Duodenum

Anatomy, histology and physiology

The duodenum is the first section of the small intestine, connecting the stomach to the jejunum. It is approximately 25-30 cm long and is divided into four parts: the superior, descending, horizontal, and ascending parts. The duodenum plays a crucial role in digestion, as it receives chyme from the stomach along with bile from the liver and gallbladder, and pancreatic enzymes from the pancreas. These secretions help to neutralize stomach acid and break down nutrients for absorption in the intestines. The lining of the duodenum contains villi and microvilli, which increase the surface area for nutrient absorption. Additionally, the duodenum contains Brunner's glands, which secrete alkaline mucus to protect the intestinal lining from the acidic chyme.
It is here that a lot of digestion takes place, and where iron and calcium are absorbed.

Histology

      Mucosa: contains villi and microvilli to increase surface area for absorption. The epithelial cells lining the villi are primarily enterocytes (absorptive cells) and goblet cells (mucus-secreting cells).
      Submucosa: contains Brunner's glands, which secrete alkaline mucus to protect the duodenal lining from acidic chyme.
      Muscularis externa: consists of smooth muscle fibers arranged in circular and longitudinal layers, facilitating peristalsis and movement of chyme (food) through the intestine.
      Serosa: the outermost layer, a protective layer of connective tissue.

Pathology

Common diseases and conditions affecting the duodenum include:

Duodenal ulcers
These are open sores that develop on the inner lining of the duodenum, often caused by Helicobacter pylori infection or prolonged use of nonsteroidal anti-inflammatory drugs (NSAIDs). Symptoms include abdominal pain, nausea, and vomiting.
      Diagnosis is typically made through endoscopy and biopsy.
      Complications of duodenal ulcers can include bleeding, perforation, and obstruction.
      Treatment involves antibiotics to eradicate H. pylori, proton pump inhibitors (PPIs) to reduce stomach acid, and lifestyle modifications.

Celiac disease
An autoimmune disorder where ingestion of gluten leads to damage in the small intestine, including the duodenum. Symptoms include diarrhea, weight loss, and malnutrition.
      Diagnosis is made through serologic tests and confirmed with duodenal biopsy showing villous atrophy.
      Complications can include malabsorption, osteoporosis, and increased risk of certain cancers.
      Treatment involves a strict gluten-free diet to prevent further damage and promote healing of the intestinal lining.

Duodenitis
Inflammation of the duodenum, which can be caused by infections, medications, or autoimmune conditions. Symptoms include abdominal pain, nausea, and vomiting.
      Diagnosis is typically made through endoscopy and biopsy.
      Complications can include bleeding and perforation.
      Treatment involves addressing the underlying cause, such as antibiotics for infections or discontinuing offending medications. Proton pump inhibitors (PPIs) may also be used to reduce stomach acid and promote healing.

Duodenal atresia
A congenital condition where the duodenum is closed or absent, leading to intestinal obstruction in newborns. Symptoms include vomiting and abdominal distension.
      Diagnosis is typically made through prenatal ultrasound or postnatal imaging studies.
      Complications can include electrolyte imbalances and malnutrition.
      Treatment involves surgical correction to create a functional duodenum.

Duodenal tumors
Both benign and malignant tumors can develop in the duodenum, leading to symptoms such as abdominal pain, weight loss, and gastrointestinal bleeding.
      Diagnosis is typically made through endoscopy and biopsy.
      Complications can include obstruction and metastasis in the case of malignant tumors.
      Treatment depends on the type and stage of the tumor and may involve surgical resection, chemotherapy, or radiation therapy.
    Types of benign tumors:
    • Adenomas
    • Leiomyomas
    • Brunner's gland hyperplasia
    Types of malignant tumors:
    • Adenocarcinomas
    • Carcinoid tumors
    • Lymphomas