Pepsin is the active enzyme in the stomach that breaks down dietary proteins into smaller peptides in the acidic environment created by hydrochloric acid.

Bile salts emulsify large fat globules into smaller droplets, increasing the surface area for lipase enzymes to act upon during fat digestion in the small intestine.

Villi are finger-like projections in the small intestine that significantly increase the surface area for the efficient absorption of nutrients into the bloodstream.

Intestinal flora (microbiota) in the large intestine synthesize Vitamin K and some B vitamins, which are then absorbed by the host.

Salivary amylase, found in saliva, initiates the breakdown of complex carbohydrates like starch into simpler sugars (maltose) within the mouth.

The pyloric sphincter is a muscular valve that controls the flow of chyme (partially digested food) from the stomach into the duodenum of the small intestine.

Cholecystokinin (CCK) is released by the duodenum in response to fats and proteins, stimulating the pancreas to release digestive enzymes and the gallbladder to contract.

The duodenum and jejunum are the primary sites for chemical digestion and nutrient absorption, facilitated by various enzymes and a large surface area.

Peristalsis is the involuntary, wave-like series of muscle contractions that propels food through the esophagus and the rest of the gastrointestinal tract.

The pancreas secretes pancreatic juice containing amylase, trypsin, and lipase, which target carbohydrates, proteins, and fats respectively.

The hepatic portal vein carries blood rich in nutrients absorbed from the small intestine directly to the liver for processing.

Hydrochloric acid provides the acidic environment necessary for converting inactive pepsinogen into the active protein-digesting enzyme pepsin.

Leucine is an essential amino acid because the human body cannot synthesize it and it must be obtained through dietary sources.

Secretin is released by the duodenum in response to low pH and acts to inhibit gastric acid secretion while stimulating pancreatic bicarbonate release.

Starch is a complex polysaccharide that is broken down into maltose and eventually into glucose, which is the primary sugar absorbed by the body.

The liver converts toxic ammonia produced from protein metabolism into urea via the urea cycle, which is then excreted by the kidneys.

Bile salts break large fat globules into smaller droplets (emulsification), significantly increasing the surface area for water-soluble lipases to digest the fats.

Fats provide approximately 9 kcal per gram, compared to about 4 kcal per gram for both carbohydrates and proteins.

Goblet cells are specialized epithelial cells that secrete mucus to protect the lining of the digestive tract and facilitate the movement of food.