Human Digestive System and Digestion Processes

The primary role of the digestive system is to break down food into smaller pieces and absorb the nutrients from the food consumed.
The system consists of various organs including the Mouth, Salivary glands, Esophagus, Stomach, Pancreas, Liver, Gall Bladder, Small intestine, Large intestine, Appendix, Rectum, and Anus.
The entire pathway from the Mouth to the Anus is referred to as the Gastrointestinal tract or the GI tract.

Salivary Glands: Responsible for moistening food into a bolus and initiating the digestion of polysaccharides.
Liver: Functions include the detoxification of certain molecules, the storage of vitamins, iron, and glycogen, and the synthesis of bile.
Oesophagus: Acts as the transport mechanism to move food from the mouth to the stomach.
Stomach: Functions as a storage site and churns food; it marks the beginning of protein digestion.
Gall Bladder: Responsible for the storage and concentration of bile.
Pancreas: Releases digestive enzymes and produces hormones, such as insulin.
Small Intestine: The primary site for the absorption of nutrients.
Large Intestine: Responsible for the absorption of water and ions.
Rectum / Anus: Responsible for the storage and subsequent expulsion of faeces.

Ingestion: The process of taking food into the body.
Digestion: The physical and chemical breakdown of food. - Mechanical Digestion: The process of breaking food into smaller pieces of food. - Chemical Digestion: Also known as enzymatic hydrolysis, this process breaks food particles down into small molecules.
Absorption: The movement of nutrient molecules into cells.
Assimilation: The process of making the absorbed food a part of the cell.
Elimination: The removal of unused and undigested material from the body.

Mechanical digestion involves physical processes that break down food without changing its chemical nature.
Chewing: Occurs in the mouth.
Churning: Occurs in the stomach where food is mixed and ground.
Peristalsis: The movement of food through the esophagus, stomach, and intestines caused by muscle contractions.
Segmentation: - Involves the physical digestion of food particles by mixing food with digestive juices. - Driven by the contraction and relaxation of smooth muscles within the intestines.

Chemical digestion utilizes chemicals and enzymes to break down complex molecules into simpler ones.
Stomach Acid: Provides a chemical environment for digestion in the stomach.
Bile: Produced by the liver and stored in the gallbladder for the emulsification of lipids.
Enzymatic Breakdown by Organ: - Salivary Glands: Produce Salivary amylase, which converts $\text{starch} \rightarrow \text{maltose}$ . - Stomach: Contains stomach acids and Proteases, which break down $\text{protein} \rightarrow \text{polypeptides}$ . - Liver / Gall Bladder: Utilize Bile salts for the emulsification of lipids. - Pancreas: Secretes a variety of substances including: - Amylase: $\text{starch} \rightarrow \text{maltose}$ - Lipase: $\text{triglycerides} \rightarrow \text{fatty acids}$ - Endopeptidase: $\text{peptides} \rightarrow \text{amino acids}$ - Nuclease: $\text{DNA/RNA} \rightarrow \text{nucleosides}$ - Bicarbonate ions: Used to neutralise stomach acid. - Small Intestine: Contains membrane-bound enzymes, such as maltase.

Mouth: Movement type is Chewing.
Esophagus: Movement type is Peristalsis.
Stomach: The upper muscle in the stomach relaxes to allow food to enter, while the lower muscle mixes the food with digestive juice through churning.
Small Intestine: Movement type is Peristalsis.
Large Intestine: Movement type is Peristalsis.
Pancreas: No movement.
Liver: No movement.