Digestive System PDF

Digestive system Participates in the ingestion, chewing, swallowing, digestion and absorption of food, as well as in the elimination of indigestible remains. It is made up: - Oral cavity - Digestive tube - Esophagus - Stomach - Intestine - Associated glands - Salivary glands - Liver - Pancrea...

Digestive system Participates in the ingestion, chewing, swallowing, digestion and absorption of food, as well as in the elimination of indigestible remains. It is made up: - Oral cavity - Digestive tube - Esophagus - Stomach - Intestine - Associated glands - Salivary glands - Liver - Pancreas Oral cavity Pharynx Parotid Salivary glands Sublingual Submandibular Liver Esophagus Stomach Pancreas Gallbladder Duodenum Transverse colon Jejunum Ascending colon Ileum Large intestine Descending colon Cecum Sigmoid colon Rectum Anus Small intestine Oral cavity Outwardly it is covered by the cheeks and lips, covered by thin skin with sweat glands, sebaceous glands and hair follicles. After the connective tissue of the skin, there is skeletal muscle that controls the movement of lips and cheeks. The interior of the oral cavity is lined by a stratified flat epithelium. In areas where there is more friction, this epithelium will also be keratinized. After the epithelium there is a dense irregular connective tissue with numerous minor salivary glands and the ducts of the main salivary glands. Saliva protects the entire oral mucosa and moistens the food, lubricating it and beginning digestion due to its enzymatic content. In the gums, after the conjunctiva, there is spongy bone that holds the teeth. The palate also has spongy bone in the anterior area, forming the hard palate. On the back is the soft palate, which contains skeletal muscle that will help swallowing and closes the passage to the nasal cavity. It ends in an extension called the uvula. Tongue It is the largest structure of the oral cavity. It's found on the floor of the oral cavity and is composed mainly by skeletal muscle fibers that give it great mobility, help chew the food and mix it with saliva to form the food bolus. There is a dense connective tissue surrounding the muscle, and here we find minor salivary glands. Covering its surface there is a flat stratified epithelium (keratinized in some areas) and with taste buds on its dorsal side. Pharynx Hollow tubular organ common for the respiratory and digestive system. It is divided into three segments: - Nasopharynx: after the nasal cavity, above the soft palate. - Oropharynx: located behind the mouth. Coated by a stratified flat epithelium; has vascularized clusters with seromucosal glands, accumulations of lymphoid tissue (tonsils) and skeletal muscle that works when swallowing. - Laryngopharynx: communicates with the larynx and esophagus. It has a respiratory epithelium in the area that leads to the larynx and flat stratified epithelium where it faces the esophagus. Hard Palate Tongue Nasopharynx Soft Palate Oropharynx Epiglottis Laringopharynx Esophagus Trachea Digestive tube Its wall is formed by four layers: - Mucosa: the innermost layer is formed by an epithelium that covers the lumen of the organ, then a loose connective tissue known as lamina propria, which is very vascularized with glands and lymphoid tissue, and also a layer of smooth muscle called muscularis mucosae. - Submucosa: dense connective tissue very vascularized and innervated. - Muscularis externa/propria: two thick layers of smooth muscle. - Serosa (or Adventitia): dense connective tissue that surrounds the digestive tract and that in the abdominal organs will be lined by the simple flat epithelium of the peritoneum (mesothelium) Esophagus It is a muscular tube that transports the food bolus from the pharynx to the stomach. It goes down behind the trachea and goes through the diaphragm to enter the abdominal cavity. Its mucosa is lined by a squamous stratified epithelium. The lamina propria does not have glands except in the vicinity of the stomach, where they secrete mucus to protect the epithelium when the bolus passes into the stomach. The muscularis mucosae has only one longitudinal layer. The submucosa contains the glands, which are seromucous. esophageal The muscularis externa consists of the two usual layers, circular and longitudinal, but in the upper third, the longitudinal layer will be mostly skeletal muscle to help swallow. Covering everything it is the adventitia layer. Stomach It is the most dilated portion of the digestive tube, in the shape of a sack, which is responsible for processing the food to turn it into chyme. Anatomically it has a greater convex curvature and a smaller concave curvature. The narrow zone of the union with the esophagus is known as cardia, where the esophageal sphincter is. Next is the region known as the fundus, then the body and finally the pylorus, where there is another sphincter controlling the gastric emptying. Its mucosa has numerous folds and glands, the submucosa is dense connective tissue without glands, the muscular is composed of three layers, oblique, circular and longitudinal, and finally, it is surrounded by a serosa layer. Small intestine The digestion of the food finishes in the small intestine and most of the nutrients are absorbed in it. It is divided into three segments: • Duodenum • Jejunum • Ileum All segments have similar histological characteristics. In addition to the circular folds in the intestine, the mucosa is also folded and forms intestinal villi to further increase its surface. The intestinal villi are covered by a simple columnar epithelium with microvilli, which further increase the absorption surface. Small intestine mucosa In the epithelium, in addition to enterocytes (absorptive cells), there are Goblet cells that secrete mucus to protect this epithelium. Tubular glands called Lieberkühn crypts appear at the bottom of the intestinal villi. At the bottom of these crypts appear stem cells and other secretory cells, Paneth cells, with serous secretion. They secrete lysozyme to protect from bacterial infections. In addition, in this epithelium there are also enteroendocrine cells. The lamina propria is a loose connective tissue rich in lymphoid tissue, which in the ileum forms Peyer's patches. The other layers of the intestinal wall have the usual components. The presence of Brunner's glands in the submucosa of the duodenum is noteworthy. They are branched tubuloalveolar glands and secrete an alkaline mucus that helps neutralize the acid chyme. Large intestine It is the last segment of the digestive tract. It is formed by the cecum, colon (ascending, transverse, descending and sigmoid), rectum and anus. This segment absorbs most of the water and ions of the chyme and forms the feces for its elimination. The cecum and the colon present very similar characteristics. There are no villi on the mucosa, but there are numerous crypts of Lieberkühn with abundant goblet cells. No Paneth cells are found. There are also absorptive cells (the most numerous) and enteroendocrine cells. The lamina propria is formed by loose connective tissue with abundant lymphoid tissue. The muscularis mucosae and the submucosa have the usual characteristics. The muscularis forms three narrow bands known as colonic tapeworms. These tapeworms maintain a constant tone making a series of sacs in the colon. From the wall of the cecum, there is a narrow and elongated extension, the appendix, which presents a structure very similar to that of the colon, but with numerous folds and abundant lymphoid tissue. At the end of the large intestine is the rectum and the anal canal. The rectum has a structure like the colon, but with deeper and less numerous crypts. In the anal canal, the mucosa forms longitudinal folds. The lamina propria presents glands and in the submucosa, there are hemorrhoidal venous plexuses. The skeletal muscle of the pelvic floor forms the external sphincter. Participates in the ingestion, chewing, swallowing, digestion and absorption of food, as well as in the elimination of indigestible remains. It is made up: - Oral cavity - Digestive tube - Esophagus - Stomach - Intestine - Associated glands - Salivary glands - Liver - Pancreas Salivary glands All salivary glands function to produce saliva to moisturize the oral cavity and assist in the breakdown of carbohydrates in the mouth. The saliva also has antimicrobial activity. There are minor salivary glands throughout the oral cavity and three pairs of major salivary glands: - Parotid - Sublingual - Submandibular They are surrounded by a conjunctive capsule from which partitions emerge, dividing them into lobes. Serous acinus Duct Mucous acinus Liver Diaphragm It is the largest gland in the body and has both exocrine and endocrine functions. Falciform ligament Left lobe Gallbladder Right lobe Caudate lobe Common bile duct Hepatic duct Right lobe Left lobe Cystic duct Square lobe Gallbladder Hepatic vein Liver receives arterial blood from the hepatic artery, but also receives venous blood from the portal vein, which comes from the intestine. This artery and this vein enter together in the liver and branch out following the same route of the bile ducts. The artery, the vein and the duct form the portal triad. The triads divide the liver into lobules. In the end, the blood of the liver drains through the hepatic vein. Bile duct Portal vein Hepatic artery The liver lobules have a polygonal shape and at their vertices are the portal spaces with the portal triads. In the center of each lobule there is a central vein, which drains each lobule and will end in the hepatic vein. The lobule parenchyma is formed by liver cells called hepatocytes. Hepatocytes secrete bile and discharge it into the bile ducts. Through these ducts, the bile reaches the gallbladder and from there to the duodenum to intervene in the digestion of fats. This would be the exocrine secretion of the liver. Among the hepatocytes there are sinusoid capillaries that collect the endocrine secretion also secreted by the hepatocytes, which includes some factors of coagulation and growth. Portal triad Hepatic artery Central veins Portal vein Bile duct Sinusoids Hepatocytes Lobule Gallbladder Small pear-shaped organ located under the liver. It is responsible for storing and concentrating the bile sent by the liver, and then releases it into the duodenum to act on the digestion of lipids. Gallbadder Gallbadder Pancreas Located in the abdominal cavity, behind the stomach. It is surrounded by a conjunctive capsule from which partitions emerge inwards, dividing it into lobes. It is an amphicrine gland, that is, it has exocrine and endocrine secretions. The exocrine part of the pancreas is a compound tubuloacinar gland with serous secretion. Secretes the pancreatic juices through ducts that dump these products into the duodenum and will intervene in digestion. Dispersed among the pancreatic acini, there are several islets of Langerhans, rounded groups of hormone-secreting cells that constitute the endocrine part of the pancreas.