BMS Clin Phys 8 PDF

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 conditions in the lumen Layers of the Alimentary Canal • Mucosa – epithelial lining, lamina propria, muscularis mucosa • Lamina propria – site of: ▪ blood and lymphatic vessels ▪ Immune tissue (resembles looselystructured 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 two layers 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 lectures 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 irritants 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 instead of serosa 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 a role in chemical digestion ▪ Acid denatures 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 the canal 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 • Insulin, glucagon, and somatostatin 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? 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 attacks, pneumonia) can also present as abdominal pain 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-GI organs 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 Lumbar – Splenic injury, renal disease Hypogastric: most of the large intestine, bladder Right iliac – appendicitis Left iliac – diverticulitis (large intestine) 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