Veterinary Histology UFF
Department of Morphology - Biomedic Institute
LaBEc - Laboratory of Cellular and Extracellular Biomorphology
Veterinary Histology Atlas
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Digestive System

• Obtain from the ingested food the necessary molecules for the maintenance, growth and other energetic needs of the organism


• Hollow Tube composed of a lumen, whose diameter is variable, surrounded by a wall formed by four distinct layers:

• Epithelial lining
• Lamina Propria: Loose Connective Tissue, rich in blood and lymphatic vessels, besides smooth muscle cells

Muscularis Mucosae
• Separates the Mucosa from the Submucosa
• Normally composed of two thin sub-layers of smooth muscle cells



Loose Connective Tissue with many blood and lymphatic vessels
• Present a Nervous Plexus or Meissner's plexus
• Can contain Glands and Lymphoid Tissue

Muscularis Layers
• Smooth muscle cells with a spiral orientation, divided into two sub-layers, Inner Circular and Outer Longitudinal



Between these two sub-layers we find the Myenteric Nervous Plexus or Auerbach’s Plexus



Thin Layer of Loose Connective Tissue, rich in blood and lymphatic vessels, and Adipose tissue
• Covered by a thin layer of Simple Squamous Epithelium called Mesothelium




Thin Layer of Loose Connective Tissue, rich in blood vessels, lymphatic vessels and Adipose tissue
• Does not possess Mesothelium
• Found where the Digestive Organ is joined with other Organs or structures.


• Keratinized(or not)Stratified Squamous Epithelium, depends on the animal’s diet
-Canines: Epithelium not keratinized
-Equines: Epithelium with little keratin
-Felines: Epithelium is keratinized
-Bovines: Epithelium not keratinized
• Striated Skeletal Muscle (Plexiform)
• Loose Connective Tissue highly vascularized and innervated
• Adipocytes(Filling)
• Acinar Glands : mucous, serous and mixed

• Taste Buds: Specialized structures that contain taste bud cells, substance detectors capable of drawing the flavor.

I - Filiform
• Have an elongated cone shape
• Numerous
• Present in the entire dorsal surface of the tongue
• Mechanical action, do not possess taste buds
II - Fungiform
• Resembles a mushroom, with a strait base and a more dilated and smooth superior surface portion
• Irregularly distributed between the filiform papillae
• Possess few taste buds
III - Foliate
• Poorly developed in humans, characteristic in rabbits
• Consists on two or more parallel folds separated by grooves
• Located on the dorsolateral surface of the tongue
• Contain many taste buds
IV - Circumvallate
• Great circular structures, whose flat surface extends itself to the top of other papillae
• A Deep Depression surrounds each papilla
• Present glands of von Ebner
-Numerous Serous glands located in the fossa of each papilla
-Continuous flow of liquid over the taste buds, important for the removal of food particles
-Secrete lipase that prevents the formation of a hydrophobic layer over the taste buds
• Distributed in the V-shaped boundary, in the posterior section of the tongue

Teeth and Associated Structures




• Low-crowned and adapted to a softer diet that results in less dental wear
• There is no regeneration of the enamel, during the tooth eruption, the coating of ameloblasts is released

• Found in Ruminants, Rodents and Equines
• Present a constant eruption, don’t have a definitive crown, neck or root
• The organ of the enamel is broken before the tooth eruption and leaves the tissue of the alveolus in contact with the enamel
• The cementum is deposited over the enamel
• Ameloblasts do not disintegrate in the eruption, they go on with their activities for a while
• Infundibular Recess and Pulp Cavity are present, visible according to the degree of wear of the teeth(old age)

Teeth Components

• Hardest component of the body, however little resistant
• Composed 97% of Ca2+ under the form of hydroxyapatite crystals
• Not innervated
• Possess Retzius’ Striae
-Incremental lines(growth lines) that mark the deposition of enamel

• The Organic Matrix is synthesized by ameloblasts
-Tall Cylindrical Cells
-Nucleus presents a basal orientation
-Numerous mitochondria located below the nucleus
-Secreting Cell Characteristics (well developed R.E.R. and G.A.)
• In brachydont animals, after the end of the enamel synthesis, the ameloblasts form a protective epithelium that covers the crown UNTIL the tooth eruption
• Tomes’ Process: Apical extension of the ameloblast, with numerous secretion granules contain proteins of the enamel matrix (amelogenin and enamelin)


• Mainly composed of collagen fibrils type I, glycosaminoglycans, phospholipids and hydroxyapatites
• Pre-Dentin: Matrix at first not mineralized
• The Organic Matrix is synthesized by the odontoblasts
-They are elongated cells that deposit the matrix only over dentine surfaces
-Nucleus with a basal orientation
-Numerous mitochondria located below the nucleus
-Characteristics of a Secreting Cell(well developed R.E.R. and G.A.)
• Tomes’ Fibers (Odontoblastic projections):
-Branched apical extension that penetrates the dentin perpendicularly.
-Become longer as dentin becomes thicker
-Dentinal Tubules: Narrow channels occupied by Tomes’ Fibers
• Caries do not develop naturally in animals due to their sucrose-free diet
• It is sensitive to stimulations even though it has few amyelinic nerve fibers connected to Tomes’ Fibers
• Hydrodynamic Theory: Stimulations cause movements in the fluids inside the dentinal tubules, sensitizing nerve fibers


Dental Pulp
• Loose Connective Tissue that contains: odontoblasts, fibroblasts, collagen fibrins and amorphous substance(many glycosaminoglycans)
• Highly vascularized tissue with many myelinic nerve fibers that penetrate the apical foramen and branch out
• Some Nerve Fibers lose their myelin and extend themselves only a short distance inside the dentinal tubules
• Pulp Fibers are sensitive only to pain(single sensory modality)

Periodontal Components

• Covers the Radicular Dentin
• Resembles the bone tissue although it does not contain vessels nor Haversian Systems
• It’s labile and reacts to forces in which it undergoes with reabsorption or production of a new tissue
• The continuous production of the cementum in the apix(bottom) compensates the physiological wear of the teeth(root/alveolus contact)
• Thicker in the apix region, where cementocytes are found:
-Cimentocytes are enclosed in lacunae, however practically don’t communicate between each other
-Nutrition comes from the Periodontal Ligament
-Low metabolic activity for it is not irrigated by blood

Periodontal Ligament
• Composed by a special type of Connective Tissue whose fibers are arranged in thick packs(Sharpey’s Fibers)
• Penetrate into the cementum of the tooth and osseous walls of the alveolus, allowing limited movements for the tooth
• Fibers are organized to support the pressures applied during chewing(dissipation of mechanical forces)
• The space between fibers are filled in by GAGs, collagen fibers and oxytalan elastic fibers

Alveolar Bone
• It is in direct contact with the periodontal ligament
• A type of immature bone with collagen fibers not grouped in the lamellar pattern
• Piercing Vessels: Blood vessels that pierce the alveolar bone and penetrate the periodontal ligament along the root
• Some vessels and nerves direct themselves toward the apical foramen of the root to penetrate the Pulp

• Mucosa Membrane firmly adhered to the periosteum of the mandible and maxilla bone
• Composed of Stratified Squamous Epithelium
• Junctional Epithelium: Specialized part of the gingival epithelium that is attached to the enamel through a cuticle (thick basal lamina)
• Between the Epithelium and the Enamel, above the Junctional epithelium, is the gingival sulcus(site of tartar accumulation)

• Extension of the Oral Cavity that connects it to the Esophagus
• Lined by Keratinized (or not)Stratified Squamous Epithelium, depends of the species
• Typical Lamina Propria, containing the tonsils, individual lymphoid nodules and disperse leucocytes.
• Present numerous papillae, similar to the dermal papillae of the skin
• There is no Muscularis Mucosae, a thin layer of elastic fibers separates this space from the submucosa
• Typical Submucosa containing mucous glands
• Muscularis Layer formed by striated skeletal muscle fibers without any particular orientation
• Present Adventitia for there is a union of the oropharynx to the esophagus


• Muscular tube whose function is to transport the food from the mouth to the stomach
• Lined by Keratinized(or not)Stratified Squamous Epithelium, depends on the species
• Typical Lamina Propria
• Muscularis Mucosae formed by well fragmented smooth muscle fibers

• Typical Submucosa containing mucous secreting esophageal glands, that facilitate the transport of food and protect the mucosa
• Muscularis Layer: Fibers are in different directions to facilitate the peristaltic movements
-Upper Third: Only Striated Skeletal Muscle Fibers
-Middle Third: Mix of Smooth muscle with Striated Skeletal muscle
-Inferior Third: Only Smooth Muscle Fibers
• Present Adventitia for there is a union of the esophagus with the trachea
• Present Serosa in the Esophagus Region that is in the Peritoneal Cavity

• The facility of ruminants and dogs to vomit and/or regurgitate is linked to the distribution of Striated Skeletal Muscle
• Fecal Emesis and Regurgitation are not physiological events in dogs
• Regurgitation is a physiological event in Ruminants
• Even though equines posses Striated Skeletal Muscle in 2/3 of their esophagus, their vomit is very rare, because the caudal esophageal sphincter has enough tonus to remain closed during gastric dilation to a point where a stomach rupture occurs without the occurrence of vomit.

• It is an organ that accomplishes exocrine and endocrine functions, digesting the food and secreting hormones
• Continues the digestion of carbohydrates begun in the mouth
• Adds an acid fluid to the ingested food
• Transforms the food into a viscous mass(chime) through muscular activity
• Promotes the initial digestion of proteins through the pepsin enzyme


Monogastric Animals


• Lined by Mucous Simple Columnar Epithelium(all of the cells secrete an alkaline mucus)
• The mucous forms a thick layer of gel that protects the cells from the stomach’s acidity
• Occlusive Junctions between superficial cells and gastric pits form a protective barrier against the acid
• HCl, Pepsins and Lipases are considered endogenous factors that damages the mucosa

• Gastric Pits:
-Epithelium that suffers invagination towards the lamina propria
-In these pits characteristic glands of each region debouch secretion

• Typical Lamina Propria containing smooth muscle cells and lymphoid cells
• Submucosa with dense connective tissue containing blood and lymphatic vessels

• Muscularis Layer contains Smooth Muscle Fibers oriented in three main directions:
-Inner Oblique
-Middle Circular
-Outer Longitudinal
• Present a Thin Serosa

Cell Types

• Low cylindrical cells with an oval nucleus with a more basal location
• Possess a high mitotic rate and originate other cell types
• Apical Regeneration: Superficial Mucous Cells and Pit Cells
• Basal Regeneration(responses are slower than the superficial mucous cells): Mucous Neck or Parietal and Cells Zymogenic or Enteroendocrine Cells
• Abundant in the neck, and a few in the isthmus of the fundus

Mucous Neck Cells
• Irregular shape with basal nucleus and secreting granules in the apical region
• Produce a mucous secretion that is less viscous than the mucous of the Surface Cells
• Can differentiate into surface lining cells and/or Gland Lining Cells
• Found in groups or isolated between the parietal cells in the neck region of the gastric cells

Parietal Cells
• Round or Pyramid-shaped Cells with a central spherical nucleus, cytoplasm intensely acidophilic
• Produce H+ and Cl-
• Gastrin and Histamine are potent stimulators of HCl production
• Gastrina possesses a trophic effect in the gastric mucosa, stimulating its growth
• Are mainly present in the upper half of the Gastric Glands, scarce in its base

Zymogenic Cells
• Secreting Characteristics, very basophilic and with cytoplasmic granules containing Pepsinogen
• Excrete pepsinogen that in contact with the stomach’s HCl transforms into pepsine.
• Present in the inferior region of the gastric glands

Enteroendocrine Cells
• Produce hormones:
-Serotonin: At the bottom of the Stomach, responsible for the increase of the intestinal mobility
-Somatostatin:Inhibits the release of some hormones such as gastrin
• Located in the base of the Gastric Glands

Histological Regions

• Transition between esophagus and stomach
• Transition from Stratified Squamous Epithelium of the Esophagus to Mucous Simple Columnar of the Stomach
• Submucosa contains cardiac glands that produce mucous and lysozyme(antibacterial)
• Present few Parietal Cells

Fundus (Corpus e Fundus are Histologically identical)
• Lined by a highly ridged Mucous Simple Columnar Epithelium
• Fairly thick mucosa
• Submucosa contains fundic glands that produce mucus
• 3 to 7 glands open at the bottom of each gastric pit
• Regions of Gastric Glands:


• Mucous cells in differentiation that will substitute the pit and surface cells
• Undifferentiated Stem-cells
• Parietal Cells


• Undifferentiated Stem-cells
• Parietal Cells
• Mucous Neck Cells(different from the mucous cells of the isthmus)
• Enteroendocrine cells


• Parietal Cells
• Zymogenic Cells
• Enteroendocrine Cells

• Lined by Mucous Simple Columnar Epithelium
• Possess Deep Gastric Pits where Pyloric glands open(mucus and lysozyme)
• Present Enteroendocrine cells that secrete gastrin intercalated by Mucous Cells
• The Middle Muscle Layer is thicker so to form a pyloric sphincter

Polygastric Animals

• Lined by Keratinized Stratified Squamous Epithelium
• Are non-glandular

Rumen (Paunçh)
• Small Rumen Papillae
• Do not possess Muscularis Mucosae (lamina propria and connective tissue of the submucosa are fused)
• Have a mechanical function
• Curiosities:
-Produce Volatile Fatty Acids
-Depend on protozoa and bacteria to digest

Reticulum (Bonnet)
• Reticulum' folds with a honeycomb aspect and spear-shaped
• Muscularis Mucosae projects itself a little, present in the apex of the papilla

Omasum (Manyplies)
•Omasum' folds
• Omasum' Folds with smaller papillae
• Muscularis Mucosae projects itself a lot, forming an axis of smooth muscle in all of its extension. There is also a layer of smooth muscle of inner circular.
• Retains food, it’s the coarsest papillae
True Stomach-Obomasum(rennet-bag)
• Same conformation as the common stomach
• Regions: Nonglandular, Cardia, Fundus and Pylorus
Small Intestine
Final part of the food digestion, nutrients absorption and endocrine secretion
• Possess many modifications that enhance the contact surface and consequently the absorption:
-Long length(5 meters)
-Folds in Mucosa and Submucosa
-Villi and Microvilli
-Absorptive Cells(Enterocytes)
*Type of epithelial cell of the superficial layer of the small and large intestines
*These cells break-down molecules and transport them inside the tissue


Lined by Simple Columnar Epithelium with a Striated Border and Goblet cells(vary according to the portion of the intestine)



• Present intestinal villi: Elongated Finger-like structures

• Crypts of Lieberkühn: Opening of Simple Tubular Glands
• Great amount of blood and lymphatic capillaries, besides veins
• Myenteric Plexus of Auerbach
• Submucosa Nerve Plexus of Meissner

Tipos Celulares

• Low cylindrical cells with an oval and basal located nucleus
• Possess a high mitotic rate and originate other types of cells

Absorptive Cells (Enterocytes)
• Tall Cylindrical Cells with an oval and basal located nucleus, granulated acidophilic cytoplasm, presence of striated border
• Absorb nutrients produced during digestion
• These cells are in constant renovation since there is a desquamation of apical cells
• Located in three portions of the Small Intestine, and situated in all of the villi portion

Goblet Cells
• Produce mucous that protects and lubricates the intestine’s lining
• Located in great amounts close to ileum, and situates itself between the absorptive cells

Paneth Cells
• Pyramid-shaped cells with acidophilic granules and basal nucleus
• Have an antibacterial activity because they produce lysozyme that destroys the bacterial cell wall
• Located in the basal portion of the glands

M Cells
• Specialized Epithelial Cells that line the lymphoid follicles of Peyer’s Patches
• The Basal Lamina below them is discontinuous, facilitating the intestinal traffic
• Possess many basal invaginations containing lymphocytes and antigen-presenting cells, like macrophages
• Capture antigens through endocytosis and transport them to the underlying lymphoid cells and macrophages
• Participate in the immunological defense of the intestines
• GALT(Gut-Associated Lymphoid Tissue)
-Plasmacytes that synthesize IgA
-Occlusive Intercellular junctions
-Present macrophages and lymphocytes located in the mucosa and submucosa


• Tube of approximately 2 to 3 centimeters in diameter that connects the stomach to the small intestine
• Villi with a leaf-like aspect, close to the ileum they acquire a finger-like shape
• Lined by Simple Columnar Epithelium with Striated Border and some RARE Goblet Cells
• Present many Absorptive Cells and Paneth Cells
• M cells and Goblet cells are characteristic of this region
• Typical Lamina Propria
• Muscularis Mucosa without any peculiarities



• Submucosa containing duodenal glands or Brünner Glands that produce mucus
-This mucus protects the mucosa against the acidity of the gastric acid and neutralizes the pH of the chime
-These glands open at the bottom of the Crypts of Lieberkühn
• Muscularis Layer with an Inner circular and Outer Longitudinal layer and present Myenteric Plexus of Auerbach
• Typical Serosa


• Portion of the small intestine that is comprised between the duodenum and ileum
• Villi are narrower and less numerous than in the duodenum, finger-like shape
• Lined by Simple Columnar Epithelium with Striated Border and SOME Goblet Cells
• Present many Absorptive Cells and Paneth Cells, some Goblet Cells
• M cells are not characteristic of this region
• Typical Lamina Propria
• Muscularis Mucosae without any peculiarities
• Submucosa does not contain any glands, present Nerve Plexus of Meissner
• Muscularis Layer with inner circular and outer longitudinal layer and presents Myenteric Plexus of Auerbach
• Characteristic Serosa



• Part of the small intestine in which the chemical digestion continues, after passing through the duodenum and jejunum
• Villi with a bat shape, folds are not present
• Lined by Simple Columnar Epithelium with Striated Border and MANY Goblet Cells
• Present many Absorptive Cells, Paneth Cells, Goblet Cells and M Cells
• Characteristic Lamina Propria with lymphoid nodules(Peyer’s Patches)
• Muscularis Mucosae without any peculiarities
• Submucosa does not contain any types of glands, has Peyer’s Patches and Nerve Plexus of Meissner
• Muscularis Layer with an inner circular and outer longitudinal layer and present myenteric plexus of Auerbach
• Characteristic Serosa

Large Intestine


• Consists of a Mucosa Membrane filled with Goblet Cells, no Folds or Villi
• Functions are water absorption, formation of feces and production of mucus
• Lined by Simple Columnar Epithelium with a Striated Border(irregular and spaced) and MANY Goblet Cells
• Present many Absorptive Cells and Goblet Cells, and some Enteroendocrine Cells
• M Cells and Paneth Cells are not typical of this region
• Lamina Propria with many lymphoid cells and nodules that frequently reach the submucosa
• Muscularis Mucosae without any peculiarities
• Typical Submucosa with lymphoid nodules
• Muscularis Externa formed by three thick laminae(taenia coli)
• Typical Serosa only until the neck after that it continues as an adventitia


Terminal part of the digestive system, after the large intestine and before the annus
• Very thick Muscularis Externa
• Adventitia

The annus is the orifice at the end of the large intestine where the feces and intestinal gases are eliminated.
• Transition from the Simple Columnar Epithelium to the Stratified Squamous, typical of the tegument
• Lamina Propria containing a plexus of large veins
• Adventitia

Accessory Gls.
Male Reprod.
Female Reprod.
Birds Histology