Digestion Flashcards
ruminants
2.8 billion domesticated ruminants ungulates Pregastric fermentation 4 compartment stomach reticulum rumen omasum abomasum
reticulum
Honeycomb lining
Formation of food bolus
Regurgitation initiated here
Collects hardware (nails, wire)
rumen
Digestion and fermentation vat
Contains anaerobic microbes, fungi, and protozoa
Papillae lining
Absorption of SCFA
omasum
Laminae/manyply lining muscular folds Reduces particle size Absorption of water Absorption of SCFA
abomasum
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)
ruminants
Continuous culture fermenters
Input and output
Lignocellulosic substrates used
8 x 1015 mouths to feed
rumen environment
pH 6.0 – 7.0 Highly reduced 10 – 15% dry matter 39°C 260 – 280 mOsm
rumen microbes- bacteria
Bacteria >2000 species with many strains 25 species at concentrations >107/mL 1010 to 1012 cells/mL 99.5% obligate anaerobes
rumen microbes- fungi
Fungi
Known only for about 25 years
Numbers usually low
Digest recalcitrant fiber
rumen microbes- protozoa
Protozoa
Large (20-200 microns) unicellular organisms
Prey on bacteria
Numbers affected by diet
symbiotic relationship
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
microbes to ruminants
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
ruminants
8 – 12 hours/day Reduces particle size Only small particles leave reticulorumen Increases surface area for microbial fermentation Breaks down impervious plant coatings
bacterial digestion (fermentation) of carbohydrate
Microbes ferment carbohydrates into volatile fatty acids
Sugar (quick)
Starch (moderate rate depends on associated factors)
Cellulose and other components of dietary fiber (slower)
bacterial digestion of protein
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
bacterial digestion of lipid
Microbial lipases act on triglycerides
Biohydrogenation
Addition of H across double bond to saturate unsaturated fatty acids
biohydrogenation
Reduction of double bonds
Result: fatty acids that are more saturated with hydrogen
Factors that Reduce Microbial Growth
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
factors that maximize microbial growth
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
why worry about rumen microbes?
microbes make ruminants less efficient
pregastric functions
Prehension Mechanisms vary with behavior and diet Forelimbs Primates, raccoon Snout Elephant, tapir Tongue Anteater, cow Lips Horse, sheep
mastication (pre-gastric function)
Mastication
Physical reduction of feed
Especially important in nonruminant herbivores
Teeth adapted to different needs
saliva
Lubricate and moisten feed
Rumen buffering
N recycling (urea)
Contains many GI regulatory hormones such as EGF, IGF, and peptide YY
deglutition (swallowing)
Reflex initiated by presence of food in pharnyx
Propulsion of food to stomach by esophageal peristalsis
gastric digestion
Reservoir for controlled release of digesta to small intestine
Mechanical breakdown
Hydrolytic digestion by acid and enzymes
Mainly protein
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
gastrin
Hormone
Regulates gastric juice
Stimulates release of HCl, intrinsic factor, & pepsinogen
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
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
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
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
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)
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
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
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
lipid digestion
Phospholipase A1 and A2
Hydrolyzes fatty acids from phospholipids
Cholesterol esterase
Hydrolyzes fatty acids from cholesterol esters
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
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)
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
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
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
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
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
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
human digestive tract
Simple gastric pouch & intestinal tract with small amounts of microbial digestion in large intestine
dog
Simple gastric pouch & intestinal tract with small amounts of microbial digestion in large intestine
horse
Simple gastric pouch but large intestine has substantial microbial digestion; cecum contributes to microbial digestion
rat
Simple gastric pouch but substantial microbial digestion in ceca
sheep
Substantial pre-gastric fermentation; some potential for microbial digestion in large intestine and caecum
kangaroo
Substantial pregastric fermentation; some potential for microbial digestion in large intestine and cecum
anatomical classification: significance of fermentative digestion
All mammals have some fermentative capacity
Importance is directly related to fiber consumption
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
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
nutrient absorption
intestinal villi
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)
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
diffusion
Small lipid molecules pass freely through membrane
Move down concentration gradient to equalize concentrations
facilitated transport
- Substrate attaches to transporter
- Transporter releases substrate on inside of cell
- Reverse
active transport
- Carrier loads particle on outside of cell
- Carrier releases particle on inside of cell
- Carrier returns to outside to pick up another particle
Unidirectional movement against a concentration gradient
ATP – Primary
Electrochemical gradient – Secondary
pinocytosis (endocytosis)
Substance contacts cell membrane
Membrane wraps around or engulfs substance
Sac formed separates from the membrane and moves into cell
nutrient absorption- carbohydrate
Active transport for glucose and galactose
Sodium-glucose transporter 1 (SGLT1)
Dependent on Na/K ATPase pump
Facilitated transport for fructose
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
nutrient absorption- lipids
Fatty acids, 2-monoglycerides, cholesterol, and cholesterol esters move down concentration gradient
Repackaged in intestinal cell
Chylomicrons
