Lecture 1a - Digestive Physiology of Dogs & Cats Flashcards
What is the primary role of the digestive system?
Break down large food molecules into simple forms that can be absorbed by the body for use
Beyond breaking down food, what is another function of the GI tract?
Epithelial layer acts as a barrier; it functions to let things through but also keep things out (ex. bacteria)
What are 2 key clinical signs of the GI tract not working well?
Diarrhea and vomiting
Dogs and cats have a relatively similar GI tract except for what?
Length of the GI tract
- dog has a longer digestive tract, cat has a shorter digestive tract
Dog: BL = 0.75m, SI = 3.9m, LI = 0.6m
Cat: BL = 0.5m, SI = 1.7m, LI = 0.4m
What does intestinal length influence?
retention time of food in the gut; animals have a longer GI tract than their body bc it allows for more digestive and absorptive capacity
What are the structures used to increase digestive and absorptive capacity of the GI tract relative to body weight?
- Villi
- Microvilli
- Coils (of SI)
- Folds
Generally, what type of gastrointestinal system do dogs and cats have?
monogastric gastrointestinal system
What type of diet is a dog adapted to?
An omnivorous diet containing a high proportion of animal tissues
For what macronutrient(s) is the capacity to digest the lowest for a dog?
Fiber!
- for fiber you need microbes and the dog has smaller capacity of GI tract
What is the consequence for fermentation for the dog?
Limited capacity to ferment fiber bc it has a smaller SI in conjunction to body size unlike other species such as a pig
What type of diet is the cat adapted to?
A carnivorous diet
What stimulates the salivary glands to produce saliva?
smell and presence of food
What are the 4 pairs of salivary glands?
- parotid
- mandibular
- sublingual
- zygomatic
What affects saliva amount and composition?
Type of food ingested and its moisture content
What are the 3 roles of the mouth (oral cavity)?
- eat and ingest
- taste
- texture
*must think of both taste and texture when developing pet food
What does saliva aid with?
- the mixing/chewing of food and lubrication before swallowing
*many dogs and cats swallow their food with minimal chewing
Unlike people, what enzyme do dogs and cats lack in their saliva?
Alpha-amylase
= starch digestion not initiated
- an implication could be that there is less glucose sensing in the mouth
For dogs, what is a very important fxn of saliva?
Evaporative cooling
What type of teeth do dogs have and what do they use them for?
- Canine teeth for ripping and tearing
- Large molars and premolars for grinding and chewing large or tough pieces of food
What are cats teeth best suited for?
Best suited for holding and killing small prey animals; less efficient in chewing and grinding food
What is a different between dog and cat teeth?
Dogs have some molars (for grinding and chewing) whereas cats barely have any
What does the cell-lining of the esophagus produce?
Mucus to help food passage
What is the use of peristalsis by the esophagus?
Peristalsis is used to move the food; it only takes a few seconds to reach the stomach
What is found at the base of the esophagus/top of stomach? What does it do?
Cardiac sphincter
- relaxation causes food to enter into the stomach
- immediately closes again to prevent the reflux of food from the stomach to the lower esophagus
What are the 4 functions of the stomach?
- Food reservoir
- Mixes food
- Regulates flow of digesta into the SI
- Initiates chemical digestion of protein; secretion of HCl and pepsinogen; no digestion of CHO and fats
Are CHOs and fats digested in the stomach?
no
What is unique to the stomach relative to the rest of the GI tract?
It’s very acidic pH (2-3)
- acidity causes break of disulfide bonds, starting to unravel the protein which can ONLY happen at an acidic pH
What 2 sections is the stomach divided into? What section expands?
- Proximal section
- expands during temporary food storage which allows dogs to eat discrete meals - Distal section
What is gastric secretion in the stomach influenced by?
- Influenced by the amount of protein in the meal, the meal volume and hormones
How is the rate of gastric emptying controlled?
Rate controlled via:
1. stomach volume
2. body wt
3. water intake
4. diet type
- high density particles empty slower than smaller sized particles
What roles of soluble fibre?
Makes digest more sticky = takes longer for stomach to empty
For what kind of animal would we want to reduce the rate of gastric emptying? How would we do this?
An animal with diabetes; if emptying is rapid there would be a big increase of glucose
Add soluble fiber to decrease the rate of glucose absorption by slowing the rate of gastric emptying
How is the stomach different in a cat vs. dog?
Stomach as a storage reservoir is less important for cats than dogs
- Average half-emptying times are: 22-449 min for a cat vs 72-240 min for a dog
Stomach is simpler for cat than dogs bc animal protein is simpler to digest
- relatively smaller with smaller glandular fundus
What is the small intestine the primary site of?
Primary site of chemical digestion and absorption of fat, starch, sugar, and protein
What is the first thing that happens when acidic chyme moves from the stomach into the SI?
- stimulates the secretion of pancreatic juice which increases pH of digesta; enzymes that work in the I have optimum pH closer to 7
- chyme is mixed with enzymes in the duodenum that come from duodenal mucosa and pancreas
What are the exocrine fxns of the pancreas?
Secretes enzymes and bicarbonate salts into gut to establish optimal pH
- enzymes: inactive proteases, lipases and amylases
What are the endocrine fxns of the pancreas?
secrete hormones into blood
What is unique about the pancreatic juices of a dog?
have antibacterial properites
The pancreas has a role in digestion but also the post-absorptive use of nutrients. What hormones are released by the pancreas and when?
INSULIN and GLUCAGON
- insulin is post absorptive
- glucagon is released during a fasting state when glucose levels are dropping; it acts to release FAs and AAs to maintain glucose profile
What is bile produced by and where is it stored?
Produced: liver
Stored: gall bladder
When is bile released?
When chyme enters SI
- gall bladder contracts in response to food ingestion
- emptying peaks ~30 min after a meal
What is the fxn of bile?
To emulsify dietary fat and activate enzymes to aid in fat digestion
How is dietary fat emulsified?
Via bile produced by the liver
What do the villi of the SI do?
increase SA to increase nutrient absorption
What is the important about the SI microbiology?
Important to prevent colonization of pathogenic microbes
When might bacteria in the SI overgrow?
With heat-(over)processed diets
- over processed food makes protein difficult to digest. if there is too much undigested protein undesired protein fermentation occurs resulting in diarrhea
How is the cat’s SI different from the dog’s?
Cat: sugar transport systems NOT adaptive to varying levels of dietary CHOs (true carnivores)
- free sugars and complex CHO are a negligible % of diet
- no energy wasting to change carrier systems
- pancreatic amylase production about 5% of that in dogs
- pancreatic amylase production is relatively non-adaptive in cats = difficult to upregulate glucose levels in SI (which they shouldn’t have to do anyway)
- AA transporters are highly adaptable
Dog as omnivore: sugar transport systems are hgihly adaptive to dietary CHO
How does the cat get (blood) glucose?
Cat is not eating starch so how is it getting glucose?
GLUCONEOGENESIS!
What are the 2 main fxns of the large intestine?
- absorption of water and electrolytes
- fermentation of dietary fiber and undigested nutrients form the SI
What are the 3 parts of the LI?
Cecum, colon and rectum
- colon is the largest part
What is the transit time for dogs and cats in the LI?
~12 hrs
What are excreted feces made up of?
- undigested food, sloughed cells and other endogenous losses, and bacteria
Can the type of diet impact fecal characteristics?
YES!
- amount of indigestible matter present is the major factor
What does bacterial fermentation in the LI produce?
- SCFA, lactate, CO2, hydrogen gas, and microbial protein
What does digesta movement depend on?
The diet’s physical and nutritional characteristics
How can transit time of digesta be determined?
Using indigestible markers
- measure time elapsed from when first fed to first appearance in feces
How can you slow down vs speed up digesta flow?
Slower = include soluble fiber
Faster = include insoluble fiber (way to reduce constipation)
What are incretions?
Intestinal Hormones
- related to how digesta flow is controlled
What 3 mechanisms are in place to control nutrient flow?
- incretins (intestinal hormones)
- pancreas (pancreatic hormones, enzymes, bicarbonate)
- nervous system
Incretion 1: Gastrin
(cell type, location of action, primary action, stimulus for secretion)
Cell type: Type G
Location: gastric antrum, duodenum
Primary action:
- stimulates: secretion of gastric acid, pepsinogen and glucagon
- inhibits: gastric emptying
Stimulus for secretion:
- peptide and AA’s in stomach
- distension of stomach
Incretin 2: CCK
(cell type, location of action, primary action, stimulus for secretion)
Cell type: Type I
Location: duodenum, jejunum
Primary action:
- stimulates: pancreatic enzyme secretion and gallbladder contraction
- inhibits: gastric emptying and secretion and relaxes sphincter of Oddi
Stimulus:
- peptides, AA’s and FA’s in duodenum
What are the 3 outcomes of control of digested nutrients?
- nutrient utilization and deposition
- satiety
- feed intake and feeding behaviour
What are 2 additional controls of food intake?
- taste receptors
- nutrient receptors
What are the implications of GI tract physiology on ‘regular’ diets for dogs and for cats?
Dogs can deal with quantities of starch and fiber (cats cannot)
