Postabsorptive period

Answer E. Hepatic fatty acid oxidation generates energy in the postabsorptive period when pyruvate is being converted to OAA for glucose biosynthesis. 

On the basis of the resnlts with the obese, starvation can be divided arbitrarily into five phases the postabsorptive period, early starvation, intermediate starvation, prolonged starvation and, finally, the premortal period. Although these are characterised by different metabolic patterns, the transition from one period to another is gradnal. Some of the changes in the postabsorptive period and early starvation are described elsewhere in this book bnt they are bronght together in this chapter for completeness. 

The postabsorptive period begins several hours after the last meal, when the contents of the small intestine have... 

Increased protein synthesis The body cannot store protein in the same way that it maintains glycogen or triacylglycerol reserves. However, a transient increase in the synthesis of hepatic proteins does occur in the absorptive state, resulting in replacement of ary proteins that may have been degraded during the previous postabsorptive period (see Figure 24.3, ) ... 

EXAMPLE 13.2 It is important to distinguish between a nondangerous decrease in blood glucose concentration that stimulates a metabolic response and an overtly hypoglycemic episode. During the postabsorptive period, blood glucose concentration falls to 4 mM, and this is sufficient to stimulate the appropriate hormonal responses that, in turn, stimulate the mobilization of glycogen stores. 

Fig. 13-1 Blood glucose concentration during postabsorptive period.

Fig. 13-5 Glucose release from glycogen in the liver into the blood in the postabsorptive period after a meal, and its use by the brain.

Infusion of too much glucose over an extended period in the treatment of hypoglycemia is dangerous (101). Glucose utilization in the postabsorptive state is 2 mg/ kg/minute and can increase, if insulin concentrations are high, to 6 mg/kg/minute (about 600 g/day in a 70 kg individual). It is better to infuse glucose in concentrations of 10 or 20% rather than 40%. 

If we eat another meal within a few hours, we return to the fed state. However, if we continue to fast for a 12-hour period, we enter the basal state (also known as the postabsorptive state). A person is generally considered to be in the basal state after an overnight fast, when no food has been eaten since dinner the previous evening. By this time, the serum insulin level is low and glucagon is rising. Figure 3.1 illustrates the main features of the basal state. 

The rate and pattern of amino acid utilization by different tissues change with dietary and physiologic state. Two such states, the postprandial period following a high-protein meal and the hypercatabolic state produced by sepsis or surgical trauma, differ from the postabsorptive state with respect to the availability of amino acids and other fuels and the levels of different hormones in the blood. As a result, the pattern of amino acid utilization is somewhat different. 

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