Digestive System

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Digestive System "The Tube"
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The Tube begins with esophagus and ends with
anus! Common structural plan tubular
saccular organs 4 concentric tunics Tunics
may be reduced or absent Minor structural
modifications (local requirements)
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Structural Plan Tunica Mucosa Epithelium Membran
a Propria Lamina Propria Mucosae Lamina
Muscularis Mucosae Tunica Submucosa Tunica
Muscularis Tunica Adventitia (Serosa)
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Esophagus
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Connects pharynx stomach Represents a transition
1.
2.
Muscularis mucosae replaces elastic layer of
pharynx
3.
Muscularis more regular
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Esophagus - panoramic
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Stratified Squamous Epithelium
Esophagus upper portion
Lamina propria
Muscularis mucosae
(Smooth muscle)
Submucosa
Tunica musclularis (circular)
Skeletal muscle
Tunica muscularis (longitudinal)
Tunica adventitia
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Esophagus - high
Epithelium stratified squamous (25 cell layers
tall papillae indent lower surface
Submucosa lax, elastic 7 10 longitudinal
folds deep esophageal glands
Muscularis 2 layers inner circular, outer
longitudinal upper ¼ skeletal, not regular
middle mix skeletal/smooth lower third
smooth (extent variable)
Adventitia loose, fibrous blood vessels
nerves
Muscularis mucosae - smooth muscle
Lamina propria - areolar C.T. poor
elasticity superficial glands (extreme upper
lower ends - mucous compound tubular)
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Esophagus high - mucosa
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Simple columnar epithelium
Stratified squamous epithelium
Esophagus
Stomach
Gastro-esophageal junction
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Gastro-esophageal junction
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Stomach
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Stomach dilated, distorted, capacious
sac Descriptive divisions Cardia Fundus Co
rpus Pylorus
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Mucosal lining Thickness 0.3 mm. (cardia) to
1.5 mm. (pylorus) Mucosa Submucosa form
longitudinal folds (rugae) Distention alters
number, height of rugae Finer system of furrows
? mound shaped areas Form gastric areas 1 to 5
mm. across Foveolae gastric pits open on
mounds foveolae vary by region 17 / sq.
mm. (fundus) 9 / sq. mm. (pylorus) Total
in stomach 3,400,000
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Surface epithelium simple columnar all are
mucous secreting mucous above nucleus mucigen
peculiar type
Surface epithelium into foveolae
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Gastric glands (general) branched tubular type
vertical
Depth full thickness of mucosa foveolae serve
as ducts for several glands 15,000,000 gastric
glands (human stomach) Very few at
birth Differentiate after birth ½ differentiate
after age 10 Total secreting surface 30 sq.
feet 3 gland groupings Cardiac glands, Fundic
glands, Pyloric glands
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Cardiac Glands narrow band (cardio-esophageal
junction) Zone 5 mm. to 40 mm. Resemble
superficial glands of lower esophagus Continuous
series small, sometimes compound, tubular
glands Foveolae ½ gland length, several glands
to 1 foveola Secretory portion tortuous Cells
resemble mucous cells of fundic pyloric
glands Gland lumen - obvious
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Fundic Glands (Gastric Glands) Fundus
corpus Straight, tubular, minor branching
(sides) Regions of gland 1. Foveola (short
duct) 2. Neck (constricted) 3. Body (long) 4.
Fundus (minor dilation bend) Duct
length/Main gland 14 Lumen narrow
1
2
3
4
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Four cell types Mucous Neck Cells numbers
increase pyloric end Nuclei flattened,
basal Mucous watery Chief Cells numbers
increase cardiac end Comprise much of gland
below neck Spherical nucleus, granular
elements Basally striate chromidial
substance Period of rest presecretion
granules Activity reduction in granules
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Parietal Cells contain pepsinogen More
abundant pyloric end Most common between
mucous neck cells appear wedged in Also
between chief cells Peripheral position Cell
shape wedge-like ? spherical Lack distinct
secretory granules Intercellular secretory
channels (secretory capillary) (between chief
cells) open to main lumen Secrete
hydrochloric acid (HCl - Secretory cap.)
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Argentaffin Cells enterochromaffin
elements Location between chief cells
basement membrane Slender cell extension may
reach lumen Granules in cell base (stain with
chrome salts) Precursors of serotonin
(vasoconstrictive hormone)
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Parietal cells
Chief cells
Stomach - fundus
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Gastric glands neck cells
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Stomach pyloric region
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Pyloric Glands 1/5th or more gastric
area Intermediate zone combines features of
fundus pylorus Pyloric glands simple,
branched, convoluted-tubular More branching than
fundic glands deeper Only one cell type in
body of gland (like mucous neck cells) Plus a
few argentaffin cells
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Lamina Propria of Stomach Mucosa L.P. tissue
sparse (consequence of large of glands) Most
abundant between foveolae Basic tissue delicate
network collagenous reticular fibers Diffuse
lymphocyte infiltration Solitary nodules can
occur esp. cardiac pyloric
regions Muscularis mucosae thin with
layers inner circular outer
longitudinal 3rd layer (outermost) some areas -
circular
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Submucosa loose, fibrous vascular rugae Muscul
aris 3 thick layers (smooth muscle) inner
oblique middle circular outer longitudinal
(most robust inner outer curvatures of
stomach Serosa usual C.T. with mesothelium
continuous with gastric mesenteries
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Small Large Intestines General
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A long tube longer than peritoneal
cavity Results in coiling of the tube Two
parts long, slender part (small
intestine) shorter, thicker part (large
intestine or colon) both parts are typical
tubular organs Common features and distinctive
features
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Features Common to Small Large
Intestines Mucosa Epithelium simple
columnar Draped over villi Dips into
glands Cells types through entire
intestine Exception Duodenal Glands of
Brunner 4 cell types present at all
levels Simple Columnar Cells Goblet
Cells Paneth Cells Argentaffin Cellws
Distribution of cell types not uniform at various
levels!
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Cell Types Simple Columnar Cells Tall, plastic,
elastic Cytoplasm finely granular Free surface
striate border (best seen near main
lumen) Cytoplasm near surface felt-like
ectoplasm ( terminal
web) Cells primarily absorptive (near main
lumen)
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Goblet Cells Typical unicellular mucous
glands All secretory stages seen Lack striate
border Numbers increase from duodenum to
rectum Paneth Cells Large cells Most numerous
small intestine Zymogenic cells Cell base
dark-staining, striated Above nucleus large,
round, refractile, acidophilic granules
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Paneth Cells
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Argentaffin Cells Largely restricted to
intestinal glands Rare on villi Most numerous
duodenum appendix Flask-shaped, small granules
under nucleus Yellow when fresh
acidophilic Serotonin production
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(No Transcript)
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Surface covering limited intervals between
glands Components Columnar cells Goblet
cells Intestinal Glands Pit-like ( intestinal
crypts of Lieberkuhn) 180,000,000 glands Extend
through lamina propria (0.1 to 0.7 mm.) Gland
base close to muscularis mucosae Epithelium
Columnar cells, Goblet cells, Paneth cells, and
Argentaffin cells Upper ½ gland cells with
striate border Goblet cells upper ½ Paneth near
base
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Lamina Propria fills in between
glands Reticular tissue framework Infiltrated
with free cells Also delicate collagenous
fibers many elastic fibers Reticular
network condenses into basement
membrane Solitary lymph nodules (30,000)
often encroach into submucosa Aggregate nodules
(Peyers Patches) commonest in
Ileum Muscularis mucosae inner circular
outer longitudinal
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Submucosa Loose areolar C.T. Vascular Nerve
plexuses Ring-like folds (Plicae circulares)
small intestine Brunners glands
(duodenum) Muscularis Inner layer
circular Outer layer longitudinal Small
intestine solid coat Large intestine 3
equally spaced bands (Taenia
coli) Serosa Continuous with mesenteries
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Small Intestine
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Lamina propria
Crypt of Lieberkuhn
Submucosa
Muscularis mucosae
Muscularis
Duodenum Brunners Glands
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Ileum lymphatic nodules
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Ileum - nodule
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Small Intestine Duodenum Ileum Jejunum
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Mesenteries Serosa leaves abdominal wall
reflects around gut Parietal peritoneum unites
(double sheet) Visceral peritoneum double
sheet splits around gut as serosal
coat Mesothelium (surface) C.T. layer under
mesothelium blood vessels, lymphatics,
nerve considerable fat some lymph
nodes Omenta dorsal ventral mesentery of
stomach ligaments mesenteries of other organs
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Large Intestine
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Large intestine 5 feet long width double that
of small intestine Caecum, appendix, colon,
rectum Lining no plicae circularies no
villi Intestinal glands of colon longer than
those of small intestine closer
together Differ only quantitatively Epithelial
cell types identical to small intestine
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Ileo-cecal Valve Apposed folds of mucosa
submucosa Support central plate smooth
muscle Circular layer provides smooth
muscle Parallel free edges ? slit-like
orifice Caecum blind sac (structurally like
rest of colon) Change from Ileum to Caecum ?
abrupt
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Vermiform Appendix Blind, finger-like process
(blind end of caecum) Wall very thick, lumen
small (relatively) Deep pockets between mucosal
folds Irregular, angular appearance More
rounded in adults Lumen detritus
filled Mucosa Glands decrease (middle/old
age) Many goblet cells, occassionally Paneth
cells Argentaffin cells most (?) numerous
compared to other parts of gut
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Lymphoid tissue (lamina propria
conspicuous Result very thick wall Closely
spaced solitary nodules Germinal centers
very large complete ring
Nodules push into submucosa Muscularis mucosae
poor broken (nodules) Submucosa ordinary,
thick may fibrose Muscularis thin Serosa
like rest of gut
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Colon Mucosa does not form folds Surface
simple columnar cells Thin striate
border Scattered goblet cells Glands longer
(0.4 mm. to 0.6 mm.) Regular verticl rows,
close Largely goblet cells Argentaffin cells
(occasional) Paneth cells (rare)
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Lamina Propria like small intestine Eosinophils
(numerous) Lymph nodules - (larger) into
submucosa Muscularis mucosae 2 typical layers
(smooth muscle)
Submucosa no peculiarities
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Musclaris internal (circular) typical external
3 longitudinal ribbon-like strips (
taeniae) Taeniae shorter than colon length
puckers colon into haustra
Colon-Taenia coli
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Between haustra wall forms crescentic Plicae
semilunares Serosa Peritoneal reflection
incomplete Colon pressed against body
wall Attached to serosa appendices epiploicae
redundant serosa
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Colon - cat
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Rectum only quantitative differences especially
true of anal canal Intestinal glands (longest
0.7 mm.) Become small, sparse, cease Lymphoid
tissue less abundant Muscularis 2 layers lack
taeniae Serosa replaced by an adventitia (lower
levels) Anal Canal short tube (lower part of
rectum pars analis recti) Mucosa 8
longitudinal anal columns joined near anal
orifice Forms pocket-like anal valves
cavities of valves anal sinuses
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Anal Canal short tube (lower part of rectum
pars analis recti) Mucosa 8 longitudinal anal
columns joined near anal orifice Forms
pocket-like anal valves cavities of valves
anal sinuses Epithelium becomes
stratified cuboidal (above valves) - level
of valves becomes stratified squamous
(uncornified) ? epidermis Muscularis mucosae
already fragmented, disappears
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Hairs, cutaneous glands appear near
orifice Glands circumanal glands Submucosa
rich plexus of hemorrhoidal vessels Circular
layer (smooth muscle) thickens ? internal anal
sphincter Superficially nearby skeletal muscle ?
external anal sphincter
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Internal anal sphinchter smooth muscle
Epidermis
External anal sphinchter skeletal muscle
Anal rectal junction longitudinal section
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Blood vessels of the digestive tube prominent
plexus in submucosa branches into mucosa
muscularis small intestine additional
branches to villi drained by one or two
venules Lymphatics of the digestive tube loops
or blindly ending vessels Each villus one
blind, central lacteal typical plexuses in
submucosa muscularis free vessels ? lymph nodes
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Nerves of the digestive tube from Vagus
autonomic ganglia myenteric plexus of
Auerbach submucous plexus of Meissner included
in plexuses ? autonomic ganglia Terminal fibers
end in muscles blood vessels (motor)
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Parasympathetic fibers (from Vagus sacral
outflow) Terminate on cells of intrinsic
ganglia gut wall fibers from intrinsic
ganglionic neurons ? muscle cells (wall wall
vessels) muscular activity vascularity
secretion Sympathetic fibers ganglia of
autonomic plexuses external to gut tube fibers
direct to endings (muscle fibers
vessels) inhibitory (antagonistic to
parasymphathetic fibers)