Endocrine system is related to the hormonal changes that take place in a human body right from the birth till they are alive and also the diseases that results due to the hormonal imbalance. Mostly, it can be noticed that when a girl or boy reaches puberty, their body undergoes lots of changes in relation to the structure and functions, that sometimes becomes a stressful situation for them, because they are not exactly aware of all those changes and initially can be mysterious and confusing to them. But, with good guidance and proper knowledge of parents they can actually understand the biological changes going inside their body.
Endocrine system controls all the activity of body and regulates almost all the cells by releasing hormones that act as the mediator molecule. These hormones are released in the body fluid thus, reaching to the target place through blood.
The endocrine gland includes pituitary gland, thyroid gland, parathyroid gland and adrenal gland.
1. Pituitary gland: it is a pea shaped gland also called master gland because it secretes different hormones that control all the other endocrine glands. Interestingly, this gland is also controlled by other major gland called hypothalamus where it is attached to pituitary by infundibulum. Pituitary is divided into two portions: anterior pituitary also called adenohypophysis and posterior pituitary called neurohypophysis.
Anterior pituitary/ Adenohypophysis: it is divided into two portions, pars distalis and pars tuberlis. It secretes different hormones that regulates the body activity from birth till death. Some of the important hormones secreted by cells of anterior pituitary are:
1. Somatotrophs: it secretes growth hormone also called somatotropin which regulates growth and development of the body.
2. Thyrotrophs: it secrete thyroid stimulating hormone that maintains yet controls all the activity of thyroid gland. It releases two hormones, T3 and T4 called triiodothyronine and thyroxine respectively. In one hand high level of T3 and T4 inhibit the secretion of TRH whereas its low level increases the secretion of TRH.
3. Gonadotrophs: it secretes two hormones: FSH and LH that stimulates the secretion of estrogen and progesterone, also stimulates the production of sperm and testosterone in testis. Most importantly, FSH triggers the development of ovarian follicles which is sac like arrangement. GnRH and FSH are suppressed by estrogen in female and testosterone in male. On the other hand LH triggers ovulation and helps the formation of corpus luteum . Corpus luteum secretes progesterone. Progesterone and estrogen prepares uterus for fertilized ovum and prepare mammary gland for milk secretion.
4. lactotrophs: these cells secrete prolactin that stimulates mammary gland for production of milk but prolactin itself does not fulfills this task alone, with the assistance of other hormone it completes this procedure of milk secretion. Dopamine inhibits the release the prolactin .
5. Corticotrophs: secretes adrenocorticotropic hormone that stimulates adrenal gland to secrete different corticotrophs. It also secrete melanocyte stimulating hormone that increase pigmentation of skin. It can be inhibited using dopamine.
Hyposecretion of anterior pituitary hormone causes dwarfism, when organs of the body fails to grow due to the early closure of epiphyseal plate whereas hypersecretion of hGH during childhood causes gigantism( increase in length of bone) and in adult causes acromegaly (failure to increase in bone length due to early closure of epiphyseal plate).
Posterior pituitary gland: it secrets two hormone oxytocine and vasopressin.
Oxytocin: it is the hormone that has greater affect during and after the pregnancy. It gets activated on two tissues, mothers uterus and the breast. On one hand, it helps in the contraction of smooth muscle and on the other hand it helps in the ejection of milk.
ADH also called anti diuretic hormone: this hormone has effect on the urine production. It makes kidneys to retain more water thus decreasing the volume of urine . not only through urine, but ADH also decreases loss of water through sweating. This hormone is also called vasopressin because it causes constriction of artioles that causes increase in Blood pressure. The release and inhibition of this hormone is influenced by neurosecretory cells in hypothalamus. Beside, this alcoholic substances particularly inhibit the action of this hormone.
Due to defect in ADH at posterior pituitary, Diabetes Insipidus is caused. Diabetes insipidus is of two types neurogenic diabetes insipidus caused due to hyposecretion of ADH and nephrogenic diabetes insipidus caused due to hyper secretion of the same.
2. Thyroid gland: it is butterfly in shaped organ that consist of two lobes, right and left. This gland is made up of many sacs like follicles consisting of follicular cells. Therefore, under the influence of TSH they change their shape from cuboidal to low columnar. TRH i.e. thyroid releasing hormone and TSH i.e. Thyroid stimulating hormone stimulates and maintain release of thyroid hormone. Some of the actions of thyroid hormones are:
Calcitonin is also one of the important hormone produced by parafollicular cells of thyroid gland. It maintains the level of calcium thus, lowering its level and increasing its reabsorption and uptake by the bones.
Hyposecretion of thyroid hormone at birth causes congenital hypothyroidism whereas in adult it causes myxedema. The hyperthyroidism of this hormone causes Graves’s diseases and goiter.
3. Parathyroid glands: these are round mass of tissue that is present in posterior surface of lateral lobes. It consist mainly two types of cell, called chief cell that produce parathyroid hormone and the other is oxyphil cell. Parathormone regulates the calcium, magnesium and phosphate ions in the blood. On the other hand it also increase the loss of HPO42- from blood into the urine. Beside these two, PTH also increase the formation of calcitriol in blood.
Hypoparathyoidism leads to deficiency of calcium in blood whereas hyperparathyroidism causes increases calcium level in blood that promotes kidney stones and even death.
4. Adrenal glands: it is a pyramid shaped gland that has two distinct regions: adrenal cortex and adrenal medulla. On one hand, adrenal cortex secrete three hormone mineralocorticoids, glucocorticoids and androgen whereas adrenal medulla secretes epinephrine, norepinephrine and dopamine.
Mineralocorticoids: it is secreted by zona glomerulosa cells of adrenal cortex. The major mineralocorticoids is aldosterone that regulates sodium and potassium ions thus, adjusting blood pressure and blood volume. It also helps in the excretion of H+ in the urine thus promoting the loss of acid from the blood. Aldosterone is regulated by the RAA pathway that is called rennin- angiotensin- aldosterone pathway.
Hypersecretion of cortisol produces Cushing’s syndrome that increase excessive secretion of cortisol.
Glucocorticoids: It is secreted by the zona fasciculata cells of adrenal cortex. It has three different hormones: cortisone, cortisol, corticosterone among which cortisol is present in maximum amount. CRH and CIH maintains the level of this hormone in the blood. Some of the effects of glucocorticoids are:
Androgens: it is secreted in very low amount and the major androgen is DHEA called dehydroepiandrosterone. It promote growth of axillary hairs and pubic hairs. It also promotes sex drive.
Hyposecretion of glucocorticoids and aldosterone causes Addison’s diseases.
Adrenal medulla: It secrets mainly two hormone, epinephrine and norepinephrine and the cells that produce this hormones are chromaffin cells. These hormones only intensifies sympathetic response in most parts of the body.
Pheochromocytomas is caused due to hypersecretion of epinephrine and norepinephrine.
Pancreatic islets: As we all know that pancreas is the gland that is endocrine as well as exocrine and is located on the first part of the small intestine. This gland consist of acini i.e. exocrine and islets and langerhans i.e. endocrine and hence produce digestive enzymes and serve in many more ways. Some of the important cell types in pancreatic islets are:
The endocrine disorder of pancreatic islets is diabetes mellitus that is inability to produce or use insulin. This is of two types, diabetes mellitus type 1 and type 2. In type 1, pancreatic beta cells are destroyed hence lowering the insulin level whereas type 2 is much more common. In this case, target cells get less sensitive due to down regulation of insulin receptor and hence insulin cannot be used by the body.
Hypersecretion of insulin results in hyperinsulinism when insulin level increases resulting in hypoglycemia.
This way our endocrine system serves in several ways so as to maintain the balance of hormone in the body and keep up free from any kind of dangers that can result due to any hormonal disproportion. For this task, different organs mentioned above takes part in different ways, so that the complete cycle from birth to death is well accomplished under their guidance and hence our body system function in effective way.
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