Endocrine glands are organs that form the endocrine system and perform the function of secreting hormones. This secretion is directly into the blood stream as opposed to through a duct, as is generally observed.
The following are the main endocrine glands:
- Hypothalamus (neuro-endocrine gland)
- Islets of Langerhans in the pancreas
Some of these glands also have regions with a non-endocrine orientation that perform functions other than hormone secretion. For example, the ovaries and testes not only secrete hormones (estrogen, progesterone and testosterone) but also produce ova and sperm respectively. Moreover, we also see some organs like the stomach, which produce hormones (ghrelin), but their primary function is not hormone production and emission.
Some major endocrine glands in detail:
Adrenal Glands: Comprising of Adrenal Medula and Adrenal Cortex, the former secretes adrenalin and noradrenalin. Adrenalin is instrumental in activating the ‘fight or flight’ response which is a reaction spurred on by increasing stress levels. Noradrenalin also has effects similar to that of adrenalin. Alternatively, adrenal cortex is responsible for the discharge of Corticosteroids (Glucocorticoids and Mineralocorticoids), which are accountable for proper utilization of carbohydrates, protein and maintaining salt and water balance.
Pituitary Gland or Hypophysis: Also termed as the ‘master gland’, it is situated at the base of the brain at the bottom of the hypothalamus. The pituitary gland consists of two components: the anterior pituitary (or adenohypophysis) and the posterior pituitary (or neurohypophysis), and is functionally linked to the hypothalamus through the pituitary stalk.
The anterior pituitary synthesizes and secretes the following important endocrine hormones:
- Adrenocorticotropic Hormone (ACTH)
- Thyroid-Stimulating Hormone (TSH)
- Growth Hormone (also referred to as ‘Human Growth Hormone’, ‘HGH’ or ‘GH’ or somatotropin)
- Prolactin (PRL), also known as ‘Luteotropic’ hormone (LTH)
The posterior pituitary stores and releases:
- Antidiuretic Hormone (ADH)
Hormones secreted from the pituitary gland help control the following body processes:
- Growth (Excess of HGH can lead to gigantism)
- Blood Pressure
- Some aspects of pregnancy and child birth including stimulation of uterine contractions during childbirth (Oxytocin)
- Thyroid Gland function
Thyroid Gland: Located in the anterior throat, it secrets the thyroid hormone (TH) which accelerates the rate of cellular metabolism. Hyperthyroidism (excess secretion) causes Grave’s Disease where as hyposecretion causes cretinism in infants.
Islets of Langerhans: Located in the pancreas (close to the abdomen), this is the endocrine portion of the pancreas. It releases insulin and glucose into the blood stream.
Gonads: This refers to the ovaries in females and the testes in males. The ovaries secrete progesterone and estrogens, where as the testes secrete testosterone. These hormones are responsible for maturation of the reproductive system and development of secondary sex characteristics in females and males respectively.
The efficiency of all endocrine glands seems to decrease gradually as aging occurs. This leads to a generalized increase in the incidence of diabetes mellitus and a lower metabolic rate.
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