BRUNNER'S GLANDS: CHARACTERISTICS, HISTOLOGY, FUNCTIONS, PATHOLOGIES - BIOLOGY - 2024

The Brunner 's glands are glands of the duodenum having the function of secreting a liquid alkaline response to the parasympathetic stimulation. Located in the submucosal layer of the duodenum wall, they are acinotubular glands with curved ducts and branching ends that open into the crypts of Lieberkühn through the muscularis mucosae.

These glands are responsible for most of the secretion of intestinal juice, a clear fluid with abundant mucus that contains bicarbonate and a hormone called urogastrone, which is a human epidermal growth factor and an inhibitor of gastric HCl secretion.

Small intestine anatomy. Brunner's glands are found in the portion corresponding to the Duodenum (Source: BruceBlaus. When using this image in external sources it can be cited as: Blausen.com staff (2014). «Medical gallery of Blausen Medical 2014». WikiJournal of Medicine 1 (2). DOI: 10.15347 / wjm / 2014.010. ISSN 2002-4436. Via Wikimedia Commons)

This secretion dilutes and neutralizes the acid gastric content that empties into the duodenum. The duodenum is the shortest segment of the small intestine, about 25 cm long, which connects the stomach to the jejunum.

Parasympathetic vagal (cholinergic) stimulation stimulates the secretion of cells in Brunner's glands, increasing the production of mucus and fluid that is released into the duodenum. The ingestion of irritating foods (physical or chemical) also stimulates the secretion in these glands.

There are multiple pathologies that affect the function of the duodenum by affecting Brunner's glands, since it receives pancreatic and bile secretions through the pancreatic and common bile ducts, respectively.

characteristics

Brunner's glands were originally described as duodenal glands by the entomologist Carl Brunner von Wattenwyl (1823-1914) in 1888. However, they are currently identified as submucosal glands, with a similar structure and function to the pyloric glands in the stomach.

The cellular structure of these glands has only been described in guinea pigs and felines. While in the guinea pig the cells of these glands have the typical structure of secretory glands, in cats these look more like serous glands.

Some doctors suggest that Brunner's glands in humans are very similar to those in guinea pigs. However, they also present some serous gland characteristics, as in felines.

Therefore, it can be considered that Brunner's glands in humans are in an "intermediate" category between those of both types of animals.

The general characteristics of Brunner's glands in mammals are:

- Typical morphology of spiral or branched tubular exocrine glands.

- Approximate length of 1 to 3 mm.

- Abundant content of cytosolic organelles.

- Small secretory granules in the apical region.

- Viscous secretions, rich in carbohydrates and with little or no digestive enzymes.

In the proximal portion of the duodenum, near its junction with the stomach, these glands are very abundant and their density decreases as they approach the distal end of the duodenum.

Histology

Brunner's glands are especially abundant in the mucosa and submucosa that surround the duodenal musculature in the small intestine.

These are tubular in shape and ramify in a highly compressed manner along the epithelia of the duodenum and jejunum. All the cells of these glands have the typical shape of glandular acini.

The cells of these glands are specialized in the secretion of substances; They are shaped like ducts grouped in arboriform clusters that end in specialized pores for secretion.

Photograph of the histological section of a Brunner's gland (Source: Leonardo M. Lustosa via Wikimedia Commons)

Some doctors classify these glands as one of the most important and abundant multicellular exocrine glands within the human body, since they are responsible for the secretion of mucus, pepsinogen and the hormone urogastrone in response to acidic agents.

Various studies have shown that these glands progressively decrease their coverage of the small intestine, inversely proportional to age (the older, the fewer glands).

In infants, it is estimated that the glands occupy 55% of the duodenum and in people over 50 years of age they only occupy 35% of the surface of the intestine.

Brunner's glands are activated in response to acidic substances in the duodenum and different investigations have found that the hormone secretin is a powerful activator of its secretion mechanisms. However, the mechanisms that trigger its activation are not yet understood with certainty.

Features

Brunner's glands are responsible for neutralizing the acidity of gastric juices, therefore, mucus and alkaline substances such as bicarbonate that they secrete are one of the main mechanisms for the protection of the intestine against high concentrations of hydrochloric acid (HCl).

The hormone urogastrone, secreted by Brunner's glands, has inhibitory effects on the secretion of acids in the stomach. The secretion of this hormone is sensitive to excessive alcohol consumption, which is why alcoholics usually suffer from irritations in the pancreas.

Urogastrone has a stimulating effect on the smooth muscles that allows the peristaltic movements of the walls of the intestine responsible for the movement of the food bolus throughout its length.

The mucus secreted by these glands, on the other hand, lubricates the interior of the small intestine so that this movement can take place.

Pathologies

Pathologies caused by conditions in Brunner's glands range from hyperplasias due to hyperstimulation to the formation of tumors or neoplasms.

Of these pathologies, the most common are the product of excessive growth of the glands, known as “Brunner's gland adenomas”. These are not very frequent and not lethal either, since they represent approximately 0.008% of all stomach autopsies examined.

There are pathologies related to these glands that involve their proliferation or excessive regrowth and these have been classified into three groups:

Diffuse nodular hyperplasia or diffuse hyperplasia

It occurs in patients with ulcers in the duodenum, generally due to hyperstimulation of the glands that secrete gastric acids to the stomach, resulting in hyperacidification and acute inflammation of the duodenum.

Circumscribed nodular hyperplasia or hyperplasia limited to the duodenal bulb

This disease is the most common in Brunner's glands and causes regrowth of small glandular nodules in the proximal duodenum region. Regrowths are generally small tumors.

Adenomatous hyperplasia or hamartoma of Brunner's glands

It is a lesion located in a single tumor, with sizes around 4 cm. Affected cellular polyps are generally pedunculated and are associated with duodenitis or inflammation of the duodenum.

References

1. Friend, DS (1965). The fine structure of Brunner's glands in the mouse. The Journal of cell biology, 25 (3), 563-576.
2. Henken, EM, & Forouhar, F. (1983). Hamartoma of Brunner's gland causing partial obstruction of the ileum. Journal of the Canadian Association of Radiologists, 34 (1), 73-74.
3. Hol, JW, Stuifbergen, WNHM, Teepen, JLJM, & van Laarhoven, CJHM (2007). Giant Brunner's Hamartomas of the Duodenum and Obstructive Jaundice. Digestive surgery, 24 (6), 452-455.
4. Marcondes Macéa, MI, Macéa, JR, & Tavares Guerreiro Fregnani, JH (2006). Quantitative study of Brunner's Glands in the Human Duodenal Submucosa. International Journal of Morphology, 24 (1), 07-12.
5. Rocco, A., Borriello, P., Compare, D., De Colibus, P., Pica, L., Iacono, A., & Nardone, G. (2006). Large Brunner's gland adenoma: case report and literature review. World Journal of Gastroenterology: WJG, 12 (12), 1966.
6. Stening, GF, & Grossman, MI (1969). Hormonal control of Brunner's glands. Gastroenterology, 56 (6), 1047-1052.
7. Yadav, D., Hertan, H., & Pitchumoni, CS (2001). A giant Brunner's gland adenoma presenting as gastrointestinal hemorrhage. Journal of clinical gastroenterology, 32 (5), 448-450.