Anat assignment-GI tract presentation

Editor's Notes

• #4: Explain briefly each process and tie in how each organ contributes to the process throughout the presentation The digestive system comprises of organs that: Ingest food Transport the ingested food Digest the food into smaller components Absorb the necessary nutrients into the blood stream and; Expel the waste products from the body
• #7: Mucosa-3 components: superficial epithelium lining; lamina propria, muscularis mucosae (thin layer of smooth muscle) Submucosa-dense irregular connective tissue, blood and lymph vessels, nerves Muscularis-2 layers of smooth muscle. Inner circular layer (inner layer of smooth muscle) and outer longitudinal layer (outside layer of smooth muscle) Adventitia-outer most layer made of areolar connective tissue with elastic fibres and collagen -retroperitoneal organs contain adventitia because they are somewhat covered by visceral peritoneum serosa-same make up as adventitia but is covered by a layer of visceral peritoneum -intraperitoneal organs contain serosa
• #8: Teeth: collectively known as the dentition. Teeth are responsible for mastication, the first part of the mechanical digestion process.  Cheeks: The buccinator muscles compress the cheeks against the teeth to hold solid materials in place during chewing. Tongue: manipulates and mixes ingested materials during chewing and helps compress the materials against the palate to turn them into a bolus. The tongue also performs important functions in swallowing.  Palate: The palate forms the roof of the oral cavity and acts as a barrier to separate it from the nasal cavity. There is a hard plate – helps the tongue manipulate materials before swallowing and the soft plate prevents ingested materials from entering the nasal region Salivary glands: collectively produce and secrete saliva, a fluid that assists in the initial activities of digestion. 
• #9: The masseter: elevates and retracts the jaw, the most powerful muscle in the body in terms of ability to exert pressure Temporalis: elevates and brings the jaw forward Lateral: bring the jaw forward as well Medial: elevates the mandible, and assists in closing the mouth All four of the muscles are skeletal muscles that are innervated by the mandibular nerve, which is a branch of the trigeminal nerve http://visitcore.com/featured-muscles-the-muscles-of-mastication/
• #10: The sequential contraction of the constrictors moves the bolus down the pharynx to the esophagus by narrowing the diameter of the pharynx behind the bolus While the constrictors are pushing the bolus, the epiglottis shuts over the larynx and trachea (opening to airways)
• #11: peristalsis= rhythmic smooth muscle contractions Why different epithelial cells? No absorption , which is what the simple columnar is useful for, so stratified aquamous for more protection from still mostly intact bolus Pic: http://blogberlinmd.com/photorii/histology-of-esophagus
• #12: The voluntary phase occurs after ingestion. Food and saliva mix in the oral cavity. Chewing forms a bolus that is mixed and manipulated by the tongue and then pushed superiorly against the hard palate. The appearance of the bolus at the entryway to the oropharynx initiates the pharyngeal phase. During this phase, (1) the soft palate and uvula elevate to block the passageway between the nasopharynx and oropharynx; (2) the bolus enters the oropharynx; and (3) the larynx and laryngeal opening elevate toward the epiglottis, ultimately covering and sealing the glottis to prevent swallowed materials from entering the trachea. The esophageal phase is involuntary. It is the time (about 5 to 8 seconds) during which the bolus passes through the esophagus and into the stomach.
• #13: The stomach follows the esophagus in the GI tract. It is a J-shaped sack which resides in the upper left quadrant of the abdomen. Rugae are gastric folds within the stomach that allow it to expand as food enters, and contract as food leaves. Its purpose is to complete the digestion of the bolus from the oral cavity into chyme. The stomach itself is made up of four main components: the cardia, the fundus, the body, and finally the pylorus. The cardia is the narrow region anterior to the stomach lumen which connects to the esophagus posteriorly, at the cardiac orifice. The fundus is then the region that lies both lateral and superior to the esophagus. The body of the stomach is the largest region of the stomach, and follows posteriorly to both the cardia and fundus regions. The pylorus is the terminal region of the stomach. It begins to narrow and is divided into two regions: the pyloric antrum and pyloric canal. The pyloric antrum is the wider region of the pylorus, while the pyloric canal is more tapered and connects to the duodenum. This region is known as the pyloric orifice, and to mediate the entry of chyme into the duodenum, there is a pyloric sphincter consisting of circular smooth muscles surrounding the orifice.
• #14: There are five cells which are used in the stomach for secretion. The first are surface mucous cells. They line the stomach lumen and continuously secrete mucin in order to protect the stomach lining from the acidic environment. The mucous neck cells are interspersed amongst parietal cells and secrete acidic mucin in order to maintain acidic conditions in the stomach. The parietal cells are the ones that secrete hydrochloric acid into the stomach lumen in order to assist in protein deanimation. Parietal cells can also secrete an intrinsic factor that binds to vitamin B12, assisting in its absorption later on in the small intestine. Chief cells then secrete pepsinogen, which turns into the active enzyme pepsin by the acidic environment of the stomach. This ensures that the enzymes do not start digesting stomach lining immediately after secretion. Finally, the enteroendocrine cells secrete the hormone gastrin which regulates the chief and parietal cells.
• #15: Circular folds: are part of the mucosa and submucosa layer, and slow down the flow of chyme to maximize absorption Villi: they increase the SA for absorption, and are formed out of columar epithelial cells and goblet cells. On the columnar epithelial cells there are microvilli on the apical surface to further increase the SA. The goblet cells release mucous to lubricate the passage of chyme. The villi each have their own capillary network, so nutrients can swiftly enter the bloodstream after absorption, and in the center is a lacteal, which is used for absorbing lipids Intestinal glands: found in between some of the villi, lined with: columnar epithelial cells, goblet cells, and enteroendocrine cells (releases hormones like secretin, and CCK, that help with digestion and signalling) Pic: http://www.webmd.com/digestive-disorders/small-intestine https://craniumcommander.wikispaces.com/Digestive+System+-+Physiology
• #16: It’s the shortest segment of the small intestine- only 10-12 inches long, and the superior end attaches to the pyloric sphincter, the inferior end attaches to the jejenum Journeying through the small intestine, the chyme, which is already partially digested is digested further, breaking down proteins, lipids and carbohydrates, to allow for absorption later in the small intestine. Firstly, Brunner’s glands secrete alkaline mucus to neutralize the acidic chyme, and to create an environment that’s favourable for the activation of the digestive enzymes. Digestion occurs via the secretion of pancreatic juice (contains digestive enzymes) by pancreatic acinar cells and bile, by the gall bladder. Secretion occurs due to neural and endocrine signals. Neural signalling involves the vagus nerve (parasympathetic nervous system, rest and digest), whereas endocrine involves hormones secreted by the enteroendocrine cells- CCK, gastrin, and secretin. These are secreted and mixed with the chyme at the middle of the duodenum- the Ampulla of Vater.
• #17: The smooth muscles contract in a localized manner called segmentations to mix up the chyme and increase contact with the walls of the jejenum CELLS: composed of villi and microvilli, in order to maximize the surface area for absorption- most of nutrients are absorbed here Absorption of carbohydrates, lipids and proteins occurs in the microvilli The villi contains a lacteal, which allows for absorption of digested lipids
• #18: ILEUM: chyme enters from the jejenum (2- 4 m long) Last of the nutrients and water are absorbed here: water flows passively through the cells, and nutrients absorption occurs via the microvilli and villi Joins the cecum (part of the large intestine) via the ileocecal sphincter, which controls the flow of chyme into the large intestine Terminal end has lymphatic tissue, known as Peyer’s patches examine the chyme for any pathogens, and Paneth cells release antimicrobial substances
• #19: Appendix: is lined by lymphocyte filled lymphatic nodules
• #21: The external sphincter is under voluntary control, while the internal is SM, so its involuntary- both must be relaxed in order for fecal matter to be released
• #22: answer: smaller food particles allow for an increase in the surface area exposed to the saliva secreted by the salivary glands. This means that more food is exposed to the digestive enzymes at once, increasing the digestive efficiency during mastication and salivation. More specifically, more amylases are able to cleave the sugar compounds through hydrolysis. Because more absorption occurs in the duodenum than in the ileum, so the circular folds increase the SA for absorption where it most occurs