Lecture 1b - Digestive Physiology of Horses Flashcards
Why would horses have such a large LI?
- energy metabolism; they have to extract sufficient energy from plant material
What does the LI of a horse include?
Caecum, ascending, and descending colon
Horses are obligate…
Obligate Hindgut Fermenters
What part of the LI is in place for fiber fermentation?
Large caecum
What macronutrient are horses best adapted for to utilize?
FIBER!!!
- they have a very large caecum for fiber fermentation
What are 6 reasons for colic?
Gas
Obstruction
Strangulation
Impaction
Inflammation
Ulceration
What is saliva secretion stimulated by?
Mastication
Why does horse saliva contain a small concentration of bicarbonate?
- provides buffer against stomach acids
- allows some microbial fermentation in stomach
What 2 adaptations allow horses to increase chewing intensity?
- mastication
- large # of molars
What are the 3 regions of the stomach and their corresponding epitheliums?
Oesophageal region
- Squamous epithelium
Fundic region
- Glandular epithelium (ability to secrete)
Pyloric region
- Glandular epithelium
In what regions of the stomach can microbial fermentation occur?
oesophageal and fundic regions
What is secreted in the Fundic region vs the Pyloric region of the stomach?
Fundic
- parietal cells = HCl
- Zymogen cells = pepsin
Pyloric
- gastrin (which increases HCl and pepsin secretion)
Can horses vomit?
NO! Strong sphincter at top of stomach prevents vomiting
How does the horses stomach compare to dogs and cats?
Horse
- The stomach is a small organ in an adult horse. Digesta passes quickly into the SI with a relative emptying time of 120 min.
Dogs/Cats
- Longer emptying time
How may short gastric emptying time (120 min) relate to feeding behaviour?
Encourages constant grazing and constant meals to ensure digesta flow continues and there is access to energy
What are the 3 parts of the SI?
- Duodenum (~3m)
- Jejunum (~20m)
- Ileum (~45 cm)
What is the SI the primary site of digestion and absorption of?
protein, starch and fat
What is the exocrine functions of the pancreas? What enzymes play a role?
- Secretes enzymes and bicarbonate salts into the gut
- Enzymes: inactive proteases, lipases and amylases
What is the endocrine fxn of the pancreas?
Secrete hormones into the blood
- insulin, glucagon
What is the role of insulin?
Anabolic hormone making sure absorbed nutrients entering the portal vein are properly stored in tissue
What is bile produced by?
Liver
What is unique about the horse in terms of bile?
No gall bladder to store it in!
- bile continuously drains into SI
What does bile do?
Emulsify dietary fat and activate enzymes to aid in fat digestion
Why the adaptive feature of missing a gall bladder?
Diet of horse is low in fat so there may not be a reason to store large quantities of bile. Secondly, horses have continual flow of digesta so they need continual release of bile.
What is at the start of the LI?
Caecum
- very large
- 1 m long; 25-35 L capacity
What does the Caecum contain? What is it responsible for?
Contains microbial population (protozoa, bacteria, and other microorganisms) to breakdown fiber
Responsible for microbial synthesis of SCFA and protein
What are the 4 large compartments and 3 major flexures of the large colon (middle of the LI)?
- Right ventral colon
- sternal flexure - Left ventral colon
- pelvic flexure - Left dorsal colon
- diaphragmatic flexure - Right dorsal colon
What is the difference between the SI and LI?
SI
- villus
- crypt
LI
- NO villi
- crypts are deeper compared to SI
What are 4 ways the intestine increases capacity?
- coils
- folds
- villi
- microvilli
What are the several categories of aa relative to how they are absorbed via the epithelial cells?
Polar or Nonpolar
Acidic or Basic or Neutral `
Why are AA characteristics important for GI physiology?
Depending on the category of AA they will have to deal with unique transporters to be absorbed and it might mean there is competition between AA to be absorbed
What is the difference between exoproteases and endoproteases?
Bonds on the far left or right of the polypeptide chain are cleaved by exoproteins.
Bonds within the peptide chain are cleaved by endoproteases
Where is Pepsin located and what does it do?
Location: Stomach
Action: cleaves bonds of aromatic AA at the N-terminus
What are the 4 enzymes that aid in protein digestion from the pancreas?
- Trypsin
- cleaves peptide bonds joining basic AA - Chymotrypsin
- cleaves peptide bonds containing uncharged AA - Elastase
- cleaves peptide bonds next to small AA - Carboxypeptidase
- cleaves carboxy-terminal peptide bonds; liberates single AA
What are the 3 enzymes involved in protein digestion and absorption from the intestine?
- Aminopeptidases
- cleaves peptide bonds next to N-terminal AA oligopeptides; releases single AA or 3-6 AA peptides - Dipeptidases
- various specificity; cleaves dipeptides into free AA - Tripeptidases
- various specificity; cleaves tripeptides into free AA + dipeptide
What might be reasons for AA absorption to happen as single AA and small peptides?
Energy preservation!
Why is brush border transport of proteins not limited in some young mammals?
To transfer maternal immunity (antibodies)
- proteins and polypeptides are able to cross the brush border
What form of AA are entering portal circulation?
Mainly free AA
What type of transport is required for most AA?
Active transport!
What is required for active transport?
ENERGY
What enzyme from the pancreas is involved in CHO digestion and absorption?
alpha-amylase
- hydrolyzes starch to alpha-limit dextrins (shorter chains of glucose)
What 4 enzymes from the intestine are involved in CHO digestion and absorption?
- Glucoamylase
- hydrolyzes alpha-limit dextrins to single glucose units - Maltase
- cleaves maltose into single glucose units - Isomaltase
- hydrolyzes short chain glucose units to single glucose units - Sucrase
- cleaves sucrose into fructose and glucose
What is the general name of cells that produce incretins?
Enteroendocrine cells
What enzyme is linked to fat digestion and absorption?
Lipase
- location: pancreas
- primary action: break down triglycerides into free fatty acids and monoglycerides
Where do absorbed fats drain into first?
The lymph vessel
Where do SCFA produced by fermentation drain into?
LCFA absorbed into SI into lymph
SCFA can be taken up via a transport mechanism in the SI or LI
What is the major site of SCFA production and absorption?
LI
What are the 3 main SCFA?
acetate, propionate, butyrate
What are the 3 modes of uptake for SCFA?
- passive
- facilitated
- symporter
Which companion animal can adapt more quickly to a change in diet?
dog (bc they are omnivores)
