Digestive System Flashcards
What does the digestive system consist of
The digestive system comprises the oral cavity and alimentary canal, which includes the esophagus, stomach, small and large intestines, and several glands (salivary, liver, and pancreas).
It consists of a hollow tube (highly modified in the oral cavity) whose lumen varies in diameter and is surrounded by four layers:
1. Tunica mucosa consisting of three sublayers (epithelium, lamina propria and muscularis mucosae), 2. Tunica submucosa, 3. Tunica muscularis, and 4. Tunica serosa (CT layer covered by mesothelium) or tunica adventitia (T covering of organs present outside the body cavities).
What is part of the Oral cavity
includes the lips, palate, teeth, tongue, and salivary glands.
What is the epithelium of the outside of lips
Outside: stratified squamous keratinized epithelium with hairs and sebaceous glands;
What is the epithelium of the inside of lips
inside: stratified squamous, which may be slightly keratinized in ruminants and horse, depending upon the type of food;
lamina propria and submucosa blends (muscularis mucosa absent in the oral cavity); muscularis consists of skeletal muscle.
What is the epithelium of the cheek
like lip, except epithelium may be modified at some places to form conical papillae in ruminants.
What is the epithelium of the hard palate
Stratified squamous keratinized, which is very thick in ruminants and forms the dental pad rostrally; lamina propria blends with submucosa that covers the bony tissue.
What is the epithelium of the soft palate
Soft palate: epithelium: stratified squamous on the oral side and pseudostratified ciliated on the nasal side; lamina propria and submucosa blend and contain lymphatic tissue.
What is the epithelium of the tong
Stratified squamous with varying degrees of keratinization on the dorsal side and non-keratinized on the ventral side. The dorsal epithelium is modified to form papillae, which are classified into five types:
Filiform
Fungiform
Foliate
Circumvallate/vallate
lenticular
What are filiform of the tongue
Most numerous, sharp, highly cornified, pointed backward, lacks taste buds
What are fungiform of the tongue
Few in numbers, mushroom-shaped, interspersed among filiform papillae, may contain taste buds on the dorsal surface;
What are Foliate of the tongue
Leaf-like, present on the lateral surface, most numerous in rabbits, contain taste buds
What are circumvallate/vallate of the tongue
Least numerous, surrounded by a deep furrow in which serous Ebner’s glands open, distributed in a V pattern rostral to the sulcus terminalis, taste buds numerous on the lateral surface;
What are Lenticular of the tongue
Flat, lentil shaped, mainly found in ruminants, lacks taste buds. The lamina propria is closely attached with submucosa, and both are penetrated by skeletal muscles oriented vertically, transversally, and longitudinally and thus enabling tongue movements in all directions.
Species Variations of the tongue
lyssa (fat and muscular tissue) in carnivores, fibrous chondroid structure in horses, and lingual bone in birds.
Taste buds
bell- shaped structures consisting of taste cells, supporting cells, and nerve fibers innervating taste cells
note, only dissolved substances can be tasted
What are the four taste qualities
sweet, salt, bitter, and acid
What do teeth consist of
Consist of hard tissues (enamel, dentin, and cement) and soft tissues (pulp cavity and periodontal ligament).
Enamel
Covers the crown and is the hardest substance of the body;
Completely acellular and avascular;
What do enamel consist of
Consists of prisms synthesized by ameloblasts, which are non-regenerable and thus enamel, if damaged, cannot be replaced
Dentin
Represents the skeleton of the tooth; living and regenerable
What do Dentin Consist of
Consists of dentinal tubules and inter-tubular tissue composed of calcified matrix containing collagen fibers that are synthesized by odontoblasts lining the pulp cavity;
note, dentin is like bone except those odontoblasts are not embedded in the calcified matrix.
Cementum
Covers dentin of the root, exception: hypsodont teeth where it also covers crown (above enamel), live, consists of calcified matrix containing collagen fibers synthesized by cementocytes.
What does the Periodontal Ligament contain
Consists of dense CT, no mineral, fibers penetrate as Sharpey’s fibers into the cementum on one side and insert into bony alveolus on the other side and thus fixing the tissue in situ.
What does Dental pulp consist of
Consists of jelly-like substance containing fibers, CT cells, blood vessels, and nerve fibers; lined by odontoblasts.
Types of teeth among animal species
Brachydont
Hypsodont
What are Brachydont teeth
Simple, short crown but long root, crown covered by enamel and root by cementum
Examples of brachydont Teeth
Examples include all teeth in man, carnivores, and swine (except canine tooth in swine, which is hypsodont), and incisors in ruminants.
What are Hypsodont teeth
Complex, long crown but short root, cement covers the root as well as the crown (outside the enamel), examples include all teeth in the horse and rodents, molars in ruminants. Development of teeth will be discussed in embryology.
What are the Layers of the Esophagus
Muscosa
Muscularis mucosa
Submucosa
Muscularis
Serosa/adventitia
The wall has all layers, but their structure differs among species.
Mucosa layer of the Esophagus epithelium
Stratified squamous non-keratinized in man and dog; however, stratified squamous keratinized in all other domestic species.
Muscularis mucosa of the esophagus
incomplete layer throughout in the horse and ruminants;
absent in the upper part and forms a thick layer in the lower part in the dog and pig.
Submucosa of the esophagus
May contain mucous glands, which are limited to a short cranial segment in the horse, cat, and ruminants; cranial half only in the pig; throughout in the dog.
Muscularis of the esophagus
Skeletal throughout in the dog and ruminants;
skeletal in the first two-third and then transition to smooth distally in the pig; skeletal in the cranial part, combined in the middle part, and smooth in the distal par in man, horse, and cat
Serosa/Adventitia of the esophagus
Serosal covering in the thoracic part and adventitial in the cervical part.
3 Types of stomachs
Simple
Compound Monogastric
Compound Poly-gastric
Simple stomach
Monogastric, lined with glandular mucosa only (man and carnivores)
Compound Monogastric
A small beginning part is lined by cutaneous epithelium and the rest with glandular mucosa (horse and pig)
Compound Polygastric
Consists of non-glandular (rumen, reticulum, and omasum) and glandular (abomasums) parts (ruminants).
What is the main functions of a simple stomach
main functions are to:
1.Continue the digestion of carbohydrate that started in the oral cavity,
- add acidic fluid to the food,
- transform the food into a viscous mass (chyme),
- promote the initial digestion of proteins with enzymes pepsin,
- and secrete hormones.
What are the 3 regions of the simple stomach
Grossly consists of three regions: cardia, fundus, and pylorus
What are Rugae
The mucosa and submucosa of the un-distended stomach form folds called rugae
Simple stomach: Tunica Mucosa
Epithelium is simple columnar composed of mucus-producing cells (note, not goblet cells
What are gastric Pits
Epithelium dips to form gastric pits into which empty gastric glands (cardiac, fundic and pyloric) that occupy the entire lamina propria.
Simple stomach: Muscularis Mucosa
Muscularis mucosa consists of a few strands of smooth muscle cells
Simple stomach: T submucosa
Contains CT cells, blood vessels, nerves, and parasympathetic ganglia
Simple stomach: What are the 3 layers of T muscularis
inner oblique, middle circular, and outer longitudinal;
Simple Stomach: T serosa
T serosa has a thin layer of CT covered by mesothelium (simple squamous epithelium).
What are Fundic Glands
predominant gastric gland occupying the entire fundus and body regions of the stomach
What are the 3 regions of fundic glands
Consists of an isthmus, neck, and base
What are the Fundic gland cells composed of
Stem Cells
Mucous neck cells
Parietal Cells
Chief Cells
Argentaffin Cells
Where can the fundic gland stem cells be found
Found in the isthmus and neck regions, continuously divide, and replace the aging cells of the gastric epithelium, including those of glands.
Where can the Mucous neck cells be found
found in the neck region of glands, like the mucous surface epithelial cells but have fewer mucin droplets.
What the Parietal Cells (oxyntic)
large, eosinophilic, triangular, concentrated in the upper half of fundic gland, characterized by many mitochondria
What are intracellular canaliculi
Located in Parietal cells and are deep invaginations of apical cell membrane
What do parietal cells contain
Contain carbonic anhydrase enzyme that breaks down H2CO3 into H and HCO3; H and Cl combine to form HCL that is secreted into the lumen
How do Parietal cells stimulate HCL production
Both gastrin and parasympathetic stimulation stimulate HCL production.
Where are Chief cells
Predominate in the lower half of the fundic glands
What do Chief cells contain
Contain basophilic cytoplasm in the basal region and zymogen granules in the apical region
What is the principal secretion of chief cells
Principal secretion is pepsinogen, which is converted into pepsin after being released into the acidic environment.
What are Argentaffin Cells
Diffuse endocrine cells, also referred to as APUD cells (amine precursor uptake and decarboxylation cells), less numerous, located in the bases of gastric glands, include more than a dozen of different types of cells, each secreting only one hormone
Where are Cardiac Glands Localized
Localized usually in a narrow zone around and near the esophageal opening into the stomach
Where are the Cardiac glands localized in the pig
They occupy half of the stomach in the pig
Cardiac Gland Cell types
Cell types are predominantly mucous, occasionally parietal
What are Cardiac Gland Cell function
Function is mucus production that protects the esophageal lining from gastric HCL.
Pyloric Gland where are they
Distributed in the pyloric region, which occupies almost half of the stomach in the dog and cat, one-third in the horse, and one-third of the abomasums in ruminants
Cells of the Pyloric Glands
Cells are only mucous (note endocrine cells are present throughout the stomach and intestine);
gastric pits are deeper, and glands are more branched and coiled
Pyloric Gland Function
function is to produce mucus.
Protective Mechanism of the Stomach
mucous coat covering the surface epithelium;
marked regeneration ability of the surface and glandular epithelium;
tight junctions between epithelial cells;
stratum compactum layer (thick CT under the lamina propria) in carnivores to prevent penetration of sharp objects;
vomitus.
