MD-6 Gastrointestinal System 1 Foregut and Midgut PDF

Gastrointestinal System 1 ANATOMY OF THE GASTROINTESTINAL TRACT: Foregut and Midgut UNIC MD-6 Anatomy Station Guides (demonstrator version) Specific Learning Outcomes Describe the boney anatomy of the oral cavity (mandible, soft palate, hard...

Gastrointestinal System 1 ANATOMY OF THE GASTROINTESTINAL TRACT: Foregut and Midgut UNIC MD-6 Anatomy Station Guides (demonstrator version) Specific Learning Outcomes Describe the boney anatomy of the oral cavity (mandible, soft palate, hard palate). Describe the gross anatomy of the pharynx. Identify the muscles of mastication. Identify the blood supply and drainage of the foregut and midgut (coeliac trunk, superior and inferior mesenteric arteries) & Lymphatic drainage of the oral cavity, salivary glands, pharynx, oesophagus, stomach, and duodenum. Describe the innervation of the oesophagus (vagus), stomach, and duodenum, viscera, tongue, salivary glands (submandibular, parotid, sublingual) and their ducts, pharynx. Describe the surface anatomy, key anatomical features, anatomical relations, vascular supply, nerve supply, and histological structure of the foregut and midgut. Describe and identify the division of the peritoneal cavity into the greater and lesser sacs. Describe and identify the origins, courses and areas of supply for the coeliac trunk and its 3 major branches (common hepatic, left gastric, splenic arteries). Describe and identify the subdivisions of the greater sac (suprahepatic recesses, hepatorenal pouch, paracolic gutters, and spaces around the root of the small intestinal mesentery. Describe and identify the omental (epiploic) foramen and bursa (lesser sac). Identify the blood supply and drainage of the foregut and midgut and related structures and lymphatic drainage. Describe the innervation of the midgut and related structures: duodenum, pancreas, jejunum (distinguishing features), ileum (distinguishing features), caecum, vermiform appendix, and colon (in midgut - ascending, transverse). Distinguish between retroperitoneal, secondarily retroperitoneal and peritoneal organs. Suggested Readings: Moore KL, Agur AMR, Dalley AF. 2011. Essential Clinical Anatomy. 4th Edition. Pages 140-1452, 165-174, 557-570, 631-638, Netter F.H. 2003. Atlas of Human Anatomy. 3rd Edition. Plates 6, 47-49, 52-56, 59, 228-237, 263-271, 278-287, 290-293297, 299, 302-304, 309-311, 316, 317 1 Station 1: The Oral Cavity, Pharynx, and Oesophagus The oral cavity Task - Identify the following structures: The oral cavity - Note the boney boundaries of the oral cavity including: the mandible and palatine bones. Tongue papillae on the anterior 2/3, and the circumvalate papillae (which form a V- shape) posteriorly. - At the apex of the “V,” identify the foramen caecum. This is a remant of what embryological structure? Teeth - Identify the different types of teeth. What is the general function of teeth? - _____________________________________________________ - Why do anterior teeth tend to fall out of skulls, while posterior molars generally remain in place? - _____________________________________________________ The hard and soft palate Epiglottis - The epiglottis projects upwards at the base of the tongue. - What is its function?_______________________________ Submandibular gland and Parotid gland - The submandibular gland lies under the body of the mandible. - The parotid gland occupies the space between the ramus (ascending part) of the mandible and the external ear. - These are both salivary glands. - The submandibular salivary ducts open in the sublingual papillae which lay at the base of the lingual frenulum. 2  - The parotid duct runs anteriorly from the parotid gland to pierce the muscle of the cheek (the buccinator). Where in the oral cavity does the parotid duct open? ____________________________________________________ *Clinical Correlations: Parotidectomy - About 80% of salivary gland tumors occur in the parotid glands with surgical excision of the parotid gland (parotidectomy) often being performed as part of the treatment. - Because the parotid plexus of the facial nerve is embedded in the parotid gland, the plexus and its branches are in jeopardy during surgery. Sublingual salivary gland - Lies beneath the mucous membrane of the floor of the mouth, lateral to the base of the tongue. Muscles of mastication Task - Identify the following muscles of mastication: Temporalis Masseter Medial and lateral pterygoid Task - Identify the proximal and distal attachments of these muscles. - Which nerve innervates these muscles? ______________________________________________ The Pharynx and Oesophagus - The pharynx is a muscular tube, open anteriorly, lying behind the nose, mouth and larynx. From superior to inferior it is divided into the: Nasopharynx - The soft palate marks the boundary between the nasopharynx and the oropharynx. - Can you find a structure that closes off the nasopharynx during swallowing?____________________________________________________ Oropharynx - The epiglottis marks the division between the oropharynx and the laryngopharynx. Laryngopharynx. Task - Identify the larynx anterior to the laryngopharynx. - The laryngopharynx is continuous inferiorly with the oesophagus. Oesophagus Note that the trachea lies anterior to the oesophagus in the neck. The oesophagus is surrounded by a nerve plexus (oesophageal plexus); branches of the vagus nerve (parasympathetic) and the sympathetic trunk. 3 Task - Follow the vagus nerve superiorly- What is its relation to the arch of the aorta on the left side of the body?_________________________________________________ The vagus initially runs on the right and left side of the oesophagus. As the oesophagus passes through the diaphragm, the left vagus courses anterior and the right vagus courses posterior. - At which vertebral level does the oesophagus pass through the diaphragm occur? _____________________________________________________________________ *Clinical Correlations: Trachoeesophageal Fistula - The most common congenital anomaly of the esophagus is the tracheoesophageal fistula. It is usually combined with some form of esophageal atresia. - In the most common type, the proximal part of the esophagus ends in a blind pouch and the distal part communicates with the trachea. In these cases, the pouch fills with mucus, which the infant aspirates. Station 2: The Stomach and Duodenum Stomach In the opened cadaver identify: Stomach - Note that there is a short length of intra-abdominal oesophagus proximal to the gastroesophageal junction. - What structures help to maintain the integrity of the lower oesophageal sphincter?________________________________________________________ Task - Identify the following features of the stomach: Fundus Body Pyloric antrum - Note that the pylorus is continuous with the duodenum. Greater and lesser curvature Anterior and posterior surfaces Rugae (ridges inside the stomach) Cardia Incisura angularis Pyloric sphincter Task - Squeeze the junction between the pylorus of the stomach and the duodenum between your fingers. The thickening you can feel is the smooth muscle of the pyloric sphincter. *Clinical Correlations: Pylorospasm -Spasmodic contraction of the pyloris (pylorispasm) sometimes occurs in infants, usually between 2 and 12 weeks of age. - Pylorospasm is characterized by failure of the smooth muscle fibres encircling the pyloric canal to relax normally. 4  - As a result food does not pass easily from the stomach into the duodenum and the stomach becomes overly full, usually resulting in vomiting. Task - Identify the lesser omentum (a double layer of peritoneum passing from the porta hepatis to the superior border of the stomach). - What are its attachments? _________________________________________________________________ Behind the lesser omentum lies the lesser sac of the peritoneal cavity (omental bursa). Task - Identify superior and inferior recesses of the omental bursa: Task - Insert two fingers into the epiploic foramen. What structures lie: a) Anterior to your fingers? b) Posterior to your fingers? c) Superior to your fingers? d) Inferior to your fingers? *Clinical Correlations: Displacement of the stomach - Pancreatic pseudocysts and abscesses in the omental bursa may push the stomach anteriorly. - This displacement is usually visible in lateral radiographs of the stomach and other diagnostic images such as CT. What is a “Pringles manoeuvre”? What is its anatomical basis? ____________________________________________________________ Task - Identify the greater omentum. What are its attachments? What is its function? ________________________________________________________________ Task - Discuss the subdivisions of the peritoneal cavity. Duodenum The duodenum forms a “C” shape and is divided into four parts. Identify them on your specimen: 1st (Superior) part 2nd (Descending) part 3rd (Horizontal) part 4th (Ascending) part What structure is enclosed within the “C” of the duodenum? _____________________ How is the duodenum related to the peritoneum?__________________________ *Clinical Correlations: Duodenal Ulcers 5  - Most (95%) inflammatory erosions of the duodenal wall (duodenal ulcers) are in the posterior wall of the superior part of the duodenum. - This is because the superior part of the duodenum closely relates to the liver and gallbladder, either of them may adhere to and be ulcerated by a duodenal ulcer. Vasculature The artery of the foregut, the coeliac trunk, is the first anterior midline branch of the abdominal aorta. - The distal duodenum and intestines constitute the midgut and hindgut. Identify the coeliac trunk coming off the abdominal aorta. Task - Identify the three major branches of the coeliac trunk: Splenic artery - What structures does this supply? ______________________________________________________ Left Gastric artery - What structures does this supply? ____________________________________________________________ Common Hepatic artery - What structures does this supply? _______________________________________________________ Station 3: Jejunum and Ileum Task - Identify the following structures: Duodenojejunal flexure - What is the surface marking of this structure? Answer: _____________________________________ _____________________________________________ Ligament of Treitz (suspensory ligament of the duodenum) What is the greater sac? Answer: ________________________________ What is the root of the mesentery? Answer:_______________________ ____________________________________________________________ - Between which two landmarks is it located? Answer_________________________________________________ _______________________________________________________ _______________________________________________________ How are the jejunum and ileum related to the peritoneum? Answer: __________________________________________ Task - Observe the mucosa in a section of proximal jejunum. - There are numerous pronounced plicae circulares. - Compare this with the appearance of the mucosa in a length of distal ileum. 6 While there is no anatomical cut-off point between the jejunum and the ileum, the jejunum is commonly considered to comprise the proximal 2/5 of the small intestine. The overall length is around 6 – 7 metres. Task - Identify the differences between jejunum and ileum. Compare the following features: Arterial arcades - Jejunum: few - Ileum: many Vasa rectae - Jejunum: long - Ileum: short Mesenteric fat - Jejunum: less than that what is found in the ileum - Ileum: more than that of the jejunum Mural (wall) thickness - Jejunum: thicker - Ileum: thinner Diameter of the lumen - Jejunum: wider - Ileum: narrower Where does the ileum terminate? Answer: _________________ What are the functional significance of Peyer’s patches? Answer: __________________________________________________ ______________________________________________________________ ______________________________________________________________ *Clinical Correlations: Ileal Diverticulum - An ilieal diverticulum (Meckel’s Diverticulum) can be remembered by the rule of 2’s: 2% of the population, 2 feet (from ileocaecal valve), 2 inches (in length), 2% are symptomatic, 2 types of common ectopic tissue (gastric and pancreatic), 2 years is the most common age at clinical presentation, 2 times more boys are affected. - The diverticulum usually appears as a fingerlike pouch (3-6cm long). - It is always on the border of the intestine opposite the mesenteric attachment. - The diverticulum is usually located approx 40cm from the ileocecal junction in infants and 50 cm in adults, and may be free (74%) or attached by a cord to the umbilicus (26%). - An ileal diverticulum may become inflamed and produce pain mimicking the pain produced by appendicitis. Task - Identify the arterial blood supply to, and venous drainage from, the small intestine. 7  - How are the vessels related to the pancreas? Answer: _________________________________ Task - Identify the lymph drainage of the small intestine. Note: Lymph vessels called lacteals line the small intestine. The lymph drain to the cisterna chyle and from there to the thoracic duct where it empties into the left subclavian vein. This system allows interstitial fluid to go back to the circulatory system. Innervation Task - Identify the greater and lesser splanchnic nerves - They supply sympathetic innervation to the jejunum and ileum. - From which spinal segments do the sympathetic fibres to the jejunum and ileum originate? Which parasympathetic nerve supplies the jejunum and ileum? Answer: _______________ - What influence does autonomic innervation exert upon the intestine? Answer: _________________________________________________ ________________________________________________________ ________________________________________________________ - To what sensory stimuli is the intestine sensitive? Answer: ______________________________________________________ _____________________________________________________________ *Clinical Correlations: Visceral Referred Pain - Organic pain arising from an organ such as the stomach varies from dull to severe; however, the pain is poorly localized. - It radiates to the dermatome level, which receives visceral afferent fibres from the organ concerned. - Visceral referred pain from a gastric ulcer, for example is referred to the epigastric region because the stomach is supplied by pain afferents that reach the T7 and T8 spinal sensory ganglia and spinal cord segments through the greater splanchnic nerve. - The pain is interpreted by the brain as though the irritation occurred in the skin of the epigastric region, which is also supplied by the same sensory ganglia and spinal cord segments. Viscera Nerve Supply Spinal Referred Site and Cord clinical Example Stomach Anterior and posterior vagal T6-T9 or Epigastric and left trunks; presynaptic sympathetic T10 hypochondriac regions fibres reach coeliac and other (eg. Gastric peptic ganglia through greater ulcer) splanchnic nerves 8 Duodenum Vagus nerves; presynaptic T5-T9 or Epigastric region (eg. sympathetic fibres reach coeliac T10 Duodenal pepticu and superior mesenteric ganglia ulcer, right shoulder (if through greater splanchnic ulcer perforates) nerves Pancreatic Vagus and thoracic splanchnic T8-T9 Inferior part of Head nerves epigastric region (eg pancreatitis) Small Posterior vagal trunks; T5-T9 Periumbilical region intestine presynaptic fibres reach coeliac (eg. acute intestinal ganglion through greater obstruction) splanchnic nerves Colon Vagus nerves; presynaptic T10-T12 Hypogastric region (eg. sympathetic fibres reach celiac, (proximal Ulcerative colitis); left superior mesenteric, and colon) lower quadrant (eg. infereior mesenteric ganglia L1-L3 Sigmoiditis) through greater splanchnic (distal nerves; parasympathetic supply colon) to distal colon derived from pelvic splanchnic nerves through hypogastric nerves and inferior hypogastric plexus. Spleen Coeliac plexus, especially from T6-T8 Left hypochondriac greater splanchnic nerves region (eg. splenic infarct) Appendix Sympathetic and T10 Periumbilical region parasympathetic nerves from and later to right lower superior mesenteric plexus, quadrant (eg. afferent nerve fibres accompany appendicitis) sympathetic nerves to T10 segment of spinal cord Gallbladder Nerves derived from celiac T6-T9 Epigastric region and and liver plexus (sympathetic), vagus right hypochondriac nerve (parasympathetic), and region; may cause pain right phrenic nerve (sensory) on posterior thoracic wall or right shoulder owing to diaphragmatic irritation Kidneys Nerves arise from renal plexus T11-T12 Small of back, flank and Ureters and consist of sympathetic, (lumbar quadrant), parasympathetic, and visceral extending to groin afferent fibres from thoracic and (inguinal region) and lumbar splanchnics and vagus genitals (eg. renal or nerve ureteric calculi) 9 Task – Define the contents of the foregut. Task – Define the contents of the midgut. Task – Define the contents of the hindgut. Task - Outline which structure are retroperitoneal, secondarily retroperitoneal, and peritoneal organs. 10