Steroidogenesis Has a Common Pathway but Hormonal Steroids Are Secreted in a Specific Manner - Essay Example

Steroidogenesis takes place in endocrine glands like the adrenal and gonads.P450side chain-linked cleaving enzyme gets involved in the interconversion of cholesterol to Carbon18, Carbon19, and Carbon21 and this is the committed step of Steroidogenesis (John 1994, p.33).

            HMG-CoA or the mevalonate pathway generates isopentenyl pyrophosphate and dimethylallyl pyrophosphate which serve as precursors for steroidal hormones biosynthesis. Isopenteyl pyrophosphate and dimethylallyl pyrophosphate become joined forming geranyl pyrophosphate that becomes lanosterol (Mary 2011, p.55). Lanosterol undergoes Steroidogenesis transformation to form other steroids. All steroid hormones in humans follow this pathway, but not all steroids are hormones (John 1994, p.77).

            Steroid hormones are crucial for the proper functioning of the body. They get synthesized from cholesterol which is also a component of the cell membrane thus the hormone is able to enter the cell and bind to its receptor. Steroid hormones get classified as androgens, estrogens, progestins, mineral corticoids, and glucocorticoids. Both estrogens and androgens get generated by the gonads and affect sexual development. Progestins mediate the menstrual cycle and pregnancy. Excretion of water and salts by the kidney get regulated by mineral corticoids while lipid carbohydrate and protein metabolism become affected by glucocorticoids. Steroid hormones become synthesized when they are needed. The brain releases a signal when the body wants a certain protein synthesized or needs a certain process done (John 1994, p.78). These signals get transmitted via the intermediary hormones in other words through trophic hormones. Once released, they act on the central nervous system and the peripheral target tissues (Richardb2010, p.67).

One can regulate the amount of steroid hormone secretion by regulating the amount of cholesterol produced because cholesterol is the precursor for these hormones. The adrenal cortex has three main tissue regions: the zona glomerulosa, zona fasciculate, and zona reticular area. These zones are histological and enzymatically distinct and the exact steroid hormone secreted depends on the enzymes present (Reginald 2010, p.34). Adrenocorticotropin (ACTH) hormone regulates hormones produced at the zona reticularis and zona fasciculata (Donald 2010, p.56). The hypothalamus releases ACTH into the bloodstream then it becomes carried to the adrenal glands where it binds to ACTH receptors on the cell membrane activating adenylate cyclase with the production of cAMP (second messenger). This leads to the ultimate secretion of cortisol. When the body needs to accumulate more sodium, angiotensinogen gets released from the liver and it becomes angiotensin( i) and later angiotensin (ii) that bind to the cell membrane receptors which get coupled to the phospholipase c of the zona glomerulosa (John 1994, p.32). This leads to the secretion of aldosterone; a mineral corticoid. Aldosterone leads to sodium retention by facilitating gene expression of messenger RNA for sodium-potassium ATPase which is responsible for the reaccumulation of sodium and potassium.

Gonadol steroid hormones become secreted by the testis and ovaries. The important hormones in this category are estradiol and testosterone. Luteinizing hormone stimulates testosterone production in men by binding to Leydig cells. Androgen binding protein transports testosterone Sertoli cells which convert it to dihydrotestosterone which is more potent. Androgen binding protein production gets increased by Follicle-stimulating hormone (FSH). Luteinizing hormone in females binds to ovary thecal cells stimulating the secretion of testosterone and androstenedione. Aromatase complex converts the latter two hormones into estrogen (John 1994, p.88).

            All steroidal hormones share a common biosynthesis pathway that involves cleavage of a six-carbon group from the precursor (cholesterol) by p450 side chain linked cleaving enzyme as the rate-limiting step. They all use cholesterol as their precursor however, they get secreted in a strongly cell-specific manner. The adrenal cortex has three zones with cells that are histologically distinct and each zone produces a different type of steroidal hormone. Each zone has different receptors on the cell membrane that anchor specific tropic hormones (John 1994, p.68).