Lactate anaerobic glycolysis

Gluconeogenesis Formation of glucose from precursors other than carbohydrates (especially by the liver and kidney) using amino acids from proteins, glycerol from fats, or lactate produced by muscle during anaerobic glycolysis. 

Hypoxia deprives the ETC of sufficient oxygen, decreasing the rate of ETC and ATP production. When ATP levels fell, glycolysis increases and, in the absence of oxygen, wiU produce lactate j (lactic acidosis). Anaerobic glycolysis is not able to meet the demand of most tissues for ATP, I especially in highly aerobic tissues like nerves and cardiac muscle. 

We know that anaerobic glycolysis of glncose yields pyruvate and/or lactate, interconvertable metabolites. Pyruvate is converted into acetyl-SCoAin the following reaction, catalyzed by the pyruvate dehydrogenase complex ... 

Figure 6.3 (a) Glucose and glycogen as substrates for aerobic and anaerobic glycolysis. For aerobic glycolysis, pyruvate is converted to acetyl-CoA for anaerobic glycolysis pyruvate is converted to lactate. 

In cells that lack mitochondria, or dnring hypoxia in aerobic tissues, NADH is oxidised to NAD+ in a reaction in which pyruvate is reduced to lactate, catalysed by lactate dehydrogenase (i.e. anaerobic glycolysis). 

During anaerobic glycolysis in the muscles and erythrocytes, glucose is converted into lactate, releasing protons in the process (see p. 338). The synthesis of the ketone bodies acetoacetic acid and 3-hydroxybutyric acid in the liver (see p. 312) also releases protons. Normally, the amounts formed are small and of little influence on the proton balance. If acids are formed in large amounts, however (e. g., during starvation or in diabetes mellitus see p. 160), they strain the buffer systems and can lead to a reduction in pH (metabolic acidoses lactacidosis or ketoacidosis). 

Figure 6-1. The steps of glycolysis. Feedback inhibition of glucose phosphorylation by hexokinase, inhibition of pyruvate kinase, and the main regulatory, rate-limiting step catalyzed by phosphofructoki-nase (PFK-I) are indicated, pyruvate formation and substrate-level phosphorylation are the main outcomes of these reactions. Regeneration of NAD occurs by reduction of pyruvate to lactate during anaerobic glycolysis.

Lactate is a useful parameter of cerebral metabolism. The level of lactate is not influenced by plasmatic concentration. Lactate is produced only in small amounts in CSF in the case of anaerobic glycolysis. Under physiological conditions, lactate penetrates the blood-brain barrier in very low concentrations. In bacterial meningitis, the main source of lactate is brain tissue. Different mechanisms are included in the production of lactate first, brain edema with reduction of cerebral blood flow, ischemia, and (consequently) anaerobic metabolism then, production... 

Efficiency of ATP Production in Muscle The transformation of glucose to lactate in myocytes releases only about 7% of the free energy released when glucose is completely oxidized to C02 and H20. Does this mean that anaerobic glycolysis in muscle is a wasteful use of glucose Explain. 

The use of alanine to transport ammonia from skeletal muscles to the liver is another example of the intrinsic economy of living organisms. Vigorously contracting skeletal muscles operate anaerobically, producing pyruvate and lactate from glycolysis as well as... 

The ANLSH challenged the classic view [2, 3]. It postulates compartmentaliza-tion of brain lactate metabolism between neurons and astrocytes the activity-induced uptake of glucose takes place predominantly in astrocytes, which metabolize glucose anaerobically. Lactate produced from anaerobic glycolysis in astrocytes is then released from astrocytes and provides the primary metabolic fuel for neurons. The increased lactate in the neurons is converted to pyruvate via lactate dehydrogenase (LDH), which enters the TCA cycle, and increases ATP production in the neurons via oxidative phosphorylation (Fig. 8.1). This view is highly discussed, pro [4, 5]) and contra [1, 6]. 

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