digestive system

• mouth- This is the first part of digestive system. We ingest food and chew it (masticate) the food gets rolled into a ball called the bolus and swallowed. This is known as mechanical digestion.
• tongue- has tiny projections known as lingual papillae. These give it a rough texture and they are covered in taste buds. There are nerves in the tongue that help in transmitting taste signals to the brain.
• salivary gland- There are 3 pairs of salivary glands that pour their secretions, known as saliva into the mouth. Saliva, contains an enzyme known as salivary amylase, which begins the digestion of carbohydrates, as well as lubricating the mouth
• oesophagus- transports the food bolus from the back of the mouth (pharynx) to the stomach in the abdomen. The oesophagus is mainly a transit for food boluses, which it moves by muscular contractions known as peristalsis
• Peristalsis – muscular contractions of the circular and longitudinal muscle in the gut wall which pushes food along the alimentary canal
• stomach- The strong stomach walls roll and churn the food around and pour secretions from the gastric glands which contain the enzyme gastric protease. that paste would be called chyme. The epithelial lining of the stomach contain goblet cells which produce thick mucus to protect the stomach lining from acid erosion.
• The duodenal wall also contains glands which secrete enzyme rich juices that continue the digestive process on proteins, carbohydrates and lipids (fats) Proteases, amylases and lipases
• ileum


  •long length and folded interior

  •Lining covered in thousands of tiny projections called villi

  •Thin Epithelial cell lining being covered in microvilli

  •These adaptations enormously increase the surface area for absorption of nutrients from digested food.
• villi- lined by columnar and goblet cells only one cell thick, with an extensive capillary network and a blind-ended branch of the lymphatic system called a lacteal
• colon- allows water to be reabsorbed and the motion /faeces, become semi- solid.  It can then be eliminated by muscular action.
• Faeces contain:

  •Cellulose (fibre and roughage) from plant cell walls left after digesting fruit and vegetables

  •Dead bacteria, including the usually harmless bacteria living in the large intestine and other bacteria that are normally killed by hydrochloric acid in the stomach

  •Cells scraped off from the gut lining
• Mucosa – is the inner most layer surrounding the lumen (the tube)
• Submucosa – consists of a dense layer of connective tissue with blood vessels, lymphatic vessels and nerves
• Muscularis – also known as the muscle layer has an inner oblique layer, a middle circular layer and an outer longitudinal layer.
• The serosa forms the outer layer and consists of several layers of connective tissue
• liver- produces bile which flows down the bile duct into the duodenum.  bile salts cause the emulsification of fats (lipids). They are broken down into smaller units-fatty acids. it also removes glucose and other sugars from the blood coming from the small intestine and converts them into glycogen for storage.
• Pancreatic enzymes go to work on all 3 macronutirents ( protein, fat and carbohydrate) and are important agents for the complete breakdown of complex food molecules into amino acids, glucose, and similar simple sugars, fatty acids and glycerol
• The pancreas also makes the hormones insulin required to metabolise glucose and glucagon, required to release stored glucose, in the islets of Langerhans.