Anatomy and Physiology of Digestive Systems and the Process of Digestion Flashcards
Carnivores
feed on animal tissues
Omnivores
feed on animal tissues and plants (ex. raccoons, humans, pigs, bears)
Herbivores
feed on plants
What is the difference between monogastrics and ruminants?
Monogastrics have one major stomach compartment while ruminants have multiple (usually 4) stomach compartments.
What monogastric did we use to model digestion?
the pig
What are the functions of the mouth?
- Prehension
- Ensalivation
- Mastication
- Bolus formation
What is prehension?
grasping food and bringing it into the mouth
prehension varies by species
ex. humans - hand
dog - tongue
goat - lips
What is ensalivation?
mixing food with saliva
What is mastication?
grinding or pulverizing food
What is bolus formation?
rolling food into balls with the tongue and pushing it to the rear of the mouth
What is the pharynx?
The structure that connects the mouth and throat
What are the two types of swallowing?
voluntary and reflex
What is the esophagus?
a muscular structure connecting the pharynx to the stomach
What are the functions of the stomach?
- stores food material
- secretes substances (like mucous and HCl)
- mixing
- moves chyme from stomach to rest of the digestive system
What is the pylorous and what does it do?
The pylorous is the structure that keeps the stomach closed from the small intestine
What is chyme?
partially digested food
What are the interior lining zones of the stomach?
Esophageal
Cardiac
Fundic
Pyloric
What is the function of the cardiac lining zone of the stomach?
it secretes mucous
What is the function of the fundic lining zone of the stomach?
Secretes acid
What is the function of mucous in the stomach?
It protects the stomach lining from the acid
What is present in the gastric fluid of the stomach?
- Mucous
- HCl
- Lipase (in small amounts)
- Rennin
- Pepsinogen (a zymogen)
What is the function of lipase in the stomach?
Lipase an enzyme that breaks down fats; it is not very active in the stomach due to the low pH
What are zymogens?
an inactive form of an enzyme that needs to be activated
How is the zymogen pepsinogen activated?
Pepsinogen is activated when it is exposed to HCl, turning it into its active form of pepsin.
Pepsinogen –(HCl)–> Pepsin
What is the function of pepsin?
Pepsin is an enzyme that breaks down proteins
What is the function of rennin in the stomach?
It coagulates milk in the stomachs of younger animals
What is gastrin? What are its functions?
Gastrin is a hormone produced by the pyloric region of the stomach.
It targets the stomach to produce more secretions.
It is an endocrine hormone.
Describe the flow regulation of gastric fluid.
- Cephalic phase: nerve impulses prepares stomach for incoming food
- Gastric phase: nerve impulses and hormonal response; food is in the stomach; this is a longer phase and gastrin is heavily involved
- Intestinal phase: hormonal response; food is ready to go to the intestines
What is required for the stomach to be emptied?
- fluidity and acidity of chyme in the stomach must be appropriate
- receptivity of the duodenum (first part of the small intestine)
- Pyloric Pump: contractions of stomach become stronger and push food through the pyloric sphincter (pylorous)
What reduces gastric flow rate?
- enterogastric reflex: nerve reflex that reduces pumping action of the stomach
- enterogastrone: a hormone produced by the small intestine; it slows gastric fluid production and flow rate
These processes are initiated by the duodenum
What is enterogastrone?
a hormone produced by the small intestine that slows the production of gastric fluid and the flow rate
Describe the structure of the small intestine
the small intestine contains a long and muscular tube and villi
What are villi and what is their function
villi increase the surface area to absorb nutrients better
What are the functions of the small intestine
- chemical degradation
- absorb nutrients into bloodstream
What are the sections of the small intestine?
- duodenum
- jejunum
- ileum
Where is the entrance of the ducts from the liver and pancreas located on the small intestine?
at the anterior end
What are the types of digestive fluid?
pacreatic, hepatic, intestinal
Describe pancreatic fluid
produced in the pancreas
alkaline pH
contains enzymes, carbonates, and bicarbonates
hormonal control with secretin and cholecystokinin (CCK) occurs
Enzymes present are trypsin (from the zymogen trypsinogen) and chymotrypsin; amylase and carbohydrase; lipase
What is secretin and what does it do?
Secretin is a hormone produced in the duodenum that causes the pancreas to secrete more pancreatic fluid, carbonates, and bicarbonates
What is cholecystokinin and what does it do?
Cholecystokinin (CCK) is a hormone produced in the duodenum that increases the enzyme output of the pancreas
What are some similarities between trypsin and chymotrypsin?
Both are proteolytic (proteases) and both result from zymogen action that work further to break down proteins into amino acids
What is trypsinogen?
a zymogen that is activated to form trypsin
Trypsinogen —(enterokinase)—> Trypsin
What is amylase?
an enzyme that breaks down amylose and amylopectin into smaller components
Why is more fat broken down in the small intestine than in the stomach?
the pH range in more suitable for lipase
Describe hepatic fluid (bile)
produced in the liver
stored in the gall bladder
alkaline pH
contains waste products of liver metabolism
Functions:
1. emulsifying agent
2. neutralize acids
3. aid in absorption
Hormonal controls include the use of CCK and pancreozymin
How does hepatic fluid act as an emulsifying agent?
it breaks up fat to increase the surface area, which helps lipase break down fats further
How does hepatic fluid neutralize acids?
it increases the alkalinity of the solution
How does cholecystokinin work with hepatic fluid?
it controls the release of hepatic fluid from the gall bladder
Describe intestinal fluid
pH is alkaline
contains all of the enzymes as the other fluids
Describe the structure of the large intestine
this intestine is a large, muscular tube
What are the functions of the large intestine?
- stores residues left from the digestive process
- lubricates residue to exit through anus; forms feces
What are the sections of the large intestine?
- cecum
- colon
- rectum
What does the cecum do?
some fermentation occurs in this structure
the cecum is not part of the long tube portion of the large intestine; food enters and leaves through the same opening
not a major part of the pig’s digestive system
similar to the appendix in humans
Define absorption in the context of digestion
movement of materials from the digestive tract into the bloodstream
What are some mechanisms of absorption?
- diffusion (passive)
- osmosis (passive transport of water)
- active transport - requires energy (moves larger materials like fatty acids)
In monogastrics, where does the majority of absorption occur?
unless its water, most things are absorbed by the small intestine
What does the small intestine absorb?
- amino acids
- simple sugars
- fatty acids and glycerol
- vitamins
- minerals
- some water
What does the large intestine absorb?
- water
- small amounts of other substances
What is the portal vein?
The portal vein carries nutrient rich blood from the gastrointestinal tract to the liver, which metabolizes and detoxifies substances before they circulate to the rest of the body.
Define digestion
breakdown of food in the GI tract
Define gastric digestion
food breakdown under acidic conditions
Define intestinal digestion
food breakdown under alkaline conditions
What are the end products of starch absorption and where are they absorbed?
glucose is the end product, absorbed in the small intestine
What are the end products of sugar digestion and where are they absorbed in the monogastric
glucose; absorbed by small intestine
What are the end products of cellulose digestion and where are they absorbed?
monogastrics cannot digest cellulose, it is expelled in feces
What are the end products of lignin digestion and where are they absorbed?
monogastrics cannot digest lignin, it is expelled in feces
What are the end products of protein digestion and where are they absorbed?
proteins broken down to peptide chains in the stomach, absorbed as amino acids in the small intestine
What are the end products of lipid digestion and where are they absorbed?
fatty acids and glycerol; absorbed by small intestine
What are the end products of mineral and vitamin and mineral digestion, and where are they absored?
absorbed as solution by the small intestine
What is the end product of water digestion and where is it absorbed?
water does not change; some absorbed by small intestine, most absorbed by large intestine
Describe the composition of feces
- undigested feed residues (ex. cellulose or lignin)
- bacteria
- mucous
- water
- other digestive process residues (ex. leftover bile)
- epithelial cells
What is the order of digestion in pigs?
- mouth
- pharynx
- esophagus
- stomach
- duodenum
- jejunum
- ileum
- cecum
- colon
- rectum
- anus
What are birds considered in terms of their digestive characteristics?
modified monogastrics
What is the function of the pharynx in birds?
same as in mammals, directs food and air
What are the functions of the beak?
- prehension
- ensalivation
- bolus formation
What is the crop (gullet)?
The crop is a structure that is an outpocket located on the esophagus.
Its functions are to moisten/lubricate food, and to store food. No chemical degradation occurs in the crop.
What is the proventriculus?
The proventriculus is the “true stomach” of the bird located at the end of the esophagus.
Its function is to secrete gastric fluid and acid like HCl.
What is the ventriculus (gizzard)?
The gizzard is the structure where the real work to break down food is done.
Its functions are to ….
1. grind food, particle size reduction
2. mix with gastric fluid (gastric digestion begins in the gizzard)
3. contains grit to help pulverize food
Describe the small intestine in birds.
The duodenum of the bird is a loop structure. The contents that enter the duodenal loop are acidic until they reach the pacreatic and bile ducts. Gastric digestion occurs in the loop too.
What is the major difference between birds and other monogastrics?
Gastric digestion occurs in the duodenum of the small intestine as well as in the gizzard.
Where does intestinal digestion occur in birds?
In the jejunum and ileum.
What digestive fluids participate in digestion for birds?
pacreatic, hepatic (bile), intestinal
Describe the large intestine of birds
The large intestine of the bird has two ceca and a colon
What is the cloaca?
The cloaca is a the common passageway for the digestive, urinary, and reproductive systems in birds
What is the vent?
The vent is the outside opening for birds, similar to the anus.
Where does absorption occur during digestion for birds?
Like regular monogastrics, most absorption occurs in the small intestine, except for water (most of the water is absorbed in the large intestine, some by the small intestine)
What is the order of the digestive process in birds?
- mouth (beak)
- pharynx
- esophagus
- crop/esophagus
- proventriculus (true stomach)
- ventriculus (gizzard)
- duodenal loop
- jejunum
- ileum
- ceca
- colon
- cloaca
- vent
How do we describe horses and rabbits in terms of their digestion?
post-gastric fermenters
What are significant differences between horses and other monogastrics?
- horses utilize their teeth and lips more
- horses have a large ceca
- the large intestine has a larger role in absorption
- horses do not have a gall bladder; the bile duct runs straight from the liver
What role does the large cecum play in horses?
In this structure, microbial fermentation of cellulose and hemicellulose into volatile fatty acids (VFAs) occurs in the cecum as well as the colon
What does the large intestine do differently in horses compared to other monogastrics?
It absorbs VFAs to provide energy
What is the order of digestion in horses?
same as pigs
How are rabbits different than other monogastrics?
- large cecum
- they engage in coprophagy
What is coprophagy and what is its purpose?
Corprophagy is the process of eating fecal pellets. It provides a “second chance” of absorption of nutrients
How do we describe ruminants in terms of their digestion?
pre-gastric fermenters
How is the mouth of a ruminant different than monogastrics?
- Instead of upper incisor teeth, ruminants have a dental pad to help them grind their food (still have upper teeth, just not upper incisors)
- Ruminants produce a large amount of saliva; the saliva also contains sodium bicarbonate, an alkaline buffer that helps keep the rumen pH constant
What are the functions of a ruminant’s mouth?
- during eating: prehension, ensalivation, mastication, bolus formation
- during rumination (aka cud chewing): regurgitation, remastication, reensalivation, reswallowing
cud is just another name for a bolus
What functions do the ruminant pharynx and esophagus have?
same as monogastrics
What are the stomach compartments of the ruminant?
- Rumen (paunch)
- Reticulum (honeycomb)
- Omasum (manyplies)
- Abomasum (true stomach)
Describe the interior surface and function of the rumen.
The rumen is the largest compartment
Interior surface: muscular and covered with millions of papillae - looks like a shag rug
Function: absorption of VFA’s
Describe the interior and function of the reticulum.
Interior surface: looks like a honeycomb
Function: traps large substances to regurgitate
Describe the interior and function of the omasum.
Interior surface: large surface area; conical papillae; several folds on the inner surface increase surface area to aid with absorption.
Function: absorption of water and particle size reduction
Describe the interior and function of the abomasum.
Interior surface: muscular - small inner surface
Function: secretion of HCl and other gastric fluids
What is hardware disease?
Hardware disease is caused when wires, nails, etc. are trapped in the reticulum and irritate the lining. The reticulum is close to the heart, which creates the risk of the foreign body stabbing it. To treat it, a magnet can be dropped into the reticulum to attract the foreign bodies.
This is more of an issue for cattle, because they are more indiscriminate with their prehension. Sheep, in comparison, have more sensitive lips and are less likely to eat nails or wires.
What is the proportion of total volume of stomach compartments for cattle compared to horses.
Cattle: much larger stomach
Stomach: 71%
S. intestine: 18%
L. Intestine: 11%
Horse: much larger intestine proportion
stomach: 8%
s. intestine: 25%
l. intestine: 67%
What are the relative compartment volumes for an immature ruminant?
rumen + reticulum = 30%
omasum + abomasum = 70%
Why do immature cattle have a larger abomasum and smaller reticulo-rumen?
Immature cattle are only drinking milk, not eating heaver foods.
What is the reticular (esophageal) groove?
This is a groove that directs milk directly to the abomasum. Closure is stimulated by suckling action of the calf/lamb/etc. This structure is prominent in immature ruminants.
Why is rennin important in immature ruminants?
Rennin in the abomasum helps the immature ruminant take advantage of immunoglobulins and other milk proteins.
What are the relative compartment volumes for a mature ruminant?
Rumen 65-80%
Reticulum 5%
Omasum 7%
Abomasum 8%
What factors affect rumen development?
- Dry feed amount and characteristics (like courseness)
- Fermentation products - VFA ratios
(butyric acid is important in rumen development)
What is an important characteristic of the digestion within the reticulo-rumen?
No enzymes are secreted by the animal - food is broken down by microbes (strict anaerobes).
What microorganisms are present in the reticulo-rumen?
bacteria and protozoa
What is symbiosis?
Living in close union with mutual benefit for all. The microorganisms have a symbiotic relationship with their host.
How does the host benefit the microorganims present in their digestive system?
- Provides feed
- Fine grinding - rumination
- regurgitation
- remastication
- reinsalivation
- reswallow
- remove microbial waste
- provide constant pH
- provide constant temp.
Why is it important to change a ruminant’s diet incrementally?
Changing a diet gradually allows the bacteria time to adjust their populations to better digest the new feed.
Discuss the microbial relationship to carbs (simple sugars, starch, hemicellulose, cellulose)
these carbs are degraded to VFA’s
What are the three main kinds of VFA’s?
acetic acid (2C)
propionic acid (3C)
butyric acid (4C)
Discuss the microbial relationship to proteins in terms of digestion.
Microorganisms split the proteins into organic acids and NH3, then repackage amino acids into forms more useful for the host.
Discuss the microbial relationship to NPN’s (Non-Protein Nitrogen) in terms of digestion.
carbs are digested to organic acids while the NPN is digested to NH3; the two are then combined into microbial amino acids and proteins, a form more useful to the host
What is the significance of a ruminant’s microbe population to repackage and make microbial proteins?
It is cheaper to use urea or other NPN’s when protein is expensive because they can be converted to proteins by microbes and used by the host.
What can ruminants do with low quality plant proteins?
They can convert these lower quality proteins into higher quality forms.
What is hydrolysis?
breakdown of triglycerides
What does it meant to be saturated in terms of fatty acids?
maxed out with hydrogens, no double bonds
Discuss microbial degradation of lipids in ruminant digestion.
The microbe population hydrolyzes the lipids and saturates them. For instance, if a feed is 15% saturated and 85% unsaturated, it is converted to 86% saturated and 14% unsaturated in the rumen.
What gases are produced by ruminant microorganism fermentation, and what happen to these gases?
- Nitrogen - stays in the rumen
- Ammonia - stays in the rumen
- Carbon Dioxide - expelled via eructation
- Methane - expelled via eructation
Define eructation
getting rid of gas; burping
Define bloat
gas build up; froth covers the esophageal opening
this can affect the diaphragm, which separates the thoracic and abdominal cavities, and cause the animal to suffocate
What materials flow from the reticulo-rumen to the omasum and abomasum?
- microorganisms/microbes
- fermentation products (leftover VFA’s, leftover components from protein fermentation)
- feed residues
- digestible (in abomasum and small intestine)
- not digestible (in abomasum and small intestine; ex.
lignin)
What is the function of the omasum?
absorption of water
What is the function of the abomasum?
same as the stomach of monogastrics; gastric digestion
What is the function of the small intestine in ruminants?
same as monogastrics; absorption
What is the function of the large intestine in ruminants?
same as monogastrics; absorption of water
What are the three types of intestinal movements?
peristalsis
segment and pendular
defecation
Define peristalsis
a wave movement that moves materials through the intestines
Describe segmented and pendular movement of the intestines
a motion that mixes the components being digested
Describe defecation
the only voluntary intestinal movement; the expelling of feces from the body
What process is mostly responsible for absorption by ruminants?
mainly active transport
What does the rumen absorb?
a large amount of VFA’s
What does the omasum absorb?
water and leftover VFA’s
What does the small intestine absorb in ruminants?
amino acids, fatty acids, glycerol, glucose, simple sugars, vitamins, minerals, some water
What does the large intestine absorb in ruminants?
water
What are protected lipids and proteins?
These are proteins and lipids that are protected so the microbe population in the ruminant does not lower the quality of the particular nutrient. This is achieved by coating the nutrient with a coating.
These protected nutrients bypass the rumen and are digested in the small intestine.
Some fats are protected so rumen microbes don’t saturate them.
What happens to proteins in the ruminant digestive process if they are too insoluble?
The microbes cannot effectively work on them, and they bypass the rumen and go directly to the small intestine.
Very low % utilized by microbes
What happens to proteins in the ruminant digestive process if they are very soluble?
If the protein in very soluble, the microbe population does not have enough time to work on the protein. This is inefficient, and much of the protein is wasted.
low % utilized by microbes, but more than insoluble protein
Why is medium solubility protein a good thing for ruminants?
Microbes have the maximum utilization of proteins that are not insoluble but not too soluble
What are some ways to treat proteins to maintain a proper solubility for them?
heating, roasting, pelleting, kibbles, etc.
Do monogastrics or ruminants digest lignin?
No, lignin is expelled in the feces of both types of animals
Compare absorption and needs of vitamins between monogastrics and ruminants.
Monogastrics needs a dietary source of all of the vitamins to be absorbed.
Ruminants only need fat soluble vitamins like Vitamins A and E to be sourced in the diet. Microbes in the rumen synthesize B complex vitamins and Vitamin K.
Compare the need and absorption of minerals between monogastrics and ruminants.
Both require a full complement in their diets.
Which nutrients primarily source energy?
carbs, lipids, and proteins
Which nutrients primarily serve structural purposes?
proteins, minerals, lipids, water
Which nutrients serve as cofactors and coenzymes?
minerals and vitamins
What specifically does digestion do to macromolecules?
splits polymers into monomers
What is intermediary metabolism?
process where nutrients are converted to use by cells
ex.
monomers are converted to simpler compounds
simpler compounds converted to CO2 and H2O by a common pathway
CO2 + H2O + ATP
How many mols of ATP are produced per 100g of carbs, proteins, and lipids respectively?
carbs: 4
proteins: 4
lipids: 9
9/4 = 2.25
lipids produce 2.25 times the amount of energy as carbs or proteins
Define catbolism
breakdown of products (usually releases energy and heat)
Define anabolism
building more complex substances from simple precursors (requires energy)
-genesis
to form (anabolic)
-lysis
to breakdown (catabolic)
-neogenesis
new formation (anabolic)
