gastrointestinal system

functions of the gi system

reception, mechanical reduction, chemical absorption of food & drink, elimination of unabsorbed materials

alimentary tract/canal

mouth to anus & other structures connected by ducts (liver, gallbladder, pancreas)

labia oris

lips

what are the 3 layers of the lips/labia oris

outer = haired

middle = muscle (mastication)

inner = mucosa/mucous membranes

philtrum

line that runs straight down the center of the lips, dividing them left & right; sometimes connected, sometimes not

oral cavity is also called…

buccal cavity

the hard palate has…

ridges

the soft palate separates…

oropharynx & nasopharynx

tongue

mostly muscle; used for grooming, tasting, pain, temperature, touch, & can be used for prehension; highly vascularized & helps with thermoregulation

how does the tongue perceive temp, touch, & pain?

through different types of receptors

what are the 3 anatomical areas of the tongue?

apex: free moveable tip

body: central mass

root: connection to the base of the body

vomeronasal/jacobson’s organ

above the hard palate; perceives non-odorous chemicals

flehmen response

redirection of air over vomeronasal/jacobson’s organ to get more “information” from it

dental pad

hard bony plate that replaces upper dentition

buccal

outer surface of the tooth, facing the cheek

labial

outer surface of the tooth, facing the lips

lingual

outer surface of the tooth, facing the tongue (mandibular/bottom of mouth)

palatal

outer surface of the tooth, facing the palate (maxillary/top of mouth)

medial

outer surface of the tooth facing towards the dental arch; in towards midline

distal

outer surface of the tooth facing away from the dental arch; away from midline

occlusal/masticatory

surfaces of teeth that meet when mouth is closed

coronal

referring to/towards the crown (visible white of the tooth)

apical

referring to/towards the root

brachydont

teeth that have small crowns, well-developed roots, & roots only open for a finite period of time (stops growing)

hypsodont

teeth that have roots that are open for prolonged/indefinite amounts of time (continuous growing)

radicular

teeth that eventually stop growing

aradicular

teeth that never stop growing

crown

part of tooth projected above gingiva/gum

neck

area of tooth where crown & root meet

root

part of tooth embedded below gingiva/gum

what are teeth connected to the maxillary & mandibular bones by?

periodontal membrane/ligament

apex

entry point of vessels & nerves in root of tooth

enamel

white stuff that covers the crown; hardest substance in the body

dentin

deep/below enamel; hardness similar to bone, forms bulk of tooth, surrounds pulp cavity.

pulp cavity

contains blood vessels & nerves in the tooth

cementum

thin, bone like covering of dentin of the root; covers almost the whole tooth of hysodont animals

deciduous

baby teeth; have a weak connection due to lack of nerve supply to the tooth or the “small” root

permanent

adult teeth

heterodont dentition

teeth of different shapes & sizes

incisors

small front teeth; used to cut/nibble, ruminants have these on the lower mouth & a dental pad on top

canine teeth

single teeth on either side; used for tearing flesh & holding prey; not found in ruminants

premolars & molars

cheek teeth

premolars

used as shears to cut & slice

what are premolars called in horses?

wolf teeth

molars

only in adult dentition, assist with grinding & shearing

carnassial teeth

largest cutting teeth in carnivores; maxillary premolar 4 & mandibular molar 1

dental formula

represents one side (1/4 of total) of mouth (top/bottom)

what is the order of the dental formula

incisors, canines, premolars, molars

dental formula for dogs

3142/3143

dental formula for cats

3131/3121

how can you determine whether something is safe for an animal to chew on or not?

pressing nail into toy/chew

salivary glands

deposit saliva into oral cavity; made of mostly water but also protein, antibodies, glycoproteins, salivary bicarbonate, & enzymes

lysozome

helps control bacterial population in the mouth

amylase

helps digest starch in the mouth (found in pigs & rats)

types of salivary glands

parotid, mandibular, sublingual, zygomatic

sialocele

tumors of salivary glands; present with a swollen area in the face

temporomandibular joint (TMJ)

where mandible meets the skull; temporal bone meeting the mandible; allows for extension, flexion, & translation

eustachian tube

goes from the inner ear to the pharynx; helps with pressure balance

what are the stages of digestion?

prehension, mastication, bolus formation, deglutition

prehension

picking up the food

mastication

chewing/breakdown of food, mixed with saliva (stimulated by autonomic nervous system)

bolus formation

forming a ball of food mixed with saliva

deglutition

swallowing; broken down into 3 phases

what are the 3 phases of deglutition?

voluntary: requires consciousness

pharyngeal: involuntary reflex where trachea gets protected

esophageal: involuntary reflex; bolus of food has entered by the esophagus & initiates peristalsis

esophagus

runs to the left of the trachea in the cervical region

upper esophageal sphincter

opening to the esophagus

lower esophageal sphincter

where the esophagus meets the stomach in the abdominal cavity; more controlled than the upper esophageal sphincter

what are the 2 muscle layers in the esophagus?

circular: contracts/squeezes inward

longitudinal: pushes down

abdominal cavity

largest cavity in the body

abdominal cavity contains…

peritoneal cavity: contains most abdominal organs

retroperitoneal cavity: contains kidneys, adrenal glands, proximal uteters

omentum

double layer of connective tissue & fat that protects abdominal organs

monogastric

single stomach

anatomy of monogastric stomach

c-shaped, composite organ, has glandular portions

pyloric antrum contains…

mucous secreting cells & glandular (g) cells

glandular (g) cells

secrete gastrin, which stimulates the release of HCl

rugae

gastric folds within the stomach; allows stomach to expand & increases surface area for absorption

gastric pits

found in the glandular fundus & body of the stomach; contains mucous neck cells, parietal cells, & chief cells

mucous neck cells

secrete thin mucous; helps protect stomach walls

parietal cells

secrete hydrogen chloride (HCl) & intrinsic factor

chief cells

secrete pepsinogen, which then turns into pepsin, further stimulating hydrochloric acid

retropulsion

the “stuff” going around in a circle again within the stomach (back up into the fundus & through stomach again)

neurohumeral control

mix of nervous system & hormone control; controlled by vagus nerve, acetylcholine, gastrin

ruminant

4 chambered stomach

forestomachs

first 3 stomach chambers of ruminant stomach

reticulum

honeycomb appearance, microorganisms to ferment; contents easily enters/exits

rumen

very large compartment that occupies most of the left side of abdominal cavity; has microorganisms to ferment

omasum

chamber between reticulorumen & abomasum; allows absorption of water & salt

esophageal groove

found in young ruminants; bypass that skips over the rumen & reticulum, going straight into the omasum & abomasum

abomasum

“true stomach”; functions similarly to monogastric stomach

mechanical breakdown

occurs when the stomach undergoes peristalsis

chemical breakdown

digestive enzymes breaking things down in the stomach

functions of the stomach

storage, mechanical breakdown, chemical breakdown, aids in b12 absorption, produces chyme

intrinsic factor

required for b12 absorption & breakdown

chyme

food sludge mixed with acid; hypertonic, acidic, slowly released from stomach into duodenum

cephalic phase

animal is anticipating/thinking food

gastrin release, acetylcholine release, histamine release

gastric phase

food enters the stomach

stretch receptors stimulate glandular production, acetylcholine continues release (stretching), proteins begin breakdown into peptides, stomach acid pH = as low as 2

small intestine

carries chyme away from the stomach towards the large intestine

duodenum

recieves chyme from pyloric sphincter, & secretes cholecystokinin, secretin, & gastric inhibitory peptide

cholecystokinin

inhibits gastric emptying (slows stomach from emptying)

causes increased secretion of bicarbonate & pancreatic digestive enzymes

triggers gallbladder contraction