Chapter 17 Digestive System
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Transcript of Chapter 17 Digestive System
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Chapter 17Lecture
PowerPoint
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2402Anatomy and Physiology II
Chapter 17
Susan Gossett
Department of Biology
Paris Junior College
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Hole’s Human Anatomyand Physiology
Twelfth Edition
Shier Butler Lewis
Chapter 17
Digestive System
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17.1: Introduction
• Digestion is the mechanical and chemical breakdown of foods into forms that cell membranes can absorb• Organs of the digestive system carry out these processes, as well as ingestion, propulsion, absorption and defecation• The digestive system consists of the alimentary canal extending from the mouth to the anus, plus accessory organs that empty into the alimentary canal
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Anus
ACCESSORY ORGANSSalivary glandsSecrete saliva, which containsenzymes that initiate breakdownof carbohydrates
LiverProduces bile, whichemulsifies fat
GallbladderStores bile and introduces it into small intestine
PancreasProduces and secretes pancreatic juice, containing digestive enzymes and bicarbonate ions, into small intestine
ALIMENTARY CANAL
MouthMechanical breakdown of food; begins chemical digestion of carbohydrates
PharynxConnects mouth with esophagus
EsophagusPeristalsis pushes food to stomach
StomachSecretes acid and enzymes; mixes foodwith secretions to begin enzymaticdigestion of proteins
Small intestineMixes food with bile and pancreatic juice; final enzymatic breakdown of food molecules; main site of nutrient absorption
Large intestineAbsorbs water and electrolytes to form feces
RectumRegulates elimination of feces
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17.2: General Characteristics of the Alimentary Canal
• The alimentary canal is a muscular tube about 8 meters long
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.5 meter (from tongueto duodenum)
5.5 – 6.0 meters(small intestine)
1.5 meters(large intestine)
Esophagus
StomachGallbladder
PancreasDuodenum
Cecum
Appendix
Anus
Tongue
Largeintestine
Ileum(3.3 – 3.6 m)
Jejunum(2.2 – 2.4 m)
1.0m
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Structure of the WallCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Intestinal gland
Lacteal
Epithelium
Mucous gland in submucosa
Mucosa
Circular muscleLongitudinal muscle
Circular muscle
Longitudinal muscle
Serosa
Artery Mesentery
Circular fold
Mucosa
Submucosa
Serosa
Capillaries
Lacteal
Microvilli
Nucleus
Goblet cell
Vein
Villi
Lymph nodule
Nerveplexuses
Muscularlayer
Simple columnarepithelium
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Movements of the TubeCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
(c)
(a)
Movement of contents(b)
Digesting material
Wave ofcontraction
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Innervation of the Tube
• Branches of the sympathetic and parasympathetic divisions of the autonomic nervous system extensively innervate the alimentary canal, including:
• Submucosal plexus – controls secretions • My enteric plexus – controls gastrointestinal motility
• Remember:• Parasympathetic impulses – increase activities of digestive system• Sympathetic impulses – inhibit certain digestive actions
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17.3: Mouth
• The mouth:• Ingests food• Mechanically breaks up solid particles using saliva• Prepares food for chemical digestion
• This action is called mastication
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Uvula
Soft palate
Hard palate
Lip
Lip
Lingual frenulum
Palatinetonsils
Tongue
Vestibule
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Cheeks and Lips
• The cheeks form the lateral walls of the mouth• The lips are highly mobile structures that surround the mouth opening
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Tongue
• The tongue is a thick, muscular organ that occupies the floor of the mouth and nearly fills the oral cavity when the mouth is closed
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Root
Body
Epiglottis
Lingual tonsils
Palatine tonsil
Papillae
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Palate
• The palate forms the roof of the oral cavity and consists of a hard anterior part and a soft posterior part
Frontal sinus
Hard palate
Hyoid bone
Trachea
Esophagus
Laryngopharynx
Epiglottis
Lingual tonsil
Oropharynx
Palatine tonsilUvula
NasopharynxSoft palate
Opening of auditory tube
Pharyngeal tonsil
Sphenoidal sinus
LipTooth
Larynx
Nasal cavity
Vestibule
TongueOral cavity
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Teeth
• The teeth are the hardest structures in the body• There are primary (deciduous) teeth numbering 20• There are secondary (permanent) teeth numbering 32
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© The McGraw-Hill Companies, Inc./Rebecca Gray, photographer
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
b: © Nick Koudis/Getty Images
Incisors
Canine (cuspid)
Canine (cuspid)
Molars
Incisors(a)
Molars
(b)
Canines
Premolars(bicuspids)
Premolars(bicuspids)
Secondpremolars
Firstpremolars
Lateralincisors
Centralincisors
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Crown
Gingiva
Root canal
Cementum
Root
Dentin
Enamel
Alveolarprocess
Periodontalligament
Pulpcavity
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17.1 Clinical Application
Dental Caries
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17.4: Salivary Glands
• Salivary glands secrete saliva• This begins the digestion of carbohydrates• There are three pairs of major salivary glands, including:
• Parotid glands• Submandibular glands• Sublingual glands
• There are many minor glands scattered throughout the mucosa of the tongue, palate, and cheeks
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Salivary Secretions
• The different salivary glands have varying proportions of two types of secretory cells, serous cells and mucous cells
• Serous cells produce a watery fluid with a digestive enzyme called salivary amylase• Mucous cells secrete mucous
• Parotid glands • Secrete clear watery, serous fluid• Rich in salivary amylase
• Submandibular glands• Secrete primarily serous fluid and some mucus
• Sublingual glands• Secrete primarily mucus
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Major Salivary Glands
Sublingual glandMandible (cut)
Parotidgland
Massetermuscle
Submandibulargland
Tongue
Submandibularduct
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Duct(a)
Serous cellDuct Mucous cell
(c)
Serous cellDuct
(b)
Serouscell
Mucouscell
a: © The McGraw-Hill Companies, Inc./Al Telser, photographer; figure b: © Biophoto Associates/Photo Researchers, Inc.; figure c: © The McGraw-Hill Companies, Inc./Al Telser, photographer
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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17.5: Pharynx and Esophagus
• The pharynx is a cavity posterior to the mouth from which the tubular esophagus leads to the stomach• Both the pharynx and esophagus muscular walls function in swallowing Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Mandible
Skull
TongueEpiglottis
Larynx
Esophagus
Superiorconstrictormuscles
Middleconstrictormuscles
Inferiorconstrictormuscles
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Structure of the Pharynx
• The pharynx can be divided into the following parts:• Nasopharynx• Oropharynx• Laryngopharynx
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Superior
Middle
Inferior
Tongue
Epiglottis
Trachea
Nasopharynxwith mucosaremoved toshow muscles
Pharyngealconstrictormuscles:
(a) The tongue forces food into the pharynx.
Foodmass
Hardpalate
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Swallowing Mechanism
• Swallowing can be divided into three stages:• Voluntary stage where saliva is mixed with chewed food• Swallowing begins and the swallowing reflex is triggered• Peristalsis transports food in the esophagus to the stomach
• Specifically:• The palate and uvula raise• The hyoid bone and larynx elevate• The epiglottis closes off top of the trachea• The longitudinal muscles of pharynx contract• The inferior constrictor muscles relax and the esophagus opens• The peristaltic waves pushes food through the pharynx
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Superior
Middle
Inferior
Tongue
Epiglottis
TracheaEsophagus
Soft palate
Larynx
Epiglottis
Hyoid bone
EsophagusLarynx
TonguePeristaltic wave
Stomach
Esophagus
Food mass
Nasopharynx with mucosa removed toshow muscles
Pharyngealconstrictormuscles:
Hardpalate
Foodmass
(a) The tongue forces food into the pharynx.
Softpalate
Superiorpharyngealconstrictormuscles
Foodmass
(c) Superior constrictor muscles contract and force food into the esophagus.
Foodmass
Inferiorpharyngealconstrictormuscles
(b) The soft palate, hyoid bone, and larynx are raised, the tongue is pressed against the palate, the epiglottis closes, and the inferior constrictor muscles relax so that the esophagus opens.
(d) Peristaltic waves move food through the esophagus to the stomach.
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Esophagus
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Esophagus
Diaphragm
Stomach
Esophagealhiatus
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Mucosa
Lumen
Submucosa
© Ed Reschke
Muscularlayer
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17.6: Stomach
• The stomach is a J-shaped, pouch-like organ, about 25-30 centimeters long• It hangs inferior to the diaphragm in the upper-left portion of the abdominal cavity• The stomach has two layers of smooth muscle
• An inner circular layer• An outer longitudinal layer• (There may be a third inner layer of oblique fibers.)
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Parts of the StomachCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Fundus
Body
Pylorus
Pyloric opening
Duodenum
Cardia
Esophagus
Esophagus
Esophagus
(b)
(a)
Circularfibers
Longitudinalfibers
Obliquefibers
Longitudinalfibers
Pyloricsphincter
Lessercurvature
Lower esophagealsphincter
Pyloriccanal
Pyloricantrum Gastric folds
(rugae)
Greatercurvature
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Parts of the Stomach
Pyloric sphincter
Duodenum
Pylorus
Fundus
Gastric folds
Body
© Dr. Kent M. Van De Graaff
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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Gastric Secretions• The mucous membrane of the stomach has tubular gastric glands that secrete:
• Pepsinogen• From the chief cells• Inactive form of pepsin
• Pepsin• From pepsinogen in the presence of hydrochloric acid• Is a protein splitting enzyme
• Hydrochloric acid• From the parietal cells• Needed to convert pepsinogen to pepsin
• Mucus• From the goblet cells and the mucous glands• Protective to stomach wall
• Intrinsic factor• From the parietal cells• Is required for vitamin B12 absorption
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Gastric pits
Chief cell
(a) (b)
Parietal cell
Gastric gland
Mucous cellMucosa
Submucosa
Serosa
Mucous cell
Gastric pit
Parietal cell
Chief cell
Portion ofa gastric gland
Portion of agastric gland
Musclelayers
b: © The McGraw-Hill Companies, Inc./Al Telser, photographer
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Regulation of Gastric SecretionsCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
1
2
3
4
Stimulation
Bloodstream
Release intobloodstreamParasympathetic
preganglionicnerve fiber (invagus nerve)
Gastrin stimulatesgastric glands torelease more gastricjuice
Parasympatheticpostganglionicimpulses stimulatethe release ofgastric juice fromgastric glands
Impulsesstimulatethe releaseof gastrin
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Gastric Absorption
• Gastric enzymes begin breaking down proteins, but the stomach is not well-adapted to absorb digestive products
• Why not ???• The stomach does absorb:
• Some water• Certain salts• Certain lipid-soluble drugs• Alcohol
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Mixing and Emptying Actions
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Stomach
Chyme
Duodenum
(a) (b) (c)
Pyloric sphincterrelaxed
Pyloric sphinctercontracted
Foodentering
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
From CNS
4
1
2
3
Nerve impulsesinhibit peristalsisin stomach wall
Duodenumfills with chyme
Sensory stretchreceptors arestimulated
Sensory nerveimpulses travelto centralnervous system
To CNS
Vagusnerve
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17.2 Clinical Application
Oh, My Aching Stomach!
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17.7: Pancreas
• The pancreas has a dual function as both an endocrine gland and exocrine gland• The exocrine function is to secrete digestive juice called pancreatic juice
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Structure of the PancreasCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Right hepatic duct Left hepatic ductCystic duct Common hepatic ductBile duct
Bile duct
Gallbladder
Sphincter muscles
Head of pancreas
Duodenum
Major duodenal papilla
Intestinal lumen
Pancreatic duct
Pyloric sphincter
Minor duodenalpapilla
Major duodenalpapilla
Tail of pancreas
Pancreatic duct
Hepatopancreaticsphincter
Hepatopancreaticampulla
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Pancreatic Juice
• Pancreatic juice contains enzymes that digest carbohydrates, fats, proteins, and nucleic acids, and include:
• Pancreatic amylase – splits glycogen into disaccharides• Pancreatic lipase – breaks down triglycerides• Trypsinogen, chymotrypsinogen, and carboxypeptidase
• Digest proteins• Nucleases – digest nucleic acids• Bicarbonate ions – make pancreatic juice alkaline
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Regulation of Pancreatic SecretionCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Bloodstream
1
5
4
3
2
Stimulation of effector organ
Acidic chymeentersduodenum
Bicarbonate ionsneutralize acidicchyme
Intestinal mucosareleases secretininto bloodstream
Secretin stimulatespancreas to secretebicarbonate ions
Hormonal signalsreleased into bloodstream
Pancreatic juice rich in bicarbonate ions passes downpancreatic ducts to the duodenum
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17.8: Liver
• The liver is the largest internal organ• It is located in the upper-right abdominal quadrant just beneath the diaphragm
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Liver Structure
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Right lobe
Coronary ligament
Inferior vena cava
Left lobe
Inferior vena cava
Right lobe
Gallbladder Quadrate lobe
Cystic duct
Left lobe
Hepatic ductHepatic artery
Bile duct
Caudate lobe
Gallbladder
(b)(a)
Roundligament
Hepatic portalvein
Falciform ligament
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Bile duct
Branch of hepatic arteryPlates of liver cells
Central vein
Bile canaliculi
Bile ductule
Bile duct
Sinusoids
(b)
(a)
(c)
Branch of hepatic portal vein
Hepaticsinusoids
Branches ofhepatic artery
Branch ofhepatic portal vein
c: © The McGraw-Hill Companies, Inc./Al Telser, photographer
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Bile duct Bile ductuleBile canaliculi Kupffer cell Hepatic cells
Branchof hepaticportal vein
Branchof hepaticartery
Hepaticsinusoids
Blood flowinto liver
Central vein(blood flowout of liver)
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Liver Functions
• The liver carries on many important metabolic activities, including:• Produces glycogen from glucose• Breaks down glycogen into glucose• Converts non-carbohydrates to glucose• Oxidizes fatty acids• Synthesizes lipoproteins, phospholipids, and cholesterol• Converts carbohydrates and proteins into fats• Deaminating amino acids • Forms urea• Synthesizes plasma proteins• Converts some amino acids to other amino acids• Stores glycogen, iron, and vitamins A, D, and B12
• Phagocytosis of worn out RBCs and foreign substances• Removes toxins such as alcohol and certain drugs from the blood
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17.1 From Science to Technology
Replacing the Liver
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Composition of Bile
• Bile is a yellowish-green liquid that hepatic cells continuously secrete• Bile contains:
• Water• Bile salts:
• Emulsify fats• Help absorb fatty acids, cholesterol, and fat-soluble vitamins
• Bile pigments• Cholesterol• Electrolytes
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17.3 Clinical Application
Hepatitis
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Gallbladder
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© Carroll Weiss/Camera M.D. Studios
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Regulation of Bile ReleaseCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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5
Gallbladder
Bile duct
Cystic duct
Duodenum
3
Bloodstream
2
Chyme withfat entersduodenum
Cells from theintestinal mucosasecrete the hormonecholecystokinin (CCK)into the bloodstream
Hormonalsignals releasedinto bloodstream
Stimulation ofeffector organ
Pancreaticduct
Hepatopancreatic sphincter relaxes and bile enters duodenum
Bile passes down the cystic duct and bile duct to duodenum
CCK stimulates muscular layer of gallbladder wall to contract
Commonhepatic duct
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Functions of Bile Salts
• Bile salts aid digestive enzymes• They reduce surface tension and break fat globules into droplets (like soap or detergent) and this is called emulsification• They enhance absorption of fatty acids and cholesterol• They help absorb fat-soluble vitamins A, D, E and K• Bile salts are recycled as they return to the liver
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17.4 Clinical Application
Gallbladder Disease
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17.9: Small Intestine
• The small intestine is a tubular organ that extends from the pyloric sphincter to the beginning of the large intestine• It completes digestion of the nutrients in chyme, absorbs products of digestion, and transports the remaining residue to the large intestine• It consists of three parts that include:
• Duodenum• Jejunum• Ileum
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Parts of the Small Intestine
Stomach
Jejunum
Duodenum
Ascending colon
Mesentery
Appendix
Cecum
Ileum
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Stomach
Small intestine
© Armed Forces Institute of Pathology
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Liver
Stomach
Gallbladder
Transverse colonunderneath
Greateromentum
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Structure of the Small Intestinal Wall
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Lacteal
Blood capillary network
Intestinal gland
Goblet cells
Simple columnarepithelium
VenuleArteriole
Lymph vessel
Villus
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Lumen
Intestinalgland
Villus
© The McGraw-Hill Companies, Inc./Al Telser, photographer
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Microvilli
Cell membrane
Mitochondrion
Golgi apparatus
Nucleolus
Nucleus
(a)
Lumen Microvilli
(b)
Roughendoplasmicreticulum
Cytoplasm ofepithelial cell
b: © The McGraw-Hill Companies, Inc./Al Telser, photographer
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Submucosa
Circular muscleLongitudinal muscle
Serosa
(a)
(b)
Plicaecirculares
Muscularlayer
Villi
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Secretions of the Small Intestine
• In addition to mucous-secreting goblet cells, there are many specialized mucous-secreting glands (Brunner’s glands) that secrete a thick, alkaline mucus in response to certain stimuli• Enzymes in the membranes of the microvilli include:
• Peptidase – breaks down peptides into amino acids• Sucrase, maltase, lactase – break down disaccharides into monosaccharides• Lipase – breaks down fats into fatty acids and glycerol• Enterokinase – converts trypsinogen to trypsin• Somatostatin – hormone that inhibits acid secretion by stomach• Cholecystokinin – hormone that inhibits gastric glands, stimulates pancreas to release enzymes in pancreatic juice, and stimulates the gallbladder to release bile• Secretin – stimulates the pancreas to release bicarbonate ions in pancreatic juice
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Regulation of Small Intestinal Secretions
• Regulation of small intestine secretion occurs by:• Mucus secretion is stimulated by the presence of chyme in the small intestine• Distension of the intestinal wall activates nerve plexuses in the wall of the small intestine• Parasympathetic reflexes triggering the release of intestinal enzymes
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Absorption of the Small Intestine
• Villi increase the surface area for absorption• Small intestine absorption is so effective that very little reaches the organ’s distal end, noting that:
• Monosaccharides and amino acids absorb:• Through facilitated diffusion and active transport• Absorbed into blood
• Large proteins are broken down and absorbed into villi• Fatty acids and glycerol absorb by:
• Several steps involved as noted• Absorbed into lymph and blood
• Electrolytes and water absorb:• Through diffusion, osmosis, and active transport• Absorbed into blood
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Maltose Glucose
MonosaccharidesDisaccharide
Glucose
H H
O
Maltase
Maltase
HO
HO
OH OH
HO
H H
HO
HO
OHHO
HO
H2O
Water
H N C
H
H
Amino acid Amino acid
Dipeptidase
R
C
H
N
O
C
R
H
H N C
H
H
R
C OH
O
H N C
H
H
R
C OH
O
C OH
O
Dipeptidase
H2O
Dipeptide(from protein digestion)
Water
Lipase
H
CHO
HO
HO
H
C H
H
C H
C
C17H35 COO
H
H
C H
3H2O
Lipase+ +Fatty acids GlycerolFat
C H
C H
O
C
O
C
O
C17H35 COO
C17H35 COO
Water
C17H35 C
C17H35 C
C17H35 C
OH
OH
OH
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Fatty acids
Lacteal
Nucleus
Chylomicrons
1
2
3
4
5
Lymph
To blood
Lymph in lactealtransports chylomicronsaway from intestine
Chylomicronsleave epithelial celland enter lacteal
Fats collect in clustersencased in protein toform chylomicrons
Fatty acids areused to synthesizefats in endoplasmicreticulum
Fatty acidsresulting from fatdigestion enterepithelial cell
Endoplasmicreticulum
Lumen ofintestine
Epithelialcell
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Movements of the Small Intestine
• The small intestine carries on mixing movements that include:
• Peristalsis – pushing movements that propel chyme• Segmentation – ring-like contractions that can move chyme back and forth
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17.10: Large Intestine
• The large intestine is named because of its diameter• It has five parts that include:
• Cecum• Colon
• Ascending, transverse, descending and sigmoid• Rectum• Anus
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Parts of the Large IntestineCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Anal canal
Sigmoid colon
Haustra
Descending colon
Rectum
Appendix
Cecum
Orifice of appendix
Ileocecal sphincter
Ascending colon
Serous layer Mucous membrane
Transverse colon
Muscular layer
Ileum
Hepatic flexure
Tenia coli
Splenicflexure
Epiploicappendage
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© Jim Wehtje/Getty Images
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Structure of the Large Intestinal Wall
© Ed Reschke/Peter Arnold
Lumen
Submucosa
Muscular layer
Serosa
Mucosa
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Functions of the Large Intestine
• The large intestine:• Has little or no digestive function• Absorbs water and electrolytes• Secretes mucus• Houses intestinal flora• Forms feces• Carries out defecation
Lumen oflargeintestine
Gobletcells
© Ed Reschke
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Movements of the Large Intestine
• Movements of the large intestine are similar to those of the small intestine• It is slower and less frequent than that of the small intestine• Movements include:
• Mixing movements • Peristalsis
• Mass movements usually follow meals• The defecation reflex relaxes the internal anal sphincter and then the external anal sphincter
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Feces• Feces is composed of materials not digested or absorbed, and include:
• Water• Electrolytes• Mucus • Bacteria• Bile pigments altered by bacteria provide the color
• The pungent odor is produced by bacterial compounds including:
• Phenol• Hydrogen sulfide• Indole• Skatole• Ammonia
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17.5 Clinical Application
Disorders of the Large Intestine
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17.11: Lifespan Changes
• Changes to the digestive system are slow and slight, and eventually include:
• Teeth may become sensitive• Gums may recede• Teeth may loosen, break or fall out• Heartburn may become more frequent• Constipation may become more frequent• Nutrient absorption decreases• Accessory organs age but typically not necessarily in ways that effect health
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Important Points in Chapter 17:Outcomes to be Assessed
17.1: Introduction
Describe the general functions of the digestive system.
Name the major organs of the digestive system.
17.2: General Characteristics of the Alimentary Canal
Describe the structure of the wall of the alimentary canal.
Explain how the contents of the alimentary canal are mixed and moved.
17.3: Mouth
Describe the functions of the structures of the mouth.
Describe how different types of teeth are adapted for different functions, and list the parts of the tooth.
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Important Points in Chapter 17:Outcomes to be Assessed
17.4-17.10: Salivary Glands – Large Intestine
Locate each of the organs and glands; then describe the general function of each.
Identify the function of each enzyme secreted by the digestive organs and glands.
Describe how digestive secretions are regulated.
Explain control of movement of material through the alimentary canal.
Describe the mechanisms of swallowing, vomiting, and defecating.
Explain how the products of digestion are absorbed.
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Important Points in Chapter 17:Outcomes to be Assessed
17.11: Lifespan Changes
Describe aging-related changes in the digestive system.
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Quiz 17
Complete Quiz 17 now!
Read Chapter 18.