Human Digestive System

Saliva contains lingual lipase for fat digestion, lysozyme for antibacterial defense, and IgA antibodies for immune protection.

The alimentary canal (primary organs) includes the mouth, pharynx, esophagus, stomach, small intestine, and large intestine (including the colon). The pancreas, gallbladder, and salivary glands are accessory organs.

The myenteric plexus (Auerbach's plexus) is located between the circular and longitudinal muscle layers and primarily controls gastrointestinal motility, including peristalsis and segmentation.

The mucosa is the innermost layer of the gastrointestinal tract that lines the lumen. It consists of an epithelial lining, a lamina propria, and a thin layer of smooth muscle.

Absorption is the process where digested nutrients move from the lumen of the GI tract into the blood or lymph. This is the point at which nutrients officially enter the body's internal environment.

Stomach acid (gastric juice) contains hydrochloric acid and has a very low pH, typically between 1.5 and 3.5, making it significantly more acidic than blood or urine.

Vomiting results in the loss of gastric hydrochloric acid. This loss of acid leads to an increase in blood pH, resulting in metabolic alkalosis.

• The alimentary canal includes the mouth, pharynx, oesophagus, stomach, small intestine, large intestine, and anus.
• The longest part of the alimentary canal is small intestine because it is the main organ of absorption and digestion of food. 
  
• The surface area of the small intestine gets increased because of the presence of villi which gives food plenty of time to break down properly. Hence, the longest part of the alimentary canal is a small intestine.  

• Bile  is a dark green to yellowish brown fluid, produced by the liver of most vertebrates, that helps in the digestion of lipids in the small intestine.
•  In humans, bile is produced continuously by the liver, and stored and concentrated in the gallbladder. Hence, Bile is secreted by the liver.

• The stomach is made of  4 layers. They are serosa, muscularis, submucosa, mucosa. These layers of smooth muscle consist of the outer longitudinal, the middle circular, and the inner oblique muscles.
• The innermost layer or lining (mucosa) contains the glands that release digestive juices which includes pepsin, chymotrypsin, hydrochloric acid etc. Hence, The inner layer of the stomach releases digestive juices.

Brunner's glands are specialized glands located in the submucosa of the duodenum, which is the first part of the small intestine.

The stomach performs multiple functions: mechanical digestion through churning, partial chemical digestion of proteins, and disinfecting food using hydrochloric acid.