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AVS 305 > Digestion > Flashcards

Digestion Flashcards

1
Q

ruminants

A 
2.8 billion domesticated ruminants
ungulates
Pregastric fermentation
4 compartment stomach
reticulum
rumen
omasum
abomasum
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2
Q

reticulum

A

Honeycomb lining
Formation of food bolus
Regurgitation initiated here
Collects hardware (nails, wire)

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3
Q

rumen

A

Digestion and fermentation vat
Contains anaerobic microbes, fungi, and protozoa
Papillae lining
Absorption of SCFA

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4
Q

omasum

A 
Laminae/manyply lining
muscular folds
Reduces particle size
Absorption of water
Absorption of SCFA
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5
Q

abomasum

A 
True gastric stomach
Proteolytic enzymes
Gastric digestion
Decreased pH from 6 to 2.5
Denatures proteins
Kills bacteria and pathogens
Dissolves minerals (e.g., Ca3(PO4)2)
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6
Q

ruminants

A

Continuous culture fermenters
Input and output
Lignocellulosic substrates used
8 x 1015 mouths to feed

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7
Q

rumen environment

A 
pH 6.0 – 7.0
Highly reduced
10 – 15% dry matter
39°C
260 – 280 mOsm
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8
Q

rumen microbes- bacteria

A 
Bacteria
>2000 species with many strains
25 species at concentrations >107/mL
1010 to 1012 cells/mL
99.5% obligate anaerobes
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9
Q

rumen microbes- fungi

A

Fungi
Known only for about 25 years
Numbers usually low
Digest recalcitrant fiber

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10
Q

rumen microbes- protozoa

A

Protozoa
Large (20-200 microns) unicellular organisms
Prey on bacteria
Numbers affected by diet

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11
Q

symbiotic relationship

A 
Microbes provide to the ruminant
Digestion/fermentation of cellulose and hemicellulose
Energy substrates
Provision of high quality protein
Provision of B vitamins
Detoxification of toxic compounds
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12
Q

microbes to ruminants

A

Digestion of cellulose and hemicellulose
Cellulases are all of microbial origin
Without microbes, ruminants would not be able to use forage crops such as pasture, hay or silage

Energy substrates
End products of fermentation include volatile fatty acids (SCFA) and lactate
Used by animal tissues for energy or lipid synthesis

Fermentation is a metabolic process that converts sugars to acids, gases, and/or alcohol.

Provision of high quality protein
50-80% of absorbed N is from microbes
Improved microbial efficiency will provide more microbial protein
Can get over 3 kg of microbial protein per day
High biological value protein source
Amino acid pattern is very similar to that required by the ruminant animal

Provision of B vitamins
Meets the ruminant’s requirements under most conditions
Niacin may be beneficial in early lactation dairy cows

Detoxification of toxic compounds
Example
Mimosine in Leucaena causes problems
Poor growth, reproduction and hair loss
Hawaiian ruminants, but not those from Australia, have microbes that degrade mimosine so Leucaena could be fed
Transferred rumen fluid to Australia
Inoculated rumen
Fed Leucaena
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13
Q

ruminants

A 
8 – 12 hours/day
Reduces particle size
Only small particles leave reticulorumen
Increases surface area for microbial fermentation
Breaks down impervious plant coatings
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14
Q

bacterial digestion (fermentation) of carbohydrate

A

Microbes ferment carbohydrates into volatile fatty acids
Sugar (quick)
Starch (moderate rate depends on associated factors)
Cellulose and other components of dietary fiber (slower)

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15
Q

bacterial digestion of protein

A

Microbes utilize N, amino acids and peptides for their protein synthesis
Microbes convert dietary proteins into their own proteins
Some amino acid conversion occurs so dietary amino acids do not equal amino acids leaving the rumen

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16
Q

bacterial digestion of lipid

A

Microbial lipases act on triglycerides
Biohydrogenation
Addition of H across double bond to saturate unsaturated fatty acids

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17
Q

biohydrogenation

A

Reduction of double bonds

Result: fatty acids that are more saturated with hydrogen

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18
Q

Factors that Reduce Microbial Growth

A

Rapid, dramatic ration changes
Takes 3-4 weeks for microbes to stabilize
Feed restricted amounts of diet
Feed lots of unsaturated fat
Bacteria do not use fat for energy
Inhibit fiber digestion and microbial growth
Different types of fat have different effects
unsaturated more problematic than saturated

Feed lots of non-structural carbohydrate (starch) to lower rumen pH (rumen acidosis)
Slug feeding
Feed barley or wheat
To prevent acidosis, must balance lactate users and producers

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19
Q

factors that maximize microbial growth

A

Maximum dry matter intake
Balanced carbohydrate and protein fractions
Bacteria need both energy and N for amino acid synthesis
Gradual ration changes
Maintain rumen pH
Keep feed available at all times

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20
Q

why worry about rumen microbes?

A

microbes make ruminants less efficient

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21
Q

pregastric functions

A 
Prehension
Mechanisms vary with behavior and diet
Forelimbs 
Primates, raccoon
Snout
Elephant, tapir
Tongue
Anteater, cow
Lips
Horse, sheep
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22
Q

mastication (pre-gastric function)

A

Mastication
Physical reduction of feed
Especially important in nonruminant herbivores
Teeth adapted to different needs

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23
Q

saliva

A

Lubricate and moisten feed
Rumen buffering
N recycling (urea)
Contains many GI regulatory hormones such as EGF, IGF, and peptide YY

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24
Q

deglutition (swallowing)

A

Reflex initiated by presence of food in pharnyx

Propulsion of food to stomach by esophageal peristalsis

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25
Q

gastric digestion

A

Reservoir for controlled release of digesta to small intestine
Mechanical breakdown
Hydrolytic digestion by acid and enzymes
Mainly protein

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26
Q

production of gastric secretions

A

Gastric pits contain:
Exocrine cells (parietal, chief, mucus cells)
Release secretions of water, hydrochloric acid (HCl), digestive enzymes, mucus, intrinsic factor
Forms gastric mucosal barrier
Endocrine cells (G cells)
Release hormones into blood

27
Q

gastrin

A

Hormone
Regulates gastric juice
Stimulates release of HCl, intrinsic factor, & pepsinogen

28
Q

HCl

A 
Dissolves food particles
Provides acidic environment (pH 2-3) in which digestive enzymes function
Converts pepsinogen to pepsin
Pepsin begins breakdown of protein
Rennin coagulates milk
29
Q

gastric digestion

A

Chief cells produce pepsinogen and gastric lipase found mainly in human infants, rabbits, horses, dogs and pigs
Parietal cells produce HCl and intrinsic factor
HCl denatures protein and assists in the activation of pepsinogen to pepsin
Intrinsic factor is a protein important for the binding and absorption of vitamin B12

30
Q

small intestine

A

Need to break apart nutrients from matrices of food/feeds before absorption
Nutrient digestion primarily in the small intestine
Depends on primary site of fermentation
Principal site of absorption of amino acids, vitamins, minerals and lipids
Glucose and other sugars in nonruminants
Digestion and absorption within SI is rapid
Within 30 minutes of entering SI

31
Q

segments of the small intestine

A 
Duodenum
About 15% of SI
Rich in endocrine cells and receptors
Regulation of digestion and absorption
Receives secretions from pancreas and gallbladder
Jejunum
Major site of absorption in most species
Ileum
Absorption
Peyer’s Patch
32
Q

enzymatic digestion in small intestine

A

Pancreatic enzymes released into duodenum
Intestinal enzymes made in epithelial cells
Constituent enzymes as they are a part of the enterocyte (disaccharidases and peptidases)

33
Q

nutrient digestion

A

Trypsin, chymotrypsin (both from the pancreas) break down polypeptides into peptides
Carboxypeptidase (from pancreas) and aminopeptidase (from small intestine) break down peptides into amino acids

34
Q

importance of pancreas for digestion

A 
Produces enzymes responsible for
50% of carbohydrate digestion
50% of protein digestion
90% of lipid digestion
Numbers for nonruminants
Produces bicarbonate for neutralization of chyme in duodenum
35
Q

pancreatic enzymes for digestion

A 
Pancreatic amylase (starch digestion)
Not secreted as zymogen
Activity limited by pH in ruminants
Pancreatic lipases (lipid digestion)
Not secreted as zymogen
Pancreatic proteases (protein digestion)
Secreted as zymogens activated by intestinal protease, enteropeptidase
Trypsin & chymotrypsin – endopeptidases
Carboxypeptidase – exopeptidase
Nucleases
Degrade DNA and RNA into nucleotides
36
Q

lipid digestion

A

Phospholipase A1 and A2
Hydrolyzes fatty acids from phospholipids
Cholesterol esterase
Hydrolyzes fatty acids from cholesterol esters

37
Q

colon and cecum

A

Site of lower GI fermentation
Site of exchange of water and electrolytes
Storage of digesta (undigested residues)
Little absorption of energy yielding nutrients in most species
Exceptions: fiber eaters that rely on hind gut fermentation (i.e., horse, elephant)
Abundance of goblet cells that secrete mucous

38
Q

nutrient digestion- carbohydrate

A 
Mouth
Salivary amylase
Gastric stomach
No digestion
Small Intestine
Site of action for amylase (from pancreas), maltase, lactase and sucrase (from small intestine)
Large Intestine
Microbial fermentation (like rumen)
39
Q

nutrient digestion- protein

A 
Mouth
No digestion of protein
Gastric stomach
Rennin in nursing animals
coagulates milk proteins
HCl denatures proteins
HCl converts pepsinogen to pepsin
Pepsin breaks down polypeptides
40
Q

nutrient digestion- lipids

A

Mouth
Little digestion of lipids (salivary lipase)
Gastric stomach
Little digestion of lipids
Gastric lipase in human infant, rabbit, horse, dog and pig
Small Intestine
Lipases from pancreas break down triacylglycerides into 2 free fatty acids and 1 monoglyceride
Pancreatic lipase and colipase

41
Q

gastrointestinal (GI) anatomical adaptations

A

GI’s evolved to a certain food supply
Digestion and absorption drastically affect metabolism and nutrient requirements
Classification by types of diets (i.e., carnivores, omnivores, herbivores, etc.) is not necessarily an accurate depiction of GI tract function
Many overlapping features such as significant hind-gut fermentation

42
Q

adaptations to feed sources

A

Gastric capacity and structure
Capacity is greatest in pregastric fermentors
Stomachs act as reservoir
Small stomach in carnivores is related to high nutrient density of the diet
Distribution and composition of epithelial lining varies between species and dietary adaptations

Intestinal length and functions
Small intestine
Less variable among species than stomach and hind gut, but generally shorter in carnivores than in herbivores
Large intestine
Importance of hind gut fermentation dictates variation in structure and size
Some hind gut fermentation occurs in most species

43
Q

fiber digestion

A

Ruminants vs Non-ruminants
In general, pre-gastric fermentation increases the efficiency of fiber digestion

Larger non-ruminants offset their digestive efficiency by eating and passing more

Smaller non-ruminants select more digestible forage components and/or practice coprophagy

44
Q

fiber digestion

A

Ruminants vs Non-ruminants
In general, pre-gastric fermentation increases the efficiency of fiber digestion

Larger non-ruminants offset their digestive efficiency by eating and passing more

Smaller non-ruminants select more digestible forage components and/or practice coprophagy

45
Q

human digestive tract

A

Simple gastric pouch & intestinal tract with small amounts of microbial digestion in large intestine

46
Q

dog

A

Simple gastric pouch & intestinal tract with small amounts of microbial digestion in large intestine

47
Q

horse

A

Simple gastric pouch but large intestine has substantial microbial digestion; cecum contributes to microbial digestion

48
Q

rat

A

Simple gastric pouch but substantial microbial digestion in ceca

49
Q

sheep

A

Substantial pre-gastric fermentation; some potential for microbial digestion in large intestine and caecum

50
Q

kangaroo

A

Substantial pregastric fermentation; some potential for microbial digestion in large intestine and cecum

51
Q

anatomical classification: significance of fermentative digestion

A

All mammals have some fermentative capacity

Importance is directly related to fiber consumption

52
Q

pregastric fermentors

A

Pregastric fermentors
Importance of domestic ruminants in animal production
Cattle, sheep
Other well-known pregastric fermentors include macropod marsupials (e.g., kangaroo), hippopotamus and hamster

53
Q

postgastric fermentors

A

Postgastric fermentors
Cecal fermentors
Mainly rodents and other small herbivores
Often associated with coprophagy
Colonic fermentors
Includes true herbiovores (e.g., horse) and elephant, omnivores (e.g., pig and human), and carnivores (e.g., cat and dog)
Degree of colonic sacculation is related to importance of fiber digestion and fermentative capacity

54
Q

nutrient absorption

A

intestinal villi

55
Q

parts of a villus

A

Villus stalk
Covered with enterocytes (absorptive cells) and goblet cells (mucous secreting cells)
Mucous blanket protects cells from physical damage
Vessels
Lacteal – lymphatic system (lipophilic)
Not found in avian species
Capillaries – Circulatory system (hydrophilic)

Crypts of Lieberkϋhn
Located at base of villus stalk
Source of new enterocytes, goblet cells and endocrine cells (stem cell)

56
Q

nutrient absorption mechanisms

A 
Variety of mechanisms
Diffusion
Facilitated transport
Active transport
Pinocytosis or endocytosis
Dependent upon
Solubility of the nutrient (fat vs water)
Concentration or electrical gradient
Size of the molecule to be absorbed
57
Q

diffusion

A

Small lipid molecules pass freely through membrane

Move down concentration gradient to equalize concentrations

58
Q

facilitated transport

A
  1. Substrate attaches to transporter
  2. Transporter releases substrate on inside of cell
  3. Reverse
59
Q

active transport

A
  1. Carrier loads particle on outside of cell
  2. Carrier releases particle on inside of cell
  3. Carrier returns to outside to pick up another particle

Unidirectional movement against a concentration gradient

ATP – Primary
Electrochemical gradient – Secondary

60
Q

pinocytosis (endocytosis)

A

Substance contacts cell membrane
Membrane wraps around or engulfs substance
Sac formed separates from the membrane and moves into cell

61
Q

nutrient absorption- carbohydrate

A

Active transport for glucose and galactose
Sodium-glucose transporter 1 (SGLT1)
Dependent on Na/K ATPase pump
Facilitated transport for fructose

62
Q

nutrient absorption- protein

A

Multiple energy-dependent transport systems with overlapping specificity for amino acids are present in SI
Na-dependent and Na-independent systems exist

63
Q

nutrient absorption- lipids

A

Fatty acids, 2-monoglycerides, cholesterol, and cholesterol esters move down concentration gradient
Repackaged in intestinal cell
Chylomicrons

AVS 305 (9 decks)

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