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The major function of the reproductive system is to ensure survival of the species. Other systems in the body, such as the endocrine and urinary systems, work continuously to maintain homeostasis for survival of the individual. An individual may live a long, healthy, and happy life without producing offspring, but if the species is to continue, at least some individuals must produce offspring.
These functions are divided between the primary and secondary, or accessory, reproductive organs. The primary reproductive organs, or gonads, consist of the ovaries and testes. These organs are responsible for producing the egg and sperm cells gametes), and hormones. These hormones function in the maturation of the reproductive system, the development of sexual characteristics, and regulation of the normal physiology of the reproductive system. All other organs, ducts, and glands in the reproductive system are considered secondary, or accessory, reproductive organs. These structures transport and sustain the gametes and nurture the developing offspring.
The study aims to discuss the effects of aging on the male reproductive system. A systematic review was performed using PubMed from 1980 to 2014. Aging is a natural process comprising of irreversible changes due to a myriad of endogenous and environmental factors at the level of all organs and systems. In modern life, as more couples choose to postpone having a child due to various socioeconomic reasons, research for understanding the effects of aging on the reproductive system has gained an increased importance. Paternal aging also causes genetic and epigenetic changes in spermatozoa, which impair male reproductive functions through their adverse effects on sperm quality and count as, well as, on sexual organs and the hypothalamic-pituitary-gonadal axis. Hormone production, spermatogenesis, and testes undergo changes as a man ages. These small changes lead to decrease in both the quality and quantity of spermatozoa. The offspring of older fathers show high prevalence of genetic abnormalities, childhood cancers, and several neuropsychiatric disorders. In addition, the latest advances in assisted reproductive techniques give older men a chance to have a child even with poor semen parameters. Further studies should investigate the onset of gonadal senesce and its effects on aging men.
Reproduction is the process by which organisms make more organisms like themselves. But even though the reproductive system is essential to keeping a species alive, unlike other body systems, it's not essential to keeping an individual alive.
In the human reproductive process, two kinds of sex cells, or gametes (pronounced: GAH-meetz), are involved. The male gamete, or sperm, and the female gamete, the egg or ovum, meet in the female's reproductive system. When sperm fertilizes (meets) an egg, this fertilized egg is called a zygote (pronounced: ZYE-goat). The zygote goes through a process of becoming an embryo and developing into a fetus.
Zinc is an essential microelement that plays many important functions in the body. It is crucial for the regulation of cell growth, hormone release, immunological response and reproduction. This review focuses on its importance in the reproductive system of women of reproductive and postmenopausal ages, not including its well described role in pregnancy. Only recently, attention has been drawn to the potential role of zinc in polycystic ovary syndrome (PCOS), dysmenorrhea, or endometriosis. This review is mainly based on 36 randomized, controlled studies on reproductive, pre- and post-menopausal populations of women and on research trying to explain the potential impact of zinc and its supplementation in the etiology of selected female reproductive system disorders. In women with PCOS, zinc supplementation has a positive effect on many parameters, especially those related to insulin resistance and lipid balance. In primary dysmenorrhea, zinc supplementation before and during each menstrual cycle seems to be an important factor reducing the intensity of menstrual pain. On the other hand, little is known of the role of zinc in endometriosis and in postmenopausal women. Therefore, further studies explaining the potential impact of zinc and its supplementation on female reproductive system would be highly advisable and valuable.
In the human reproductive process, two kinds of sex cells, or gametes (GAH-meetz), are involved. The male gamete, or sperm, and the female gamete, the egg or ovum, meet in the female's reproductive system. When sperm fertilizes (meets) an egg, this fertilized egg is called a zygote (pronounced: ZYE-goat). The zygote goes through a process of becoming an embryo and developing into a fetus.
Like other living things, human beings reproduce. It's what keeps the population going.
In humans, this happens when the male and female reproductive systems work together to make a baby.
The external part of the female reproductive organs is called the vulva, which means covering. Located between the legs, the vulva covers the opening to the vagina and other reproductive organs inside the body.
The male reproductive system consists of the internal structures: the testes, epididymis, vas deferens, prostate, and the external structures: the scrotum and penis. These structures are well-vascularized with many glands and ducts to promote the formation, storage, and ejaculation of sperm for fertilization, and to produce important androgens for male development.[1] The major male androgen is testosterone, which is produced from Leydig cells in the testes. Testosterone can be converted in the periphery to a more active form, dihydrotestosterone via 5-alpha-reductase, or estradiol via aromatase. Other key hormones include inhibin B and Mullerian inhibiting substance (MIS) hormone, both produced by the Sertoli cells in the testes. Important hormones that modulate these include follicle-stimulating hormone (FSH) and luteinizing hormone (LH), which are released from the anterior pituitary gland and are regulated by gonadotropin-releasing hormone (GnRH), produced by the hypothalamus. Together, these hormones form the hypothalamic-pituitary-gonadal axis that promotes and maintains sexual development and function in the male.[2]
Functional cells of the male reproductive system primarily consist of Leydig and Sertoli cells found in the testes. Leydig cells are found in the interstitium of the testes adjacent to the seminiferous tubules. On histology, they have pink cytoplasm and can be identified by pink crystals of Reinke. They produce testosterone, a steroid hormone that exerts its effects by binding intracellular receptors of different tissues and regulating protein expression.[3] Sertoli cells are found in the periphery of the seminiferous tubules. They promote spermatogenesis, which begins at the periphery of the tubules. They bind together to form a blood-testis barrier to keep germ cells contained in the seminiferous tubules and connect with each other through tight junctions. These cells are characterized by their relation to germ cells or primitive spermatogonia. Sertoli cells are much larger than germ cells, which are found nearby, and have less prominent nuclei. Germ cells line the interior of the seminiferous tubules and progress toward the lumen as they mature. These cells feature prominent, dark and dense nuclei.[4]
In human embryos, the default sexual differentiation is female. However, having the Y chromosome defines differentiation into the male phenotype and the male reproductive system. The Y chromosome contains the sex-determining region (SRY) gene, which encodes for development of the testes. The testes descend from the posterior abdominal wall during development to lie in the scrotum at maturity. The testes develop Sertoli cells, which produce MIS to induce regression of the Mullerian ducts, which form the female reproductive tract. The testes also develop Leydig cells that produce testosterone, the major driver of male reproductive development.
Testosterone plays an important role in stimulating the development of the Wolffian ducts in the male fetus, which become the testes, epididymis, vas deferens and seminal vesicles. Testosterone is also responsible for erythropoiesis, pubertal growth spurt, bone density, closure of epiphyseal plates, deepening of the voice, increase in muscle mass, male physique development and libido. Additionally, testosterone can be converted to dihydrotestosterone (DHT) via 5-alpha-reductase, an enzyme produced by the prostate peripherally. Both DHT and testosterone bind to the same androgen receptors intracellularly, but DHT has a higher affinity. DHT stimulates the development of the prostate, scrotum, and penis. DHT is also responsible for male hair pattern (facial, axial, and pubic hair), including the pathology of male pattern balding, increased sebaceous gland secretion and acne. Together, these hormones promote puberty and subsequent maintenance of the male reproductive system.[5]
Typically, the growth of the testes marks the beginning of puberty in males, which occur between 11 to 13 years of age. This is stimulated by a sudden rise in GnRH from the hypothalamus, which stimulates FSH and LH release from the anterior pituitary. LH stimulates Leydig cells to increase testosterone, which causes growth and pigmentation of the scrotum and penis. Secondary sexual characteristics such as facial, axillary, chest and pubic hair growth, deepening of the voice and growth spurt occur next. At this stage, first fertile ejaculations appear, marking mature reproductive function. Eventually, the epiphyseal growth plates close, marking the end of pubertal development. Pubertal development can continue into a male's 20s.
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