Intestinal Immune System — MCQs
Which type of carbohydrate is absorbed most efficiently from the gastrointestinal tract?
IgE is secreted by which of the following cells?
The histological features of celiac disease include all of the following EXCEPT:
What are the characteristics of polymorphonuclear leukocytes (PMNs) in the oral cavity?
Which of the following is the predominant immunoglobulin isotype secreted in the human mucosa-associated lymphoid tissue (MALT)?
Slow wave potential originates in which of the following structures in the intestine:
What is the primary function of the myenteric plexus?
Which cells are referred to as "Pacemaker cells" with relation to "BER"?
Slow wave potentials originate in which cells of the intestine?
Small intestinal peristalsis is controlled by :
Intestinal Immune System Indian Medical PG Practice Questions and MCQs
Question 1: Which type of carbohydrate is absorbed most efficiently from the gastrointestinal tract?
- A. Disaccharides
- B. Polysaccharides
- C. Monosaccharides (Correct Answer)
- D. 5-carbon sugars
Explanation: ***Monosaccharides*** - **Monosaccharides**, like glucose and fructose, are the simplest forms of carbohydrates and do not require further digestion. - They are directly absorbed into the bloodstream from the intestinal lumen via specific **transporters** on the enterocyte membrane. *Disaccharides* - **Disaccharides**, such as sucrose and lactose, must first be broken down into their constituent monosaccharides by **brush border enzymes** (e.g., lactase, sucrase) before absorption can occur. - This additional enzymatic step makes their absorption less efficient than that of monosaccharides. *Polysaccharides* - **Polysaccharides**, including starch and glycogen, are complex carbohydrates requiring extensive digestion by enzymes like **amylase** in the mouth and small intestine. - This multi-step breakdown into monosaccharides is the least efficient process and takes the longest time. *5-carbon sugars* - While 5-carbon sugars (**pentoses**) like ribose and deoxyribose are monosaccharides and can be absorbed, they are not a primary energy source in the diet and are not absorbed as efficiently or in as large quantities as the metabolically more significant 6-carbon monosaccharides (hexoses like glucose). - The question asks which *type* of carbohydrate is most efficiently absorbed, and **monosaccharides** as a general category (including 6-carbon sugars) are the most efficient.
Question 2: IgE is secreted by which of the following cells?
- A. Mast cell
- B. Basophils
- C. Eosinophils
- D. Plasma cells (Correct Answer)
Explanation: ***Plasma cells*** - Plasma cells are **terminally differentiated B lymphocytes** that are specialized in producing and secreting large quantities of antibodies, including **IgE**. - While other cells like mast cells and basophils have receptors for IgE and play roles in IgE-mediated reactions, they do not synthesize **IgE** themselves. *Mast cell* - Mast cells are key players in allergic reactions and express **FcεRI receptors** that bind to IgE antibodies. - Upon binding the antigen, they degranulate, releasing **histamine** and other mediators, but they do not produce IgE. *Basophils* - Basophils also express **FcεRI receptors** for IgE and are involved in allergic responses, releasing inflammatory mediators. - Similar to mast cells, they do not synthesize IgE, but rather bind pre-formed **IgE** antibodies. *Eosinophils* - Eosinophils are involved in allergic reactions and defense against **parasitic infections**, and their granules contain toxic proteins. - They can be activated by IgE-mediated mechanisms but are not producers of **IgE** antibodies.
Question 3: The histological features of celiac disease include all of the following EXCEPT:
- A. Crypt hyperplasia
- B. Increase in intraepithelial lymphocytes
- C. Increase in inflammatory cells in lamina propria
- D. Increase in thickness of the mucosa (Correct Answer)
Explanation: ***Increase in thickness of the mucosa*** - Celiac disease typically causes **villous atrophy**, leading to a **thinner intestinal mucosa**, not an increase in thickness [1]. - The architectural changes in celiac disease primarily involve blunting or absence of villi [2]. *Crypt hyperplasia* - This is a characteristic feature of celiac disease, where the **crypts of Lieberkühn** become elongated and hyperplastic to compensate for the damaged villi [1]. - It reflects increased cell turnover in response to mucosal injury. *Increase in intraepithelial lymphocytes* - An increase in **intraepithelial lymphocytes (IELs)** is a hallmark histological finding in celiac disease, often seen even before significant villous atrophy [1]. - These lymphocytes are typically CD3+ T-cells that infiltrate the epithelial layer. *Increase in inflammatory cells in lamina propria* - The lamina propria in celiac disease shows an increased infiltration of **chronic inflammatory cells**, including plasma cells and lymphocytes [2]. - This reflects the ongoing immune response to gluten peptides in the intestinal wall. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Gastrointestinal Tract, pp. 789-790. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Alimentary System Disease, pp. 361-362.
Question 4: What are the characteristics of polymorphonuclear leukocytes (PMNs) in the oral cavity?
- A. PMNs function mainly as antigen-presenting cells in oral tissues.
- B. Granulocytes found in the gingival connective tissue.
- C. PMNs actively migrate to the gingival crevicular fluid as part of the immune response. (Correct Answer)
- D. None of the options.
Explanation: **PMNs actively migrate to the gingival crevicular fluid as part of the immune response.** - **Polymorphonuclear leukocytes (PMNs)**, primarily neutrophils, are highly motile phagocytes that play a crucial role in the innate immune response to oral microbes. - Their active migration into the **gingival crevicular fluid (GCF)** is a hallmark of the body's defense against bacterial plaque, forming a crucial first line of defense against periodontal pathogens. *Granulocytes found in the gingival connective tissue.* - While PMNs are granulocytes that reside in the **gingival connective tissue**, this statement alone does not fully encompass their dynamic role and key characteristics in the oral cavity. - Their most significant characteristic in the context of oral health is their **active migration** to the epithelial surface and into the GCF, not just their presence in the connective tissue. *PMNs function mainly as antigen-presenting cells in oral tissues.* - **PMNs** are primarily involved in **phagocytosis** and intracellular destruction of pathogens, not as primary antigen-presenting cells (APCs). - **Dendritic cells** and **macrophages** are the main APCs that bridge innate and adaptive immunity by presenting antigens. *None of the options.* - This option is incorrect because the statement regarding **PMNs** actively migrating to the **gingival crevicular fluid** accurately describes a major characteristic and function of these cells in oral immunity.
Question 5: Which of the following is the predominant immunoglobulin isotype secreted in the human mucosa-associated lymphoid tissue (MALT)?
- A. IgA (Correct Answer)
- B. IgD
- C. IgG
- D. IgE
Explanation: ***IgA*** - **Secretory IgA (sIgA)** is the most abundant immunoglobulin in mucosal secretions, including those found in the MALT, playing a critical role in **mucosal immunity**. - It forms a **dimeric structure** which makes it highly resistant to proteolysis and effective at preventing microbial adherence to epithelial surfaces. *IgD* - **IgD** is primarily found on the surface of naïve B lymphocytes, acting as an **antigen receptor**. - Its secreted form is found in very low concentrations in serum and is not a major component of mucosal immunity. *IgG* - **IgG** is the most abundant immunoglobulin in serum and is crucial for **systemic immunity**, including opsonization and complement activation. - While present in some mucosal tissues, especially during inflammation, it is not the predominant isotype secreted in healthy MALT. *IgE* - **IgE** is primarily associated with **allergic reactions** and defense against parasites, binding to mast cells and basophils. - It is present in very low concentrations in secretions and does not play a dominant role in general mucosal defense.
Question 6: Slow wave potential originates in which of the following structures in the intestine:
- A. Interstitial cells of Cajal (Correct Answer)
- B. Smooth muscle cells
- C. Myenteric plexus
- D. Parasympathetic neurons
Explanation: ***Interstitial cells of Cajal*** - The **interstitial cells of Cajal (ICCs)** are specialized **pacemaker cells** located throughout the gastrointestinal tract. - They generate spontaneous rhythmic depolarizations and repolarizations of the cell membrane, known as **slow waves**, which set the pace for smooth muscle contractions. *Smooth muscle cells* - While smooth muscle cells are the target of slow waves and contract in response to them, they do not **spontaneously generate** the slow waves themselves. - Their contractions are primarily regulated by the **electrical activity** transmitted from the ICCs. *Myenteric plexus* - The **myenteric plexus (Auerbach's plexus)** is a network of neurons that primarily controls **gastrointestinal motility**. - It modulates the frequency and amplitude of contractions but does not originate the fundamental rhythm of slow waves. *Parasympathetic neurons* - **Parasympathetic neurons** regulate various gastrointestinal functions, including motility and secretion, by releasing **neurotransmitters** like acetylcholine. - They can modulate the activity of ICCs and smooth muscle cells but are not the source of the electrical slow wave potentials themselves.
Question 7: What is the primary function of the myenteric plexus?
- A. Regulating GI secretion
- B. Regulating local blood flow
- C. Regulating motility (Correct Answer)
- D. Regulating absorption
Explanation: ***Regulating motility*** - The myenteric plexus, also known as **Auerbach's plexus**, is primarily responsible for coordinating the **rhythmic contractions** and **relaxation of the gastrointestinal (GI) smooth muscle**. - Its strategic location between the **longitudinal and circular muscle layers** allows it to directly influence the strength and frequency of peristalsis, thus regulating the movement of food through the digestive tract. *Regulating GI secretion* - While it has some indirect influence, the **submucosal plexus** (Meissner's plexus) is the primary neural network regulating **secretory functions** of the GI tract. - The myenteric plexus's main role is more directly related to muscle contraction and relaxation rather than glandular secretion. *Regulating local blood flow* - Local blood flow in the GI tract is primarily regulated by the **sympathetic and parasympathetic nervous systems**, along with local metabolic factors and hormones. - The myenteric plexus has a minimal direct role in the control of **GI blood vessel smooth muscle**. *Regulating absorption* - Absorption is primarily a function of the **intestinal epithelial cells** and is regulated by various transport mechanisms, hormones, and local factors. - While the enteric nervous system influences mucosal function indirectly, the myenteric plexus's primary role is **motor control** rather than directly regulating nutrient absorption processes.
Question 8: Which cells are referred to as "Pacemaker cells" with relation to "BER"?
- A. SA node
- B. AV node
- C. Interstitial cells of Cajal (Correct Answer)
- D. Pyramidal cells
Explanation: ***Interstitial cells of Cajal*** - The **Interstitial cells of Cajal (ICC)** are specialized cells in the gastrointestinal tract that act as the **pacemaker cells** for the **Basic Electrical Rhythm (BER)**. - They generate slow waves of **depolarization** and **repolarization**, which determine the frequency and rhythm of smooth muscle contractions. *SA node* - The **sinoatrial (SA) node** is the natural pacemaker of the **heart**, initiating the cardiac electrical impulse. - It controls the heart rate, not the **BER** of the gastrointestinal tract. *AV node* - The **atrioventricular (AV) node** is part of the heart's electrical conduction system, responsible for delaying and transmitting impulses from the atria to the ventricles. - It does not regulate the **BER** of the gastrointestinal system. *Pyramidal cells* - **Pyramidal cells** are a type of neuron found in various parts of the brain, particularly the cerebral cortex and hippocampus. - They are involved in cognitive functions and motor control, and have no role in generating the **BER** in the gut.
Question 9: Slow wave potentials originate in which cells of the intestine?
- A. Myenteric plexus
- B. Parasympathetic neurons
- C. Smooth muscle cells
- D. Interstitial cells of Cajal (Correct Answer)
Explanation: ***Interstitial cells of Cajal*** - The **interstitial cells of Cajal (ICC)** are specialized mesenchymal cells that act as **pacemaker cells** for the gastrointestinal tract. - They generate **slow wave potentials** (basic electrical rhythm), which are oscillating depolarizations and repolarizations of the smooth muscle cell membrane potential. *Myenteric plexus* - The **myenteric plexus (Auerbach's plexus)** primarily controls **gastrointestinal motility** through neural pathways. - It modulates the frequency and strength of contractions but does not directly generate the slow wave potentials. *Parasympathetic neurons* - **Parasympathetic neurons** release neurotransmitters (e.g., acetylcholine) that **modulate the activity** of smooth muscle and ICC, enhancing or inhibiting slow wave activity. - They do not, however, originate the slow wave potential itself. *Smooth muscle cells* - **Smooth muscle cells** are the effector cells that contract in response to the slow waves and action potentials. - While they undergo the depolarization and repolarization of slow waves, the **initiating pacemaker activity** comes from the ICC.
Question 10: Small intestinal peristalsis is controlled by :
- A. Meissner's plexus
- B. Vagus nerve
- C. Parasympathetic system
- D. Myenteric plexus (Correct Answer)
Explanation: ***Myenteric plexus*** - The **myenteric (Auerbach's) plexus** is located between the longitudinal and circular muscle layers of the muscularis propria and is primarily responsible for **controlling gastrointestinal motility**, including peristalsis. - Its neurons coordinate the contractions and relaxations of these muscle layers to propel contents through the alimentary canal. *Meissners plexus* - The **Meissner's (submucosal) plexus** is located in the submucosa and mainly controls **glandular secretion**, local blood flow, and absorption, rather than muscle motility. - While it subtly influences motility through local reflexes, it is not the primary controller of peristalsis. *Vagus nerve* - The **vagus nerve (cranial nerve X)** provides parasympathetic innervation to the small intestine, modulating activity but not directly initiating or solely controlling peristalsis. - It influences the activity of the enteric nervous system (including the myenteric plexus) but does not itself generate the complex, coordinated patterns of muscle contraction. *Parasympathetic system* - The **parasympathetic nervous system**, through nerves like the vagus, generally **stimulates gastrointestinal motility**, but it acts by modulating the intrinsic enteric nervous system. - The local control and generation of specific peristaltic movements are primarily mediated by the enteric nervous system, especially the myenteric plexus.
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