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AVS 305 > Digestion > Flashcards

Digestion Flashcards

(63 cards)

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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
gastric digestion
Reservoir for controlled release of digesta to small intestine Mechanical breakdown Hydrolytic digestion by acid and enzymes Mainly protein
26
production of gastric secretions
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
gastrin
Hormone Regulates gastric juice Stimulates release of HCl, intrinsic factor, & pepsinogen
28
HCl
``` 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
gastric digestion
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
small intestine
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
segments of the small intestine
``` 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
enzymatic digestion in small intestine
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
nutrient digestion
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
importance of pancreas for digestion
``` 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
pancreatic enzymes for digestion
``` 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
lipid digestion
Phospholipase A1 and A2 Hydrolyzes fatty acids from phospholipids Cholesterol esterase Hydrolyzes fatty acids from cholesterol esters
37
colon and cecum
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
nutrient digestion- carbohydrate
``` 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
nutrient digestion- protein
``` 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
nutrient digestion- lipids
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
gastrointestinal (GI) anatomical adaptations
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
adaptations to feed sources
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
fiber digestion
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
fiber digestion
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
human digestive tract
Simple gastric pouch & intestinal tract with small amounts of microbial digestion in large intestine
46
dog
Simple gastric pouch & intestinal tract with small amounts of microbial digestion in large intestine
47
horse
Simple gastric pouch but large intestine has substantial microbial digestion; cecum contributes to microbial digestion
48
rat
Simple gastric pouch but substantial microbial digestion in ceca
49
sheep
Substantial pre-gastric fermentation; some potential for microbial digestion in large intestine and caecum
50
kangaroo
Substantial pregastric fermentation; some potential for microbial digestion in large intestine and cecum
51
anatomical classification: significance of fermentative digestion
All mammals have some fermentative capacity | Importance is directly related to fiber consumption
52
pregastric fermentors
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
postgastric fermentors
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
nutrient absorption
intestinal villi
55
parts of a villus
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
nutrient absorption mechanisms
``` 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
diffusion
Small lipid molecules pass freely through membrane | Move down concentration gradient to equalize concentrations
58
facilitated transport
1. Substrate attaches to transporter 2. Transporter releases substrate on inside of cell 3. Reverse
59
active transport
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
pinocytosis (endocytosis)
Substance contacts cell membrane Membrane wraps around or engulfs substance Sac formed separates from the membrane and moves into cell
61
nutrient absorption- carbohydrate
Active transport for glucose and galactose Sodium-glucose transporter 1 (SGLT1) Dependent on Na/K ATPase pump Facilitated transport for fructose
62
nutrient absorption- protein
Multiple energy-dependent transport systems with overlapping specificity for amino acids are present in SI Na-dependent and Na-independent systems exist
63
nutrient absorption- lipids
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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