ALIMENTARY TRACT. Veterinary histology science

Veterinary histology

1. DIGESTIVE SYSTEMDIGESTIVE SYSTEM
ALIMENTARY CANALALIMENTARY CANAL

3. ORAL CAVITYORAL CAVITY
•Beginning of the digestive Beginning of the digestive
systemsystem
–CheeksCheeks
–LipLip
–TongueTongue
–TeethTeeth
–Salivary glandsSalivary glands
•Oral epidermis derived Oral epidermis derived
from surface ectodermfrom surface ectoderm
•Continuous with Continuous with
integumentintegument
•Mucocutaneous junctionMucocutaneous junction

4. LIP/CHEEKLIP/CHEEK
•Integument outsideIntegument outside
•Mucosal inner Mucosal inner
surface usually surface usually
keratinizedkeratinized
•Mucocutaneous Mucocutaneous
junction junction
•Skeletal Skeletal musclemuscle
•CT under CT under
epithelium merges epithelium merges
with ICNwith ICN

5. TEETHTEETH
•NOT part of NOT part of
the skeletonthe skeleton
•Not made of Not made of
bone bone
–Set into boneSet into bone
•Three hard Three hard
materials:materials:
–EnamelEnamel
–DentinDentin
–CementumCementum

6. TOOTHTOOTH
•Bulk of tooth is Bulk of tooth is
DENTINDENTIN
–80% mineral, 20% 80% mineral, 20%
organic, mostly organic, mostly
collagencollagen
•ENAMEL covers ENAMEL covers
CROWNCROWN
–Hard but brittleHard but brittle
–98% mineral, 1% 98% mineral, 1%
organic materialorganic material
•CEMENTUMCEMENTUM
•NECK IS junction at NECK IS junction at
gum linegum line
•ROOT CANAL ROOT CANAL
–BV’s, nerves, etc.BV’s, nerves, etc.

7. TOOTH REGIONSTOOTH REGIONS
•PULP CAVITYPULP CAVITY
•Hollow space Hollow space
contains contains
“pulp,”“pulp,”
–Living material Living material
•PERIODONTAL PERIODONTAL
CT anchors CT anchors
tooth in tooth in
alveolus, alveolus,
serves as serves as
periosteumperiosteum

9. CELLS OF THE TEETHCELLS OF THE TEETH
•Several cell types recognizableSeveral cell types recognizable
–OdontoblastsOdontoblasts of pulp cavity of pulp cavity
–CementocytesCementocytes of cementum of cementum
–Ameloblasts Ameloblasts (temporary in brachydont (temporary in brachydont
teeth)teeth)

10. ODONTOBLASTSODONTOBLASTS
•Bulk of tooth is Bulk of tooth is
acellular, BUT acellular, BUT
made by cellsmade by cells
•ODONTOBLASTS ODONTOBLASTS
produce dentinproduce dentin
•Tall columnar Tall columnar
“epithelioid” cell “epithelioid” cell
with processeswith processes
•Secretory cell with Secretory cell with
some similarities to some similarities to
fibroblastsfibroblasts

11. •Odontoblasts lay down Odontoblasts lay down pre-pre-
dentin, cdentin, calcify it and “retreat” alcify it and “retreat”
towards center of cavitytowards center of cavity
•Remain active throughout life, Remain active throughout life, 
size of pulp cavitysize of pulp cavity

12. AMELOBLASTSAMELOBLASTS
•Elongated cell, Elongated cell,
columnar columnar
“epithelioid”“epithelioid”
•Produce Produce
enamel enamel
•Lay down pre-Lay down pre-
enamel and enamel and
harden itharden it
•In brachydont In brachydont
teeth, live only teeth, live only
to eruption of to eruption of
toothtooth

13. •Elongated cell, Elongated cell,
columnar columnar
“epithelioid”“epithelioid”
•Produce Produce
enamel enamel
•Lay down pre-Lay down pre-
enamel and enamel and
harden itharden it
•In brachydont In brachydont
teeth, live only teeth, live only
to eruption of to eruption of
toothtooth

14. •Ameloblast activity requires constant
induction
–Stellate Reticulum (Embryonic CT)
•As enamel made, ameloblasts retreat
•Eruption terminates induction &
enamel formation

15. ERUPTING TOOTHERUPTING TOOTH
•Deciduous Deciduous
toothtooth
–No more No more
enamel enamel
formationformation
–Permanent Permanent
toothtooth
•Still forming Still forming
enamelenamel
•Stellate Stellate
reticulum still reticulum still
presentpresent

16. RODENTSRODENTS
•Some Some
reticulum reticulum
remains remains
trappedtrapped
•Incisors grow Incisors grow
enamel enamel
continuouslycontinuously
•Maintains Maintains
chisel shapechisel shape

17. TONGUETONGUE
•Functions: eating, Functions: eating,
drinking, drinking,
vocalizationvocalization
•Muscular and Muscular and
mobilemobile
•Keratinized stratified Keratinized stratified
squamous dorsal squamous dorsal
surface surface
•Epithelial Epithelial
specializations specializations
•Sensitive and highly Sensitive and highly
innervatedinnervated
•Contains Contains
chemoreceptor siteschemoreceptor sites

18. MUSCLE OF THE TONGUEMUSCLE OF THE TONGUE
•Bulk of the tongue is SKELETAL MUSCLE in Bulk of the tongue is SKELETAL MUSCLE in
three planes at right angles to each otherthree planes at right angles to each other

19. MUSCLE OF THE TONGUEMUSCLE OF THE TONGUE
•Bulk of the tongue is SKELETAL MUSCLE in Bulk of the tongue is SKELETAL MUSCLE in
three planes at right angles to each otherthree planes at right angles to each other

20. LINGUAL PAPILLAELINGUAL PAPILLAE
•Special structures covering tongue Special structures covering tongue
surfacesurface
•Four types, categorized by shape:Four types, categorized by shape:
–FILIFORMFILIFORM
–FUNGIFORMFUNGIFORM
–VALLATEVALLATE
–In some species, FOLIATEIn some species, FOLIATE
•All except filiform have sensory functionAll except filiform have sensory function

21. FILIFORM PAPILLAEFILIFORM PAPILLAE
•Cover most of surfaceCover most of surface
•Keratinized projectionsKeratinized projections
•Pointed or “swallow-tailed” shapePointed or “swallow-tailed” shape
•Function as “rakes” or combs in grooming;Function as “rakes” or combs in grooming;
•No sensory functionNo sensory function

22. FUNGIFORM PAPILLAEFUNGIFORM PAPILLAE
•Larger, less common Larger, less common
•““Mushroom” shapeMushroom” shape
–Core of CTCore of CT
–Have sensory structuresHave sensory structures

23. VALLATEVALLATE
PAPILLAE PAPILLAE
•Very large paired Very large paired
structuresstructures
•2-6 pairs per 2-6 pairs per
tonguetongue
•Located near rootLocated near root
•Sunk below Sunk below
surface surface
•Have numerous Have numerous
taste budstaste buds
–May be on “moat” May be on “moat”
wallswalls
•Salivary glandsSalivary glands

24. “MOAT”
VALLATE IN LM & SEMVALLATE IN LM & SEM

25. FOLIATE PAPILLAEFOLIATE PAPILLAE
•Not found in all species: Lagomorpha have Not found in all species: Lagomorpha have
themthem
•On sides of the tongueOn sides of the tongue
•““Foliate” as in “leaves” of a bookFoliate” as in “leaves” of a book
•Flat-topped and vertically orientedFlat-topped and vertically oriented
•Have taste budsHave taste buds

26. TASTE BUDSTASTE BUDS
•Well-defined structuresWell-defined structures
•TransducersTransducers of chemical of chemical
information to neural stimuliinformation to neural stimuli
•Sunk below epithelium of Sunk below epithelium of
tonguetongue

27. TASTE BUDSTASTE BUDS
•Banana-shaped transducer cells Banana-shaped transducer cells
with long microvilliwith long microvilli
•Microvilli have chemoreceptor Microvilli have chemoreceptor
sites; nerve fibers wrap sites; nerve fibers wrap
transducerstransducers
•Nerve axons are bundled Nerve axons are bundled
together together

28. TASTE BUDSTASTE BUDS
•Banana-shaped transducer cells Banana-shaped transducer cells
with long microvilliwith long microvilli
•Microvilli have chemoreceptor Microvilli have chemoreceptor
sites; nerve fibers wrap sites; nerve fibers wrap
transducerstransducers
•Nerve axons are bundled Nerve axons are bundled
together together

29. TASTE PORESTASTE PORES
& “HAIRS”& “HAIRS”
•““Taste hairs” Taste hairs”
are exposed are exposed
to the lumen to the lumen
via “taste via “taste
pores”pores”
•Specialized Specialized
sites of sites of
chemo-chemo-
reception are reception are
on membrane on membrane
of the “hairs”of the “hairs”
•Taste poorly Taste poorly
understood understood
phenomenonphenomenon

30. TUBULAR STRUCTURE OF CANALTUBULAR STRUCTURE OF CANAL

31. ESOPHAGUSESOPHAGUS
Muscular, flexible & distensible Muscular, flexible & distensible
Wall has elastic fibers, Wall has elastic fibers, skeletal and smooth skeletal and smooth musclemuscle
Stratified squamous epithelium liningStratified squamous epithelium lining

32. ESOPHAGEAL MUSCULARIS MUCOSAEESOPHAGEAL MUSCULARIS MUCOSAE
•Muscularis mucosae is discontinuous at first
–Becomes continuous in deep regions
•Muscularis mucosae smooth muscle only
•Fibers run parallel to tube
•Glands in submucosa

34. M. MUCOSAE
GLANDS
M. MUCOSAE
GLANDS

37. ESOPHAGEAL-GASTRIC JUNCTIONESOPHAGEAL-GASTRIC JUNCTION
•Abrupt Abrupt
transitiontransition
–Stratified Stratified
squamous squamous
to simple to simple
columnarcolumnar
•NO goblet NO goblet
cells!cells!
•Location of Location of
changeover changeover
varies with varies with
speciesspecies

53. GASTRIC REGIONS & GLANDSGASTRIC REGIONS & GLANDS

54. GASTRIC MUCOSA GASTRIC MUCOSA
•Lining epithelium Lining epithelium
simple columnarsimple columnar
•No goblet cells No goblet cells
•Scattered gastric Scattered gastric
pitspits
–Glands open into Glands open into
base of pitsbase of pits

55. CARDIAC CARDIAC
GLANDSGLANDS
•Fill the Fill the
thickness thickness
of the of the
tunica tunica
mucosamucosa
•Protective Protective
mucous mucous
secretions secretions
emptied emptied
into gastric into gastric
pitspits

56. FUNDIC GLANDSFUNDIC GLANDS
•Simple branched tubularSimple branched tubular
•CHIEF, PARIETAL, and ENDOCRINE cellsCHIEF, PARIETAL, and ENDOCRINE cells

57. FUNDIC GLANDSFUNDIC GLANDS
PRODUCE ENZYMES & HCLPRODUCE ENZYMES & HCL

58. FUNDIC GLANDSFUNDIC GLANDS
PRODUCE ENZYMES & HCLPRODUCE ENZYMES & HCL

59. CHIEF AND PARIETAL CELLSCHIEF AND PARIETAL CELLS

61. CHIEF CELLSCHIEF CELLS
•Enzyme secretionsEnzyme secretions
•Typical secretory Typical secretory
appearance in LM appearance in LM
and EMand EM
•Pepsinogen & Pepsinogen &
trypsinogentrypsinogen

62. PARIETAL CELLSPARIETAL CELLS
•Extensive invaginations of surfaceExtensive invaginations of surface
•Vast numbers of mitochondriaVast numbers of mitochondria
•High level of oxygen consumptionHigh level of oxygen consumption

63. PYLORIC GLANDSPYLORIC GLANDS
•Produce a protective Produce a protective
PAS+ mucous PAS+ mucous
secretion secretion

64. ENTERO-ENTERO-
ENDOCRINE ENDOCRINE
CELLSCELLS
•Single cells Single cells
scattered scattered
through GI through GI
mucosamucosa
–Producing Producing
hormones hormones
•A diffuse A diffuse
endocrine endocrine
organorgan
–Cells polarized Cells polarized
to BV’s in to BV’s in
lamina propria lamina propria
and secrete to and secrete to
them, them, notnot
lumenlumen
•20+ Types 20+ Types
knownknown

65. TUNICA TUNICA
MUSCULARISMUSCULARIS
•Stomach has 3 Stomach has 3
layers: layers:
intestines have intestines have
2 layers2 layers
•Contractions Contractions
coordinated by coordinated by
nerve plexus nerve plexus
between layersbetween layers
•Produce Produce
peristalsisperistalsis
•All smooth All smooth
musclemuscle

66. ORGANIZATION OF THE INTESTINESORGANIZATION OF THE INTESTINES
•Tunica
mucosa
–Epithelium
–Lamina
propria
–Muscularis
mucosae
•Tunica
submucosa
•Tunica
muscularis
•Tunica serosa

67. SMALL INTESTINE
MUCOSA

68. INTESTINAL VILLIINTESTINAL VILLI
•Present only in small intestinePresent only in small intestine
•Crypts spaced between themCrypts spaced between them
•Do not confuse with “microvilli”!Do not confuse with “microvilli”!

69. INTESTINAL FOLDS
INVOLVE THE ENTIRE MUCOSA

70. •Core loose Core loose
irregular CT, the irregular CT, the
lamina propria; lamina propria;
has lymphatics, has lymphatics,
BV’s, smooth BV’s, smooth
muscle & cellsmuscle & cells

71. VASCULAR SUPPLY OF THE
VILLUS

72. CELLS OF THE INTESTINAL MUCOSACELLS OF THE INTESTINAL MUCOSA
•ENTEROCYTESENTEROCYTES
–Absorptive functionAbsorptive function
•GOBLET CELLSGOBLET CELLS
–Make mucous coatMake mucous coat
–Found in small and large intestineFound in small and large intestine
–Numbers greatest in large intestineNumbers greatest in large intestine
–Protective and lubricant coatingProtective and lubricant coating
•ENTEROENDOCRINE CELLSENTEROENDOCRINE CELLS
•PANETH CELLSPANETH CELLS
–Antibacterial productsAntibacterial products
–Small intestine onlySmall intestine only

73. ABSORPTIVE ABSORPTIVE
EPITHELIUMEPITHELIUM
•Tall columnar cells Tall columnar cells
with brush borderwith brush border
•Simple epitheliumSimple epithelium
•Goblet cells and Goblet cells and
enteroendocrine enteroendocrine
cells interspersed cells interspersed
among enterocytesamong enterocytes
•Proliferative and Proliferative and
“expendable”“expendable”

74. GOBLET GOBLET
CELLSCELLS
•Mucous secretions Mucous secretions
coat surface, coat surface,
minimize erosionminimize erosion
•Scattered among Scattered among
enterocytesenterocytes
•Secretion Secretion
mechanism is a mechanism is a
form of exocytosisform of exocytosis
•Most numerous in Most numerous in
large intestinelarge intestine

75. PANETH CELLSPANETH CELLS
•Do not proliferate or multiplyDo not proliferate or multiply
•Reside in bases of intestinal crypts Reside in bases of intestinal crypts
as groupsas groups
•Typical secretory cell appearanceTypical secretory cell appearance
•Antibacterial or antiparasitic: contain Antibacterial or antiparasitic: contain
LYSOZYMELYSOZYME

76. NEURAL NEURAL
ELEMENTSELEMENTS
–SEMI-AUTONOMOUS ENTERIC DIVISION PNS
•CNS preganglionic fibers
•Most control is local but can be overridden
•Complete feedback loops
•Two coordinated nerve plexuses
•SUBMUCOSAL PLEXUS
–Contraction of smooth muscle in lamina propria
•MYENTERIC PLEXUS
–Contraction of muscularis externa

77. SUBMUCOSAL PLEXUSSUBMUCOSAL PLEXUS

78. MYENTERIC MYENTERIC
PLEXUSPLEXUS
•Located Located between layers of tunica muscularisbetween layers of tunica muscularis
•Coordinates contractions of muscularisCoordinates contractions of muscularis
•Controls stomach contraction & peristalsisControls stomach contraction & peristalsis
•Responsive to ANS inputResponsive to ANS input

79. MYENTERIC PLEXUSMYENTERIC PLEXUS

80. DUODENUMDUODENUM
•LANDMARKSLANDMARKS
–Short, blunt villiShort, blunt villi
–Glands in the SUBMUCOSA!Glands in the SUBMUCOSA!
•Brunner’s glands produce alkaline secretion; Brunner’s glands produce alkaline secretion;
neutralizes acid chymeneutralizes acid chyme

82. JEJUNUMJEJUNUM
•Villi longer, leaf-like or “foliate”Villi longer, leaf-like or “foliate”
–““Islands” in lumen, NO glands in Islands” in lumen, NO glands in
submucosasubmucosa
Note NO glands in
submucosa!

84. SMALL INTESTINE: ILSMALL INTESTINE: ILEEUMUM
•LANDMARKS:LANDMARKS:
–Elongated villiElongated villi
–““Islands” presentIslands” present
–Aggregated lymphatic nodules, Aggregated lymphatic nodules, i.e.i.e., “Peyer’s Patches” in the , “Peyer’s Patches” in the
SUBMUCOSASUBMUCOSA

86. LARGE LARGE
INTESTINEINTESTINE
•NO villi, only NO villi, only
cryptscrypts
•Many goblet & Many goblet &
entero-endocrine entero-endocrine
cellscells
•No Paneth cellsNo Paneth cells
•Absorbs water, Absorbs water,
compacts fecal compacts fecal
bolusbolus
•Similar Similar
muscular & muscular &
neural neural
architecture to architecture to
rest of tractrest of tract

87. LARGE INTESTINELARGE INTESTINE
Crypt openings (SEM) & vertical section Crypt openings (SEM) & vertical section
through cryptsthrough crypts

88. ANO-RECTAL JUNCTIONANO-RECTAL JUNCTION
•ANUS derived from surface ectoderm, RECTUM from hindgutANUS derived from surface ectoderm, RECTUM from hindgut
•Abrupt transition between simple columnar with goblet cells to Abrupt transition between simple columnar with goblet cells to
stratified squamous epitheliumstratified squamous epithelium