Digestion lecture

• reception
• mechanical reduction (chewing)
• chemical absorption of food and drink
• elimination of unabsorbed material

• mouth to anus, and certain other structures connected by ducts. 
• Inside of the GI tract is considered outside the body.  Things are only considered inside the body after going through the intestinal membrane. 

• lips
• oral cavity
• pharynx
• esophagus
• stomach
• small intestine
• large intestine
• rectum
• anus

the side of the body between the ribs and ilium

areas pertaining to the groin

right and left cranial, right and left caudal

the scar marking the site of entry of the umbilical cord in the fetus, also called the navel.  A surgical landmark

sits directly on peritoneal organs such as intestines. 

lines abdominal wall

in abdomen between abdominal wall and peritoneum.  Kidneys and adrenal gland are considered retroperitoneal

section of mesentery that is closest to the spine

sections of mesentery (not everywhere) that are further from the spine, surround liver

suspends parts of small and large intestine.  Contain blood vessels, lymphatics and nerves for the part of the GI tract they supply. 

suspends colon.  Part of the mesentery.  Add "meso" to any organ. 

• Double-layered connecting peritoneum between stomach and abdominal organs or abdominal wall. 
• split into greater and lesser.
• blanket

greater curvature of the stomach to body wall.  Wraps around self to create two folds.  Blanket covering intestines.

stomach and duodenum to liver.

• includes teeth, tongue and salivary glands
• Functions: prehension (picking up), mastication (chewing), insalivation (mixing with saliva)
• Also for agression and defense, airway and sound amplifier

lips, cheeks, oral cavity to palatoglossal arch (at ramus of mandible)

• mucocutaneous border where skin meets mucuous membrane. 
• flexible and pliable structure bounding the oral fissure. 
• Prehension
• long, tactile hair and regular hair
• muscle, glands, blood vessels and nerves (5th and 7th cranial)

leavtor nasolabialis, buccinator, orbicularis oris

caudolateral wall of the oral cavity

oral mucosa over the jaws enclosing the necks of the teeth

• rostral bony part.  Includes palatine, maxillary and incisive bones. 
• Palatine ridges

caudal musculomembranous part.  Hangs off back. 

• replaces upper incisors and canines in ruminants. 
• Provides heavily cornified epithelium against which the lower incisors can grind

olfactory sense organ used to detect pheromones (carry info between animals of the same species).  In front part of top jaw, between mouth and nasal passages. 

• 3142/3143  =  42
• Incisor, canine, premolar, molar. Each half. Multiply by 2 for total number.

• 3131/3121   =   30
• Incisor, canine, premolar, molar. Each half. Multiply by 2 for total number.

• 313-43/3133   =   40-42
• Incisor, canine, premolar, molar. Each half. Multiply by 2 for total number.

• 0033/3133  =  31
• Incisor, canine, premolar, molar.  Each half.  Multiply by 2 for total number. 

• system of nomenclature for teeth
• Upper right are 100s
• Upper left are 200s
• lower left are 300s
• lower right are 400s

24

canine teeth

• slowly erupt as they are worn away--not hypsodont.  Length of reserve crown is shorter every year, so you can tell a horse's age. 
• Form sharp ridges or "points" (lingual and buccal) and need to be "floated".

• crown (above gum)
• root (below gum)
• neck (between crown and root)
• Enamel (hardest substance in body. Covers crown)
• Dentin (bulk of tooth, surrounds pulp cavity like bone)
• pulp (sensory, vascular part of tooth inside)
• cementum (bone-like material covering root in a canine, whole tooth in an equine)

dense fibrous connective tissue connecting alveoli with cementum

bone-like material that extends to the neck of the tooth.  Gums cover it. 

large sheering teeth of cat and dog.  Premolar 4 on top and Molar 1 on bottom.

a horse's rudimentary upper 1st premolar. Often absent.  Equines are always missing lower 1st premolar on lower jaw. 

• absent: mare, cow and gelding
• present: stallion (and cat, dog, etc)
• exaggerated: pig.  Open-rooted. 

cartilege embedded in the tongue of a dog. 

taste buds, mechanical and sensory functions. 

• Intrinsic: transverse, vertical, superior longitudinal and inferior longitudinal. 
• Extrinsic: Geniglossus, Geniohyoideus, Hypoglossus, Styloglossus
• Canine tongue vascular to shed heat

• Sensation (pain, temperature and tactile) CrV Trigeminal
• Taste (rostral two thirds) Cr XII Hypoglossal
• Taste (caudal third) CrIX glossopharyngeal , X Vagus
• Motor innervation Cr XII Hypoglossal

• glands that empty into digestive system via ducts
• Include: parotid, mandibular (or submandibular), sublingual, and accessory (including zygomatic)

• primarily water, some protein, glycoprotein, a significant amount of electrolytes, antibodies (IgA), mucus and enzymes. 
• amylase: present in omnivores (pig) and to a limited degree in horse.  Absent in ruminants and carnivores (cat and dog)

Salivary, encapsulated, ventral to ear, enters near premolar, long duct.

salivary, encapsulate.  Bottom of mouth.  Sublingual.  Round. 

• Salivary gland under tongue. 
• Has two parts: polystomatic and monostomatic
• Dog: Poly near mouth opening, mono near jaw. 
• Horse: only has polystomatic
• Ruminant: have both, but positions are reversed

one of the small, minor cheek salivary glands.

top part of pharynx, respiratory section

lower part of distal pharynx, for food

proximal part of pharynx, common region for food and respiratory.  Where Oro- and nasopharynx meet

• common passageway for the digestive and respiratory systems. 
• Nasopharynx: on top, for respiratory
• oropharynx: on bottom, for food
• laryngopharynx: behind oropharynx, common region where both neet. 

• Muscular tube that transports food from oral cavity and pharynx down neck and through thorax to the stomach
• Dorsal to and left of the trachea, caudal to diaphragm. 
• Layers: Serosa, longitudinal muscle, circular muscle, submucosa, mucosa. 
• In cat: distal end smooth muscle
• In ruminants and dogs: skeletal muscle fibers run throughout

• Lumen
• 1. Mucosa
• 2. submucosa
• 3. circular muscle
• longitudinal muscle
• 4. serosa

a circular muscle that surrounds the cardia (where esophagus enters the stomach).  Has sympathetic and parasympathetic innervations

swallow

• single compartment in carnivores, horse and pig. 
• Dilating GI caudal to esophagus receives and briefly stores ingesta until muscles mix with enzymes and move into duodenum.
• Blood supply comes from the celiac artery and goes to the portal vein

Cardia, fundus, body, omentum (sort've), greater and lesser curvatures, pyloric antrum, ;yloric canal, pyloric sphincter

blind expanded portion adjacent to cardia.  Often filled with gas and visible on a radiograph

Lumen, mucosa, submucosa, muscle layers, serosa

• dog and cat: glandular. 
• Pig, horse and ruminant: composite. 
• Luminal surface of stomach is lined by a glandular epithelium, a nonglandular epithelium or both. 
• The fore-stomachs of a ruminant are non-glandular. 

ridges of the lining of the stomach when it is contracted.  These stretch out when the stomach is distended. 

grossly visible line in body of stomach that separates the glandular/nonglandular tissue in a horse.  Horses have simple composite stomachs.

• 3 forstomach chambers (reticulum, rumen and omasum) are nonglandular lined with stratified squamous epithelium. 
• The abomasum is the glandular stomach (enzymes), on the right side next to the abdominal wall. 
• Rumen is the fermentation vat to break down cellulose.  On the left side, it displaces organs to the right. 
• Omasum is spherical and caudal to reticulum

• consists of duodenum, jejunem and ileum.  Principle digestion and absorption
• Carnivores have a short gut, sheep have a LOOOONG gut

• first part of the small intestine.  Relatively short.  Receives ingesta from stomach.  Runs next to pancreas.  Mesoduodenum (attached mesentery), duodenal-jejunal flexor (bridge to jejunum). 
• Exocrine glands: digestion enzymes
• Endocrine glands: hormones.

2nd part of small intestine.  Contains villi (finger-like to increase surface area) and crypts (bottom of villi, with glands).  Loops, long mesentery, lots of motion. 

last portion of small intestine.  Indistinguishable.  Empties into large intestine through ileocolic opening.  Contains villi (finger-like projections to increase surface area), crypts (bottom of villi, with glands) and peyer's patches (lymph nodules)

finger-like projections that line the mucosa of the GI tract to help absorb.  Increse surface area.  Crypts are valleys between villi that contain glandular tissue. 

• non-glandular congregations of lymphoid tissue in the walls of the small intestine below villi.  Prominent in ileum. 
• Control populations of bacteria
• antibody production
• fluid filtration.

• Tunica serosa (outside)
• Tunica muscularis
• Tunica submucosa
• Tunica mucosa
• Lumen

• Made by liver, goes through hepatic ducts to cystic duct (these together are the bile duct).  Stored in the gallbladder until goes down the bile duct into the duodenum through the major duodenal papilla. 
• Bile breaks down and absorbs fats

• no gallbladder or cystic duct
• constantly secreting bile through biliferous ducts into hepatic duct into duodenum. 

• dogs and oxen have two
• cats, horses, sheep and goats have one. 

• Dehydrates fecal contents--absorbs water.  No villi, lots of lymph glands, has crypts. 
• Cecum (blind pouch, varies with species)
• Ascending (short in varnivore, varies with species, LOOK AT DRAWING)
• Transverse (right to left, oten between stomach and small intestine)
• Descending (longest part. Follows left flank, then medial to rectum)

• blind diverticulum at the beginning of the colon. 
• Cecocolon--the one opening into the colon. 
• Crucial fermentation center to horses.  Ileum opens into cecum in horses. 
• Huge, comma-shaped, has a base, body and apex in the right part of the abdomen of the equine. 
• Blind tube extending caudally in ruminants.

• Carnivores: short and straight
• Pig and ruminant: coil, the spiral colon
• Horse: double horseshoe shaped loop (like a spiral but doubles back.  HUGE.  "Great colon"

• bands (teniae) that pucker to form saccules (haustra) in horses and pigs.  Help tell what part of the LI you're looking at. 
• Not in cat and dog

retroperitoneal.  From descending colon to anal canal, which is the short termination of GI.  External sphincter is skeletal and voluntary. 

pouches located between intermal smooth and external striated sphincter muscles of the carnivore anus.  At 4 and 8 o'clock. 

• cranial and caudal mesenteric arteries. Collateral circulation. 
• proximal duodenum uses shepatic branch of celiac artery
• caudal rectum uses rectal branch of internal pudendal
• Portal vein drains. Liver then systemic. 
• Lots of lymph, particularly in SI, drain to thoracic duct
• sympathetic and parasympathetic

• largest digestive gland in body.  Extramural (outside lumen of GI tract).  Caudate lobe encloses cranial right kidney. 
• Detoxification, formation and secretion of bile, digestion of carbs, protein and fat. 
• 6 lobes (L&R lateral, L&R medial, quadrate, caudate)
• 2 processes (papillary, caudate)
• 2 surfaces (diaphragmatic and visceral)
• Dual blood supply from hepatic and portal, sympathetic and parasympathetic

• Left lateral
• left medial
• quadrate
• right medial
• right lateral
• caudate

• papillary: lying in the lesser curvature of the stomach
• caudate: most caudal,  Cups the cranial pole of the right kidney in all domestics but the pig. 

• diaphragmatic: convex, incontact with diaphragm. 
• visceral: incontact with intestintes

• between quadrate and right medial lobe of liver.  Green. 
• Sac storing and concentrating bile.  Pours into duodenum from cystic then bile duct. 
• Digestion and lubrication of food, break down of fats
• Horse doesn't have one. 

attaches liver to diaphragm

• 2 lobes joined by a body.  Exocrine is large part secreting digestive enzymes.    Pancreatic duct exports. 
• Fed by celiac and cranial mesenteric, drained by portal vein. 
• Sympathetic and parasympathetic. 
• Lies along greater curve of stomach and duodenum. 

endocrine part of pancreas.  Produce insulin and glucagon to help control concentration of glucose in blood.