Human Digestive System: Glands and Processes

Annex Glands

The digestive system includes several annex glands that aid in the breakdown of food:

• Salivary Glands

  These glands empty into the oral cavity and are grouped into three pairs:

  • Parotid Glands: Located in front of the ear.
  • Sublingual Glands: Situated under the tongue.
  • Submaxillary Glands: Found under the lower jaw.

  Their primary function is to lubricate food, facilitating easy passage through the digestive tract.

• Liver

  The liver is the largest gland in the body and performs numerous functions. One key role is secreting bile into the duodenum. Bile, stored in the gallbladder, is essential for dissolving fats.

• Pancreas

  The pancreas has dual functions:

  • It produces insulin, which regulates blood glucose levels.
  • It produces pancreatic juice, which, along with bile, enters the duodenum to aid in digestion.

The Digestive System Works

Digestion is the process of transforming food into simpler, soluble substances.

Phases of Digestion

• Chewing (Mastication)

  This is a mechanical process performed by the teeth. It divides food and mixes it with saliva, forming a bolus. Digestion begins in the mouth with saliva containing the enzyme Ptyalin, which breaks down starch (polysaccharides) into maltose (a disaccharide).

• Swallowing (Deglutition)

  Swallowing is an involuntary action that moves the food bolus to the pharynx. During swallowing, the soft palate rises to block the nasal cavity, and the epiglottis covers the trachea's entrance, directing the bolus into the esophagus.

• Gastric Digestion

  The bolus travels down the esophagus via peristalsis. Upon reaching the stomach, it can remain for up to five hours. Here, it mixes with gastric juices, which consist of three main components:

  • Mucin: Provides lubrication and protects the stomach lining from self-digestion.
  • Hydrochloric Acid: Possesses bactericidal properties and aids in the degradation of food by gastric enzymes.

  Intense agitation within the stomach, driven by peristaltic contractions, further aids digestion. The mixture of food and gastric juices forms a semi-liquid substance called chyme. Chyme then passes through the pyloric sphincter into the duodenum.

  In the duodenum, chyme mixes with substances like:

  • Bile Salts: Neutralize the acidic chyme.
  • Cholesterol: Contributes to stool formation.
  • Bile Pigments: Give color to the stool.

  The mixture of chyme, bile, and pancreatic juice forms 'chilo'.

• Absorption

  Absorption primarily occurs in the small intestine, specifically the jejunum and ileum, due to the presence of villi and microvilli that increase surface area.

• Formation and Disposal of Waste

  Undigested food material is directed to the large intestine. Here, bacteria cause putrefaction. Through peristalsis, the waste material (stool) moves through the large intestine and is eventually expelled from the body via the rectum and anus.