Glossary of Physiology Terms

Anus

The most distal sphincter in the gastrointestinal (GI) tract.

Chyme

The semi-solid, partially-digested contents of the stomach that exit via the pyloric valve to enter the duodenum (initial region) of the small intestine.

Colon

The colon is part of the large intestine within the digestive tract that is located between the cecum and the rectum. The colon is subdivided into the ascending colon, transverse colon, descending colon, and sigmoid colon.

Duodenum

The first region (i.e., most proximal region) of the small intestine. Chyme leaving the stomach (through the pyloric valve) first enters the duodenum. The contents of the duodenum empty into the jejunum (middle region of the small intestine). In adult humans, the duodenum is about 25-38 cm (10-15 inches) long.

Jejunum
Ileum

Electrogenic

An electrogenic transport process is one that leads to the translocation of net charge across the membrane. For example, ion channels such as Na⁺, K⁺, Ca²⁺, and Cl⁻ channels are electrogenic.

The Na⁺/K⁺ ATPase is electrogenic because for every ATP molecule hydrolyzed, 3 Na⁺ ions are transported out of the cell and 2 K⁺ ions are transported into the cell (leading to the translocation of one net positive charge out of the cell).

Many secondary active transporters are also electrogenic. For example, the Na⁺/glucose cotransporter (found in the small intestine and kidney proximal tubules), transports 2 Na⁺ ions and 1 glucose molecule into the cell across the plasma membrane (leading to the translocation of two net positive charges into the cell per transport cycle).

I band

The I band is the region of a striated muscle sarcomere that contains thin filaments. This region is closest to the Z disk, and is the lightest region of the sarcomere when viewed in under the light or electron microscope. The I band is occupied by the thin filaments only. Each Z disk runs through the middle of the I band. Therefore, half of each I band belongs to one sarcomere, and the other half belongs to the neighboring sarcomere. The I band shortens as the muscle contracts and the sarcomere shortens.

A band
H zone
M line
Z disk

Ileum

The last region (i.e., most distal region) of the small intestine. Ileum receives the contents of the jejunum and, in turn, the contents of ileum leave the small intestine by emptying into the cecum. In adult humans, the ileum is about 2-4 meters (about 6.5-13 feet) long.

Duodenum
Jejunum

Intrinsic factor

A glycoprotein released by parietal cells (also know as oxyntic cells) located in the fundus region of the stomach. Intrinsic factor is required for vitamin B₁₂ absorption in the small intestine.

Jejunum

The middle region of the small intestine between the duodenum and the ileum. The jejunum receives the contents of the duodenum and, in turn, its contents empty into the ileum. In adult humans, the jejunum is about 2.5 meters (about 8 feet) long.

Duodenum
Ileum