Functional Endocrinology: Understanding Hormones From the Pituitary to the Receptor Sites

The body secretes and circulates 50 different hormones to different organs in the body. Hormones are the chemical substances that coordinate the activities of living organism growth. They are secreted through the endocrine glands and travel through the bloodstream to different organs in the body to function properly. When there is an excessive quantity or an reduced quantity of hormones being produced, it can cause the body to malfunction and develop chronic illnesses.

The Pituitary Gland Functions

In neuroendocrinology, an endocrine gland can’t make a hormone without activation from a pituitary-stimulating hormone. The pituitary-stimulating hormone helps regulate hormones by secreting them to the endocrine glands. The pituitary gland is known as the “master gland” since it controls the activity of the other endocrine glands and it consists of 3 parts known as the anterior, intermediate and posterior lobes.

Anterior Lobe

The anterior pituitary gland is located in the sella turcica and is controlled by the hypothalamus in the brain. It secretes a quantity of peptides and glycoprotein hormones that help regulate the growth, metabolism, reproduction and stress response. The anterior pituitary gland produces 6 hormones that circulate to their respective targets in the body.

• ACTH (Adrenocorticotropic hormone): This hormone is a tropic hormone as it regulates cortisol and androgen production to the adrenal cortex. Cortisol or stress hormones stimulates the release of ACTH, while the adrenal cortex secretes glucocorticoids to the body’s metabolism.
• GH (Growth hormone): This hormone helps regulate the body’s growth, metabolism, and composition. GH is secreted by the somatotroph cells located primarily in the lateral wings of the anterior lobe. GH can also secrete in al pulsatile fashion and can have a maximal release during a circadian rhythm at night.
• TSH (Thyroid stimulating hormone): This hormone is involved by coordinating the signal regulation of the hypothalamus, the pituitary, and the thyroid. It requires the oxidation of dietary iodine, since iodine is absorbed through the small intestine and transported to the thyroid. After the iodine is transported it can be concentrated, oxidized and then incorporated into thyroglobulin to be formed to T4 and T3 later on.
• LH (Luteinizing hormone): This hormone is highly important to both men and women, since it affects the sex organs and plays a role in puberty, menstruation and fertility. For women, it creates progesterone, which help regulate menstruation and supports pregnancy in the female body. For men, it creates testosterone, which helps regulates fertility, muscle mass, fat distribution, and red blood production in the male body.
• FSH (Follicle stimulating hormone): This hormone plays an important part in the reproductive system and is responsible for ovarian follicles. For females, FSH helps produce estrogen, which is a group of sex hormones that help promote the development and maintenance of female characteristics in the human body, For males, FSH helps produce spermatogenesis and regulates sperm function in the male body.
• Prolactin: This is a protein hormone in the anterior lobe. It has the ability to promote lactation to nursing mothers. It synthesizes within the pituitary gland, the central nervous system, the immune system, and the uterus.

Intermediate lobe

The intermediate lobe is composed of a homogeneous population of the endocrine cells, the melanotrophs and secretes several bioactive peptides. It contains very few blood vessels and can be virtually avascular. The melanotrophs are richly supplied by nerve fibers that originate from the hypothalamus.

• Melanocyte-stimulating hormone: This hormone has many functions in a diverse physiological role. It affects skin pigmentation and studies have shown that it has antiapoptotic and anti-inflammatory effects that help decrease in nephrotoxin exposure to the body.

Posterior lobe

The posterior lobe is similar to the anterior lobe since they both control endocrine function and the body’s hormonal response to the environment. The hypothalamus receives neural signals from the brain and secretes polypeptide and neuropeptide hormones for storage in the posterior lobe until they are ready to be released. The hormones in the posterior lobe are in charge of regulating water retention and inducing uterine contractions.

• ADH (Antidiuretic hormone): Also known as vasopressin, this hormone is a nonapeptide that is synthesized in the hypothalamus. It plays a bunch of important roles in controlling the body’s osmotic balance, regulates blood pressure, and makes sure that the kidneys are working. ADH is mainly responsible for tonicity homeostasis as they act primarily in kidneys to increase water reabsorption.
• Oxytocin: Also known as the “love hormone”, oxytocin is also a neurotransmitter that is involved in childbirth and breast-feeding. It has benefits as a treatment for a number of conditions like depression, anxiety and intestinal problems and is produced in the hypothalamus. Studies show that females have a higher level of oxytocin than males, especially to nursing mothers with their babies.

Free-fraction Hormones

When an endocrine gland synthesizes a hormone, it is released into circulation and bound to as a protein. Hormones attach themselves to proteins but they can’t bind to hormone receptors. So what a hormone needs to do is to lose its binding protein to become a “free-fraction” hormone. Studies have stated that a fraction of a hormone that is free is called in vitro and it is equivalent to the fraction of a hormone that is free and available to be transported into tissues are called in vivo. Free-fraction hormones make up less than 1% of all circulating hormones since they don’t impact the hypothalamus-pituitary feedback loop.

Hormone Metabolites

Hormones are metabolized by hepatic and microbiome biotransformation pathways into various hormone metabolites. Hormone metabolites have their own impact on cell receptors, studies have shown that this impact is not fully understood yet but hormone metabolites are not a reflection of direct endocrine gland production but it can be metabolized in the liver as well. Hormone metabolites can bind to hormone receptors or can be eliminated by renal or fecal clearance pathways.

Conclusion

All in all, the body secretes and circulates 50 different hormones to different organs in the body. These hormones are chemically produced in the body and keep an eye on what each of the different organs is doing. It is important that the hormone receptors are functioning properly so that an individual is feeling good both inside and out. If there is a hormonal imbalance in the body, it can cause dysfunction and chronic illnesses to a person.

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