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Chapter 27
The human digestive system consists of two major parts: the gastrointestinal — GI — tract and the accessory organs. The GI tract begins with ...
The peritoneum is the body's largest serous membrane enveloping the abdominal cavity. It has two portions — the parietal and visceral peritoneum ...
The gastrointestinal tract has four tissue layers. The innermost layer, mucosa, is characterized as a mucous membrane. It consists of an epithelium, ...
The gastrointestinal tract has its own intrinsic set of nerves forming the enteric nervous system or ENS, which is partly controlled by the ...
Along with the enteric nervous system, digestive activity is regulated by mechanical and chemical stimuli and hormones. Various receptors located within ...
Blood supply to the digestive system is facilitated through the splanchnic circulation. The celiac trunk and the mesenteric arteries provide oxygenated ...
The oral cavity, or mouth, comprises the lips, cheeks, palate, and tongue. The walls of the mouth are lined with thick, stratified squamous epithelium, ...
The tongue, an accessory digestive organ, forms the floor of the oral cavity and extends into the oropharynx. It is composed of two types of skeletal ...
Saliva is composed of 97 to 99.5% water. The remaining proportion includes enzymes such as lipases and amylases, electrolytes, dissolved gasses, IgA, ...
Teeth are accessory digestive organs that aid in physically breaking down food. The gums, or gingivae, of both the mandible and maxilla hold the ...
The tooth has a crown and a root connected via a constricted area known as the neck. The crown is visible above the gingivae and is protected by enamel. ...
The esophagus is a muscular conduit approximately 25 cm long that helps transport food from the mouth to the stomach. It courses through the mediastinum ...
Deglutition, or swallowing, is a mechanism that transports food from the mouth to the stomach. This process has three stages — the buccal, ...
The stomach is a J-shaped organ connecting the esophagus to the duodenal end of the small intestine in the abdominal cavity. The size and shape of the ...
The stomach wall consists of several layers, including the serosa, muscularis externa, submucosa, and mucosa. The outermost layer, the serosa, is composed ...
The specialized enteroendocrine cells of the gastric glands secrete most of the digestive hormones. These cells, such as the G, D, and ...
Digestion has three overlapping phases — cephalic, gastric, and intestinal — based on the location of their control center. The cephalic phase ...
Local, neural and hormonal mechanisms trigger the gastric phase after food enters the stomach, lasting approximately 3-4 hours. The incoming food bolus ...
After the gastric phase, the chyme from the stomach moves into the small intestine, gradually decreasing the stomach distention. In contrast, the arrival ...
In the gastric glands, the parietal cells are involved in hydrochloric acid or HCl formation. These cells first synthesize carbonic acid, which ...
Gastric motility is the coordinated movement of stomach muscles and secretions, which propels food and liquids through the stomach. As the swallowed food ...
Gastric emptying is the gradual release of chyme from the stomach into the duodenum. Stomach distention triggers the gastroenteric reflex, releasing ...
The liver is the largest gland in the body, weighing approximately 1.4 kg in adults. It is wedge-shaped and located more in the right hypochondriac and ...
The liver comprises several histological components, such as hepatocytes, bile canaliculi, and sinusoids. Hepatocytes are specialized epithelial cells ...
Bile is a yellow-green alkaline liquid secreted by the liver into the right and left hepatic ducts and then into the common hepatic duct. From here, it ...
The gallbladder is a muscular sac located in a shallow fossa on the inferior surface of the liver. It measures about 10 cm in length and is roughly the ...
Liver functions primarily include bile production, metabolic regulation, and hematological functions. During carbohydrate metabolism, the liver regulates ...
Prominent liver and gallbladder diseases include cirrhosis, hepatitis, non-alcoholic fatty liver disease or NAFLD, and gallstones. Cirrhosis is a liver ...
The pancreas is a pinkish-gray organ located behind the stomach. It extends from the duodenum to the spleen. It can be divided into a broad head located ...
Pancreatic juice is a colorless liquid composed of water, salts, sodium bicarbonate, and enzymes secreted by the exocrine cells. During digestion, chyme ...
The small intestine is a tubular structure extending from the pyloric sphincter of the stomach to the ileocecal valve of the large intestine. This long, ...
The histology of each part of the small intestine varies. The jejunum has the most prominent folds and villi, while the distal ileum has fewer folds but ...
Mechanical digestion in the small intestine involves two types of movements — segmentations and migration motility complexes or MMC. Segmentations ...
The large intestine surrounds the small intestine on three sides and extends from the ileocecal valve to the anus. The large intestine starts at the ...
The wall of the large intestine comprises four layers: the mucosa, submucosa, muscularis, and serosa. The mucosa, lined by intestinal glands, consists of ...
The vast and varied community of bacteria colonizing the large intestine forms the gut microbiome. Bacteria start residing in the gut at birth and ...
The final stages of digestion occur in the large intestine when the cecum receives chyme, which has little nutritional value except for the indigestible ...
During digestion in the small intestine, macromolecules— carbohydrates, proteins, and fats — are broken down into their simplest forms. These ...
After 3 to 10 hours in the large intestine, chyme undergoes considerable water loss to form feces, the end product of digestion. It comprises undigested ...
The gastrointestinal tract of the digestive system is susceptible to various disorders. The incompetence of the lower esophageal sphincter results in the ...
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