Clinical Biochemistry of Domestic Animals (Sixth Edition) - UMK ...

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Chapter | 14 Gastrointestinal Function
TABLE 14-7 Relationship between Results of the Glutaraldehyde Coagulation Test, Serum (-Globulin)
Concentration, and Death Rate
Source of Calves No. Glutaraldehyde
Reaction
Serum (-Globulin (/dl))
Mean ( SD) Extremes
Death Rate (%)
Calves before ingestion of colostrums 10 Negative 0.18 ( 0.06) 0.1–0.25 —
a
Calves from production unit 60 Negative 0.35 ( 0.13) 0.11–0.63 16.7
b
13 Incomplete 0.60 ( 0.13) 0.42–0.85 7.7
208 Positive 1.46 ( 0.63) 0.42–4.4 3.4
a
Samples of serum were obtained at birth, but no follow-up of calves was made.
b
The death rate of calves that were test-negative was signifi cantly (p 0.01) greater than that of test-positive calves, using t-test for signifi cance of differences between two percentages.
D . Lipids
1 . Absorption of Fats
a . Luminal Phase
The fat in the diet is primarily in the form of triglycerides
or long-chain fatty acids. In the dog, gastric lipase
plays a credible role in fat digestion, leading to the formation
of fatty acids, which help coordinate gastric emptying
and pancreatic secretions. In other species, the initial
step in utilization of triglycerides occurs in the lumen of
the proximal small intestine, where hydrolysis is catalyzed
by pancreatic lipase. The pancreas secretes lipase in active
form. The enzyme requires an oil-water interface for activity,
so only emulsions of fat can be hydrolyzed. Enzyme
activity is directly related to the surface area of the emulsion,
so the smaller the emulsion particle, the greater the
total surface area of a given quantity of triglyceride and the
greater the rate of hydrolysis ( Benzonana and Desnuelle,
1965 ). Bile salts are not an absolute requirement but favor
hydrolysis by their detergent action, which causes formation
of emulsions with small particle sizes and by stimulating
lipase activity within the physiological pH range
of the duodenum. A colipase is present in the pancreatic
secretion, which facilitates the interaction of lipase with its
triglyceride substrate and protects lipase from inactivation
( Borgstrom and Erlanson, 1971 ).
Pancreatic lipase splits the ester bonds of triglycerides
preferentially at the 1 and 3 positions so that the major end
products of hydrolysis are 2-monoglycerides and free fatty
acids. Both compounds are relatively insoluble in water but
are brought rapidly into micellar solution by the detergent
action of bile salts. The mixed micelles so formed have a
diameter of approximately 2 nm and are believed to be the
form in which the products of fat digestion are actually
taken up by the mucosal cell ( Hofmann and Small, 1967 ).
The intraluminal events that occur in fat absorption are
schematically summarized in Figure 14-6 .
Conjugated
bile salts
(liver)
Lipase
(pancreas)
Reabsorbed
(ileum)
Lumen
Diglycerides
Monoglycerides
Fatty acids
Micelle
Triglycerides
(stomach)
Chylomicrons
(lymphatics)
FIGURE 14-6 Intraluminal events during fat absorption. From
Isselbacher (1967) .
b . Mucosal Phase
The initial step in intestinal transport of fat is the uptake of
fatty acids and monoglycerides by the mucosal cell from
micellar solution. The precise mechanism is yet unclear,
but present evidence suggests that the lipid contents of the
micelle are somehow discharged at the cell surface and
enter the mucosal cell in molecular rather than micellar
form ( Isselbacher, 1967 ). The net effect is the absorption of
the end products of lipolysis and the exclusion of bile salts,
which are absorbed farther down the intestine, primarily
in the ileum. Uptake of fatty acids appears to be a passive
process having no requirement for metabolic energy.