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C. Chace Tydell, DVM
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Veterinarian/surgeon for more than 15 years Immunology researcher for 10 years
UCI Caltech
Scientific publications Taught Developmental Biology at Caltech
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Your name Your career goals One disease about which you would like to know
more Does someone in your family have a health problem?
Diabetes? Heart attack? Stroke? A disease or disorder that you have heard about?
Lupus? Leprosy? Hepatitis?
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Chapter 25Lecture Outline
Copyright (c) The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
-osis = condition or process eg- cyanosis, cirrhosis, leukocytosis
-itis = inflammation eg- gastritis, colitis, hepatitis
-ostomy = a surgically created opening for waste products to move out of the body colostomy, ileostomy, ostomy
-scopy = to view, to have a look colonoscopy, gastroscopy, endoscopy
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Mechanical digestion physical breakdown of food into smaller particles teeth and churning action of stomach and intestines
Chemical digestion series of hydrolysis reactions that break macromolecules into
their monomers enzymes from saliva, stomach, pancreas and intestines results
polysaccharides into monosaccharides proteins into amino acids fats into glycerol and fatty acids
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Ingestion intake of food
Digestion breakdown of molecules
Absorption uptake nutrients into blood/lymph
Defecation elimination of undigested material
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Motility muscular contractions that break up food, mix it with
enzymes and move it along Secretion
digestive enzymes and hormones Membrane transport
absorption of nutrients
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Digestive tract (GI tract) 30 foot long tube extending
from mouth to anus
Accessory organs teeth, tongue, liver,
gallbladder, pancreas, salivary glands
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Mucosa epithelium lamina propria muscularis mucosae
Submucosa Muscularis externa
inner circular layer outer longitudinal layer
Adventitia or Serosa areolar tissue or mesothelium
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Able to function independently of CNS Composed of two nerve networks
submucosal plexus controls glandular secretion of mucosa contractions of muscularis mucosae
myenteric plexus controls peristalsis contractions of muscularis externa
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Peristalsis is alternate waves of longitudinal and circular muscular contraction that pushes food along the alimentary canal.
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Serous membrane that lines the peritoneal cavity of the abdomen and covers the mesenteries and viscera
Of the GI tract, only duodenum, pancreas and parts of large intestine are retroperitoneal
Dorsal mesentery suspends GI tract and forms serosa (visceral peritoneum) of stomach and intestines
Ventral mesentery forms lesser and greater omentum lacy layer of connective tissue that contains lymph nodes,
lymphatic vessels, blood vessels
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Lesser - attaches stomach to liver Greater - covers small intestines like an apron
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Mesentery of small intestines holds many blood vessels Mesocolon anchors colon to posterior body wall
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Neural control short myenteric reflexes (swallowing) long vagovagal reflexes (parasympathetic
stimulation of digestive motility and secretion) Hormones
messengers diffuse into bloodstream, distant targets
Paracrine secretions messengers diffuse to nearby target cells
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Cheeks and lips keep food between teeth for chewing; essential for
speech and suckling in infants vestibule - space between teeth and cheeks lips: cutaneous area versus red area (vermilion)
Tongue is sensitive, muscular manipulator of food papillae and taste buds on dorsal surface lingual glands secrete saliva, tonsils in root
Hard and soft palate allow breathing and chewing at same time palatoglossal and palatopharyngeal arches
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Baby teeth (20) by 2 years; Adult (32) between 6 and 25
Occlusal surfaces and cusp numbers differ
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Periodontal ligament is modified periosteum anchors into alveolus
Cementum and dentin are living tissue
Enamel is noncellular secretion formed during development
Root canal leads into pulp cavity nerves and blood vessels
Gingiva or gums
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Breaks food into smaller pieces to be swallowed surface area exposed to digestive enzymes
Contact of food with sensory receptors triggers chewing reflex tongue, buccinator and orbicularis oris manipulate
food masseter and temporalis elevate the teeth to crush
food medial and lateral pterygoids swing teeth in side-to-
side grinding action of molars
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Functions of saliva moisten begin starch and fat digestion cleanse teeth inhibit bacteria bind food together into bolus
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Functions of saliva moisten, begin starch and fat digestion, cleanse teeth, inhibit
bacteria, bind food together into bolus Hypotonic solution of 99.5% water and solutes
salivary amylase, begins starch digestion lingual lipase, digests fat activated by stomach acid mucus, aids in swallowing lysozyme, enzyme kills bacteria immunoglobulin A, inhibits bacterial growth electrolytes = Na+, K+, Cl-, phosphate and bicarbonate
pH of 6.8 to 7.025-25
Small intrinsic glands found under mucous membrane of mouth, lips, cheeks and tongue - secrete at constant rate
3 pairs extrinsic glands connected to oral cavity by ducts parotid submandibular sublingual
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Compound tubuloacinar glands (see pg 177)
Mucous cells secrete mucus Serous cells secrete thin fluid
rich in amylase Mixed acinus has both
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Total of 1 to 1.5 L of saliva per day Cells filter water from blood and add other substances Food stimulates receptors that signal salivatory
nuclei in medulla and pons parasympathetic stimulation salivary glands produce thin
saliva, rich in enzymes sympathetic stimulation produce less abundant, thicker
saliva, with more mucus Higher brain centers stimulate salivatory nuclei so sight,
smell and thought of food cause salivation
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Skeletal muscle deep layer –
longitudinal orientation
superficial layer – circular orientation superior, middle
and inferior pharyngeal constrictors
Straight muscular tube 25-30 cm long nonkeratinized stratified squamous epithelium esophageal glands in submucosa skeletal muscle in upper part and smooth in bottom
Extends from pharynx to cardiac stomach passing through esophageal hiatus in diaphragm inferior pharyngeal constrictor excludes air from it
Lower esophageal sphincter closes orifice to reflux
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Series of muscular contractions coordinated by centers in the brain
Buccal phase tongue collects food and pushes it back into oropharynx
Pharyngeal-esophageal phase soft palate rises and blocks nasopharynx infrahyoid muscles lift larynx; epiglottis folded back pharyngeal constrictors push bolus down esophagus
liquids in 2 seconds -- food bolus may take 8 seconds lower esophageal sphincter relaxes
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Mechanically breaks up food, liquifies food and begins chemical digestion of protein and fat resulting soupy mixture is called chyme
Does not absorb significant amount of nutrients absorbs aspirin and some lipid-soluble drugs
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Muscular sac (internal volume from 50ml to 4L) J - shaped organ with lesser and greater curvatures regional differences
cardiac region just inside cardiac orifice fundus - domed portion superior to esophageal opening body - main portion of organ pyloric region - narrow inferior end
antrum and pyloric canal Pylorus - opening to duodenum
thick ring of smooth muscle forms a sphincter
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Notice: bulge of fundus, narrowing of pyloric region, thickness of pyloric sphincter and greater and lesser curvatures
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Cardia
Fundus
Body
Pylorus
Innervation by parasympathetic fibers from vagus sympathetic fibers from celiac plexus
All blood from stomach enters hepatic portal circulation and is filtered through liver before returning to heart
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Mucosa simple columnar glandular epithelium lamina propria is filled with tubular glands (gastric pits)
Muscularis externa has 3 layers outer longitudinal, middle circular and inner oblique layers
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Mucous cells secrete mucus
Regenerative cells divide rapidly to produce new cells
that migrate to surface Parietal cells
secrete HCl acid and intrinsic factor Chief cells
secrete pepsinogen chymosin and lipase in infancy
Enteroendocrine cells G cells
Make gastrin Others secrete hormones and
paracrine messengers
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Parietal cells contain carbonic anhydrase (CAH) CO2 + H2O H2CO3 HCO3
- + H+
H+ is pumped into stomach lumen by H+K+ATPase HCO3
- in blood causes alkaline tide (blood pH )
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2 to 3 L of gastric juice/day (H2O, HCl and pepsin)
Activates pepsin and lingual lipase Breaks up connective tissues and plant cell walls
liquefies food to form chyme Converts ingested ferric ions (Fe3+) to ferrous ions (Fe2+)
absorbed and used for hemoglobin synthesis Destroys ingested bacteria and pathogens
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Intrinsic factor essential for B12 absorption by small intestine RBC production (lack causes pernicious anemia)
Pepsin - protein digestion secreted as pepsinogen (inactive) HCl converts it to pepsin (active)
Gastric lipase and chymosin lipase digests butterfat of milk in infant chymosin curdles milk by coagulating proteins
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Many produced by enteroendocrine cells hormones enter blood distant cells paracrine secretions neighboring cells
Gut-brain peptides signaling molecules produced in digestive tract and
CNS
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