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There is no single way in which endocrine glands store and secrete their hormones. But there are many general patterns that occur for most hormones that differ according to the nature of the hormone and the chemistry of the hormones. For example; All protein hormones are formed in the granular endoplasmic reticulum of glandular cells in the same way as other secretory proteins. But the initial protein that is formed in the endoplasmic reticulum is never the last hormone. As it is greater than the active hormone and is called the precursor of the preprohormone. Then this large protein is cleaved again, usually while it is still in the endoplasmic reticulum, to form a smaller protein called prohormone, and this in turn is transported in the transport vesicles of the endoplasmic reticulum to the Golgi apparatus, where it cleaves another segment of the protein.

In this way, the final active protein hormone is formed. Normally, the Golgi apparatus also houses hormone molecules in membrane-bound vesicles called secretory vesicles or secretory granules.

And these vesicles remain stored in the cytoplasmic space of the endocrine cell until a special signal such as: a nerve signal, or another hormonal, or a chemical signal, or a local physical signal reaches it to stimulate its secretion.

The two groups of hormones derived from tyrosine, which are the thyroid hormones and the adrenal medulla hormones, are formed by the action of enzymes in the cytoplasmic spaces of the glandular cells. In the case of the adrenal medulla hormones norepinephrine and adrenaline, they are absorbed into preformed vesicles and stored there until secretion.

On the other hand, the metabolic hormones of the thyroid gland – thyroxine and triiodothyronine – are component parts of a large protein molecule called thyroglobulin which is then stored in large vesicles within the cells of the thyroid gland. And when the time comes for thyroid hormones to be secreted, special enzyme systems inside the thyroid cells cleaved the thyroglobulin molecule, thus releasing thyroid hormones into the blood. As for the steroid hormones made in the adrenal cortex, ovary, or testis; The quantities that are stored in their glandular cells are very few, but there are large quantities of precursor molecules, especially cholesterol, and various intermediates between cholesterol and final hormones. final, almost immediately followed by its secretion.

The start of hormone secretion after stimulation, and the duration of action of various hormones[عدل]

Some hormones, such as norepinephrine and adrenaline, are secreted within a few seconds after stimulating the gland and can generate its full function within a few seconds to minutes. And the activities of some other hormones, such as: thyroxine and growth hormone, may need several months to develop their full effectiveness. And with this; Each of the different hormones has the characteristics of starting its action and its own duration according to the response of the hormone receptors. Each of them has a specific system in a way that serves its own control function.

The concentration of hormones in the circulating blood, and the speeds of hormone secretion[عدل]

The quantitative amounts of the hormones necessary to control most metabolic and endocrine functions are very small, and their concentrations in the blood range from as low as 1 picogram (which is one millionth of a millionth of a gram) per milliliter of blood to as large as a few micrograms. (several millionths of a gram) in every milliliter of blood. Similarly, the speed of secretion of various hormones is also very small, usually measured in micrograms or milligrams per day. Therefore, highly specialized mechanisms are available in the target tissues, allowing even these minute amounts of hormones to exert their intense control over physiological systems.

Controlling the rate of hormone secretion, the role of negative feedback[عدل]

The speed of secretion of each of the known hormones, without exception, is precisely controlled by its own internal control system. This control is generated in most cases through a negative feedback mechanism as follows:

1. The endocrine glands have a natural tendency to overproduce their hormones.

2. Because of this tendency, this hormone generates more and more of its controlling effect on the target organ.

3. However, when an excessive action occurs, one of the factors feeds back into the endocrine gland responsible for the secretion of this hormone, and it generates a negative effect on the gland and reduces the speed of its secretion.

Thus, the function of the hormone is monitored very accurately by the control mechanism, and this information in turn provides a negative feedback control of the speed of secretion by the apocrine gland. When examining each feedback mechanism, it turns out that the important factor that must be governed is not the speed of hormone secretion, but the degree of effectiveness of the target organ with this secreted hormone. Therefore, only when the target organ’s activity has risen to an appropriate level does the apocrine endocrine feedback become so intense that it slows the secretion of the hormone. If the target organ responds to the hormone poorly, the endocrine gland almost always secretes more and more of its hormone until the target organ’s activity finally reaches an appropriate level, but at the expense of excessive secretion of the controlled hormone.

See also[عدل]

nature of the hormone.

Hormone chemistry.

hormone receptors.

Hormone mechanisms of action.

Measurement of the concentration of hormones in the blood.

Measurement of the rate of metabolic clearance of hormones.

Measuring the rate of hormone secretion.

Hormones affecting the genetic machinery of the cell.

Reference[عدل]

cell components
cell membrane | Cytoplasm | Cytoplasmic microfibrils | microtubules | ribosomal particles | Golgi Apparatus | particle state | cytoplasmic reticulum | Mitochondria | Chloroplasts | kernel | oxidative particles

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