epitheal cells Flashcards
(12 cards)
Surface vs grandular cells
Surface epithelial cells form continuous sheets.
Glandular epithelial cells often form clusters, cords, or tubules, but the cells are still tightly joined using junctions like tight junctions and desmosomes.
Just to clarify :
Glandular cells don’t usually form multilayered sheets.
But they can be closely packed together and sometimes still connect to surface epithelial tissue (especially in exocrine glands).
They may still use tight junctions and desmosomes, especially when forming glandular clusters or acini.
The membranes always have one free (unattached) surface or edge. This apical surface is exposed to the body’s exterior or to the cavity of an internal organ. The exposed surfaces of some epithelia are slick and smooth, but others exhibit cell surface modifications, such as microvilli or cilia. this is the top layer of organs.
When they say the apical surface “isn’t attached to anything,” they specifically mean:
The front (top) of the cell—the apical surface—is not connected to another cell or tissue.
It’s facing open space, like the inside of a hollow organ (lumen) or the outside of the body.
The back of an epithelial cell (called the basal surface) is definitely connected to something.
The anchored (basal) surface of epithelium rests on a basement membrane, a structureless material secreted by both the epithelial cells and the connective tissue cells deep to the epithelium. Think of the basement membrane as the “glue” holding the epithelium in place.
how the first name of the epithillium tissue represents how much layers it has.
Each epithelium is given two names. The first indicates the number of cell layers it has (Figure 3.17a). The classifications by cell arrangement (layers) are simple epithelium (one layer of cells) and stratified epithelium (more than one cell layer).
Stratified refers to multiple layers of cells, but only the top layer’s shape is used to name the tissue (squamous, cuboidal, columnar, etc.).
The deeper layers support the tissue and help in regeneration (new cell formation), but they don’t influence the naming.
The second name describes the shape of its cells
The second describes the shape of its cells (Figure 3.17b). There are squamous (skwa′mus) cells, flattened like fish scales (squam = scale), cuboidal (ku-boi′dal) cells, which are cube-shaped like dice, and columnar cells, shaped like columns.
The terms describing the shape and arrangement are then combined to describe the epithelium fully.
Simple Epithelia
The simple epithelia are most concerned with absorption, secretion, and filtration. Because simple epithelia are usually very thin, protection is not one of their specialties.
Simple Squamous Epithelium
Simple squamous epithelium is a single layer of thin squamous cells resting on a basement membrane. The cells fit closely together, much like floor tiles. This type of epithelium usually forms membranes where filtration or exchange of substances by rapid diffusion occurs. Simple squamous epithelium is in the air sacs of the lungs (called alveoli), where oxygen and carbon dioxide are exchanged (Figure 3.18a), and it forms the walls of capillaries, where nutrients and gases pass between the blood in the capillaries and the interstitial fluid. Simple squamous epithelium also forms serous membranes, or serosae (se-ro′se), the slick membranes that line the ventral body cavity and cover the organs in that cavity. (We describe the serous membranes in more detail in Chapter 4.)
-filltration-diffusion-gas exchange.
Simple cuboidal epithelium,
Simple cuboidal epithelium, which is one layer of cuboidal cells resting on a basement membrane, is common in glands and their associated small tubes called ducts (for example, the salivary glands and pancreas). It also forms the walls of the kidney tubules (Figure 3.18b) and covers the surface of the ovaries.
Simple cuboidal epithelium is involved in secretion and absorption and is found in glands, kidneys, and ducts.
Remember that simple cubical can’t do gas exchange because it’s to thick to do the gas exchange it needs a thin thing like simple squamous.
Simple columnar epithelium
Simple columnar epithelium is made up of a single layer of tall cells that fit closely together and whose nuclei appear to form a straight line. Goblet cells, which produce a lubricating mucus, are often seen in this type of epithelium. Simple columnar epithelium lines the entire length of the digestive tract from the stomach to the anus (Figure 3.18c). Epithelial membranes that line body cavities open to the body exterior are called mucosae (mu-ko′se), or mucous membranes.
Mucus secretion (thanks to goblet cells)
Absorption of nutrients
Protection of internal surfaces — especially in the digestive tract
Stratified Epithelia
Stratified epithelia consist of two or more cell layers. Being considerably more durable than the simple epithelia, these epithelia function primarily in protection.
Stratified squamous epithelium
Stratified squamous epithelium is the most common stratified epithelium in the body. It usually consists of many cell layers. The cells at the (top)free edge are squamous cells, whereas those close to the basement membrane are cuboidal or columnar. Stratified squamous epithelium is found in sites that receive a good deal of abuse or friction, such as the surface of the skin, the mouth, and the esophagus (Figure 3.18e).
Stratified Cuboidal and Stratified Columnar Epithelia
Stratified cuboidal epithelium typically has just two cell layers with (at least) the surface cells being cuboidal in shape. The surface cells of stratified columnar epithelium are columnar cells, but its basal cells vary in size and shape. Both of these epithelia are fairly rare in the body, found mainly in the ducts of large glands. (Because the distribution of these two epithelia is extremely limited, they are not illustrated in Figure 3.18. We mention them here only to provide a complete listing of the epithelial tissues.)
stratified cuboidal and stratified columnar epithelium are rare, they still have important roles — mostly in protection and sometimes secretion in certain glands.
Transitional Epithelium
Transitional epithelium is a highly modified, stratified squamous epithelium that forms the lining of only a few organs—the urinary bladder, the ureters, and part of the urethra. As part of the urinary system, all of these organs are subject to considerable stretching (Figure 3.18f). Cells of the basal layer are cuboidal or columnar; those at the free surface vary in appearance. When the organ is not stretched, the membrane is many-layered, and the superficial cells are rounded and domelike. When the organ is distended with urine, the epithelium thins like a rubber band being stretched, and the surface cells flatten and become squamouslike. This ability of transitional cells to slide past one another and change their shape (undergo “transitions”) allows the ureter wall to stretch as a greater volume of urine flows through that tubelike organ. In the bladder, the ability of transitional epithelium to stretch allows more urine to be stored without increasing pressure in the bladder.
Transitional epithelium is a stretchable, stratified tissue found only in the urinary system. Its cells can change shape depending on the amount of urine present — becoming flat when stretched and rounded when relaxed. This allows organs like the bladder and ureters to expand without damage or leaks.
Glandular Epithelium
A gland is made up of one or more cells that produce and secrete a specific product.
The product secreted by glands is called a secretion, which often contains protein molecules in an aqueous (water-based) fluid.
The process by which glandular cells obtain materials from the blood and release them in the form of a secretion is called exocytosis. ✅ (Spelling note: not “exyocitosis”)
Endocrine glands do not have ducts and release their secretions, such as hormones, directly into the blood vessels.
Some examples of endocrine glands are the thyroid, adrenals, and pituitary.
Exocrine glands, on the other hand, have ducts that carry their secretions to the epithelial surface.
Examples of exocrine glands include sweat glands, oil glands, liver, and pancreas.
The secretion process in both endocrine and exocrine glands is an active process.
