Tissues and Slides
The most common stain used is the Hameatoxylin and Eosin (H&E). The haemotoxylin has an affinity for nucleic acids and stains them blue, thus the nucleus is blue while eosin will stain proteins pink or esinophilic thus the cytoplasm is pink. There are 4 basic tissue types consisting of epithelium, connective tissue, muscle and nervous tissue.
Epithelium
Epithelium is the layer of cells that covers all external and internal surfaces o the body and forms the bulk of some organs, including liver, kidney and glandular tissue and may be derived from any one of the three embryological layers.
Epithelial cells form continuous sheets that act as boundaries between the environment face the free surface and underlying tissues. Cell to cell adhesion is facilitated by adhering junctions which anchor cells to each other and consist of adherens junction (zonular adherens) which forms a bult around the circumference and provides attachment for a strip of contractile filaments rich in actin and enables the cell to change shape. As well as desmosomes (macula adherens) which are intracellularly located laterally on the inside of cells’ membrane. These act as a rive for attachment of cytoskeletal elements and extracellularly adhesion proteins ar attached to desmosomes and therefore enable cell-cell adhesion. Tight junctions are ones which make an epithelium ‘leak-proof’ and are also known as occluding junctions (zonula occludens), they are usually located just below the apical surface and provide adhesion and control intercellular passage of molecules.
Epithelial layers have 4 main barrier function roles. Protection such as the skin of an organism, absorption such as in the intestine, secretory such as in the stomach, and sensory such as in taste buds, olfactory mucosa, hair cells and photoreceptors.
Based on proliferative capacity, epithelial cells can be divided into 3 groups. Permanent cells in which cell division does not occur during adult life (such as auditory air cells and those in the lens). Stable cells which may still be able to replicate under certain conditions (such as hepatic cells). Labile cells which are renewable (such as intestinal and skin epithelial cells).
Almost all cells demonstrate polarity but it becomes most obvious in epithelial cells. Polarity allows cells to compartmentalise specialised functions to specific areas and gives rise to three different cell surfaces: apical, basal and lateral. The apical surface is one that faces a lumen, the basal surface is one that faces the extracellular matrix and consists of basal lamina and blood supply while the lateral surface is adherent to adjacent cells.
Epithelial sheets are avascular so there is no blood vessels on the epithelial side of the basement membrane and as such epithelial cells must gain the oxygen and nutrients via diffusion. However, some groups of epithelial cells (such as those with a secretory function) need to be located near a rich blood supply to take up and release materials.
The presence of a basement membrane is a definitive feature of epithelial cells as it separates the cells from the underlying supportive structures. However, the basement membrane is only visible with electron microscopy o special stains.
Most glands are also derived from epithelium as they are collections of secretory cells specialised to synthesise and secrete specific products. There are two types of glads the exocrine which secrete into ducts and the endocrine which secrete directly into the vascular stream.
Types of Epithelium
Learn More
Crash Course: Epithelium
Human Biology Explained: Classfication of Epithelia
Study.com: What is Epithelial Tissue
Cram.com: Epithelial Tissue
Purpose Games: Epithelial Tissue
Fun Trivia: Epithelial Tissue
Veterinary Anatomy: Epithelial Tissue Quiz
Questions
The most common stain used is the Hameatoxylin and Eosin (H&E). The haemotoxylin has an affinity for nucleic acids and stains them blue, thus the nucleus is blue while eosin will stain proteins pink or esinophilic thus the cytoplasm is pink. There are 4 basic tissue types consisting of epithelium, connective tissue, muscle and nervous tissue.
Epithelium
Epithelium is the layer of cells that covers all external and internal surfaces o the body and forms the bulk of some organs, including liver, kidney and glandular tissue and may be derived from any one of the three embryological layers.
Epithelial cells form continuous sheets that act as boundaries between the environment face the free surface and underlying tissues. Cell to cell adhesion is facilitated by adhering junctions which anchor cells to each other and consist of adherens junction (zonular adherens) which forms a bult around the circumference and provides attachment for a strip of contractile filaments rich in actin and enables the cell to change shape. As well as desmosomes (macula adherens) which are intracellularly located laterally on the inside of cells’ membrane. These act as a rive for attachment of cytoskeletal elements and extracellularly adhesion proteins ar attached to desmosomes and therefore enable cell-cell adhesion. Tight junctions are ones which make an epithelium ‘leak-proof’ and are also known as occluding junctions (zonula occludens), they are usually located just below the apical surface and provide adhesion and control intercellular passage of molecules.
Epithelial layers have 4 main barrier function roles. Protection such as the skin of an organism, absorption such as in the intestine, secretory such as in the stomach, and sensory such as in taste buds, olfactory mucosa, hair cells and photoreceptors.
Based on proliferative capacity, epithelial cells can be divided into 3 groups. Permanent cells in which cell division does not occur during adult life (such as auditory air cells and those in the lens). Stable cells which may still be able to replicate under certain conditions (such as hepatic cells). Labile cells which are renewable (such as intestinal and skin epithelial cells).
Almost all cells demonstrate polarity but it becomes most obvious in epithelial cells. Polarity allows cells to compartmentalise specialised functions to specific areas and gives rise to three different cell surfaces: apical, basal and lateral. The apical surface is one that faces a lumen, the basal surface is one that faces the extracellular matrix and consists of basal lamina and blood supply while the lateral surface is adherent to adjacent cells.
Epithelial sheets are avascular so there is no blood vessels on the epithelial side of the basement membrane and as such epithelial cells must gain the oxygen and nutrients via diffusion. However, some groups of epithelial cells (such as those with a secretory function) need to be located near a rich blood supply to take up and release materials.
The presence of a basement membrane is a definitive feature of epithelial cells as it separates the cells from the underlying supportive structures. However, the basement membrane is only visible with electron microscopy o special stains.
Most glands are also derived from epithelium as they are collections of secretory cells specialised to synthesise and secrete specific products. There are two types of glads the exocrine which secrete into ducts and the endocrine which secrete directly into the vascular stream.
Types of Epithelium
- Simple squamous: is flattened and acts as a frictionless surface for selective fluid exchange. Located in lining blood and lymphatic vessels, alveoli, pleural and peritoneal cavities.
- Simple cuboidal: shaped like a cube and functions include: secretion, absorptio, acting as a conduit and protection. Located in renal convoluted tubuls and ducts, gland duct and secretory portions, ovarian surface epithelium and capsule of the lens.
- simple columnar: usually the same height and arranged in columns with nuclei generally at the same level. Functions to absorb, secret, protect and transport. Located in the GI tract, larger calibre ducts draining exocrine glands, uterin tubes and endometrium.
- Stratified squamous: can be keratinzed or non-keratinized andprovides resistance to wear and tear and forms a physical barrer to protect underlying tissues. It is located in teh skin, oral cavity, eosophagus, part of the anal canal, vagina and lining parts of the GI tract.
- Pseudostratifid columnar: appears multi-layeredbut every cell has an attachment to a basement membrane. However not ever cell reaches the free surface and nuclei appear at different levels. Functions include protection and mvoement of substances. Located in cells lining upper respiratory tract, escretory assages of male reprductive tract.
- Transitional: multilayered and called transitional as it represents a transition from stratified squaous to stratified columnar and allows tissue to stretch. Its function include protection and ability to distend. I is locatedin cells lining renal calyces, ureters, bladder and portion of ureter.
Learn More
Crash Course: Epithelium
Human Biology Explained: Classfication of Epithelia
Study.com: What is Epithelial Tissue
Cram.com: Epithelial Tissue
Purpose Games: Epithelial Tissue
Fun Trivia: Epithelial Tissue
Veterinary Anatomy: Epithelial Tissue Quiz
Questions
- list the different types of epithelium, what is their function and where are they found?
- List and describe 2 characteristics of epithelium.
- What embryological layer is epithlium derived from?