The Digestive System

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The Digestive System
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Pancreas

The pancreas is a major organ functioning as an accessory digestive gland in the digestive system. It is both an endocrine gland and an exocrine gland. The endocrine part secretes insulin when the blood sugar becomes high; insulin moves glucose from the blood into the muscles and other tissues for use as energy. The exocrine part releases glucagon when the blood sugar is low; glucagon allows stored sugar to be broken down into glucose by the liver in order to re–balance the sugar levels. Digestive enzymes are also produced. The pancreas lies below and at the back of the stomach. It connects to the duodenum via the pancreatic duct where it can act on the chyme that is released from the stomach into the duodenum. There is a nearby connection of the common bile duct to the duodenum. Aqueous pancreatic secretions from duct cells contain bicarbonate ions which are alkaline and help to neutralise the acidic chyme that is churned out by the stomach. The pancreas is also the main source of enzymes for the digestion of fats (lipids) and proteins. The cells are filled with secretory granules containing the precursor digestive enzymes. The major proteases, the pancreatic enzymes which work on proteins, are trypsinogen and chymotrypsinogen. Elastase is also produced. Smaller amounts of lipase and amylase are secreted.

GI: The lower gastrointestinal Tract;

The lower gastrointestinal tract, includes the small intestine and all of the large intestine. It is also called the bowel or the gut. It starts at the pyloric sphincter of the stomach and finishes at the anus.

The small intestine is subdivided into the duodenum, the jejunum and the ileum. The caecum marks the division between the small and large intestine.
The large intestine includes the rectum and anal canal.

Food once eaten, starts to arrive in the small intestine after one hour, and after two hours the stomach has emptied. Until this time the food is termed a bolus. It then becomes the partially digested semi-liquid termed chyme.

In the small intestine, the pH becomes crucial; it needs to be finely balanced in order to activate digestive enzymes. The chyme is very acidic, with a low pH, having been released from the stomach and needs to be made much more alkaline. This is achieved in the duodenum by the addition of bile from the gall bladder combined with the bicarbonate secretions from the pancreatic duct and also from secretions of mucus-rich bicarbonate from duodenal glands known as Brunner's glands.
The chyme arrives in the intestines having been released from the stomach through the opening of the pyloric sphincter. The resulting alkaline fluid mix, neutralises the gastric acid which would damage the lining of the intestine. The mucus component lubricates the walls of the intestine. When the digested food particles are reduced enough in size and composition, they can be absorbed by the intestinal wall and carried to the bloodstream. The first receptacle for this chyme is the duodenal bulb. From here it passes into the first of the three sections of the small intestine, the duodenum.

(The next section is the jejunum and the third is the ileum).
A milky fluid called chyle consisting mainly of the emulsified fats of the cholymicrons results from the absorbed mix with the lymph in the lacteals. Chyle is then transported through the lymphatic system to the rest of the body.

The last part of the small intestine is the ileum. This also contains villi and vitamin B12; bile acids and any residue nutrients are absorbed here. When the chyme is exhausted of its nutrients the remaining waste material changes into the semi solids called faeces, which pass to the large intestine, where bacteria in the gut flora further break down residual proteins and starches.

Caecum

The caecum is a pouch marking the division between the small intestine and the large intestine. The caecum receives chyme from the last part of the small intestine, the terminal ileum, and connects to the ascending colon of the large intestine. At this junction there is a sphincter or valve, which slows the passage of chyme from the ileum, allowing further digestion. It is also the site of the appendix attachment.

Large intestine

In the large intestine, the passage of the digesting food in the colon is a lot slower, taking from 12 to 50 hours until it is removed by defecation. The colon mainly serves as a site for the fermentation of digestible matter by the gut flora. The time taken varies considerably between individuals. The remaining semi-solid waste is termed faeces and is removed by the coordinated contractions of the intestinal walls, termed peristalsis, which propels the excreta forward to reach the rectum and exit via defecation from the anus. The wall has an outer layer of longitudinal muscles, the taeniae coli, and an inner layer of circular muscles. The circular muscle keeps the material moving forward and also prevents any back flow of waste. Also of help in the action of peristalsis is the basal electrical rhythm that determines the frequency of contractions.   Most parts of the Gastro intestinaI tract are covered with serous membranes and have a mesentery. Other more muscular parts are lined with adventitia.

Clinical significance

Each part of the digestive system is subject to a wide range of disorders. In the esophagus Schatzki rings can restrict the passageway, causing difficulties in swallowing. They can also completely block the esophagus.

A common disorder of the bowel is diverticulitis. Diverticula are small pouches that can form inside the bowel wall, which can become inflamed to give diverticulitis. This disease can have complications if an inflamed diverticulum bursts and infection sets in. Any infection can spread further to the lining of the abdomen (peritoneum) and cause potentially fatal peritonitis.

Crohn's disease is a common chronic inflammatory bowel disease (IBD), which can affect any part of the GI tract, but it mostly starts in the terminal ileum.

Ulcerative colitis an ulcerative form of colitis, is the other major inflammatory bowel disease which is restricted to the colon and rectum. Both of these IBDs can give an increased risk of the development of colorectal cancer. Ulcerative coliltis is the most common of the IBDs

There are several idiopathic disorders known as functional gastrointestinal disorders that the Rome process has helped to define.   The most common of these is irritable bowel syndrome (IBS).

Giardiasis is a disease of the small intestine caused by a protist parasite Giardia lamblia. This does not spread but remains confined to the lumen of the small intestine.[33]It can often be asymptomatic, but as often can be indicated by a variety of symptoms. Giardiasis is the most common pathogenic parasitic infection in humans.

Conclusion:

It is surprising that we humans pay so little attention to the main system what makes us what we are, and dwell on the exterior, enhancing our skin and facial appearance to please others, and get their attention, while we leave our personal health to the care of the doctors to attend to when needed.    All our exterior features are given for our survival, and often it becomes a cause of our extinction.   Just see how much thought has gone into designing our inner parts of our body, and this has been done, so that we can contribute to a society that allows us the live.   How often do we raise our thoughts to the Creator who was instrumental in making such a marvellous system of existence.    How often we brush it under the carpet, saying it is all a matter of "evolution", and leave our thinking powers in the dust bin of ingnorance.