By glands It is understood as an organized and hyperspecialized set of cells whose function in the body is the secretion of certain chemical substances such as hormones, lipids or mucus. For instance: pituitary, thyroid, sweat glands.
According to the way they have to lead these secreted substances to their ideal destination, they are classified into:
- Endocrine or closed. That they pour it into the blood capillaries, in the absence of specialized conduits.
- Exocrine or open. They have an excretory tube that leads both to the surface and to the light of some hollow organ. The exocrines, furthermore, are subdivided into:
- Apocrine. They lose part of the body cells during secretion.
- Holocrines. All cellular content disintegrates during the secretion process.
- Mesocrine. They secrete their substances by exocytosis, without cell sacrifice.
Examples of endocrine cells
- Hypophysis. Also known as the pituitary gland, it is located inside the skull and brain, from where it produces the hormones that regulate the functioning of the entire endocrine system, operating as its primary center of functioning.
- Hypothalamus. Also located in the brain, like the pituitary gland, it hormonally controls sleep and hunger, water level and body temperature, as well as other aspects of blood life. It is the crossing point between the nervous and endocrine systems.
- Thyroid. The central gland of metabolism, located in the front of the neck. It is particularly sensitive to iodine and is responsible for regulating the processing of sugars and lipids, which is why it is vital for body health. Its deficient or excessive functioning can lead to radical weight loss or gain.
- Pancreas. A mixed gland (exocrine and endocrine) located behind the stomach. Its endocrine functions play a vital role in the metabolism of sugar (and therefore energy), through the generation of insulin and glucagon.
- Kidney glands. So called because they are located in the upper part of the kidneys, they are responsible for the production of vital hormones for certain bodily reactions, such as adrenaline (for states of tension or stress) or aldosterone (for urinary elimination of salts) .
- Ovaries. The female sexual glands play a vital role in the sexual maturation of women, especially in the activation of menstrual cycles and the physical and behavioral alterations typical of sexual awakening. Its main hormones are progesterone and estrogen.
- Testicles. The male sex glands, responsible for the production of testosterone and hormones that will activate seminal production and trigger the physical changes typical of male puberty and the entrance to reproductive maturity.
- Conarium or pineal gland. Present in the brain of all vertebrates, this small gland is responsible for producing mainly melatonin, a derivative of serotonin that affects sleep cycles, circadian and seasonal rhythms.
- Parathyroid. Located in the neck, behind the thyroid lobes, as the name implies. They are responsible for the production of parathormone (PTH), which is involved in the processes of absorption of calcium and its resorption in the bones of the body.
- The liver, lungs, and intestine. These organs are not properly glands, but they act as such by producing certain hormones directly into the bloodstream that have an effect on other organs of the body and not on themselves.
Examples of exocrine glands
- Sweat glands. Located throughout the skin, it consists of thin tubes that connect to the outside through the pores, through which they secrete sweat: a salty substance made of excess liquid fat, whose role is to cool and refresh the skin .
- Sebaceous glands. Also located in the skin, at the end of the hair follicles, they secrete the necessary sebum to keep the skin lubricated and moisturized, thus avoiding drying out. Its obstruction leads to folliculitis and acne.
- Tear glands. Responsible for producing tears, composed of water, sodium chloride and albumin, to keep the ocular surface clean and the external cornea nourished, in addition to acting as a humectant to allow blinking.
- Meibomian glands. These are sebaceous glands located in the eyelids, where they secrete a lipid substance that constitutes part of the tear film that prevents the eye from drying out. There are about fifty in the upper eyelid and twenty-five in the lower one.
- Salivary glands. In them saliva is produced, a substance in charge of starting the digestive process, moistening the food and covering it with enzymes and defensive cells, which facilitate the work of the stomach. It also acts as a first defense barrier for the oral mucosa.
- Mammary glands. Similar to all female mammals, since they are responsible for producing the milk that will feed the young during their first vital stages. They are a glandular set that pours its substances directly into a single conduit that leads to the outside.
- Bartholin’s gland. Known as the major vestibular glands, they are located on each side of the opening of the vagina and secrete lubricating fluids that facilitate penetration during intercourse.
- Cowper’s glands. Also called bulbourethral glands, they are the male counterparts of the female Bartholin’s glands: they clean and lubricate the urethra and smooth the acidity of the path that semen will travel during ejaculation.
- Prostate. The exclusive organ of the male reproductive system, located at the outlet of the urinary bladder, is responsible for secreting the various substances that will accompany the semen during ejaculation, such as nutrients, enzymes and various antigens.
- Pancreas. In its exocrine facet (we have already said that it has another endocrine), the pancreas secretes digestive enzymes that it sends directly to the small intestine to start the process of decomposition of nutrients.