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Saladin Ch. 25

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Saladin Ch. 25

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    1. Saladin Ch. 25 The Digestive System

    2. Digestion Digestion breakdown of larger food molecules into particles small enough for absorption Digestive System organs that collectively perform digestion

    3. Digestive System: Overview

    4. Digestive Process The GI tract is a “disassembly” line Nutrients become more available to the body in each step There are six essential activities: Ingestion, propulsion, and mechanical digestion Chemical digestion, absorption, and defecation

    5. Digestive Process

    6. Gastrointestinal Tract Activities Ingestion – eating Propulsion – swallowing & peristalsis Peristalsis – waves of contraction & relaxation of muscles in organ walls Mechanical digestion – chewing, mixing, & churning food

    7. Peristalsis and Segmentation

    8. Gastrointestinal Tract Activities Chemical Digestion – Secretion of water, acid, buffers, enzymes. Large molecules are split into smaller pieces. Absorption – material enters epithelial cells lining GI tract and is passed on to the lymph or blood. Defecation – elimination of indigestible solid wastes.

    9. Digestive & Accessory Organs Digestive Gastrointestinal (GI) Tract = Alimentary Canal - continuous tube running from mouth to anus. Digests and absorbs. Mouth, pharynx, esophagus, stomach, small intestine, large intestine Accessory Digestive Organs Aid in processing - food doesn't go into these organs. Teeth, tongue, salivary glands, liver, gallbladder, pancreas.

    10. Histology of the Alimentary Canal All the walls of the GI tract have the same four tunics: From the lumen outward they are the mucosa, submucosa, muscularis externa, & serosa.

    11. Histology of the Alimentary Canal

    12. Mucosa Moist epithelial layer that lines the lumen of the alimentary canal. Three layers: a lining epithelium, lamina propria, & muscularis mucosae.

    13. Mucosa: Epithelial Lining Mouth, pharynx, esophagus, anal canal =non-keratinized stratified squamous. Stomach, intestines= simple columnar epithelium. Exocrine glands: Put mucus & fluid in Enteroendocrine glands - secrete hormones into blood stream.

    14. Lamina Propria: layer of areolar tissue deep to lining - Connects to muscularis mucosae. Muscularis mucosae - thin smooth muscle fibers - helps increase surface area by moving folds of mucosa so they are fully exposed to nutrients. Mucosa: Lamina Propria and Muscularis Mucosae

    15. Submucosa Submucosa - binds mucosa to muscularis externa; Areolar CT Contains submucosal plexus - part of the enteric nervous system Also contains - glands, blood, lymph

    16. Muscularis Externa & Serosa Muscularis Externa – Smooth muscle layer. Contains the myenteric plexus - the other enteric nervous system component. Serosa - superficial layer of GI organs in the abdominal cavity CT and epithelium; Visceral layer of peritoneum - serous membrane.

    17. Enteric Nervous System Composed of two major intrinsic nerve plexuses: Submucosal nerve plexus – regulates glands and smooth muscle in the mucosa. Myenteric nerve plexus – Major nerve supply that controls GI tract mobility.

    18. Enteric Nervous System Segmentation & peristalsis are largely automatic involving local reflex arcs. Linked to the CNS via long autonomic reflex arc.

    19. Peritoneum and Peritoneal Cavity Peritoneum – serous membrane of the abdominal cavity. Parietal – lines the body wall. Visceral – covers external surface of most digestive organs.

    20. Peritoneum and Peritoneal Cavity Peritoneal cavity: Narrow space between parietal and visceral layers. Lubricates digestive organs. Allows them to slide across one another.

    21. Peritoneum and Peritoneal Cavity

    22. Peritoneum and Peritoneal Cavity Lesser Omentum - from stomach and duodenum - attaches these to the liver. Greater Omentum - fatty apron hanging down over colon and small intestine on the anterior aspect. Mesocolon - fold that binds the large intestine to the posterior abdominal wall

    24. Peritoneum and Peritoneal Cavity Retroperitoneal organs – organs outside the peritoneum. Only have peritoneum on anterior surface. Peritoneal organs (intraperitoneal) – organs surrounded by peritoneum.

    25. Regulation of GI Tract Regulation of digestion involves: Mechanical & chemical stimuli – stretch receptors, osmolarity, & presence of substrate in the lumen Extrinsic control Intrinsic control

    26. Nervous Control of the GI Tract Intrinsic controls: Nerve plexuses near the GI tract initiate short reflexes. Short reflexes are mediated by local enteric plexuses (gut brain).

    27. Nervous Control of the GI Tract Extrinsic controls: Long reflexes arising within or outside the GI tract. Involve CNS centers and extrinsic autonomic nerves.

    28. Regulation of GI Tract Hormones: Gastrin, secretin, CCK, histamine, paracrines [see hormone chart]

    29. Mouth Oral or buccal cavity: Is bounded by lips, cheeks, palate, & tongue. Vestibule – bounded by the lips & cheeks externally, & teeth and gums internally.

    30. Anatomy of the Oral Cavity: Mouth

    31. Tongue Skeletal muscle covered with mucous membrane. Intrinsic muscles – originate and insert in tongue - For swallowing and speech Extrinsic muscles – originate outside the tongue & insert in it. Move side to side &in & out. Aid in movement of food into bolus.

    32. Palate Palate: Hard [palatine bones + palatine processes of maxilla; Soft – skeletal muscle

    33. Oral Cavity and Pharynx: Anterior View

    34. Teeth Primary and permanent dentitions have formed by age 21. Primary – 20 deciduous “milk” teeth. Permanent – 32 secondary teeth,

    35. Classification of Teeth Teeth are classified according to their shape and function. Incisors – chisel-shaped - adapted for cutting or nipping. Canines – conical or fanglike - tear or pierce Premolars (bicuspids) & molars – broad crowns with rounded tips - for grinding or crushing

    36. Deciduous Teeth

    37. Permanent Teeth

    38. Tooth Structure Two main regions – crown & root. Crown – exposed part above the gingiva (gum). Root – portion embedded in the jawbone.

    39. Tooth Structure Enamel – acellular, brittle material composed mostly of calcium phosphate. Enamel is the hardest substance produced by the body. Encapsulates the crown of the tooth.

    40. Tooth Structure Anatomy of a tooth: Crown, neck, root, apical foramen. Enamel – hardest substance produced, covers crown; Mostly calcium phosphate Dentin – bone-like, secreted by cells of pulp

    41. Tooth Structure Cementum – covering of root, similar to bone Periodontal ligament – anchors tooth to alveolar socket, which is surrounded by gingiva (gums)

    42. Tooth Structure

    43. Salivary Glands Parotid – anterior to ear over the masseter. Parotid duct – opens into vestibule next to the second upper molar. Secretes salivary amylase. Swollen when infected by mumps virus

    44. Salivary Glands Submandibular – beneath posterior tongue. Secretes saliva with salivary amylase. Sublingual – anterior to submandibular gland under the tongue. Opens into the floor of the mouth.

    45. Salivary Glands

    46. Saliva Saliva 1-1.5 L/day Blood filtrate + salivary amylase, mucin & lysozyme

    47. Saliva Control – ANS – food stimulates tactile, pressure and taste sensor ? salivatory nuclei in medulla Parasympathetic – normal salivation – facial and glossopharyngeal nerves Sympathetic – decreased salivation

    48. Pharynx From the mouth, the oro- & laryngopharynx allow passage of: Food and fluids to the esophagus. Air to the trachea. See Ch. 22

    49. Esophagus Muscular [skeletal to smooth] – a collapsible tube. All 4 layers, modified. Mucosa – stratified squamous epithelium; esophageal glands in submucosa; musc. Ext. has both smooth and skeletal muscle; serosa replaced with adventitia

    50. Esophagus Passes through mediastinum and diaphragm [esophageal hiatus] “hiatal hernias” Functions: secretes mucus, transports bolus to stomach [cardiac orifice]

    51. Swallowing Deglutition – swallowing controlled by medulla & pons swallow center – involves trigeminal, facial, glossopharyngeal, & hypoglossal nerves. 2 phases – Buccal phase – bolus formation, pharyngealesophageal phase –moves to stomach Peristalsis – waves of muscular contraction – move bolus

    52. Deglutition (Swallowing)

    53. Stomach Functions Storage Mechanical breakdown of food Enzymatic digestion of food Absorption of simple compounds Produces gastrin Bacterial protection Produces intrinsic factor

    54. Stomach Cardiac region – surrounds the cardiac orifice. Fundus – dome-shaped region beneath the diaphragm. Body – midportion of the stomach. Pyloric region – made up of the antrum and canal, through the pyloric sphincter.

    55. Stomach

    56. Stomach Innervation & circulation Para = vagus, sym = celiac ganglion Arterial – celiac artery, venous – hepatic portal system

    57. Stomach Wall Muscularis – 3 layers instead of two – longitudinal, circular and oblique smooth layers Submucosa & mucosa - Ruggae – large folds in mucosa Mucosa – simple columnar epithelium

    58. Glands of the Stomach Fundus and Body Gastric Pits of the fundus & body have a variety of secretory cells: Mucous cells –> mucus Parietal cells –> HCl & intrinsic factor Chief cells –> pepsinogen Pepsinogen is activated to pepsin by:

    59. Glands of the Stomach Fundus and Body Enteroendocrine cells –> gastrin, histamine, serotonin, & somatostatin into the lamina propria

    60. Microscopic Anatomy of the Stomach

    61. Gastric Secretions Produces 2-3L of gastric juice/day HCl – get H from CO2 – carbonic anhydrase reaction [parietal cells] pumped out by active transport. Pepsin – digests protein; also get chymosin & gastric lipase in infants

    62. Gastric Secretions Intrinsic factor - also from parietal cells – needed to absorb B12 [only indispensable function of stomach] Chemical messengers enteroendocrine cells make up to 20 – include gut-brain peptides like substance P, vasoactive intestinal peptide, secretin, etc.

    63. Stomach Lining To keep from digesting itself, the stomach has a mucosal barrier with: A thick coat of bicarbonate-rich mucus on the stomach wall. Epithelial cells that are joined by tight junctions. Gastric juices released only in presence of food which dilutes its effects

    64. Gastric Motility Receptive-relaxation response – stomach relaxes to receive food [stim. by medulla] Peristaltic contractions – increasing in strength. Squirts 3 mL of chime into duodenum/ wave

    65. Vomiting Emetic center of medulla Usually preceded by nausea & retching Projectile vomiting – no prior nausea, etc. – common in infants. Bulimia – eating disorder – erodes tooth enamel, aspiration of acid injures respiratory tree, acid reflux damages esophagus

    66. Regulation of Gastric Secretion Neural & hormonal mechanisms regulate release of gastric juice. 3 phases of events: Cephalic (reflex) phase: prior to food entry. Gastric phase: once food enters the stomach. Intestinal phase: as partially digested food enters the duodenum.

    67. Cephalic Phase Events include: Sight or thought of food; Stimulation of taste or smell receptors. Stimulate secretions from parietal cells, Chief cells, and mucus cells.

    68. Gastric Phase Events include: Release of gastrin to the blood. Stomach distension & increase in pH due to food.

    69. Intestinal Phase Mostly inhibitory – small intestine receptors are activated by influx of chyme – enterogastric reflex. Slows exit of chyme and prevents duodenal overload.

    70. Intestinal Phase Chyme also stimulates enteroendocrine cells to release secretin, CCK and gastric inhibitory protein. Secretin & CCK stim. pancreas and gallbladder. All 3 suppress gastric secretion & motility  

    71. Release of Gastric Juice

    72. Liver The largest gland in the body Functions: Synthesis of bile salts Excretion of bile

    73. Liver 2 Lobes [R,L] separated by falciform running from diaphragm between lobes. The right lobe is further subdivided into two lobes - the quadrate and caudate. Falciform Ligament - binds liver to anterior wall. The round ligament exits the falciform ligament from the liver - former umbilical vein.

    75. Liver: Microscopic Anatomy Lobes are divided into working units called lobules Plates of hepatocytes [specialized epithelium] that secrete bile Central vein

    76. Liver: Microscopic Anatomy Liver sinusoids – enlarged, leaky capillaries located between hepatic plates. Blood from stomach & SI is filtered and glucose, amino acids, iron, vitamins, etc are removed, as are toxins, drugs, etc. Kupffer cells – hepatic macrophages found in liver sinusoids.

    77. Microscopic Anatomy of the Liver

    78. Liver: Bile Produced by hepatocytes. Bile leaves the liver via: Bile canalculi to bile ducts Bile ducts fuse into the common hepatic duct

    79. Liver: Bile The common hepatic duct fuses with the cystic duct? the bile duct Bile duct [joins pancreatic duct ? hepatopancreatic ampulla ? SI

    81. Gallbladder Thin-walled, green muscular sac on the ventral surface of the liver. Releases bile via the cystic duct, which flows into the bile duct. Stores and concentrates bile by absorbing its water and ions.

    82. Composition of Bile Bile - Yellow, brownish to olive green - 500-1000mL/day Water, bile acids, bile salts, cholesterol, ions, phospholipids [lecithin] bile pigments [bilirubin etc.] Bile Salts [acids] = steroids made from cholesterol–emulsify fats

    83. Composition of Bile Recycled – 80% reabsorbed by SI and re-secreted by liver Wastes – include from RBC breakdown ? bilirubin from heme -- intestine ? broken into stercobilin,

    84. Gallbladder and Associated Ducts

    85. Pancreas Size – 5 inches long and 1 inch thick Regions – head, body, tail Ducts – 1 – pancreatic duct fuses with common bile duct forming the hepatopancreatic ampulla - enters duodenum about 4 inches below pylorus 2 – accessory duct – enters 1 inch above ampulla

    86. Pancreas Exocrine function - Secretes pancreatic juice which breaks down all categories of foodstuff. Endocrine function – release of insulin & glucagon.

    87. Acinus of the Pancreas

    88. Pancreatic Juice Pancreatic Juice – clear, colorless, 1.2-1.5L/day, pH about 8 Mostly water Sodium bicarbonate – increase pH, buffers acidic chyme, stops pepsin action Salts

    89. Composition & Function of Pancreatic Juice Enzymes secreted: Trypsinogen is activated to trypsin Carboxypeptidase Chymotrypsinogen Amylase, lipases, & nucleases These enzymes require ions or bile for optimal activity

    90. Regulation of Secretion Increased with parasympathetic, decreased with sympathetic. Bile & pancreatic juice stim. By CCK, gastrin & secretin CCK released from duodenum response to acid & fat ? contraction of gallbladder, secretion of pancreatic enzymes, relaxation of hepatopancreatic sphincter

    91. Regulation of Secretion Secretin – stimulates secretion of bicarbonate to neutralize stomach acid in duodenum.

    92. Small Intestine: Gross Anatomy Runs from pyloric sphincter to the ileocecal valve. 3 subdivisions: duodenum, jejunum, & ileum. Ileocecal valve = sphincter to the large intestines. Mesentery – peritoneum supporting the small intestines.

    94. Small Intestine: Microscopic Anatomy Structural modifications of the small intestine wall increase surface area. Circular folds of the mucosa Villus – structure with a lamina propria core containing arterioles, venules, capillary nets and lymphatic lacteals, covered with simple columnar epithelium with microvilli , goblet cells and absorptive cells

    95. Small Intestine: Microscopic Anatomy Lacteals-absorption of fats Goblet cells - secrete mucus Absorptive cells – simple columnar epithelium - absorb and make brush border enzymes Intestinal Crypts - tubular glands in floor of SI between villi bases – secrete intestinal juice [enzymes]

    96. Small Intestine: Microscopic Anatomy Paneth Cells - phagocytic - produce lysozyme Enteroendocrine glands - secrete secretin and CCK Duodenal [Brunner's] in submucosa -secrete alkaline mucus – neutralizes stomach acid

    97. Small Intestine: Microscopic Anatomy

    98. Intestinal Juice Clear yellow - 1-2 L/day, pH 7.6 Contains water, mucus, enzymes - aid absorption of nutrients from chyme Resorbed by villi

    99. Motility in the Small Intestine Segmentation- Localized mixing motions bring contents in contact with mucosa. Regulated by pacemaker cells – 12 contractions/ min – duod.; 8-9 ileum. After nutrients have been absorbed: Peristalsis begins. Meal remnants, bacteria, mucosal cells, & debris are moved into large intestine.

    100. Control of Motility and Secretion Local enteric neurons of the GI tract coordinate intestinal motility: Distension Presence of Chyme Vasoactive intestinal polypeptide [VIP] increases secretions Gastrin

    101. Control of Motility and Secretion ANS: Parasympathetic – increases motility. Sympathetic-decreases motility.

    102. Chemical Digestion: Carbohydrates Enzymes: salivary amylase, pancreatic amylase, & brush border enzymes Absorption - glucose and galactose enter epithelial cells via symporters, accompanied by Na+ ions. Fructose enters by facilitated diffusion. All exit to the blood by facilitated diffusion.

    103. Lactose intolerance – lack enzyme lactase [large proportion of world population]

    104. Chemical Digestion: Proteins Enzymes used: pepsin in the stomach. Enzymes acting in the small intestine: Pancreatic enzymes – trypsin, chymotrypsin Brush border enzymes – peptidases.

    105. Chemical Digestion: Proteins Absorption Amino acids, di and tripeptides - aa - by simple active transport or in symporters with Na+ Di and tripeptides - by symporters with H+. All exit to blood by diffusion.

    106. Chemical Digestion: Proteins

    107. Chemical Digestion: Fats Lipids - digested by lipases Fats emulsified by bile salts first Products are fatty acids[FFA’s]and monoglycerides Micelles in bile take up phospholipids & cholesterol, fat soluble vitamins, FFA’s and monoglycerides and transport to intestinal cells

    108. Chemical Digestion: Fats

    109. Chemical Digestion: Fats FFA’s and monoglycerides enter epithelial cells and are re-assembled into triglycerides, combine with cholesterol, phospholipids and protein to form chylomicrons and exit by exocytosis into lacteals

    110. Fatty Acid Absorption

    111. Chemical Digestion: Nucleic Acids Enzymes used: pancreatic nucleases in the small intestines. Brush Border enzymes: nucleosidases, phosphatases. Sugars, bases and phosphate ions absorbed by active transport ? across epithelium and into blood

    112. Vitamins & Minerals Vitamins - water soluble diffuse, lipid soluble enter with lipids [A,D,E,K] Minerals [Electrolytes] - absorbed through entire length of SI by diffusion or active transport - Na+/K+ and chloride/bicarbonate pumps. Fe & Ca absorbed as needed, rest absorbed at constant rate regardless of need.

    113. Water Water - absorbed by osmosis - 9L into system - about 8L absorbed - into blood Diarrhea occurs when the large intestine absorbs too little Constipation occurs when passage through the LI is too slow and too much water is absorbed

    114. Large Intestine Functions: Absorption, manufacture of some vitamins. Formation & expulsion of feces.

    115. LI Anatomy 1.5 M long, runs from cecum to rectum Ileocecal sphincter - joins SI to LI. Cecum - region of LI inferior to the ileocecal sphincter. Appendix - next to the cecum.

    116. LI Anatomy Colon - above sphincter - ascending, transverse, descending and Sigmoid regions Rectum & valves- region inferior to sigmoid colon Anal Canal - below rectum

    117. LI Anatomy Taenia coli - longitudinal bands of muscles running the length of the LI Haustra - pouches produced in the LI by tonal contraction of taenia coli.

    118. Large Intestine

    119. Large Intestine: Microscopic Anatomy Mucosa – Simple columnar epithelium – no villi or enzyme secreting cells goblet cells

    120. Bacterial Flora These bacteria: Colonize the colon Ferment indigestible carbohydrates Release irritating acids and gases (flatus) Synthesize B complex vitamins and vitamin K

    121. Motility of the Large Intestine Haustral contractions: Slow segmenting movements that move the contents of the colon. Haustra sequentially contract as they are stimulated by distension. Presence of food in the stomach: Activates the gastrocolic reflex. Initiates peristalsis that forces contents toward the rectum.

    122. Defecation Defecation Reflexes – initiated by rectal stretching Intrinsic – entirely within enteric system – weak peristalsis Sympathetic = Spinal cord reflex - Sends message to CNS – to decide whether to relax external sphincter.

    123. Defecation

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