The Permissive Function of Hormones in the Body

Introduction

Hormones are chemical substances that regulate many body functions, like development, growth, behavior, and reproduction. Over 50 hormones are produced in the body. The hormones are produced by specialized glands and are secreted into the bloodstream. They are secreted as chemical messengers by the endocrine cells that act on the targeted tissues and produce desired metabolic effects and result in both inhibitory and excitatory actions.

The main function of hormones is the maintenance of homeostasis. The hormone acts by binding to a receptor present in the target tissue, which results in the formation of the hormone-receptor complex. The effects are produced only after binding to specific receptors. This reaction leads to biochemical changes in the target tissues that lead to the regulation and integration of body functions.

What Are the Permissive Functions of Hormones?

Hormones act by sending signals to the target tissues or organs. In permissive function, the hormone is effective only in the presence of another hormone. Permissiveness is a relationship between hormones and the target cells. It is the situation in which one hormone, at a certain concentration, combines or induces the second hormone to be fully effective at the target cell. For example, the best examples of permissive hormones are thyroid hormones and growth hormones. Thyroid hormones stimulate the production of growth factors and induce the metabolic and anabolic effects of growth hormones. Growth hormone also depresses the secretion of thyroid hormones. Also, it increases the conversion of thyroxine into triiodothyronine in the peripheral tissues. Normal thyroid hormone secretion is required for the optimal effect of growth hormone.

What Is the Role of Growth Hormones?

Growth is a complex process that involves genetic, nutritional, and hormonal factors. The hormones involved in growth are growth hormones, insulin-like growth factors, and thyroid hormones. Deficiency in growth hormone causes reduced somatic growth and delayed bone maturation. The hormones concerned with growth are thyroid hormone, growth hormone, and sex hormones (estrogen and testosterone and the pituitary gonadotropic hormones). The thyroid hormone increases the synthesis of growth hormone from the pituitary gland.

Which Hormones Work by Permissive Mechanisms?

Cortisol has a permissive effect on growth hormones. Growth hormones and cortisol are hormones that supply energy to the body. Glucocorticosteroids such as cortisol are produced by the zona fasciculate of the adrenal cortex in the adrenal gland. These hormones play vital roles in the body's defense mechanisms when dealing with stress.

There are two adrenal glands, one at the top of each kidney, and consists of two parts:

• The outer adrenal cortex.

• The inner adrenal medulla.

The adrenal cortex is divided into three zones that secrete the following hormones:

• Zona glomerulosa secretes mineralocorticoids.

• Zona fasciculata secretes glucocorticoids (cortisol).

• Zona reticularis secretes sex steroids

Cortisol and corticosterone are examples of glucocorticoids. Glucocorticoids are involved in protein, carbohydrate, fat, and bone metabolism. Growth hormones are released from the anterior lobe of the pituitary gland and are involved in protein, carbohydrate, and fat metabolism. High levels of glucocorticoids cause osteoporosis, therefore growth hormone is required for normal bone remodeling. The glucocorticoids regulate the growth hormone’s response by regulating growth hormone receptor expression in osteoblast-like cells.

High levels of cortisol causes the following symptoms:

• Weight gain.

• High blood sugar level.

• High blood pressure.

• Weak bones and fractures.

Low levels of cortisol cause the following symptoms:

• Fatigue.

• Unintentional weight loss.

• Poor appetite.

• Low blood pressure.

What Is the Connection Between Growth Hormones and Thyroid Hormones?

The connection between growth hormone and thyroid hormone is:

• Growth hormones and thyroid hormones interact in the hypothalamus and peripheral and pituitary tissues. The thyroid hormones exert permissive effects on growth hormones.

• Thyroid hormones activate the expression of the growth hormone gene. Triiodothyronine also controls the glucocorticoid's effect on growth hormone. Thyroid hormones also increase the pituitary gland's synthesis of growth hormones.

• Thyroid hormones are required for the full effect of growth hormones on DNA deoxyribonucleic acid) replication. Thyroxine (T4) released from the thyroid gland is important for normal body growth and skeletal maturation because it increases protein synthesis and can cause the increased release and action of growth hormone.

• Thyroxine is useful in tissue differentiation and maturation. The thyroid hormone is essential for life, but its removal in adults leads to poor resistance to cold with mental and physical slowing. In children, it causes mental retardation and dwarfism.

• Low thyroid hormones result in reduced growth hormone levels in the pituitary and reduced growth hormone secretion.

• Some patients who have decreased thyroxine levels can receive recombinant human growth hormone treatment.

• Thyroid hormones regulate growth by several mechanisms. The negative feedback effect on stimulatory hormones thyrotropin-releasing hormone (TRH) and thyrotropin (TSH), thyroid hormones regulate the receptors in various physiological and pathological conditions.

• Thyroid hormones act synergistically (effect of two hormones together) with growth hormone to stimulate bone growth. It stimulates the chondrocytes, osteoblasts, and osteoclasts for bone growth and development. The thyroid hormone also helps with axonal growth and myelin sheath formation which leads to brain development.

What Is Growth Hormone Deficiency?

Growth hormone deficiency in children is an indication of the therapy with recombinant human GH (rhGH). This therapy is done to increase the patient’s height velocity. Growth hormone replacement therapy is used to treat adult growth hormone deficiency. The significant peripheral mediator of growth hormone is the insulin-like growth factor-I. The normal thyroid hormone secretion or appropriate substitution of L-thyroxine is necessary for the endogenous growth hormone and recombinant human growth hormone substitution for the growth rate.

Conclusion

Hormones are a significant part of human existence. They work by sending signals to the target tissues or organs. The hormones concerned with growth are thyroid, growth, and sex hormones. The permissive function denotes that the full effect is exerted by one hormone only in the presence of the other hormone. The best examples of permissive hormones are thyroid hormones and glucocorticoids. The body balances hormones through various signaling pathways. If there is any problem with the body's metabolism, it is solely related to endocrine dysfunction. An endocrinologist is a specialist who specializes in the field of endocrinology and who can diagnose hormone dysfunctions and develop treatment plans and prescribe medications accordingly.