# Brunner's glands

Brunner's glands (or duodenal glands) are compound tubuloalveolar submucosal glands found in that portion of the duodenum proximal to the hepatopancreatic sphincter (i.e sphincter of Oddi).
For decades, it was believed that the main function of the glands is to secrete alkaline (bicarbonate-containing) mucus in order to:
* protect the duodenum from the acidic content of chyme (which enters the duodenum from the stomach),
* provide an alkaline environment which promotes the activity of intestinal enzymes,
* lubricate the intestinal walls.
However, more recent studies have demonstrated that Brunner’s glands actually act as major modulators of the gut microbiome and systemic immunity.
They are the distinguishing feature of the duodenum, and are named for the Swiss physician who first described them, Johann Conrad Brunner.

## Structure

Duodenal glands are situated within the mucosa and submucosa of the duodenum. They are most abundant near the pylorus, growing shorter and more sparse distally towards the terminal portion of the duodenum.
The duodenum can be distinguished from the jejunum and ileum by the presence of Brunner's glands in the submucosa.

## Histology

Their excretory cannals are tortuous, opening at the bases of the villi.
Two forms of duodenal glands are distinguished: the external group (which are more voluminous and extend into the duodenal submucosa), and the internal group (which are smaller and are situated within the duodenal mucosa).

## Function

They also secrete epidermal growth factor, which inhibits parietal and chief cells of the stomach from secreting acid and their digestive enzymes. This is another form of protection for the duodenum.
The Brunner glands, which empty into the intestinal glands, secrete an alkaline fluid composed of mucin, which exerts a physiologic anti-acid function by coating the duodenal epithelium, therefore protecting it from the acid chyme of the stomach. Furthermore, in response to the presence of acid in the duodenum, these glands secrete pepsinogen and urogastrone, which inhibit gastric acid secretion.
More recent studies have demonstrated that Brunner’s glands are major modulators of the gut microbiome and systemic immunity. Studies conducted by Ivan De Araujo’s laboratory revealed that Brunner’s gland secretions promote the proliferation of probiotics and protect the host against foreign pathogens.

## Clinical significance

Hyperplasia of Brunner glands with a lesion greater than 1 cm was initially described as a Brunner gland adenoma. Several features of these lesions favor their designation as hamartomas, including the lack of encapsulation; the mixture of acini, smooth muscles, adipose tissue, Paneth cells, and mucosal glands; and the lack of any cell atypia. These hamartomas are rare, with approximately 150 cases described in the literature. It is estimated that they represent approximately 5–10% of benign duodenal tumors. They are variable in size, typically 1–3 cm, with only a few reported cases of lesions larger than 5 cm.
Most patients with Brunner gland hamartomas are asymptomatic or have nonspecific complaints such as nausea, bloating, or vague abdominal pain.
Most reports in the literature describe local surgical resection of Brunner gland hamartoma via duodenotomy. Increasingly, successful endoscopic resection has been reported and is primarily used for pedunculated Brunner gland hamartomas. The endoscopic approach in selective cases appears to be safe, less invasive, and less costly.
Consistent with the more recent idea that Brunner’s glands influence systemic immunity via the microbiome, patients who had the duodenal bulb removed (where the glands are mostly located) showed greater alterations in immune factors compared to patients having more distal parts of the duodenum removed.