BIOCHEMISTRY - Textbook - Ostapchenko L. I. - 2012

Chapter 15. INTEGRATION OF METABOLIC PATHWAYS. HORMONES

Multicellular Organisms function as integrated systems due to the close interconnections between individual Cells, Tissues, and Organs. This communication is mediated by major regulatory systems, including the central and peripheral nervous systems, as well as the endocrine and immune systems. The primary control over Cellular METABOLISM is exerted by chemical messengers. Traditionally, the term "Hormones" refers to substances synthesized and secreted by one tissue that exert their effects at a considerable distance. However, many Peptide Hormones also act as Neurotransmitters across very short distances. Many Other Hormones affect adjacent cells (paracrine action) or regulate the cells that produce them (autocrine action).

The action of most hormones is characterized by feedback regulation, which may involve multiple stages and be modulated by the Central Nervous system.

Metabolic Integration is determined by:

✵ the presence of common intermediates in the majority of metabolic pathways;

✵ the possibility of interconversions via shared metabolites;

✵ the utilization of common Coenzymes and the necessity for their continuous recycling;

✵ the presence of a common catabolic pathway and a unified system for energy release and utilization (the Respiratory Chain);

✵ the presence of similar regulatory mechanisms.

An Overview of the Major Metabolic Pathways of CARBOHYDRATES, Proteins, and fats, discussed in the previous chapters, is presented in Fig. 15.1.

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Fig. 15.1. Integration of metabolism