Pylorus

The pylorus (/paɪˈlɔːrəs/ or /pɪˈloʊrəs/) connects the stomach to the duodenum. The pylorus is considered as having two parts, the pyloric antrum (opening to the body of the stomach) and the pyloric canal (opening to the duodenum). The pyloric canal ends as the pyloric orifice, which marks the junction between the stomach and the duodenum. The orifice is surrounded by a sphincter, a band of muscle, called the pyloric sphincter. The word pylorus comes from Greek πυλωρός, via Latin. The word pylorus in Greek means "gatekeeper", related to "gate" (Greek: pyle) and is thus linguistically related to the word "pylon".

The pylorus is the furthest part of the stomach that connects to the duodenum. It is divided into two parts, the antrum, which connects to the body of the stomach, and the pyloric canal, which connects to the duodenum.

The antrum also called the gastric antrum or the pyloric antrum is the initial portion of the pyloric region. It is near the bottom of the stomach, proximal to the pyloric sphincter, which separates the stomach and the duodenum. It may temporarily become partially or completely shut off from the remainder of the stomach during digestion by peristaltic contraction of the prepyloric sphincter; it is demarcated, sometimes, from the pyloric canal by a slight groove.

The pyloric canal (Latin: canalis pyloricus) is the opening between the stomach and the duodenum. The wall thickness of the pyloric canal is up to 3 millimeters (mm) in infants younger than 30 days, and up to 8 mm in adults.

The pyloric sphincter, surrounding the pyloric orifice is a strong ring of smooth muscle at the end of the pyloric canal which lets food pass from the stomach to the duodenum. It acts as a valve, controlling the outflow of gastric contents into the duodenum and release of chyme. Its function is modulated by both the central and enteric nervous systems. It receives sympathetic innervation from the celiac ganglion.

Under microscopy, the pylorus contains numerous glands, including gastric pits, which constitute about half the depth of the pyloric mucosa. They consist of two or three short closed tubes opening into a common duct or mouth. These tubes are wavy, and are about one-half the length of the duct. The duct is lined by columnar cells, continuous with the epithelium lining the surface of the mucous membrane of the stomach, the tubes by shorter and more cubical cell which are finely granular. The glands contain mucous cells and G cells that secrete gastrin.

The pylorus also contains scattered parietal cells and neuroendocrine cells. These endocrine cells include D cells, which release somatostatin, responsible for shutting off acid secretion. (There is a second hormone-sensitive population near the fundus.) Unstriated muscles, which are entirely involuntary, are located at the pylorus.

The pylorus is one component of the gastrointestinal tract. Food from the stomach, as chyme, passes through the pylorus to the duodenum. The pylorus, through the pyloric sphincter, regulates entry of food from the stomach into the duodenum.