The Thyroid or hormones in the endocrine system coordinate and control the energy level of the human body’s internal metabolism (or homeostasis), growth and development, and response to stress, injury, and environmental factors. The following hormones and their functions in the endocrine system are considered.
Aldosterone is a steroid hormone that is produced in the cortex of the adrenal glands, which are located above the kidneys. The hormone plays a significant role in regulating the blood pressure, which is by acting on organs such as the colon and the kidneys, thereby increasing the concentration of sodium reabsorbed into the bloodstream.
In addition, it increases the concentration of potassium excreted in the urine. The hormone also leads to the reabsorption of water with sodium, which increases blood volume and blood pressure.
Corticosteroids are synthetic or human-made drugs. These hormones are used in many medical specialties. The hormones reduce the production of certain chemicals, thereby lowering inflammation in the human body. When administered at higher doses, these hormones also reduce the activity of the immune system. Corticosteroids are similar to cortisol, which is a hormone produced by the adrenal glands in the human body.
Vasopressin or antidiuretic hormone (ADH) is a nonapeptide, which is synthesized in the hypothalamus. It plays an important role in controlling the osmotic balance, sodium homeostasis, blood pressure regulation, and kidney functioning. The kidneys’ ability to reabsorb water is affected by ADH. It induces the expression of proteins in water transport in the collecting duct and late distal tubule, thereby increasing water reabsorption.
Adrenocorticotropic hormone is produced in the corticotroph cells, which belong to the anterior pituitary gland. Like cortisol, adrenocorticotropic hormone levels are generally high in the morning as we wake up. It decreases throughout the day. It is the lowest during sleep. This phenomenon is called a diurnal (circadian) rhythm.
The adrenocorticotropic hormone reaches the adrenal glands, binds to the receptors, and leads to more secretion of cortisol by the adrenal glands, which results in higher cortisol levels in the blood.
The anterior pituitary gland releases the growth hormone into the bloodstream. The hormone acts on many body parts and promotes growth in children. In children when the growth plates have fused in the bones, the increase in height by the growth hormone stops.
In adults, the hormone does not cause growth; however, it helps in maintaining metabolism and normal body structure and aiding in maintaining the set blood glucose levels.
One of the gonadotrophic hormones is a follicle-stimulating hormone (FSH); the other hormone is luteinizing. The pituitary gland releases both hormones into the bloodstream. FSH is essential in pubertal development and the functioning of testes in men and ovaries in women.
The growth of the ovarian follicles is stimulated by FSH in the ovary before an egg is released from a follicle at the stage known as ovulation, in women. In the testes in men, FSH acts on the Sertoli cells to stimulate spermatogenesis.
The posterior pituitary gland produces oxytocin in the hypothalamus and secretes it into the bloodstream. The two important functions of oxytocin in the human body are that during childbirth, it causes contraction of the uterus and then lactation. In men, oxytocin plays a role in the production of testosterone and sperm transport. Oxytocin functions as a chemical messenger in the brain and plays a significant role in many human behaviors.
Prolactin hormone, also known as lactotroph, is secreted by the pituitary gland and is responsible for lactation and the development of breast tissue. Normally, in non-pregnant and non-lactating women and people assigned male at birth, prolactin levels are low. It is normally high in pregnant or breastfeeding women.
The anterior pituitary produces the thyroid-stimulating hormone (TSH), which is a glycoprotein hormone. The hormone primarily stimulates the production of thyroid hormone by the thyroid gland. TSH release is regulated by the hypothalamic-pituitary axis. Specifically, the thyroid-releasing hormone is released by the neurons in the hypothalamus, which secrete TSH by stimulating the thyrotrophin in the anterior pituitary.
In turn, TSH stimulates thyroid follicular cells and releases the thyroid hormones as T3 or T4. The active form of thyroid hormone is triiodothyronine or T3. Tetraiodothyronine (thyroxine or T4) forms more than 80% of the hormone secreted.
Renin and angiotensin
The renin-angiotensin–aldosterone system (RAAS) is an important regulator of systemic vascular resistance and blood volume. RAAS is composed of three major compounds: aldosterone, angiotensin II, and renin. These compounds increase the arterial pressure as a consequence of decreased delivery of salt to the distal convoluted tubule and decreased renal blood pressure.