An Sc 464 Term Exam 1

What is the role of the gastrointestinal tract?

To break down large food molecules into simple forms that can be absorbed by the body for use. To get nutrients out of the diet and immunity via barrier function (epithelial cells keep bacteria out).

What are clinical signs if the GI tract is not working well?

Feces becomes thinner to the point of diarrhea (the body is attempting to flush something out, nutrient loss occurs). Vomiting (usually due to something in the stomach)

Dogs and cats have similar GI tracts with the exception of what? What does this difference influence?

length, cats are shorter which influences retention time of food in the gut

What are the structures used to increase absorptive capacity relative to body weight? (From largest to smallest)

Coils → folds → villi → microvilli

List the four macronutrients

• protein

• lipids/fat

• starch (CHO)

• fibre (CHO)

Starch vs fibre: which is more easily broken down?

starch

For what macronutrient is the capacity to digest the lowest?

fibre

What is the consequence for fermentation?

Fibre can only be fermented in the body with a monogastric system, not degraded for nutrients. Pigs have a higher capacity to degrade fiber than dogs do, but still cannot completely because they are monogastric.

True or false: Cats have a hard time digesting raw starch

True

What are the roles of the mouth (oral cavity)?

• aiding mixing/chewing of food and lubrication

• in dogs evaporative cooling

• protection for the esophagus

• very limited anitbacterial function

• no digestion

What do dogs and cats lack in their saliva that prevents starch digestion from being initiated?

a-amylase

What is the difference between dog and cat teeth?

Dog teeth is better suited for ripping and tearing. They have large premolars for grinding and chewing food. Cats have teeth suited for holding and killing small prey animals, but are less efficient for chewing and grinding food.

How does the esophagus move food from the mouth to the stomach?

peristalsis, only takes a few seconds

True or false: The cardiac sphincter at the top of the stomach causes food to enter into the stomach when relaxed

True

What are the roles of the stomach?

Acts as a food reservoir, mixes food, regulates flow of digesta into the SI, and initiates chemical digestion of protein. Allows an animal to separate food intake behaviour from digestion.

How does the stomach disrupt the 3D-structure of food?

Kickstarts protein digestion via the secretion of HCL and pepsinogen. There is no digestion of carbohydrates or fats.

What about the stomach allows dogs to eat discrete meals?

It is expanded into proximal and distal sections. The proximal expands during temporary food storage.

Why is the functionality of the stomach difficult to study?

It is difficult to do surgery or put probs into the stomach

What influences gastric secretion?

• the amount of a protein in the meal

• meal volume

• hormones

• pH varies depending on the type of meal consumed and the buffering capacity of the food

What are the roles of soluble fibre?

Slows down gastric emptying

What is the difference between a cat and dog stomach?

Cats eat more frequently than dos. Their stomach is simpler and better set up to deal with protein and fat than plant based particles. The stomach as a storage reservoir is less important for cats than dogs.

What occurs in the small intestine?

primary site of chemical digestion and absorption of fat, starch, sugar and protein. Contains acidic chyme from the stomach that stimulates the secretion of pancreatic juice to increase the pH of digesta.

What are the exocrine functions of the pancreas?

Secretes enzymes and bicarbonate salts into the gut to establish optimal pH like inactive proteases, lipases and amylases. The location allows for the easy secretion of enzymes at the start of the SI.

What are the endocrine functions of the pancreas?

Secrete hormones into the blood. Insulin is secreted after a meal and glucagon is released several hours after a meal.

True or false: The pancreas has a role in digestion but also post absorptive use of nutrients

True

What is the role of the liver?

digestion and post absorptive use of nutrients. Produces bile that is stored in the gall bladder. The gall bladder secretes gall for fat digestion of long chain FA. Bile is released when chyme enters the SI to emulsify dietary fat and activate enzymes to aid in fat digestion.

How is dietary fat emulsified?

Bile acids

What is important about small intestine microbiology?

To prevent colonization of pathogenic microbes. Bacteria may overgrow with heat processed/over processed diets because they are poorly digestible. Undigested protein cannot be used as AA, so it stays in the gut and can be used by pathogenic bacteria like e coli.

Cat versus dog small intestine

Cat sugar transport systems are not adaptive to varying levels of dietary carbohydrates because they are true carnivores. This is not a problem because free sugars and complex carbs are usually a negligible percentage of their diet. They don’t waste energy to change carrier systems. Pancreatic amylase production is about 5% that of dogs, and is relatively non adaptive in cats. But AA transporters are highly adaptable, especially for arginine. Because dogs are omnivores their sugar transport systems are highly adaptive to dietary carbs. They have a very good capacity to digest starch to get glucose.

How does the cat get (blood) glucose?

Protein gets converted into glucose by gluconeogenesis.

What are the main functions of the large intestine?

The absorption of water and electrolytes. The fermentation of dietary fibre and undigested nutrients from the SI. Contains a complex microbial ecosystem made up several hundred species of bacteria that are mostly strict anaerobes.

What are the parts of the LI and which is the largest?

Cecum, colon, and rectum. The colon is the largest.

What is excreted feces made up of?

Undigested food, sloughed cells, endogenous losses, bacteria.

What does bacterial fermentation produce?

SCFA, lactate, CO2, hydrogen gas, and microbial protein.

What is the outcome of the GI tract?

Digested nutrients to get control over nutrient flow from the intestine to portal vein via enzymes, nutrient transporters, peristalsis, and some nervous system control. Also incretins. The pancreas releases pancreatic hormones, enzymes and bicarbonates.

How does communication work to control the GI tract?

Incretins (intestinal hormones)

Incretions: Gastrin

Cell type: Type G

Location of action: gastric, antrum, duodenum

Primary action: (stimulates) secretion of gastric acid, pepsinogen and glucagon (inhibits) gastric emptying

Stimulus for secretion: peptides and AA’s in stomach, distention of stomach

Incretions: CCK

Cell type: Type I

Location of action: duodenum, jejunum

Primary action: (stimulates) pancreatic enzyme secretion and gallbladder contraction (inhibits) gastric emptying and secretion and relaxes sphincter of Oddi

Stimulus for secretion: peptides, AA’s and FA’s in duodenum

Outcome of control of digested nutrients

• nutrient utilization and deposition

• satiety

• feed intake and feeding behaviour

True or false: horses are monogastric hindgut fermenters or obligate hindgut fermenters, with a large caecum for fermentation

True

Why would horses have such a large LI?

They graze and eat a lot of grain (so fiber). There are lots of microbes in their LI, and they have no rumen. The length ensures that they absorb nutrients properly.

List reasons horses might colic?

• gas colic (excessive gas production, which can occur in the large colon)

• (simple) obstruction

• strangulation (something on the outside putting pressure on the GI tract)

• infarction

• inflammation

• ulceration

What macronutrient are horses best and worst adapted for to utilize?

Best is fibre

Worst is fat

What adaption would allow horses to increase chewing intensity?

Their teeth are constantly growing and are worn down all the time when they chew.

Oral cavity in horses

Saliva secretion is stimulated by mastication. They have very intense chewing compared to dogs and cats. Their saliva contains a small concentration of bicarbonate to provide a buffer against stomach acids and allows some microbial fermentation in the stomach.

Horse teeth

Require lifetime maintenance. There are approx 36: 12 incisors, 12 premolars, 12 molars. May have canines and wolf teeth.

Can horses vomit?

No because they have a very strong cardiac sphincter at the top of their stomach

What are the three regions of the horses stomach and what to they do?

Oesophageal region (squamous epithelium), Fundic region (glandular epithelium: HCl from parietal cells and pepsin from zymogen cells), Pyloric region (glandular epithelium that secretes gastrin)

What is the relative emptying time of a horses stomach and how does it compare to that of dogs and cats?

In horses it is about 120 minutes, which is short. In dogs it is 5-10 hours and in cats it is 3-6 hours. Horses must eat more frequently (grazers).

How may short gastric emptying time relate to feeding behaviour?

Horses must eat much more frequently due to their short relative emptying time. This is why they are grazing animals.

What is the small intestine in horses composed of and what occurs there?

Composed of the duodenum, jejunum and lleum which each have a distinctive mesentery. It is the primary site of digestion and absorption of protein, starch, and fat.

What is the exocrine and endocrine rolls of the pancreas in horses?

Exocrine: Secretes enzymes and bicarbonate salts into the gut. The enzymes include inactive proteases, lipases and amylases.

Endocrine: Secretes hormones into the blood. Insulin immediately post a meal and glucagon during starvation.

What is the role of insulin?

Post absorptive control of nutrients (takes up glucose into cells)

Liver and bile in horses

Bile is produced by the liver. But horses DO NOT have a gall bladder, so instead bile is constantly trickling into the SI. It emulsifys dietary fat and activates enzymes to aid in fat digestion.

Cecum in horses

Is very large and contains a microbial population similar to the rumen. Is responsible for microbial synthesis of SCFA and protein. Kickstart of large quantities of fermentation of fibre.

What are the 4 large compartments and 3 major flexures in the large colon of a horse?

1. Right ventral colon

(sternal flexure)

2. Left ventral colon

(pelvic flexure)

3. Left dorsal colon

(diaphragmatic flexure)

4. Right dorsal colon

Which companion animal can adapt quickest to a change in diet?

Dog

What is the difference between the GI tract of a horse, dog and cat?

Horses have an extensive large intestine. Dogs have a larger LI than horses, longer GIT than cats. Cats have the shortest GIT.

What is the key energy substrate for each passing through the enterocyte of horses?

SCFA/VFA (gets converted to glucose)

What is the key energy substrate for each passing through the enterocyte of dogs?

Glucose (from starch digestion and gluconeogenesis)

What is the key energy substrate for each passing through the enterocyte of cats?

AA (need gluconeogenesis to convert to glucose)

What are the five basic functions of the body that nutrients are involved in?

1. Act as structural components

2. Enhance (or involved in) chemical reactions of metabolism (energy and protein metabolism)

3. Transport substances into, throughout or out of the body

4. Maintain body temperature

5. Supply energy

What is the easiest way to disrupt the basic functions in the body that nutrients are involved in?

fasting

Essential nutrients

Nutrient can not be synthesized by the animal and must be obtained in the food

Conditionally essential nutrients

a non essential nutrient that becomes an essential nutrient when certain physiologic conditions result in relative deficiency (like lactation)

Non-essential nutrients

nutrient can be synthesized in adequate quantities by animals and are not specifically required in the food

Digestibility

The percentage of food’s gross nutrient content released following mechanical and chemical digestive processes. Is influenced by both food characteristics and the digestive efficiency of the host. Can be measured by collecting a fecal sample. Then subtracting the fecal nutrient content from the diet nutrient content to get the undigested nutrient.

What are some examples of nutrients that sometimes are digestible but not available?

Lysine: lysine with a sugar attached cannot be used for protein synthesis. The body cannot store it so it leaves the body in urine.

Bioavailability

The degree to which a nutrient becomes available to support metabolism after digestion and absorption

Apparent digestibility

Nutrient intake minus nutrient excretion in feces

True digestibility

Nutrient intake minus nutrient excretion in feces corrected for all intestinal endogenous losses

Intestinal endogenous losses

Excretion of nutrients into gut due to cell turn over, intestinal secretions, sloughing of intestinal cells, etc

What are examples of intestinal secretions?

Bicarbonate and bile salts

Simple carbohydrates

Monosaccharides (like glucose, fructose, and galactose) and disaccharides (like maltose, sucrose, and lactose)

Complex carbohydrates

Oligosaccharides (like fructo-, galacto-oligosaccharides) and polysaccharides (like starch, cellulose, and glycogen)

Do glucose and VFA provide the same amount of energy when absorbed?

No

How do NSP relate to dietary fibre?

NSP + lignin creates dietary fiber

Glycosidic bonds affect the digestibility of carbohydrates. What are the two types of glycosidic bonds? They determine whether the carbohydrate is digestible by mammalian enzymes, which is which?

Alpha (starch) and Beta (fiber)

What carbs are digestible for mammalian enzymes?

Sucrose, maltose, lactose, starch, and glycogen

What carbs are digestible for bacterial enzymes?

Oligosaccharides and non-starch polysaccharides (which arent dietary fiber) like cellulose, hemicellulose, and pectin.

What are the implications of GI tract physiology on regular diets for dogs?

They can include plant based diets and be heat processed.

What are the implications of GI tract physiology on regular diets for cats?

Cats should not have heat processed diets. They should have mostly protein and fat from animal based tissues. Kibble has some plant based products since they are needed for binding.

Do glucose and VFA provide the same amount of energy when absorbed?

No. Because glucose is already in the correct energy form. VFAs must be converted to glucose. During this process some energy is lost during conversion.

What affects the digestibility of starch? What are the types of starch?

Granular structure. Rapidly digestible (starches in cooked and extruded petfood), slowly digestible starch (raw or uncooked), resistant starch (RS, some plant starches resist enzymatic digestion).

The amount of starch types depends on starch source type, and extent of processing.

What is the difference between amylose and amylopectin?

Amylose is more coily. Amylopectin is more structured and is rapidly digestible.

Are starchy foodstuffs important for dogs and cats?

Yes, it is used as a binding ingredient in kibble. Its not that important in canned food.

What are examples of cereal grains, pulse grains, and tubers?

Cereal grains → corn, wheat, rice, barley

Pulse grains → lentils, chickpeas, kidney beans, black beans

Tubers → potatoes, yams

How is energy produced from carbohydrates? Pathways?

The TCA cycle via beta oxidation of fats

What are the functions of carbohydrates?

• energy (ATP)

• source of heat

• DNA and RNA framework (ribose, deoxyribose)

• building blocks for other nutrients (non-essential amino acids, fat, vitamins, glycolipids)

• storage of energy

Can mammals digest prebiotics?

No, only bacteria can

What are examples of prebiotics?

Oligosaccharides, resistant starch

What are prebiotics?

They are mostly carbohydrates. A substrate that is selectively utilized by host microorganisms conferring a health benefit.

What do you need to produce fermentation end products?

Bacteria

Function of dietary fibre?

• to increase in bulk and water in intestinal contents

• regular normal bowel function (constipation or diarrhoea)

• Fermentation end products (acetate, propionate, butyrate) important in maintaining health of colon

• Fermentation decreases colonic pH (pathogenic bacteria is pH sensitive and for the prevention of intestinal disorder)

• However fibre may reduce absorption of other nutrients

Do cats and dogs need crude protein?

No, what they need is essential amino acids. The requirement for sufficient nitrogen to allow synthesis of non-essential amino acids.

What is measured to obtain CP values?

The amount of protein in the diet. N x 2.65 = crude protein

What is the first most limiting essential amino acids and why?

Lysine because plant protein contains less lysine than animal protein

What are the second most limiting essential amino acids?

Tryptophan and methionine

Which diets should be supplemented with synthetic taurine?

Vegetarian or plant based diets

Taurine are essential for cats, why?

They cannot make enough because of their rapid amino acid metabolism.