Copyright © 2010 Pearson Education, Inc. Figure 23.1 Alimentary canal and related accessory digestive organs. Mouth (oral cavity) Tongue Esophagus Liver

Copyright © 2010 Pearson Education, Inc.

Figure 23.1 Alimentary canal and related accessory digestive organs.

Mouth (oral cavity)Tongue

Esophagus

LiverGallbladder

Anus

DuodenumJejunumIleum

Small intestine

Parotid glandSublingual glandSubmandibulargland

Salivaryglands

Pharynx

StomachPancreas(Spleen)

Transverse colonDescending colonAscending colonCecumSigmoid colonRectumVermiform appendixAnal canal

Largeintestine


Figure 23.2 Gastrointestinal tract activities.

FoodIngestion

PropulsionEsophagus

Stomach

PharynxMechanicaldigestion

Chemicaldigestion

• Chewing (mouth)• Churning (stomach)• Segmentation (small intestine)

Smallintestine Largeintestine

Defecation Anus

Feces

Bloodvessel

Lymphvessel

Absorption

• Swallowing (oropharynx)• Peristalsis (esophagus, stomach, small intestine, large intestine)

Mainly H2O


Figure 23.3 Peristalsis and segmentation.

Frommouth

(b) Segmentation: Nonadjacent segments of alimentary tract organs alternately contract and relax, moving the food forward then backward. Food mixing and slow food propulsion occurs.

(a) Peristalsis: Adjacent segments of alimentary tract organs alternately contract and relax, which moves food along the tract distally.


Figure 23.3a Peristalsis and segmentation.

From mouth

(a) Peristalsis: Adjacent segments of alimentary tract organs alternately contract and relax, which moves food along the tract distally.


Figure 23.3b Peristalsis and segmentation.

(b) Segmentation: Nonadjacent segments of alimentary tract organs alternately contract and relax, moving the food forward then backward. Food mixing and slow food propulsion occurs.


Figure 23.4 Neural reflex pathways initiated by stimuli inside or outside the gastrointestinal tract.

External stimuli(sight, smell, taste,

thought of food)

Central nervous systemand extrinsic autonomic nerves

Afferent impulses Efferent impulses

Long reflexes

Internal(GI tract)stimuli

Chemoreceptors,osmoreceptors, ormechanoreceptors

Local (intrinsic)nerve plexus(“gut brain”)

Effectors:Smooth muscle

or glands

Gastrointestinalwall (site of shortreflexes)

Response:Change in

contractile orsecretory activityLumen of the

alimentary canal

Short reflexes


Figure 23.5 The peritoneum and the peritoneal cavity.

Peritonealcavity

Parietalperitoneum

Visceralperitoneum

Ventralmesentery

Abdominopelviccavity

Mesenteryresorbedand lost

Dorsalmesentery

Vertebra

Alimentarycanal organ

(a) Schematic cross sections of abdominal cavity illustrate the peritoneums and mesenteries.

(b) Some organs lose their mesentery and become retroperitoneal during development.


Alimentary canal organ ina retroperitoneal position

Liver


Figure 23.5a The peritoneum and the peritoneal cavity.

Peritonealcavity

Parietalperitoneum

Visceralperitoneum

Ventralmesentery


Dorsalmesentery

Vertebra


(a) Schematic cross sections of abdominal cavity illustrate the peritoneums and mesenteries.

Liver


Figure 23.5b The peritoneum and the peritoneal cavity.


Mesenteryresorbedand lost

(b) Some organs lose their mesentery and become retroperitoneal during development.


Alimentary canal organ ina retroperitoneal position


Figure 23.6 Basic structure of the alimentary canal.

Glands in submucosa

Submucosa

LumenMucosa-associatedlymphoid tissue

Duct of gland outsidealimentary canal

Gland in mucosa

NerveArteryVein

Lymphaticvessel Mesentery

Intrinsic nerve plexuses• Myenteric nerve plexus• Submucosal nerve plexus

Mucosa• Epithelium• Lamina propria• Muscularis mucosae

Muscularis externa

• Longitudinal muscle • Circular muscleSerosa• Epithelium• Connective tissue


Figure 23.7 Anatomy of the oral cavity (mouth).

Uvula

Uvula

Soft palate Palatoglossal arch

Palatinetonsil

Palatinetonsil

Sublingualfold withopenings ofsublingual ducts

Hard palate

Oral cavity

Tongue

Tongue

Upper lip

Lower lip

VestibuleGingivae (gums)

Gingivae(gums)

Hard palate

Soft palate

Lingual frenulumOpening ofsubmandibularduct

Palatineraphe

Inferior labialfrenulum

Lingual tonsil

Oropharynx

Posterior wallof oropharynx

Palatopharyngealarch

Superior labialfrenulum

Palatoglossalarch

Epiglottis

Hyoid bone

Laryngopharynx

Esophagus

Trachea

(a) Sagittal section of the oral cavity and pharynx (b) Anterior view


Figure 23.7a Anatomy of the oral cavity (mouth).

UvulaSoft palate Palatoglossal arch

Palatine tonsil

Hard palate

Oral cavity

Tongue

Lingual tonsilOropharynx

EpiglottisHyoid bone

Laryngopharynx

Esophagus

Trachea(a) Sagittal section of the oral cavity and pharynx


Figure 23.7b Anatomy of the oral cavity (mouth).

UvulaPalatine tonsil

Sublingual foldwith openings ofsublingual ducts

Tongue

Upper lip

Lower lip

VestibuleGingivae (gums)

Gingivae (gums)

Hard palate

Soft palate

Lingual frenulum

Opening ofsubmandibular duct

Palatine raphe

Inferior labialfrenulum

Posterior wallof oropharynx

Palatopharyngealarch

Superior labialfrenulum

Palatoglossal arch

(b) Anterior view


Figure 23.8 Dorsal surface of the tongue, and the tonsils.

Epiglottis

PalatopharyngealarchPalatine tonsil

Lingual tonsil

Palatoglossalarch

Foliate papillae

Circumvallatepapilla

Terminal sulcus

Dorsum of tongue

Midline grooveof tongue

Filiform papilla

Fungiform papilla


Figure 23.9 The salivary glands.

Teeth

Ducts ofsublingualgland

Sublingualgland

Submandibularduct

Posterior belly ofdigastric muscle

Parotid ductMasseter muscleBody of mandible (cut)

Parotidgland

Tongue

Submandibulargland

(a)

Lingualfrenulum

Mylohyoidmuscle (cut)Anterior belly ofdigastric muscle

Mucouscells

(b)

Serous cellsforming demilunes


Figure 23.9a The salivary glands.

Teeth

Ducts ofsublingualgland

Sublingualgland

Submandibularduct

Posterior belly ofdigastric muscle

Parotid ductMasseter muscleBody of mandible (cut)

Parotidgland

Tongue

Submandibulargland

(a)

Lingualfrenulum

Mylohyoidmuscle (cut)Anterior belly ofdigastric muscle


Figure 23.9b The salivary glands.

Mucouscells (b)

Serous cellsforming demilunes


Figure 23.10a Human dentition.

IncisorsCentral (6–8 mo)

IncisorsCentral (7 yr)

Canine (eyetooth)(16–20 mo)

Canine (eyetooth)(11 yr)

Premolars(bicuspids)First premolar(11 yr)

MolarsFirst molar(10–15 mo)

MolarsFirst molar (6–7 yr)

Lateral (8–10 mo) Lateral (8 yr)

Second molar(about 2 yr)

Second molar(12–13 yr)Third molar(wisdom tooth)(17–25 yr)(a)

Permanentteeth

Deciduous(milk) teeth Second premolar

(12–13 yr)


Figure 23.10b Human dentition.

Deciduous teeth Permanent teeth(b)


Figure 23.11 Longitudinal section of a canine tooth within its bony alveolus.

Crown

Neck

Root

EnamelDentinDentinal tubulesPulp cavity (containsblood vessels and nerves)Gingiva (gum)

Cementum

Root canalPeriodontalligament

Apical foramen

Bone


Figure 23.12 Microscopic structure of the esophagus.

Mucosa(contains a stratifiedsquamous epithelium)

Submucosa (areolarconnective tissue)

Lumen

Muscularis externa

Adventitia (fibrousconnective tissue)

(a) (b)

• Circular layer • Longitudinal layer


Figure 23.12a Microscopic structure of the esophagus.

Mucosa(contains a stratifiedsquamous epithelium)Submucosa (areolarconnective tissue)

LumenMuscularis externa

Adventitia (fibrousconnective tissue)(a)

• Circular layer • Longitudinal layer


Figure 23.12b Microscopic structure of the esophagus.

Mucosa(contains a stratifiedsquamous epithelium)

(b)


Figure 23.13 Deglutition (swallowing) (1 of 5).

Tongue

Trachea

Pharynx

Epiglottis

Glottis

Bolus of food

1 Upper esophageal sphincter is contracted. Duringthe buccal phase, the tongue presses against the hard palate, forcing the food bolus into the oropharynx where the involuntary phase begins.



Epiglottis

Esophagus

Uvula

Bolus

2 The uvula and larynx rise to prevent food fromentering respiratory passageways. The tongue blocks off the mouth. The upper esophageal sphincter relaxes, allowing food to enter the esophagus.



Bolus

3 The constrictor muscles of the pharynx contract, forcing food into the esophagus inferiorly. The upper esophageal sphincter contracts (closes) after entry.



Relaxed muscles

Circular musclescontract

Bolus of food

Longitudinal musclescontract

Stomach

Gastroesophagealsphincter closed

4 Food is moved throughthe esophagus to the stomach by peristalsis.



Relaxedmuscles

Gastroesophagealsphincter opens

5 The gastroesophageal sphincter opens, and food enters the stomach.


Figure 23.14a Anatomy of the stomach.

Cardia

Esophagus

Pyloric sphincter(valve) at pylorus

Pyloriccanal

Pyloricantrum

Rugae ofmucosa

Body

Lumen

Serosa

Fundus

Lessercurvature

Greatercurvature

Muscularisexterna • Longitudinal layer • Circular layer • Oblique layer

(a)

Duodenum


Figure 23.14b Anatomy of the stomach.

Liver(cut)

Lessercurvature

Body

Fundus

Spleen

Greatercurvature

(b)


Figure 23.15a Microscopic anatomy of the stomach.

Mucosa

Surfaceepithelium

Lamina propria

Muscularismucosae

Oblique layer

Circular layer

Longitudinallayer

Serosa

(a) Layers of the stomach wall (l.s.)Stomach wall

Muscularis externa(contains myentericplexus)

Submucosa(contains submucosalplexus)


Figure 23.15b Microscopic anatomy of the stomach.

(b) Enlarged view of gastric pits and gastric glands

Mucous neck cells

Parietal cell

Surface epithelium(mucous cells)

Gastric pits

Chief cell

Enteroendocrine cell

Gastric pit

Gastric gland


Figure 23.15c Microscopic anatomy of the stomach.

(c) Location of the HCl-producing parietal cells and pepsin-secreting chief cells in a gastric gland

Pepsinogen

Mitochondria

PepsinHCl

Chief cell

Enteroendocrinecell

Parietal cell


Figure 23.16 Photographs of a gastric ulcer lesion and of the bacteria that most commonly cause it.

Bacteria

Mucosalayer ofstomach

(a) A gastric ulcer lesion (b) H. pylori bacteria


Figure 23.16a Photographs of a gastric ulcer lesion and of the bacteria that most commonly cause it.


Figure 23.16b Photographs of a gastric ulcer lesion and of the bacteria that most commonly cause it.

Bacteria

Mucosalayer ofstomach

(b) H. pylori bacteria


Figure 23.17 Neural and hormonal mechanisms that regulate release of gastric juice.

Presence of lowpH, partially digested foods, fats, or hypertonic solution in duodenum when stomach begins to empty

Distension;presence offatty, acidic,partiallydigested foodin theduodenum

Briefeffect

Intestinal(enteric)gastrinreleaseto blood

Entero-gastricreflex

Release of intestinalhormones (secretin,cholecystokinin, vasoactiveintestinal peptide)

Localreflexes

Vagalnucleiin medulla

Pyloricsphincter

Stimulate

Inhibit

1

1

2

Stomachsecretoryactivity

Sight and thoughtof food

Stomachdistensionactivatesstretchreceptors

Stimulation oftaste and smellreceptors

Food chemicals(especially peptides and caffeine) and rising pHactivate chemoreceptors

Loss ofappetite,depression

Emotionalupset

Lack ofstimulatoryimpulses toparasym-patheticcenter

Cerebralcortex

Cerebral cortexConditioned reflex

Vagovagalreflexes

Localreflexes

Medulla

G cells

Hypothalamusand medullaoblongata

Vagusnerve

Vagusnerve

Gastrinreleaseto blood

Gastrinsecretiondeclines

G cells

Overridesparasym-patheticcontrols

Sympatheticnervoussystemactivation

1

11

1

2

2

2

Stimulatory events Inhibitory events

Cephalicphase

Gastricphase

Intestinalphase

Excessiveacidity (pH <2) in stomach

Distension of duodenum; presence of fatty, acidic, hypertonic chyme, and/or irritants in the duodenum


Figure 23.18 Mechanism of HCl secretion by parietal cells.

Stomach lumenChief cell

Parietal cell

Inter-stitialfluid

Carbonicanhydrase

Alkalinetide

HCO3–

Bloodcapillary

CO2

Cl–

CO2 + H2O

H2CO3

HCO3–- Cl–

antiporter

HCO3–

H+

Cl– Cl–l

K+ K+

H+

H+-K+

ATPase

HCI


Figure 23.19 Peristaltic waves in the stomach.

1 Propulsion: Peristaltic waves move from the fundus toward the pylorus.

2 3 Grinding: The most vigorous peristalsis and mixing action occur close to the pylorus.

Retropulsion: The pyloric end of the stomach acts as a pump that delivers small amounts of chyme into the duodenum, simultaneously forcing most of its contained material backward into the stomach.

Pyloricvalveclosed

Pyloricvalveclosed

Pyloricvalveslightlyopened


Figure 23.20 Neural and hormonal factors inhibiting gastric emptying.

Presence of fatty, hypertonic,acidic chyme in duodenum

Duodenal entero-endocrine cells

Chemoreceptors andstretch receptors

Enterogastrones(secretin, cholecystokinin,vasoactive intestinalpeptide)

Duodenalstimulidecline

Via shortreflexes

Via longreflexes

Entericneurons

Initial stimulus

Physiological response

Result

Contractile force andrate of stomachemptying decline

CNS centers sympathetic activity; parasympathetic activity

Stimulate

Inhibit

Secrete Target


Figure 23.21 The duodenum of the small intestine, and related organs.

Jejunum

Mucosawith folds

Cystic duct

DuodenumHepatopancreaticampulla and sphincter

Gallbladder

Right and lefthepatic ducts of liver

Bile duct and sphincter

Main pancreatic ductand sphincter

PancreasTail of pancreas

Head of pancreas

Common hepatic duct

Major duodenalpapilla

Accessory pancreatic duct


Figure 23.22a Structural modifications of the small intestine that increase its surface area for digestion and absorption.

Vein carrying blood tohepatic portal vessel

MusclelayersCircularfoldsVilli

(a)

Lumen


Figure 23.22b Structural modifications of the small intestine that increase its surface area for digestion and absorption.

(b)

Absorptive cells

Lacteal

Intestinal crypt

Mucosaassociatedlymphoid tissue

MuscularismucosaeDuodenal gland Submucosa

EnteroendocrinecellsVenuleLymphatic vessel

Goblet cellBloodcapillaries

Vilus

Microvilli(brush border)


Figure 23.22c Structural modifications of the small intestine that increase its surface area for digestion and absorption.

(c) Intestinal crypt

Absorptive cells

Villi

Gobletcells


Figure 23.23 Villi and microvilli of the small intestine.

(b)

Microvilli

Absorptivecell

(a)

Desquamatingcells

Villi


Figure 23.23a Villi and microvilli of the small intestine.

(a)

Desquamatingcells

Villi


Figure 23.23b Villi and microvilli of the small intestine.

(b)

Microvilli

Absorptivecell


Figure 23.24a Gross anatomy of the human liver.

SternumNipple

Liver

Right lobeof liver

Gallbladder

(a)

Bare area

Falciformligament

Left lobe of liver

Round ligament(ligamentum teres)


Figure 23.24b Gross anatomy of the human liver.

Lesser omentum(in fissure)

Left lobe of liver

(b)

Porta hepatiscontaining hepaticartery (left) andhepatic portal vein(right)Quadrate lobeof liverLigamentum teres

Gallbladder

Hepatic vein (cut)

Sulcus forinferiorvena cava

Caudate lobeof liver

Bare area

Bile duct (cut)

Right lobe ofliver

Sternum

Nipple

Liver


Figure 23.25a-b Microscopic anatomy of the liver.

(a) (b)Lobule Central vein Connectivetissue septum


Figure 23.25c Microscopic anatomy of the liver.

(c)

Interlobular veins(to hepatic vein) Central vein

Sinusoids

Portal triad

Plates ofhepatocytes

Portal vein

Fenestratedlining (endothelial cells) of sinusoids

Bile duct (receivesbile from bile canaliculi)

Bile duct

Portal arteriolePortal venuleHepatic

macrophagesin sinusoid walls

Bile canaliculi


Figure 23.26 Structure of the enzyme-producing tissue of the pancreas.

Small duct

Acinar cells

Basement membrane

Zymogen granules

Rough endoplasmicreticulum(a)

(b)

Acinar cells


Figure 23.26a Structure of the enzyme-producing tissue of the pancreas.

Smallduct

Acinar cells

Basementmembrane

Zymogengranules

Roughendoplasmicreticulum

(a)


Figure 23.26b Structure of the enzyme-producing tissue of the pancreas.

(b)

Acinarcells


Figure 23.27 Activation of pancreatic proteases in the small intestine.

Stomach

Pancreas

Epithelialcells

Trypsinogen(inactive)Chymotrypsinogen(inactive)Procarboxypeptidase(inactive)

Trypsin

Chymotrypsin

Carboxypeptidase

Membrane-boundenteropeptidase


Figure 23.28 Mechanisms promoting secretion and release of bile and pancreatic juice.

1

2

3

4

5

6

Chyme enter-ing duodenum causes release ofcholecystokinin (CCK) and secretin from duodenal enteroendocrine cells.

CCK (red dots) and secretin (yellow dots) enter the bloodstream.

CCK induces secretion of enzyme-rich pancreatic juice. Secretin causes secretion of HCO3

–-rich pancreatic juice.

Bile salts and, to a lesser extent, secretin transported via bloodstream stimulate liver to produce bile more rapidly.

CCK (via bloodstream) causes gallbladder to contract and hepatopancreatic sphincter to relax; bile enters duodenum.

During cephalic and gastric phases, vagal nerve stimulation causes weak contractions of gallbladder.


Figure 23.29a Gross anatomy of the large intestine.

Left colic(splenic) flexure

Transversemesocolon

Epiploicappendages

Descendingcolon

Teniae coli

Sigmoidcolon

Cut edge ofmesentery

External anal sphincter

Rectum

Anal canal(a)

Right colic(hepatic) flexureTransversecolon SuperiormesentericarteryHaustrum

Ascendingcolon IIeum

IIeocecal valve

Vermiform appendix

Cecum


Figure 23.29b Gross anatomy of the large intestine.

(b)

Rectal valveRectum

Anal canal

Levator animuscle

Anus

Anal sinuses

Anal columns

Internal analsphincter

External analsphincter

Hemorrhoidalveins

Pectinate line


Figure 23.30a Mesenteries of the abdominal digestive organs.

Falciform ligament

Liver

Gallbladder

Spleen

Stomach

Ligamentum teres

Greater omentum

Small intestine

Cecum

(a)


Figure 23.30b Mesenteries of the abdominal digestive organs.

Liver

Lesser omentumGallbladder

StomachDuodenum

Transverse colon

Small intestine

Cecum

Urinary bladder(b)


Figure 23.30c Mesenteries of the abdominal digestive organs.

Transverse colon

Greater omentum

Descending colonJejunumMesentery

Transversemesocolon

Sigmoidmesocolon

Sigmoid colon

Ileum

(c)


Figure 23.30d Mesenteries of the abdominal digestive organs.

(d)

Pancreas

LiverLesser omentum

Stomach

Duodenum

Transversemesocolon

Greater omentumMesentery

Jejunum

Visceral peritoneum

Urinary bladder

Transverse colon

Ileum

Parietal peritoneum

Rectum


Figure 23.31 Defecation reflex.

Impulses fromcerebral cortex(consciouscontrol)

Voluntary motornerve to externalanal sphincter

External analsphincter(skeletal muscle)

Internal anal sphincter(smooth muscle)

Sensorynerve fibers

Involuntary motor nerve(parasympathetic division)

Stretch receptors in wall

Rectum

Sigmoidcolon

3

1

2

Distension, or stretch, of therectal walls due to movement of feces into the rectum stimulates stretch receptors there. The receptors transmit signals along afferent fibers to spinal cord neurons.

A spinal reflex is initiated in which parasympathetic motor (efferent) fibers stimulate contraction of the rectal walls and relaxation of the internal anal sphincter.

If it is convenient to defecate, voluntary motor neurons are inhibited, allowing the external anal sphincter to relax so that feces may pass.


Figure 23.32 Flowchart of chemical digestion and absorption of foodstuffs (1 of 4).

Carbohydrate digestion

• Glucose and galactose are absorbed via cotransport with sodium ions.• Fructose passes via facilitated diffusion.• All monosaccharides leave the epithelial cells via facilitated diffusion, enter the capillary blood in the villi, and are transported to the liver via the hepatic portal vein.

Starch and disaccharides

Oligosaccharidesand disaccharides

Lactose Maltose Sucrose

Glucose Fructose

Salivaryamylase

Mouth

Pancreaticamylase

Brush borderenzymes in small intestine(dextrinase, gluco-amylase, lactase, maltase, and sucrase)

Smallintestine

Smallintestine

Foodstuff

Galactose

Path of absorptionEnzyme(s)and source

Site ofaction



Protein digestion

• Amino acids are absorbed by cotransport with sodium ions.• Some dipeptides and tripeptides are absorbed via cotransport with H+

and hydrolyzed to amino acids within the cells.

+

• Amino acids leave the epithelial cells by facilitated diffusion, enter the capillary blood in the villi, and are transported to the liver via the hepatic portal vein.

Smallintestine

Smallintestine

Stomach

Foodstuff

Protein

Large polypeptides

Pepsin(stomach glands)in presence of HCl

Small polypeptides,small peptides

Pancreaticenzymes (trypsin, chymotrypsin,carboxypeptidase)

Amino acids(some dipeptidesand tripeptides)

Brush border enzymes(aminopeptidase,carboxypeptidase,and dipeptidase)


Site ofaction



Fat digestion

Small intestine

Small intestine

Foodstuff

Unemulsifiedfats

Emulsification by the detergent action of bile salts ductedin from the liver

Pancreatic lipases

Monoglyceridesand fatty acids

Glyceroland

fatty acids


Site ofaction

• Fatty acids and monoglycerides enter the intestinal cells via diffusion. • Fatty acids and monoglycerides are recombined to form triglycerides and then combined with other lipids and proteins within the cells, and the resulting chylomicrons are extruded by exocytosis.

• The chylomicrons enter the lacteals of the villi and are transported to the systemic circulation via the lymph in the thoracic duct.• Some short-chain fatty acids are absorbed, move into the capillary blood in the villi by diffusion, and are transported to the liver via the hepatic portal vein.



Nucleic acid digestion

• Units enter intestinal cells by active transport via membrane carriers.

• Units are absorbed into capillary blood in the villi and transported to the liver via the hepatic portal vein.

Smallintestine

Smallintestine

Foodstuff

Nucleic acids

Pancreatic ribo-nuclease and deoxyribonuclease

Brush borderenzymes(nucleosidasesand phosphatases)

Pentose sugars,N-containing bases,

phosphate ions


Site ofaction


Figure 23.33 Protein digestion and absorption in the small intestine.

Absorptiveepithelialcell

Apical membrane (microvilli)

Aminoacid carrier

Capillary

Lumen of intestine

Pancreaticproteases

Amino acids of protein fragmentsBrush border enzymes

Na+

Na+

1 Proteins and protein fragments are digested to amino acids by pancreatic proteases (trypsin, chymotrypsin, and carboxypeptidase), and by brush border enzymes (carboxypeptidase, aminopeptidase, and dipeptidase)of mucosal cells.

2 The amino acids are then absorbed by active transport into the absorptive cells, and move to their opposite side (transcytosis).

3 The amino acids leave the villus epithelial cell by facilitated diffusion and enter the capillary via intercellular clefts.

Active transport

Passive transport


Figure 23.34 Emulsification, digestion, and absorption of fats.

Epithelialcells ofsmallintestine

Fat dropletscoated withbile salts

Fat globule

Lacteal

Bile salts

Micelles made up of fatty acids, monoglycerides,and bile salts

1 Large fat globules are emulsified (physically broken up into smaller fat droplets) by bile salts in the duodenum.

2 Digestion of fat by the pancreatic enzyme lipase yields free fatty acids and monoglycerides. These then associate with bile salts to form micelles which “ferry” them to the intestinal mucosa.

3 Fatty acids and monoglycerides leave micelles and diffuse into epithelial cells. There they are recombined and packaged with other lipoid substances and proteins to form chylomicrons.

4 Chylomicrons are extruded from the epithelial cells by exocytosis. The chylomicrons enter lacteals. They are carried away from the intestine by lymph.


Figure 23.35 Embryonic development of the digestive system.

Stomodeum

Foregut

Site ofliverdevelopmentMidgut

Spinal cord

Hindgut

Proctodeum

Endoderm

Brain

Oralmembrane

Heart

Yolk sac

Cloacalmembrane

Bodystalk

(a)

Lung bud

Liver

Gall-bladder

Cystic ductVentral pancreatic bud

Dorsalpancreaticbud

Duodenum

Stomach

(b)

Bileduct


Figure 23.35a Embryonic development of the digestive system.

Stomodeum

Foregut

Site ofliverdevelopmentMidgut

Spinal cord

Hindgut

Proctodeum

Endoderm

Brain

Oralmembrane

Heart

Yolk sac

Cloacalmembrane

Bodystalk (a)


Figure 23.35b Embryonic development of the digestive system.

Stomodeum

Lung bud

Liver

Gall-bladder

Cystic ductVentral pancreatic bud

Dorsalpancreaticbud

Duodenum

Stomach

(b)

Bileduct


Table 23.1 Hormones and Paracrines that Act in Digestion (1 of 2)


Table 23.1 Hormones and Paracrines that Act in Digestion (2 of 2)


Table 23.2 Overview of the Functions of the Gastrointestinal Organs (1 of 2)


Table 23.2 Overview of the Functions of the Gastrointestinal Organs (2 of 2)


Table 23.3 Control of Small Intestinal Motility


Making Connections 23.1 Homeostatic Interrelationships Between the Digestive System and Other Body Systems

Documents

Copyright © 2010 Pearson Education, Inc. Figure 23.1 Alimentary canal and related accessory digestive organs. Mouth (oral cavity) Tongue Esophagus Liver