1 / 106

TOPIC 8 Digestive System

Biology 221 Anatomy & Physiology II. TOPIC 8 Digestive System. Chapter 18 pp. 651-677. E. Lathrop-Davis / E. Gorski / S. Kabrhel. Digestive System Functions. Provide nutrients in usable form Remove unusable wastes. Digestive System Overview . Two main groups of organs:

Roberta
Télécharger la présentation

TOPIC 8 Digestive System

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Biology 221 Anatomy & Physiology II TOPIC 8Digestive System Chapter 18 pp. 651-677 E. Lathrop-Davis / E. Gorski / S. Kabrhel

  2. Digestive System Functions • Provide nutrients in usable form • Remove unusable wastes

  3. Digestive System Overview Two main groups of organs: • Alimentary canal (a.k.a. Gastrointestinal tract) • tube through which food passes • responsible for digestion and absorption of food • mouth, pharynx, esophagus, stomach, small intestines, large intestines • Accessory organs • organs, glands and structures which aid digestion but not part of GI tract itself • teeth, tongue, salivary glands, pancreas, liver, gall bladder Fig. 24.1, p. 888

  4. Processes of Digestion • Ingestion – entrance of food and drink into mouth • Mechanical digestion – physical breakdown into smaller pieces • Propulsion – movement through gut • Chemical digestion – breakage of molecules into smaller compounds • Absorption – uptake of nutrients from lumen • Defecation – removal of indigestible material Fig. 24.2, p. 889

  5. Peritoneum • Serous membrane • parietal peritoneum – lines abdominal cavity • organs posterior to the parietal peritoneum are retroperitoneal • visceral peritoneum (serosa)– covers surfaces of most abdominal organs • Mesenteries – double layer of peritoneum extending from body wall to digestive organs • intraperitoneal organs are those in mesentaries • Peritoneal cavity – fluid-filled “space” between visceral and parietal peritoneum • Peritonitis – inflammation of the peritoneum See also Fig. 24.5, p. 891 Fig,. 24.30, p. 929

  6. Splanchnic Circulation Arteries serving the digestive organs: • Celiac Trunk – very short; gives rise to: • hepatic artery – liver; gall bladder; stomach; duodenum • left gastric artery – stomach; inferior esophagus • splenic artery – spleen; stomach; pancreas • Superior Mesenteric Artery – small intestines; most of large intestine; pancreas • Inferior Mesenteric Artery – large intestine Fig. 20.22, p. 761 Fig. 20.22, p. 759

  7. Hepatic Circulation: Hepatic portal system • Veins draining digestive organs and carrying nutrient-rich blood to liver • gastric vein– drains stomach • superior mesenteric vein– drains small intestine • splenic vein– drains spleen • inferior mesenteric vein – drains large intestine • Venous blood from hepatic portal system mixes with arterial blood (hepatic artery) in liver Fig. 20.27, p. 771

  8. Hepatic Circulation: Hepatic Veins • drain venous blood from liver into inferior vena cava Fig. 20.27, p. 771

  9. Mucosa • Mucous membrane lining gut • Consists of: • epithelium – lining • lamina propria – areolar connective tissue layer • muscularis mucosae – smooth muscle http://www.usc.edu/hsc/dental/ghisto/gi/d_1.html

  10. Mucosa: Epithelium • Type varies depending on location • stratified squamous epithelium found in mouth, esophagus and anal canal • simple columnar epithelium found in stomach and intestines • Secretes mucus, digestive enzymes, hormones • Provides intact barrier to protect against entry of bacteria http://www.usc.edu/hsc/dental/ghisto/gi/c_2.html http://www.usc.edu/hsc/dental/ghisto/gi/d_15.html

  11. Mucosa: Lamina Propria • Layer of areolar connective tissue • Blood capillaries nourish epithelium, absorb and transport digested nutrients • Lymphatic capillaries provide drainage for interstitial fluid and transport fats to venous circulation http://www.usc.edu/hsc/dental/ghisto/gi/d_60.html

  12. Mucosa: Muscularis Mucosae • Smooth muscle used for local movement and to hold mucosa in folds (small intestine) http://education.vetmed.vt.edu/Curriculum/VM8054/Labs/Lab19/EXAMPLES/Exileum.htm

  13. Submucosa • Dense connective tissue superficial to mucosa • Highly vascularized • Many lymphatic vessels • Lymph nodules • MALT = mucosa-associated lymphatic tissue • especially in small (Peyer’s Patches) and large intestines http://education.vetmed.vt.edu/Curriculum/VM8054/Labs/Lab19/EXAMPLES/Exileum.htm

  14. Muscularis Externa (Muscularis) • Two layers in most organs (3 in stomach) • circular layer • longitudinal layer • Peristalsis moves material through gut • Segmentation helps mix material with digestive enzymes in small intestine Fig. 24.3, p. 890

  15. Serosa • Visceral peritoneum – simple squamous epithelium (mesothelium) with areolar CT • Adventitia – dense connective tissue covering without epithelium; found around esophagus • Retroperitoneal organs have both a serosa (of parietal peritoneum) and adventitia (on side abutting body wall)

  16. Enteric Nervous System Intrinsic nerve plexuses: • Enteric neurons • neurons able to act independently of central nervous system • communicate with each other to control GI activity • Two main enteric plexuses: • submucosal nerve plexus – regulates glands in submucosa and smooth muscle of muscularis mucosae • myenteric nerve plexus – regulates activity of muscularis externa (with aide of submucosal nerve plexus)

  17. Central Nervous System Control • Enteric nerve plexuses linked to CNS by visceral afferent (sensory) fibers • Digestive system receives motor input from sympathetic and parasympathetic divisions of autonomic nervous system • parasympathetic outflow generally increases activity • sympathetic outflow generally decreases activity

  18. Mouth (Oral Cavity) • Oral oriface is anterior opening • Mouth is continuous with oropharynx • Lips and cheeks keep food in oral cavity • Three layers of tissue: • mucosa (stratified squamous epithelium) • submucosa • muscularis externa (skeletal muscle)

  19. Mouth: Palate • Hard palate • palatine process of maxilla • palatine bones • Soft palate • muscle only • prevents food from entering nasopharynx during swallowing • uvula (part that hangs down in middle) Fig. 24.7, p. 895

  20. Mouth: Arches • Palatoglossal arch – anchors soft palate to tongue • Palatopharyngeal arch anchors soft palate to wall of oropharynx • Fauces – area between arches • palatine tonsils – located in fauces Fig. 24.7, p. 895

  21. Mouth: Tongue • Lingual tonsil – sits at base of tongue; protects against invasion by bacteria • Taste buds • contain receptors for taste • found in some papillae Fig. 24.8, p. 896

  22. Mouth: Tongue • Tongue forms bolus • ball of food • makes food easier to swallow • keeps food between teeth • Muscles – served by nerve XII • intrinsic muscles – within tongue (not attached to bone); allow tongue to change shape for swallowing and speech • extrinsic muscles – attach to bone or soft palate; alter tongue position (protrusion, retraction, side-to-side) Fig. 24.7, p. 895

  23. Salivary Glands • Produce saliva • Two groups of salivary glands • intrinsic glands (buccal glands) – within oral cavity • extrinsic glands – 3 pairs (see A&P I Unit VI for innervation) • parotid glands (connected to oral cavity by parotid duct; mumps is a viral infection of the parotid glands) • sublingual glands • submandibular glands Fig. 24.9, p. 897

  24. Saliva • Mucus cells produce mucus (less common) • Watery saliva produced by serous cells; composition: • 97-99.5% water • slightly acidic (pH ~ 6.8) • electrolytes (ions such as Na+, K+, Cl-, PO4=, HCO3-) • metabolic wastes (urea, uric acid) • proteins

  25. Salivary Proteins • Mucin – glycoprotein portion of mucus that lubricates oral cavity) • Lysozyme – antibacterial • IgA– antibodies that prevent antigens from attaching to mucus membrane • Defensins – secreted by neutrophils; act as local antibiotic and chemotatic agent when mucosa is damaged • Salivary amylase – hydrolyzes starch

  26. Control of Salivation • Sympathetic division • stimulates production of mucin-rich saliva, or • inhibits salivation altogether at high levels

  27. Control of Salivation • Parasympathetic division of ANS stimulates activity • chemoreceptors (excited most by acidic substances) and baroreceptors (excited by mechanical stimuli) send messages to salivatory nuclei in pons and medulla • parasympathetic motor output results in salivation • psychological control – response to visual, olfactory stimuli, even thoughts of food • salivary nuclei are stimulated by irritation to lower GI tract • Parasympathetic nerves • facial – to submandibular, sublingual • glossopharyngeal – to parotids

  28. Teeth • Lie in alveoli of mandible and maxilla (see A&P I axial skeleton lab) • Primary dentition = deciduous teeth (20 milk or baby teeth) • roots are absorbed as permanent teeth grow in, causes baby teeth to fall out Fig. 24.10, p. 899

  29. Teeth Permanent dentition = adult teeth (32) • 8 Incisors (central and lateral) • 4 Canines (eyeteeth) • 8 Bicuspids = premolars • Molars • 4 first molars • 4 second molars • 4 third molars • wisdom teeth • may become impacted as grow in Fig. 24.10, p. 899

  30. Tooth Structure • Crown - covered by enamel (hardest substance in body); underlain with dentin • Neck • Root • cementum – calcified connective tissue covering dentin of root; attaches root to periodontal ligament which anchors tooth to alveolus • no enamel (dentin is under cementum) • pulp cavity – houses blood vessels and nerves that enter/leave via apical foramen in the root canal Fig. 24.11, p. 900

  31. Pharynx • Only oropharynx and laryngopharynx are involved in digestion (nasopharynx is only respiratory) • Lined with nonkeratinized stratified squamous epithelium • Mucus-producing glands in submucosa produce mucus that lubricates food • Skeletal muscle responds to somatic reflexes to move food quickly past laryngopharynx • No serosa or adventitia

  32. Esophagus • Runs from laryngopharynx through mediastinum to stomach • All 4 layers present in wall • Mucosa – consists of stratified squamous epithelium • Submucosa – mucus-secreting esophageal glands http://www.usc.edu/hsc/dental/ghisto/gi/c_2.html

  33. Esophagus • Muscularis – changes type as goes down • top 1/3 – skeletal muscle • middle 1/3 – mix • bottom 1/3 – smooth muscle • Adventitia – dense connective tissue covering http://www.usc.edu/hsc/dental/ghisto/gi/d_8.html http://www.usc.edu/hsc/dental/ghisto/gi/d_3.html

  34. Structures Associated with the Esophagus • Upper esophageal sphincter – controls movement of material from pharynx into esophagus • Esophageal hiatus – opening in diaphragm that allows esophagus to pass from thoracic cavity into abdominal cavity • Gastroesophageal (cardiac) sphincter • thickening of smooth muscle of inferior esophagus • aided by diaphragm to close bottom of esophagus • helps prevent reflux of acidic gastric juice

  35. Esophageal Disorders • heartburn – failure of lower esophageal sphincter to close completely allowing acidic gastric juice into esophagus • hiatus hernia – protrusion of the superior portion of stomach above diaphragm • esophageal ulcer – erosion of wall due to chronic reflux of stomach acid

  36. Digestive Processes in Mouth, Pharynx and Esophagus • Ingestion • Mechanical Digestion • mastication by teeth (with aid of tongue) • formation of bolus • Chemical digestion by salivary amylase produced by salivary glands • breaks starch and glycogen into smaller fragments (including maltose [disaccharide] if left long enough) • continues activity until reaches acid stomach • Absorption– essentially none (except some drugs, e.g., nitroglycerine)

  37. Digestive Processes in Mouth, Pharynx and Esophagus • Movement – deglutition (swallowing) • moves food from oral cavity to stomach • voluntary in oral cavity (buccal phase) • reflexive in pharynx • involuntary peristalsis where smooth muscle is found Fig. 24.13, p.904

  38. Stomach: Gross Anatomy • Cardiac region (cardia) • Fundus - temporary storage area • Body • greater curvature • lesser curvature • Pyloric region– distal portion • Pyloric sphincter– controls movement of chyme into small intestine http://medlib.med.utah.edu/WebPath/GIHTML/GI194.html Fig. 24.14, p. 905 http://medlib.med.utah.edu/WebPath/GIHTML/GI194.html

  39. Stomach Histology • Mucosa • simple columnar epithelium • muscularis mucosae throws mucosa into folds called rugae • Submucosa– connective tissue • Muscularis – 3 layers create mixing waves in addition to peristalsis • longitudinal layer • circular layer • oblique layer • Serosa - covers stomach http://www.gutfeelings.com/STOMACH.HTML Fig. 24.14, p. 905

  40. Microscopic Anatomy • Surface composed mainly of goblet cells (secrete mucus) • Gastric pits • tight junctions between epithelial cells prevent acidic gastric juice from reaching underlying layers • contain gastric glands which secrete gastric juice • mucus neck cells • parietal (oxyntic) cells • chief (zymogenic) cells • enteroendocrine cells Fig. 24.15, p. 906 http://www.usc.edu/hsc/dental/ghisto/gi/d_15.html

  41. Gastric Pit Cells • Mucous neck cells secrete bicarbonate-rich mucus • Parietal (oxyntic) cells secrete: • HCl (buffered by bicarbonate rich mucus) • intrinsic factor (essential to absorption of Vit. B12 by small intestine) • Chief (zymogenic) cells secrete: • pepsinogen (inactive form of the protease pepsin for protein hydrolysis) • minor amounts of lipases (lipid hydrolysis)

  42. Gastric Pit Cells • 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 • gastrin – generally stimulatory • histamine – stimulates H+ secretion • somatostatin – generally inhibitory

  43. Digestive Processes in Stomach • Mechanical digestion • mixing waves help break food into smaller particles • Chemical digestion – produces chyme (pH ~ 2) • acid (HCl) secreted by parietal cells breaks some bonds and activates pepsinogen into pepsin • pepsin – • produced as pepsinogen by chief cells • hydrolyses proteins • rennin – protease secreted in children that acts on milk proteins

  44. Digestive Processes in Stomach • Movement • mixing waves mix food with acid and enzymes • peristalsis moves material through stomach and into small intestine • Absorption – limited to lipid soluble substances • alcohol • aspirin • some other drugs

  45. Regulation of Gastric Secretion Controlled by nervous system and hormones • Hormonal control • gastrin stimulates secretion • somatostatin, gastric inhibitory protein (GIP), and cholecystokinin inhibit secretion • Neural control: • autonomic control (CNS) • parasympathetic division • Vagus (X) nerve • sympathetic division - thoracic spinal nerves • local enteric nerve reflexes • distension of stomach stimulates activity • distension of duodenum inhibits activity See Fig. 24.16, p. 910

  46. Stimulation of Gastric Secretion • Cephalic Phase (cerebral) • Gastric Phase (stomach) • Intestinal Phase (duodenum) Fig. 24.16, p. 910

  47. Inhibition of Gastric Secretion • Cephalic Phase (cerebral) • Gastric Phase (stomach) • Intestinal Phase (duodenum) Fig. 24.16, p. 910

  48. Gastric Disorders • Gastritis –inflammation of underlying layers of wall • Gastric ulcers –erosions of stomach wall • Helicobacter infections associated with ~90% of all ulcers (uncertain as to whether it is causitive agent) • non-infectious ulcers associated with persistent inflammation

  49. Gastric Disorders (con’t) • Emesis = vomiting • usually caused by • extreme stretching of stomach or small intestine, or • presence of irritants in stomach (e.g., bacterial toxins, excessive alcohol, spicy foods, certain drugs) • emetic center in medulla initiates impulses to • contract abdominal muscles (increases intra-abdominal pressure) • relax cardiac sphincter • raise soft palate (closes off nasal passages) • excessive vomiting results in dehydration and metabolic alkalosis (increased blood pH)

  50. Small Intestine: Gross Structure • Diameter ~ 2.5 cm • Length ~ 2-4 m (8-13’) (in cadaver, 6-7 m [20-21’] because muscle is not contracted) • Small intestine designed for secretion (especially proximal end) and absorption • site of most chemical digestion • site of most absorption • pH 7-8 • Three areas: • duodenum (25 cm) • jejunum • ileum Fig. 24.21, p. 916

More Related