how food travels through the GI tract

• 1. Mouth:

  • Mechanical Digestion: The teeth play a vital role in mechanical digestion by chewing and breaking down food into smaller pieces. The tongue helps mix the food with saliva, forming a bolus that can be easily swallowed.
  • Chemical Digestion: Salivary glands release saliva into the mouth. Saliva contains an enzyme called amylase that begins the breakdown of starches (complex carbohydrates) into simpler sugars like maltose. This process of chemical digestion starts in the mouth and continues briefly as the food travels down the oesophagus.
• 2. Stomach:

  • Mechanical Digestion: The stomach is responsible for further mechanical digestion. It contracts and relaxes, mixing the food with gastric juices to form a semi-liquid substance called chyme.
  • Chemical Digestion: The stomach releases gastric juices consisting of hydrochloric acid and the enzyme pepsin. Hydrochloric acid creates an acidic environment, which activates pepsin. Pepsin begins breaking down proteins into smaller peptides.
• 3. Small Intestine:

  • Chemical Digestion: Most chemical digestion and nutrient absorption occur in the small intestine. The pancreas releases digestive enzymes into the small intestine, including:
  • Lipase
  • Amylase
  • Protease
  • Additionally, the liver produces bile, which is stored in the gallbladder.
  • Mechanical Digestion: The inner surface of the small intestine is covered with villi and microvilli. These structures increase the surface area for nutrient absorption. As the chyme moves through the small intestine, it comes into contact with the villi and microvilli, where nutrient absorption occurs.
• 4. Large Intestine:

  • Mechanical Digestion: The large intestine's main function is to reabsorb water and some electrolytes from the waste material, making it more solid and forming faeces.
  • Chemical Digestion: While most chemical digestion occurs in the small intestine, some beneficial bacteria in the large intestine help break down certain undigested food particles. These bacteria also produce specific vitamins, such as vitamin K and some B vitamins, which can be absorbed and used by the body.
• other organs- Salivary Glands:

  • The salivary glands are accessory organs located around the mouth.
  • They produce saliva, which contains the enzyme amylase that initiates the breakdown of starches into simpler sugars during chemical digestion in the mouth.
• other organs- Liver:

  • The liver is the largest internal organ in the body, located just below the diaphragm on the right side of the abdomen.
  • While the liver is not a part of the gastrointestinal tract, it is a crucial accessory organ involved in digestion and metabolism.
  • The liver produces bile, a greenish-yellow fluid that helps digest fats. Bile is stored in the gallbladder before being released into the small intestine to aid in the digestion and absorption of fats.
• other organs- Gallbladder:

  • The gallbladder is a small, pear-shaped organ situated beneath the liver.
  • Its primary function is to store and concentrate bile produced by the liver.
  • When the small intestine needs bile to digest fats, the gallbladder contracts and releases the concentrated bile into the common bile duct, which then transports it to the small intestine.
• other organs- Pancreas:

  • The pancreas is a long, narrow gland located behind the stomach.
  • It functions as both an endocrine gland (producing hormones) and an exocrine gland (producing digestive enzymes).
  • As an exocrine gland, the pancreas releases digestive enzymes, such as lipase (for fat digestion), amylase (for carbohydrate digestion), and protease (for protein digestion), into the small intestine to aid in chemical digestion.
  • The pancreas also produces bicarbonate, which neutralises the acidic chyme from the stomach, creating a more suitable environment for the pancreatic enzymes to work.