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  1. 1. TOPIC 8 Digestive System Chapter 18 pp. 651-677 Biology 221 Anatomy & Physiology II E. Lathrop-Davis / E. Gorski / S. Kabrhel
  2. 2. Digestive System Functions <ul><li>Provide nutrients in usable form </li></ul><ul><li>Remove unusable wastes </li></ul>
  3. 3. Digestive System Overview <ul><li>Two main groups of organs: </li></ul><ul><li>Alimentary canal (a.k.a. Gastrointestinal tract) </li></ul><ul><ul><li>tube through which food passes </li></ul></ul><ul><ul><li>responsible for digestion and absorption of food </li></ul></ul><ul><ul><li>mouth, pharynx, esophagus, stomach, small intestines, large intestines </li></ul></ul><ul><li>Accessory organs </li></ul><ul><ul><li>organs, glands and structures which aid digestion but not part of GI tract itself </li></ul></ul><ul><ul><li>teeth, tongue, salivary glands, pancreas, liver, gall bladder </li></ul></ul>Fig. 24.1, p. 888
  4. 4. Processes of Digestion <ul><li>Ingestion – entrance of food and drink into mouth </li></ul><ul><li>Mechanical digestion – physical breakdown into smaller pieces </li></ul><ul><li>Propulsion – movement through gut </li></ul><ul><li>Chemical digestion – breakage of molecules into smaller compounds </li></ul><ul><li>Absorption – uptake of nutrients from lumen </li></ul><ul><li>Defecation – removal of indigestible material </li></ul>Fig. 24.2, p. 889
  5. 5. Peritoneum <ul><li>Serous membrane </li></ul><ul><li>parietal peritoneum – lines abdominal cavity </li></ul><ul><ul><li>organs posterior to the parietal peritoneum are retroperitoneal </li></ul></ul><ul><li>visceral peritoneum (serosa)– covers surfaces of most abdominal organs </li></ul><ul><ul><li>Mesenteries – double layer of peritoneum extending from body wall to digestive organs </li></ul></ul><ul><ul><li>intraperitoneal organs are those in mesentaries </li></ul></ul><ul><li>Peritoneal cavity – fluid-filled “space” between visceral and parietal peritoneum </li></ul><ul><li>Peritonitis – inflammation of the peritoneum </li></ul>See also Fig. 24.5, p. 891 Fig,. 24.30, p. 929
  6. 6. Splanchnic Circulation <ul><li>Arteries serving the digestive organs: </li></ul><ul><li>Celiac Trunk – very short; gives rise to: </li></ul><ul><ul><li>hepatic artery – liver; gall bladder; stomach; duodenum </li></ul></ul><ul><ul><li>left gastric artery – stomach; inferior esophagus </li></ul></ul><ul><ul><li>splenic artery – spleen; stomach; pancreas </li></ul></ul><ul><li>Superior Mesenteric Artery – small intestines; most of large intestine; pancreas </li></ul><ul><li>Inferior Mesenteric Artery – large intestine </li></ul>Fig. 20.22, p. 759 Fig. 20.22, p. 761
  7. 7. Hepatic Circulation: Hepatic portal system <ul><li>Veins draining digestive organs and carrying nutrient-rich blood to liver </li></ul><ul><ul><li>gastric vein – drains stomach </li></ul></ul><ul><ul><li>superior mesenteric vein – drains small intestine </li></ul></ul><ul><ul><li>splenic vein – drains spleen </li></ul></ul><ul><ul><ul><li>inferior mesenteric vein – drains large intestine </li></ul></ul></ul><ul><li>Venous blood from hepatic portal system mixes with arterial blood (hepatic artery) in liver </li></ul>Fig. 20.27, p. 771
  8. 8. Hepatic Circulation: Hepatic Veins <ul><li>drain venous blood from liver into inferior vena cava </li></ul>Fig. 20.27, p. 771
  9. 9. Mucosa <ul><li>Mucous membrane lining gut </li></ul><ul><li>Consists of: </li></ul><ul><ul><li>epithelium – lining </li></ul></ul><ul><ul><li>lamina propria – areolar connective tissue layer </li></ul></ul><ul><ul><li>muscularis mucosae – smooth muscle </li></ul></ul>http://www. usc . edu / hsc /dental/ ghisto / gi /d_1.html
  10. 10. Mucosa: Epithelium <ul><li>Type varies depending on location </li></ul><ul><ul><li>stratified squamous epithelium found in mouth, esophagus and anal canal </li></ul></ul><ul><ul><li>simple columnar epithelium found in stomach and intestines </li></ul></ul><ul><li>Secretes mucus, digestive enzymes, hormones </li></ul><ul><li>Provides intact barrier to protect against entry of bacteria </li></ul>http://www. usc . edu / hsc /dental/ ghisto / gi /c_2.html http://www. usc . edu / hsc /dental/ ghisto / gi /d_15.html
  11. 11. Mucosa: Lamina Propria <ul><li>Layer of areolar connective tissue </li></ul><ul><li>Blood capillaries nourish epithelium, absorb and transport digested nutrients </li></ul><ul><li>Lymphatic capillaries provide drainage for interstitial fluid and transport fats to venous circulation </li></ul>http://www. usc . edu / hsc /dental/ ghisto / gi /d_60.html
  12. 12. Mucosa: Muscularis Mucosae <ul><li>Smooth muscle used for local movement and to hold mucosa in folds (small intestine) </li></ul>http://education. vetmed . vt . edu /Curriculum/VM8054/Labs/Lab19/EXAMPLES/ Exileum . htm
  13. 13. Submucosa <ul><li>Dense connective tissue superficial to mucosa </li></ul><ul><li>Highly vascularized </li></ul><ul><li>Many lymphatic vessels </li></ul><ul><li>Lymph nodules </li></ul><ul><ul><li>MALT = mucosa-associated lymphatic tissue </li></ul></ul><ul><ul><li>especially in small ( Peyer’s Patches ) and large intestines </li></ul></ul>http://education. vetmed . vt . edu /Curriculum/VM8054/Labs/Lab19/EXAMPLES/ Exileum . htm
  14. 14. Muscularis Externa (Muscularis) <ul><li>Two layers in most organs (3 in stomach) </li></ul><ul><ul><li>circular layer </li></ul></ul><ul><ul><li>longitudinal layer </li></ul></ul><ul><li>Peristalsis moves material through gut </li></ul><ul><li>Segmentation helps mix material with digestive enzymes in small intestine </li></ul>Fig. 24.3, p. 890
  15. 15. Serosa <ul><li>Visceral peritoneum – simple squamous epithelium (mesothelium) with areolar CT </li></ul><ul><li>Adventitia – dense connective tissue covering without epithelium; found around esophagus </li></ul><ul><li>Retroperitoneal organs have both a serosa (of parietal peritoneum) and adventitia (on side abutting body wall) </li></ul>
  16. 16. Enteric Nervous System <ul><li>Intrinsic nerve plexuses : </li></ul><ul><li>Enteric neurons </li></ul><ul><ul><li>neurons able to act independently of central nervous system </li></ul></ul><ul><ul><li>communicate with each other to control GI activity </li></ul></ul><ul><li>Two main enteric plexuses: </li></ul><ul><ul><li>submucosal nerve plexus – regulates glands in submucosa and smooth muscle of muscularis mucosae </li></ul></ul><ul><ul><li>myenteric nerve plexus – regulates activity of muscularis externa (with aide of submucosal nerve plexus) </li></ul></ul>
  17. 17. Central Nervous System Control <ul><li>Enteric nerve plexuses linked to CNS by visceral afferent (sensory) fibers </li></ul><ul><li>Digestive system receives motor input from sympathetic and parasympathetic divisions of autonomic nervous system </li></ul><ul><ul><li>parasympathetic outflow generally increases activity </li></ul></ul><ul><ul><li>sympathetic outflow generally decreases activity </li></ul></ul>
  18. 18. Mouth (Oral Cavity) <ul><li>Oral oriface is anterior opening </li></ul><ul><li>Mouth is continuous with oropharynx </li></ul><ul><li>Lips and cheeks keep food in oral cavity </li></ul><ul><li>Three layers of tissue: </li></ul><ul><ul><li>mucosa (stratified squamous epithelium) </li></ul></ul><ul><ul><li>submucosa </li></ul></ul><ul><ul><li>muscularis externa (skeletal muscle) </li></ul></ul>
  19. 19. Mouth: Palate <ul><li>Hard palate </li></ul><ul><ul><li>palatine process of maxilla </li></ul></ul><ul><ul><li>palatine bones </li></ul></ul><ul><li>Soft palate </li></ul><ul><ul><li>muscle only </li></ul></ul><ul><ul><li>prevents food from entering nasopharynx during swallowing </li></ul></ul><ul><ul><li>uvula (part that hangs down in middle) </li></ul></ul>Fig. 24.7, p. 895
  20. 20. Mouth: Arches <ul><li>Palatoglossal arch – anchors soft palate to tongue </li></ul><ul><li>Palatopharyngeal arch anchors soft palate to wall of oropharynx </li></ul><ul><li>Fauces – area between arches </li></ul><ul><ul><li>palatine tonsils – located in fauces </li></ul></ul>Fig. 24.7, p. 895
  21. 21. Mouth: Tongue <ul><li>Lingual tonsil – sits at base of tongue; protects against invasion by bacteria </li></ul><ul><li>Taste buds </li></ul><ul><ul><li>contain receptors for taste </li></ul></ul><ul><ul><li>found in some papillae </li></ul></ul>Fig. 24.8, p. 896
  22. 22. Mouth: Tongue <ul><li>Tongue forms bolus </li></ul><ul><ul><li>ball of food </li></ul></ul><ul><ul><li>makes food easier to swallow </li></ul></ul><ul><ul><li>keeps food between teeth </li></ul></ul><ul><li>Muscles – served by nerve XII </li></ul><ul><ul><li>intrinsic muscles – within tongue (not attached to bone); allow tongue to change shape for swallowing and speech </li></ul></ul><ul><ul><li>extrinsic muscles – attach to bone or soft palate; alter tongue position (protrusion, retraction, side-to-side) </li></ul></ul>Fig. 24.7, p. 895
  23. 23. Salivary Glands <ul><li>Produce saliva </li></ul><ul><li>Two groups of salivary glands </li></ul><ul><ul><li>intrinsic glands (buccal glands) – within oral cavity </li></ul></ul><ul><ul><li>extrinsic glands – 3 pairs (see A&P I Unit VI for innervation) </li></ul></ul><ul><ul><ul><li>parotid glands (connected to oral cavity by parotid duct; mumps is a viral infection of the parotid glands) </li></ul></ul></ul><ul><ul><ul><li>sublingual glands </li></ul></ul></ul><ul><ul><ul><li>submandibular glands </li></ul></ul></ul>Fig. 24.9, p. 897
  24. 24. Saliva <ul><li>Mucus cells produce mucus (less common) </li></ul><ul><li>Watery saliva produced by serous cells ; composition: </li></ul><ul><ul><li>97-99.5% water </li></ul></ul><ul><ul><li>slightly acidic (pH ~ 6.8) </li></ul></ul><ul><ul><li>electrolytes (ions such as Na + , K + , Cl - , PO 4 = , HCO 3 - ) </li></ul></ul><ul><ul><li>metabolic wastes (urea, uric acid) </li></ul></ul><ul><ul><li>proteins </li></ul></ul>
  25. 25. Salivary Proteins <ul><li>Mucin – glycoprotein portion of mucus that lubricates oral cavity) </li></ul><ul><li>Lysozyme – antibacterial </li></ul><ul><li>IgA – antibodies that prevent antigens from attaching to mucus membrane </li></ul><ul><li>Defensins – secreted by neutrophils; act as local antibiotic and chemotatic agent when mucosa is damaged </li></ul><ul><li>Salivary amylase – hydrolyzes starch </li></ul>
  26. 26. Control of Salivation <ul><li>Sympathetic division </li></ul><ul><ul><li>stimulates production of mucin-rich saliva, or </li></ul></ul><ul><ul><li>inhibits salivation altogether at high levels </li></ul></ul>
  27. 27. Control of Salivation <ul><li>Parasympathetic division of ANS stimulates activity </li></ul><ul><ul><li>chemoreceptors (excited most by acidic substances) and baroreceptors (excited by mechanical stimuli) send messages to salivatory nuclei in pons and medulla </li></ul></ul><ul><ul><li>parasympathetic motor output results in salivation </li></ul></ul><ul><ul><li>psychological control – response to visual, olfactory stimuli, even thoughts of food </li></ul></ul><ul><ul><li>salivary nuclei are stimulated by irritation to lower GI tract </li></ul></ul><ul><li>Parasympathetic nerves </li></ul><ul><ul><li>facial – to submandibular, sublingual </li></ul></ul><ul><ul><li>glossopharyngeal – to parotids </li></ul></ul>
  28. 28. Teeth <ul><li>Lie in alveoli of mandible and maxilla (see A&P I axial skeleton lab) </li></ul><ul><li>Primary dentition = deciduous teeth (20 milk or baby teeth) </li></ul><ul><ul><li>roots are absorbed as permanent teeth grow in, causes baby teeth to fall out </li></ul></ul>Fig. 24.10, p. 899
  29. 29. Teeth <ul><li>Permanent dentition = adult teeth (32) </li></ul><ul><li>8 Incisors (central and lateral) </li></ul><ul><li>4 Canines (eyeteeth) </li></ul><ul><li>8 Bicuspids = premolars </li></ul><ul><li>Molars </li></ul><ul><ul><li>4 first molars </li></ul></ul><ul><ul><li>4 second molars </li></ul></ul><ul><ul><li>4 third molars </li></ul></ul><ul><ul><ul><li>wisdom teeth </li></ul></ul></ul><ul><ul><ul><li>may become impacted as grow in </li></ul></ul></ul>Fig. 24.10, p. 899
  30. 30. Tooth Structure <ul><li>Crown - covered by enamel (hardest substance in body); underlain with dentin </li></ul><ul><li>Neck </li></ul><ul><li>Root </li></ul><ul><ul><li>cementum – calcified connective tissue covering dentin of root; attaches root to periodontal ligament which anchors tooth to alveolus </li></ul></ul><ul><ul><li>no enamel (dentin is under cementum) </li></ul></ul><ul><ul><li>pulp cavity – houses blood vessels and nerves that enter/leave via apical foramen in the root canal </li></ul></ul>Fig. 24.11, p. 900
  31. 31. Pharynx <ul><li>Only oropharynx and laryngopharynx are involved in digestion (nasopharynx is only respiratory) </li></ul><ul><li>Lined with nonkeratinized stratified squamous epithelium </li></ul><ul><li>Mucus-producing glands in submucosa produce mucus that lubricates food </li></ul><ul><li>Skeletal muscle responds to somatic reflexes to move food quickly past laryngopharynx </li></ul><ul><li>No serosa or adventitia </li></ul>
  32. 32. Esophagus <ul><li>Runs from laryngopharynx through mediastinum to stomach </li></ul><ul><li>All 4 layers present in wall </li></ul><ul><ul><li>Mucosa – consists of stratified squamous epithelium </li></ul></ul><ul><ul><li>Submucosa – mucus-secreting esophageal glands </li></ul></ul>http://www. usc . edu / hsc /dental/ ghisto / gi /c_2.html
  33. 33. Esophagus <ul><li>Muscularis – changes type as goes down </li></ul><ul><ul><li>top 1/3 – skeletal muscle </li></ul></ul><ul><ul><li>middle 1/3 – mix </li></ul></ul><ul><ul><li>bottom 1/3 – smooth muscle </li></ul></ul><ul><li>Adventitia – dense connective tissue covering </li></ul>http://www. usc . edu / hsc /dental/ ghisto / gi /d_3.html http://www. usc . edu / hsc /dental/ ghisto / gi /d_8.html
  34. 34. Structures Associated with the Esophagus <ul><li>Upper esophageal sphincter – controls movement of material from pharynx into esophagus </li></ul><ul><li>Esophageal hiatus – opening in diaphragm that allows esophagus to pass from thoracic cavity into abdominal cavity </li></ul><ul><li>Gastroesophageal (cardiac) sphincter </li></ul><ul><ul><li>thickening of smooth muscle of inferior esophagus </li></ul></ul><ul><ul><li>aided by diaphragm to close bottom of esophagus </li></ul></ul><ul><ul><li>helps prevent reflux of acidic gastric juice </li></ul></ul>
  35. 35. Esophageal Disorders <ul><li>heartburn – failure of lower esophageal sphincter to close completely allowing acidic gastric juice into esophagus </li></ul><ul><li>hiatus hernia – protrusion of the superior portion of stomach above diaphragm </li></ul><ul><li>esophageal ulcer – erosion of wall due to chronic reflux of stomach acid </li></ul>
  36. 36. Digestive Processes in Mouth, Pharynx and Esophagus <ul><li>Ingestion </li></ul><ul><li>Mechanical Digestion </li></ul><ul><ul><li>mastication by teeth (with aid of tongue) </li></ul></ul><ul><ul><li>formation of bolus </li></ul></ul><ul><li>Chemical digestion by salivary amylase produced by salivary glands </li></ul><ul><ul><li>breaks starch and glycogen into smaller fragments (including maltose [disaccharide] if left long enough) </li></ul></ul><ul><ul><li>continues activity until reaches acid stomach </li></ul></ul><ul><li>Absorption – essentially none (except some drugs, e.g., nitroglycerine) </li></ul>
  37. 37. Digestive Processes in Mouth, Pharynx and Esophagus <ul><li>Movement – deglutition (swallowing) </li></ul><ul><ul><li>moves food from oral cavity to stomach </li></ul></ul><ul><ul><li>voluntary in oral cavity (buccal phase) </li></ul></ul><ul><ul><li>reflexive in pharynx </li></ul></ul><ul><ul><li>involuntary peristalsis where smooth muscle is found </li></ul></ul>Fig. 24.13, p.904
  38. 38. Stomach: Gross Anatomy <ul><li>Cardiac region (cardia) </li></ul><ul><li>Fundus - temporary storage area </li></ul><ul><li>Body </li></ul><ul><ul><li>greater curvature </li></ul></ul><ul><ul><li>lesser curvature </li></ul></ul><ul><li>Pyloric region – distal portion </li></ul><ul><ul><li>Pyloric sphincter – controls movement of chyme into small intestine </li></ul></ul>Fig. 24.14, p. 905 http:// medlib .med. utah . edu / WebPath /GIHTML/GI194.html http:// medlib .med. utah . edu / WebPath /GIHTML/GI194.html
  39. 39. Stomach Histology <ul><li>Mucosa </li></ul><ul><ul><li>simple columnar epithelium </li></ul></ul><ul><ul><li>muscularis mucosae throws mucosa into folds called rugae </li></ul></ul><ul><li>Submucosa – connective tissue </li></ul><ul><li>Muscularis – 3 layers create mixing waves in addition to peristalsis </li></ul><ul><ul><li>longitudinal layer </li></ul></ul><ul><ul><li>circular layer </li></ul></ul><ul><ul><li>oblique layer </li></ul></ul><ul><li>Serosa - covers stomach </li></ul>http://www. gutfeelings .com/STOMACH.HTML Fig. 24.14, p. 905
  40. 40. Microscopic Anatomy <ul><li>Surface composed mainly of goblet cells (secrete mucus) </li></ul><ul><li>Gastric pits </li></ul><ul><ul><li>tight junctions between epithelial cells prevent acidic gastric juice from reaching underlying layers </li></ul></ul><ul><ul><li>contain gastric glands which secrete gastric juice </li></ul></ul><ul><ul><ul><li>mucus neck cells </li></ul></ul></ul><ul><ul><ul><li>parietal (oxyntic) cells </li></ul></ul></ul><ul><ul><ul><li>chief (zymogenic) cells </li></ul></ul></ul><ul><ul><ul><li>enteroendocrine cells </li></ul></ul></ul>http://www. usc . edu / hsc /dental/ ghisto / gi /d_15.html Fig. 24.15, p. 906
  41. 41. Gastric Pit Cells <ul><li>Mucous neck cells secrete bicarbonate-rich mucus </li></ul><ul><li>Parietal (oxyntic) cells secrete: </li></ul><ul><ul><li>HCl (buffered by bicarbonate rich mucus) </li></ul></ul><ul><ul><li>intrinsic factor (essential to absorption of Vit. B 12 by small intestine) </li></ul></ul><ul><li>Chief (zymogenic) cells secrete: </li></ul><ul><ul><li>pepsinogen (inactive form of the protease pepsin for protein hydrolysis) </li></ul></ul><ul><ul><li>minor amounts of lipases (lipid hydrolysis) </li></ul></ul>
  42. 42. Gastric Pit Cells <ul><li>Enteroendocrine cells – release hormones and hormone-like products into the lamina propria where they are picked up by blood and carried to other digestive organs </li></ul><ul><ul><li>gastrin – generally stimulatory </li></ul></ul><ul><ul><li>histamine – stimulates H + secretion </li></ul></ul><ul><ul><li>somatostatin – generally inhibitory </li></ul></ul>
  43. 43. Enteroendocrine Cells: Gastrin <ul><li>most diverse action: </li></ul><ul><li>increases gastric cell activity, especially H + secretion </li></ul><ul><li>stimulates gastric emptying </li></ul><ul><li>stimulates contraction of small intestine </li></ul><ul><li>relaxes ileocecal valve </li></ul><ul><li>stimulates mass movement (large intestine) </li></ul>
  44. 44. Enteroendocrine Cells: Somatostatin <ul><li>also secreted by small intestine in larger amounts </li></ul><ul><li>inhibits gastric secretion, motility and emptying </li></ul><ul><li>inhibits pancreatic secretion </li></ul><ul><li>inhibits activity in small intestine </li></ul><ul><li>inhibits contraction of gall bladder </li></ul>
  45. 45. Digestive Processes in Stomach <ul><li>Mechanical digestion </li></ul><ul><ul><li>mixing waves help break food into smaller particles </li></ul></ul><ul><li>Chemical digestion – produces chyme (pH ~ 2) </li></ul><ul><ul><li>acid (HCl) secreted by parietal cells breaks some bonds and activates pepsinogen into pepsin </li></ul></ul><ul><ul><li>pepsin – </li></ul></ul><ul><ul><ul><li>produced as pepsinogen by chief cells </li></ul></ul></ul><ul><ul><ul><li>hydrolyses proteins </li></ul></ul></ul><ul><ul><li>rennin – protease secreted in children that acts on milk proteins </li></ul></ul>
  46. 46. Digestive Processes in Stomach <ul><li>Movement </li></ul><ul><ul><li>mixing waves mix food with acid and enzymes </li></ul></ul><ul><ul><li>peristalsis moves material through stomach and into small intestine </li></ul></ul><ul><li>Absorption – limited to lipid soluble substances </li></ul><ul><ul><li>alcohol </li></ul></ul><ul><ul><li>aspirin </li></ul></ul><ul><ul><li>some other drugs </li></ul></ul>
  47. 47. Regulation of Gastric Secretion <ul><li>Controlled by nervous system and hormones </li></ul><ul><li>Hormonal control </li></ul><ul><ul><li>gastrin stimulates secretion </li></ul></ul><ul><ul><li>somatostatin, gastric inhibitory protein (GIP), and cholecystokinin inhibit secretion </li></ul></ul><ul><li>Neural control : </li></ul><ul><ul><li>autonomic control (CNS) </li></ul></ul><ul><ul><ul><li>parasympathetic division </li></ul></ul></ul><ul><ul><ul><ul><li>Vagus (X) nerve </li></ul></ul></ul></ul><ul><ul><ul><li>sympathetic division - thoracic spinal nerves </li></ul></ul></ul><ul><ul><li>local enteric nerve reflexes </li></ul></ul><ul><ul><ul><li>distension of stomach stimulates activity </li></ul></ul></ul><ul><ul><ul><li>distension of duodenum inhibits activity </li></ul></ul></ul>See Fig. 24.16, p. 910
  48. 48. Stimulation of Gastric Secretion <ul><li>Cephalic Phase (cerebral) </li></ul><ul><li>Gastric Phase (stomach) </li></ul><ul><li>Intestinal Phase (duodenum) </li></ul>Fig. 24.16, p. 910
  49. 49. Inhibition of Gastric Secretion <ul><li>Cephalic Phase (cerebral) </li></ul><ul><li>Gastric Phase (stomach) </li></ul><ul><li>Intestinal Phase (duodenum) </li></ul>Fig. 24.16, p. 910
  50. 50. Gastric Disorders <ul><li>Gastritis – inflammation of underlying layers of wall </li></ul><ul><li>Gastric ulcers – erosions of stomach wall </li></ul><ul><ul><li>Helicobacter infections associated with ~90% of all ulcers (uncertain as to whether it is causitive agent) </li></ul></ul><ul><ul><li>non-infectious ulcers associated with persistent inflammation </li></ul></ul>
  51. 51. Gastric Disorders (con’t) <ul><li>Emesis = vomiting </li></ul><ul><ul><li>usually caused by </li></ul></ul><ul><ul><ul><li>extreme stretching of stomach or small intestine, or </li></ul></ul></ul><ul><ul><ul><li>presence of irritants in stomach (e.g., bacterial toxins, excessive alcohol, spicy foods, certain drugs) </li></ul></ul></ul><ul><ul><li>emetic center in medulla initiates impulses to </li></ul></ul><ul><ul><ul><li>contract abdominal muscles (increases intra-abdominal pressure) </li></ul></ul></ul><ul><ul><ul><li>relax cardiac sphincter </li></ul></ul></ul><ul><ul><ul><li>raise soft palate (closes off nasal passages) </li></ul></ul></ul><ul><ul><li>excessive vomiting results in dehydration and metabolic alkalosis (increased blood pH) </li></ul></ul>
  52. 52. Small Intestine: Gross Structure <ul><li>Diameter ~ 2.5 cm </li></ul><ul><li>Length ~ 2-4 m (8-13’) (in cadaver, 6-7 m [20-21’] because muscle is not contracted) </li></ul><ul><li>Small intestine designed for secretion (especially proximal end) and absorption </li></ul><ul><ul><li>site of most chemical digestion </li></ul></ul><ul><ul><li>site of most absorption </li></ul></ul><ul><li>pH 7-8 </li></ul><ul><li>Three areas: </li></ul><ul><ul><li>duodenum (25 cm) </li></ul></ul><ul><ul><li>jejunum </li></ul></ul><ul><ul><li>ileum </li></ul></ul>Fig. 24.21, p. 916
  53. 53. Small Intestine: Duodenum <ul><li>Receives chyme from stomach </li></ul><ul><li>Hepatopancreatic ampulla </li></ul><ul><ul><li>union of common bile duct and pancreatic duct </li></ul></ul><ul><ul><li>opens via major duodenal papilla </li></ul></ul><ul><ul><li>hepatopancreatic sphincter (sphincter of Oddi) controls entry of fluid from ampulla </li></ul></ul><ul><li>Duodenal (Brunner’s) glands – secrete alkaline mucus </li></ul>Fig. 24.20, p. 915 http://www. usc . edu / hsc /dental/ ghisto / gi /d_36.html
  54. 54. Small Intestine: Jejunum & Ileum <ul><li>Jejunum </li></ul><ul><ul><li>extends from duodenum to ileum </li></ul></ul><ul><li>Ileum </li></ul><ul><ul><li>extends from jejunum to large intestine </li></ul></ul><ul><ul><li>ileocecal valve controls movement of material into large intestine </li></ul></ul>http://www. usc . edu / hsc /dental/ ghisto / gi /d_43.html http://www. usc . edu / hsc /dental/ ghisto / gi /d_53.html
  55. 55. Small Intestine: Innervation <ul><li>Parasympathetic impulses supplied by Vagus nerve stimulates activity </li></ul><ul><li>Sympathetic impulses supplied by thoracic splanchnic nerves inhibit activity </li></ul><ul><li>Enteric nerves act locally </li></ul>Fig. 14.5, p. 519 Fig. 14.4, p. 517
  56. 56. Small Intestine: Blood Supply <ul><li>Arteries: </li></ul><ul><ul><li>common hepatic artery serves duodenum </li></ul></ul><ul><ul><li>superior mesenteric artery serves most of small intestine </li></ul></ul><ul><li>Veins: </li></ul><ul><ul><li>superior mesenteric vein drains entire small intestine </li></ul></ul>Fig. 20.22, p. 761 Fig. 20.27, p. 771
  57. 57. Small Intestine: Overview of Special Anatomical Features <ul><li>Plicae circularis – circular folds </li></ul><ul><li>Villi – fingerlike projections of intestinal wall </li></ul><ul><li>Microvilli – projections of cell membranes </li></ul>See Fig. 24.21, p. 916 http://www. usc . edu / hsc /dental/ ghisto / gi /c_43.html http:// remf . dartmouth . edu /images/ humanMicrovilliTEM /source/1.html
  58. 58. Small Intestine: Plicae Circularis <ul><li>Circular folds </li></ul><ul><li>Deep, permanent folds of mucosa and submucosa </li></ul><ul><li>Force chyme to spiral through lumen </li></ul><ul><ul><li>mixes chyme with intestinal juice </li></ul></ul><ul><ul><li>slows movement </li></ul></ul><ul><ul><li>Why is this helpful? </li></ul></ul>Fig. 24.21, p. 916 http://www. udel . edu /Biology/Wags/ histopage / colorpage / csi / csiipcv .gif http://www. shu . edu /ha/ anirefs /8751. htm
  59. 59. Small Intestine: Villi <ul><li>Finger-like projections of mucosa (over 1 mm tall) </li></ul><ul><li>Each villus contains: </li></ul><ul><ul><li>blood capillary bed </li></ul></ul><ul><ul><li>lacteal </li></ul></ul><ul><ul><li>smooth muscle - allows villus to shorten </li></ul></ul><ul><ul><ul><li>increases contact between villus and “soup” in lumen </li></ul></ul></ul><ul><ul><ul><li>“ milks” lacteal </li></ul></ul></ul>See also Fig. 24.22, p. 917; Fig. 24.21, p. 916 http://www. udel . edu /Biology/Wags/ histopage / colorpage / csi / csiivgc .GIF http://www. udel . edu /Biology/Wags/ histopage / colorpage / csi / csivv .GIF
  60. 60. Small Intestine: Microvilli <ul><li>Extensions of cell membrane </li></ul><ul><li>Called brush border </li></ul><ul><li>Functions: </li></ul><ul><ul><li>secrete brush border enzymes </li></ul></ul><ul><ul><li>increase surface area for absorption </li></ul></ul>Fig. 24.21, p. 916 See also Fig. 24.22, p. 917 http:// remf . dartmouth . edu /images/ humanMicrovilliTEM /source/1.html
  61. 61. Small Intestine: Mucosa <ul><li>Renewed every 3-6 days </li></ul><ul><li>Simple columnar epithelium </li></ul><ul><ul><li>goblet cells – secrete mucus </li></ul></ul><ul><ul><li>absorptive cells – absorb nutrients </li></ul></ul><ul><ul><ul><li>bound by tight junctions </li></ul></ul></ul><ul><ul><ul><li>microvilli </li></ul></ul></ul><ul><li>Lamina propria </li></ul><ul><ul><li>blood vessels </li></ul></ul><ul><ul><li>lacteals </li></ul></ul><ul><li>Intestinal crypts (crypts of Lieberkuhn) – between villi </li></ul><ul><ul><li>most cells secrete intestinal juice </li></ul></ul><ul><ul><li>Paneth cells secrete lysozyme (antibacterial) </li></ul></ul>See Fig. 24.21, p. 916 http://www. usc . edu / hsc /dental/ ghisto / gi /c_38.html http://www. udel . edu /Biology/Wags/ histopage / colorpage / csi / csidmbg .GIF
  62. 62. Small Intestine: Submucosa <ul><li>Peyer’s patches – lymphatic tissue for protection against disease </li></ul><ul><li>Duodenal (Brunner’s) glands </li></ul><ul><ul><li>secrete alkaline mucus rich in bicarbonate to raise pH of chyme from <3 to >7 </li></ul></ul><ul><ul><li>only in duodenum </li></ul></ul>http://www. udel . edu /Biology/Wags/ histopage / colorpage / csi / csidmbg .GIF http://medicine. ucsd . edu /pathology/~som213/ HistologyImageBank /chapter_4/slide_61_ peyers /pages/a.4.61.1.1. htm
  63. 63. Small Intestine: Muscularis & Serosa <ul><li>Muscularis – two layers of smooth muscle create two kinds of movement </li></ul><ul><ul><li>peristalsis moves chyme through intestine </li></ul></ul><ul><ul><li>segmentation mixes chyme with intestinal juice </li></ul></ul><ul><ul><ul><li>moves between segments a few cm at a time </li></ul></ul></ul><ul><ul><ul><li>intrinsic control in longitudinal muscle (intrinsic pacemaker cells ) </li></ul></ul></ul><ul><ul><li>intensity altered by nervous system and hormones </li></ul></ul><ul><ul><ul><li>parasympathetic impulses increase strength of contraction </li></ul></ul></ul><ul><ul><ul><li>sympathetic impulses decrease it </li></ul></ul></ul>
  64. 64. Small Intestine: Muscularis & Serosa <ul><li>Serosa (visceral peritoneum) – outer covering </li></ul><ul><ul><li>Mesenteries </li></ul></ul><ul><ul><ul><li>visceral peritoneum </li></ul></ul></ul><ul><ul><ul><li>attach small intestine to posterior body wall </li></ul></ul></ul><ul><ul><li>Intraperitoneal organs - surrounded and supported by mesenteries </li></ul></ul>
  65. 65. Small Intestine: Digestive Processes <ul><li>Mechanical digestion – bile salts secreted by liver (stored in and released from gall bladder) emulsify fat globules (make them into smaller droplets) to increase surface area lipases have available to work on </li></ul><ul><li>Chemical digestion – hydrolysis of macromolecules </li></ul><ul><ul><li>lipid digestion </li></ul></ul><ul><ul><li>protein digestion </li></ul></ul><ul><ul><li>carbohydrate digestion </li></ul></ul><ul><ul><li>nucleic acid digestion </li></ul></ul>See Fig. 24.33, p. 933
  66. 66. Small Intestine: Lipid Digestion <ul><li>Pancreatic lipase </li></ul><ul><li>Most common lipids are neutral fats (triglycerides) </li></ul><ul><ul><li>glycerol + 1 fatty acid = monoglyceride </li></ul></ul><ul><ul><li>glycerol + 2 fatty acids = diglyceride </li></ul></ul><ul><ul><li>glycerol + 3 fatty acids = triglyceride </li></ul></ul><ul><li>Triglycerides cleaved into glycerol and 3 fatty acids or monoglycerides and 2 fatty acids </li></ul>Fig. 2.14, p. 48
  67. 67. Small Intestine: Protein Digestion <ul><li>Pancreatic and intestinal proteases break proteins into amino acids </li></ul><ul><li>Pancreatic proteases : trypsin, chymotrypsin and carboxypolypeptidase </li></ul><ul><ul><li>secreted as inactive precoursers (trypsinogen, chymotrypsinogen, and procarboxypolypeptidase, respectively) to protect intestinal mucosa from being digested </li></ul></ul><ul><ul><li>cleave large proteins into small peptides </li></ul></ul><ul><li>Intestinal proteases </li></ul><ul><ul><li>include aminopeptidase, carboxypeptidase, dipeptidase </li></ul></ul><ul><ul><li>cleave small peptides into amino acids </li></ul></ul>See Fig. 2.17, p. 52
  68. 68. Small Intestine: Carbohydrate Digestion <ul><li>Starches – cleaved into short chains (oligosaccharides) and maltose (disaccharide) by pancreatic amylase secreted by pancreas </li></ul><ul><li>Disaccharides hydrolyzed by intestinal (brush border) enzymes: </li></ul><ul><ul><li>maltase – cleaves maltose </li></ul></ul><ul><ul><li>lactase – cleaves lactose </li></ul></ul><ul><ul><li>sucrase – cleaves sucrose </li></ul></ul>Fig. 2.13, p. 46
  69. 69. Small Intestine: Nucleic Acid Digestion <ul><li>Pancreatic nucleases – cleave nucleic acids into nucleotides </li></ul><ul><li>Nucleosidases and phosphatases – cleave nucleotides into sugars, phosphates, bases </li></ul>Fig. 2.22, p. 58
  70. 70. Small Intestine: Absorption of Carbohydrates <ul><li>Absorption moves nutrients from lumen into cells, thence into interstitial fluid to blood or lymph </li></ul><ul><li>Carbohydrates – absorbed as monosaccharides by: </li></ul><ul><ul><li>cotransport with Na + (based on setting up Na + gradient using active transport; glucose and galactose) </li></ul></ul><ul><ul><li>facilitated transport (fructose) </li></ul></ul>
  71. 71. Small Intestine: Absorption of Proteins and Nucleic Acids <ul><li>Proteins – absorbed as amino acids </li></ul><ul><ul><li>cotransport with Na + (based on setting up Na + gradient using active transport) </li></ul></ul><ul><ul><li>proteins rarely taken up intact (absorbed peptides may cause food allergies) </li></ul></ul><ul><li>Nucleic acids – actively absorbed as components: sugar (ribose/deoxyribose), phosphate, nitrogen bases </li></ul>
  72. 72. Small Intestine: Absorption of Lipids <ul><li>Lipids </li></ul><ul><ul><li>combine with bile salts to form micelles </li></ul></ul><ul><ul><li>absorbed passively through lipid bilayer as glycerol and fatty acids or monoglycerides </li></ul></ul><ul><ul><li>combine with proteins within cell to form chylomicrons which are then released into interstitial fluid </li></ul></ul><ul><ul><ul><li>chylomicrons enter lymph through lacteals (lymphatic capillaries) in villi and are transported to subclavian veins </li></ul></ul></ul>
  73. 73. Small Intestine: Absorption of Vitamins <ul><li>Fat-soluble vitamins (DAKE) incorporated into micelles and absorbed in same manner as fats (passively through lipid bilayer) </li></ul><ul><li>Water-soluble vitamins (C, B complex) mostly absorbed by diffusion </li></ul><ul><ul><li>exception is B 12 , which must bind to intrinsic factor produced in stomach to be actively absorbed in ileum (recognition of B 12 -intrinsic factor complex by receptors in plasma membrane of cells triggers active receptor-mediated endocytosis ) </li></ul></ul>
  74. 74. Small Intestine: Absorption of Electrolytes <ul><li>Most actively absorbed throughout small intestine </li></ul><ul><ul><li>absorption based on how much is in food </li></ul></ul><ul><ul><li>Na + /K + pump plays role (Na + into/ K + out) </li></ul></ul><ul><ul><li>K + passively absorbed based on gradient created by pump </li></ul></ul><ul><li>Iron (Fe) and calcium (Ca) only absorbed in duodenum </li></ul><ul><ul><li>depends on needs of body </li></ul></ul><ul><ul><li>iron actively transported into cells where it becomes bound to ferritin </li></ul></ul><ul><ul><li>calcium absorption regulated by vitamin D which serves as cofactor in Ca transport </li></ul></ul>
  75. 75. Small Intestine: Movement <ul><li>Peristalsis moves chyme through intestine </li></ul><ul><li>Segmentation mixes chyme with intestinal juice </li></ul>Fig. 24.3, p. 890
  76. 76. Hormonal Control of Small Intestine Activity <ul><li>Gastrin – secreted by stomach </li></ul><ul><ul><li>stimulates contraction of intestinal smooth muscle </li></ul></ul><ul><ul><li>stimulates relaxation of ileocecal valve </li></ul></ul><ul><li>Vasoactive intestinal peptide (VIP) – from duodenum; acts on duodenum </li></ul><ul><ul><li>stimulates secretion of bicarbonate-rich intestinal juice </li></ul></ul><ul><li>Somatostatin – from stomach and duodenum </li></ul><ul><ul><li>inhibits blood flow and absorption from small intestine </li></ul></ul>
  77. 77. Nervous System Control of Small Intestine Activity <ul><li>Sympathetic impulses decrease activity </li></ul><ul><li>Gastroileal reflex – initiated by increased activity in stomach </li></ul><ul><ul><li>long reflex involving brain and parasympathetic innervation </li></ul></ul><ul><ul><li>parasympathetic impulses increase activity </li></ul></ul>
  78. 78. Accessory Glands: Liver Gross Anatomy <ul><li>Largest gland in body, approximately 1.4 kg </li></ul><ul><li>Upper right hypochondriac and epigastric regions </li></ul><ul><li>4 primary lobes: right, left, caudate, quadrate </li></ul><ul><li>Covered by serosa except for uppermost region just under diaphragm </li></ul>Fig. 24.1, p. 888 See Fig. 24.23, p. 919 http://telpath2.med. utah . edu / WebPath /LIVEHTML/LIVER002.html
  79. 79. Liver: Hepatic Ducts <ul><li>Right hepatic duct – serves right lobe </li></ul><ul><li>Left hepatic duct – serves other lobes </li></ul><ul><li>Common hepatic duct </li></ul><ul><ul><li>formed from union of right and left hepatic ducts </li></ul></ul><ul><ul><li>joins with cystic duct of gall bladder to form common bile duct , which joins with pancreatic duct to form hepato-pancreatic ampulla </li></ul></ul>Fig. 24.20, p. 915
  80. 80. Liver: Ligaments <ul><li>Falciform ligament </li></ul><ul><ul><li>piece of mesentery that separates right and left lobes </li></ul></ul><ul><ul><li>suspends liver from diaphragm and anterior abdominal wall </li></ul></ul><ul><li>Round ligament (= ligamentum teres) – remnant of umbilical vein </li></ul><ul><li>Ligamentum venosum </li></ul><ul><ul><li>remnant of ductus venosus </li></ul></ul>See Fig. 24.23, p. 919 http://www. shu . edu /ha/ imgs /00000/8000/000/8052. jpg http://storm. aecom . yu . edu / virtualDissector /New_online_dissector/Abdomen/Abdomen5-6/photos/STEP3/PAGES/ ligamentum %20venosum_ jpg . htm
  81. 81. Liver: Blood supply <ul><li>Hepatic artery – arterial blood </li></ul><ul><li>Hepatic portal vein – receives nutrient-rich venous blood from stomach, intestines, pancreas, spleen (see lab for vessels) </li></ul><ul><li>Hepatic vein – drains venous blood into inferior vena cava </li></ul>Fig. 20.27, p. 771
  82. 82. Liver: Microscopic Anatomy <ul><li>Designed to filter and process nutrient-rich blood </li></ul><ul><li>Composed of lobules with portal triad at each corner of hexagonal structure </li></ul><ul><ul><li>branch of hepatic artery (HA) </li></ul></ul><ul><ul><li>branch of hepatic portal vein (HPV) </li></ul></ul><ul><ul><li>bile duct (BD) </li></ul></ul>Fig. 24.24, p. 921 http://www. usc . edu / hsc /dental/ ghisto / gi /d_88.html
  83. 83. Liver: Microscopic Anatomy (con’t) <ul><li>Sinusoids – specialized capillaries in which venous and arterial blood mix </li></ul><ul><ul><li>hepatocytes (liver cells) just inside walls of sinusoid perform functions of liver </li></ul></ul><ul><ul><li>Kupffer cells (macrophages) found along wall – remove debris, bacteria, worn out RBCs </li></ul></ul>Fig. 24.24, p. 921
  84. 84. Liver: Microscopic Anatomy (con’t) <ul><li>Central vein drains lobule </li></ul><ul><ul><li>join to form hepatic veins </li></ul></ul><ul><li>Bile canaliculi = channels between hepatocytes </li></ul><ul><ul><li>join to form bile ducts </li></ul></ul><ul><ul><li>bile flow is counter to blood flow </li></ul></ul>Fig. 24.24, p. 921 http://www- edlib .med. utah . edu / WebPath /LIVEHTML/LIVER003.html
  85. 85. Liver Functions <ul><li>Process blood-borne nutrients </li></ul><ul><li>Store glucose (as glycogen) </li></ul><ul><li>Store fat-soluble vitamins </li></ul><ul><li>Store iron (Fe) </li></ul><ul><li>Detoxify poisons </li></ul><ul><li>Produce plasma proteins (see Topic 1) </li></ul><ul><li>Cleanse blood of debris, including bacteria and worn out RBCs </li></ul><ul><li>Produce bile </li></ul>
  86. 86. Liver Functions: Bile <ul><li>Consists of bile salts, bile pigments, cholesterol, neutral fats, phospholipids, electrolytes in water </li></ul><ul><li>Aid digestion of fat </li></ul><ul><ul><li>emulsify (break up) fat globules into droplets </li></ul></ul><ul><ul><li>form micelles (ferry fats to mucosal wall) </li></ul></ul><ul><li>Conserved by enterohepatic circulation (some is reabsorbed by ileum and returned to liver via hepatic portal system) </li></ul><ul><li>Main bile pigment is bilirubin </li></ul><ul><ul><li>formed from breakdown of hemoglobin </li></ul></ul><ul><ul><li>metabolized by bacteria in large intestine (becomes brown pigment) </li></ul></ul>
  87. 87. Control of Bile Production <ul><li>Stimulated by bile salts returning via hepatic portal blood </li></ul><ul><li>Stimulated by secretin (hormone secreted by small intestine in response to fats in chyme) </li></ul>Fig. 24.25, p. 923
  88. 88. Liver Disorders/Disease <ul><li>Hepatitis – inflammation of liver, often caused by viral infection </li></ul><ul><ul><li>transmitted enterically (HVA) or through blood (HVB, HVC, HVD) </li></ul></ul><ul><ul><li>blood-borne viruses are linked to chronic hepatitis and cirrhosis </li></ul></ul><ul><li>Cirrhosis – chronic disease characterized by growth of scar tissue </li></ul><ul><li>Jaundice – yellowing of skin due to build up of bilirubin from liver disease or excessive destruction of RBCs (e.g., neonatal jaundice) </li></ul>
  89. 89. Accessory Glands: Gall Bladder <ul><li>Lies in depression on ventral surface of liver </li></ul><ul><li>Thin-walled, muscular sac (holds about 50 ml) </li></ul><ul><li>Stores and concentrates bile </li></ul><ul><li>Releases bile via cystic duct </li></ul><ul><li>Histology </li></ul><ul><ul><li>mucosa – cells contain microvilli for reabsorption of water </li></ul></ul><ul><ul><li>submucosa – dense CT </li></ul></ul><ul><ul><li>muscularis – contracts to expel bile </li></ul></ul><ul><ul><li>serosa – over ventral portion only </li></ul></ul>http://www. usc . edu / hsc /dental/ ghisto / gi /d_91.html
  90. 90. Control of Bile Release <ul><li>Bile produced by liver backs up into gall bladder when hepatopancreatic sphincter is closed </li></ul><ul><li>Gall bladder releases bile into cystic duct when stimulated by cholecystokinin (secreted by duodenum) and/or parasympathetic impulses </li></ul><ul><li>Release inhibited by somatostatin produced by stomach and duodenum </li></ul>Fig. 24.25, p. 923
  91. 91. Disorders of the Gall Bladder <ul><li>Gallstones (biliary calculi) – result from crystallization of cholesterol due to excess of cholesterol or too little bile salts </li></ul><ul><li>Obstructive jaundice – yellowish coloration of skin due to build up of bile pigments caused by blockage of bile ducts </li></ul>
  92. 92. Accessory Glands: Pancreas <ul><li>Mostly retroperitoneal , head encircled by duodenum, tail abuts spleen </li></ul><ul><li>Acinar cells (acini) </li></ul><ul><ul><li>secrete pancreatic juice rich in enzymes, which are stored in zymogen granules until release </li></ul></ul><ul><ul><li>pancreatic juice excreted through pancreatic duct </li></ul></ul><ul><li>Islets of Langerhans – endocrine cells </li></ul><ul><ul><li>secrete insulin, glucagon, somatostatin </li></ul></ul>See Fig. 24.20, p. 915 http://www. usc . edu / hsc /dental/ ghisto / gi /d_95.html
  93. 93. Composition of Pancreatic Juice <ul><li>Watery, rich in bicarbonate (HCO 3 - ) </li></ul><ul><ul><li>bicarbonate makes it alkaline and neutralizes acidity of chyme </li></ul></ul><ul><li>Digestive enzymes – see Small Intestine: Digestion </li></ul><ul><ul><li>proteases released as zymogens (inactive precursors) </li></ul></ul><ul><ul><ul><li>trypsin – released as trypsinogen (activated by enterokinase enzyme in brush border cells) </li></ul></ul></ul><ul><ul><ul><li>carboxypeptidase & chymotrypsin – activated from precursors by trypsin </li></ul></ul></ul>
  94. 94. Pancreatic Enzymes (con’t) <ul><li>Digestive enzymes </li></ul><ul><ul><li>amylase – hydrolyzes starch and glycogen (animal “starch”) into short carbohydrate chains and maltose </li></ul></ul><ul><ul><li>lipases – hydrolyze neutral fats into fatty acids and glycerol (or mono- and diglycerides) </li></ul></ul><ul><ul><li>nucleases – hydrolyze nucleic acids into nucleotides </li></ul></ul><ul><ul><li>nucleosidases – hydrolyze nucleotides into ribose, nitrogen bases and phosphate </li></ul></ul>
  95. 95. Control of Pancreatic Secretion <ul><li>Secretin </li></ul><ul><ul><li>released from small intestine in response to acidic chyme entering duodenum </li></ul></ul><ul><ul><li>stimulates acini to produce juice rich in bicarbonate </li></ul></ul><ul><li>Cholecystokinin </li></ul><ul><ul><li>released from duodenum in response to fatty or protein-rich chyme </li></ul></ul><ul><ul><li>stimulates acini to secrete juice rich in enzymes </li></ul></ul><ul><li>Vagus nerve – stimulates secretion during cephalic and gastric phases of digestion </li></ul>Fig. 24.28, p. 925
  96. 96. Pancreas’ Endocrine Role: Insulin <ul><li>Secreted when blood glucose increases </li></ul><ul><li>Lowers blood sugar by </li></ul><ul><ul><li>stimulating uptake by body cells (except liver, kidney and brain) </li></ul></ul><ul><ul><li>stimulates glycogen formation in liver and skeletal muscle </li></ul></ul><ul><ul><li>inhibits gluconeogenesis (conversion of fats and protein to glucose) in liver </li></ul></ul><ul><ul><li>stimulates carbohydrate metabolism in most cells </li></ul></ul>
  97. 97. Pancreas’ Endocrine Role: Glucagon <ul><li>Secreted in response to low blood glucose </li></ul><ul><li>Increases blood sugar by: </li></ul><ul><ul><li>Promotes breakdown of glycogen by liver (glycogenolysis) </li></ul></ul><ul><ul><li>Stimulates synthesis of glucose from lactic acid and noncarbohydrate sources (gluconeogenesis) by liver </li></ul></ul><ul><ul><li>Stimulates release of glucose into blood by liver </li></ul></ul><ul><ul><li>Inhibits uptake and use of carbohydrates by skeletal muscle </li></ul></ul>
  98. 98. Disorders of the Pancreas <ul><li>Pancreatitis – inflammation of the pancreas </li></ul><ul><li>may be caused by excessive fat in blood </li></ul><ul><li>activation of enzymes within pancreas (pancreas digests itself) </li></ul>
  99. 99. Large Intestine <ul><li>Located primarily in abdominal cavity, distal end is in pelvic cavity </li></ul><ul><li>Larger in diameter, but shorter (~1.5 m) than small intestine </li></ul><ul><li>Modifications: </li></ul><ul><ul><li>teniae coli – reduction of longitudinal layer of muscularis </li></ul></ul><ul><ul><li>haustra – pocket-like sacs formed by motor tone of teniae coli </li></ul></ul><ul><ul><li>epiploic appendages – small, fat-filled pouches of visceral peritoneum </li></ul></ul>Fig. 24.29, p. 928
  100. 100. Large Intestine: Subdivisions <ul><li>Cecum </li></ul><ul><ul><li>vermiform appendix </li></ul></ul><ul><li>Colon </li></ul><ul><ul><li>ascending </li></ul></ul><ul><ul><li>transverse </li></ul></ul><ul><ul><li>descending </li></ul></ul><ul><ul><li>sigmoid </li></ul></ul><ul><li>Rectum </li></ul>Fig. 24.29, p. 928
  101. 101. Large Intestine: Anal Canal <ul><li>Arranged as anal columns (long folds of anal mucosa) </li></ul><ul><ul><li>composed of stratified squamous epithelium </li></ul></ul><ul><ul><li>anal sinuses secrete mucus when compressed by feces </li></ul></ul><ul><li>Sphincters control defecation </li></ul><ul><ul><li>internal anal sphincter – smooth muscle </li></ul></ul><ul><ul><li>external anal sphincter – skeletal muscle </li></ul></ul>Fig. 24.29, p. 928
  102. 102. Large Intestine: Histology <ul><li>Mucosa – thicker than in small intestine </li></ul><ul><ul><li>crypts contain numerous goblet cells </li></ul></ul><ul><ul><li>simple columnar epi. with lots of goblet cells </li></ul></ul><ul><ul><li>stratified squamous in anal canal </li></ul></ul><ul><li>Submucosa – thinner than in small intestine </li></ul><ul><ul><li>less lymphatic tissue </li></ul></ul><ul><li>Muscularis – longitudinal layer is modified as teniae coli </li></ul><ul><li>Serosa – covers all but region in pelvic cavity </li></ul>See Fig. 24.31, p. 930 http://www. usc . edu / hsc /dental/ ghisto / gi /d_60.html
  103. 103. Intestinal Flora <ul><li>Resident bacteria dominated by Escherichia coli ( E. coli ) </li></ul><ul><li>Ferment some indigestible carbohydrates </li></ul><ul><ul><li>results in mixture of irritating acids and gases </li></ul></ul><ul><li>Synthesize B vitamins and vit. K </li></ul>
  104. 104. Digestion in Large Intestine <ul><li>No additional breakdown of molecules except by bacteria </li></ul><ul><li>Reabsorption of water and electrolytes (very important to water and electrolyte balance) </li></ul><ul><li>Absorption of vitamins produced by bacteria </li></ul>
  105. 105. Movements in Large Intestine <ul><li>Formation of feces </li></ul><ul><li>Haustral churning </li></ul><ul><ul><li>slow process in which distention of hastrum stimulates contraction which moves food into next haustrum </li></ul></ul><ul><ul><li>mixes food residue and aids water reabsorption </li></ul></ul><ul><li>Mass peristalsis </li></ul><ul><ul><li>long, slow movements along length of large intestine force food toward rectum </li></ul></ul><ul><ul><li>stimulated by gastrocolic reflexes based on stretching of stomach </li></ul></ul>
  106. 106. Defecation <ul><li>Parasympathetic reflex relaxation of smooth muscle (internal) sphincter </li></ul><ul><li>Voluntary relaxation of external sphincter (skeletal muscle) </li></ul>Fig. 24.32, p. 931
  107. 107. Large Intestine: Disorders <ul><li>Appendicitis – inflammation of the appendix, usually caused by bacterial infection </li></ul><ul><li>Diarrhea </li></ul><ul><ul><li>watery stools due to shortened residence time </li></ul></ul><ul><ul><li>caused by irritants, bacterial or viral disease </li></ul></ul><ul><ul><li>loss of water and electrolytes can lead to dehydration and electrolyte imbalances </li></ul></ul><ul><li>Constipation </li></ul><ul><ul><li>hard stools due to increased time for water reabsorption </li></ul></ul><ul><ul><li>can also lead to electrolyte and pH imbalances </li></ul></ul>
  108. 108. Large Intestine: Disorders <ul><li>Hemorrhoids – inflammation of the superficial anal veins </li></ul><ul><li>Colitis – inflammation of the colon </li></ul><ul><li>Diverticulosis </li></ul><ul><ul><li>formation of small herniations in mucosa of large intestine </li></ul></ul><ul><ul><li>common in elderly, especially those whose diets are low in bulk (fiber from fruits and vegetables provides bulk) </li></ul></ul><ul><li>Diverticulitis – inflammation of diverticula </li></ul><ul><li>Crohn’s disease – chronic inflammation; usually in ileum or large intestine </li></ul>

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