Human Digestive System

Ruminants chew their cud through retro-peristalsis, which is the reverse movement of stomach contents from the rumen back to the mouth for additional mastication. This process, called rumination, allows more thorough breakdown of fibrous plant material. Regular peristalsis moves food forward through the digestive tract, not backward.

Present in the inner lining of the intestine

After descending through the esophagus, food enters the stomach. The duodenum is the first part of the small intestine (stomach comes before it). The liver and pancreas are accessory organs that secrete into the duodenum but food doesn't enter them directly.

Pepsin is produced in the stomach as pepsinogen (inactive precursor) and activated by stomach acid to digest proteins. Trypsin comes from the pancreas, amylase from salivary glands and pancreas (not liver), and maltase is an intestinal brush-border enzyme.

The efficacy of an antacid depends upon its duration of stay in the stomach and so the neutralization process causes the prevention of activation of pepsin and secretion of excess HCl.

Herbivorous animals have symbiotic bacteria and protozoa in their digestive tract (especially in the rumen or cecum) that produce cellulase enzymes to break down cellulose. Humans lack these microbial symbionts in their digestive system, making cellulose indigestible. Cellulose digestion is not mechanical but enzymatic.

Frogs possess digestive enzymes like maltase, lactase, and pepsin. However, rennin (chymosin) - the enzyme that curdles milk in mammalian infants - is absent since frogs don't nurse their young with milk.

Gastrin, secreted by G cells in the stomach lining, stimulates parietal cells to release HCl and chief cells to release pepsinogen. Pancreozymin and cholecystokinin stimulate pancreatic enzymes, while secretin stimulates bicarbonate secretion - these don't directly control gastric juice.

The primary function of the large intestine is water absorption from indigestible food matter and transport of waste. While it does store waste materials (option A), this is secondary to its critical role in extracting water to prevent dehydration. Digestion completes in the small intestine.

G cells in the gastric mucosa are correctly matched with gastrin secretion. The other pairings are incorrect: B cells secrete insulin (in pancreas, not somatostatin), D cells secrete somatostatin (not insulin), and somatostatin is actually produced by delta cells in the pancreas and D cells in the stomach.

A retrocaecal appendix lies in close proximity to the psoas muscle. When inflamed, it irritates the psoas muscle, causing pain on extension of the hip. This is because extension stretches the inflamed psoas against the irritated appendix. This clinical sign is known as a positive psoas sign and helps localize the appendix when it is in a retrocaecal position.

Assimilation is the metabolic process where absorbed nutrients are converted into complex protoplasmic molecules for growth and repair. Digestion breaks down food, absorption moves nutrients into blood, and assimilation builds body tissues.

Ptyalin (salivary amylase) is the digestive enzyme secreted by salivary glands present in the buccal cavity. Trypsin and pepsin are proteases found in the stomach and small intestine, while lipase is primarily pancreatic.

Secretin is the hormone released from the small intestine that stimulates the pancreas to secrete bicarbonate-rich fluid to neutralize acidic chyme from the stomach. Insulin and glucagon regulate blood sugar, while oxytocin is involved in reproduction.

The farmer was infected by Schistosoma mansoni because sub-terminal eggs are only produced by Schistosoma mansoni.