Oesophagus
The oesophagus is a muscular tube, approximately 25 cm long. The main
function of the oesophagus is to transport ingested food and fluids to the
stomach in wavelike contractions. A lower oesophageal sphincter (LES)
stops reflux of acid from the stomach back into the oesophagus.
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The diaphragm is a dome shaped muscle that is responsible for breathing and separates the chest cavity from the abdominal cavity. The oesophagus passes through the diaphragm through an opening called the oesophageal hiatus
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The stomach is an expandable pouch between the oesophagus and the small bowel that temporarily stores food. During a meal, the stomach can extend to hold between 1500 to 4000mls. When food enters the stomach, digestive juices are secreted from glands within the stomach to start the digestion of food. The contents are gradually emptied into the duodenum (beginning of the small bowel) through the pyloric sphincter, where absorption of nutrients and fluids occurs.
An average meal of food and fluids takes about 1.5 to 2 hours to be emptied.
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The stomach empties into the small bowel, which is the longest portion of the digestive tract (6m). By the time food reaches the small bowel, it has been mechanically broken down and reduced to a liquid substance. Pancreatic enzymes and bile are then released which further assists in digestion.
The small intestine has thousands of folds on its surface called villi,
which increase the total surface area and the absorption of digestive
products.
Almost all of the nutrients and water is absorbed in the small bowel which
includes vitamins, minerals, proteins, fats and carbohydrates. Any food
not absorbed in the small intestine goes into the large intestine as
liquid waste.
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The Liver is the largest organ, weighing approximately 1.5kgs. All of the blood leaving the stomach and intestines must pass through the liver before reaching the rest of the body. The liver essentially, refines and processes nutrients and drugs absorbed from the digestive tract into forms that are available for the body to use.
The main functions include:
- Removes the toxic substances by converting them to substances that can be easily eliminated from the body
- Production of bile, a greenish-brown fluid which is essential for digestion
- Production of energy and storage of vitamins, minerals and sugars
- Manufacturing of new proteins
- Regulation and transport of fat stores
- Regulation of blood clotting
- Controls the production and excretion of cholesterol
- Neutralises and destroying poisonous substances
- Metabolises alcohol
- Cleanses the blood and discharges waste products into the bile
- Maintains hormone balance
- Stores iron
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The gallbladder is a small sac on the surface of the liver which stores bile, received from the liver. After eating, the gallbladder contracts and discharges bile into the intestine, to aid in digestion.
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The pancreas is a small, long organ, approximately 15cm that lies close to the duodenum (small bowel). The main function of the pancreas is to produce digestive enzymes to aid in digestion. The pancreas also produces the hormones glucagon and insulin which regulate carbohydrate metabolism.
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The colon, or large intestine is approximately 1.5 metres in length. The colon has four sections: the ascending colon, the transverse colon, the descending colon, and the sigmoid colon The main function of the colon is to absorb water from the stool (faecal matter), producing a solid waste and to store the stool prior to a bowel movement. As the stool progresses through the colon, more water is absorbed until the stool is formed.
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The rectum is approximately 15cm long. The rectum acts as a reservoir for faeces and it has the ability to become distended (stretch). During defecation, the pressure within the rectum increases because of contraction of the abdominal wall and pelvic muscles.
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The anus is the excretory opening at the end of the digestive system.
Within the lining of the anal canal, connective tissue and muscle form
what is known as anal cushions. The role of these cushions is similar to
the washer in a tap, preventing leakage of faeces. The anal sphincter
muscles guard the anal opening and maintain continence. When the rectum is
distended with faeces a sensation is produced and signals the call for
defecation. The person can then choose to evacuate the bowels.
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