Digestive System Flashcards
What are functions of the gastrointestinal system?
- prehension: ingestion followed by fragmentation
- mechanical + enzymatic breakdown (fermentation) of nutrients: digestion
- absorption of nutrients
- synthesis/secretion (hormones)
- excretion of waste
What are differences between the stomach/colon of equines, ruminants, and canines?
- equine: large cecum
- bovine: 4-chambered stomach
- canine: “normal’
What features of the digestive system are endoderm derived? Mesoderm? Ectoderm?
- endoderm-derived: epithelium (mucosa), parenchymatous organs (ex: liver + pancreas) and associated glands
- mesoderm-derived: submucosa, muscle layers, serosa, mesentery
- ectoderm-derived: stratified squamous epithelium (oral cavity + anus) and nerve plexi
What is the lining epithelium of the lips to the non-glandular stomach? The glandular stomach and intestine? The anus?
- stratified squamous epithelium
- simple columnar epithelium
- also stratified squamous!
What are some features of the oral cavity?
- formed by: lips, cheeks, palate, pharynx, and tongue
- mucosa lined by: stratified squamous epithelium (keratinized or not)
- submucosa of connective tissue
- salivary glands and tonsils
- ruminants have a dental pad
What are some features of the tongue?
- covered by mucosa: stratified squamous epithelium, keratinized on dorsal surface
- papillae (mechanical + gustatory) on dorsal surface
- some have taste buds
- skeletal muscle arranged longitudinally, transversely, and vertically (think of tongue motion)
What are some factors that influence dentition?
- type of food consumed
- prehension
- mastication
What are some structures of teeth?
- hard structures:
- enamel: covers external surface above gum line
- cementum: covers external surface below gumline
- dentin: beneath enamel and cementum
- soft structures:
- pulp
- peridontal ligament
What cells form the structures of teeth?
- hard structures:
- enamel: ameloblasts
- cementum: cementoblasts
- dentin: odontoblasts
- soft structures:
- pulp: loose CT + nerves
- peridontal ligament: fibroblasts
In what orientation do enamel and dentin form during tooth development?
- odontoblasts cover the surface of the mesenchymal papilla and produce dentin
- ameloblasts are tall columnar cells that produce enamel
- enamel forms more distal to dentin
What are the two kinds of teeth, in reference to height?
- brachydont (low crowned) + hypsodont (high crowned)
What are features of brachydont dentition?
- short + cease to grow after eruption
- crown (above gingiva), neck (restricted region below gingiva)
- one or more roots embedded in a boney socket (alveolus)
- all teeth of carnivores, incisors of ruminants, teeth of pigs (- incisors)
What are features of hypsodont dentition?
- tall and continue to grow after eruption
- no crown and neck (elongated body)
- horses, cheek teeth of ruminants, canine teeth of pigs
What is the general organization of tubular digestive organs?
- muscular tube with 4 tunics:
- mucosa
- inner epithelium
- middle lamina propria
- thin outer muscularis mucosae
- submucosa
- muscularis
- inner circular
- outer longitudinal
- serosa
- (adventitia if abuts other structures)
- mucosa
What are features of the mucosa?
- epithelial lining
- simple columnar + glandular
- lamina propria
- loose connective tissue
- blood vessels, lymphatics, lymphocytes, smooth muscle cells
- supports epithelium
- muscularis mucosae
- always SMOOTH muscle
What are features of the submucosa?
- loose connective tissue (looser than in lamina propria)
- facilitates MOTILITY of the mucosa
- contains vessels, a nerve plexus (submucosa plexus), +/- lymphatic nodules, glands
- P = papilla
- MM = muscularis mucosa
- MP = muscularis
- SM = submucosa
- M = mucosa
What are features of the muscularis?
- may be smooth or skeletal muscle
- usually 2 layers of smooth muscle: inner circular + outer longitudinal
- controls lumen size, motility of tube
- contains myenteric nerve plexus and vessels
What are features of the enteric nervous system?
- division of autonomic nervous system
- 2 distinct regions:
- submucosal plexus: meissner’s plexus
- myenteric plexus: auerbach’s plexus
- each region is a net of nerves connecting ganglia
What are differences between the external coverings, serosa and adventitia?
- serosa: MESOTHELIUM + loose connective tissue +/- adipose tissue
- adventitia: loose/dense connective tissue only
What is this feature of the digestive system?
- What kind of lining?
- What type of muscle?
- What type of external covering?
- esophagus
- stratified squamous
- skeletal + smooth
- adventitia
What are some features of the esophagus?
- lined by non-keratinized or keratinized stratified squamous epithelium
- submucosa contains mucous glands
- muscularis may be composed of skeletal muscle only, or a mix of skeletal/smooth
- adventitia over most
- SS: non-keratinized stratified squamous epithelium
- LP: lamina propria
- MM: muscularis mucosae (SM)
- GL: submucosal glands will empty via ducts (D)
What kinds of muscle surround the esophagus comparatively across species?
What type of lining is in the stomach? What type of muscle? What type of external covering?
- simple columnar/glandular
- smooth
- serosa
What are features of the stomach?
- distinction of digestive tube with sphincters at entry (cardia) and at exit (pyloris)
- mucosa may be non-glandular ( stratified squamous) or glandular (simple columnar epithelium)
What are the types of stomach structures?
- simple
- compound mutichambered
- composite
What are the species-specific differences in stomach structures?
T/F: equines have a simple stomach, with a feature called margo plicatus
- false; composite stomach
What are the components of a ruminant compound multi-chambered stomach? Which parts are forestomach vs “true”stomach?
- forestomach
- rumen
- reticulum
- omasum
- true stomach
- abomasum
What feature of the ruminant stomach is this? What are some features?
- rumen
- largest chamber of the forestomach
- low papillae
- increased surface area enhances passive absorption of VOLATILE FATTY ACIDS
- lined by keratinized squamous epithelium
What feature of the ruminant stomach is this? What are some features?
- reticulum
- honeycomb pattern
- small segments of smooth muscle along ridges
- lined by keratinized squamous epithelium
What feature of the ruminant stomach is this?
- omasum
- lined by keratinized squamous epithelium
What are the functions of the ruminant forestomach?
- rumen + reticulum
- mixing, eructation, regurgitation, movement of ingesta, absorption of VFAs
- omasum
- squeezes ingesta, liquifies and moves it to the abomasum for further ingestion
What is the flow of digesta through a ruminant stomach?
- rum road
What is the abomasum?
- glandular “true” stomach of ruminants
What are the three stomach glandular regions?
- cardia
- fundus/body
- pylorus
What are some features of the glandular stomach?
- simple columnar mucous cells line surface of glandular mucosa in all 3 regions
- gastric pits: invaginations of lining epithelium leading to glands
- rugae (folds): allow distinction
- muscularis: consists of 3 layers of smooth muscle (oblique, circular, longitudinal)
- outer serosa
What are features of the glandular regions of the stomach?
- cardiac region: composed mainly of mucous glands
- fundic region: with proper gastric glands
- composed of:
- parietal cells (secrete HCl)
- chief cells (produce pepsinogen)
- endocrine G cell produce the GI hormone gastrin (enters blood stream)
- composed of:
- pyloric region: mucus glands and endocrine G cells
- ** all regions covered by surface mucous cells**
What region of the stomach is this? What are some features?
- cardiac region
What region of the stomach is this? What are some features?
- fundic region
- parietal cells: eosinophilic, central nucleus
- chief cells: basophilic, peripheral nucleus
What region of the stomach is this? What are some features?
- pyloric region
- mucous glands and endocrine G cells produce the GI hormone gastrin (enters bloodstream)
- ** G cells not visible without special stains
What type of lining is in intestines? Muscle? External covering?
- simple columnar/glandular
- smooth only
- serosa (mostly)
What are the splits of the intestines?
What are some features of small intestines?
- lined by simple columnar epithelium (enterocytes and goblet cells)
- enterocytes are absorptive
- goblet cells make mucus
- has circular folds, villi and microvilli to increase surface area
- submucosal glands located in duodenum (Brunner’s glands)
- lymphatic nodules in distal small intestine (Peyer’s patches)
What is this feature? What part of the digestive system is it found in?
- villi
- small intestine
What are some features of intestinal villi?
- villi
- confined to the small intestine
- papillary projections into lumen
- site of absorption
- intestinal crypts
- at the base of the villi
- invaginations of lining epithelium
- site of production/division
What are features of intestinal epithelium?
- enterocytes (absorptive cells with microvilli)
- goblet cells (mucus)
- stem cells
- enteroendocrine cells
What is indicated in this image? What part of the intestine system are they present in?
- crypts of lieberkuhn
- small intestines
Label the features of this longitudinal section of a villus
What are features of lamina propria of villi?
- microvasculature, lymphatics, and muscle in villi
What are lacteals? Some features?
- blind-ended lymphatic vessels in intestinal villi
- the chyle (lymph) found in lacteals is filtered through intestinal lymph nodes before ultimately reentering the blood at the jugular veins
T/F: there are few lymphocytes and plasma cells throughout the lamina propria
- false; vast numbers
What are the structures indicated ? What are some features?
- peyer’s patches
- aggregations of lymphoid nodules present in the lamina propria and submucosa of the small intestine
- seen in distal jejunum and ileum, but varies according to species
What are M cells?
- specialized epithelial cells that sample antigens from the luminal environment
- APC: antigen presenting cells
What gland produces alkaline mucus to protect the duodenum from acidic chyme?
- Brunner’s glands
- not present in non-mammalian species
What is the function of the large intestine?
- absorb H2O and secrete mucus in all species; fermentation and volatile fatty acid absorption in hind gut fermenters
What part of the digestive system is this? Label A/B. What are some features?
- large intestine (of a horse)
- A: taenia coli, B: haustra
- no villi
- intestinal crypts (glands) present as in small intestine,but relatively long
- lined by simple columnar epithelium (mostly goblet cells)
- pigs and horses have longitudinal flat bands called taenia coli,composed of smooth muscle an elastic fibers - form haustra
How can one distinguish different parts of the intestine? **
- small intestine: both villi + intestinal crypts
- duodenum: Brunner’s glands in mucosa
- jejunum: there are no specific structures in connective tissue of submucosa
- ileum: peyer’s patches (groups of lymphatic nodules)in submucosa
- large intestine: no villi, surface is smooth, only intestinal glands are present
What are some features of the rectum + anus?
- rectum: lined by simple columnar epithelium, stores feces, secretes mucus
- anus: lined by stratified squamous epithelium
- in the pelvic cavity
What are the glandular regions of the anus?
- anal glands: empty into the lumen of the anus
- anal sac glands: empty into anal sacs (carnivores)
- circumanal glands (dogs): nonpatent ducts; unknown function, can form benign tumors
T/F: there is a single anal sac gland above the anus in carnivores
- false; paired, below the anus
What is the green arrow indicating? What are some features?
- anal sac (in the recto-anal junction)
- lined by keratinized stratified squamous epithelium
- located between smooth muscle of the internal anal sphincter and the skeletal muscle of the external anal sphincter
- the glands of the anal sacs are:
- dog: tubular apocrine sweat glands
- cat: both sebaceous and tubular apocrine sweat glands
What structure is indicated? What are some features?
- circumanal/perianal glands
- present n the subcutis around the anus in dogs (also in skin near the prepuce, tail, flank, and groin)
- glands resemble hepatocytes, thus the name hepatoid glands
What part of the digestive tract is this? What features prove this?
- esophagus
- stratified squamous epithelium
- glands
What part of the digestive tract is this? What features prove this? What is labeled as 6?
- tongue
- muscle layers in 3 directions
- stratified squamous epithelium
- 6: taste buds
What part of the digestive tract is this? What features prove this?
- colon
- no intestinal villi or glands
- lots of crypt cells
What part of the digestive tract is this? What features prove this?
- stomach
- chief and parietal cells
- glands
What is saliva? What does it contain? What are its functions?
- liquid secreted by salivary glands
- contains: water, salts, mucin, enzymes (amylase, maltase, lipase), IgA, lysozyme, lactoferrin, and suspended cells (desquamated epithelial cells, leukocytes, bacteria)
- function: digestion, provide moisture and lubrication, local immunity, evaporative cooling
What are the divisions of salivary glands? What kinds of secretion?
- divided into major and minor glands:
- major salivary glands: parotid, sublingual, mandibular
- minor salivary glands are intramural: lingual, palatal, labial, buccal, zygomatic (carnivores), molar (cats)
- types of secretion: serous, mucous, mixed
What is the structure of salivary glands?
T/F: salivary glands are lobulated
- true
What kind of salivary gland is this? What kind of secretion does it have?
- parotid salivary gland
- serous
What kind of salivary gland is this? What kind of secretion is from structure A? structure B?
- sublingual salivary gland
- A: mucous
- B: serous
What are some features of the liver?
- largest visceral organ in the body, 1-4% of BW
- situated in the abdominal cavity caudal to the diaphragm
- strategic position in blood circulation
- 1/3 blood from hepatic artery
- 2/3 blood from portal vein
- ~25% of weight of liver is blood
What are some components of the liver?
- hepatocytes
- vasculature
- biliary trees
- kupffer cells (macrophage)
- ito/stellate cells
- oval/stem cells
- pit cells
- connective tissue
What feature of the digestive system is this?
- liver
What are hepatocytes?
- polygonal, epithelial liver cells
- workhorses:
- detoxification
- deamination (aa —> urea)
- produce bile
- produce various blood proteins
- gluconeogenesis
- store energy (glycogen and triglycerides)
- arrange in cords or plates
What is this image a example of? What are some features?
- vasculature in the liver
- portal triad: hepatic artery (HA), bile duct (BD), portal vein (PV) and several lymphatic vessels (LV)
- surrounded by collagenous extracellular matrix that forms an abrupt border with a circumferential row of hepatocytes aka the inviting plate (LP-dotted line)
T/F: blood and bile flow in the same direction from the portal field to the central vein
- false; blood flows from the portal field to the central vein, bile flows towards the portal field after production
What is the site of exchange between blood and hepatocytes?
- perisinusoidal space (space of disse)
What are features of the intrahepatic biliary tree?
- canaliculi: potential spaces
- canals and ductules lined by cuboidal epithelium (cholangiocytes)
- bile ductules located in the portal triads
What is shown in the image? Label the terms
- vasculature of the liver
What structure is shown here?
- intrahepatic biliary tree
What are features of kupffer cells?
- resident phagocytes of liver
- located within the blood sinusoids
- remove aged blood cells (may have intracellular iron pigment: hemosiderin, pathogens, some toxins
What feature of the liver is indicted here? What are some features?
- ito cells (stellate cells)
- vitamin a metabolism
- collagen production
- large round lipid vacuoles
- in space of disse
What are oval cells? Pit cells?
- oval cells
- pluripotent cells
- found in biliary tree
- pit cells
- resident granular leukocytes
- found in sinusoids
What is shown in this image? Be specific. What are some features?
- liver (pig)
- each lobe is covered by mesothelium (serosa) located over a connective tissue layer, the capsule
- organized into lobules separated by variable amounts of connective tissue septa
What is the anatomical and functional arrangement of the liver?
Which zone is more susceptible to direct-acting toxins? Which of the acinar zones is most susceptible to hypoxia?
- zone 1 (periportal)
- hepatocytes closest to O2 and nutrient rich arterial and portal inflow
- more susceptible to direct-acting toxins
- zone 3 (centrilobular)
- nearest venule - more susceptible to hypoxia
- detoxification enzymes: more susceptible to metabolites from toxins
What structure is shown in these images? What are some features?
- gallbladder
- accepts bile from cystic duct for storage
- abundant mucosal “folds” seen when gallbladder is empty
- bile ducts lined by short columnar epithelium
- gallbladder is lined by tall columnar epithelium
- epithelial cells capable of modifying bile (absorption of H2O and inorganic salts)
- muscularis of smooth muscle
- serosa surrounds almost the whole organ
What structure is shown in this image? What are some features?
- pancreas
- dual gland: exocrine and endocrine
- exocrine pancreas
- composed of tubuloacinar secretory units - produce digestive enzymes
- trypsinogen, chymotrypsinogen, lipase, amylase
- endocrine pancreas
- consists of pancreatic islets (islets of langerhans)
- produce hormones
- insulin, glucagon, somatostatin, pancreatic polypeptide
What is this structure? What are features of its structure?
- pancreas
What is this figure an example of?
- exocrine pancreas
- serous acinar glands
- product visible as zygotes granules
What is this structure? What are the features indicated?
- pancreas
- serous acinus (exocrine)
- islet of langerhans (endocrine)
- capillary
- eosinophilic zygote granules
What is this structure?
- pacinian corpuscle
