Micro of Esophagus, Stomach, SI and LI Flashcards
Describe the eptihelium of the Tunica Mucosa in the different tissues of the GI system
Variable in the esophagus - it can be keratinized or non-keratinized stratified squamous epithelium.
The glandular stomach regions are lined by simple columnar epithelium WITHOUT goblet cells
Describe the lamina muscularis of the Tunica Mucosa in different tissues of the GI system
- +/- in esophagus of different species
- different regions of the glandular stomach
- Absent in rumen of ruminant animals
- When present, ALWAYS smooth muscle
- When the lamina muscularis is absent, the lamina propria and submucosa blend insensibly together
Describe the Tunica Submucosa in different tissues of the GI system
- In some species, esophagus will contain submucosal glands
- Glandular stomach regions in mammals DO NOT contain submucosal glands
- Instead, glands are located in tunica mucosa, but they don’t necessarily produce mucous secretion.
- Proventriculus or glandular stomach in birds contains submucosal glands
Describe the Tuncia Muscularis in different tissues of the GI system
- Inner circular layer
- Outer longitudinal layer
- In the esophagus, tunica muscularis can be variable with all skeletal muscle, all smooth muscle, or a combination between the two
- Tunica muscularis of the stomach is ALWAYS smooth muscle in mammals and birds
Describe the Tunica Serosa/Adventitia in different tissues of the GI system
- Last layer will be a tunica adventitia in portions of the organ outside of a body cavity (e.g., cervical esophagus)
- When the esophagus connects to the stomach in the badominal cavity, the last layer will be considered tunica serosa, as a mesothelial lining will be present
- All sections of stomach have tunica serosa
Key features of mammalian esophagus - canine
- Non-keratinized stratified squamous eptiehlial lining
- Lamina muscularis
- Submucosal glands
- Tunica muscularis = skeletal muscle
Key features of mammalian esophagus - ruminant
- Keratinized stratified squamous epithelial lining
- Lamina muscularis
- No submucosal glands
- Tunica muscularis = skeletal muscle
Key features of mammalian esophagus - porcine
- Keratinized stratified squamous epithelial lining
- Lamina muscularis can be scant (cranially) to thick (caudally)
- Submucosal glands only in cranial region
- Tunica muscularis = skeletal muscle cranially; mixture of skeletal and smooth muscle caudally
Key features of avian esophagus
- Keratinized stratified squamous epithelial lining
- Mucosal glands
- Lamina muscularis
- No submucosal glands
- Tunica muscularis = smooth muscle
Key features of avian crop
- Keratinized stratified squamous epithelial lining
- No mucosal glands
- Lamina muscularis
- No submucosal glands
- Tunica muscularis = smooth muscle
What organs may be included in the esophageal-stomach junction?
Depending on the species, a section through the esophageal-stomach junction may contain the esophagus and cardiac gland stomach (such as the pig) or even the esophagus, cardiac gland stomach, AND fundic gland stomach.
Tunica muscularis in esophagueal-stomach junction
Striated muscle (in case of dogs and ruminants) to smooth muscle
How do you distinguish esophageal-stomach junction from a recto-anal canal junction?
The absence of goblet cells in the stomach distinguishes the esophageal-stomach junction from the recto-anal canal junction.
What class of mammals have the best developed nonglandular stomach?
Ruminant
What species have simple glandular stomach and what are its characteristics?
It is present in all species.
Characterized by rugae (macroscopic) and gastric pits (microscopic).
Where are gastric pits and gastric glands present in the stomach?
Present in all regions of the glandular stomach.
The length of the gastric pits and gastric glands is one method to distinguish the cardiac stomach from the pyloric stomach.
Microanatomy of Tunica mucosa of the glandular stomach
- Simple columnar epithelium - secretory (mucous)
- L. propria-gastric glands
- L. muscularis - three layers of smooth muscle
Microanatomy of tunica submucosa of the glandular stomach
Glands only at junction with duodenum
Microanatomy of Tunica muscularis of glandular stomach
All smooth muscle:
- Inner - oblique
- Middle - circular
- Outer - longitudinal
What is the outer must layer of the glandular stomach?
Tunica SEROSA
What are the four regions of the stomach?
- Non-glandular
- Cardiac region
- Fundic region
- Pyloric region
Characteristics of cardiac gland region:
- Branched, coiled tubular glands
- Mucous cells with few endocrine cells
- May see in combination with esophagus (non-glandular stomach)
- Short gastric pits, deep gastric glands
- Nuclei of mucous glands round and tend to be centrally located.
Characteristics of Fundic or Proper Gastric Glands
- Branched, straight tubular glands
- Mucous cells
- Chief cells - basophilic; produce pesinogen (converted to pepsin in low acidic environment)
- Parietal cells - acidophilic, produce HCL to activate pepsinogen
- Endocrine cells, such as G cells that produce gastrin
- Chief and parietal cells predominant in this region but NOT exclusively in fundic region. Can use the presence of these cells to identify fundic gland region
Characteristics of pyloric gland region
- Branched, coiled tubular glands-short
- Mucous cells (few parietal and endocrine cells)
- Deep gastric pits; short gastric glands
- Nuclei of glands tend to be like “smooshed bugs” - flattend and located at base of cells
- T. muscularis tends to be thicker than that of cardiac region
What are the four cell types in the fundic gland region:
- Mucous cells
- Chief cells
- Parietal cells
- Endocrine cells
What are two types of mucous cells?
- Surface cells - secrete mucins, lubricate epithelial surface, renewed every three days
- Mucous neck cells - located in neck of gland, mucins may differ
Chief cells
- Produce gastric enzymes
- secrete into lumen of gland
- Pepsinogen, rennin (enzyme that leads to milk curdling), gastric lipase
- Tend to be more inwards compared to parietal cells in gastric glands and basophilic
Parietal cells
- Produce hydrochloric acid
- Secrete into gland lumen
- HCL converts pepsinogen to pepsin
- Tends to be outward compared to chief cells in gastric glands and acidophilic
Endocrine cells of GI
- Produce hormones of GI tract
- Secrete into lamina propria, then blood stream
- At least 13 different types of cells in stomach and small and large intestine
Gastrin released by G cells is stimulated by?
- distension of stomach, food
- Neuronal stimulation
- Chemicals, caffeine
- pH above 2
Blood supply to stomach facilitates?
- Absorption of nutrients
- Maintenance of pH
- Hormonal transport
Surface area modifications for small intestine:
- Increased length
- mucosal folds
- villi
- microvilli
- Glycocalyx
Small intestine - characteristics of tunica mucosa and absorptive cells
- Epithelium - simple columnar epithelial cells (absorptive cells) with goblet cells
- Junctional complexes between cells
- Microvilli on luminal surface of cell
- Smooth ER abundant
- Golgi well developed
- Absorb water and nutrients across the plasmalemma
- Enzymes on the glycocalyx breakdown peptides and carbohydrates to simple sugars and amino acids which then enter the cell by selective transporters
- Fats are emulsified and packaged as micelles before entering the cell. Fats are released as chylomicrons into the lymphatic system.
Small intestine - structure of mucosal glands, what is another name for them?
- Simple branched tubular glands (crypts of lieberkuhn)
Three cell types found in mucosal glands of small intestine
- Progenitor cells: renewal of surface villi cells
- granular cells of paneth (ruminants, horses, humans) produce peptidases (digestive function) and lysozyme (anti-bacterial function)
- Endocrine cells
Contents of lamina propria of small intestine:
- Loose connective tissue
- Intestinal glands = crypt glands = crypts of lieberkuhn
- Blood vessels (collect absorbed nutrients other than fats)
- Lympth vessels (accumulate chylomicrons-absorbed fats) = lacteals because after fats absorbed the lymph vessels have a milky white appearance
- Nerves
- Smooth muscle = lamina muscularis
Contents of Villi of small intestine:
- Arteriole
- Venule (AV shunt)
- Capillary network
- Lacteal = lymphatic vessels for fat absorption
- Neuronal plexus
- Smooth muscle = lamina muscularis - helps to control the movement of individual villi
How many layers of smooth muscle does the lamina muscularis have in the small intestine and differentiate between the two.
Two layers:
- Inner circular - projects into villi, shortens villi, pumps lymph from lacteal, pumps blood from capillary network
- Outer longitudinal
Where do submucosal glands of Brunner predominate?
Predominantly present in duodenum; may be asbent in other sections of small intestine.
Types of submucosal glands of small intestine
- Simple tubuloalveolar
- Mucous in dog, ruminants
- Serous - pig, horse
- seromucous - cat
Differentiate the two layers of muscle in the tunica muscularis of the small intestine.
- Inner circular
2. Outer longitudinal
Intrinsic innervation of small intestine
- Submucosal plexus (meissner’s)
- Myenteric plexus (auerbach’s)
- Interstitial cells of cajal (pacemaker cells, mediate input from extrinsic innervation)
Extrinsic innervation of small intestine
- Parasympathetic cholinergics (increase motility)
2. Sympathetic adrenergics (decrease motility)
Three organs in ileo-cecal junction:
- Cecum
- Colon
- Rectum
Most identifying features of the ileo-cecal junction:
- No plicae circulares, presence of longitudinal folds
- Lack of villi in cecum
- Increase in goblet cells in cecum
- Well developed T. muscularis
Large intestine: Characteristics of tunica mucosa
Muscoal epithelium is simple columnar absorptive eptiehlium similar to small intestine
- Absorbs water and nutrients
- Increased number of goblet cells
- NO VILLI in large intestine
- Tends to have greater number of Goblet cells than small intestine
Large intestine: characteristics of tunica muscularis
- Inner circular layer is typical
- Outer longitudinal layer condenses and forms thickened bands of smooth muscle (taenia coli, taenia ceci, whcih are prominent in the hrose and the number of bands allow for gross anatomical identification of the cecum and different segments of the colon)
Recto-Anal Canal junction in ruminants:
Rectal mucosa forms longitudinal folds called rectal columns
Recto-anal canal junction in canines
Lymphatic nodules present, form grossly visible depressions called rectal pits
Characteristics of anorectal junction
- Lamina muscularis terminates
- T. muscularis - inner circular layer becomes internal anal sphincter; longitudinal layer terminates
- Simple columnar epithelium with GOBLET cells to nonkeratinized stratified squamous epithelium
What are the three different regions of the anal canal in pigs and carnivores?
- Columnar zone - nonkeratinized stratified squamous epithelium
- Intermediate zone - in-between columnar and cutaneous zones; not well-defined
- Cutaneous zone - keratinized stratified squamous epithelium contains GLANDS
Three different glands in cutaneous zone of anal canal (NONE of which are expressed by vets)
- Sebaceous glands
- Sweat glands
- Circumanal glands = hepatoid glands = perianal glands
- modified sebaceous glands
- lobulated glands
Anal Sacs
- Anal sacs are bilateral evaginations of the mucosa and are located betwee internal and external anal sphincter muscle.
Glands of the anal sac in the feline consist of…..
Sebacceous and apocrine secretory units in felines
Glands of the anal sac in the canine contain…..
Pure apocrine glands in canines
