Secretin

Your body has a tiny helper. It is a chemical messenger. This helper lives in your small gut.

It works when food enters your gut. The food can be very sour. This sourness can hurt your body. The helper stops the sourness.

It tells your stomach to slow down. It tells your pancreas to help. The pancreas sends out a liquid. This liquid stops the sourness.

This helper also helps with water. It helps your body keep the right amount. It even helps you feel full.

Your body is very smart. It knows how to stay safe.

Your body uses a special messenger called secretin. It is a hormone. A hormone is a chemical that travels through your blood to send messages. Secretin is made in a part of your small gut called the duodenum.

Secretin works to keep your gut safe. When food leaves your stomach, it can be very acidic. This acid can be harsh. When the duodenum senses this acid, it lets out secretin.

Secretin then sends messages to other parts of your body. It tells the pancreas to make a liquid called bicarbonate. This liquid is a base. It works to neutralize the acid. It also tells the stomach to stop making so much acid. This helps the duodenum stay at a safe level.

Secretin does more than just help with food. It also helps your body manage water. This is called osmoregulation. It helps the kidneys and the brain keep the right amount of water in your body. It can even help tell your brain when you should stop eating.

Secretin is a special hormone that keeps your body in balance. A hormone is a chemical messenger that travels through your blood. Secretin is made in the S cells of your duodenum. The duodenum is the first part of your small intestine. This hormone helps manage water levels and protects your gut. It makes sure the environment in your intestine stays safe for digestion. Without it, the acid from your stomach could cause damage.

This messenger works in a very clever way. First, it starts as a larger protein called prosecretin. When stomach acid enters the duodenum, it activates this prosecretin into active secretin. Once active, secretin tells the pancreas to release a liquid full of bicarbonate. Bicarbonate is a base that neutralizes harsh stomach acid. Secretin also tells the stomach to slow down its acid production. This step-by-step process creates a safe space for digestive enzymes to work.

Scientists first discovered how this works in 1902. Two researchers named William Bayliss and Ernest Starling studied digestion. They noticed the pancreas released juices even when nerves were cut. This proved the signal was a chemical, not a nerve message. They named this new messenger secretin. Starling later created the word "hormone" in 1905 to describe these messengers. While secretin was famous, adrenaline was actually the first hormone discovered in 1894.

Secretin has a very specific structure made of 27 amino acids. It has a molecular weight of 3055. In humans, the SCT gene provides the instructions to make it. In 2007, researchers found it also helps with osmoregulation. This is the way your body manages water and salt. It acts on the hypothalamus, the pituitary gland, and the kidneys. This helps keep your body's water levels just right.

You can think of secretin like a smart thermostat for your body. Just as a thermostat senses heat and turns on the air, secretin senses acid. When the acid level gets too high, secretin turns on the bicarbonate. It also helps your brain decide when you have eaten enough. In mice, secretin can actually help reduce how much food they eat. Doctors even use a man-made version of secretin to test how well a pancreas is working.

Secretin is a peptide hormone that maintains water homeostasis throughout the body. Homeostasis is the process of keeping a stable internal environment. This hormone plays a vital role in managing the environment of the duodenum. The duodenum is the first part of the small intestine. It regulates secretions in the stomach, the pancreas, and the liver. In humans, the SCT gene provides the instructions to encode this peptide. Secretin is essential because it protects the small intestine from damage caused by stomach acid.

The production of secretin begins in specialized S cells. These cells are located in the intestinal glands of the duodenum mucosa. They are also found in smaller numbers in the jejunum. Secretin is released when the pH level in the duodenum drops between 2 and 4.5. This acidity comes from hydrochloric acid in the chyme. Chyme is the mixture of food and gastric juices. When this acid enters the duodenum through the pyloric sphincter, it triggers the S cells. The secretion of secretin also increases when protein digestion products bathe the mucosa.

Secretin works through a precise chemical mechanism to regulate pH. It starts as a larger precursor protein called prosecretin. This precursor contains 120 amino acids, including a signal peptide and a spacer. When gastric acid arrives, it activates this prosecretin into mature secretin. The mature hormone is a linear peptide made of 27 amino acids. It has a molecular weight of 3055. Once active, secretin targets the pancreas by binding to receptors on the plasma membrane of centroacinar cells. This binding stimulates adenylate cyclase activity. This process converts ATP into cyclic AMP, which acts as a second messenger to trigger the release of bicarbonate-rich fluid.

This bicarbonate-rich fluid serves a critical purpose in digestion. Bicarbonate is a base that neutralizes the acidic chyme. This neutralization allows digestive enzymes like pancreatic amylase and pancreatic lipase to function optimally. Secretin also works to reduce acid production in the stomach. It does this by stimulating the release of somatostatin. It also inhibits the release of gastrin in the pyloric antrum. Finally, it can directly downregulate the acid secretory mechanics of the parietal cells. Additionally, secretin stimulates cholangiocytes in the bile duct to secrete bicarbonate and water. This protects the duct from bile acids by controlling the pH and promoting flow.

The discovery of secretin changed how we understand biology. In 1902, William Bayliss and Ernest Starling studied how the nervous system controls digestion. They observed that the pancreas secreted juices when food passed into the duodenum. However, they found that this happened even when they cut all the nerves to the pancreas. This proved the signal was not controlled by the nervous system. Instead, they determined a substance in the bloodstream stimulated the pancreas. They named this substance secretin. Starling later coined the term "hormone" in 1905 to describe these chemical messengers.

While secretin is a famous discovery, it was not the first hormone identified. In 1894 and 1895, George Oliver and Edward Albert Schäfer published findings on adrenaline. They showed that an adrenal extract could increase blood pressure and heart rate. Beyond digestion, secretin is involved in osmoregulation. Osmoregulation is the control of water and salt levels in the body. In 2007, researchers found secretin plays a role in this process by acting on the hypothalamus and the pituitary gland. It helps regulate renal water reabsorption in the kidneys. It also helps carry out the central effects of angiotensin II.

Secretin also influences energy balance and medical diagnostics. In the hypothalamus, secretin is found in the paraventricular and arcuate nuclei. These areas are primary sites for regulating body energy homeostasis. Research in mice shows that injecting secretin can reduce food intake. This suggests it has an anorectic role, meaning it can suppress appetite. In medicine, doctors use a recombinant human version of secretin for diagnostic tests. They inject it to check pancreatic function. This can be done using magnetic resonance imaging to see the pancreatic output.