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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