Download The Digestive System

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Overview of the Digestive System
PART 1
The Digestive System
•  Organs are divided into two groups
•  Alimentary canal
•  Mouth, pharynx, and esophagus
•  Stomach, small intestine, and large intestine
•  Accessory digestive organs
•  Teeth and tongue
•  Gallbladder, salivary glands, liver, and pancreas
•  Accessory organs are connected to the
alimentary canal by ducts
PowerPoint® Lecture Presentations prepared by
Leslie Hendon
•  Secretions contribute to breakdown of foodstuffs
University of Alabama, Birmingham
© 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc.
Figure 23.1 The alimentary canal and the accessory digestive organs.
Abdominal Regions
Mouth (oral cavity)
Parotid gland
Sublingual gland
Submandibular
gland
Tongue
Salivary glands
•  Four lines divide abdominal wall into nine
regions
•  Midclavicular lines—vertical lines of grid
Pharynx
Esophagus
Stomach
Pancreas
(Spleen)
Liver
Transverse
colon
Small
intestine
•  Connects tubercles of iliac crests
Descending
colon
Jejunum
•  Connects inferior points of costal margin
•  Transtubercular plane—inferior horizontal line
Gallbladder
Duodenum
•  Subcostal plane—superior horizontal line
Ascending
colon
Ileum
Cecum
Large intestine
Sigmoid colon
Rectum
Appendix
Anus
Anal canal
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© 2014 Pearson Education, Inc.
Figure 23.2a Divisions of the anterior abdominal wall.
Right
hypochondriac
region
Right
lumbar
region
Right iliac
(inguinal)
region
Figure 23.2b Divisions of the anterior abdominal wall.
Epigastric
region
Umbilical
region
Hypogastric
(pubic)
region
Left
hypochondriac
region
Left
lumbar
region
Left iliac
(inguinal)
region
Nine regions delineated by four planes
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Liver
Diaphragm
Gallbladder
Stomach
Ascending colon
of large intestine
Transverse colon
of large intestine
Small intestine
Descending colon
of large intestine
Cecum
Appendix
Initial part of
sigmoid colon
Urinary bladder
Anterior view of the nine regions showing the superficial organs
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1
Figure 23.3 Peritoneum and the Digestive System Organs (1 of 2)
Abdominal Quadrants
•  A simpler method of sectioning the anterior
abdominal wall
•  Right upper quadrant
•  Left upper quadrant
•  Right lower quadrant
•  Left lower quadrant
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© 2014 Pearson Education, Inc.
Figure 23.3 Peritoneum and the Digestive System Organs (2 of 2)
The Peritoneal Cavity and Peritoneum
•  Peritoneum—a serous membrane
•  Visceral peritoneum—surrounds digestive
organs
•  Parietal peritoneum—lines the body wall
•  Peritoneal cavity—a slitlike potential space
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© 2014 Pearson Education, Inc.
The Peritoneal Cavity and Peritoneum
The Peritoneal Cavity and Peritoneum
•  Mesentery—a double layer of peritoneum
•  Ventral mesenteries
•  Holds organs in place
•  Sites of fat storage
•  Provides a route for circulatory vessels and
nerves
•  Falciform ligament
•  Binds anterior part of liver to anterior abdominal
wall
•  Lesser omentum
•  Attaches liver to the lesser curvature of stomach
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© 2014 Pearson Education, Inc.
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Figure 23.4a The mesenteries.
The Peritoneal Cavity and Peritoneum
Falciform ligament
•  Dorsal mesenteries
Gallbladder
Liver
•  Greater omentum
Spleen
Stomach
•  Connects greater curvature of stomach to
posterior abdominal wall
Ligamentum teres
•  A fatty apron
Greater omentum
•  Transverse mesocolon
Small intestine
•  Holds transverse colon in place
•  Sigmoid mesocolon
Cecum
•  Connects the sigmoid colon to posterior pelvic wall
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© 2014 Pearson Education, Inc.
Figure 23.4b The mesenteries.
Figure 23.4c The mesenteries.
Greater
omentum
Liver
Gallbladder
Transverse colon
Lesser omentum
Transverse
mesocolon
Stomach
Duodenum
Transverse colon
Descending colon
Mesentery
Small intestine
Sigmoid
mesocolon
Jejunum
Cecum
Sigmoid colon
Ileum
Urinary bladder
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© 2014 Pearson Education, Inc.
Figure 23.4d The mesenteries.
The Peritoneal Cavity and Peritoneum
Ligamentum teres
Gallbladder
Lesser omentum
Spleen
Liver
Gastrosplenic ligament
Transverse
mesocolon
Pancreas
Duodenum,
superior part
Transverse colon
Duodenum,
horizontal part
Stomach, pyloric part
Duodenojejunal flexure
•  Retroperitoneal organs
•  Behind the peritoneum
•  Peritoneal organs
•  Digestive organs that keep their mesentery
Greater omentum
Descending colon
Ascending colon
Mesentery (cut)
Sigmoid
mesocolon
Rectum
Ileum
Cecum
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© 2014 Pearson Education, Inc.
3
Table 23.1 Summary of Intraperitoneal and Secondarily Retroperitoneal Digestive Organs in the Abdomen and Pelvis
Secondarily Retroperitoneal Organs
•  Initially formed within peritoneum
•  Become retroperitoneal
•  Fuse to posterior abdominal wall
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© 2014 Pearson Education, Inc.
Digestive Processes
Digestive Processes
•  Ingestion—occurs in the mouth
•  Chemical digestion—complex molecules
broken down to chemical components
•  Propulsion—movement of food
•  Peristalsis—major means of propulsion
•  Mechanical breakdown—prepares food for
chemical digestion
•  Chewing, churning food in stomach,
segmentation
•  Segmentation is rhythmic local constrictions of
intestine
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•  Mouth
•  Stomach
•  Small intestine
•  Absorption—transport of digested nutrients
•  Defecation—elimination of indigestible
substances as feces
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Figure 23.5 Activities of the gastrointestinal tract.
Peristalsis
Ingestion
Food
Mechanical
breakdown
•  Chewing (mouth)
•  Churning (stomach)
•  Segmentation
(small intestine)
•  Major means of propulsion
Pharynx
Esophagus
Propulsion
•  Swallowing
(oropharynx)
•  Peristalsis
(esophagus,
stomach,
small intestine,
large intestine)
Digestion
•  Adjacent segments of the alimentary canal
relax and contract
Stomach
Absorption
Lymph
vessel
Small
intestine
Blood
vessel
Large
intestine
Mainly H2O
Feces
Defecation
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Anus
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Figure 23.6a Peristalsis and segmentation.
From
mouth
Segmentation
•  Rhythmic local contractions of the intestine
•  Mixes food with digestive juices
Peristalsis: Adjacent segments
of alimentary tract organs
alternately contract and relax,
moving food along the tract
distally.
© 2014 Pearson Education, Inc.
© 2014 Pearson Education, Inc.
Figure 23.6b Peristalsis and segmentation.
Histology of the Alimentary Canal Wall
•  Same four layers from esophagus to anus
•  The mucosa—innermost layer
•  Consists of
•  Epithelium
•  Lamina propria
•  Muscularis mucosae
Segmentation: Nonadjacent
segments of alimentary tract
organs alternately contract and
relax, moving the food forward
then backward. Food is mixed
and slowly propelled.
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•  The submucosa—external to the mucosa
•  Contains blood and lymphatic vessels, nerve
fibers
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Figure 23.7a Histological layers of the alimentary canal.
Histology of the Alimentary Canal Wall
Intrinsic nerve plexuses
Myenteric nerve plexus
Submucosal nerve plexus
•  The muscularis externa—external to the
submucosa
Glands in submucosa
•  Two layers
Mucosa
Epithelium
Lamina propria
Muscularis mucosae
•  Circular muscularis—inner layer
•  Longitudinal muscularis—outer layer
Submucosa
Muscularis externa
Circular layer
Longitudinal layer
•  The serosa—the outermost layer
•  Is the visceral peritoneum
Serosa
Epithelium
Connective tissue
Mesentery
Nerve
Artery
Vein
Lymphatic vessel
Lumen
Gland in mucosa
Duct of gland outside
alimentary canal
Mucosa associated
lymphoid tissue
Longitudinal and cross-sectional views through the small intestine
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© 2014 Pearson Education, Inc.
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Figure 23.7b Histological layers of the alimentary canal.
Smooth Muscle
•  Primarily found in walls of viscera
Mucosa
Submucosa
•  Fibers elongated
•  Have one centrally located nucleus
•  Grouped into sheets
Muscularis externa
Serosa
Light micrograph cross section through the small intestine (85×)
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•  Longitudinal layer—parallel to long axis of
organ
•  Circular layer—deeper layer, fibers run around
circumference of organ
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Figure 23.8 Arrangement of smooth muscle in the walls of hollow organs.
Smooth Muscle Contraction
•  Mechanism of contraction
Longitudinal layer of
smooth muscle (shows
smooth muscle fibers in
cross section, 215×)
Small intestine
Mucosa
Location and plane of
section shown in (b)
Cross section of the intestine
showing the smooth muscle
layers (one circular and the
other longitudinal) running at
right angles to each other
Circular layer of smooth
muscle (shows longitudinal
views of smooth muscle
fibers, 215×)
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•  Myofilaments operate by interaction with
cytoskeleton
•  Dense bodies—correspond to Z-discs of
skeletal muscle
•  Sliding myofilaments shorten the muscle cell by
pulling on cytoskeleton
•  Entry of Ca2+ into sarcoplasm stimulates
contraction
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Figure 23.9 Cytoskeletal elements involved in the contraction of smooth muscle.
Smooth Muscle Contraction
•  Contraction is slow and sustained
•  Takes 30x longer to contract and relax
•  Resistant to fatigue
•  Smooth muscle of arteries and visceral organs
must sustain contraction over long periods
Intermediate
filament
Caveolae
Nucleus
Gap junctions
Dense bodies
Relaxed smooth muscle fiber (note that gap
junctions connect adjacent fibers)
Nucleus
•  Energy requirements are low
Dense bodies
•  Mitochondria are not abundant
Contracted smooth muscle fiber
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Figure 23.10 Innervation of smooth muscle.
Innervation of Smooth Muscle
Varicosities
•  Innervated by ANS
•  Few fibers per sheet innervated
•  Sheet of smooth muscle contracts as a unit
•  Called single-unit innervation
Autonomic
nerve fibers
innervate
most smooth
muscle fibers.
Smooth
muscle
cell
•  Multiunit innervation
•  Each smooth muscle cell innervated
•  Iris of eye and arrector pili muscles
Synaptic
vesicles
Mitochondrion
Varicosities release
their neurotransmitters
into a wide synaptic
cleft (a diffuse junction).
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© 2014 Pearson Education, Inc.
Nerve Plexuses
The Mouth and Associated Organs
•  Myenteric nerve plexus
•  Mouth (oral cavity)
•  Lies between circular and longitudinal muscularis
•  Controls peristalsis and segmentation
•  Submucosal nerve plexus
•  Lies in submucosa
•  Signals glands to secrete
•  Innervation
•  Sympathetic and parasympathetic motor fibers
•  Mucosa-lined cavity
•  Boundaries are
•  Lips anteriorly
•  Cheeks laterally
•  Palate superiorly
•  Tongue inferiorly
•  Fauces of oropharynx posteriorly
•  Visceral sensory fibers
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© 2014 Pearson Education, Inc.
Figure 23.11a Anatomy of the mouth.
The Mouth and Associated Organs
•  The mouth—oral cavity
•  Mucosal layer
Soft palate
Palatoglossal arch
Oral cavity
Palatine
tonsil
•  Stratified squamous epithelium
Tongue
•  Lamina propria
Oropharynx
•  The lips and cheeks
•  Formed from orbicularis oris and buccinator
muscles, respectively
Uvula
Hard palate
Lingual tonsil
Epiglottis
Hyoid bone
Laryngopharynx
Esophagus
Trachea
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Sagittal section of the oral cavity and pharynx
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Figure 23.11b Anatomy of the mouth.
Anatomy of the Mouth
Gingivae
(gums)
•  The labial frenulum
Palatine
raphe
•  Connects lips to gum
•  The palate
•  Forms the roof of the mouth
•  Boundaries of the fauces
•  Palatoglossal arches
•  Palatopharyngeal arches
Hard palate
Soft palate
Uvula
Palatine
tonsil
Sublingual
fold with
openings of
sublingual ducts
Oral vestibule
Lower lip
Upper lip
Superior labial
frenulum
Palatoglossal
arch
Palatopharyngeal
arch
Posterior wall
of oropharynx
Tongue
Lingual frenulum
Opening of
submandicular
duct
Gingivae (gums)
Inferior labial
frenulum
Anterior view
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© 2014 Pearson Education, Inc.
The Tongue
The Superior Surface of the Tongue
•  Interlacing fascicles of skeletal muscle
•  Tongue papillae
•  Grips food and repositions it
•  Filiform papillae—no taste buds
•  Helps form some consonants
•  Fungiform papillae
•  Intrinsic muscles—within the tongue
•  Vallate papillae
•  Extrinsic muscles—external to the tongue
•  Lingual frenulum
•  Secures tongue to floor of mouth
•  Sulcus terminalis
•  Marks border between mouth and pharynx
•  Posterior one-third of tongue lies in oropharynx
•  Lined with lingual tonsil
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© 2014 Pearson Education, Inc.
Figure 23.12 The dorsal surface of the tongue.
Epiglottis
Palatopharyngeal
arch
Palatine tonsil
Lingual tonsil
Palatoglossal
arch
Terminal sulcus
Foliate papillae
Vallate papilla
Medial sulcus
of the tongue
Dorsum of tongue
The Teeth
•  Deciduous teeth—20 teeth
•  First appear at 6 months of age
•  Permanent teeth—32 teeth
•  Most erupt by the end of adolescence
•  Dental formula—shorthand
•  Formula for adult dentition indicates number and
position of teeth
•  2I, 1C, 2P, 3M
Fungiform papilla
Filiform papilla
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Figure 23.13a Human dentition.
Figure 23.13b Human dentition.
Incisors
Central (6–8 mo)
Lateral (8–10 mo)
Canine (eyetooth)
(16–20 mo)
Molars
First molar
(10–15 mo)
Second molar
(about 2 yr)
Deciduous
(milk) teeth
Incisors
Central (7 yr)
Lateral (8 yr)
Canine (eyetooth)
(11 yr)
Premolars
(bicuspids)
First premolar
(11 yr)
Deciduous teeth
Permanent teeth
Second premolar
(12–13 yr)
Molars
First molar (6–7 yr)
Second molar
(12–13 yr)
Third molar
(wisdom tooth)
(17–25 yr)
Permanent
teeth
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© 2014 Pearson Education, Inc.
Vessels and Nerves to the Teeth
Tooth Structure
•  Upper teeth
•  Crown—exposed surface
•  Innervation is superior alveolar nerves
branching from maxillary division of CN V
•  Lower teeth
•  Innervation is inferior alveolar nerves
branching from mandibular branch of CN V
•  Root—in tooth socket
•  Outer layer is enamel
•  Dentin—underlies enamel
•  Pulp cavity—center of tooth
•  Arterial supply to teeth
•  Superior and inferior alveolar arteries (branching
from maxillary arteries)
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© 2014 Pearson Education, Inc.
Figure 23.14 Longitudinal section of a canine tooth within its bony tooth socket.
Enamel
The Salivary Glands
Dentin
Crown
Dentinal tubules
Pulp cavity (contains
blood vessels
and nerves)
Neck
Gingival sulcus
Gingiva (gum)
Cement
Root
Root canal
Periodontal
ligament
•  Produce saliva
•  Compound tubuloalveolar glands
•  Parotid glands
•  Parotid duct—parallel to zygomatic arch
•  Contain only serous cells
•  Submandibular glands
•  Lie along medial surface of mandible
•  Sublingual glands
Apical
foramen
Bone
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•  Lie in floor of oral cavity
•  Contain primarily mucous cells
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Figure 23.15 The major salivary glands.
The Pharynx
•  Oropharynx and laryngopharynx
•  Passages for air and food
Tongue
Teeth
•  Lined with stratified squamous epithelium
Parotid
gland
Ducts of
sublingual
gland
Parotid duct
•  External muscle layer
Masseter muscle
Frenulum
of tongue
Body of mandible
(cut)
Sublingual
gland
•  Consists of superior, middle, and inferior
pharyngeal constrictors
Posterior belly of
digastric muscle
Mylohyoid
muscle (cut)
Anterior belly of
digastric muscle
Submandibular
duct
Submandibular
gland
Mucous cells
Serous cells
forming
demilunes
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© 2014 Pearson Education, Inc.
The Esophagus
The Esophagus
•  Gross anatomy—muscular tube
•  Microscopic anatomy
•  Begins as a continuation of the pharynx
•  Epithelium is stratified squamous epithelium
•  Joins the stomach inferior to the diaphragm
•  When empty, mucosa and submucosa are in
longitudinal folds
•  Cardiac sphincter—closes lumen to prevent
stomach acid from entering esophagus
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•  Mucous glands—primarily compound
tubuloalveolar glands
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Figure 23.16 Microscopic structure of the esophagus.
The Esophagus
•  Muscularis externa
•  Skeletal muscle
•  First one-third of length
Mucosa
(stratified squamous
epithelium)
•  Mixture of skeletal and smooth muscle
Submucosa
(areolar connective
tissue)
•  Middle one-third of length
Lumen
Muscularis externa
Circular layer
Longitudinal layer
•  Smooth muscle
•  Inferior one-third of length
•  Adventitia
Esophagusstomach
junction
Simple columnar
epithelium of
stomach
Adventitia (fibrous
connective tissue)
Cross section through
esophagus (3×)
Esophagus-stomach junction,
longitudinal section (85×)
•  Most external layer of esophagus
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10
Figure 23.17a Gross anatomy of the stomach.
The Stomach
Cardia
Fundus
Esophagus
•  Site where food is churned into chyme
•  Secretion of pepsin begins protein digestion
•  Functions under acidic conditions
Serosa
Muscularis externa
Longitudinal layer
Circular layer
Oblique layer
Body
Lumen
Lesser
curvature
•  Food remains in stomach approximately 4
hours
Rugae of
mucosa
•  Regions of the stomach
•  Cardial part
Greater
curvature
•  Fundus
•  Body
Duodenum
•  Pyloric part
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Pyloric
antrum
Pyloric
canal
Pyloric sphincter
(valve) at pylorus
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Figure 23.17b Gross anatomy of the stomach.
Microscopic Anatomy of the Stomach
Fundus
Liver
(cut)
Body
Spleen
Lesser
curvature
•  Muscularis has three layers
•  Circular and longitudinal layers and oblique layer
•  Epithelium is simple columnar epithelium
•  Mucosa dotted with gastric pits
Greater
curvature
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•  Gastric glands—deep to gastric pits
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Figure 23.18 Microscopic anatomy of the stomach.
Microscopic Anatomy of the Stomach
Gastric pits
Surface epithelium
(mucous cells)
•  Gastric glands of fundus and body
•  Mucous neck cells
•  Secrete a special mucus
•  Parietal (oxyntic) cells
•  Secrete hydrochloric acid and gastric intrinsic
factor
Surface
epithelium
Gastric
gland
Lamina
propria
Submucosa
(contains
submucosal
plexus)
Muscularis
externa
(contains
myenteric
plexus)
Serosa
Chief cell
Muscularis
mucosae
Oblique
layer
Enteroendocrine cell
Pepsinogen
Enlarged view of
gastric pits and
gastric glands
Circular
layer
Longitudinal
layer
HCl
Pepsin
Mitochondria
Parietal cell
Stomach wall
Layers of the stomach wall, longitudinal section
Gastric pits
Mucus-secreting
cells
Surface mucous cell
Mucous neck cells
Chief cell
Enteroendocrine
cell
Location of the HCl-producing parietal
cells and pepsin-secreting chief cells in
a gastric gland
HCl-secreting parietal cells
Gastric
gland
•  Pepsinogen is activated to pepsin when it
encounters acid in the gastric glands
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Mucous neck cells
Parietal cell
Mucosa
•  Chief (zymogenic) cells
•  Secrete pepsinogen
Gastric
pit
Enzyme-secreting chief cells
Muscularis
mucosae
Micrograph of the stomach mucosa, view similar to part (b) (110×)
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The Small Intestine—Gross Anatomy
The Duodenum
•  Longest portion of the alimentary canal
•  Receives digestive enzymes and bile
•  Site of most enzymatic digestion and
absorption
•  Main pancreatic duct and common bile duct
enter duodenum
•  Three subdivisions
•  Sphincters control entry of bile and pancreatic
juices
•  Duodenum
•  Jejunum
•  Ileum
•  Innervation
•  Parasympathetic fibers from vagus nerve
•  Sympathetic from thoracic splanchnic nerves
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© 2014 Pearson Education, Inc.
Figure 23.19 The duodenum of the small intestine, and related organs.
The Small Intestine—Microscopic Anatomy
•  Modifications for absorption
Right and left hepatic
ducts of liver
Common hepatic duct
Cystic duct
Bile duct and sphincter
Accessory pancreatic duct
•  Circular folds
•  Transverse ridges of mucosa and submucosa
•  Villi
•  Fingerlike projections of the mucosa
Mucosa
with folds
Tail of pancreas
Pancreas
Gallbladder
Jejunum
Major duodenal
papilla
Hepatopancreatic
ampulla and sphincter
Main pancreatic duct and sphincter
Duodenum
•  Covered with simple columnar epithelium
•  Microvilli
•  Further increase surface area for absorption
Head of pancreas
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© 2014 Pearson Education, Inc.
Figure 23.20 Structural modifications of the small intestine that increase the surface area for digestion and absorption.
Vein carrying
blood to
hepatic portal
vessel
Histology of the Intestinal Wall
Muscle
layers
•  Absorptive enterocytes
•  Uptake digested nutrients
Circular
folds
Lumen
Villi
Microvilli
(brush border)
•  Goblet cells
•  Secrete mucus that lubricates chyme
•  Enteroendocrine cells
•  Secrete hormones
•  Intestinal crypts
•  Epithelial cells secrete intestinal juice
Absorptive enterocytes
Absorptive
enterocytes
Goblet
cells
Lacteal
Goblet
cell
Villi
Vilus
Blood
capillaries
Mucosa
associated
lymphoid
tissue
Intestinal
crypt
Muscularis
mucosae
Duodenal
gland
Enteroendocrine
cells
Venule
Lymphatic vessel
Submucosa
Intestinal crypt
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