Glandular Epithelial Tissue: Videos & Practice Problems

Glandular epithelial tissue forms glands specialized for secretion, categorized into exocrine and endocrine glands. Exocrine glands release products via ducts onto body surfaces or cavities, while endocrine glands secrete hormones directly into the bloodstream. Unicellular exocrine glands, like goblet cells, secrete mucin for lubrication, whereas multicellular exocrine glands utilize merocrine, holocrine, or apocrine secretion modes. Merocrine secretion uses exocytosis, holocrine involves cell rupture, and apocrine sheds the apical portion without cell death, exemplified by salivary, sebaceous, and mammary glands, respectively.

Exocrine vs. Endocrine Glands

Glandular epithelial tissue is a specialized type of epithelial tissue that forms glands, which are structures designed for secretion. A gland can be defined as a single cell or a group of cells that release products into the environment, such as sweat, bile, or hormones. Glands are categorized into two main types: exocrine and endocrine glands.

Exocrine glands secrete their products onto body surfaces or into body cavities, which can be remembered by the prefix "ex-" indicating exit. These glands can be unicellular, consisting of a single cell, or multicellular, which utilize ducts to transport their secretions. Examples of exocrine gland secretions include mucus, sweat, oil, and milk.

In contrast, endocrine glands release their secretions directly into the bloodstream, allowing hormones to travel throughout the body and affect distant organs. The prefix "en-" in endocrine signifies entry into the blood. Endocrine glands are typically multicellular and do not have ducts for secretion. Notably, while most epithelial tissues are adjacent to open spaces, endocrine glands are an exception; they initially form with ducts that later regress, making them appear disconnected from open spaces.

Understanding the distinction between these two types of glands is crucial, as exocrine glands will be the primary focus in upcoming lessons, while endocrine glands will be explored in detail later in the course when discussing the endocrine system.

Glandular Epithelial Tissue Example 1

In this example, we analyze a gland to determine whether it is an endocrine or exocrine gland based on its structure and function. The key distinction between these two types of glands lies in their secretion mechanisms. Endocrine glands release hormones directly into the bloodstream, while exocrine glands secrete their products through ducts to body surfaces or cavities.

Upon examining the glandular epithelial tissue in the provided image, we observe that the tissue is folding inwards, forming ducts that retain connecting cells. This structural feature is characteristic of multicellular exocrine glands, which utilize ducts to transport their secretions. The presence of these ducts indicates that the gland is likely exocrine.

Furthermore, the glandular epithelial tissue is shown to be secreting products, represented by small blue circles, into these ducts. This process aligns with the function of exocrine glands, where secretions exit onto body surfaces or into body cavities. The mnemonic "EX" in exocrine can help recall that these secretions are exiting the gland.

In contrast, if the gland were endocrine, we would expect to see secretions entering the bloodstream, which is not the case here. Therefore, based on the evidence from the image and the characteristics of the gland, we conclude that the correct answer is option B: exocrine gland.

A mother breastfeeding her infant is utilizing what type of gland for that process? 

• A. Paracrine.
• B. Endocrine.
• C. Exocrine.
• D. Stratified.

Answer: (C)

Unicellular Exocrine Glands - Goblet Cells

Unicellular exocrine glands are specialized single-celled structures that play a crucial role in the secretion of substances. The most prominent example of these glands is the goblet cell, which is named for its distinctive goblet or wine glass shape. Goblet cells are primarily located within the epithelial tissue of the respiratory and intestinal tracts, where they are interspersed among columnar epithelial cells.

These cells are responsible for secreting mucin, a glycoprotein that is essential for the formation of mucus. It is important to note that mucin and mucus are not the same; mucin is the precursor that, upon secretion, contributes to the production of mucus. The secretion process occurs through exocytosis, where vesicles filled with mucin are released from the goblet cells into the surrounding area.

In the respiratory and intestinal tracts, goblet cells serve a vital function by producing mucus, which lubricates and protects the epithelial lining. This protective layer is crucial for maintaining the health of the tissues, as it helps to trap pathogens and particulates, facilitating their removal from the body. Additionally, goblet cells possess microvilli, which enhance their absorptive capabilities, further supporting their role in maintaining epithelial integrity.

In summary, goblet cells are essential unicellular exocrine glands that contribute significantly to the protective and lubricating functions of mucus in the respiratory and intestinal systems. Understanding their structure and function is key to appreciating how our body maintains its epithelial health.

Which of the following is a primary function of goblet cells? 

• A. Lubricating and protecting the epithelium. 
• B. Secreting mucus. 
• C. Producing hormones. 
• D. Absorbing wastes.

Answer: (A)

If you had many more goblet cells than you're supposed to, which symptom are you most likely to experience?

• A. A dry throat. 
• B. Low hormone levels. 
• C. Difficulty breathing. 
• D. High blood pressure.

Answer: (C)

Modes of Secretion: Merocrine, Holocrine & Apocrine

Multicellular exocrine glands are complex structures made up of multiple cells, distinguishing them from unicellular glands. These glands can be categorized into three primary types based on their modes of secretion: merocrine, holocrine, and apocrine secretion.

Merocrine secretion, also referred to as eccrine secretion, is the most common mode. In this process, cells utilize exocytosis to release their products. During exocytosis, secretory vesicles containing the product fuse with the cell membrane, allowing the contents to be expelled into a duct. An example of a gland that employs merocrine secretion is the salivary gland, which produces saliva that can exit onto body surfaces or into internal cavities.

In contrast, holocrine secretion involves the entire cell rupturing and dying to release its product. The term "holocrine" derives from the root "hollow," indicating that the whole cell is involved in the secretion process. This mode requires the gland to continuously replace dying cells to maintain function. A classic example of holocrine secretion is found in the sebaceous glands, which secrete oil.

Apocrine secretion is characterized by the shedding of the apical portion of the cell, allowing for product release without cell death. This mode of secretion allows the cell to remain intact and continue functioning after the apical portion is expelled. The mammary gland is a well-known example of a gland that utilizes apocrine secretion, particularly in the production of milk.

Understanding these modes of secretion is crucial for grasping how multicellular exocrine glands operate and their roles in various physiological processes. Each type of secretion has distinct mechanisms and implications for glandular function and maintenance.

Which type of multicellular gland needs to be completely regenerated each time it secretes product? 

• A. Merocrine.
• B. Apocrine.
• C. Holocrine.
• D. None of these.

Answer: (C)

Which type of gland doesn't need to be repaired at all after secretion?  

• A. Merocrine.
• B. Apocrine.
• C. Holocrine.
• D. None of these.

Answer: (A)

Which type of secretion is most consistent with how goblet cells secrete? 

• A. Merocrine.
• B. Apocrine.
• C. Holocrine.
• D. None of these.

Answer: (A)

Here’s what students ask on this topic:

What is the difference between exocrine and endocrine glands?

Exocrine and endocrine glands are both types of glandular epithelial tissue, but they differ in their methods of secretion. Exocrine glands release their products through ducts onto body surfaces or into body cavities. Examples include sweat, oil, and salivary glands. In contrast, endocrine glands secrete hormones directly into the bloodstream, allowing these hormones to travel to distant organs and tissues. Examples of endocrine glands include the thyroid and adrenal glands. The key distinction is that exocrine glands use ducts for secretion, while endocrine glands do not.

What are goblet cells and where are they found?

Goblet cells are unicellular exocrine glands named for their goblet-like shape. They are primarily found in the epithelial lining of the respiratory and intestinal tracts. Goblet cells secrete mucin, a glycoprotein that forms mucus when hydrated. This mucus serves to lubricate and protect the epithelial tissue. Goblet cells are typically located among columnar cells, which are tall and narrow, and they release their mucin via exocytosis.

What are the three modes of secretion in multicellular exocrine glands?

Multicellular exocrine glands can secrete their products through three different modes: merocrine, holocrine, and apocrine secretion. Merocrine secretion, the most common type, involves exocytosis, where secretory vesicles release their contents without harming the cell. Holocrine secretion involves the entire cell rupturing and dying to release its product, as seen in sebaceous glands. Apocrine secretion involves the apical portion of the cell shedding off to release its product, without the cell dying, as seen in mammary glands.

How do merocrine, holocrine, and apocrine secretions differ?

Merocrine secretion involves the release of products via exocytosis, where secretory vesicles fuse with the cell membrane to expel their contents. Holocrine secretion involves the entire cell rupturing and dying to release its product, necessitating the replacement of the dead cells. Apocrine secretion involves the apical portion of the cell shedding off to release its product, but the cell itself does not die. These modes of secretion are exemplified by salivary glands (merocrine), sebaceous glands (holocrine), and mammary glands (apocrine).

What is the function of mucin secreted by goblet cells?

Mucin is a glycoprotein secreted by goblet cells, which are unicellular exocrine glands found in the respiratory and intestinal tracts. When mucin is hydrated, it forms mucus. The primary functions of mucus are to lubricate and protect the epithelial tissue. In the respiratory tract, mucus traps dust, microbes, and other particles, preventing them from reaching the lungs. In the intestinal tract, mucus facilitates the smooth passage of food and protects the lining from digestive enzymes and acidic conditions.