Free «The Reproductive System» Essay Sample
The function of the female reproductive system is to produce female gametes. They are also referred to as oocytes (Ganong, 2003). The female reproductive system holds oocytes to enable forming an embryo during fertilization. In addition, it produces hormones that control its function. Beginning from menarche, the female reproductive organs undergo changes both in their structure and functions. Modifications are under control of neurohumoral mechanisms. Menopause occurs approximately at the age of 45 (Scanlon & Sanders, 2007). During it, cyclic changes become irregular and disappear.
In females, the ovaries play a vital role in egg production. They are almond-shaped organs having the size of approximately 3cm by 1.5 cm by 1cm. Their surface is covered with the germinal epithelium. Below the latter, there is the tunica albuginea, which makes the ovary appear whitish. The cortical region is located underneath it. The ovarian follicles that give rise to oocytes dominate in this region (Junqueira & Carneiro, 2005). They are suspended in the stroma of the cortical region. The medullary region is the inner part of the ovaries. There is no sharp demarcation between the cortical region and the medullary one.
The ovaries develop from primordial germ cells that migrate from the yolk sac into the gonadal primordium. The cells divide intensely to transform into millions of oogonia. At the beginning of the third month, the oogonia divide and pass to the prophase stage of the first meiotic division. At this stage, the cells are referred to as primary oocytes (Junqueira & Carneiro, 2005). The latter are then surrounded by follicular cells. Some of the primary oocytes undergo degeneration, and at puberty, there are only 300,000 oocytes. Only one oocyte is produced during ovulation. The remaining ones will undergo atresia. The oocyte that is surrounded by one or more layers of follicular cells, which are collectively referred to as an ovarian follicle. At puberty, primordial follicles start growing. It is characterized by the modification of the oocyte, granulosa cells and fibroblasts of the stroma. This process is referred to as follicular growth. During it, there is only one primordial follicle, which is selected. The growth of follicles is stimulated by the follicle-stimulating hormone (FSH) (Ganong, 2003). It is produced in the hypophysis. Oocyte growth is more intense during the initial stages of follicular growth. There is an increase in the nucleus size, mitochondria also increase in number and are distributed uniformly. The endoplasmic reticulum hypertrophies. Follicular cells divide mitotically to form a unlaminar primary follicle. With continued proliferation, these cells form the granulosa layer. The cells of granulosa communicate via gap junctions. At this stage, it is referred as a preantral follicle. The zona pellucida, a thick and amorphous layer made up of glycoprotein, surrounds the oocyte. The latter together with follicular cells are thought to contribute to the formation of the zona pellucida. Oocyte’s microvilli and the filopodia of follicular cells penetrate into the zona pellucida, where they contact with each other via gap junctions (Scanlan & Sanders, 2007). An increase in the number and size of granulosa cells contributes greatly to the growth of follicles. There is the increased accumulation of liquor folliculi within follicular cells. The portions of the liquor coalesce to form the antrum. It changes the name of follicles to secondary ones. During the formation of the antrum, some granulosa cells concentrate at a point to form the cumulus oophorus that has the oocyte. More granulosa cells surround the oocyte to form the corona radiata. At the same time, stroma’s fibroblasts differentiate into the theca folliculi that later subdivide into theca interna and externa cells. The former differentiate completely to acquire steroid producing characteristics. They synthesize androstenedione hormone that is transported to the granulosa layer. Under the influence of FSH, granulosa cells synthesize aromatase enzyme. Androstenedione is converted to estrogen by this enzyme. The theca externa is made up of organized fibroblast layers surrounding the theca interna.
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In the ovarian cycle, only one follicle grows at a faster rate to become dominant. The remaining growing follicles undergo atresia. The dominant follicle reaches maturity at the stage of being a preovulatory or graafian follicle. At its peak, it is around 2.5 cm in size. The increased accumulation of fluids increases the size of the graafian follicle, while the oocyte attaches to its wall via the cumulus oophorus. The growth of a primordial follicle to a graafian one lasts for 90 days (Junqueira & Carneiro, 2005). The oocyte is released during ovulation
During ovulation, the mature follicle raptures to liberate the oocyte. This process happens in the middle of the menstrual cycle. In humans, mostly one oocyte is released, though at times there is none, which is liberated (the anovulatory cycle). At times, two or more oocytes are released, and as a result, two or more fetuses are formed, in case they are fertilized. The ovulation process is stimulated by luteinizing hormone (LH) (Ganong, 2003). It is produced by the anterior lobe of the pituitary gland as a response to increased levels of estrogen produced by the growing follicle. LH causes an increase in blood flow to the ovary. There is also edema that develops because of plasma proteins leaking from capillaries. There is the increased release of collagenase, vasopressin, prostanglandins, and histamine. As a result, there is the development of a weak area on the follicle wall. Compounded with the increased pressure from inside, the oocyte is forced to leave the follicle through the weak area. It is a process called ovulation (Junqueira & Carneiro, 2005). The first stage of meiotic division is completed prior to ovulation. Chromosomes are shared equally between daughter cells, but one such cell has more cytoplasm. A daughter cell with less cytoplasm (the first polar body) is expelled. The remaining daughter cell (secondary daughter cell) starts second meiotic division, which stops at the metaphase. The oocyte is then picked up by the fimbria of oviducts, where it is transported to the Fallopian tube for fertilization to occur.
After ovulation, the theca interna and granulosa cells of the ovulated follicle reorganize to form the corpus luteum. It develops in lymphatic and blood vessels. The reorganization of the corpus luteum is maintained by LH released before ovulation. Under the influence of this hormone, the corpus luteum starts secreting estrogen and progesterone, which inhibit the secretion of FSH (Ganong, 2003). The destiny of the corpus luteum is influenced by the establishment of pregnancy. If there is pregnancy, trophoblastic cells of the embryo secrete human chorionic gonadotropin (HCG) to maintain the corpus luteum. The latter secretes more progesterone, that is needed for the maintenance of pregnancy. Furthermore, progesterone hormone will stimulate uterine glands that provide nutritive support to the embryo, as the placenta is developing. The corpus luteum of pregnancy lasts for 4-5 months, after which it degenerates. By the point of degeneration, the placenta will have been developed fully, and it takes over the role of the corpus luteum, which is maintaining pregnancy. During pregnancy, there is no menstruation, until the time it will be terminated.
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As far as the menstrual cycle is concerned, it lasts averagely for 28 days. The first day of the cycle is assumed to be the day, when bleeding appears. This phase is called the menstrual phase and lasts for 3-4 days. The proliferative phase follows the menstrual one. During this time, the uterine walls are thin because of sloughing off. At the beginning of the proliferative phase, there is the release of follicle stimulating hormone (FSH) from the hypophysis. It stimulates the growth of ovarian follicles. The latter release estrogen that affects the vagina. In addition, it also stimulates the proliferation and reconstruction of the lost endometrium. The proliferative phase ends when the follicle has reached the preovulatory phase (Junqueira & Carneiro, 2005). Afterwards, the luteal phase follows. During this time, the pituitary gland produces luteinizing hormone (LH) that stimulates ovulation. It also induces the development of the corpus luteum, which produces progesterone, which is essential for maintaining the pregnancy. It also increases the supply of blood to the endometrium. If there is no pregnancy, the corpus luteum degenerates to form the corpus albicans. The production of progesterone also ceases. As a result, the thick and tortuous endometrium becomes too heavy and is shed of. This shedding constitutes the menstrual phase. The cycle begins afresh after menses. Figure 3 below depicts changes that happen during the menstrual cycle (Scanlon & Sanders, 2007
It should be noted that the menstrual cycle is also referred to as the uterine cycle. The ovarian cycle can be said to be part of the uterine one. It entails activities that happen within the ovary. As it has been discussed earlier, the cycle begins at the time, when the primary follicle starts to develop, until the time it matures to the graafian follicle. Once it releases the oocyte during ovulation, the latter enters the luteal phase of the uterine cycle. These cycles are controlled by hormones produced by the hypophysis, the anterior-lobe of the pituitary gland, follicles and the corpus luteum.
The paper also analyzes how the male reproductive system produces sperms. Sperms in males are synthesized in seminiferous tubules in a process called spermatogenesis. It requires temperature less than the normal body one. It is ensured by the hanging of the scrotum outside the body. It allows continuous circulation of air to maintain the testes at the temperature of 32° C. The primitive germ cell, the spermatogonia, lies next to the seminiferous tubules’ basal lamina. During adolescence, the spermatogonia develops into the primary spermatocyte (Scanlon & Sanders, 2007). The latter divides meiotically reducing its chromosome number by half. It undergoes two stages to be divided into secondary spermatocytes and later into spermatids. The latter contain 23 chromosomes, and they mature into spermatozoa in sertoli cells. In humans, the formation of a mature sperm takes 74 days. Sperms are motile cells rich in DNA. They have an acrosome covering its head. It is rich in enzymes that aid sperms to penetrate the ova. Ones sperms have matured; they are released into the lumen of the tubules. The testis’ gametogenic function is maintained by androgens and FSH. By the time, spermatozoa leave the testis, they will not have achieved full mobility. As a result, they continue with maturation to acquire mobility while in the epididymis. It is achieved by activating CatSper proteins (Ganong, 2003). A spermatozoon that has achieved full mobility is ejaculated as a result of vas deferens contracting. Ejaculation is a two-part process that starts with the emission of semen to the urethra. The second part is ejaculation proper, where semen is propelled out of the urethra into the vagina at the time of orgasm. The propelling of semen is aided by the contraction of muscles called bulbocarvenosus. At the time of ejaculation, sperms are delivered in a fluid called semen. In addition to sperms, semen also contains secretions from seminal vesicles, Cowper’s gland, prostate and urethral glands. On average, the volume of semen is 2 - 3.5 ml, and it decreases with continuous ejaculation. An ovum is only fertilized with one sperm, though at the time of ejaculation, there are roughly 100 million sperms produced. Once ejaculated, sperms move at the pace of 3 mm/min in the female tract and reach the uterine tubes 30 – 60 minutes after sex (Ganong, 2008). Sperms travel to the Fallopian tubes, where they undergo capacitation. It prepares sperms for the fertilization of the ovum.
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There are two sexually transmitted diseases, which are syphilis and gonorrhea, analyzed in the paper. Syphilis spreads mainly through sexual activities, both oral and anal sex. It is a bacterial infection caused by Treponema pallidum(Fauci, 2008). The disease has also been reported to be transmitted through prolonged kissing. It is mainly characterized by sores that act as foci for spreading. Most of the time, an infected person is not aware of the disease. Syphilis is termed congenital, if it is spread from a pregnant mother to an unborn child. Such type of syphilis may interfere with the normal development of the child.
The disease occurs at three stages. Primary syphilis is the initial stage, when an affected person may have one or more sores. They are hard and painless. They occur mostly around the genitals and the mouth after 10 – 90 days of the exposure. They heal without scarring after six weeks. It is the most infectious stage. Then, there is the secondary stage. It starts within 6 weeks to 6 months after the exposure. It may last for 1 – 3 months. The infected person has a characteristic copper, like rash in the palms and soles, though rashes may develop in other parts of the body. Moist warts appear in the groin. Orally, there are white patches. Constitutional symptoms are common at this stage. Just like primary syphilis, it can be resolved without any treatment. The third stage is the latent one, when the disease lies dormant with no symptoms. The tertiary stage is the fourth one. It is reached, if the disease is not treated. It has severe complications, such as paralysis, blindness, impotence and deafness, among others. In case of no treatment, it can result into death. A penicillin dose is the best and most effective drug for treating syphilis. Patients allergic to penicillin can use doxycycline or tetracycline (Fauci, 2008).
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Gonorrhea is transmitted sexually. Having contact with infected bodily fluids can also cause the disease. It affects both men and women, and is more common in people with many sexual partners. Neisseria gonorrhea causes gonorrhea (Fauci, 2008). Symptoms vary in men and women, though in both, they are noticed 2 – 10 days after the exposure. In women, there is a greenish or yellowish vaginal discharge, abdominal pain, dysuria, vulvitis, and conjunctivitis along with constitutional symptoms. In men, the symptoms are burning sensation, when urinating, greenish discharge from the penis, painful testicles, and burning sensation in the throat (oral sex). The diagnosis is by the use of a Gram-stained urethral smear. Treatment is by the use of antibiotics either orally or through injections. A sex partner should be informed and treated.