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Chapter 27

Chapter 27

Digestive System

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 …
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 …
During digestion in the small intestine, macromolecules— carbohydrates, proteins, and fats — are broken down into their simplest forms. These …
Helicobacter pylori is a gastric pathogen that is present in half of the global population and is a significant cause of morbidity and mortality in …
Non-alcoholic steatohepatitis (NASH) is the most common chronic liver disease in the United States, affecting more than 70 million Americans. NASH can …
The squamous epithelium of the esophagus is directly exposed to the environment, continuously facing foreign antigens, including food antigens and …