Human Digestive System

The rumen is the first and largest chamber of a cow's stomach where microbial fermentation of cellulose begins. Partially digested food is regurgitated as cud for further chewing. The oesophagus transports food, liver produces bile, and small intestine absorbs nutrients.

Fats are broken down during digestion into glycerol and fatty acids. Glycerol is the backbone of fat molecules. Proteins digest into amino acids, and carbohydrates like starch break down into simple sugars like glucose or fructose.

Bile is produced by the liver, not the pancreas. All other pairings are correct: pepsin is the main enzyme in gastric juice, hydrochloric acid is secreted by stomach lining, and ptyalin (salivary amylase) is found in saliva.

 Secretin and cholecystokinin are digestive hormones. They are secreted in duodenum when acidic food enters there. Secretin stimulates release of bicarbonate rich fluid from the pancreas to counteract the acid. CCK stimulates pancreatic enzyme section like amylase and lipase, which aid in breaking down food. It also causes contraction of the gallbladder, which releases bile into the duodenum.

  Epithelial cells of the intestine involved in food absorption have on microvilli on their surface. Microvilli effectively increase the surface area of the cell and are useful for absorption and secretion functions.

Milk sugar or lactose, is difficult for many adults to digest due to an inability of their bodies to produce enough of a particular chemical to break it down. Also, there are other possible causes of these symptoms, including allergies.

Starch is a polysaccharide that requires breakdown into simpler sugars before absorption. It must first be digested by salivary and pancreatic amylase into maltose, then further broken down by maltase into glucose. Lactose (a disaccharide) only requires lactase, while glucose and fructose are monosaccharides that can be absorbed directly without digestion.

The rectum is the final section of the large intestine (about 12-15 cm long) that serves as a temporary storage chamber for fecal matter before elimination. While the large intestine as a whole absorbs water and electrolytes, the rectum specifically functions as a reservoir. The anus is the opening, and the appendix is a vestigial structure with no storage function.

The small intestine consists of three sections: duodenum (shortest, ~25 cm), jejunum (~2.5 meters), and ileum (longest, ~3-4 meters). The ileum makes up approximately 60% of the small intestine's total length and connects to the large intestine at the ileocecal valve. The colon is part of the large intestine, not the small intestine.

Food follows a specific anatomical pathway through the digestive system. It begins in the mouth where mechanical and chemical digestion starts, then travels down the esophagus via peristalsis, enters the stomach for further breakdown, and finally passes to the small intestine for most nutrient absorption and the large intestine for water absorption. This sequence reflects the actual path food takes through the alimentary canal.

The inactive prorennin is converted to active rennin by HCl.

   A man cannot digest cellulose whereas cows can do so because their gut contains certain bacteria capable of digesting cellulose.

Glucose is a monosaccharide that requires no digestion - it can be absorbed directly through the intestinal wall into the bloodstream via specific transporters. Sucrose is a disaccharide that must first be broken down by the enzyme sucrase into glucose and fructose before absorption. Starch is a polysaccharide requiring extensive enzymatic breakdown by amylase into maltose and eventually glucose. Cellulose cannot be digested by humans at all due to lack of cellulase enzyme. Therefore glucose is the most easily and rapidly absorbed.

This is the correct option. The function of oxyntic cell is to secrete hydrochloric acid and activate pepsinogen into the functional pepsin. The function of zymogen cell is to secrete a proenzyme of protein digestive enzyme. The function of mucous cell is to secrete mucus for lubricating the food.