Posted in Psychology & Medicine

Viscera: Large Intestine

(Learn more about the organs of the human bodies in other posts in the Viscera series here:

The final destination of food travelling through the digestive tract is the large intestine, or colon. It is the site where digested food is transformed into faeces, ready for excretion. The large intestine is much shorter than the small intestine – roughly 1.5m in length. Unlike the small intestine which is relatively free and mobile, the colon is fixed to the abdominal wall. It starts in the lower-right corner of the abdomen in a pouch called the caecum (connected to the small bowel). This is where the appendix is located. The colon then ascends the right-side of the abdomen (ascending colon) all the way to the diaphragm, does a 90-degree turn to the left (transverse colon) until it hits the spleen, then goes downwards to the lower-left corner (descending colon). Here, the colon bends into an S-shape towards the centre (sigmoid colon) until it ends as the rectum, which opens out to the anus. The colon essentially frames the contents of the abdomen.

The colon’s main function is the absorption of water and salts from the food that has been processed by the small bowel. As it sucks out the water in this liquid, it becomes more and more solidified. The brown colour of normal stool comes from bile and bilirubin (from the breakdown of red blood cells) secreted by the liver into the duodenum. For this reason, biliary obstruction (e.g. due to gallstones) causes pale stool and dark urine (overflow). Stool also contains undigested material like fibre, giving it bulk. Because it is at the end of the digestive tract, stool can be used to diagnose many diseases, such as an infection in the gut (bacterial, viral or parasitic).

The colon is a common site for cancer to occur in. Because there is room to grow, colon cancers are often found late when they have already spread and is incurable. The key symptoms of colon cancer are bloody stool (although this can be due to many reasons such as haemorrhoids), worsening constipation, anaemia (from blood loss causing iron deficiency), change in bowel habit and general symptoms of cancer (e.g. weight loss, fatigue).

(Appearance of colon cancer on colonoscopy)

Posted in Psychology & Medicine

Viscera: Small Intestine

(Learn more about the organs of the human bodies in other posts in the Viscera series here:

Abdominal organs are often grouped into the colloquial term gut. “Gut” also refers to a specific organ – the small intestine (or small bowel). It is an important part of the gastrointestinal (digestive) tract, connecting the stomach to the colon and involved in digesting and absorbing nutrients. The small intestine is extremely long, roughly 7m in an adult. It fits in the abdomen by folding and packing neatly, lying under the liver, stomach and pancreas while being framed by the large intestine. The small intestine is not freely hanging so you cannot just pull it out like a rope. It is connected to the body by a fan-like membrane called the mesentery, which provides blood supply to the gut. The mesentery is attached along one side of the gut the entire way through.

The small bowel is composed of three parts: the duodenum, jejunum and ileum. Although people think digestion mainly happens in the stomach, it is actually primarily performed in the duodenum. The duodenum not only receives liquefied food from the stomach, but is also the place where the pancreas and liver drain digestive juices such as pancreatic enzymes and bile. The enzymes breakdown large molecules like fat, protein and carbohydrates into smaller building blocks, while bile acts like detergent to allow fat to mix better with water (emulsification).

The digested food then travels down the GI tract through a process called peristalsis, where the gut squeezes behind the bolus of food to push it forward, much like squeezing toothpaste out of the tube. The broken down products are mainly absorbed in the second part of the bowel (jejunum) via the walls. The small bowel wall looks like a carpet due to microscopic finger-like projections called villi. Villi allow for a much greater surface area for enhanced absorption. In coeliac disease, these villi are flattened by an autoimmune process and the patient cannot absorb as much nutrients (including vitamins).

By the time the food reaches the ileum, most of the nutrients have been absorbed. The ileum finishes the job by absorbing some extra things like vitamin B12 and bile salts, then sends the food through the ileocoecal valve, which is the door between the small and large intestine.

The small bowel is used by various cultures for culinary purposes. Other than simply eating the bowel itself after cooking, it is often used to pack different meats or other food inside, such as sausages or soondae (Korean sausages, filled with chop sui noodles).