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Digestive System II
Terms in this set (99)
What parts of the gastrointestinal tract are covered by adventitia?
Cranial part of esophagus, some parts of colon and rectum, and parts of gall bladder
Describe the tunics of the pharynx
- Tunica mucosa has stratified squamous epithelium
- No lamina muscularis (propria-submucosa instead)
- Tunica muscularis formed by skeletal muscle
- Tunica adventitia composed of dense irregular connective tissue
How does the epithelium of the esophagus differ among species?
Stratified squamous epithelium
- Non-keratinized in dog and cat
- Slightly keratinized in pig
- Keratinized in horse and ruminants
(Degree of keratinization is related to character of food)
How is the lamina propria of the esophagus different from other organs?
Connective tissue of lamina propria is denser than that of submucosa (exception to general principle)
How is the lamina muscularis of the esophagus different from other organs?
Has only longitudinally oriented smooth muscle fibers (all other organs have circular orientation)
How does the density of muscle fibres change with the regions of the esophagus in lamina muscularis?
Amount of muscle fibres increase towards caudal esophagus
How does the tunica mucosa differ among species?
Lamina muscularis is absent at cranial end of esophagus in dogs and cats but is well developed in caudal part of esophagus in pig
How does the tunica submucosa of the esophagus differ among species?
Horse, cat and ruminants: submucosal glands located only at pharyngeal junction
Pig: seromucous submucosal glands in cranial half (do not extend to caudal half)
Dog: seromucous submucosal glands throughout the length of the esophagus and extend into cardiac region of stomach. Gland density is 4 times greater near stomach than at beginning of esophagus
How does the tunica muscularis of the esophagus vary among species?
Composed mainly of skeletal muscle
- Cats and horses have smooth muscle in the caudal one-third of esophagus
What are the two muscle layers of the tunica muscularis of esophagus?
What is the cardiac sphincter in a horse composed of?
Inner circular layer of smooth muscle from the tunica muscularis
- Very prominent (10-15 mm thick)
Does the esophagus have a tunica serosa or adventitia?
Adventitia in cervical part
Serosa in thoracic and abdominal parts
How does the esophagus-stomach junction vary among species?
Carnivores: abrupt change from stratified squamous epithelium of esophagus to simple columnar epithelium of stomach. Occurs cranial to cardia
Herbivores: Stratified squamous epithelium of esophagus extends into non glandular part of stomach
How many layers of the tunica muscularis does the stomach have?
- Inner oblique
- Middle circular
- Outer longitudinal
How does the stomach differ among species?
Carnivores: composed exclusively of glandular part lined by simple columnar epithelium
Herbivores: have an additional non glandular area lined by stratified squamous epithelium
What is the stratum compact?
Dense connective tissue in carnivores that divides the lamina muscularis and the glandular mucosa
What are the three regions of the glandular stomach? (in the tunica mucosa)
1. Cardiac gland region
2. Proper (Fundic) gastric gland region
3. Pyloric gland region
How does the tunica mucosa of the non glandular stomach region differ among species?
Absent in carnivores
Small in pig
Large in horse (ends at margot placatus)
Greatest in ruminants and keratinized (forms rumen, reticulum, and omasum)
How does the epithelium differ between the non glandular and glandular stomach mucosa?
Non-glandular mucosa: stratified squamous epithelium
Glandular mucosa: simple columnar epithelium
What are cardiac glands and what are their function?
Short, simple branched, coiled, tubular mucous glands present at the junction of non-glandular and glandular stomach mucosae
Major function is to produce mucous
What are proper gastric glands?
Straight branched tubular glands consisting of short neck, long body, and slightly dilated blind end (the fundus)
Where is the proper gastric gland region located?
Fundus of stomach in dogs and cats but not in other domestic animals
How much room does the proper gastric region occupy among species?
Ruminants: 2/3 of the abomasum
Dog: 1/2 the stomach
Horse: 1/3 of stomach
Pig: 1/4 of stomach
What types of cells are found in the proper gastric glands?
1. Mucous neck cells
2. Chief cells
3. Parietal cells
4. Enteroendocrine cells
What are mucous neck cells?
Typical mucous cells with flattened nucleus near base. Located in neck of the gland.
How are mucous neck cells different from surface mucous cells?
i. Have more basophilic cytoplasm
ii. contain PAS positive material throughout the cytoplasm
What are chief cells?
AKA zymogen cells
Most numerous, typical protein secreting cells. Cuboidal or pyramidal cells with spherical nucleus located near base of cell. Basal basophilia due to rER. Zymogen granules fill apical cytoplasm.
What do chief cells secrete?
What are parietal cells?
Larger in size and less numerous than chief cells. Occur singly and peripheral to chief cels. Have a narrow apex and base usually bulges outwards from external surface of gland. Deeply eosinophilic and granular appearance due to numerous mitochondria
What do parietal cells contain?
Carbonic anhydrase for carbonic acid formation. H+ from carbonic acid is transported to combine with Cl to form free HCl in canaliculus
What are enteroendocrine cells?
Located in glandular stomach, small intestine, and large intestine.
Produce gastrin, secretin, cholecystokinin, and gastric inhibitory peptid.
What are enteroendocrine cells apart of?
APUD cells (amine precursor uptake and decarboxylation)
How does the pyloric gland region differ among species?
Carnivores: occupies 1/2 stomach
Horse: occupies 1/3 stomach
Ruminants: occupies 1/3 abomasum
Pigs: occupies 1/4 stomach
What are pyloric glands?
Short, branched, coiled, tubular, mucous glands. Cells have basally located flattened nuclei with lightly stained apical cytoplasm.
What are the species differences associated with the stomach?
Dog: Narrow cardiac gland region. Proper gastric gland region divisible into two zones.
Pig: Very large cardiac gland region that contains numerous lymphatic nodules in lamina propria. Parietal cells occur in clusters.
Horse: Extensive nonglandular region that terminates abruptly at margot plicatus. Almost non existent cardiac gland region
What two zones is the proper gastric gland divided into in dogs?
i. Light zone - thinner mucosa with deeper gastric pits, short tortuous glands that do not reach lamina muscularis
ii. Dark zone - adjacent to pyloric gland region, thicker mucosa with shallow gastric pits and resembles closely to fund glands of other species
What is a foveola?
What are the forestomachs of the ruminant?
Nonglandular parts: rumen, reticulum, and omasum
What is the glandular stomach of a ruminant?
Abomasum (enzymatic digestion)
What are the ruminant fore stomachs lined with?
Stratified squamous keratinized epithelium
What are the mucosal folds called in the rumen, reticulum, and omasum?
Rumen = ruminal papillae
Reticulum = reticular crest
Omasum = Omasal laminae
What is the rumen?
Performs protection, metabolism, and absorption
A fermentation vat that produces short chain volatile fatty acids by the action of bacteria and protozoa
VFAs absorbed by mucosa into the blood
How does ruminal papillae change with diet?
Remain small on milk diet
Grow rapidly on roughage diet
Describe the epithelial layers of the rumen
Stratum corneum varies from 2 - 20 layers thick
Stratum granulosum is 1-3 layers thick
Stratum spinosum has 1 - 10 layers of polyhedral cells with numerous mitochondria and ribosomes
Stratum basale is formed from columnar cells that have numerous processes extending to basement membrane to increase SA
Does the rumen have a lamina muscularis?
Describe the propria-submucosa of the rumen
Contains dense felt-work of collagen, elastic and reticular fibres and extends into core of each papilla. It contains fenestrated capillaries underneath epithelium
Describe the tunica muscularis of the rumen
Composed of an inner circular and outer longitudinal layer
Myenteric plexus is located between inner and outer layer
What are the reticulum and omasum for?
What is the main histologic structure of ruminal papillae?
What is the main histologic structure in reticular crests?
Connective tissue at base and throughout but smooth muscle (from lamina muscularis mucosa) located at top of projection
How is the word papilla used in the reticulum?
Describes the sub projections from the main structures
How is the tunica muscularis of the reticulum arranged?
Two obliquely placed layers of smooth muscle fibres that cross each other at right angles
What is the lamina muscularis of the reticulum made of and where is it located?
Formed by smooth muscle fibres and located only in upper parts of reticular crests
What is the reticular sulcus?
A groove that extends from cardia to reticulo-omasal orifice. Lined by stratified squamous keratinized epithelium
Lamina muscularis extends from esophagus (incomplete) and tunica muscularis is formed of smooth muscle fibres with skeletal muscle present near cardia
What type of epithelium lines the omasum?
Stratified squamous keratinized epithelium
What is the tunica muscularis of the omasum composed of?
Inner (thicker) circular layer and outer (thinner) longitudinal layer.
What is the main histological feature of the omasal lamina?
See three layers of muscle all the way from the base to the tip of the projection
- Inner circular layer of tunica muscularis is sandwiched between two layers of lamina muscularis mucosae
How does the epithelium change between the omasum and abomasum?
Changes abruptly from stratified squamous keratinized to simple columnar in abomasum
What marks the abomasum?
Vela abomasica (2 mucosal folds) at the omaso-abomasal junction
What does the lamina propria of the abomasum frequently exhibit?
Lymphatic nodules at the omaso-abomasal junction
How is the small intestine divided?
Duodenum, jejunum, and ileum
What is the small intestine lined with?
Simple columnar absorptive epithelium
What 3 adaptations increase the surface area of the small intestine?
1. Plicae circulares: circular folds
2. Villi: finger like projections
3. Microvilli: on apical surface of columnar cells
How does the villi of the small intestine vary among species?
Carnivores: long and slender
Ruminants: short and wide
Is lamina muscularis mucosae present in the small intestine?
What are crypts of lieberkuhn?
Intestinal mucosal glands that are lined by undifferentiated columnar cells.
Contain acidophilic granular (paneth) cells and enteroendocrine cells
How do the number of goblet cells change along the small intestine?
Increases from cranial towards caudal end
What are columnar absorptive cells?
Epithelial cells of the small intestine that contain ovoid nuclei near the cell base and prominent microvilli that form the brush border
What are Paneth cells?
Acidophilic granular cells that are present near base of intestinal mucosal glands in ruminants and horses. They produce peptidase and lysozyme.
What are globule leukocytes?
Cells present in the intestinal mucosa that have eosinophilic globular material in cytoplasm with a small nucleus.
Function is unknown.
How often is the epithelium of the small intestine renewed?
Every 2 - 3 days
Describe the lamina propria of the small intestine
Loose connective tissue with prominent reticular fiber framework. Contain many leukocytes, smooth muscle fibres, fibrocytes, plasma cells and mast cells. Contain lacteal in centre of lamina propria of each villus
Describe the lamina muscularis mucosae of the small intestine
Thin and incomplete. May be composed of inner circular and outer longitudinal layer of smooth muscle but varies among species, individual, and region
Describe the tela submucosa of the small intestine
Denser connective tissue than lamina propria. Contains submucosal glands, peyer's patches and submucosal plexus. Has isolated lymphatic nodules throughout the small intestine.
What are submucosal glands?
AKA Brunner's glands
Located in duodenum. Produce alkaline mucous to neutralize stomach contents
How do brunner's glands differ among species?
Pigs and horses: serous
Dogs and ruminants: mucous
What are peyer's patches?
Aggregates of lymphatic nodules located in the small intestine (Ileum)
What is the tunica muscularis of the small intestine composed of?
Inner circular and outer longitudinal layer of smooth muscle. Connective tissue between layers has myenteric plexus (auerbach's)
Does the small intestine have a tunica serosa or adventitia?
Tunica serosa (has mesothelial covering)
How does mucous production differ between stomach and small intestine?
Stomach: surface cells and mucous neck cells.
Small intestine: submucosal glands and goblet cells
How does absorption differ between stomach and small intestine?
Stomach: stratified squamous keratinized epithelium
Small intestine: Absorptive cells of simple columnar epithelium
How do the stomach and small intestine differ in regards to villi?
Stomach: villi are absent
Small intestine: villi are present
What are the four regions of the large intestine?
Caecum, colon, rectum, and anal canal
What processes occur in the large intestine?
- Microbial action on ingesta
- absorption of water, vitamins, and electrolytes
- secretion of mucous
What two things are absent in the large intestine but present in the small intestine?
2. Plicae circulare
Describe the glands in the large intestine
Long straight simple unbranched tubular glands with many goblet cells
What is the caecum and how does it differ among species?
Acts as bacterial fermentation reservoir.
- Small in carnivores
- Large in herbivores with simple stomach (eg. horse)
What are taenia ceci?
Bands formed from the outer longitudinal layer of the tunica muscularis of the caecum
Why is the mucosa of the large intestine thicker and smoother than the small intestine?
- Increased intestinal glands
- Absence of villi
What causes the submucosa of the large intestine to be distended?
Which species have a thicker rectal wall?
Horses and cattle
What are rectal pits?
100 lymphatic nodules present in the rectum of dogs
How does the epithelium change at the anal canal?
Simple columnar epithelium changes to non-keratinized stratified squamous epithelium at anorectal line
What are the 3 zones of the anal canal in pigs and dogs?
1. Columnar zone
2. Intermediate zone
3. Cutaneous zone
What is the columnar zone of the anal canal?
Contains longitudinal folds called anal columns, between these are anal sinuses
What is the intermediate zone of the anal canal?
A narrow strip
Columnar and intermediate zones have anal glands in propria submucosa
What type of epithelium lines the cutaneous zone of the anal canal?
Keratinized stratified squamous epithelium
What are circumanal glands?
Sebaceous glands in the mucosa near the junction of cutaneous zone and skin of dogs anal canal
Where do the inner and outer layer of the tunica muscularis terminate in the anal canal?
Outer layer terminates at anorectal junction
Inner layer terminates as internal anal sphincter muscle
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