Biochemical Foundations of Human Body Functioning - Volkov, N. I., & Nesen, E. N. 2000

Biochemical Foundations of Human Body Functioning
Hormones as Regulators of Metabolism
Properties of Hormones

Hormones exhibit high biological activity because they exert regulatory effects at very low concentrations (10-8—10-11 mol). The concentration of individual Blood hormones in a state of relative rest ranges from 0.2 to 500 µg, while under stress their levels increase severalfold (Table 12).

Possessing high functional Specificity, hormones regulate METABOLISM exclusively in target Tissues that possess receptors for the specific hormone (Fig. 46). Receptors are specific Proteins located in The Cell's Plasma Membrane or in the Cytosol, which bind the hormone to exert its regulatory effect. A single cell may contain multiple types of receptors for different hormones or even for the same hormone. Acting through different receptors, a hormone can regulate various organ Functions. For instance, adrenaline acts via α-adrenergic receptors to cause contraction, and via β-adrenergic receptors to cause relaxation of Blood Vessels, the Urinary Bladder, and the Spleen, thereby increasing or decreasing blood pressure.

Hormones are characterized by action at a distance: they are synthesized in one Location, such as the Pituitary Gland, and regulate processes in another, more distant site—such as the Adrenal Glands or Gonads—to which they are transported via the bloodstream (see Fig. 46). Hormone transport is carried out in bound form with specific blood proteins, namely globulins and transcortin. The concentration of these proteins in the blood, and consequently The amount of hormone delivered to Cells, depends on the functional state of the Organism.

Class="center">TABLE 12 Blood hormone concentrations at relative rest

Hormones

Concentration, µg per 5 L of blood

ACTH and other Pituitary Hormones

0.2 (under stress — 0.8-1.0)

Thyroxine (T4)

300-500

Triiodothyronine (T3)

6-12

Insulin

5 (postprandial — 25)

Glucagon

0.5 (during fasting — 2)

Cortisol

500 (under stress — 2000)

Aldosterone

0.5

Catecholamines (total)

1.5-2.5 (under stress — 4-8 times higher)

Testosterone:

in men

20-40

in women

2-4

Estrogens:

in women

0.25-2.50

in men

0.10-0.20

Fig. 46 Long-range and specific Action of Hormones

Hormones must be continuously synthesized by glands since they are rapidly degraded. The half-life of individual hormones spans several tens of minutes. Impairments in hormone synthesis lead to alterations in the rate and direction of metabolic processes, which impacts human health and physical performance.



Last update: 06/08/2026

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