Anatomy of small bowel disease

2021-05-11 11:53 AM

The epithelium lined by the cavities differs from that of the villi. There are four types of epithelial cells of the cavity: Paneth cells, non-differentiated cells, radioactive cells, and endocrine cells.

The small intestine in an adult is about 3.6-6 meters long and consists of several sections. The duodenum, the first segment, connected to the stomach, is the widest, most fixed segment and is C-shaped. The duodenum with the bile duct, the Vater balloon, the pancreatic canal, the proximal part of the liver, gall bladder, and the colon, which forms the most susceptible area of ​​the entire small intestine. The second paragraph is the jejunum. The third paragraph is the ileum.

There is no clear boundary between the jejunum and ileum. Usually, the jejunum, from the junction with the duodenum, is 40% of the length of the remaining small intestine. The diameter of the proximal part of the ileum is twice as large as the diameter of the end ileum.

Arteries that supply blood to the small intestine come from the upper mesenteric artery. These arteries branch gradually as they reach the intestinal wall. Between the branches there are pine branches, only when they come very close to the intestinal wall, there are terminal arteries. Therefore, there is no significant damage in the presence of a branch block.

The lymphoid vessels are usually parallel to the artery but do not have a catheter branch such as the artery, so if there is a small lesion in the lymph node or the lymphatic circuit, it can cause oedema over a long segment.

The histological features of the small intestine are the intestinal villi. These villi are most abundant in the duodenum, less gradually and shaped like fingers, which are the intestinal valves at the end of the ileum. Between the bottom of the villi, the cavities of the mucosa, have a depth equal to one-third of the height of villi. The duodenum has a unique feature, which is the branched Brunner gland located deep in the submucosa.

The mucous layer of the small intestine contains phagocytosis, lymphocytes (abundant in the Peyer plate of the ileum), cytoplasm. Immuno-globulins, especially IgA, are synthesized by these cells and play a role in preventing bacterial penetration.

The epithelium lined by the cavities differs from the epithelium of the villi. There are four types of epithelial cells of the cavity: Paneth cells, non-differentiated cells, radioactive cells, and endocrine cells.

Paneth cells have alkaline cytoplasm containing large secretory granules (secretory properties not known) containing lysozymes, IgG and IgA. The undifferentiated cells, the most abundant in the cavities, take IgA from the mucosal stromal tissue, divide them with a secreting component, secrete water and electrolytes, containing small secretory particles (apparent when staining. PAS). Syst cells, filled with mucin granules, have no apical enlargement, which are the main cells that secrete mucus in the small intestine. Endocrine cells, of at least 9 types (differentiated by histochemical and superstructure methods, containing positive silver-loving and chromatophilic secretory granules, with the function of secreting digestive hormones as secretin, cholecystokinin,

The surface of the villi has 3 types of cells, mainly absorption cells, mixed with radioactive cells and a few endocrine cells. These cells stick together, forming a barrier that prevents the permeability of the contents of the intestinal lumen with the subepithelial stroma. All the smallest molecules (such as sodium, chloride, water) that are dispersed between cells must pass through the cells of the mucosal surface. Absorbed cells have a special structure on the surface of the intestinal lumen. These are microscopic villi that can only be seen under an electron microscope. On the villi, these villi are uniform, straight and tall. In the cavities, the microflora is shorter and irregular. They are coated with a thin layer of glycoprotein secreted by the uptake cells. All form an ideal environment for food digestion by amylases and proteases. The microvilli membrane also contains disaccharidase, some peptidase, other enzymes, transport proteins, specific receptors (eg in the ileum that can receptors for intrinsic factor and vitamin B12) thus helping. digestion and absorption of nutrients.

The regeneration capacity of the small intestinal epithelium is very strong. Cells begin to proliferate from the bottom of the cavities, then slide along the cavity to the villi in 5-7 days. As a result, the entire small intestinal surface of the epithelium is replaced every week.

The main types of diseases of the small intestine are inflammation and disorders that lead to malabsorption. Small bowel obstruction is also a common complication when sick because the intestinal lumen is narrow. Unlike the stomach and colon, primary tumours are rare in the small intestine.

Birth defects

Stomach and stenosis of the small intestine

The small intestine may be blocked in a section, making the lumen of the intestine not clear. Sometimes the upper and lower intestines are only connected by a piece of hard fibrous tissue.

The small intestine may also be more or less narrow, causing mild or severe intestinal obstruction.

Small intestinal stenosis and stenosis may be present in the intestine or more places in any part of the jejunum and ileum. The disease can be accompanied by other defects.

Diverticulosis of the duodenum, jejunum and ileum

In the wall of the ileum and jejunum, where blood vessels and nerves enter, there are weak spots, where the mucosa and submucosa can enter the desert to connect to form the diverticula. In the duodenum is rarer (only 1/20).

The disease is more common in the elderly than the young, perhaps related to the presence of constant pressure in the lumen of the intestine. Because the sac often gets into the fat layer of the mesenteric membrane, it is difficult to detect.

Under the microscope, the muscular layer of the diverticula is lost or thinned, leaving only the mucosa and submucosa.

The excess sacs can provide food stagnation, giving bacteria the opportunity to grow and consume more vitamin B12, causing malignant anaemia. Very rarely, the diverticulum is haemorrhagic and perfected.

Meckel diverticulum

Is located in the wall, part without mesenteric part, of the end ileum, from a few cm to 30cm from the ileum valve, composed of all layers of the small intestine. Usually lined by the small intestinal mucosa, but in 25% of cases, it is lined with gastric mucosa with or without pancreatic tissue.

There may be conditions such as chronic ulcers with haemorrhage, obstruction, cage (like small intestine) and inflammation.

Residual pancreatic tissue

Normal pancreatic tissue foci can be found in the form of small polyps less than 1-2 cm in diameter in the mucosa of any part of the small intestine (rarely in the jejunum), which may cause confusion with tumours. development of the small intestine. The tissue is yellow with many lobes.

Bowel disease caused by anaemia

Infarction of the entire intestinal wall

It is more common in the small intestine than in the colon. Diseases caused by thrombosis or thrombosis of the upper mesenteric artery, or thrombosis of the mesenteric vein, or due to partial narrowing of blood vessels. The causes can be atherosclerosis (thrombosis), pressure tumours, heart failure ...

Lesions may be only one segment, possibly the length of the small intestine. Initially, the damaged intestine is red-purple, congested with discoloured foci under the mucosa and under the serosa. After that, the intestinal wall is swollen, thick, chewy, haemorrhagic, while the intestinal lumen contains blood mucus or is whole blood. If the infarction is due to an artery, the lesion is clearly limited; if it is due to a vein, the injury has an unknown limit. About 24 hours later, fibrin or fibrin-purulent discharge appears in the serosa. The inflammatory response depends on the duration of the injury. The mucous layer can be ulcerated, infiltrating inflammation.

The disease can cause death quickly.

Infarction of the mucosa and wall

Formerly known as an acute haemorrhagic gastrointestinal disease because it can damage anywhere from stomach to anus, due to decreased blood-feeding in heart failure, dizziness.

Anaemia lesions are found only in the inner layers, not affecting the muscle layer and serosa, of each segment, mainly in the small intestine and colon.

When the intestine is split open, the intestinal mucosa can be seen with bleeding, oedema, thickening, and sometimes ulceration. Oedema and bleeding may be present in deeper parts, in the submucosa and smooth muscle.

Under the microscope, there are vasodilators, with extravascular erythrocytes, haemorrhagic necrosis of the mucous layer, usually superficial, sometimes deeper.

Bacterial superinfection can cause pseudomembranous inflammation, usually found in the colon.

Inflammatory bowel diseases

Bacterial enteritis

Bacteria enter the gut through contaminated food. There are many types of bacteria such as Clostridium botulinum, Staphylococcus aureus, Campylobacter jejuni, Escherichia coli, Salmonella, Shigella, Yersinia enterocolitica, Mycobacterium tuberculosis. Especially in the anorectal area, it can be caused by bacteria Treponema pallidum, gonorrhoea or Chlamydia or Herpes simplex virus, transmitted through the genital tract.

Damage depends on the type of bacteria that cause the disease. Macroscopic lesions can range from mucosal hyperaemia to enlargement of lymphoid tissues to deep ulcers. Sometimes there is a fake membrane.

Microbial morphology differs depending on the type of bacteria but is either an acute or chronic inflammatory response. TB bacteria cause damage to the tuberculosis cyst. Salmonella bacteria induce mononuclear phagocytosis, hyperplasia of tissue, sometimes phagocytic red blood cells. Campylobacter bacteria create ulcerative granular tissue.

To diagnose pathogenic bacteria, it is necessary to culture faeces or transplant diseased tissue.

Non-bacterial enteritis

Inflammation caused by a virus

Some viruses are the cause of acute gastroenteritis. Parvovirus-like agents cause disease in adults. Retrovirus-like agents cause illness in children. More recently, Rotavirus causes diarrhoea, especially in young children.

Although all viral diarrhoea is occasional, it can be fatal or cause malnutrition.

Lesions include shortened small intestinal villi with infiltration of polymorphonuclear and mononuclear leukocytes in the mucosal stroma. Surface absorbing cells, altered as vacuole, missing or shortened microvilli, are highly lysosomal.

Fungal inflammation and mucomycetes

Most cases are the result of fungal blood-borne infections in frail patients following some serious illness. In people taking antibiotics for a long time, the intestines are susceptible to inflammation caused by the fungus Candida albicans. Whatever the disease, lesions, present in the small intestine and colon, including congestion, oedema, superficial necrosis, deep ulcers, sometimes pseudo membrane.

Inflammation caused by Protozoa

Includes Entamoeba histolytica and Giardia lamblia. In particular, amoeba causes extensive ulcers in the colon, difficult to distinguish from necrotizing enterocolitis or bacterial enteritis. Schistosoma mansoni can also cause disease in the small intestine.

Crohn's disease

Also known as regional small intestinal inflammation, it has some common properties with ulcerative colitis. Although the two diseases have some in common, they are classified according to their clinical, radiological and anatomical features. The incidence of the disease is unknown. Whites and Jews have a higher incidence of illness than other races. Men and women have the same disease, although ulcerative colitis is more common in women. Any age can get the disease, but the highest probability is in young people, about 20-30 years old.


Currently not clear. Bacterial agents have also not been clearly demonstrated, although injecting homogeneous diseased tissues into animals causes a change in the intestines of these animals. The high prevalence of the disease in some families as well as the association of the disease with polyarthritis, uveitis of the eye, liver damage, skin damage, and ankylosing spondylitis makes people think of the role of genetic factors. Psychological factors also play an important role in ulcerative colitis. Most recently, attention has been given to immune-mediated mechanisms of disease.

Clinical manifestations

Both illnesses may have an acute or vague onset, which may progress abnormally as they worsen with spontaneous recovery with diarrhoea and rectal bleeding. In ulcerative colitis, the above symptoms are less common and milder, but often with abscesses around the rectum, fistula, narrowing of the intestine.

Morphological injury

It can be anywhere in the stomach and intestines, although mostly at the end of the ileum, usually spreading to the cecum, sometimes up to the colon. In half of the cases, multiple lesions are present on several sections of the small intestine and colon, forming diseased areas alternating with normal areas. In the colon, the lesions may be fragmentary but may occupy the entire colon.

Crohn's disease, also known as granulomatous colitis, is reported to be of a high degree.

Anus lesions are often comorbid and maybe the first manifestation of the disease.

Macroscopic lesions are nonspecific, granulomatous inflammation. The surface of the intestinal mucosa is dotted with red pebbles, with long, zigzag sores. Both intestinal walls is thickened. The mucosa is infiltrated with inflammation, mainly cells and cytoplasm. The submucosa and subarosa are fibrosis, the muscle layer is enlarged.

Under the microscope, the ulcer is irregular with a neutrophil response. Mucosal abscesses are unknown (as in ulcerative colitis). Glands are dilated, radio cells are missing or few. Paneth cells are clearer than usual. Tubular glands such as the Brunner gland or pyloric gland are often present. The muscular layer is enlarged. Nerves in the diseased sections increase in number and size. The lymphoid cysts are clearly visible in the submucosa and sub-serosa. In some places there may be tuberculosis-like structures, but not pea necrosis. Deep sores can cause perforation and are often covered with fishing grease or neighbouring structures. There may also be fistula openings to other sites, with the postoperative abdominal wall.


Complications inside and outside the intestine are possible in 2 diseases.

Bowel obstruction due to narrowing or sticking, fistula, perforation is more common in Crohn's disease than in ulcerative colitis.

Toxic acute aneurysms leading to perforation are rare in Crohn's disease, but more common in ulcerative colitis.

Carcinoma is also a complication of ulcerative colitis, in 3-5% of patients with long-term illness. This type of cancer often has many similar, often invasive and differentiated types.

Extra-intestinal complications are more likely to occur in Crohn's disease such as peri-bile duct inflammation, primary fibrosis bile duct inflammation, chronic hepatitis, cirrhosis, carcinoma of the bile duct, arthritis, spondylitis, pink erythema nodosum, purulent dermatitis, uveitis.

Clogging lesions

Blockage can be anywhere in the gastrointestinal tract, but the most commonplace is the small intestine (due to small intestinal diameter).

Causes of choking include

Mechanical blockage:

Congenital stenosis or acquired congenital bit.

Stuffy due to penny.

No anus.

Molasses, hard feces, foreign bodies.

Sticky wire.


Intestinal twisting.

Intestinal cage.

Intestinal paralysis due to neurological causes.


Blockage of blood vessels:

Intestinal infarction.

Tumours and infarction, although the most severe, only account for about 10-15% of cases of choking. Four diseases, including hernia, sticky wire, intussusception and intestinal twisting, account for about 80%.


Due to lack or weakness in a certain position of the abdominal wall. There, under permanent pressure in the abdominal sinuses, a bulging pocket of hernias lined by the peritoneum will appear. The most common herniated sites are the anterior abdominal wall where the groin canal, femoral duct, umbilical canal, and surgical scars. Rarely has a herniation in the posterior abdominal wall, mainly around the Treitz ligament.

The organs in the abdomen may go underground and become trapped in the hernia sac. This is most likely to occur in an inguinal hernia sac because it is large and has narrow herniation.

The small intestine, when entering the hernia sac, may become partially or completely blocked, and blood in the veins is also clogged by the neck of the herniation sac blocking the veins. As a result, the small intestine can become twisted and necrotic in the part of the hernia sac, and the upper part is blocked.

Intestinal cage

Rarely. In children and young children, a segment of the small intestine due to peristalsis can enter and insert into the posterior intestinal segment, dragging its mesenteric part. Pathogenesis is unknown.

In adults, the cause of the intestinal cage is tumours. When inserted, intestinal infarction can occur.

Intestinal twisting

Can occur in the small intestine or in the sigmoid colon, and can cause congestion and infarction.

Intestinal cord

Occurs after peritonitis, after abdominal surgery. The resulting sticky wires can form tight loops of the intestine, causing partial or complete congestion. These sticky wires are usually from the peritoneum part of the abdominal wall, from the old incision in the abdominal sinus.

It is very rare to have a congenital cord not caused by peritonitis, nor due to surgery.

Tumours of the small intestine

Tumours of the small intestine, benign tumours and cancer, are very rare. This problem is also a medical mystery. Although the small intestine accounts for 75% of the entire length of the digestive tract, tumours of the small intestine account for only 3 to 6% of gastrointestinal tract tumours.

Many speculative theories have been put forward to explain this mysterious phenomenon; the short dwell time of food in the small intestine causes the intestinal mucosa to be in short contact with carcinogens, less mechanical stimulation in the small intestine thanks to the liquid substances in the small intestine. A high concentration of IgA helps to increase immunity, there are fewer bacteria in the small intestine, so it produces fewer carcinogens.

In most studies, cancer has a slightly higher incidence than benign tumours, with a rate of about 1.5 / 1.

Small bowel tumours

Most are discovered during an autopsy or by accident when taking an x-ray of the small intestine because of another disease.

Occasionally, large tumours can cause partial or intermittent obstruction, haemorrhage, intermittent, or twisted bowel. The most common is smooth muscle tumours. Then, adipoma, adenoma, haemangioma and fibroids respectively. These tumours all have a morphology similar to other places. Only the polyps have their own characteristics.

Polyps can be solitary or multiple lumps, most often in the duodenum and ileum. Morphologically, they resemble adenomas of the stomach and colon, which may be stalked or sessile (a branching type of adenoma: villous adenoma). Larger adenomas, especially those that look like colon-like tumours (branching adenomas), can easily become carcinomas (more than 50% of cases). Stalk polyps may be found in the small intestine of patients with Peutz-Jeghers syndrome and familial polyps.

Small bowel cancer

More than half of small bowel cancers are found in the ileum.

The two types with the highest incidence are endocrine cell tumours (silver cell tumours) and lymphoma. Next are adenocarcinomas and smooth muscle sarcomas. Very rare striated muscle sarcoma, fatty sarcoma, vascular sarcoma, fibrous sarcoma, sarcoma of nerve tissue.

Lymphomas of the small intestine is like that of the other part of the gastrointestinal tract (see tumour part of the stomach).

Endocrine cell tumours

Also known as silver-cell tumours, can be found elsewhere such as breast, thymus, liver, gallbladder, lungs, ovaries, and urethra, but most originate from anywhere in the digestive tract (from mouth to anus). No matter where the tumour is located, there is common histology unchanged.

Because the tumour has cancerous properties but grows slowly over many years, it is also called "malignant neoplasm" or "carcinoma-like" or "carcinoid", (carcinoma like, carcinoid).

Tumours come from endocrine cells of the gastrointestinal tract, i.e., Kulchitsky cells or chromium-loving intestinal cells (because of an affinity for chrome salts). Due to endocrine origin, tumour cells often contain secretory particles that have an affinity for dissolved silver salts (thus easily observed under an electron microscope). Some tumours have cells that can deposit dissolved silver salts, hence the name silver-loving cell tumours. Other tumours, due to less differentiation, do not have a silver-loving response.

Most of these tumours have the ability to secrete a type of amine product and peptide such as histamine, serotonin, 5-hydroxyethyl-tophane, ACTH, kallikrein and sometimes prostaglandin. Some of these substances can cause a systemic symptom, called a carcinoma-like syndrome or carcinoid syndrome. Because of these properties, these tumours are classified in the group of tumours of the APUDOMA diffuse endocrine system.

In terms of location, tumours are present in the appendix (35% of cases), small intestine (25%), rectum and sigmoid colon (12%), colon (except the appendix, 7%), oesophagus and stomach. (2%), lungs and bronchi (14%), elsewhere (5%). U in many positions at the same time in 20-30% of cases. Multifocal primary lesions are usually found in the small intestine due to a large number of endocrine cells located throughout the intestine.

Lesions are usually small, less than 3cm in diameter (rarely 4-5cm), round or plaque, very mobile, without surrounding tissue sticking. The mucosa is still intact. Very rarely, it attaches to the muscular layer or enlarges, the ulcer has the form of polyps or penetrates the intestinal wall to enter the mesenteric or peri-rectal tissue. Particularly in the appendix, the lesions are usually 1-2 cm small lumps, and can also penetrate the muscles and serosa.

No matter where in the gastrointestinal tract, the tumours are also yellow gray when cut in half, difficult to distinguish from other types of tumours.


Typical morphologies are nocytes on a sparse connective matrix. Sometimes these cells converge into tubular, lobed, rose-like form. These cells are very similar, homologous with a round nucleus, oval, dark-speckled chromatin with secretory cytoplasm (eosin-red stained, brown-yellow with chrome salts, black with haematoxylin, and sometimes metallic black with silver salts). Very rare macrophages, cells degenerate, mitosis. Despite their benign cell morphology, these cells can penetrate the intestinal wall.

Most tumours for metastasis to regional lymph nodes, liver, lungs, bones, if the tumour size is greater than 2 cm in the small intestine, greater than 5 cm in the colon. In contrast, in the appendix, the incidence of metastasis was only 0.2%.

Clinical manifestations: 

Patients with carcinoma-like tumour syndrome are influenced by tumour secretions.

Vasomotor disorders; erythema and cyanosis attacks (in most patients).

Increased bowel movements; diarrhoea, abdominal cramps, vomiting, and nausea (in most patients).

Tracheal spasm; coughing, shortness of breath, and hissing breath like asthma (in over one-third of patients).

Damage to the right heart; heart valve thickening and narrowing with endocardial fibrosis (over 1/2 of patients).

Enlarged liver due to metastasis (some cases).


Adenocarcinoma of the small intestine is very rare. The anatomical morphology of a macroscopic disease resembles a glandular carcinoma of the colon, in the form of a ring-like, hard-eating, ulcerative lesion in the lumen of the intestine, rarely in a polyp-like mass.

Clinical manifestations are usually late when the tumours have progressed, including abdominal cramps, nausea, vomiting, and weight loss. Tumours can penetrate the intestinal wall, metastasis of regional lymph nodes, liver, or further metastasis.

Despite metastasis, the 5-year survival rate is still 10% if widely cut.


As with all parts of the gastrointestinal tract, sarcomas can be found in the small intestine, which originates from the stromal lining of the intestinal wall but is very rare.

The macroscopic morphology of the sarcomas is relatively similar, in the form of a multilobular, soft, necrotic, haemorrhagic mass.

The microscopic morphology is similar elsewhere, be it smooth muscle sarcoma, rhabdomyosarcoma, fatty sarcoma, vascular sarcoma, fibrosarcoma, neurologic sarcoma. Most of these sarcomas, when found to have large size and have metastasized through the bloodstream.