The gut C3.1.16

• What is the digestive system?

  The digestive system is a collection of organs that work together to digest food into nutrients, absorb these nutrients into the body, and get rid of waste.
• What is ingestion?


  Ingestion- the process of taking in food or other substances into the body, by swallowing.
• What is digestion?


  Digestion- the hydrolysis of the large polymer molecules in food into monomers like amino acids, fatty acids and glucose. This is catalysed by enzymes in the mouth, stomach and small intestine.
• What is absorption?


  Absorption- the uptake of digested molecules by cells in the small intestine, e.g. glucose.
• What is egestion?


  Egestion- removal of undigested food, fluid and old cells from the digestive tract lining. The large intestine absorbs water from the waste, turning it into stool. The stool is stored in the rectum until it is eliminated through the anus.
• What is the alimentary canal?

  The alimentary canal is the long tube of organs of the digestive system that runs from the mouth to the anus (also known as the gut). The alimentary canal contains several types of muscles that help move food through the digestive system:

  - Smooth muscles- these line the walls of the alimentary canal. They contract and relax involuntarily in a process known as peristalsis, which moves food through the digestive tract in one direction.

  - Skeletal muscles- these are found in the mouth, pharynx, and external anal sphincter. They allow voluntary control over swallowing and egestion.
• What does the CNS control, regarding the digestive system?

  Processing of sensory (visual/smell) information about food, triggering the salivary glands and stomach to prepare for food

  Swallowing and movement from the mouth to the oesophagus

  Egestion of faeces from the rectum via the anus
• What does the ENS control, regarding the digestive system?

  Local blood flow and secretion of digestive juices from glands

  The muscles controlling peristalsis

  The vomiting reflex
• What is the ENS?

  The ENS is a mesh-like system of neurons within the walls of the alimentary canal. It acts independently of the CNS and is sometimes known as the 'brain of the gut'.
• What is the gut-brain axis?

  The gut-brain axis (GBA) is the communication system between the gut microbiome, the ENS and the CNS.

  It is involved in many aspects of brain and body function, including:

  mental health

  chronic intestinal inflammation and neurodegenerative conditions

  response to injury or disease in the gut

  secretion of hormones that communicate hunger, fullness and stress.