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First year semester 2 > Equine GI > Flashcards

Equine GI Flashcards

1
Q

Broadly describe differences in ascending, transverse and descending colon between species

A
  1. Ascending smallest section = modified

2. T and D = largely similar

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2
Q

Describe the functional anatomy of the equine GI

A
  1. Ascending colon vastly modified into a fermentation chamber
  2. 3 compartments which are separated by physiological valves
  3. different types of fermentation occurs in each compartment
  4. compartments: Caecum, ventral colon, dorsal colon
  5. relatively short transverse colon narrows to meet descending colon
  6. Longitudinal muscle not continuous strand but arranged into taeial bands - diff number in each part
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3
Q

Name the valves and where they are in the equine large intestine

A 
Ileum
1. ileo-caecal valve
Caecum
2. caeco-colic valve
Ventral colon
3. narrow pelvic flexure
dorsal colon
4. Narrowing transverse colon
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4
Q

In horse what is unique about the caecum?

A
  1. ileum f SI goes INTO caecum in other species caecum is plopped on the side
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5
Q

Fermentation of non hydrolysable CHO in horse

  • What does it depend on?
  • How different to cow
  • microbial products
  • positioning of LI means what?
A
  1. degree/ type depends on material reaching large intestine (like cow)
  2. But SI before fermentation in H, cow = other way around
  3. vast majority/all of non-hydrolysable CHO reaches large intestine so fermentation extensive
  4. Microbial products of fermentation are VFAs / CH4 / CO2
    • Large intestinal mucosa can absorb these VFAs
    • Gases passed to rectum by peristalsis and expelled (flatulence)
  5. Microbial balance easily upset, just as in ruminants – diarrhea and acidosis
  6. As large intestine is terminal part of GI tract some VFAs AND ALL microbial protein egested / wasted
    • Rabbits / rats practice coprophagy to avoid this waste (some sick horses can do)
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6
Q

What about fermentation in carnivores?

A
  1. Most digestion/ absorption has already occurred prior to large intestine therefore fermentation is minimal
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7
Q

Equine colic

A
  • Colic is not a disease but a clinical sign of abdominal pain
  • True colic relates to gastro-intestinal pain
  • False colic relates to other abdominal organ pain (e.g. bladder, kidney, uterus, foal etc)
  • Colic results in the highest levels of equine morbidity & mortality therefore an accurate diagnosis is essential in order to treat successfully
  • The most useful procedure in diagnosis of colic is rectal examination
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8
Q

Metabolism of VFA in equine GI

A
  1. similar to ruminants = used as an energy source
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9
Q

What are the main VFAs

Improtance of one?

A

acetate, propionate and Butyrate. Can only generate glucose from propionate!

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10
Q

How is Acetate used?

A
  1. used in liver
  2. oxidised in most other cells to generate ATP
  3. Major source of acetly CoA for lipid synthesis
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11
Q

How is Propionate used?

A
  1. Substrate for gluconeogenesis
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12
Q

How is Butyrate used?

A
  1. Energy production

2. Cellular homeostasis

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13
Q

Absorption of VFAs

A
  1. (acetate, propioante, butyrate) absorbed by short chain fatty acids/ in exchange for HCO3- - this helps control pH
  2. VFAs absorbed intact rather than metabolised as they’re absorbed like with R
  3. propionate = gluconeogenesis to produce glucose
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14
Q

What is another name for VFA

A

short chain fatty acid

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15
Q

Absorption of Na

A
  • Absorbed by sodium channels & Na+/H+ exchanger (NHE transporter)
  • Sodium absorption enhanced by aldosterone
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16
Q

Absorption of Cl-

A

• Absorbed by bicarbonate / hydroxyl exchange

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17
Q

Absorption of water

A
  • Most of rest of water passing from SI absorbed in large intestine
  • Osmotic pressure
  • Hydrostatic pressure
  • Solvent drag
  • Extensive re-absorption in horses – 100s of litres
18
Q

Water absorption in horse vs most animals

A
  1. SI is where main water re absorption occurs (70-80%)
  2. Horse LI still absorbs some but most water is secreted into SI so most occurs here
  3. by same process
19
Q

COMPARATIVE PHYSIOLOGY

A
  • Large intestine physiology similar in most domestic species EXCEPT horse
  • In feral horse on diet of grass 75% energy derived from VFAs produced by microbial fermentation in the hind-gut
  • Fermentation similar process to that occurring in ruminant fore-stomach
  • EXCEPT small intestine occurs before fermentation vessel
  • In ruminants any hCHO immediately fermented so none passes into SI
  • However in horse potentially lots of hCHO can pass into LI if overload of SI capacity to digest / absorb it  can upset microbial populations
20
Q

CARBOHYDRATE FERMENTATION

A
  1. Fibre (containing β-glycosidic bonds) requires microbial fermentation
  2. Products of fermentation are principally VFAs
  3. VFAs cause a decline in pH of luminal contents - acidic
    • Neutralised by copious pancreatic secretion containing HCO3-
    • Goblet cells in large intestine secrete mucous & HCO3-
    • Ileum also secretes HCO3-
  4. If production of VFAs excessive H+ ions too numerous to be neutralised by HCO3- secretions
    • pH of luminal contents declines
    • Favours multiplication of acid resistant microbes (amylolytic bacteria / lactate producers)
    • Lactic acid poorly absorbed cf VFAs causing further pH decline
21
Q

PROTEIN FERMENTATION

A
  1. Probably similar to ruminants
  2. HOWEVER
    • Equine hind-gut (LI) more capable of absorbing amino acids / peptides
    • Hence less amino acids / peptides taken up by microbes, more being absorbed by the host
    • This is a good thing as (all) microbial protein is lost in faeces in hind-gut fermenters
    • Microbial nitrogen requirements satisfied by urea secreted by ileum / large intestine
    Broken down by microbial urease into NH3 to be used as NPN source for microbial protein synthesis
22
Q

WATER ABSORPTION

A
  • Compared to other species more water reabsorption occurs in large intestine
  • At luminal pH (6.5) most VFAs in ionic form which are poorly absorbed
  • Local mechanism of secretion of H+ in exchange for Na+ converts ions to their respective acids thus enhancing their absorption
  • When VFAs absorbed there is also a net absorption of NaCl which enhance water reabsorption via osmotic pressure & solvent drag – inc efficiency
  • HCO3- secreted in exchange for Cl- maintain pH at level suitable for fermentation
23
Q

FOREGUT VS HINDGUT FERMENTATION efficiency

A
  • Hind-gut fermentation 70% as efficient as fore-gut fermentation. Ruminant = 90%
  • Microbes less efficient lower prop of amyloytic fermenters
  • Hind-gut fermenters lose microbial protein in faeces
  • Coprophagy - rabbits / rodents eat certain component of their faeces high in microbial protein
24
Q

Gut transit time fore gut vs hind

A
  1. gut-transit time in fore-gut fermenters dependent on rate of fermentation and can’t be reduced whatever the nutrient quality of the fibre
    • Horses on poor quality forage can decrease gut transit time and therefore consume more
    • Ruminants more efficient on good quality forage
    • Horses more efficient on poor quality forage as long as it’s in abundance
25
Q

What is the main neutralised of VFAs decreasing pH in foregut vs hind gut

A
  1. foregut = mainly saliva

2. hind = copious pancreatic secretion containing HCO3-

26
Q

Acidosis in horses

A
  1. Too high level of hydrolysable CHO
  2. Amylolytic poliferate at expense of cellylolytic
  3. A = rapid fermentors = inc VFA
  4. also favours lactate producers
  5. both lactate p and amylolytic bacteria are acid resistant
  6. LActic acid poorly absorbed = further pH decline
27
Q

Where does most water reabsorption occur?

A
  1. Caecum
  2. ventral colon
    in particular
28
Q

Microbiology:

Bacteria

A

Similar categories to ruminants
1. horses tend to have less amylolytic (rapid fermenter) and more celluloytic (slow fermenter) = overall F = slwoer process

29
Q

Microbiology: Protozoa

A
  1. contribution unknown as if removed v little difference

2. Protozoa lost in faeces therefore can’t be digested as in ruminant

30
Q

Microbiology: Fungi

A
  • Probably similar to ruminants

* Split apart lignin thereby rendering it susceptible to digestion by celluloytic bacteria

31
Q

Motility - why slow?

Different in hind and fore gut time

A
  • Large intestinal transit time must be slow enough to allow fermentation to occur
  • Hind-gut fermenters - several days
  • Fore-gut fermenters - 24 hours
32
Q

Caecum adn colon, most species vs horse

A
  • In most species caecum & colon form continuous compartment – pelvic flexures slows
  • In horses caecum separated from colon by caeco-colic valve
  • Separate fermentation compartment with no retrograde flow of material from colon to caecum
33
Q

Point of caecum

A

Reserve capacity to allow food to pass back into it

  1. main reason to slow down rate of fermentation, must have peristalsis occurring
  2. food moving backwards = slows down
  3. In most animals it can’t go back into illeum due to physiological valve
  4. If caecum didn’t exist it would cause distension of gut = pain = not contribute to normal digestive process of animal
34
Q

Horse caecum contractions

What is the point

A

MAss movement occur ev 3-5 mins extra as well as peristalsis, antiperistalsis, segmental contractions
1. empty all contents into ventral colon

35
Q

How to tell if healthy

A

should hear toilet flushing sound every 3-5 mins on RHS = caecal contraction

36
Q

Colonic contractions in most species:

A
  1. Main = segmental, peristaltic and anti p
  2. Anti p contractions are more prominant in proximal colon
  3. Retrograde movement of chyme from colon into caecum NOT into ileum
37
Q

Colonic contractions in horse

A
  1. NO retrograde movement from colon into caecum - once emptied caeco-colic valve SHUT
  2. reverse P in distal ventral colon not proximal like in other species
  3. Slow movement of passage fo chyme from ventral to dorsal colon via pelvic flexure
  4. Only small particles/ well fermented material can pass via pelvic flexure into dorsal colon
  5. Ensures slow enough transit time to allow efficient fermentation
38
Q

How to diagnose Equine colic

A
  1. REctal examination

2. Abdomincal Auscultation

39
Q

How many ribs in horse

A

18 pairs

40
Q

Normal sound of horse gut on LHS

A
  1. Left dorsal = SI and small colon (descending)
    Fluidy in nature, higher pitch
  2. Left ventral = pelvic felxure
41
Q

Normal gut sounds on RHS

A 
1. R dorsal/ ventral = caecum
Loud sound, like toilet flushing = emptying via caeco-colic valve
3-5 per 5 min
42
Q

Abnormal sounds

A
  1. Inc frequency = enteritis, spasmodic colon
  2. Tympanitic = gut distension with gas, obstruction
  3. Decreased frequency = ileus, obstruction

First year semester 2 (50 decks)

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