1: Digestive physiology of dogs and cats

Question 1

The role of the digestive system is to…

Answer 1

break down large food molecules into simple forms that can be absorbed by the body for use

Also barrier function

Question 2

What is a clinical sign if the GI tract is not working well

Answer 2

Diarrhea (secretory or malabsorptive)
Vomiting

Question 3

Length of the GI tract of the dog vs the cat

What does intestinal length influence?

Answer 3

Dog
Body length = 0.75m
SI =3.9m
LI =0.6m

Cat
Body length = 0.5m
SI = 1.7m
LI = 0.4m

Length influences retention time of food in the gut

Question 4

What are the structures used to increase capacity of the GI tract relative to body weight?

Answer 4

Coils, folds, villi, microvilli

Question 5

Describe the GI tract of the dog

Answer 5

• Monogastric GI system
• Adapted to an omnivorous diet containing a high proportion of animal tissues

Question 6

Starch digestion in cats vs dogs

Answer 6

Domestic dog has more capacity to digest starch (have amylase)
Cats have trouble digesting starch

Question 7

Describe the cat GI tract

Answer 7

• Monogastric GI system
• Adapted to a carnivorous diet
• Eat protein and fat, with some CHO found in animal tissues

Question 8

Where is CHO found in animal tissues?

Answer 8

Glycogen is in muscle and liver, can be mobilized into glucose

Question 9

What affects production of saliva by salivary glands? 4 pairs of glands:

Answer 9

Smell and presence of food stimulates the salivary gland to product saliva
- type of food ingested and its moisture content affect saliva amount and composition

glands: parotid, mandibular, sublingual and zygomatic

Question 10

What is the role of saliva? What do dogs and cats lack in salivary glands that humans have?

Answer 10

Saliva aids with the mixing/chewing of food and lubrication before swallowing

Dogs and cats lack alpha-amylase (starch digestion is not initiated in the oral cavity)

Question 11

Important function of saliva in dogs

Answer 11

Evaporative cooling

Question 12

Describe teeth in dogs

Answer 12

• cutting canine teeth for ripping and tearing
• large molars and premolars can grind and chew large or tough pieces of food (more omnivorous = more chewing)

Question 13

Describe teeth in cats

Answer 13

• teeth are suited for holding and killing small prey animals
• less efficient in chewing and grinding food

Question 14

What is the esophagus? its role?

Answer 14

• short, hollow, muscular tube
• cell-lining produces mucus to help food passage
• uses peristalsis to move the food

Question 15

What is found at the base of the esophagus? Role?

Answer 15

The cardiac sphincter
- relaxation causes food to enter the stomach
- immediately closes again (prevents reflux of food from the stomach to the lower esophagus)

Question 16

What is the stomach? Its roles?

Answer 16

A food reservoir

• mixes food
• regulates flow of digesta into the SI via a sphincter
• initiates chemical digestion of protein (secretion of HCl and pepsinogen = protein unravels)

NO digestion of CHO and fats

Question 17

Sections of the stomach

Answer 17

Proximal and distal
Proximal expands during temporary food storage (allows dogs to eat discrete meals)

Question 18

What affects gastric secretions?

Answer 18

• influenced by the amount of protein in the meal, the meal volume and hormones
• gastric pH varies depending on the type of meal consumed (buffering capacity of the food)

Question 19

What controls the rate of gastric emptying? What is the role of soluble fibre in gastric emptying?

Answer 19

• stomach volume, body weight, water intake and diet type
• high density particles empty slower than smaller sized particles
• hormonal control via macronutrient composition and characteristics

Soluble fiber decreases rate of gastric emptying

Question 20

Differences in the stomach of cats vs dogs

Answer 20

Stomach as storage reservoir is less important for cats than dogs
- Average half emptying times are 22 to 449 mins for cats vs. 72 to 240 mins for dogs
- stomach is simpler for cat than dog (smaller with smaller glandular fundus)

Question 21

What is the SI the primary site of? What happens to chyme

Answer 21

Site of chemical digestion and absorption of fat, starch, sugar, and protein

Acidic chyme moves from stomach into small intestine which stimulates secretion of pancreatic juice which increases the pH of the digesta.
Chyme is mixed with enzymes in the duodenum (which come from duodenal mucosa and pancreas)

Question 22

Functions of the pancreas

Answer 22

Exocrine: secretes enzymes and bicarbonate salts into the gut to establish optimal pH
- enzymes: inactive proteases, lipases and amylases

Endocrine: secrete hormones into the blood

Question 23

What do pancreatic juices of dogs have?

Answer 23

Antibacterial properties

Question 24

Which hormones are released by the pancreas and when?

Answer 24

Insulin released after a meal in dogs

Glucagon stimulates release of aa from muscle

Question 25

What does the liver produce? What happens to it?

Answer 25

Bile
Stored in gall bladder
Released when chyme enters SI (GB contracts in response to food ingestion, emtpying peaks ~30min after meal)
Function: emulsify dietary fat and activate enzymes to aid in fat digestion

Question 26

Describe the dog/cat small intestine microbiology. What is it important for? When might bacteria overgrow?

Answer 26

Dog has simple microbial population
Cat has more bacteria per unit of small intestine digesta, but dogs have more digesta

Important to prevent colonization of pathogenic microbes
Bacteria may overgrow with heat-(over)processed diets (poorly digested = more undigested residue as substrate)

Question 27

Clear distinction between the small intestine of cats vs dogs

Answer 27

Cat: sugar transport systems are not adaptive to varying levels of dietary CHO

Dog: sugar transport systems are highly adaptive to dietary CHO

Slide 19

Question 28

Pancreatic amylase production in cats

Answer 28

About 5% of that in dogs
Relatively non-adaptive

Question 29

How does a cat get blood glucose?

Answer 29

Gluconeogenesis (dietary protein into glucose)
Glycogen

Question 30

Functions, parts, transit time for large intestine

Answer 30

Functions:
- absorption of water and electrolytes
- fermentation of dietary fiber and undigested nutrients from the SI

Parts: cecum, colon and rectum
No villi on surface

Transit time for dogs and cats approx 12h

Question 31

Excreted feces are made up of what? Characteristics changed depending on…

Answer 31

Undigested food, sloughed cells and other endogenous losses, and bacteria

Change depending on type of diet fed (amount of indigestible matter present)

Question 32

Bacterial fermentation produces what?

Answer 32

Short chain fatty acids, lactate, CO2, hydrogen gas, and microbial protein

Fiber used as energy source for bacteria which produce SCFA and microbial protein

Question 33

Control of the GI tract

Answer 33

Nutrient flow:
- from intestine to portal vein
- Functions to control: enzymes, nutrient transporters, peristalsis

Mechanisms
- incretins (intestinal hormones)
- Pancreas (pancreatic hormones, enzymes, bicarbonate)
- nervous system

Question 34

Slide 23

Answer 34

incretins

Question 35

Stimulus for secretion and primary action of gastrin

Answer 35

Stimulus: peptides and aa’s in stomach, distention of stomach

Stimulates: secretion of gastric acid, pepsinogen and glucagon
Inhibits: gastric emptying

Question 36

Stimulus for secretion and primary action of CCK

Answer 36

Stimulus: peptides, aa’s and fa’s in duodenum

Stimulates: pancreatic enzyme secretion and gall bladder contraction
Inhibits: gastric emptying and secretion and relaxes sphincter of oddi

Question 37

Outcome of the control of digested nutrients

Answer 37

• nutrient utilization and deposition
• satiety
• feed intake and feeding behaviour

Question 38

Other control of food intake

Answer 38

• taste receptors
• nutrient receptors