What are the endocrine glands?
The endocrine glands in humans are production sites for important hormones. They do not have an excretory duct, but release their secretions (hormones) directly into the blood. This is why endocrine glands are called endocrine glands. Their counterparts are exocrine glands, which release their secretions via excretory ducts to internal or external surfaces. These include salivary glands, sweat glands and lacrimal glands.
The most important endocrine glands and their hormones
The following endocrine glands produce important messenger substances for bodily processes.
Hypothalamus
It is an important control organ in the hormone system. It regulates the hormone production of the pituitary gland via so-called “releasing hormones” (such as GnRH) and “inhibiting hormones” (such as somatostatin, dopamine).
Pituitary gland (hypophysis)
It produces various hormones in its anterior and posterior lobes. These include, among others:
- Growth hormone (somatotropin): important for growth and development.
- Thyroid-stimulating hormone (TSH): stimulates hormone production by the thyroid gland
- adrenocorticotropic hormone (ACTH): stimulates hormone production in the adrenal cortex
- Follicle-stimulating hormone (FSH) and luteinizing hormone (LH): In women, they stimulate egg maturation, ovulation and oestrogen production, among other things. In men, they promote sperm production.
- Oxytocin: causes contraction of the uterine muscles during birth (labor pains) and contraction of the muscle cells of the mammary gland after birth (milk letdown).
- Vasopressin (antidiuretic hormone, ADH): inhibits urine excretion (diuresis) and constricts the blood vessels (which increases blood pressure).
Thyroid gland
It produces the two thyroid hormones triiodothyronine (T3) and thyroxine (T4). These are important for growth, development, oxygen consumption and heat production.
Parathyroid glands
It produces parathyroid hormone, which regulates the calcium and phosphorus levels in the blood.
Adrenal glands
The following hormones are produced in the adrenal cortex:
- Glucocorticoids (cortisol): Regulation of metabolic processes, stress hormone, etc.
- Aldosterone: involved in the regulation of salt and water balance
- Androgens (such as testosterone): male sex hormones
The “stress hormones” adrenaline, noradrenaline and dopamine are produced in the adrenal medulla. They prepare the body for a stress reaction, for example by increasing blood pressure, accelerating the heartbeat and stopping intestinal movements.
Pancreas
Only certain islet-shaped tissue parts of the pancreas (the so-called islets of Langerhans) have an endocrine gland function, i.e. they produce hormones. These are
- Insulin: lowers the blood sugar level
- Somatostatin: is also produced by the hypothalamus and inhibits various hormones (insulin, glucagon, growth hormone, etc.)
Ovaries
They produce the female sex hormones oestrogens and gestagens (such as progesterone) and, in small quantities, the male sex hormone testosterone.
Testicles
The testicles produce testosterone and, in small amounts, the oestrogen oestradiol.
What function do endocrine glands have?
The endocrine glands control numerous organ functions and bodily processes via the hormones they produce. These include, for example, various metabolic processes, salt and water balance, body temperature, circulation, behavior and sexual function.
Where are the endocrine glands located?
The hypothalamus, pituitary gland and pineal gland are located in the brain: the hypothalamus is part of the diencephalon. It is connected to the pituitary gland (hypophysis) at the base of the skull via the so-called pituitary stalk.
The small pineal gland is located deep inside the brain: it lies on the posterior wall of the third ventricle (ventricles are cavities in the brain filled with cerebrospinal fluid).
The two-lobed thyroid gland is located at the front of the neck just below the larynx. Its two lobes lie to the right and left of the trachea. The four small parathyroid glands are located at the top and bottom of the back of the thyroid lobes.
The female gonads – the two ovaries – are located in the pelvis on either side of the uterus. The male gonads, the two testicles, lie together in the scrotum and are therefore located outside the body. It is a few degrees cooler here than inside the body, which is necessary for sperm production.
What disorders can affect the endocrine glands?
Disorders of the endocrine glands can lead to reduced or increased production of the respective hormones. Such disorders can be of a very different nature.
For example, the endocrine glands may no longer be able to produce sufficient hormones as a result of inflammation or injury (due to an accident or operation). The same can happen if a tumor puts a lot of pressure on an endocrine gland.
However, tumors can also “mimic” the tissue of endocrine glands so that excessive amounts of hormones are produced.
Infectious diseases and autoimmune diseases can also impair the function of endocrine glands. One example of an autoimmune disease that affects endocrine glands and their hormone production is type 1 diabetes: in those affected, the immune system destroys the insulin-producing cells of the pancreas. This results in a dangerous insulin deficiency that must be treated.
