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Digestive System DIGESTIVE SYSTEM

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Ingegneria delle tecnologie per la salute Fondamenti di anatomia e istologia aa 2017-18 Digestive system DIGESTIVE SYSTEM After this lesson, you will be able to: • List and describe the functional anatomy of the organs and accessory organs of the digestive system • Discuss the processes and control of ingestion, propulsion, mechanical digestion, chemical digestion, absorption, and defecation • Discuss the roles of the liver, pancreas, and gallbladder in digestion • Compare and contrast the digestion of the three macronutrients Overview of the Digestive System function of DS is to break down the foods, release their nutrients, and absorb those nutrients (small intestine is workhorse of DS) DIGESTIVE SYSTEM digestive system does not work in isolation! DIGESTIVE SYSTEM Digestive System Organs Alimentary Canal Organs Accessory Structures = gastrointestinal (GI) tract or gut = a one-way = aids in breakdown of food : within tube about 7.62 meters (25 feet) in length during mouth, teeth and tongue begin life (10.67 meters (35 feet) after death, once mechanical digestion, whereas salivary smooth muscle tone is lost), beginning at mouth glands begin chemical digestion once and terminating at anus (between those: food products enter small intestine, pharynx, esophagus, stomach, and small and gallbladder, liver, and pancreas release large intestines) to fit functional needs of the secretions (bile + enzymes) essential for body digestion called accessory organs because main function of alimentary canal organs = they sprout from lining cells of nourish the body. developing gut (mucosa) and augment its Both mouth and anus are open to external function (= vital contributions), environment: thus, food and wastes within maintaining a connection to gut by way of alimentary canal are technically considered to ducts, even after complete development be outside the body. only through the process of absorption nutrients in food enter into and nourish the body’s “inner space.” DIGESTIVE SYSTEM Histology of Alimentary Canal Layers: 1. mucosa, 2. submucosa, 3. muscularis, 4. serosa, continuing with mesentery Throughout its length, the alimentary tract is composed of the same 4 tissue layers, varying details of their structural arrangements to fit their specific functions. Histology of Alimentary Canal mucosa = mucous membrane, because of mucus production of gut epithelium, consisting: a. epithelium = (in mouth, pharynx, esophagus, anal canal = non-keratinized, stratified squamous epithelium, in stomach, intestines = simple columnar epithelium); in direct contact with lumen: interspersed among epithelial cells = goblet cells, secreting mucus and fluid, + enteroendocrine cells, secreting hormones into interstitial spaces between cells; epithelial cells = very brief lifespan, averaging from only a couple of days (mouth) to about a week (gut). b. lamina propria = layer of loose connective tissue containing numerous blood and lymphatic vessels, transporting nutrients absorbed and also serving immune function by housing clusters of lymphocytes = mucosa-associated lymphoid tissue (MALT), particularly substantial in distal ileum (= Peyer’s patches) immune system evolved as means of defending against pathogens encountered within because alimentary canal is exposed to foodborne bacteria and foreign matter c. muscularis mucosa (not to be confused with the muscularis layer) = thin layer of smooth muscle in constant state of tension, pulling mucosa of stomach and small intestine into undulating folds, dramatically increasing surface area available for digestion and absorption Johann Conrad Peyer (26 December 1653 – 29 February 1712) was a Swiss anatomist who was a native of Schaffhausen. He studied medicine in Paris under Guichard Joseph Duverney (1648–1730), in Montpellier under Raymond Vieussens (1635–1713) and received his medical degree in 1681 at Basel. Later, he returned to Schaffhausen in order to practice medicine. Here, he performed research with Johann Jakob Wepfer (1620–1695), and Wepfer's son-in-law Johann Conrad Brunner (1653–1727). in 1677 Peyer published Exercitatio anatomico- medica de glandulis intestinorum earumque usu et affectionibus, in which he describes the eponymous Peyer's patches. These anatomical structures are aggregated lymphatic nodules found in the lining of the small intestine. He was also the author of an influential work on veterinary medicine titled Merycologia sive de Ruminantibus et Ruminatione Commentariae. Histology of Alimentary Canal Submucosa = lying immediately beneath mucosa, broad layer of dense connective tissue connecting mucosa to underlying muscularis and including blood and lymphatic vessels (transporting absorbed nutrients), with submucosal glands releasing digestive secretions and additional submucosal plexus (=dense branching network of nerves) muscalaris = (also called muscularis externa), in small intestine [= double layer of smooth muscle: inner circular layer + outer longitudinal layer their contractions promote mechanical digestion, expose more of food to digestive chemicals, and move food along canal], in mouth, pharynx, anterior part of esophagus, and external anal sphincter [= made up of skeletal muscle, voluntary control over swallowing and defecation], in stomach [= addition of a third layer, oblique muscle], in colon [= 2 layers as small intestine, but longitudinal layer segregated into 3 narrow parallel bands, tenia coli, making it to look like series of pouches rather than a simple tube] serosa = portion of alimentary canal superficial to muscularis, present only in regions of alimentary canal within abdominal cavity, consisting of a layer of visceral peritoneum overlying a layer of loose connective tissue [instead of serosa, mouth, pharynx, and esophagus = dense sheath of collagen fibers called adventitia, serving to hold alimentary canal in place near ventral surface of vertebral column]. Histology of Alimentary Canal Histology of Alimentary Canal Histology of Alimentary Canal Histology of Alimentary Canal DIGESTIVE SYSTEM: Nerve Supply 1. Intrinsic innervation = provided by enteric nervous system, running from esophagus to anus, containing approximately 100 million motor, sensory, and interneurons (unique to this system compared to all other parts of peripheral nervous system), grouped into 2 plexuses: myenteric plexus (plexus of Auerbach, lying in muscularis layer, responsible for motility, especially rhythm and force of contractions of muscularis), submucosal plexus (plexus of Meissner, in submucosal layer, responsible for regulating digestive secretions and reacting to presence of food) 2. Extrinsic innervations = provided by autonomic nervous system, including both sympathetic (fight-or-flight response, restricts activity of enteric neurons, thereby decreasing GI secretion and motility) and parasympathetic nerves (rest-and-digest response increases GI secretion and motility by stimulating neurons of enteric nervous system) DIGESTIVE SYSTEM: Nerve Supply Auerbach, Leopold. - Neurologo e anatomopatologo (Breslavia 1828 - ivi 1897). Il suo nome è legato particolarmente alla scoperta di un plesso (plesso mienterico di A.) situato nello spessore della tunica muscolare dello stomaco e dell'intestino tenue dell'uomo e degli altri mammiferi. Tale plesso, dal quale sembra che partano gli stimoli che determinano la contrazione dell'intestino, è formato da fibre provenienti dal plesso celiaco ed è collegato con l'analogo plesso di Meissner mediante numerosi ramuscoli nervosi. DIGESTIVE SYSTEM: Nerve Supply Georg Meissner (Hannover, 19 novembre 1829 – 30 marzo 1905) è stato un anatomista e fisiologo tedesco. Studiò medicina all'Università di Göttingen dove lavorò a stretto contatto con Rudolf Wagner. Nel 1851 accompagnò Wagner e Theodor Billroth in un viaggio a Trieste dove perfezionò alcuni studi sui pesci torpedine. Nel 1852 terminò il dottorato a Göttingen e dal 1855 diventò professore all'Università di Basilea, di Friburgo (dal 1857) e di Göttingen (dal 1860 al 1901). Il suo nome è associato al corpuscolo di Meissner, terminazioni nervose incapsulate, anche chiamati corpuscoli tattili, che si trovano nello strato superficiale del derma. È inoltre ricordato con il plesso di Meissner, un plesso nervoso intercalato nella tonaca sottomucosa del tubo gastroenterico; insieme al plesso di Auerbach va a formare il sistema nervoso enterico. DIGESTIVE SYSTEM: Nerve Supply DIGESTIVE SYSTEM: Nerve Supply AP - Auerbach's plexus GC - ganglionic cells ME - muscularis externa ME(c) - muscularis externa (circular sublayer) ME(l) - muscularis externa (longitudinal sublayer) MP - Meissner's plexus Ser - serosa Sub - submucosa DIGESTIVE SYSTEM: Blood Supply blood vessels serving DS have 2 functions: 1.transport protein and carbohydrate absorbed by mucosal cells after digestion (lipids absorbed via lacteals of lymphatic system), 2.supply organs with nutrients + O2 needed to drive cellular processes. a) more anterior parts of alimentary canal = supplied with blood by arteries branching off aortic arch and thoracic aorta; b) below this point = supplied with blood by arteries branching from the abdominal aorta [celiac trunk = liver, stomach, duodenum, sup and inf mesenteric arteries = remaining small and large intestines]. veins collecting nutrient-rich blood from small intestine (where most absorption occurs) hepatic portal system liver (nutrients are either processed or stored for later use) back to heart (during “resting and digesting,” about 1/4 of blood pumped enters arteries serving the intestines).
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