Human Tissue Types I: Epithelial Tissue Quiz

Answer: Cells arranged in sheets of single or multiple layers

The cells in epithelia (the plural of epithelium) are closely packed together in sheets, which can have either a single layer, or multiple. They are held together by many cell junctions, which can be of many types, including gap junctions which are formed by connexin protein tunnels between the cells. Because epithelial cells are so densely packed, there is little intracellular space between the plasma membrane of one cell and its neighbor.

The option "Groups of elongated cells that use ATP to produce energy" actually
defines muscle cells.

Answer: Lateral surfaces

As to the locations of these surfaces, their names actually tell you a lot, as you would expect: the apical, or free, surface is the surface of the epithelial cell which faces the lumen (interior space) of an organ, or the body surface, or a body cavity, depending on where in the body it is. If the epithelium is multi-layered, the apical surface is simply the most superficial surface. These surfaces can contain cilia (little hairs) or microvilli (membrane folds or protrusions which increase surface area).

The lateral surface is on the side of the cell("latus" in Latin means "side"), and is the surface which joins each cell to its epithelial neighbor, and thus must contain the intraepithelial cell junctions.

The basal surface is the bottom surface of the epithelial cell and joins the cell to extracellular components, and the basement membrane anchors the epithelium to connective tissues.

Answer: Tight junctions

Tight junctions contain strands of transmembrane protein which cinch the plasma membranes together at several points, leaving small gaps between them. They are found in abundance in the epithelia of the stomach and intestines; their function is to hinder the passage of materials between cells, which prevents the cell contents leaking out.

Adherens junctions have a block of plaque protein on the inside of the plasma membranes, and transmembrane proteins called cadherins stretch across the junction, "plugging in" to the plaque on the other cell, thus binding the two cells together.

Desmosomes have the same basic structure as that of adherens junctions, and have in addition intermediate keratin filaments which extend from the desmosome to other desmosomes on the other side of the cell, giving the junction more stability. They are common in skin cells, particularly in the outermost layer, the epidermis. They also prevent cardiac muscle cells from tearing apart during contraction of the heart.

Hemidesmosomes are basically half-desmosomes: instead of attaching a cell to another cell, they attach cells to the basement membrane. Instead of cadherins, they have proteins called integrins, which bind to proteins in the basement membrane called laminin.

Answer: basal lamina

It is the basal lamina. This lamina (thin layer) joins onto the basal surface of the epithelial cells and is actually secreted by them. It contains proteins which attach the cells to the basement membrane.

The reticular lamina is closer to the connective tissue underneath the epithelium, and contains proteins which are secreted by this connective tissue called fibroblasts.

Basement membranes function to support the epithelium, and also provide a route through which epithelial cells can move, for example during growth, or healing of wounds.

Answer: True

This is true; although the epithelia have a nerve supply, their blood supply actually comes from the adjacent connective tissues. Substances are exchanged by diffusion, e.g. gases, or nutrients coming in and out of the cells.

Epithelial tissue can be sub-divided into two further groups: Covering and lining epithelium, which as the name suggests forms the inner lining of structures like blood vessels, ducts, and also structures of various body systems, e.g. respiratory, urinary. This type also forms the outside layer of your skin.
The second sub-type is Glandular epithelium, which forms the secreting sections of glands in the body, such as adrenal or sweat glands.

Answer: Squamous

It may have been clearer to you which shape columnar and cuboidal cells are: as their names suggest, columnar cells are very tall and thin, and cuboidal cells are shaped like cubes - as tall as they are wide.

Transitional is the name given to cells that can change shape within the epithelium - as organs stretch and shrink back to a smaller size, so do their epithelial cells.

The flat cells then are the squamous cells. Their shape allows a very rapid flow of substances through them, which is useful in structures like blood vessels, which require movement of substances through them as the basis of their function.

Answer: Simple and pseudo-stratified

Both simple and pseudo-stratified are one-layered. Simple epithelium is a single layer which functions for diffusion, secretion and absorption. An example is blood vessels which are simple squamous epithelia.

Pseudo-stratified epithelia look like they have multiple layers, because the cells are not all at the same level, but they do actually only contain one layer. Cells that don't extend up to the apical surface either normally have cilia, or they secrete mucus. Examples are the epithelia in the upper respiratory tract and part of the male urethra, both of which are pseudo-stratified columnar epithelia.

Stratified epithelia have simply two or more layers, which helps to protect the layers underneath that would otherwise be prone to abrasion (wear-and-tear).

Answer: Vagina

I hope you can relate the function of the body parts to their possible structure: Cells in the eardrum, air sacs, and lymphatic vessels all rely on transfer of materials (or sound waves in the case of the eardrum) through them for their function, and in previous questions, we decided that a simple squamous epithelium is best for this kind of function.

This leaves the vagina, and indeed the vagina contains stratified squamous epithelium: a multi-layered tissue of flat, thin cells which helps to protect the lower layers against abrasion. The vagina is prone to abrasion due to the passage of mucus, and also sexual intercourse, and when apical cells are lost, they are replaced from the basal cells of the epithelium.

This is the basis of the Papanicolaou (Pap) test, or Pap smear, which checks for any abnormalities in the vagina and cervix by analyzing the epithelial cells that have naturally come off. It is very important in catching pre-cancerous cells early and thus women can be treated more effectively if they do go on to develop cancer, so it is vital that women get one performed regularly.

Answer: Goblet cells

Goblet cells, as stated in the question, secrete mucus, and are mainly found in the respiratory and digestive tracts.

Salivary glands are multicellular exocrine glands and adrenal glands are endocrine glands, and alveolar cells are not glands at all!

More info on glands: The secretions of endocrine glands are transported in the bloodstream, and are called hormones. Endocrine glands include the adrenal glands and thyroid gland.
Exocrine glands, on the other hand, secrete products into ducts which carry them to the site of function - examples include the salivary glands, where the product of saliva is transported to the mouth.

Answer: False

This statement is false. Bone is classed as a connective tissue, which you can learn about in the next part of this series, Human Tissue Types II: Connective Tissue.

As has been covered in this quiz, epithelial tissue can be of two main types: covering and lining epithelium, and glandular epithelium. I hope you can see why bone comes under neither of these headings.