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NUTR 3210 > Digestive system > Flashcards

Digestive system Flashcards

1
Q

What does the GI tract consist of?

A

Mouth, esophagus, stomach, small intestine, large intestine, caecum, rectum

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2
Q

what components are added to the GI tract to create the digestive system?

A
  • salivary glands, gall-bladder, liver, pancreas
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3
Q

general function of the mouth in digestion

A
  • mechanical breakdown of food
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4
Q

general function of the esophagus in digestion

A
  • unidirectional tube that connects the mouth to the stomach
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5
Q

general function of the stomach in digestion

A
  • holds food
  • distinguishes the 4 systems from each other
  • can be monogastric, avian, or 4 compartment
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6
Q

general function of the small intestine in digestion

A
  • takes up nutrients into the body
  • “nutrient gateway”
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7
Q

general function of the large intestine in digestion

A
  • flows into caecum
  • majority of gut bacteria resides here
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8
Q

general function of the caecum in digestion

A
  • abundance of gut bacteria
  • roll in breaking down indigestible carbs
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9
Q

general function of the rectum in digestion

A
  • things not digested are excreted from the body
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10
Q

what are different ways you can classify a dietary CHO by for digestion?

A
  • solubility
  • digestability
  • fermentability
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11
Q

solubility of CHOs

A

is a CHO soluble in the aqueous environment of the digestive tract?
yes = soluble
no = insoluble
- determined by physicochemical properties of CHO

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12
Q

digestability of CHOs

A

does the host organism have the enzymes necessary to digest a CHO?
yes = digestible
no = not digestible (fibre)
- determined by the host digestive enzymes

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13
Q

fermentability of CHOs

A

do gut bacteria have the enzymes necessary to break down a CHO?
yes = fermentable
no = non-fermentable
- determines by gut bacteria

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14
Q

4 types of digestive systems

A
  1. simple system (w/o caecum)
  2. simple system (w/ functional caecum)
  3. ruminant system
    4.avian system
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15
Q

simple system w/o caecum: key features

A
  • human, cat, pig, dog
  • monogastric (single stomach)
  • non-functional caecum (still there but does not contribute to fermentation of digestible CHO)
  • hindgut fermenter
  • suited for a nutrient-dense, low fibre diet
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16
Q

how does the oral cavity work in a simple system?

A
  • food is chewed and mixed with saliva
  • 2 enzymes get the ball rolling…
    1. a-amylase: starts to break down CHO
    2. lingual lipase: starts to break down dietary fats
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17
Q

How does the stomach work in a simple system?

A
  • includes the cardia, fundus, body and antrum
  • empty = 50mL, filled = 1-1.5L (remarkable ability to expand when food is consumed)
  • gastric emptying takes 2-6 hours
  • pH is about 2 (acidic)
  • food becomes chyme (food + acid)
  • gastric glands secrete gastric juice (includes H2O, electrolytes, HCl, enzymes)
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18
Q

how does the small intestine work in a simple system?

A
  • includes the duodenum, jejunum and ileum
  • main site for nutrient digestion and absorption
  • surface area = 30m^2
  • intestinal motility is controlled by longitudinal and circular muscles
  • chyme acidity neutralized by pancreatic juice
  • food is digested by pancreatic juice and bile acids
  • soluble fibre = slows down digestion, insoluble = speed up
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19
Q

how does the large intestine (aka colon) work in a simple system?

A
  • by the time food reached the LI most nutrients have already been taken up
  • site of fermentation - break down indigestible carbs
  • production of SCFA aka volatile fatty acids
  • site for water absorption
  • bile acids are taken back up and recycled
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20
Q

What gives the small intestine such a large surface area

A
  1. kercking folds
  2. villi (and crypts) - pertrusions
  3. microvilli
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21
Q

What are the different nutrient transport mechanisms for molecules to pass through the intestinal lumen?

A
  1. Diffusion
    - molecules follow a concentration gradient
    - small molecules with the right chemical properties can pass through with no energy needed
  2. Facilitated diffusion
    - like diffusion but involves a transporter
  3. Active transport
    - requires energy (ATP) to move molecules against a concentration gradient
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22
Q

how can we decide which transport mechanism to use to get molecules from the intestinal lumen to the cytoplams

A
  • solubility of the molecule
  • concentration gradient
  • molecular size
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23
Q

Gut bacteria

A
  • region specific - not evenly distributed along the tract
  • 1000:1 anaerobic to aerobic bacteria
  • very important for the fermentation of non-digestible CHO
  • CHO fermentation produces many compounds (e.g lactate and SCFA)
  • associated with disease
24
Q

simple system w/ functional caecum: key features

A
  • horse, rabbit and hamster
  • pseudo-ruminant
  • hindgut fermenter
  • functional caecum
  • all other regions of the gut function similar to the monogastric system
  • suited for a diet with large amounts of fodder and foraging
25
Q

what is the purpose of a functional caecum in a simple system?

A
  • enormous hindgut (20-30L capacity) filled with bacteria
  • SCFA provide 70% of total energy needs for host
  • site for the production of vitamins
26
Q

what are signs of an energy or nutrient deficiency for animals with a functional caecum?

A
  • Coprophagy (eating dung or feces)
  • young animals eating feces colonize their guts with bacteria
27
Q

where are nutrients absorbed in a simple system w/ a functional caecum?

A

stomach: nothing
small intestine: glucose, amino acids, fatty acids
large intestine/caecum: lactic acid, amino acids, SCFA
- indigestible fibre does not get absorbed
- few of the fat, proteins and CHO are not digested and are excreted from the body

28
Q

lactic acid in horses

A
  • lactic acid is produced in a diet high in carbs for horses
  • horses cannot vomit
  • colic will develop if there is too much lactic acid produced
29
Q

Ruminant (multiple) system: key features

A
  • cattle, sheep, goats
  • stomach is divided into 4 regions: reticulum, rumen, omasum, abomasum
  • system highly suited for animals that eat a high quantity of fodder and forage plant materials
  • all other regions of the gut function similar to the monogastric system
30
Q

ruminant digestion: reticulum

A
  • honeycomb appearance serves as a filter: can capture and trap foreign materials that are accidentally swallowed
  • can cause hardware diease
  • rich in bacteria (fermentation vat)
31
Q

ruminant digestion: rumen

A
  • the largest section of the stomach
  • rich in bacteria (fermentation vat)
  • rumen papillae: similar to vili, increase surface area for absorption
  • food is mixed and partially broken down and stored temporarily
  • 60-80% of total energy produced here as SCFA
32
Q

ruminant digestion: omasum

A
  • resorption of water and some electrolytes
  • filters large particles
33
Q

ruminant digestion: Abomasum

A

digestive enzymes secreted from gastric glasnds (HCl, mucin, pepsinogen, lipase, etc)

34
Q

fermentation in the ruminant system

A
  • fermentation takes place before entering the intestine (foregut digestion)
  • nutrients produced by bacteria are available for digestion and absorption by the ruminant
    2 ways to get rid of products of fermentation…
    1. rumination: partially digested food called cud is regurgitated and chewed further then re-swallowed
    2. eructation: periodic belching where methane gas is released from the stomach - can be bad because energy is lost
35
Q

pros and cons of the ruminant system

A

pros
- vitamin synthesis (B and K)
- non-protein nitrogen used for making protein
cons
- carbohydrates degraded into gases and lost through eructation
- heat production (large methane released)

36
Q

avian system: key features

A
  • chickens, turkeys
  • beaks and claws break up foods into smaller pieces that birds can swallow (don’t have teeth)
  • rapid digestion (can starve if deprived of food for even a few hours)
37
Q

unique components of the avian system

A
  • crop
  • two chambered stomach
  • small intestine
  • ceca
  • large intestine (slight different function)
  • cloaca
38
Q

avian system: crop

A
  • enlarged area of the esophagus
  • well developed in most species but not in all
  • temporary storage location for food
  • food is softened here and often regurgitated to feed offspring
39
Q

avian system: two-chambered stomach

A

Glandular portion: proventriculus
- chemical digestion, gastric enzymes and HCl secreted
- most comparable with monogastric stomach
Muscular portion: Gizzard
- has stone-like objects used for mechanical breakdown
- grind and digest tough food

40
Q

avian system: ceca

A
  • minor site of bacterial fermentation
  • fermentation is not critical for avians but happens because bacteria are here
41
Q

avian system: large intestine

A
  • very short and serves predominantly to connect the small intestine and cloaca
  • a bit of storage of undigested material
  • water absorption
42
Q

avian system: cloaca

A
  • very unique
  • where the digestive, urinary and reproductive system meets
  • makes it difficult to understand how much is actually absorbed in birds
43
Q

What is digestibility?

A
  • measure of the fraction of a specific nutrient (or of energy) that is extracted by the GI tract
    -how much nutrient actually gets absorbed by the body
  • calculated from the amount of nutrient consumed and the amount appearing in feces
  • represents a combination of nutrient release from the food matrix, microbial fermentation and absorption
44
Q

why is determining digestibility important?

A
  • can prevent deficiency and ensure essential nutrients are available to the organism ( to support their lifestyle)
45
Q

measuring digestibility: total collection method

A
  • measures everything that goes in (food) and comes out (feces)
  • allow the animal to adapt to a diet over 7-21 days
  • isolate the animal for quantitative analyses
  • measure intake over a 3-10 day period
  • collect and weight all feces
  • analyze for nutrient
46
Q

how do you calculate the apparent digestibility coefficient?

A

apparent digestibility coefficient = (total intake - total feces) / total intake
the closer to 100%, = almost complete absorption of the nutrient

47
Q

limitations of the total collection method

A
  • accuracy in measuring food intake (e.g. crumbs)
  • metabolic cages create anxiety in animals, causing them to behave abnormally
  • labour intensive
  • animals confined in costly equipment
  • not feasible for captive wild animals (not much control)
48
Q

what do metabolic cages do

A

collect and analyze urine and feces

49
Q

measuring digestibility: Indicator method

A
  • incorporates a marker into the food and tracks it
  • internal marker: a natural component of the feed
  • external marker: a component added to the feed
  • adapt the animal to test diet containing the marker
  • collect a feed and fecal sample
  • analyze each for the marker and nutrient of interest relative to your indicator
50
Q

what is the difference between the total collection method and the indicator method

A
  • indicator method just requires a sample since the marker will appear in both the feed and feces
51
Q

what are characteristics of a marker for the total collection method?

A
  1. non-absorbable
  2. must not affect / be affected by the GI tract (not upset stomach)
  3. must mix easily with the food
  4. easily and accurately measured in samples
52
Q

apparent digestibility coefficient for indicator method

A

(A - B) / A
A = ratio of nutrient/marker in the feed
B = ratio of nutrient/marker in feces

53
Q

advantages of indicator method

A
  • less labour intensive
  • ideal for wild animals
54
Q

What is apparent digestibility?

A
  • under-estimates the true digestibility
    doesn’t take into account…
    1. endogenous secretions
  • epithelial cells (e.g. fatty actids released from dying intestinal cells)
  • secreted into lumen and appear in feces
    2. Bacterial growth in gut
  • nutrient synthesis takes place (e.g. biotin produced by gut bacteria)
    3. Digestive enzymes
  • protein secretion (e.g. digestive enzymes released by cells)
55
Q

What is true digestibility?

A
  • perform a digestibility study using a test diet
  • switch to diet containing none of the nutrient of interest
  • analyze the feces after test diet is cleared
  • subtract the level of nutrient in feces of animals fed the zero nutrient diet from a test diet
56
Q

how can you calculate the true digestibility coefficient?

A

use indicator marker method
(A - (B -C)) / A
A = ratio of nutrient/marker in TEST DIET
B = ratio of nutrient/marker in feces
C = ratio of nutrient/marker in feces after ZERO NUTRIENT DIET

57
Q

what are some factors that affect digestibility?

A
  • feed intake (what are they eating?)
  • particle size (smaller particles have faster transit time)
  • chemical composition (what nutrients?)
  • climate (hotter temps have different digestibility than colder)
  • age (younger can have different efficiency as older)

NUTR 3210 (12 decks)

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