This organ, whose Latin name is Intestinum crassum, is distally adjacent to the small intestine, extending from the ileocecal valve to the anus.
It is divided into the cecum with a vermiform appendix, colon and rectum. Therefore, it is forming the terminal part of the human digestive tract.
Particularly relevant to the examination are the relationship of different intestinal sections to the peritoneum, the differences between the large and small intestines, and the general understanding of anatomy and physiology.
Location of the large intestine
The large intestine begins at the ileocecal valve that protects the small intestine from bacterial reflux. The adjacent cecum in the lower right part of the abdomen is a blind pouch (cecum: cecum). The appendix of the cecum, also known as the vermiform appendix, is attached to it.
It is usually located retrocecally, therefore behind the blind. However, the fact that the location of the appendix is variable is of clinical relevance. The ascending colon is continuous with the cecum and passes up to the thorax.
External appearance of the large intestine
The large intestine has a length of approximately 1.5 m and a diameter of approximately 5-8 cm. It runs around parts of the small intestine like a frame.
One of the most important macroscopic features are the haustra, which are sacculations or pouches in the wall of the large intestine. If they are found on the inner wall of the intestinal lumen, they are called semilunar plicae coli.
Tapeworms are bands of longitudinal muscles, each about 1 cm wide. You can distinguish between the taenia libera, which is freely visible, the taenia omentalis, which is found near the omentum majus, and the mesocolic taenia.
Epiploic appendages, appendages filled with adipose and connective tissue located in tapeworms, are also characteristic.
The large intestine in relation to the peritoneum
The large intestine in relation to the peritoneum is a popular subject for examinations. Its complexity is rooted in embryonic development and the accompanying intestinal rotation. It can be seen in general that the sections of the large intestine alternate between intraperitoneal and retroperitoneal locations.
Therefore, the cecum with the vermiform appendix is intraperitoneal. The blood vessels of the appendix pass through the mesoappendix and lead to the cecum and the ileum.
The ascending and descending sections of the colon are secondarily retroperitoneal. The transverse and sigmoid colon are in turn intraperitoneal. The gastrocolicum ligament connects the greater curvature of the stomach and the transverse colon.
To surgically reach the pancreas and other retroperitoneal organs, this ligament must be cut. The bursa omentalis is behind it.
The large intestine in relation to adjacent organs
- The ascending colon extends from the lower right part of the abdomen to the chest. The small intestine is usually on your left side.
- Flexura coli dextra borders the liver and partially touches the right kidney.
- The transverse colon touches both the liver and the gallbladder.
- The flexura coli sinistra is slightly higher than the right side, approximately at the level of the 10th rib. It borders the spleen and touches the left kidney.
- The jejunum is often found on the right side of the colon descendants.
Vasculature of the large intestine
The large intestine is supplied by the colic branches of the superior mesenteric artery, namely A. ileocolica, A. colica dextra, and A. colica media. The arterial blood supply changes in flexura coli sinistra.
The blood supply and innervation change at the so-called Cannon point. The remaining parts are supplied by A. colica sinistra, A. sigmoideae, and A. rectalis superior, main branches of the inferior mesenteric artery.
Nervous supply of the large intestine
The movement of the large intestine is possible thanks to its plexuses in the intestinal wall. Sympathetic fibers reduce intestinal motility. Parasympathetic fibers elevate it. They originate in N. vagus and run to the flexure coli sinistra.
At this point, the parasympathetic innervation is derived from the pelvic splanchnic nerves of the S2-S4 segments. This area is called the cannon tip, just as it does with regard to the blood supply.
The differences between the large and small intestine
Macroscopically, the large intestine can be distinguished from the small one by its haustra, tapeworms, and epiploic appendages. Also at the microscopic level, the wall of the large intestine has characteristics that differ from the small intestine. The large intestine does not have villi, but rather deep crypts (0.4-0.6 mm in length) with many goblet cells.
Noduli lymphoidei solitarii occasionally exists on the wall. For the most part, digestion takes place in the small intestine, where many nutrients are absorbed.
Rather, the large intestine is primarily the site where the water is removed. Simultaneously, the goblet cells secrete mucus that serves as a lubricant for the stool produced.
Functions of the large intestine
- The vermiform appendix is rich in lymphatic tissue and part of the immune system.
- The stool passes into the colon in 12-48h due to slow peristaltic movements and segmentation. The water is absorbed and the stool thickens. Every day, 0.5 to 2 liters of liquid are absorbed. With an absorption capacity of 5 to 6 L of water in the large intestine, there is a possibility to compensate for the lack of absorption in the small intestine.
- Goblet cells located in deep crypts secrete mucins. The resulting mucus facilitates the passage of stool through the intestines. The epithelial cells that line the crypt secrete and reabsorb electrolytes.
- The epithelial sodium channel (ENaC) regulates sodium reabsorption from feces. This process is controlled by the steroid hormone aldosterone. Potassium is secreted, however it can be reabsorbed in a deficient state.
- The acidic medium of the pH in the large intestine is between 5.5 and 6.8, so the pH increases towards the more distal segments.
- In the rectum, feces are stored for excretion only after the accumulation of large amounts. Otherwise, the feces would be continuously excreted.
The intestinal flora
Another special feature of the large intestine is the variety of colonizing bacteria. Around 100 billion primarily anaerobic bacteria ensure that otherwise indigestible food components are accessible.
In addition, intestinal bacteria produce substances that are essential for humans, such as vitamin K.
The sensitive intestinal flora can be affected as a result of repeated antibiotic therapies. This, in turn, can cause diarrhea disorders.
Large intestine pathology
Appendicitis in the large intestine
In the course of life, approximately 10% of the population suffers from appendicitis. The inflammation is commonly caused by a lumen obstruction due to calcified stools, tumors, or foreign bodies.
Acute appendicitis can manifest itself within hours. Initially, the pain usually arises in the umbilical area, then in the lower right abdomen. In addition, nausea, vomiting and fever appear.
A point on the right abdomen, one third of the distance on the connecting line between the right upper anterior iliac spine and the umbilicus. Pressure applied to this area can trigger pain in patients with appendicitis.
A possible complication of an untreated appendicitis is perforation in the peritoneal cavity and, subsequently, peritonitis that can even be life-threatening. Generally, the treatment is an appendectomy.
Irritable bowel syndrome
Irritable bowel syndrome is a group of intestinal diseases that often lack organic findings. Its etiology is often unclear. The symptoms are, among others:
- Digestive problems with pain.
- Diarrhea or constipation
Gluten sensitivity and psychological factors are associated with irritable bowel syndrome.
Diverticulosis del colon
An intestinal diverticulum is a sac-like protrusion of the intestinal wall or even the intestinal mucosa. Diverticulosis is a disorder of civilization. Due to a low fiber diet, the transport of intestinal contents is slower. The large intestine has to contract harder and therefore builds up more pressure.
As a result, these bumps arise, usually on the sigmoid of the colon. Diverticulosis rarely occurs before the age of 30, but afterwards, the probability of its occurrence increases by 6-8% per year.
It is often an incidental finding due to lack of symptoms. Possible complications include, but are not limited to, diverticulitis, bleeding, perforation, fistulas, and strictures.
Inflammation in the large intestine is called colitis. A distinction is made between acute and chronic inflammatory bowel diseases.
Acute intestinal inflammation is also called enteritis. Ulcerative colitis is one of the chronic diseases of relevance to the examination. It is an inflammation of the intestinal tract that is repeated for decades. Ulcerative colitis is limited to the colon and rectum.
Polyps in the colon
A polyp is a collection of tissue in the large intestine, whether it is wide and flat, branched, or polypoid. They are generally smaller than 1 cm and do not cause any symptoms. However, possible symptoms are constipation, pain, or blood in the stool.
Especially large polyps can become malignant tumors, thus a colorectal carcinoma (adenoma-carcinoma sequence).
A malignant tumor of the colon is called colon carcinoma. Most of the time the carcinoma arises from benign polyps still existing by adenoma-carcinoma sequence. Bowel cancer occurs most often in the 60 to 70 age group.
A possibly undiagnosed chronic inflammatory bowel disease may appear in younger patients.
Risk factors are older age, intestinal polyposis, genetic factors, and ulcerative colitis. Diet plays a particularly important role. A diet high in fat increases the risk of cancer, while a diet high in fiber reduces it. Therefore, intestinal cancer is more common in industrialized countries.
Symptoms like hidden bleeds usually develop late. The prognosis generally depends on the stage of the cancer at discovery. It is determined by the TNM classification.
The metastases linfogénicas occur early, infecting the regional lymph nodes. Hematogenously, colon carcinoma predominantly metastasizes to the liver, lungs, and skeleton.
Colon resection is a partial removal of the colon. Indications include diverticulosis, colon polyps, colon carcinoma, or chronic inflammatory bowel diseases, such as ulcerative colitis.