Reproductive System: Spermatogenesis, Prostate Cancer, and Testicular Cancer, Assignments of Philosophy

Download Reproductive System: Spermatogenesis, Prostate Cancer, and Testicular Cancer and more Assignments Philosophy in PDF only on Docsity! Spermatogenesis Spermatogenesis is the process of sperm cell production in the seminiferous tubules of the testes. It begins at puberty (when a boy is about 11 to 15 years old) and continues throughout life with 100 to 200 million sperms being made each day. Spermatogonia (singular, spermatogonium) develop from primordial germ cells that migrate into the testes early in embryogenesis. (i) Spermatogonia are immature cells that remain dormant until puberty. (ii) They are diploid cells with each containing 46 chromosomes (23 pairs). (iii) They are located surrounding the periphery of the seminiferous tubules. At puberty, hormones stimulate these cells to divide by mitosis. (i) Some of the daughter cells produced will remain at the periphery of the seminiferous tubules as spermatogonia while some are pushed towards the lumen and undergo some changes to become primary spermatocytes. (ii) Primary spermatocytes are diploid cells with 46 chromosomes. Each primary spermatocyte undergoes the first meiotic division to produce two secondary spermatocytes, which are haploid cells with 23 chromosomes. In the second meiotic division, each secondary spermatocyte divides to produce two spermatids. Thus, four spermatids are produced from the original primary spermatocyte. In the final stage of spermatogenesis, the spermatids differentiate into spermatozoa (singular, spermatozoon) or sperm. The sperm are then released into the lumen of the seminiferous tubule and leave the testes into the epididymis. Below is a transverse section of seminiferous tubules showing that it is packed with cells in various stages of development. Interspersed among these cells are large cells that extend from the periphery of the tubule to the lumen. These cells are called the Sertoli cells or nurse cells which function in supporting and nourishing the developing sperm. (a) Sertoli cells help convert the spermatids into spermatozoa by engulfing their extra cytoplasm. (b) Sertoli cells are joined to one another by tight junctions which form a blood-testis barrier and also form compartments that separate sperm cells at various stages of development. At puberty, the gonadotropin releasing hormone (GnRH) from the hypothalamus of the brain will stimulate the anterior pituitary gland to secrete two gonadotropic hormones, namely, the follicle- stimulating hormone (FSH) and luteinizing hormone (LH) . FSH initiates spermatogenesis while LH sti mulates the production of testosterone by Leydig cells. Testosterone and FSH stimulate Sertoli cells to secrete androgen binding protein and other signaling molecules that are necessary for spermatogenesis. Testosterone is the main sex hormone in males. (a) Testosterone is responsible for initiating and maintaining the secondary sexual characteristics of the human male such as the growth of the sex organs and body hair, deepening of the voice, protein synthesis/production in skeletal muscle (why boys have bigger built), sex drive (aggresiveness at times) and general muscular and skeletal development. (b) It is also necessary for the maturation of sperm. Hormonal actions in spermatogenesis are regulated by a negative feedback mechanism Overproduction of testosterone inhibits t he secretion of LH by acting on the hypothalamus which decreases the secretion of GnRH. This results in decreased FSH and LH secretion by the anterior pituitary. Sertoli cells also release inhibin , a hormone which inhibits the secretion of FSH by the anterior pituitary gland. FSH itself stimulates inhibin secretion. Structure of a sperm Plasma membrane a Middle piece —@ | { Mitochondrion | Neck Tail Acrosome (flagellum) Centriole Nucleus Mature sperm or spermatozoa consist of three parts—the head, middle piece and a tail. The head is flattened and oval in shape. The nucleus, enclosed in a thin membrane, is contained within the head. The acrosome forms a cap at the anterior end of the nucleus. It secretes hydrolytic enzymes which help the head to penetrate the oocyte. The middle piece consists of a tightly coiled spiral sheath of elongated mitochondria. The mitochondria provide energy for sperm motility The tail or flagellum has the typical ‘9 + 2' microtubule arrangement. It allows the sperm to swim towards the egg. Erectile dysfunction (ED) is sexual dysfunction characterized by the regular and repeated inability of a sexually mature individual to obtain or maintain an erection. Itis a common disorder that affects about 40 percent of people with penises. Causes of Erectile Dysfunction The penis normally stiffens and becomes erect when the columns of spongy tissue within the shaft of the penis (the corpora cavernosa and corpus spongiosum) become engorged with blood. Anything that hampers normal blood flow to the penis may, therefore, interfere with its potential to fill with blood and become erect. The normal nervous control of sexual arousal or penile engorgement may also fail and lead to problems obtaining or maintaining an erection Specific causes of ED include both physiological and psychological causes. Physiological causes include the use of therapeutic drugs (such as antidepressants), aging, kidney failure, diseases (such as diabetes or multiple sclerosis), tobacco smoking, and treatments for other disorders (such as prostate cancer). Psychological causes are less common but may include stress, performance anxiety, or mental disorders. The risk of ED may also be greater in people with obesity, cardiovascular disease, poor dietary habits, and overall poor physical health. Having an untreated hernia in the groin may also lead to ED. Treatments for Erectile Dysfunction Treatment of ED depends on its cause or contributing factors. For example, for tobacco smokers, smoking cessation may bring significant improvement in ED. Improving overall physical health by losing weight and exercising regularly may also be beneficial. The most common first-line treatment for ED, however, is the use of oral prescription drugs, known by brand names such as Viagra® and Cialis®. These drugs help ED by increasing blood flow to the penis. Other potential treatments include topical creams applied to the penis, injection of drugs into the penis, or the use of a vacuum pump that helps draw blood into the penis by applying negative pressure. More invasive approaches may be used as a last resort if other treatments fail. These usually involve surgery to implant inflatable tubes or rigid rods into the penis. Epididymitis is inflammation of the epididymis. The epididymis is one of the paired organs within the scrotum where sperms mature and are stored. Discomfort or pain and swelling in the scrotum are typical symptoms of epididymitis, which is a relatively common condition, especially in young individuals. In the U.S. alone, more than half a million cases of epididymitis are diagnosed annually between the ages of 18 to 35. Epididymitis may be acute or chronic. Acute diseases are generally short-term conditions, whereas chronic diseases may last years — or even lifelong. Acute Epididymitis Acute epididymitis generally has a fairly rapid onset and is most often caused by a bacterial infection. Bacteria in the urethra can back-flow through the urinary and reproductive structures to the epididymis. In sexually active individuals, many cases of acute epididymitis are caused by sexually transmitted bacteria. Besides pain and swelling, common symptoms of acute epididymitis include redness, warmth in the scrotum, and a fever. There may also be a urethral discharge. Chronic Epididymitis Chronic epididymitis is epididymitis that lasts for more than three months. In some, the condition may last for years. It may relatively late in life and is usually slow growing, so treatment may not be necessary. In younger patients or those with faster-growing tumors, treatment is likely to include surgery to remove the prostate, followed by chemotherapy and/or radiation therapy. Testicular cancer, or cancer of the testes, is the most common cancer in individuals between the ages of 20 and 39 years. It is more common in European than African ancestry. A lump or swelling in one testis, fluid in the scrotum, and testicular pain or tenderness are possible signs and symptoms of testicular cancer. Testicular cancer can be diagnosed by a physical exam and diagnostic tests, such as ultrasound or blood tests. Testicular cancer has one of the highest cure rates of all cancers. It is typically treated with surgery to remove the affected testis, and this may be followed by radiation therapy and/or chemotherapy. If the remaining testis is healthy, normal male reproductive functions are still possible after one testis is removed. Female Reproductive System Oogenesis e Female gametes develop in the ovaries by a process called oogenesis e Oogenesis begins soon after fertilization. The primordial germ cells in the ovary begin to proliferate mitotically from a few thousand to almost 7 million and differentiate into oogonia (2n) . However, after the seventh month of embryonic development, most of the oogonia (singular, oogonium) die. e The remaining oogonia divide by mitosis and mature into primary oocytes. e The primary oocytes progress through the first meiotic division but is arrested at prophase |, at which point they are maintained until puberty. e At puberty, secretion of FSH (Follicle stimulating hormone) triggers only one primary oocyte to complete meiosis I. (i) The division of the cell is unequal, producing one large cell, the secondary oocyte , and one tiny cell called the polar body. (ii) Both cells are haploid. The secondary oocyte begins the second meiotic division but the process stops at metaphase. At this point, ovulation occurs. If fertilization occurs (i.e., nuclear fusion of egg and sperm), meiosis II will be completed producing an ovum and the second polar body. The first polar body also usually divides to produce two smaller polar bodies which later degenerate. Structure of the secondary oocyte At birth, each oocyte is enveloped by a primordial follicle consisting of a single layer of epithelial granulosa cells and thecal cells. Periodically, a group of primordial follicles enters a stage of follicular growth. (a) During this time, the oocyte undergoes a 500-fold increase in volume and it is now called a primary follicle . (b) Granulosa cells form concentric layers around the oocyte. In addition, an antrum (a cavity), which is filled with a complex mixture of proteins, hormones and other molecules, forms. The follicle now becomes a secondary follicle . e The granulosa cells also secrete a glycoprotein substance that forms a clear membrane around the oocyte known as the zona pellucida . e The oocyte lies at the edge ina mound of granulose epithelial cells, the cumulus oophorous . The cumulus is shed along with the egg at ovulation. e The fully developed ovarian follicle is also called a Graafian follicle. Read This: The ovarian and menstrual (uterine) cycles The female reproductive cycle consists of two important cycles: (a) The ovarian cycle and (b) The uterine or menstrual cycle. The ovarian cycle The ovarian cycle is a series of events in the ovaries that occur during and after the maturation of the oocyte It comprises three phases: the follicular phase, ovulatory phase and luteal phase During the follicular phase, three to thirty follicles begin to grow. However, only one of these follicles called the dominant follicle continues to grow while the other stimulated follicles disintegrate. This phase lasts about 13 to 14 days. In the ovulatory phase, the dominant follicle bulges from the surface of the ovary and finally ruptures, releasing the oocyte (ovulation). This phase usually lasts 16 to 32 hours. It lasts about 14 days, unless fertilization occurs. In this phase, the ruptured follicle forms a structure called a corpus luteum which will secrete progesterone and estrogen to prepare the uterus for any possible pregnancy. The menstrual cycle Menstruation can be defined as the shedding of the lining of the endometrium accompanied by bleeding. The average time for each menstrual cycle is typically stated as 28 days. However, it varies from 25 to 36 days. The cycle has three phases: the menstrual flow phase, proliferative phase and secretory phase. The menstrual flow phase begins on the first day of menstrual bleeding (day 1). At the beginning of the menstrual flow phase , the lining of the endometrium is thick with fluids and nutrients designed to nourish the embryo. If there is no fertilization, the top layers of the endometrium will be shed and menstrual bleeding occurs. Bleeding lasts 3 to 7 days, averaging 5 days. In the proliferative phase , regeneration and thickening of the endometrium takes place. The duration is about 1 to 2 weeks. During the secretory phase , the endometrium continues to thicken and the vascularization of the endometrium increases The endometrium also develops glands that secrete a glycogen-rich fluid to nourish a potential fetus. This phase takes about 2 weeks. If by the end of the secretory phase an embryo has not been implanted in the uterus, a new menstrual flow commences. Both the ovarian and menstrual cycles are regulated by a complex interaction of hormones secreted by the hypothalamus, anterior pituitary gland and the ovaries. The follicular phase of the ovarian cycle is coordinated with the menstrual flow phase and the proliferative phase of the menstrual cycle. At the beginning of the follicular phase, that is, during menstrual bleeding, GnRH from the hypothalamus stimulates the release of FSH (Follicle stimulating hormone) and a little LH (luteinizing hormone) from the anterior pituitary gland into the bloodstream which in turn initiates follicular growth and maturation. The growing follicles secrete small amounts of estrogen. As the follicles mature over a period of 7 days, they secrete more estrogen. The secretion of estrogen during the follicular phase stimulates endometrial thickening, gland formation and vascularization (blood vessel formation). A rising level of LH induces the final maturation of the follicle. The growing oocyte within the follicle then completes the first Note meiotic division forming a secondary oocyte. When the estrogen level reaches a certain point it causes the anterior pituitary gland to release a large amount of LH. This sudden increase of LH (LH surge) triggers ovulation. The when pregnancy occurs. The corpus luteum does dominant follicle ruptures and releases the secondary oocyte into the Fallopian tube take place. Instead, the endometrium thickens to permit the implantation of the embryo and its development within it. The luteal phase of the ovarian cycle is coordinated with the secretory phase of the menstrual cycle. Following ovulation, under the continued influence of LH, the empty follicle develops into the corpus luteum. The corpus luteum will secrete a large amount of progesterone and some estrogen which: (a) Causes the continued thickening of the endometrium for a possible pregnancy (b) Inhibits the contraction of the uterus (c) Causes the body/basal temperature to increase slightly and remain The high level of progesterone together with estrogen, however, exerts negative feedback on the hypothalamus. These hormones inhibit the release of GnRH which, in turn, inhibit further release of FSH and LH. (note: negative feedback- inhibition) A small amount of the gonadotropin hormones are, nevertheless, required to maintain the function of the corpus luteum. If fertilization does not occur, the corpus luteum degenerates into corpus albicans . This will: decrease progesterone and estrogen levels. stop the inhibition of uterine contraction, cause follicular growth to resume and a new menstrual cycle to begin. However, if the oocyte is fertilized and begins to divide, the corpus luteum will continue to exist. Itis prevented from deteriorating by the human chorionic gonadotropin (HCG) hormone produced by the chorion of the embryo. Note: The presence of HCG in urine confirms a women's pregnancy. Test kits could be bought whenever one's suspicious of being pregnant. DISORDERS Cervical cancer occurs when cells of the cervix grow abnormally and develop the ability to invade nearby tissues or spread to other parts of the body. Worldwide, cervical cancer is the second-most common type of cancer and the fourth most common cause of cancer deaths. Early on, cervical cancer often has no symptoms. Later, symptoms (such as abnormal vaginal bleeding and pain) are likely. Most cases of cervical cancer occur because of infection with human papillomavirus (HPV), so the HPV vaccine is expected to greatly reduce the incidence of the disease Other risk factors include smoking and a weakened immune system A Pap smear can diagnose cervical cancer at an early stage. Where Pap smears are done routinely, cervical cancer death rates have fallen dramatically. Treatment of cervical cancer generally includes surgery, which may be followed by radiation therapy or chemotherapy Vaginitis is an inflammation of the vagina. A discharge is likely, and there may be itching and pain. About 90 percent of cases of vaginitisare caused by infection with microorganisms, typically by the yeast Candida albicans. A minority of cases are caused by irritants or allergens in soaps, spermicides, or douches. Diagnosis of vaginitis may be based on characteristics of the discharge, which can be examined microscopically or cultured. Treatment of vaginitis depends on the cause and is usually an oral or topical anti-fungal or antibiotic medication. Endometriosis is a disease in which endometrial tissue grows outside the uterus. This tissue may bleed during the menstrual period and cause inflammation, pain, and scarring. The main symptom of endometriosis is pelvic pain, which may be severe. Endometriosis may also lead to Infertility. Endometriosis is thought to have multiple Retrograde menstruation may be the immediate cause of endometrial tissue escaping the uterus and entering the pelvic cavity. Endometriosis is usually treated with surgery to remove the abnormal tissue and medication for pain. If surgery is more conservative than hysterectomy, endometriosis may recur.