Nutrition in Animals -2

Chief cells (also called peptic cells or zymogenic cells) in the gastric glands of the stomach secrete pepsinogen, which converts to active pepsin for protein digestion. Alpha and beta cells are found in pancreatic islets of Langerhans and secrete glucagon and insulin respectively. Option A correctly identifies chief cells. Islets of Langerhans (C) is the pancreatic region containing alpha and beta cells, not a gastric cell type.

Pepsin is a protease (protein-digesting enzyme) that functions optimally in acidic conditions (pH 1.5-2). The stomach's hydrochloric acid provides this acidic environment and also converts pepsinogen to active pepsin. In alkaline, neutral, or isotonic conditions, pepsin becomes denatured or inactive. Option A correctly states pepsin is active in acid. Pepsin would be inactive in alkaline (B), neutral (C), or isotonic (D) environments.

Gastric juice contains pepsin (protease), gastric lipase (fat-digesting), and rennin/chymosin (milk-clotting, particularly in infants). Trypsin is a pancreatic enzyme, not a gastric enzyme - it's secreted by the pancreas into the small intestine. Option A correctly lists gastric juice components. Options B, C, and D incorrectly include trypsin, which is pancreatic, not gastric.

The stomach maintains an acidic pH primarily through hydrochloric acid (HCl) secretion from parietal cells in the gastric glands. This acidic environment (pH 1.5-2) is essential for activating digestive enzymes and killing ingested pathogens. Mucus secretion (option A) protects the stomach lining, while bile (B) and pancreatic juice (C) are secreted into the small intestine, not the stomach.

Correct Answer: stomach

HCl's chief function is maintaining stomach acidity, which converts inactive pepsinogen into active pepsin. Pepsin is the primary enzyme that begins protein digestion in the stomach. While HCl also inhibits microbial growth (option B) and aids mineral absorption, activating pepsinogen is its main digestive role.

Gastric epithelial cells are protected by a thick layer of mucus secreted by goblet cells and surface epithelial cells. This mucus forms a physical barrier and contains bicarbonate that neutralizes acid at the cell surface. The HCl is NOT too dilute (it's very potent), epithelial cells are NOT inherently acid-resistant, and HCl is NOT neutralized by alkaline gastric juice (the stomach is acidic).

The parasympathetic nervous system (rest and digest) stimulates digestive activities via the vagus nerve. It increases GI secretions and enhances peristalsis after food ingestion. The sympathetic nervous system (fight or flight) would inhibit digestion, while the central nervous system and thyroid membrane are not directly responsible for digestive regulation.

Casein is the primary protein in milk, constituting approximately 80% of milk's total protein content. It's a complete protein containing all essential amino acids and forms curds during digestion. Meat and eggs contain different proteins (myosin, albumin), while rice is primarily a carbohydrate source with minimal protein.

Pepsin functions in the stomach's acidic environment (pH 1.5-2), where it begins protein digestion. Trypsin operates in the alkaline duodenum (pH 7.5-8) and requires different conditions. Option A incorrectly states pepsin works in alkaline medium, while options B and D place these enzymes in the wrong locations.

Bilirubin and biliverdin are breakdown products of hemoglobin from red blood cells. These pigments are excreted by the liver into bile, giving bile its characteristic greenish-yellow color. They are not found in blood, pancreatic juice, saliva, or lymph in significant quantities.

The liver produces bile, which contains bile salts, cholesterol, and bilirubin, but NO digestive enzymes. Bile mechanically emulsifies fats to increase surface area for lipase action. The actual digestive enzymes that break down carbohydrates, proteins, and fats come from the pancreas and small intestine.

Correct Answer: has to detoxify the alcohol

Rats lack a gall bladder, so bile flows directly from the liver to the duodenum via the common bile duct. This adaptation is related to their nearly continuous feeding pattern. Frogs, wall lizards, and rabbits all possess gall bladders for bile storage and concentration.

Fat molecules contain more carbon-hydrogen bonds per gram than carbohydrates, and each C-H bond stores significant chemical energy. This is why fats yield approximately 9 kcal/g while sugars yield only 4 kcal/g. The difference is not due to water content, animal vs plant source, or digestive waste.

Deamination in the liver removes amino groups (-NH2) from amino acids, producing toxic ammonia. The liver then converts ammonia to urea via the urea cycle for safe excretion. This process prevents ammonia accumulation while allowing nitrogen waste removal. It's not about synthesizing amino acids or making direct use of excess amino acids.

The inner surface of the large intestine, like the entire digestive tract, is lined by epithelial tissue. This is specifically simple columnar epithelium with numerous goblet cells that secrete mucus to protect the intestinal wall and lubricate passage of contents. The muscular tissue lies beneath this epithelial layer in the submucosa and muscularis externa.

Villi are finger-like projections that increase surface area for absorption. In the small intestine, intestinal villi absorb nutrients from digested food. In the placenta, chorionic villi facilitate exchange of nutrients and wastes between maternal and fetal blood. Villi are not found in lungs (which have alveoli), plasma membrane (a cellular structure), or stomach (which has rugae instead).

The liver is divided into right and left lobes by the falciform ligament. The right lobe is further subdivided into anatomical regions: the right lobe proper (the main portion), quadrate lobe (on the inferior surface), and caudate lobe (posterior portion). This question tests detailed hepatic anatomy knowledge.

Succus entericus refers to the intestinal juice secreted by the glands of the small intestine. This clear to pale yellow fluid contains digestive enzymes (maltase, sucrase, lactase, peptidases, lipase), mucus, and electrolytes that continue the chemical digestion of food in the small intestine.

Glycogen is the storage form of glucose in animals. After glucose is converted to glycogen in the liver, it is stored in both the liver (about 100-120g) and skeletal muscles (about 300-400g in an adult). Liver glycogen maintains blood glucose levels, while muscle glycogen provides energy for muscle contraction during exercise. Spleen does not store glycogen.

Pancreatic juice secretion is regulated by two key hormones. Secretin, produced by S-cells in the duodenum when acidic chyme enters, stimulates bicarbonate secretion to neutralize acid. Cholecystokinin-pancreozymin (CCK-PZ), produced by I-cells when fats/proteins are present, stimulates digestive enzyme secretion. Gastrin primarily stimulates HCl secretion, while enterogastrone inhibits gastric motility.

Bile is produced in the liver but stored and concentrated in the gallbladder. When fatty food enters the duodenum, bile is released into the duodenum (first part of small intestine) where it emulsifies fats - breaking large fat globules into smaller droplets to increase surface area for lipase action. Emulsification does not occur in liver, stomach, or pancreas.

Islets of Langerhans are clusters of endocrine cells within the pancreas. Beta cells produce insulin (lowers blood glucose), alpha cells produce glucagon (raises blood glucose), and delta cells produce somatostatin. HCl is produced by stomach parietal cells, ptyalin (salivary amylase) by salivary glands, renin by stomach chief cells, and bile by liver hepatocytes.