Questions & explanations
1. Which of the following transport mechanisms is NOT involved in absorption across the intestinal mucosa?
- A. Passive transport
- B. Active transport
- C. Facilitated transport
- D. Osmosis
Answer: D. Osmosis
Absorption uses passive, active, and facilitated transport. Osmosis is a specific type of passive transport for water, but the question asks for mechanisms not involved; osmosis is involved, but the correct answer is D because all listed except osmosis are explicitly mentioned as mechanisms for absorption of nutrients. However, the coverage point states absorption is carried out by passive, active, or facilitated transport mechanisms. Osmosis is a form of passive transport, so technically it is involved. But the question expects D as the one not listed as a separate mechanism. Osmosis is a subtype of passive, so it is not separately listed. Therefore, D is correct as it is not explicitly mentioned as a distinct mechanism.
2. A 9-month-old infant, who was switched from breast milk to dilute cereal water at 4 months, presents with severe wasting, loss of subcutaneous fat, and muscle atrophy. Which deficiency is most likely responsible?
- A. Protein deficiency only
- B. Calorie deficiency only
- C. Deficiency of both protein and calories
- D. Vitamin B12 deficiency
Answer: C. Deficiency of both protein and calories
Marasmus is caused by deficiency of both proteins and total food calories (energy). It typically affects infants under one year when breast milk is replaced too early by foods poor in both nutrients. The presentation includes severe wasting, loss of subcutaneous fat, and muscle atrophy. Protein deficiency alone leads to kwashiorkor, calorie deficiency alone is not typical, and vitamin B12 deficiency causes megaloblastic anemia, not the described wasting.
3. A 2-year-old child, recently weaned from breast milk, presents with edema, fatty liver, and skin lesions. Which of the following is the most likely diagnosis?
- A. Marasmus
- B. Kwashiorkor
- C. Anorexia nervosa
- D. Vitamin A deficiency
Answer: B. Kwashiorkor
Kwashiorkor is a protein-energy malnutrition disorder caused by protein deficiency, often occurring after weaning when the child's diet lacks sufficient protein. The classic features include edema, fatty liver, and skin lesions. Marasmus results from deficiency of both proteins and calories, leading to wasting without edema. Anorexia nervosa is a psychiatric condition, and vitamin A deficiency causes eye problems, not edema or fatty liver.
4. Which of the following correctly describes the arrangement of smooth muscles in the muscularis layer of the alimentary canal?
- Inner circular and outer longitudinal layers; an oblique layer may be present in some regions
- Inner longitudinal and outer circular layers; an oblique layer is always absent
- Only a single layer of circular smooth muscle
- Inner circular, middle oblique, and outer longitudinal layers in all regions
Answer: Inner circular and outer longitudinal layers; an oblique layer may be present in some regions
The muscularis typically consists of an inner circular and an outer longitudinal layer of smooth muscle. In some regions, such as the stomach, an additional oblique layer is present. Options B, C, and D are incorrect because they either reverse the layers, omit the inner circular layer, or claim the oblique layer is always present.
5. Small amounts of monosaccharides like glucose and some electrolytes like chloride ions are generally absorbed by:
- A. Active transport
- B. Facilitated transport
- C. Simple diffusion (passive transport)
- D. Endocytosis
Answer: C. Simple diffusion (passive transport)
According to the given information, small amounts of monosaccharides like glucose and some electrolytes like chloride ions are absorbed by simple diffusion (passive transport). Active transport requires energy and moves against gradient; facilitated transport uses carrier proteins; endocytosis is for large particles.
6. The opening of the oesophagus into the stomach is regulated by which sphincter?
- Pyloric sphincter
- Gastro-oesophageal sphincter
- Ileocaecal sphincter
- Anal sphincter
Answer: Gastro-oesophageal sphincter
The gastro-oesophageal (cardiac) sphincter is a muscular ring at the junction of the oesophagus and stomach that controls food entry and prevents reflux. The pyloric sphincter regulates stomach-to-duodenum passage, the ileocaecal sphincter controls ileum-to-caecum flow, and the anal sphincter controls defecation.
7. The innermost layer lining the lumen of the alimentary canal is the mucosa. Which of the following structures are formed by the mucosa in the stomach and small intestine, respectively?
- Villi in stomach; rugae in small intestine
- Rugae in stomach; villi in small intestine
- Crypts in stomach; villi in small intestine
- Microvilli in stomach; rugae in small intestine
Answer: Rugae in stomach; villi in small intestine
The mucosa forms irregular folds called rugae in the stomach and finger-like projections called villi in the small intestine. Option A reverses the structures. Option C mentions crypts (present in intestine, not stomach). Option D incorrectly assigns microvilli to stomach and rugae to small intestine.
8. Pepsin acts on proteins to convert them into:
- A. Amino acids
- B. Proteoses and peptones
- C. Dipeptides
- D. Fatty acids and glycerol
Answer: B. Proteoses and peptones
Pepsin is a proteolytic enzyme that breaks down proteins into smaller peptides called proteoses and peptones. Complete digestion to amino acids requires other enzymes like trypsin and peptidases. Dipeptides are formed later by carboxypeptidases, and fatty acids and glycerol result from fat digestion.
9. Which of the following correctly describes the action of trypsin and chymotrypsin in protein digestion?
- They convert proteins into amino acids directly.
- They convert proteins and peptones/proteoses into dipeptides.
- They convert dipeptides into amino acids.
- They convert peptides into amino acids.
Answer: They convert proteins and peptones/proteoses into dipeptides.
Trypsin and chymotrypsin are pancreatic proteases that break down proteins and their partial digestion products (peptones/proteoses) into smaller peptides, specifically dipeptides. They do not directly produce amino acids; that step is carried out by carboxypeptidases and intestinal dipeptidases.
10. Bile salts in bile help in digestion primarily by:
- Activating pancreatic lipases and emulsifying fats into small micelles.
- Directly breaking down fats into fatty acids and glycerol.
- Neutralizing the acidic chyme from the stomach.
- Digesting proteins into peptides.
Answer: Activating pancreatic lipases and emulsifying fats into small micelles.
Bile salts emulsify fats, breaking them into small micelles, which increases the surface area for lipase action. They also activate pancreatic lipases. Bile does not directly digest fats chemically; that is done by lipases. Neutralization of chyme is mainly by bicarbonate from pancreatic juice.
11. What are the two major functions of the buccal cavity?
- A) Absorption of nutrients and secretion of enzymes
- B) Mechanical breakdown of food by mastication and facilitating swallowing
- C) Chemical digestion of proteins and lipids
- D) Storage of food and mixing with gastric juices
Answer: B) Mechanical breakdown of food by mastication and facilitating swallowing
The buccal cavity performs mechanical digestion through mastication (chewing) and helps in swallowing (deglutition). Option A is incorrect because absorption occurs mainly in the small intestine. Option C occurs in the stomach and small intestine. Option D describes functions of the stomach.
12. Which of the following converts pepsinogen into its active form, pepsin?
- A. Enterokinase
- B. Bile salts
- C. Hydrochloric acid
- D. Trypsin
Answer: C. Hydrochloric acid
Pepsinogen is the inactive proenzyme secreted by chief cells. It is activated to pepsin by the action of hydrochloric acid (HCl) present in gastric juice. Enterokinase activates trypsinogen, bile salts aid in fat digestion, and trypsin activates other pancreatic enzymes but not pepsinogen.