Lining and Glandular Epithelium

Question 1

State four key features of epithelial tissue.

Answer 1

(1) Polarity: the presence of unique cellular features on the basal, lateral and apical domains of the epithelial cells. [Basal features are adjacent to the underlying basement membrane; lateral features are shared by contiguous epithelial cells, and apical features are found on the luminal side of epithelial cells.]

(2) Presence of a basal lamina on their basal side, which separates teh cells from teh underlying connective tissue.

(3) Absence of inercellular substance between contiguous cells.

(4) Close apposition to one another. This is due to the presence of special junctional structures such as desmosomes, occluding junctions, gap junctions, glycoproteins and calcium ions.

(5) Avascularity, since epithelial tissues do not have direct blood vessels. They are nourished through the basement membrane.

Question 2

What is the basement membrane?

Answer 2

The basement membrane is a thin, fibrous extracellular matrix that separates the epithelium from the underlying connective tissue.

Question 3

What are the two layers of the basement membrane?

Answer 3

The two layers are the basal lamina and the reticular lamina.

Question 4

State four functions of basement membranes.

Answer 4

(1) Provide physical binding of the epithelium to the underlying tissue and physical support.
(2) Control of epithelial growth and differentiation, they form a barrier to downward epithelial growth; this is only breached if epithelia undergo malignant transformation (cancer)
(3) Permit the flow of nutrients, metabolites and other molecules to and from an epithelium, as epithelium is devoid of blood vessels
(4) Where a cell layer acts as a selective barrier to the passage of molecules from one compartment to another (e.g. between the lumen of blood vessels and adjacent tissues), the basement membrane assumes a critical role in regulating permeability.

Question 5

What are the main components of the basement membrane?

Answer 5

The main components are collagen (especially type IV), laminin, nidogen, and heparan sulfate proteoglycans.

Question 6

Where is simple columnar ciliated epithelium found and what is its function?

Answer 6

It lines the lumen of the fallopian and uterine tubes, aiding in the movement of ova from the ovary to the uterine cavity.
It is also found in the respiratory tract where its cilia push mucus away from the lungs.

Question 7

Explain how you would differentiate pseudostratified columnar ciliated epithelia from true stratified epithelia. (2)

Answer 7

1. Individual cells of pseudostratified columnar ciliated epithelium exhibit polarity with the nucleus being confined to the basal 2/3 of the epithelium.
2. Cilia are never present on true stratified epithelia.
3. [Histological image: pseudostratified columnar ciliated epithelium]

Question 8

Name four sites lined by stratified squamous epithelium.

Answer 8

Anal canal, oral cavity, vaginal tract, oesophagus

Question 9

Where is stratified cuboidal epithelium found?

Answer 9

It is usually confined to the lining of the larger excretory ducts of exocrine glands such as the salivary glands, sweat glands and mammary glands.

[Histological slide: stratified cuboidal epithelium]

Question 10

State the function of stereocilia in the epididymis.

Answer 10

They increase the surface area for absorption of testicular fluid; this absorption creates a fluid current that moves the immobile sperm from the seminiferous tubules to the epididymis.

Question 11

Describe the classification of exocrine glands based on their morphology.

Answer 11

Exocrine glands may be divided into the secretory component and the duct.
1. The duct system may be unbranched (simple gland) or branched (compound gland).
2. The secretory component may be tubular or acinar (roughly spherical). Both types of secretory component may also be coiled or branched.

Question 12

Describe the classification of exocrine glands based on their means of secretion.

Answer 12

Merocrine secretion: involves the process of exocytosis
Apocrine secretion: the apical portion of the cells, together with the secretory contents, are budded off and released to the lumen or external environment
Holocrine secretion: discharge of whole secretory cells, with subsequent disintegration of the cells to release the secretory product

[Diagram: merocrine, apocrine and holocrine secretion]

Question 13

Give one example of simple coiled tubular glands.

Answer 13

Sweat glands

Question 14

What is the difference between acinar and alveolar glands?

Answer 14

The difference between acinar and alveolar glands lies in the size of the lumen. An acinar gland has a bulbous base with a small lumen, while an alveolar gland has a larger lumen. However, these terms may sometimes be used interchangeably.

Question 15

Name two sites where goblet cells can be found. (Hint: category of epithelium based on site)

Answer 15

1. intestinal epithelium
2. respiratory epithelium

Question 16

The three salivary glands differ in terms of their secretions. Expound on this.

Answer 16

Parotid glands: almost entirely serous cells
Submandibular glands: mostly serous cells (95%), some mucous cells (5%)
Sublingual glands: mostly mucous cells (65%), some serous cells (35%)

Question 17

What are two components of the stroma with respect to exocrine glands.

Answer 17

1. capsule: connective tissue that encapsulates the gland
2. septa: connective tissue that divides the gland into lobes and lobules

Question 18

Name two types of intralobular ducts found within the parotid gland and give a brief description of each.

Answer 18

1. intercalated ducts: small ducts that insert into and drain individual acini. They are more lightly stained than acini cells and are simple cuboidal.
2. striate ducts: arise from intercalated ducts. They are columnar with basal striations and are surrounded by capillaries.

Follow this link to appreciate these structures: [Virtual microscope].

Question 19

State the proteins in macula adherens/desmosome.

Answer 19

plakoglobin, plakophilins, desmoplakin, desmogleins, desmocollins

Further notes:
Desmogleins and desmocollins are classified as cadherins.
If you wish to learn more about the structure of desmosomes: [8-minute video].

Question 20

State the diseases associated with macula adherens/desmosomes.

Answer 20

Pemphigus foliaceus and pemphigus vulgaris, targeting desmosomal cadherins.

Further notes:
Pemphigus foliaceus: this is a rare autoimmune blistering disease affecting the skin and mucous membranes. It is characterised by superficial blisters that form on the skin, especially on the scalp, face and neck. The blisters are fragile and break open easily, turning into sores with a scaly, crusty texture. The condition is caused when the immune system produces proteins that attack the body’s healthy skin cells. Specifically, autoantibodies bind to a protein called desmoglein-1, found in desmosomes in the keratinocytes near the top of the epidermis. This results in the surface keratinocytes separating from each other and being replaced by fluid, forming a blister. Pemphigus foliaceus can be provoked by sun exposure and certain drugs.

Pemphigus vulgaris: This is a rare, chronic autoimmune disease that causes painful blisters and erosions on the skin and mucous membranes. It is the most common form of pemphigus and often first presents with lesions in the mouth and on genital mucous membranes. The condition is caused by the immune system producing antibodies against desmoglein-3, a protein found in desmosomes in the keratinocytes. This results in the keratinocytes separating from each other and being replaced by fluid, forming a blister.

Question 21

What are the differences between mucous cells and serous cells?

Answer 21

Mucous cells:
☛ rounded acidophilic cells typically with basal flattened nuclei
☛ rich in glycoproteins
☛ produce a mucoid secretion

Serous cells:
☛ basophilic cells that are more cuboidal or columnar, with fairly centrally located nuclei
☛ secrete polypeptides or proteins
☛ secretory granules may be visible in the apical portion of the cells
☛ basal regions of the cells have accumulations of rough endoplasmic reticulum that provide the basal staining

[Histological slide 1] [Histological slide 2]

Question 22

Click on Answer to view images of cell junctions.

Answer 22

[Image 1] [Image 2] [Image 3] [Image 4]