Lecture 1b - Digestive Physiology of Horses

Question 1

Why would horses have such a large LI?

Answer 1

• energy metabolism; they have to extract sufficient energy from plant material

Question 2

What does the LI of a horse include?

Answer 2

Caecum, ascending, and descending colon

Question 3

Horses are obligate…

Answer 3

Obligate Hindgut Fermenters

Question 4

What part of the LI is in place for fiber fermentation?

Answer 4

Large caecum

Question 5

What macronutrient are horses best adapted for to utilize?

Answer 5

FIBER!!!
- they have a very large caecum for fiber fermentation

Question 6

What are 6 reasons for colic?

Answer 6

Gas
Obstruction
Strangulation
Impaction
Inflammation
Ulceration

Question 7

What is saliva secretion stimulated by?

Answer 7

Mastication

Question 8

Why does horse saliva contain a small concentration of bicarbonate?

Answer 8

• provides buffer against stomach acids
• allows some microbial fermentation in stomach

Question 9

What 2 adaptations allow horses to increase chewing intensity?

Answer 9

1. mastication
2. large # of molars

Question 10

What are the 3 regions of the stomach and their corresponding epitheliums?

Answer 10

Oesophageal region
- Squamous epithelium

Fundic region
- Glandular epithelium (ability to secrete)

Pyloric region
- Glandular epithelium

Question 11

In what regions of the stomach can microbial fermentation occur?

Answer 11

oesophageal and fundic regions

Question 12

What is secreted in the Fundic region vs the Pyloric region of the stomach?

Answer 12

Fundic
- parietal cells = HCl
- Zymogen cells = pepsin

Pyloric
- gastrin (which increases HCl and pepsin secretion)

Question 13

Can horses vomit?

Answer 13

NO! Strong sphincter at top of stomach prevents vomiting

Question 14

How does the horses stomach compare to dogs and cats?

Answer 14

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

Question 15

How may short gastric emptying time (120 min) relate to feeding behaviour?

Answer 15

Encourages constant grazing and constant meals to ensure digesta flow continues and there is access to energy

Question 16

What are the 3 parts of the SI?

Answer 16

1. Duodenum (~3m)
2. Jejunum (~20m)
3. Ileum (~45 cm)

Question 17

What is the SI the primary site of digestion and absorption of?

Answer 17

protein, starch and fat

Question 18

What is the exocrine functions of the pancreas? What enzymes play a role?

Answer 18

• Secretes enzymes and bicarbonate salts into the gut
• Enzymes: inactive proteases, lipases and amylases

Question 19

What is the endocrine fxn of the pancreas?

Answer 19

Secrete hormones into the blood
- insulin, glucagon

Question 20

What is the role of insulin?

Answer 20

Anabolic hormone making sure absorbed nutrients entering the portal vein are properly stored in tissue

Question 21

What is bile produced by?

Answer 21

Liver

Question 22

What is unique about the horse in terms of bile?

Answer 22

No gall bladder to store it in!
- bile continuously drains into SI

Question 23

What does bile do?

Answer 23

Emulsify dietary fat and activate enzymes to aid in fat digestion

Question 24

Why the adaptive feature of missing a gall bladder?

Answer 24

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.

Question 25

What is at the start of the LI?

Answer 25

Caecum - very large - 1 m long; 25-35 L capacity

Question 26

What does the Caecum contain? What is it responsible for?

Answer 26

Contains microbial population (protozoa, bacteria, and other microorganisms) to breakdown fiber Responsible for microbial synthesis of SCFA and protein

Question 27

What are the 4 large compartments and 3 major flexures of the large colon (middle of the LI)?

Answer 27

1. Right ventral colon - sternal flexure 2. Left ventral colon - pelvic flexure 3. Left dorsal colon - diaphragmatic flexure 4. Right dorsal colon

Question 28

What is the difference between the SI and LI?

Answer 28

SI - villus - crypt LI - NO villi - crypts are deeper compared to SI

Question 29

What are 4 ways the intestine increases capacity?

Answer 29

1. coils 2. folds 3. villi 4. microvilli

Question 30

What are the several categories of aa relative to how they are absorbed via the epithelial cells?

Answer 30

Polar or Nonpolar Acidic or Basic or Neutral `

Question 31

Why are AA characteristics important for GI physiology?

Answer 31

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

Question 32

What is the difference between exoproteases and endoproteases?

Answer 32

Bonds on the far left or right of the polypeptide chain are cleaved by exoproteins. Bonds within the peptide chain are cleaved by endoproteases

Question 33

Where is Pepsin located and what does it do?

Answer 33

Location: Stomach Action: cleaves bonds of aromatic AA at the N-terminus

Question 34

What are the 4 enzymes that aid in protein digestion from the pancreas?

Answer 34

1. Trypsin - cleaves peptide bonds joining basic AA 2. Chymotrypsin - cleaves peptide bonds containing uncharged AA 3. Elastase - cleaves peptide bonds next to small AA 4. Carboxypeptidase - cleaves carboxy-terminal peptide bonds; liberates single AA

Question 35

What are the 3 enzymes involved in protein digestion and absorption from the intestine?

Answer 35

1. Aminopeptidases - cleaves peptide bonds next to N-terminal AA oligopeptides; releases single AA or 3-6 AA peptides 2. Dipeptidases - various specificity; cleaves dipeptides into free AA 3. Tripeptidases - various specificity; cleaves tripeptides into free AA + dipeptide

Question 36

What might be reasons for AA absorption to happen as single AA and small peptides?

Answer 36

Energy preservation!

Question 37

Why is brush border transport of proteins not limited in some young mammals?

Answer 37

To transfer maternal immunity (antibodies) - proteins and polypeptides are able to cross the brush border

Question 38

What form of AA are entering portal circulation?

Answer 38

Mainly free AA

Question 39

What type of transport is required for most AA?

Answer 39

Active transport!

Question 40

What is required for active transport?

Answer 40

ENERGY

Question 41

What enzyme from the pancreas is involved in CHO digestion and absorption?

Answer 41

alpha-amylase - hydrolyzes starch to alpha-limit dextrins (shorter chains of glucose)

Question 42

What 4 enzymes from the intestine are involved in CHO digestion and absorption?

Answer 42

1. Glucoamylase - hydrolyzes alpha-limit dextrins to single glucose units 2. Maltase - cleaves maltose into single glucose units 3. Isomaltase - hydrolyzes short chain glucose units to single glucose units 4. Sucrase - cleaves sucrose into fructose and glucose

Question 43

What is the general name of cells that produce incretins?

Answer 43

Enteroendocrine cells

Question 44

What enzyme is linked to fat digestion and absorption?

Answer 44

Lipase - location: pancreas - primary action: break down triglycerides into free fatty acids and monoglycerides

Question 45

Where do absorbed fats drain into first?

Answer 45

The lymph vessel

Question 46

Where do SCFA produced by fermentation drain into?

Answer 46

LCFA absorbed into SI into lymph SCFA can be taken up via a transport mechanism in the SI or LI

Question 47

What is the major site of SCFA production and absorption?

Answer 47

LI

Question 48

What are the 3 main SCFA?

Answer 48

acetate, propionate, butyrate

Question 49

What are the 3 modes of uptake for SCFA?

Answer 49

1. passive 2. facilitated 3. symporter

Question 50

Which companion animal can adapt more quickly to a change in diet?

Answer 50

dog (bc they are omnivores)