Animal nutrition - monogastric digestion Flashcards
most important salivary glands for digestion
parotid
mandibular
sublingual
pH of various species’ saliva
pig 7.3;
horse 7.5;
dog 7.5;
cattle 8.3
what enzyme does carnivore saliva contain in addition to amylase
lysozyme
(also found in milk, tears etc.)
Salivary α-amylase occurs in which 5 (main) species?
human, monkey, pig, rat, rabbit
Salivary α-amylase does not occur in which 6 (main) species?
very little or absent in
dog, cat, horse,
sheep, cow, goat
amylase digests
starch, glycogen, other polysaccharides
Amylase cleaves only internal alpha (1-4) glycosidic bonds, thereby reducing starch to three different oligosaccharides:
maltose (disaccharide), maltotriose (trisaccharide), and a group of alpha-limit dextrins which contain branch points from amylopectin.
at what pH is amylase active and inactive at?
is active at neutral pH,
is inactivated in stomach at pH of 2
The most important enzyme in the stomach is
pepsin
how is pepsin produced
Gastric chief cells produce pepsinogen which is cleaved to pepsin.
– pepsinogens are activated either
▪ by HCl (produced in parietal cells)
▪ autocatalytically (the existing formed pepsin activates new pepsinogen molecules)
pepsinogen types
pepsinogen A &
pepsinogen C or gastricsin (lesser known name)
pepsinogen A is secreted exclusively by
the chief cells of the gastric corpus, located in the fundic region of stomach
pepsinogen A includes
5 different, but chemically similar compounds
pepsinogen A optimal pH for function
vs pepsinogen C optimal pH for function
A: pH optimum of 1.5…2.2
C: pH optimum 3.0…3.5
pepsinogen C is secreted mainly by
pylorus cells and by the chief cells of the gastric corpus
pepsinogen C incudes 2 distinct compounds
pepsins are
acid-resistant proteinases
specificity is low
degrades about 10…18% of proteins
– prefers to break the peptide bonds near aromatic
amino acids (from the carboxyl acid side of the AA)
such as Phe, Tyr, and Trp
– do not split bonds near Glu, Asp and Leu
Note that Proteins do not degrade in the stomach into…?
into free AAs
they’re broken down into polypeptides/peptides
The pancreas secretes digestive juice that contains proteases (enzymes) that break down polypeptides into smaller peptides or single amino acids. The two major pancreatic enzymes that digest proteins are trypsin and chymotrypsin.
enzyme complex in young animals that coagulates milk
chymosin or rennin or rennet
(Chymosin, known also as rennin)
affects the milk casein in the presence of Ca2+, changes into para casein and coagulates milk
chymosin pH optimum is
5.0
what activates chymosin
exposure to acid
e.g. lactic acid (produced by microbes in forestomachs)
what Gastric enzyme helps to digest the
coagulated milk clot produced by chymosin
cathepsin
in the stomach, lipase is secreted by
the gastric chief cells in the fundic mucosa of the stomach
Has an important role only in young animals’
digestion of fats
– helps to digest curdled milk fats, as the young
animals can not create the necessary amount of
liquid bile to emulsify it in the duodenum
Note that lipase is secreted in the stomach only in young animals, this ability ceases into adulthood.
monogastrics’ gastric lipase pH optimum is
5.0…5.6
what occurs in the ileum
▪ active absorption of digested nutrients (water, vitamins and minerals)
▪ some bacterial fermentation
Nutrient absorption takes place at
the top of the microvilli
turnover of microvili
3…6 days
Duodenum secretion is
intestinal mucus produced by duodenal or Brunner’s gland.
excreted through the duct between the villi of the duodenum
does not contain any enzymes, but acts as lubricant to protect the duodenal wall
pH of duodenum secretion
is alkali (containing bicarbonate)
neutralises the acidic status of chyme coming from the stomach
Bile contains (3)
bile salts, bile pigments, and cholesterol.
Bile is not an enzyme, it emulsifies fats by action of bile acids and their salts.
Bile activates
pancreatic lipase
3 duodenal secretions (secreted into duodenal lumen)
duodenal mucus
bile acid
pancreatic juice
Pancreatic juice contains 3 different types of digestive enzymes
➢ proteolytic -> 50% of protein digestion
➢ amylolytic -> 50% of carbohydrate digestion
➢ lipolytic -> 90% of lipid digestion
division for proteolytic pancreatic enzymes
endopeptidases
exopeptidases
What do endopeptidases do?
proteolytic enzymes that break peptide bonds inside the
molecule of non-terminal AAs (from the carboxyl side)
what type of enzyme is trypsin?
a proteolytic endopeptidase that cuts polypeptides (?) after Arginine or Lysine
what type of enzyme is chymotrypsin?
a proteolytic endopeptidase that cuts polypeptides (?) after Phe, Trp, Tyr & His, Met, Leu
name 3 proteolytic endopeptidases that arent trypsin or chymotrypsin
elastase
collagenase
serine protease
What do exopeptidases do?
splits terminal peptide bonds (i.e. process releases a single AA or dipeptide from the carboxyl acid side of a peptide chain)
name 2 proteolytic exopeptidases
carboxypeptidase A & B
precursor to carboxypeptidase
procarboxypeptidase
precursor to trypsin and chymotrypsin
trypsinogen
chymotrypsinogen
Trypsin has autocatalytic properties meaning
it can activate:
– new molecules of trypsin
– other proteolytic enzymes
This makes it the most important proteolytic enzyme.
name the main amylolytic pancreatic enzyme
alfa-amylase
is similar in its effect to salivary α-amylase
continues the hydrolysis of starch and glycogen
started by salivary α-amylase
is active in the lumen of the duodenum, because
here is the main amount α-amylase
how does pancreatic amylase differ between species?
It’s active in monogastric animals, but lacks in herbivores (small amount + low activity).
Main lipolytic pancreatic enzyme
alfa-lipase
describe lipases’ cleaving action
hydrolyses triglycerides, and removes the FA
residues preferably from 1st and 3rd positions
forms 2-monoglycerides and free FAs
(smaller part of the 2-monoglycerides hydrolyse
further into glycerol and FA, but only to a smaller extent)
Name 4 lesser lipolytic pancreatic enzymes
Phospholipases (A1, A2, C etc.)
cholesterol esterase
tocopherol esterases
retinyl esterases
what degrades cholesterides
cholesterol esterase (specificity is low)
▪ produces cholesterol and FA
what releases α-tocopherol from tocopherol esters
tocopherol esterases
what hydrolyses retinol esters
retinyl esterases
▪ produces retinol and free FAs
Key moment in lipid digestion is their
emulsification
The main fat emulsifying agents are the bile acids and their salts.
Lipids are also emulsified by some proteins such as
casein.
Lipids are also emulsified by some salts of
free FAs
(and monoglycerides which were liberated during digestion)
another name for enteropeptidase
and what is its function
enterokinase
activates pancreatic juice proteolytic enzymes
aminopeptidase does what
breaks peptide bonds from the amino terminus (NH2) side of oligopeptides (as does exopeptidase)
dipeptidase does what
breaks dipeptides
Nucleoprotein degrading enzymes: (3)
– nucleases
– nucleotidase
– nucleosidase
name 2 nucleases
RNA → ribonuclease
DNA → deoxyribonuclease
▪ occurs in oligo- and mononucleotides
nucleosidase cleaves
nucleosides
for example: adenosine into ribose + adenine
name 4 saccharolytic enzymes produced by small intestinal mucosa
- sucrase
- lactase
- maltase
- isomaltase
sucrase splits
sucrose into fructose and glucose
lactase splits
lactose into galactose and glucose
maltase splits
maltose into two glucose
isomaltase splits
the bonds which cannot be broken by amylase or maltase due to α-1,6 linkages
isomaltose and dextrins are hydrolysed into
respectively into glucose and maltose
All saccharolytic enzymes are located, and act, in
the brush border of the small intestine
Final hydrolysis of proteins and carbohydrates in the small intestine takes place at
the top of the microvilli (brush border) membrane (glycocalyx), where the active site of the enzymes is positioned into the gut lumen
Protein digestion in the small intestine results in
amino acids
– also a certain amount of di- and tripeptides are
produced, which are transported into the intestinal cells,
where they are then finally digested into amino acids
Carbohydrate digestion in the small intestine results
in
monosaccharides
– undigestable remaining carbohydrates contain β-type links (hemicellulose, cellulose), and lignin
there are no enzymes synthesized in what part of GI tract
mammalian large intestine
– but there are plentiful symbiotic microbes which produce enzymes
So, indigestible nutrients are subjected to further degradation in the large intestine by microbial enzymes.
name the final products of microbial digestion
of polysaccharides (3)
the volatile fatty acids (VFA)
▪ acetic acid
▪ propionic acid
▪ butyric acid
Note that simple sugars are not produced!
Microorganisms synthesize what type of vitamins
B-group vitamins, which are used by the host animal (but extent of absorption is questionable via the large intestine)
+ vit K
salivary amylase begins the break down of?
starch and glycogen
mono-, di-, oligo- and polysaccharides are produced via cleavage
Where does carbohydrate digestion not take place?
in the stomach
but it does take place in the mouth and duodenum
disaccharides are digested in?
disaccharides into maltose, sucrose, lactose in the duodenum
disaccharides are digested where by what?
disaccharides are digested in the later parts of the small intestine, into glucose, fructose, galactose, by disaccharidase (maltase, sucrase) isomaltase
cruded protein digestion in a monogastric animal begins where by what to produce what?
in the stomach by pepsins and hydrochloric acid (HCl) which produce polypeptides and oligopeptides (NOT amino acids yet)
(in nursing animals this is slightly different. they use chymosin + lactic acid & then cathepsin which can digest the coagulated milk) confirm this.
crude protein digestion after the stomach in monogastrics:
activator enteropeptidase in the duodenum is required to activate proteolytic pancreatic enzymes:
trypsin
chymotrypsin
carboxypeptidase
to produce di- & tripeptides, and amino acids
crude protein digestion in monogastrics after the duodenum use what to produce what
aminopeptidase
dipeptidase
to produce
dipeptides, amino acids (which can be absorbed into the intestinal wall and partially excreted with feces)
Salivary α-amylase is produced more in …
A. cattle
B. dogs
C. pigs
D. goats
C. pigs
actually not very active in dogs
Protein is digested in the stomach into …
A. polypeptides
The enzymes trypsin and chymotrypsin are …
A. exopeptidases –> split terminal peptide bonds
B. endopeptidases –> break peptide bonds inside
the molecule
B. endopeptidases –> break peptide bonds inside
the molecule
Enzyme α-lipase digests …
C. fats
Proteolytic pro-enzymes produced in the pancreas are activated in the duodenum by …
A. enteropeptidase
B. enterokinase
C. trypsin
D. all the above mentioned enzymes
D. all the above mentioned enzymes
The end product of carbohydrate digestion in the large intestine is…
A. volatile fatty acids
