In this topic, we will be able to have an overview about one of the most important system in our body, the Endocrine System.
Endocrine system plays a very important role in our body. It is one of the physiologic regulatory systems, just like the Nervous System. The term "endocrine" refers to the internal secretion of biologically active substances. It is capable of producing a chemical messengers, so called hormones which regulate our body's growth, metabolism, sexual development and function. These hormones are being released into the bloodstream for transport in specific tissues that brings specific actions.
According to Kaplan, et. al., the functions of hormones are as follows:
a. It maintains a constant internal environment in the body fluids (homeostasis).
b. It regulates the growth and development of the body as a whole.
c. It promotes sexual maturation, maintain sexual rhythms, and facilitate the reproductive process.
d. It regulates energy production and stabilize the metabolic rate.
e. It helps the body to adjust to stressful or emergency situations.
f. It promotes or inhibit the production and release of certain other hormones.
Hormones are divided into three chemical classes, (1)protein hormones, (2)aromatic amines, and the (3)steroid hormones. They differ from one another in structure, chemical composition, transport, metabolism, and mechanism of action.
Endocrine glands includes the Adrenal, Hypothalamus, Islet of Langerhans in the pancreas, Ovaries, Parathyroid, Pineal, Pituitary, Testes, and Thyroid glands. Among of these the anterior pituitary and the hypothalamus are the most important because they function as the primary regulators of the entire endocrine system.
Photo source: http://www.ama-assn.org/ama/pub/physician-resources/patient-education-materials/atlas-of-human-body/endocrine-system.page
ANTERIOR PITUITARY HORMONES
The pituitary gland is composed of two distinct parts, the anterior lobe or adenohypophysis and the posterior lobe or the neurohypophyis. The anterior pituitary gland controls the hormonal outputs of some of the other endocrine glands by its secretion of tropic hormones.
Effector Hormones
a. Growth Hormone (GH, Somatotropin) - is the hormone produced in the largest quantity by the anterior pituitary.
b. Prolactin - a hormone similar in the structure to GH which participates with gonadal steroids in breast growth during pregnancy.
Tropic Hormones
a. Thyroid Stimulating Hormone (TSH, Thyrotropin) - is the major regulator of thyroid secretion and function.
b. Adrenocorticotropin (ACTH) - stimulates the formation of adrenal steroids by increasing the synthesis of pregnenolone from cortisol.
c. Gonadotropins (FSH, LH) - these are glycoproteins secreted by the anterior pituitary that are necessary for the proper maturation and function of the gonads in both men and women.
POSTERIOR PITUITARY HORMONES
The posterior lobe of the pituitary gland is connected anatomically to the hypothalamus by a stalk through which a nerve tract and blood vessels pass. It stores and secretes two closely related peptide hormones, ADH and Oxytocin.
a. Anti-Diuretic Hormone - increases the reabsorption of water by the renal tubules when plasma osmolality becomes elevated.
b. Oxytocin - a potent stimulant for the contraction of smooth muscle.
Pineal Hormones
The pineal gland, which is attached to the midbrain secretes 2 neurotransmitters, melatonin and serotonin which modulates some circadian rhythms of the endocrine system.
THYROID HORMONES, T4, AND T3
Thyroid gland is a small tissue situated in the neck just below our voice box. Its hormones increase the basal metabolic rate and are necessary for proper growth and development. It also secretes Calcitonin, which is a hormone that participates in the regulation of plasma concentration by inhibiting bone resorption.
ADRENOCORTICAL HORMONES
An adrenal gland is situated above each kidney. It is composed of an outer cortex and an inner core or medulla. The cortex produces many steroid hormones derived from cholesterol.
a. Cortisol - the principal glucocorticoid, acts on target cells by penetration and transport to the cell nucleus, binding to DNA, and alters the transcription of RNA.
b. Androgens - The adrenal androgens are dehydroepiandrosterone (DHEA), DHEA sulfate, androstenedione, and testosterone.
c. Aldosterone - is the most potent mineralocorticoid secreted by the adrenal cortex, even though several corticosteroids, including the glucocorticoids, have some mineralocorticoid activity.
References:
3.Clinical Chemistry Interpretation and Techniques 4th Edition by Alex Kaplan, Bent Toibola, Kent E. Ophein, Andrew E. Lyon
4.Clinical Chemistry , Theory, Analysis and Correlation 2nd Edition by Lawrence A. Kaplan, Amadeo L. Pesce
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