Digestive System

What are the components of the digestive tract?

Buccal cavity, mouth opening (± lips/teeth/cheeks), palate, tongue, pharynx, esophagus, stomach(s), small & large intestines, cecum, cloaca, anus/vent.

What are the accessory digestive organs?

Salivary glands, liver, pancreas.

What are the functions of the digestive system?

Acquire food, mechanical/chemical breakdown, absorb nutrients, fermentation, detoxification, waste elimination, immune defense, communication.

What is the difference between primary and secondary palate?

Primary palate is bone-supported and connects nares to mouth; secondary palate separates nasal cavity from oral cavity (in mammals & crocodiles).

What is a cleft palate?

Abnormal opening between oral and nasal cavities due to incomplete palate formation.

What are the components of a tooth?

Enamel (outer surface, no regrowth), dentin (beneath enamel, grows), cementum (covers root below gum).

What are the main types of teeth in mammals and their functions?

Incisors: clipping/shearing; Canines: puncturing/holding; Premolars & Molars: grinding/crushing.

What are dental formulas used for?

To describe number and types of teeth in each half of the upper/lower jaws.

Give an example of a dental formula.

Dog: I 3/3, C 1/1, P 4/4, M 2/3 = 42 teeth.

What is polyphyodonty?

Continuous tooth replacement throughout life (e.g., reptiles, fish).

What is diphyodonty?

Two sets of teeth: deciduous (baby) and permanent (adult); typical of mammals.

What is the difference between brachydont and hypsodont teeth?

Brachydont: short crowns, stop growing (humans, carnivores); Hypsodont: tall crowns, continue growing (horses, rabbits).

What happens if occlusion is improper in hypsodont animals?

Overgrowth or uneven wear (e.g., “wavemouth” in horses).

What is the function of the tongue?

Taste, prey capture, swallowing, grooming, communication, vomeronasal sensing.

How does tongue mobility vary among vertebrates?

Jawed fish: immobile; amphibians/reptiles: often extensible; birds/turtles/whales: limited; mammals: mobile (frenulum connects to floor).

What is the pharynx and where is it located?

Passageway between nasal/oral cavities and esophagus.

What is the esophagus and its function?

Tube connecting pharynx to stomach; moves food via peristalsis.

What is a crop, and which species have it?

Diverticulum of esophagus for temporary food storage; in pigeons, doves, some raptors, and poultry.

What are the functions of the stomach?

Store food, mechanically mix, and chemically digest using acid and enzymes.

Describe the bird stomach structure.

Proventriculus (glandular) and ventriculus/gizzard (muscular, grinding, keratinized).

What is the ventriculus (gizzard)?

Thick-walled muscular stomach region for grinding food in birds and some reptiles.

What are the glandular and non-glandular parts of the mammalian stomach?

Glandular: secretes acid/enzymes; Non-glandular: no secretion, may store/ferment (seen in horses, ruminants).

What is the margo plicatus in the equine stomach?

Line dividing glandular from non-glandular regions.

Name the four chambers of the ruminant stomach and their functions.

Rumen: fermentation vat; Reticulum: traps dense material (“hardware disease”), honeycomb wall; Omasum: absorbs water (“book stomach”); Abomasum: true glandular stomach.

What is hardware disease?

Ingestion of metal objects lodging in reticulum, causing inflammation or perforation.

What are the three sections of the small intestine (in order)?

Duodenum → Jejunum → Ileum.

What are the main functions of the intestines?

Move food (peristalsis), secrete enzymes, absorb nutrients and water.

How does diet affect intestine length?

Herbivores have longer intestines; carnivores shorter; fish/amphibians relatively simple.

What is the spiral valve in cartilaginous fish?

Internal fold increasing surface area and slowing food passage for absorption.

Describe the intestinal structure in reptiles, birds, and mammals.

Reptiles: simple, ± cecum; Birds: short, cloaca present, may have paired ceca; Mammals: well-differentiated small/large intestines, ± cecum.

What is a cloaca and which vertebrates have one?

Common opening for digestive, urinary, and reproductive tracts; found in fish (cartilaginous), amphibians, reptiles, birds, and monotremes.

What is the cecum and its function?

Pouch at small–large intestine junction for microbial fermentation (especially in herbivores).

What is the difference between foregut and hindgut fermentation?

Foregut: fermentation in stomach (ruminants, camels); Hindgut: fermentation in intestines/cecum (horses, rabbits, pigs).

What is coprophagy, and which animals use it?

Re-ingestion of fecal pellets to recover nutrients; rabbits and some rodents.

What is colic in horses?

Abdominal pain from gas, impaction, strangulation, or inflammation of intestines.

What are salivary glands for?

Lubricate food, begin digestion, secrete toxins or nest glue in some species.

Which vertebrates lack prominent salivary glands?

Fish and most birds.

What are the major salivary glands in mammals?

Mandibular, sublingual, parotid, zygomatic.

What are reptile venom glands derived from?

Modified oral glands (e.g., Duvernoy’s gland).

What are the exocrine functions of the pancreas?

Secrete digestive enzymes and bicarbonate into duodenum to neutralize acid.

What are the endocrine functions of the pancreas?

Secrete insulin and glucagon to regulate blood sugar.

What is an insulinoma?

Pancreatic tumor causing overproduction of insulin → hypoglycemia.

What are the functions of the liver?

Metabolism (fats, carbs, proteins), detoxification, bile production, nutrient storage.

What is the function of bile?

Emulsifies fats for digestion; stored in gall bladder (if present).

Which species lack a gall bladder?

Deer, rats, horses, whales, seals, many birds.

What is the cloaca or vent used for in animals that have it?

Common exit for digestive, urinary, and reproductive products.

What is the small intestinal submucosa (SIS)?

Collagen-based tissue layer used for medical grafting, derived from porcine intestine.

What is the difference between ruminants and pseudo-ruminants?

Ruminants have four stomach chambers; pseudo-ruminants (camels, llamas) have three.

What are carnassial teeth and in which animals are they found?

Shearing teeth (upper 4th premolar, lower 1st molar) found in carnivores.

What is “floating” in equine dentistry?

Filing down overgrown molars to correct uneven wear.

What is gastric dilatation and volvulus (GDV)?

Twisting of the stomach causing obstruction and shock in dogs (“bloat”).

What is LDA (Left Displaced Abomasum)?

Abomasum shifts to left side post-calving; common in dairy cows.

Your first patient is a Bulldog who helped himself to giblets and leg bones from the Thanksgiving table.  The client asks about the path the ingesta would take through the dog's digestive tract.  Order these structures from start to finish (AKA oral to aboral):

Mouth → Pharynx → Esophagus → Stomach → Pylorus → Duodenum → Jejunum → Ileum → Large intestine → Rectum

Where is the linea alba (where an incision will be made)?

Ventral midline, abdominal muscle

Finally, she wants you to name one species that does not (normally) have a gall bladder:

rat, horse, giraffe, whale, elephant, camel, moose, horse, elk, deer, pigeon, hummingbird, ostrich, parakeet, peregrine falcon

Your next client (Mrs. O'Leary) has 1 cow, 3 horses, 2 dogs, and 5 chickens at home, and she knows that ruminant and avian stomachs are not the same as those of dogs.  Place each of these components under the most appropriate species (attribute each anatomical part to only one animal): Cow

Rumen, Reticulum, Omasum, Abomasum

Your next client (Mrs. O'Leary) has 1 cow, 3 horses, 2 dogs, and 5 chickens at home, and she knows that ruminant and avian stomachs are not the same as those of dogs.  Place each of these components under the most appropriate species (attribute each anatomical part to only one animal): Dog

Cardia, Fundus

Your next client (Mrs. O'Leary) has 1 cow, 3 horses, 2 dogs, and 5 chickens at home, and she knows that ruminant and avian stomachs are not the same as those of dogs.  Place each of these components under the most appropriate species (attribute each anatomical part to only one animal): Bird 

Cloaca, Proventriculus, Ventriculus, Gizzard, Paired ceca, Crop

Your next client (Mrs. O'Leary) has 1 cow, 3 horses, 2 dogs, and 5 chickens at home, and she knows that ruminant and avian stomachs are not the same as those of dogs.  Place each of these components under the most appropriate species (attribute each anatomical part to only one animal): None of these

Margo plicatus 

Mrs.  O'Leary: My cows don't have any upper incisors.  Is this normal?

Yes - it is normal

The cow had a recent hardware disease scare; she ate baling wire while she was grazing. Where in her gut is the wire most likely lodged?

Reticulum

I've been told one option is surgery to remove the wire.  What else can I do?

Feed the cow a magnet, but watch out for signs of internal trauma.

Which of her (the cow, not Mrs. O'Leary) four stomach components is largest?

Rumen

There should be one word from the chart above that doesn't fit into the chart (Question 4).  In which species would you find it?

Horse, horses, equine, equines

My squirrel's incisors are yellow-orange on the front.  Is this normal? What makes them that color?

Yes it is normal - it is caused by iron deposits on the teeth

I've been told my squirrel has a diastema in her mouth.  What does that mean? 

She has a space in between her incisors and pre-molars

The rabbit has tiny teeth behind his upper incisors.  What are these? Should they be there?

They are auxiliary incisors or peg teeth; they should be there

Which portion of my rabbit's GI tract is the largest? (hint: it helps with fermentation) 

The cecum

For the sheep, you retrieve this dental formula: I 0/4, PM 3/3, M 3/3.  

The owner wants to know: 
Blank 1: How many teeth (total) should she have?
Blank 2: How many incisors are missing?                                       
Blank 3: Is this picture of her lower or upper jaw?

#1: 32

#2: 4

#3: Lower jaw