0401 - Epithelium - RM Flashcards
Describe appearance of different types of epithelia seen on light microscopy Be able to provide different examples of location of epithelial types in the body List the basic functions of different types of epithelia Describe the basic appearances and purpose of cilia, microvilli and goblet cells, revise function and appearance of desmosomes.
Describe the appearance of simple squamous epithelium.
Also known as ‘pavement epithelium’ or ‘endothelium’ – a single layer of flat cells at the free edge, above the basement membrane. Each cell wider than it is tall, providing a large surface area. Cytoplasm may be very difficult to see. Nuclei may look as though they protrude into the lumen.
Describe the appearance of simple cuboidal epithelium.
Single layer of cells as round as tall as they are wide, and usually have a large central nucleus.
Describe the appearance of simple columnar epithelia.
Single layer of cells that are taller than they are wide, with nucleus towards the base. Can be ciliated or non-ciliated. May contain goblet cells (glandular epithelium).
Describe the appearance of pseudostratified ciliated columnar epithelium.
More complex and less regular than simple columnar. Appears to be more than one layer of cells due to nuclei on different levels. Actually a single layer with all cells actually resting on basement membrane. Ciliated.
Describe the appearance of stratified squamous epithelium.
2 or more layers, transitioning from a cuboidal or columnar basal layer to a squamous surface layer. Consists of a distinct basal layer (lowest) and spinous layer (above) that includes desmosomes, which appear as striations between the cells. May be keratinised, in which case there will be a granular layer, with overlying keratin.
Describe the appearance of stratified cuboidal epithelium.
2 or 3 layers of cuboidal or low-columnar cells, other cell types may be present beneath the top layers. Not much absorption or excretion, so unlikely to contain microscopic pores or goblet cells.
Describe the appearance of stratified columnar epithelium.
Several layers of epithelial cells of any type, with a surface layer of columnar cells.
Describe the appearance of transitional (urothelium) epithelium.
4-5 layers. Basal layer is cuboidal, surface layer larger and rounded. Transitional between stratified cuboidal and stratified squamous, so may be hard to identify.
Where would you find simple squamous epithelium? What is its function in each place?
Lungs – Gas exchange Blood vessels – gas, waste, nutrient exchange Kidney – urine filtration Mesothelium – secretion of lubricating fluid
Where would you find simple cuboidal epithelium? What is its function in each place?
Lining the ducts of the kidney – absorbing substances to give urine its final composition. Lining the ducts of salivary glands and pancreas – secreting fluids.
Where would you find simple columnar epithelium?
Gallbladder Fallopian tubes (with cilia) Small and large bowel, stomach, and uterus (with microvilli).
Where would you find pseudostratified ciliated columnar epithelium?
Lining of the bronchi.
Where would you find stratified squamous epithelium?
Anywhere where abrasion is a risk – skin (keratinised), mouth, oesophagus, tongue, vagina (all non-keratinised in healthy people).
Where would you find stratified cuboidal epithelium?
Lining the larger ducts of the exocrine glands, such as salivary glands.
Where would you find stratified columnar epithelium?
Very rare – found in parts of male urethra, conjunctiva of eye, and uterus.
Describe the appearance and purpose of cilia.
Short (3-4micron) extensions of cytoplasm that protrude from the cell membrane. Generally curved or hair-like appearance. They develop from basal bodies. Each cell can have up to 300. Involved in secretion and movement of particles via MOTILE cilia that beat like a wave to form a current.
Under electron microscopy, cross section shows a central pair of microtubules surrounded by nine peripheral pairs of microtubules.
What is the appearance and purpose of microvilli?
Closely bunched, tiny (1micron) projection from the free surface of cell – have an appearance similar to cricket bats laid side by side. Core of actin. Main function is absorption (bowel), but also excrete GLYCOCALYX (bowel, stomach, uterus).
What is the appearance and purpose of goblet cells?
Modified columnar cells, appearing as large, round bodies in an area of otherwise columnar cells. Mucigen granules at the top, and nucleus and organelles at the base. Secrete mucigenic substances, good for lubrication.
Can show up as either light or dark under light microscopy.
What is the appearance and function of desomosomes?
Very strong adhesions that link the cytoskeletons of neighbouring cells. Appear to be ‘dotted’ along the border of the two cells under light microscopy (artifact of shrinkage in slide preparation). Cannot be disjoined without destroying the cells.
More commonly viewed under EM - darkened area where cytoskeletons converge.
