Exam 3 – Dr. Brashier Equine GI Flashcards
Do herbivores have grinding or shearing teeth?
Grinding
What happens when herbivores grind high silica content feed?
Wears away teeth
What are hypsodont teeth?
Teeth which have a limited growth period, but prolonged eruption
What happens to odontoblasts in horses?
They remain active throughout the life of the tooth synthesizing regular secondary dentin and also irregular secondary dentin on the periphery of the pulp horn throughout most of the life of the tooth
What does the synthesizing of secondary dentin do?
Gradually reduces the size of the pulp cavity and thus of the pulp and eventually fully occludes the pulp horn
What are the 3 main types of dentin?
Primary dentin
Secondary dentin
Tertiary dentin
What is primary dentin?
Laid down as the tooth forms before it erupts and is in wear
What is secondary dentin?
Continues to form as the occlusal surfaces worn away and the pulp cavity retracts so that the secondary dentin seals off the pulp cavity so that it is not exposed as the tooth wears away
When is tertiary dentin formed?
In response to local insults
Where do odontoblasts reside?
At the periphery of the pulp cavity, but their odontoblast processes extend through the dental tubules
What is the bulk of the tooth composed of?
Dentin
What is dentin?
A cream colored, calcified tissue composed of approximately 70% minerals and 30% organic components
What happens to the pulp cavity?
It is constantly retracting
What is secondary dentin doing?
Constantly being laid down to seal pulp cavity
When do the permanent premolars erupt?
06s: 2.5 years
07s: 3 years
08s: 4 years
When do the molars erupt?
1, 2, and 3.5 years, respectively
When do the incisors erupt?
2.5, 3.5, and 4.5 years
What should the teeth be like by 5 years?
All caps should be gone and all teeth fully in wear against the opposite member
How much do teeth wear away?
2-3 mm/yr
What happens at 7 years of age with teeth?
The root development slows and overall length of all teeth begins to become shorter
When does tooth development stop?
12-15 years
What is anisognathic?
Upper arcade 25-30% wider than lower
What does anisognathic teeth lead to?
Naturally leads to sloped occlusal surface, which increases feed efficiency
What happens since incisors meet?
Cheek teeth do not meet
What are points?
Where teeth do not meet
What is the consequence of hypsodont teeth?
Any malocclusion lead to dental overgrowth, which can lead to poor feed utilization and loss of body condition
What are ulcers created by points prevented by?
Rasping sharp edges
What is the most common malocclusion?
Points
What is the second most common malocclusion?
Hooks
Having the upper arcade set relative to the lower arcade, which results in the rostral aspect of the upper first cheek tooth having nothing to wear against and subsequently getting overly long
What is the rostral 2/3 of the esophagus made of?
Striated muscle
What is the causal 1/3 of the esophagus made of?
Smooth muscle
What is the lower esophageal sphincter of the esophagus like?
Very well developed
Horses do not like vomiting. What will they do before regurgitating or vomiting?
They will rupture their stomach
What can be lifesaving with colic?
Passing a stomach tube
Which GI tract tends to be more complex, herbivores or carnivores?
Herbivores
What is the nervous control of the GI tract through?
Enteric nervous system
What is the volume of the stomach?
8-15 L
What percentage of the GI tract is the stomach?
8%
What is the length of the small intestine?
70 ft.
What is the volume of the small intestine?
40-60 L
What percentage of the GI tract is the small intestine?
30%
What is the length of the cecum?
4 ft.
What is the volume of the cecum?
28-36 L
What percentage of the GI tract is the cecum?
15%
What is the length of the large colon?
10-12 ft
What is the volume of the large colon?
80-90 L
What percentage of the GI tract is the large colon?
38%
What is the length of the small colon?
10-12 ft
What is the volume of the small colon?
16 L
What percentage of the GI tract is the small colon?
9%
Look at GI tract
Look at GI tract
What kind of non-ruminant herbivores are horses?
Hind-gut fermenter
What is the stomach of a horse like?
Simple stomach that digests simple CHO sources, but can utilize fibrous sources
Where does all true enzymatic digestion occur in the horse?
In the fore gut ahead of the cecum
What does the enzymatic digestion in the fore gut account for?
52-58% of the crude protein digestion, all protein absorption, all long chain lipid absorption, and virtually all soluble CHO digestion and absorption
Where does bacterial or microbial digestion of fiber CHO occur?
In the cecum and colon where large quantities of VFAs are produced through fermentation and absorbed
What happens since there is no enzymatic digestion in the large intestine?
All other products of microbial proliferation are lost to the horse
What are the 4 major regions of the stomach?
Stratified squamous epithelium, cardiac, fundic, and pyloric
What is the stratified squamous epithelium of the stomach like?
Does not contain any glands or mucus producing cell and ends abruptly at the margo plicatus
What does the cardiac mucosa contain?
Mainly mucus and bicarbonate producing glands
What are the glands in the fundic region responsible for?
Produce some mucus, but primarily responsible for acid and protease production
What do the pyloric glands do?
Mucus production (rich in mucus producing glands)
Some bicarbonate production
Some protease production
What breaks down food in the stomach?
Acids and the enzyme pepsin
What does pepsin do?
Causes the breakdown of proteins into amino acid chains
What is the end product of the stomach?
Food broken down into chyme
How much of the digestive system is made up by the stomach?
8-10%
How long does it take fluid to move through the stomach?
20-30 minutes
How long does it take grain, pellets, and short grass to move through the stomach?
0.5 to 5 hours
How long does it take long stem dry hay to move through the stomach?
16 hours
When will the stomach empty?
When it is 2/3 full regardless whether full digestion has taken place or not
Horses are continuous grazers. What are facts about the horse that pertain to this fact?
Produce acid 24 hours/day regardless
No gall bladder
Often fed once or twice a day
How much of their body weight can horses consume of dry matter?
2 to 2.5%
What is the pH of an empty stomach of a horse?
1.5
What does forage act as?
Buffer
What is the pH of an empty stomach of a carnivore?
6
What assists with small intestine with digestion?
Pancreas and liver
What does the liver produce?
Bile, which assist with fat absorption by the small intestine
How frequently is bile secreted in a horse?
Constantly because there is no gall bladder
What does the pancreas secrete?
A mixture containing enzymes and bicarb into the small intestine, which his in breaking down protein and AA chains into individual AA and soluble CHOs into simple sugars
What percentage of fat in a diet can horses digest?
15-20%
What is the small intestine responsible for?
Secretory H2O
Nutrient absorption
Rapid transit
What are the difference of the small intestine in horses compared to small animals?
The proximal half is more secretory than absorptive for water
Even though the SI is long, the rate of passage is relatively fast
How much of the horses total body water circulates through the GI tract on a daily basis?
1/2
What is cellulase?
Microbial enzyme to break down fermentable fiber into simple sugars
What is acetic acid?
Can be used directly by mammalian cells or used by the liver for synthesis of longer chain fatty acids for formation of triglycerides
Directly accounts for 30% of energy needs
What happens with propionic acid?
Goes to liver for glucose synthesis
What is butyric acid used by/?
Colonic cells
What do proteases do?
Breakdown plant protein into peptides
Take in and converted into microbial protein
What is within the anaerobic fermentation vat?
VFAs
Some water soluble vitamins
How much do VFAs account for energy needs?
50-80%: 30% from colon, 50% from cecum
What is the cecum?
Inlet and outlet near the top of the large intestine
Microbial fermentation vat
What does grain overload cause?
An increase in lactic acid which can cause damage to the cecal wall
So much lactic acid can be produced that microbes eventually die off
What happens in the cecum and colon for every 24 hours off feed?
Microbial populations drop by 50%
How bog is the colon?
100-140 L
What is the colon?
H2O reservoir
What does the colon have an effect on during exercise?
Respiratory rate
What does the large colon do?
Provides an additional location for fermentation of fibrous digesta and a site where absorption of the products of fermentation can occur
How much water does an average horse at rest consume?
About 7 gallons
What is the function of the small colon?
To absorb water and form fecal balls
What does the rectum do?
Excrete feces
