BMS100_PHL1-08v1_Fall2022.pptx

Clinical Physiology VIII Gastrointestinal Anatomy & Physiology In Relation to the Abdominal Exam BMS 100 Week 9 The GI system The Alimentary Canal – basic structure and function of: Esophagus Stomach Small Intestine Large Intestine The Digestive Accessory Organs – basic structure and function of:...

Clinical Physiology VIII Gastrointestinal Anatomy & Physiology In Relation to the Abdominal Exam BMS 100 Week 9 The GI system The Alimentary Canal – basic structure and function of: Esophagus Stomach Small Intestine Large Intestine The Digestive Accessory Organs – basic structure and function of: Liver & Gall Bladder Pancreas The Alimentary Canal • Tubular structure that:  Makes direct contact with food (or former food)  Has a typical set of histologic layers that surround a lumen • Composed of:  Oral cavity and pharynx (future lectures)  Esophagus  Stomach  Small Intestine • Duodenum, jejunum, ileum  Large intestine • Cecum, appendix, ascending, transverse, descending colon, rectum The Accessory Digestive Organs • All of these organs are derived embryologically as “outgrowths” of the early alimentary canal • All of these organs function as glands that secrete substances into the alimentary canal  The liver and pancreas have additional very important functions that impact the rest of the body • Include:  Salivary glands (future lectures)  Liver & gall bladder  Pancreas What, in general, does the alimentary canal do? • Propulsion – food is moved along the “tube” as it is digested • Secretion – two types:  Hormonal secretions that impact digestion, secretion, and overall metabolism  Fluid or mucous secretions that aid propulsion and digestion • Digestion  Chemical – enzymes and acid break chemical bonds in food material or substances facilitate enzymatic interactions  Mechanical – movements of the canal mix food, break it apart, and increase the SA:volume ratio of food What, in general, does the alimentary canal do? • Absorption (movement from lumen  bloodstream)  Water – we ingest over 1 L of water today, and secrete 4 – 6 L of water into the canal  Macro- and micronutrients • Immune function  Protection from ingested microbes that are harmful  Aiding microbes that are useful  “Educating” the immune system about whether something that has been ingested is harmful or harmless Layers of the Alimentary Canal • Mucosa – epithelial lining, lamina propria, muscularis mucosa • Type of epithelium varies from organ to organ  Columnar with villi for absorption/secretion, cuboidal or squamous for protection from abrasion  Goblet cells are usually present in the epithelial layer  mucous secretion  Neuroendocrine cells – cells that are interspersed among the epithelium and release signals in response to different nutrients or chemical Layers of the Alimentary Canal • Mucosa – epithelial lining, lamina propria, muscularis mucosa • Lamina propria – site of:  blood and lymphatic vessels  Immune tissue (resembles loosely-structured lymphatic nodules, known as MALT) • Muscularis mucosa  Alters the shape of the mucosa to optimize mixing and exposure of the epithelial cells to lumen contents Layers of the Alimentary Canal • Submucosa – loose connective tissue with larger blood vessels and lymphatics  Larger glands can be found here  Very large lymphatic nodules can also be found in the submucosa of the proximal small intestine  A plexus (network) of neurons exist in the submucosa • Known as Meissner’s (submucosal ) plexus – tends to regulate secretions and convey sensory info about what’s in the lumen Layers of the Alimentary Canal • Muscularis - usually just an inner and an outer layer  Inner layer – “circular layer” – smooth muscle fibres concentrically surround the lumen • When it contracts, it “squeezes” the lumen shut  Outer layer – “longitudinal layer” – smooth muscle fibres run along the length of the canal • When it contracts, it “shortens” the canal  Another plexus – Auerbach’s or myenteric plexus – regulates the movements of these muscular layers • Found between the Layers of the Alimentary Canal • Outer layer – adventitia or serosa  Adventitia – in the esophagus – connective tissue that anchors the esophagus in the chest cavity  Serosa – Loose connective tissue that is covered by a simple squamous mesothelium • The mesothelium secretes fluid that collects in the abdominal (peritoneal) cavity • Source of peritoneal fluid • The serosa is continuous with what is known as the visceral peritoneum • More in later Layers of the Alimentary Canal • Peritoneal cavity = fluid filled gap between the wall of the abdomen and the organs contained within the abdomen  Visceral is formed by the serosa of the alimentary canal and the capsule of the liver • The mesothelium secretes fluid that collects in the abdominal (peritoneal) cavity  Parietal is the inner lining of the abdominal wall • The parietal peritoneum is extremely sensitive to inflammation and other chemical Peritoneal cavity - FYI Esophagus • Tube that extends from the pharynx to the stomach, only role is propulsion of food to the stomach  25 cm long tube located retrosternally  Upper esophageal sphincter – when it closes, it pushes food from the pharynx to the esophagus  Lower esophageal sphincter – limits movement of stomach acid into the esophagus  relaxes to receive swallowed food  Stratified squamous epithelium, adventitia Stomach • A sack that can expand to receive and store ingested food • Muscular movements accomplish mechanical digestion (churning and breaking up food into acidic chyme) and propulsion into the small intestine • Also has denatures a role in chemical digestion  Acid proteins and kills ingested bacteria  Secreted enzymes help to digest protein (collagen in particular) • The stomach also tells you when you’re “full”  Role in regulating food intake Stomach • Mucosa has low columnar cells that have a wide range of functions:  Parietal cells – secrete acid and intrinsic factor • IF is needed for absorption of B12  Other cells secrete mucous to protect the lining or digestive enzymes specialized for digesting proteins • Muscularis has 3 layers  Innermost layer is the oblique layer • Pyloric sphincter – regulates the amount of acidic chyme that enters the duodenum Small Intestine • Main digestive organ:  Site of most chemical digestion, absorption, and secretion in the alimentary canal  Largest surface area – makes sense given its function • 3 separate components – but no true anatomic distinction between them  Duodenum – short, C-shaped tube that receives chyme from the stomach and overlies the head of the  pancreas Jejunum – both the duodenum and jejunum have specialized immune tissue (Peyer’s patches)  Ileum – longest portion, main function is reabsorption of bile salts, micronutrients/vitamins, and water Small Intestine • Highly folded epithelium (microvilli), mucosa (villi) and submucosal layers (circular folds) meant to optimize surface area  Columnar epithelium with many microvilli  interspersed with goblet cells and cells that secrete chemical messengers into the blood • Messengers help regulate propulsion, overall metabolic function, secretions from the pancreas or liver Large Intestine • Main function is absorption of water from stool, storage of stool, and housing the majority of the microbes in the gut  Negligible role in nutrient absorption • Low columnar cells with fewer microvilli, plenty of goblet cells • Muscular layer is unique  Continuous circular muscle layer  Longitudinal muscle layer is separated into bands that do not completely surround Accessory Organs – Liver, Gallbladder, and Pancreas • These organs don’t contact ingested substances directly  They all have ducts that convey their secretions to the lumen of the duodenum  The pancreas has important endocrine functions related to overall nutrient metabolism  The liver has very wide array of important metabolic functions Liver • Roles of the liver:  Carbohydrate metabolism  Protein synthesis and degradation • Most proteins secreted into the bloodstream are from the liver  Lipid metabolism  Detoxification of molecules so that they can be secreted into the bile and defecated  Making hydrophobic molecules water soluble so that they can be eliminated by the kidney  Storage of vitamins and minerals  Synthesis of bile – essential for lipid digestion  Endocrine – secretion of IGF-1, important hormone regulating growth Gall Bladder and Pancreas • Gall bladder – storage and modification of bile  Contraction  bile release into the duodenum • Pancreas:  Exocrine – secretes digestive enzymes that are crucial for carbohydrate, protein, and lipid chemical digestion • These enzymes are secreted into the pancreatic duct, which drains into the duodenum  Endocrine – secretes hormones that impact glucose, protein, and lipid metabolism into the bloodstream Basic Physical Exam of the Abdomen Bowel sounds Abdominal discomfort Pain vs. tenderness Guarding vs. rigidity Organomegaly Hepatomegaly Bowel Sounds • May be…  Increased (hyperactive) • Diarrhea, gastroenteritis, inflammatory bowel disease, laxative use, gastrointestinal bleed • Or early bowel obstruction (often described as a high-pitched “tinkling” sound  Decreased (hypoactive) • Often suggests more emergent conditions • Bowel obstruction, peritonitis, intestinal ischemia  How long should we listen before assuming absence of bowel sounds? • 2 minutes Abdominal Pain vs. Tenderness • Abdominal pain is present regardless of whether you palpate (press) the abdomen  Tenderness = pain in a region where you palpate  I.e. tender to light or deep palpation • Abdominal pain is one of the most challenging presentations  “Deep” or visceral pain can come from stretching, ischemia, or chemical irritation of a component of the alimentary tract or accessory organ  Sometimes pathologies in the thorax (heart Guarding vs. Rigidity • Guarding is voluntary contraction of the abdominal musculature due to abdominal discomfort  Can be exacerbated by anxiety  Can be serious pathology, but often less serious • Rigidity is involuntary contraction of the abdominal musculature, usually accompanied by severe pain  More serious pathology  Due to chemical irritation of the parietal peritoneum lining or “rubbing” of an inflamed organ against it • Bile (ruptured cholecystitis), infected material (ruptured or ischemic intestinal wall), pancreatic secretions (pancreatitis), gastric or duodenal contents (perforated peptic ulcer) • Inflamed structure rubbing against the parietal peritoneum – appendicitis, diverticulitis Abdominal Pain • Often the location of the abdominal pain is helpful – see diagram  Abdominal pain in the three areas in the “centre” can be visceral pain from the alimentary tract or accessory organs • Can also be due to irritation of the parietal peritoneum  Abdominal pain in the six regions on the “sides” are often due to irritation of the parietal peritoneum • Can also be due to visceral pain from non- Abdominal Pain – basic locations (FYI) Epigastric: stomach, esophagus, duodenum, pancreas, bile ducts, sometimes liver Hypochondriac: right side commonly liver, gall bladder, left can be stomach Umbilical: small intestine, cecum, appendix Right iliac – appendicitis Left iliac – diverticulitis (large intestine) Hypogastric: most of the large intestine, bladder Lumbar – Splenic injury, renal disease Right & left iliac – reproductive organs Hepatomegaly (Enlarged Liver) • A palpable liver does not necessarily indicate hepatomegaly (an enlarged liver) • Pathologic changes in consistency could be noted – from the normal softness to an abnormally firm or hard liver  Pathologies often also cause an increase in the size of the liver • Pathologies and their findings:  Liver cirrhosis – large liver with firm, nontender edge  Hepatocellular carcinoma – large liver that is firm and an irregular edge. May or may not be tender 

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