Hormones: Chemical messengers

Hormones are substances secreted by endocrine glands and other organs that act as chemical messengers, controlling and regulating the functioning of several internal organs. They travel through the bloodstream and are spread throughout the body, but only target organs respond to them (like the thyroid, suprarenal gland and gonads), which have points of specific recognition for hormones.
The amount of hormones released must be perfectly controlled because if there is a deficit or excess of them, disorders or diseases are produced in the body.

Hormones of the hypophysis and hypothalamus

The master gland, as the hypophysis is known, releases hormones that affect other glands for them to release specific hormones the body needs. These are stored in the two lobes the hypophysis has. 
– Anterior lobe or adenohypophysis: in it, hormones are produced which stimulate the functioning of other endocrine glands, and they are:

1. Thyrotropin or thyroid stimulating hormone (TSH): triggers the release of thyroid hormones.
2. Follicle stimulating hormone (FSH): it has to do with the maturation of the female ovules and male spermatozoa.
3. Adrenocorticotropic hormone (ACTH): stimulates the cortex of the suprarenal glands in order for them to secrete their hormones (aldosterone and cortisol)
4. Luteinizing hormone (LH): induces ovulation in women and stimulates the production of the male hormone testosterone in men.
5. Prolactin (PRL): stimulates the manufacturing of milk in the mammary glands during breastfeeding.
6. Somatotropine or growth hormone (GH): stimulates an individual’s bodily growth.
7. Melanocyte stimulating hormone (MSH): activates the development of pigment (melanin) in the skin.
– Posterior lobe or neurohypophysis: stores the hormones secreted by the hypothalamus. They are oxytocin and the anti-diuretic hormone (ADH) or vasopressin. The first stimulates muscle contractions, especially those of the uterus, and the fabrication and release of breast milk in the mammary glands.
The second one controls the amount of water excreted by the kidneys and increases blood pressure.

Hormones of the thyroid and parathyroid

Thyroxin or tetraiodothyronine (T4) and triiodothyronine (T3) are two hormones of the thyroid gland and among its functions we count: stimulating metabolism, increasing oxygen consumption and body temperature and participating in the development of organs and tissues, especially in the nervous and osseous systems. The other thyroid hormone is calcitonin, which decreases the levels of calcium and phosphorus in the circulation flow and inhibits osseous re-absorption.
The only hormone released by the parathyroid glands is parathormone or parathyroid hormone and it is in charge of increasing the levels of calcium and phosphorus concentration in the blood and stimulates osseous re-absorption.

Pancreatic and suprarenal hormones

The endocrine pancreas (islets of Langerhans) produces two hormones that influence the metabolism of glucose (sugar) depending on the body’s needs.
One of them is insulin –hormone produced by beta cells of the islets- which lowers the level of glucose in the blood. And the other is glucagon –hormone produced by the alpha cells- which increases the levels of sugar, extracting all the reserves of glucose from the liver which go to the blood flow. Somatostatin –another pancreas hormone produced by delta cells- is directly involved in the regulation of glucose, diminishing the secretion of insulin and glucagon.  
The medulla of the suprarenal glands produces hormones known as catecholamines, among the most important ones we find adrenalin or epinephrine and noradrenalin or norepinephrine. 
They are secreted in certain stress situations (fight, fear, or flight), reason for which they speed up the heart rate, increase blood (arterial) pressure, muscle activity is stimulated due to them tensing and the skin is moistened because of sweat. Two hormones are released in the cortex of this gland, aldosterone and cortisol (see box).
In addition, suprarenal glands produce small amounts of male and female hormones (androgens, estrogens and progesterone).

Hormones of the sexual glands

The sexual glands or gonads secrete different hormones. In women, the ovaries manufacture and release estrogens, important for the development of the reproductive organs and secondary sexual characteristics (like the growth of breasts, pubic and axillary hair and the widening of the hips).
This hormone is also important in the ovarian cycle because it helps the ovule develop, mature and, if fertilized, implant itself in uterus correctly.
Progesterone is another hormone secreted by the ovaries and is also involved in the ovarian cycle, causing a sort of uprise among the estrogens, because if a pregnancy is produced, it is in charge of taking care of it. Also, the ovaries manufacture a hormone called relaxin, which acts upon the pelvic ligaments and cervix and causes their relaxation during labor (childbirth).
In men, the testicles produce and secrete hormones called androgens and they are testosterone, androsterone and androstenedione. However, the most important one is the first, because it manufactures spermatozoa and stimulates the development of the secondary sexual characteristics. Among the latter we point out: growth of the prostate, seminal vesicles, appearance of hair on the legs, arms, cheeks, chest and pubis and increase in muscle mass.