four primary types of tissues in the human body are epithelial, connective, muscular, and nervous.
The epithelial tissue serves as the primary barrier for the entry and exit of substances in an organ.
The human body comprises various types of epithelial tissue. Epithelial tissue is comprised of various examples, such as:
•The peritoneum, which is the serous membrane that lines the abdominal cavity,
•The epidermis is the outermost layer of the integumentary system. (epidermis).
•The mucosal layer that coats the inner surface of the gastrointestinal tract
•The mucosal lining of the respiratory tract.
•The sudoriferous glands.
Are you aware that epithelial tissues possess their distinct cells?
Epithelial tissue comprises cells that are classified as epithelial. Cells exhibit varying morphologies and can be organized in either a monolayer or multilayer configuration, contingent upon their anatomical location and physiological roles.
In the field of biology, the smallest autonomous living entity is referred to as a cell. The fundamental building blocks of all living organisms and bodily tissues are cells. The human body is comprised of over 30 trillion cells.
Certain categories of cells, such as specific epithelial cells, possess distinctive surface features that facilitate their specialized functionalities, such as:
Cilia
Cilia are small, hair-like structures that possess motility and are located on the surface of a cell. They aid in the movement of entire cells or facilitate the movement of substances along the outer surface of the cell. Typically, ciliated cells exhibit a multitude of cilia on their exterior. The respiratory tract is lined with epithelial cells that possess cilia, which function to ensnare inhaled particles such as dust and transport them toward the nostrils, thereby preventing their entry into the lungs. The epithelial cells that are present in the fallopian tubes are equipped with cilia, which facilitate the transportation of an ovum from the ovary to the uterus.
Stereocilia
Stereocilia are a type of specialized microvilli that exhibit a cilia-like appearance and protrude from the surface of specific epithelial cells. The presence of stereocilia on the epithelial tissue of the inner ear is essential for the processes of hearing and balance.
Microvilli
MicroVilli are non-motile (they don’t move) finger-like structures on the surface of epithelial cells that function to increase the cell’s surface area so that it can better absorb substances. The small intestine's epithelial cells possess numerous microvilli that facilitate the absorption of nutrients from ingested food and provide a protective barrier against intestinal bacteria.
The arrangement of cells can also result in variations in epithelial tissue. Here is the terminology used to describe the arrangement of cells in epithelial tissue
In academic terms, simple epithelium refers to a type of tissue characterized by a single layer of cells.
A stratified epithelium is a type of tissue that consists of multiple layers of cells.
And a pseudostratified epithelium is a type of tissue composed of densely packed cells that exhibit a layered appearance due to their varying sizes, despite being comprised of a single layer of cells.
The various classifications of epithelial cells present in the human body
Epithelial tissue can manifest in various types owing to the diverse shapes and configurations of its constituent cell layers. These types may include:
The simple squamous epithelium is a type of tissue characterized by a single layer of flattened cells that form a thin and smooth surface.
This particular form of epithelium is commonly found lining both vascular structures and anatomical cavities, where it serves to modulate the translocation of molecules and compounds across the underlying tissue.
The simple cuboidal epithelium is a type of tissue characterized by a single layer of cube-shaped cells.
This particular type of epithelium is commonly observed in the glandular tissue that secretes substances and in the tubules of the kidneys.
The simple columnar epithelium is a type of tissue characterized by a single layer of column-shaped cells that line the surface of organs and tissues.
This particular epithelial tissue is frequently specialized for the process of absorption and typically features apical cilia or microvilli. The aforementioned cells are located in the lining of the individual's stomach and intestines.
Stratified squamous epithelium is a type of tissue that is composed of multiple layers of flattened cells.
This particular type of epithelium typically serves protective roles, such as safeguarding against the infiltration of microorganisms into the underlying tissue and/or preventing loss of water. The epidermis, which constitutes the outermost layer of the integumentary system, is primarily composed of stratified squamous epithelial cells.
The stratified cuboidal epithelium is a type of tissue characterized by multiple layers of cube-shaped cells.
This particular type of epithelial tissue is relatively uncommon and is typically located within the excretory ducts of both sweat and salivary glands.
The stratified columnar epithelium is a type of tissue characterized by multiple layers of column-shaped cells.
This particular type of epithelium is relatively infrequent and is observed in the mucous membrane, specifically the conjunctiva, which lines the eyelids. Its function is both protective and involves the secretion of mucus.
The pseudostratified columnar epithelium is a type of epithelial tissue that appears to be stratified due to the varying heights of its cells, but in reality, all cells are in contact with the basement membrane. This type of tissue is commonly found in the respiratory tract and reproductive system.
The upper respiratory tract is typically lined by a type of epithelium that is characterized by a high density of cilia.
What is the function of epithelial tissue?
Epithelial tissue performs crucial physiological roles that are indispensable for sustaining life. The function and purpose of epithelial cells vary depending on their location, given that they are distributed throughout the body.
Epithelial tissue can perform various functions, either singly or in combination, which include:
Epithelial tissue serves as a protective barrier for various physiological components of the human body. The integumentary system comprises epithelial tissue that functions as a protective barrier for the underlying tissues, including blood vessels, muscles, and internal organs. The epithelial cells that form the lining of the intestines are equipped with cilia, which serve the purpose of safeguarding the body against the harmful effects of intestinal bacteria.
The glandular epithelium of the epithelial tissue can secrete various substances, such as enzymes, hormones, and fluids.
The process of absorption involves the uptake of specific substances through the epithelial lining of internal organs, such as the liver and lungs. The internal epithelial lining of the intestines is responsible for the absorption of nutrients from ingested food.
Excretion refers to the physiological process of eliminating metabolic waste products from the body. The renal epithelial tissue is responsible for the excretion of waste in the kidneys, while the sweat glands' epithelial tissue is responsible for the excretion of sweat.
The respiratory tract's epithelium performs the function of filtration by removing dirt and particles from the inhaled air, thereby purifying it. The renal epithelium is responsible for blood filtration in the kidneys.
Diffusion refers to the process of passive movement of particles or molecules from areas of high concentration to areas of low concentration, as observed in biological systems. The membrane, composed of simple squamous epithelial cells, facilitates the process of selective diffusion of materials. The process of diffusion facilitates the functions of filtration, absorption, and secretion.
The process of sensory reception involves the activation of sensory nerve endings that are situated within the epithelial tissue, enabling the body to perceive and respond to external sensory stimuli. The stereocilia present on the epithelial tissue surface within the ear play a crucial role in the auditory and vestibular systems, contributing to hearing and balance. Furthermore, the taste receptors are located within the stratified squamous epithelium of the tongue.
What are the factors that impact the functioning of epithelial tissue?
One of the primary considerations regarding epithelial tissue pertains to the possibility of the emergence of malignancies such as adenocarcinoma or papillary thyroid carcinoma, both of which are classified as forms of cancer.
Adenocarcinoma is a prevalent form of cancer that primarily affects the glandular epithelial tissue lining various organs.
Papillary thyroid carcinoma accounts for a significant proportion, approximately 80%, of all malignancies affecting the thyroid gland. This particular type of cancer exhibits a slow rate of growth. Whilst papillary thyroid cancer frequently metastasizes to cervical lymph nodes, it exhibits a high degree of responsiveness to therapeutic interventions. Papillary thyroid carcinoma exhibits a high curative potential and infrequently results in mortality.
References
• Editors, BD. “Epithelial Tissue (Epithelium) - Definition, Types and Function.” Biology Dictionary, 25 Dec. 2016, biologydictionary.net/epithelial-tissue.
•
@ClevelandClinic. “Epithelium: What It Is, Function and Types.” Cleveland Clinic, my.clevelandclinic.org/health/articles/22062-epithelium. Accessed 10 Apr. 2023.
• “Epithelium - Wikipedia.” Epithelium - Wikipedia, 28 Sept. 2012, en.m.wikipedia.org/wiki/Epithelium.
• “Epithelial Tissue | SEER Training.” Epithelial Tissue | SEER Training, training.seer.cancer.gov/anatomy/cells_tissues_membranes/tissues/epithelial.html. Accessed 10 Apr. 2023.
•
https://www.kenhub.com/en/library/anatomy/overview-and-types-of-epithelial-tissue• “Epithelium.” Biology Articles, Tutorials & Dictionary Online, 30 Nov. 2019,
www.biologyonline.com/dictionary/epithelium.
• Biga, Lindsay M., et al. “4.2 Epithelial Tissue – Anatomy and Physiology.” 4.2 Epithelial Tissue – Anatomy & Physiology, open.oregonstate.education/aandp/chapter/4-2-epithelial-tissue. Accessed 10 Apr. 2023.
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