Board Review Series (BRS)- Histology - Epithelia & Glands

E = Flattened Cell with Nuclei

Shape: Flattened

Locaton: Endothelium (lining of blood vessels), mesothelium (lining of peritoneum and pleura)

In simple squamous epithelium, cells of the single layer are flat and usually very thin, with only the thicker cell nucleus appearing as a bulge to denote the cell.

Shape: Cuboidal

Location: Lining of distal tubule in kidney and ducts in some glands, surface of ovary

Shape:All cells rest on basal lamina, but not all reach the lumen; thus the epithelium appears falsely stratified

Location: Lining of trachea, primary bronchi, nasal cavity, and excretory ducts in parotid gland

Shape: Flattened (nucleated)

Location: VaMET = Vagina and Mouth, Esophagus (lining),True vocal cords.

K = Keratin is a protein that is non-living. Notice the lack of nuclei

Shape: Flattened (and without nuclei)

Location: Epidermis of skin.

Shape: Cuboidal

Location: Lining of ducts in sweat glands

Stratified cuboidal are fairly rare, but are found in excretory ducts of some glands

Shape: Columnar

Location: Lining of large excretory ducts in some
glands and cavernous urethra

B= Bi-nucleated

Shape: Dome-shaped (when relaxed), flattened (when stretched)

Location: Lining of urinary passages from renal
calyces to the urethra

1. Transcellular transport of molecules from one epithelial surface to another.
2.Absorption - Via endocytosis or pinocytosis.
3. Secretion of various molecules (e.g., hormones, mucus, proteins) occurs
by exocytosis.
4. Selective permeability results from the presence of tight junctions between epithelial cells and permits fluids with different compositions and concentrations to exist on separate sides of an epithelial layer (e.g., intestinal epithelium).
5. Protection from abrasion and injury is provided by the epidermis, the epithelial layer of the skin.

a. Diffusion of oxygen and carbon dioxide across the epithelial cells of lung alveoli and capillaries
b. Carrier protein-mediated transport of amino acids and glucose across intestinal epithelia
c. Vesicle-mediated transport of immunoglobulin A (IgA) and other molecules.

Muscular
Epithelial
Nervous
Connective

A section showing the apical regions of two epithelial cells reveals a junctional complex with its zonula occludens (ZO), zonula adherens (ZA), and a desmosome (D).

1. The Tight Junction (Zonula Occludens) is a zone that surrounds the entire apical perimeter of adjacent cells and is formed by fusion of the outer leaflets of the cells.

The Tight Junction (ZO) prevents movement of substances into the intercellular space from the lumen.

2. The Intermediate Junction (Zonula Adherens) is the zone that surrounds the entire perimeter of epithelial cells just basal to the tight junction:

a. It is characterized by a 10- to 20-nanometer (nm) separation between the adjacent plasma membranes, where the extracellular portions of cadherin molecules occupy the intercellular space.
b. A mat of actin filaments is located on each of its cytoplasmic surfaces. The actin filaments are linked, via a-actinin and vinculin, to the transmembrane glycoprotein E-cadherin.

3. Desmosome (Macula Adherens) is a small, discrete, disk-shaped adhesive site. It is also commonly found at sites other than the junctional complex, where it joins epithelial cells.

a. It is characterized by a dense plaque of intracellular attachment
proteins, called desmoplakins, on the cytoplasmic surface of each opposing cell.

b. Intermediate keratin filaments (tonofilaments) loop into and out of the dense plaque from the cytoplasm.

A: Specialized junctions that provide adhesion between cells and restrict movement of materials into and out of lumina.

A: Basal Lamina, Hemidesmosomes, Basal Plasma-membrane infolding

BL = Basal Lamina
Arrows = Hemidesmosomes.

A: Consists of two zones: the lamina lucida (or lamina rara), which lies next to the plasma membrane, and the lamina densa, a denser meshwork (of type IV collagen, glycoproteins, and glycosaminoglycans), which lies adjacent to the reticular lamina of the deeper connective tissue.

A: Basal lamina plus reticular lamina

This section of kidney shows the typical basement membranes (arrows) of several tubules and of structures within the single glomerulus included here. In renal glomeruli the basement membrane, besides having a supporting function, has an important role as a filter

A:
Specialized junctions that resemble one-half of a desmosome.

They mediate adhesion of epithelial cells to the underlying extracellular matrix.

They consist of a dense cytoplasmic plaque, which is linked via transmembrane receptor proteins (integrins) to laminins in the basal lamina.

A: Are common in ion-transporting epithelia (e.g., distal convoluted tubule of the kidney, striated ducts in salivary glands).
1. They form deep invaginations that compartmentalize mitochondria.
2. Function. They increase the surface area and bring ion pumps [Na+-K-F adenosine triphosphatase (ATPase)] in the plasma membrane

A: These surfaces may possess specialized structures such as microvilli, stereocilia, and cilia.

A: Finger-like projections of epithelia that extend into a lumen and increase the cell's surface area. The can be seen by light microscope.

They are MUCH shorter than Cilia which have the purpose of moving back and forth to move.


1. A glycocalyx (sugar coat) is present on their surfaces
2. A bundle of actin filaments runs longitudinally through the core of each microvillus.
3. Microvilli constitute the brush border of kidney proximal tubule cells and the striated border of intestinal absorptive cells.

A: are very long microvilli (not cilia) and are located in the epi- didymis and vas deferens of the male reproductive tract.

A: are actively motile processes (5-10 gm in length) extending from certain epithelia (e.g., tracheobronchial and oviduct epithelium) that propel substances along their surfaces.

1) Covering or lining epithelium
2) Glandular epithelium

The basal body is a cylindrical structure located at the base of each cilium that consists of nine triplet microtubules arranged radially in the shape of a pinwheel (9 + 0 configuration).

Function: Serves as a nucleation site for the growth of the axoneme microtubules.

Remember MEEP
1) Merocrine glands use exocytosis
2) Edocrine - Directly into blood stream
3) Exocrine - Into ducts
4) Paracrine

HAM

1) Holocrine
2) Apocrine
3) Merocrine

HOLOCRINE - are produced in the cytoplasm of the cell and released by the rupture of the plasma membrane, which destroys the cell and results in the secretion of the product into the lumen.

Holocrine secretion is the most damaging type of secretion, with merocrine secretion being the least damaging and apocrine secretion falling in between.

APOCRINE - Cells which are classified as apocrine bud their secretions off through the plasma membrane producing membrane-bound vesicles in the lumen.

MEROCRINE - A cell is classified as merocrine if the secretions of that cell are excreted via exocytosis from secretory cells into an epithelial-walled duct or ducts and thence onto a bodily surface or into the lumen.

Merocrine is the most common manner of secretion.

1) Unicellular glands are composed of a single cell (e.g., goblet cells in tracheal epithelium)
2) Multicellular glands:

a) are classified according to duct branching as simple glands (duct does not branch) or compound glands (duct branches).

b) They are further classified according to the shape of the secretory unit as acinar or alveolar (sac or flask-like) or tubular (straight, coiled, or branched). They secrete mucus and serous secretions (Watery, rich in enzymes)

Endocrine glands are glands of the endocrine system that secrete their products, hormones, directly into the blood rather than through a duct. The main endocrine glands include the pituitary gland, pancreas, ovaries, testes, thyroid gland, and adrenal glands.

Results from a genetic defect that causes an ab- normal ciliary beat or the absence of a beat.

Cilia have axonemes that lack ciliary dynein arms and have other abnormalities.

Associated with recurrent lower respiratory tract infec- tions, reduced fertility in women, and sterility in men.

occur when cells fail to respond to normal growth regulatory mechanisms.
1. These tumors are benign when they remain localized.
2. They are malignant when they metastasize to other parts of the body.

a. Carcinomas are malignant tumors that arise from surface epithelia.
b. Adenocarcinomas are malignant tumors that arise from glands.

an autoimmune disease in which antibodies against hemidesmosomes are produced.
• • • • • • •
1. This disease is characterized by chronic, generalized blisters in the skin.
2. These blisters cause the epithelium to separate from the underlying sub-
stratum.

1-E. Desmosomes are sites of adhesion characterized by dense cytoplasmic plaques and associated keratin filaments. Only gap junctions permit cell-to-cell communication of small molecules via their connexon "channels."

2-C. Individuals with abnormal respiratory cilia often have recurrent respiratory infections if the cilia are unable to clear the respiratory epithelium of microorganisms, debris, and so forth. The student may have immotile cilia syndrome, which is caused by a genetic defect resulting in cilia with axonemes that lack ciliary dynein arms and thus are unable to beat.

3-C. The gap junction "channel" regulates the passage of ions and small molecules from cell to
cell, excluding those having a molecular weight greater than 1200 daltons. The tight junction is the zone of adhesion around the apical perimeter of adjacent cells. The other statements are char- acteristics of desmosomes.

4-D. Serous secretions produced by glands are often rich in enzymes and watery in consistency. Exocrine glands secrete into ducts, and endocrine glands lack ducts. Merocrine glands use exocytosis to release their products.

5-A. Epithelia are polarized, meaning they show a "sidedness" and have apical and basolateral surfaces with specific functions.

6-C. Cilia contain an axoneme with ciliary dynein arms extending unidirectionally from one member of each doublet. Ciliary dynein has ATPase activity, and when it splits adenosine triphosphate (ATP), the adjacent doublets slide past one another and the cilium moves.

7 - B . Stratified squamous epithelium is characterized by flattened cells (with or without nuclei) in its superficial layer. It may or may not be keratinized, and it rests on a basal lamina produced by the epithelium.

To help you remember:
Simple Cubes Like Tubes (as in Distal)
Simple CLOIS (Columnar Lining Of Intestines, Stomach)

The peritoneum is the serous membrane that forms the lining of the abdominal cavity

Pleura (lung area) is a serous membrane which folds back onto itself to form a two-layered, membrane structure.

serous membrane (or serosa) is a smooth membrane consisting of a thin layer of cells, which secrete serous fluid (a lubricating fluid which reduces friction from muscle movement).

Transformation of one tissue type to another.
In people that smoke the normal simple columnar epithelium lining of the bronchus is replace by nonkeratinized stratified squamous epithelium.

See Pic

Zonulae Occuludens = Tight Juncitons
Maculae Adherens = Desmosomes

Pseudo. ciliated columnar and they can change to stratified squamous.

Intermediate filaments.

Most types of intermediate filaments are cytoplasmic, but one type, the lamins, are nuclear.

Lubricating such area as the pleura of the lungs and the pericardium of the heart.

Transitional ... The bladder needs to expand.

Simple squamous mesothelium

Mesothelium derives from the embryonic mesoderm cell layer, that lines the coelom (body cavity) in the embryo. It develops into the layer of cells that covers and protects most of the internal organs of the body.

Basal Lamina

Are very long microvilli (not Cilia)

Are located in the epididymis and vas deferens of the male reproductive tract

Transitional

Lipid

Cilia and flagella have the classic “9 + 2” microtubular arrangement emanating from basal bodies.

Apical specializations are prominent in epithelia and include microvilli that increase surface area

stereocilia, which are non-motile modified microvilli.

They are characterized by their length (distinguishing them from microvilli) and their lack of motility (distinguishing them from cilia). They contain actin filaments.

They are found in three regions of the body:

the ductus deferens
the epididymis
the inner ear

Ducts of some exocrine glands

Adheres to Basal lamina
Line lymphatic vessels
Polarity
Tight junctions

Exocrine.

Epithelial tissue

Mircrovilli

Larynx

Simple squamous

Pericyte

A pericyte is a type of cell found in the central nervous system. Pericytes are more specifically located surrounding the endothelial cell layers of the capillary network in the brain. Pericytes play an integral role in the maintenance of the blood–brain barrier