Regulation of Gastrointestinal Secretions

A group of related short-chain polypeptides secreted by G cells in the stomach and duodenum. It is triggered by the presence of food in the stomach or duodenum.

A mixture of several related polypeptides released by cells in gastric glands, pancreas, and hypothalamus. It inhibits various secretions from the stomach, duodenum, and pancreas, slowing down nutrient absorption.

A polypeptide released by duodenal cells in response to low pH (increased acidity) in the duodenum. It stimulates bicarbonate secretion from the pancreas to neutralize chyme and inhibits further stomach acid secretion.

A group of similar small polypeptides secreted by cells in the duodenum and jejunum primarily in response to the presence of lipids and their breakdown products. It stimulates the release of bile from the gallbladder and pancreatic enzymes.

A polypeptide released by cells in the small intestine and other parts of the body. It helps with relaxation of smooth muscle in the digestive tract, stimulates the secretion of digestive enzymes, and has other regulatory functions.

The autonomic nervous system (ANS) and the enteric nervous system (ENS) collaborate to regulate gastrointestinal secretions. The ANS involves the sympathetic and parasympathetic branches, influencing overall digestive activity. The ENS, known as the 'gut brain', controls local digestive processes.

Different components of the gastrointestinal tract have distinct secretions, ensuring proper digestion. The stomach secretes gastric juice, the pancreas releases pancreatic juice, the liver produces bile, and the small and large intestines secrete mucus and enzymes.

Hormonal regulation of gastrointestinal secretions often involves feedback mechanisms. For instance, upon eating, the release of gastrin, a hormone promoting stomach acid secretion, is eventually regulated by somatostatin, a hormone that inhibits gastric secretions.

The small intestine secretes bicarbonate-enriched mucous to neutralize acidic chyme coming from the stomach, and antibacterial lysozyme and defensins.

The colon secretes mucin-rich mucous, which aids in lubrication and protection.

The pancreas secretes proteolytic enzyme precursors (trypsinogen, chymotrypsinogen, etc.), pancreatic lipase for fat digestion, pancreatic amylase for carbohydrate digestion, and ribonucleases.

The liver produces bile, which contains bile salts and acids that emulsify fats, aiding in digestion.

The liver synthesizes and releases plasma proteins, VLDLs (very low density lipoproteins), and HDLs (high density lipoproteins) into the blood.

The enteric nervous system (ENS) monitors and controls the digestive system via sensory receptors that respond to stimuli like stretch, temperature, osmotic pressure, and chemicals.

The vagus nerve carries sensory information from the digestive system to the central nervous system (CNS).

The parasympathetic nervous system stimulates digestive activity by controlling salivary glands, most of the digestive tract, and the colon.

The sympathetic nervous system influences the digestive system by controlling the salivary glands and most of the digestive tract.

Digestive reflexes are automatic responses triggered by food in the digestive tract. They are named based on where they begin and where they have an effect.

The gastrocolic reflex happens when food enters the stomach, triggering increased colon motility.

The esophagus secretes a mucous layer for lubrication and protection.

The stomach secretes hydrochloric acid, pepsinogen, mucus, gastroferrin, and intrinsic factor, which are essential for digestion and absorption.

Cholecystokinin (CCK) is a hormone that plays a critical role in digestion. It is released in the small intestine in response to the presence of fats and proteins. CCK stimulates the gallbladder to contract, releasing bile into the duodenum to emulsify fats, making them easier to digest. It also prompts the pancreas to secrete digestive enzymes, slowing down gastric emptying to allow for efficient fat digestion. Additionally, CCK stimulates the satiety center, contributing to feelings of fullness after eating.

Vasactive Intestinal Polypeptide (VIP) is a hormone that acts as a neurotransmitter in the digestive system. It is released at loose synapses and plays a role in vasodilation, widening blood vessels in the gastrointestinal tract during digestion. This widening allows for increased blood flow to the digestive area, providing oxygen and plasma for efficient functioning of the digestive cells, including the enterocytes that produce mucous secretions. Ultimately, this enhances nutrient absorption from the gut.

The Enteric Nervous System (ENS) is a complex network of neurons located in the digestive tract, running from the esophagus to the external anal sphincter. It is often referred to as the 'brain of the gut' and is comprised of as many neurons as the spinal cord. The ENS, with its two layers, the Myenteric Plexus and Submucosal Plexus, plays a crucial role in regulating digestion.

The Myenteric Plexus, also known as Auerbach's Plexus, is one of the two main layers of the Enteric Nervous System. It primarily regulates the contractions of smooth muscle, facilitating peristalsis (wave-like muscle contractions that move food through the digestive tract) and sphincter control.

The Submucosal Plexus, also known as Meissner's Plexus, is the other major layer of the Enteric Nervous System. It primarily regulates secretions and blood flow along the digestive tract. This includes controlling the release of digestive juices and ensuring adequate blood supply to support digestive processes.

The autonomic nervous system, specifically the parasympathetic nervous system, plays a crucial role in regulating gastrointestinal function. While not directly innervating all gastrointestinal cells, the parasympathetic nervous system primarily modulates the activity of the Enteric Nervous System (ENS), enhancing digestive processes during meals.

The Enteric Nervous System (ENS) functions autonomously (without direct input from the brain) but is also modulated by the autonomic nervous system. The ENS contains motor neurons that trigger secretions and muscle contractions, interneurons that coordinate local control, and sensory neurons that relay feedback to the central nervous system.