chapter 24: system - deanza.edu digestsys1.pdf · the human digestive system consists of:
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Welcome to Bio40C
Dr. Ann Reisenauer“Dr. R”
Bio40C – Human A&P Class schedule Text: Principles of Anatomy and Physiology, 12th edition My faculty website
http://www.deanza.edu/faculty/reisenauerann/ Lecture outlines, lab assignments, presentations, extra credit
How to contact me: Email: [email protected] Office hours: TuTh 12-12:30 pm in SC2106 or by appt
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Chapter 24:The Digestive System
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Overview of the digestivesystem
Digestive organs & accessory organsLayers of the GI tract
Upper GI tract
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2 groups of organs composethe digestive system
The human digestivesystem consists of: A digestive tube–the
alimentary canal or GItract
Accessory organs thatsecrete digestiveenzymes
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2 groups of organs composethe digestive system
Alimentary canal orGastrointestinal (GI) tract mouth, most of pharynx,
esophagus, stomach, smallintestine, and large intestine
Accessory digestive organs teeth, tongue, salivary
glands, liver, gallbladder, andpancreas
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Digestion includes 6 basicprocesses1. Ingestion2. Secretion of water, acid, buffers, and
enzymes into lumen3. Mixing and propulsion4. Digestion
Mechanical digestion – churns food Chemical digestion – breaks it down
5. Absorption of nutrients into blood or lymph6. Defecation – elimination of feces
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Layers of the GI TractCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Lumen
veinartery
Mucosa
Submucosa
Muscularis
Serosa
lymphvessel
nervesupply
Wall of GI tractfrom loweresophagus toanal canal hasthe same 4basic layers
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Layers of the GI Tract Wall Mucosa:
Innermost layer of cells produces
mucus that protects thelining
digestive enzymes
Submucosa: layer of loose connective
tissue that contains bloodvessels, lymphaticvessels and nerves.
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Layers of the GI Tract Wall
Muscularis: made of 2 layers of smooth
muscle that move food alongthe GI tract
inner – circular outer – longitudinal
Serosa: Outer lining that is part of the
peritoneum muscularis
serosa
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Mixing and propulsion: peristalsis vs segmentation
Peristalsis Coordinated waves
of contractions of thecircular andlongitudinal layers ofthe muscularis
Push bolus forward Segmental
contractions Mixing movements
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Neural regulation of theGI tract
Enteric nervous system (ENS) Intrinsic set of nerves - “brain of
gut” Neurons extend from esophagus to
anus Neurons of ENS are arranged in 2
plexuses Myenteric plexus – located between
smooth muscle layers of themuscularis
Controls GI tract motility Submucosal plexus
controls secretions
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ENS regulation of the GI tract Motor neurons supply the
longitudinal and circularsmooth muscles of themuscularis
Sensory neurons supplythe mucosal epithelium
Functions Chemoreceptors – activated
by chemicals in food Stretch receptors – activated
when food distends the wallof GI tract
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ANS regulation of the GI tractAutonomic nervous system
regulates the ENS Vagus (X) nerves supply
parasympathetic fibers to mostof GI tract Increase GI secretion and
motility by stimulating the ENS Sympathetic nerves decrease
GI secretions and motility byinhibiting the ENS Emotions (anger, anxiety) slow
digestion because theystimulate the sympatheticnerves that supply the GI tract
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Both the enteric nervous systemand ANS regulate the GI tract
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Peritoneum Largest serous membrane
of the body Divided into
Parietal peritoneum – lineswall of cavity
Visceral peritoneum – coverssome organs and is theirserosa
Space between is peritonealcavity
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Peritoneal Folds Peritoneal folds weave
between the viscera andbind the organs togetherand to walls of abdominalcavity
5 major peritoneal folds: Greater omentum falciform ligament lesser omentum mesentery mesocolon
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Peritoneal Folds
‘fatty apron’
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Mouth Oral cavity Formed by cheeks,
hard and soft palates,and tongue
Oral cavity properextends from gums andteeth to the fauces(opening between oralcavity and pharynx orthroat )
epiglottis
hard palate nasopharynx
softpalate
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The salivary glands Secrete saliva Saliva
functions to keep mucusmembranes of mouthand throat moist
lubricates and dissolvesfoods
begins digestion ofcarbohydrates
3 major salivary glands Parotid Submandibular Sublingual
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Saliva Saliva
Mostly water 99.5% 0.5% solutes – mucus, immunoglobulin A, lysozyme
(bactericidal), and salivary amylase (enzyme thatdigests starch), ions, dissolved gases, urea, uric acid
Not all salivary glands produce the same saliva Salivation is entirely under nervous control
Controlled by ANS Parasympathetic stimulation promotes secretion of saliva Sympathetic stimulation decreases salivation
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Mumps An inflammation and
enlargement of theparotid salivaryglands caused byinfection with themumps virus(myxovirus).
Vaccine developedin 1967
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Tongue Tongue
Accessory digestive organ Skeletal muscle covered by
mucous membrane Functions
Maneuvers food for chewingand swallowing
Speech Lingual glands secrete
salivary lipase
epiglottis
hard palate nasopharynx
softpalate
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Teeth Accessory digestive organ
adapted for mechanicaldigestion
3 major regions – crown, neck,and root
Composition primarily made up of dentin, a
calcified connective tissue Enamel - protective Cementum - attaches root to
periodontol ligament Pulp - connective tissue
containing blood vessels,nerves, lymphatic vessels
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Teeth –adapted for mechanical digestion
Incisors Adapted for cutting into
food Cuspids
Used to tear and shredfood
Premolars and molars Crush and grind food
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Digestion in the mouth Mechanical digestion
Chewing or mastication Food manipulated by tongue, ground by teeth, and mixed
with saliva Forms bolus
Chemical digestion Salivary amylase – converts starches to disaccharides
Acts in the mouth; inactivated by stomach acid Lingual lipase – breaks down triglycerides
Secreted by lingual glands of tongue Becomes activated in acidic environment of stomach
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Pharynx (throat) Extends from the internal
nares to the esophagus 3 parts
Nasopharynx Functions only in respiration
Oropharynx Digestive and respiratory
functions Laryngopharynx
Digestive and respiratoryfunctions
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Esophagus Muscular tube that connects the
pharynx to the stomach Functions
Secretes mucous Transports food No enzymes produced, no
absorption Contains an upper and a lower
esophageal sphincter
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Esophagus - anatomy Histology (4 layers)
Mucosa – protects against wear and tear from food particles Submucosa Muscularis
Superior 1/3 is skeletal muscle Middle 1/3 is skeletal and smooth muscle Inferior 1/3 is smooth muscle
2 sphincters upper esophageal sphincter (UES) regulates movement of food
into esophagus lower esophageal sphincter (LES) regulates movement of food
into stomach Superficial layer is adventitia – rather than serosa
attaches esophagus to surrounding structuresCopyright 2009, John Wiley &
Sons, Inc.
Swallowing (deglutition) Facilitated by saliva and mucus Involves mouth, pharynx, and esophagus 3 stages
Voluntary – bolus passed to oropharynx Pharyngeal – involuntary passage through
pharynx into esophagus Esophageal – involuntary passage through
esophagus to stomach Peristalsis pushes bolus forward
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Swallowing (deglutition)3 stages Voluntary – bolus
passed to oropharynx Pharyngeal – the
tongue rises against thepalate, the epiglottisseals off the entrance tothe trachea
Esophageal – foodmoves to stomach byperistalsis
Swallowinghttp://www.youtube.com/watch?v=08VyJOEcDos
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Anatomy of the Stomach 4 main regions
Cardia, fundus, body, pylorus Lesser and greater curvatures Same 4 layers
Mucosa Exocrine and endocrine cells Large folds called rugae
Submucosa Muscularis – additional 3rd layer
of smooth muscle Inner oblique layer
Serosa – part of visceralperitoneum
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Anatomy of the stomach Muscularis
3 layers of muscle 2 sphincters
Mucosa Rugae Gastric pits
Secretions from severalgastric glands flow intoeach gastric pit and theninto the stomach
Exocrine gland cells –secrete gastric juice
2-3 L per day Endocrine cells
esophagus
gastroesophagealsphincter
pyloricsphincter
gastric pit
gastric gland
a. Stomach
cells thatsecretegastricjuice
muscularis layer has three layersof musclemucosa layerhas rugae
LES
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Functions of the Stomach Mixes saliva, food and gastric
juice to form chyme Stomach controls movement
of chyme into the smallintestine
Serves as mixing chamberand holding area for food Most expandable part of GI
tract Secretes gastric juice
HCl, digestive enzymes Secretes gastrin into blood
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Gastric secretions
Chief cells → pepsinogen and gastric lipase
Parietal cells → HCl and intrinsic factor
Mucous neck cells → mucous
G cells → gastrin, stimulates gastric activity
3 types of exocrine gland cells
Endocrine cells
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Gastric secretions Mucous cells
Mucus protects themucosal cells lining thestomach
Parietal cells Secrete HCl → acidifies the
stomach contents (pH of 2) Kills microorganisms
found in food Denatures proteins Activates pepsinogen
Secrete intrinsic factor Facilitates absorption of
vitamin B12 in the ileum
gastric pitSEM 3,260×
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Gastric secretions Chief cells
Secrete an inactiveproenzyme, pepsinogen
Protein digestion Rennin is secreted in
infants Coagulates proteins in
milk aids in milk digestion
Gastric lipase fat digestion
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Gastric secretionsEndocrine function G cells secrete gastrin
Released when foodenters the stomach
Stimulates secretion ofgastric acid (HCl) by theparietal cells and aids ingastric motility
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Recap:Digestion by the stomach Mechanical digestion
Mixing waves – gentle, rippling peristaltic movements –creates chyme
Chemical digestion Carbohydrate Digestion
Salivary amylase breaks down carbs to disaccharides until itsinactivated by acidic gastric juice
Lipid digestion Lingual lipase is activated by acidic gastric juice Gastric lipase Digest triglycerides into fatty acids and mono- or diglycerides
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Digestion by the stomach Protein digestion
Parietal cells secrete H+ and Cl- separatelybut net effect is HCl
Kills many microbes Acidic pH denatures proteins
Pepsin breaks down proteins into smallerpeptides
Enzyme is secreted as inactive precursor,pepsinogen
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Protein digestion – Pepsin
Pepsin is an enzyme that degrades food proteins into peptides secreted by the chief cells
The inactive pro-form, pepsinogen, is activated by HCl HCl allows pepsinogen to unfold and cleave itself into the active
enzyme, pepsin
Pepsinogen (inactive) Pepsin
HCl
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Nutrient absorption in stomach Small amount of nutrient absorption
Some water, ions, short chain fatty acids,certain drugs (aspirin) and alcohol
Digestive sys - swallowing and stomach 1:48http://www.youtube.com/watch?v=Q-n_Q0qKXzg&feature=fvw
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Stomach Ailments Peptic ulcers
open sores that develop in areasexposed to acidic gastric juice
the lining of the stomach, uppersmall intestine or esophagus.
Causes Infection with the bacterium
Helicobacter pylori Aspirin and other nonsteroidal anti-
inflammatory drugs Hypersecretion of HCl But NOT stress or diet
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Peptic ulcer disease Helicobacter pylori is the
most frequent cause of PUD. This bacterium lives in the
mucus and can causegastric ulcers.
H. pylori is especially well-adapted for survival in thestomach. It produces an enzyme that,
through a series ofbiochemical reactions,shields the bacterium fromthe acidity of the stomach
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Gastroesophageal refluxdisease (heartburn)
The lower esophagealsphincter fails to closeadequately after food entersthe stomach
The stomach contents refluxinto the inferior portion of theesophagus.
HCl from the stomach contentsirritates the esophageal wallresulting in heartburn.