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Spermatogenesis and Oogenesis
Spermatogenesis by definition is a process during which sperms are produced with half the number of chromosomes, which is haploid, as somatic cells. The process progresses first from diploid and then to haploid state, which then changes its shape to form spermatozoa. These are mature male gametes in sexually reproducing organisms (Johnson 2008). Sperm formation through spermatogenesis occurs through the process of meiosis, which is also known as gametogenesis. This process is, however, highly dependent on optimal conditions for it to occur correctly.
Oogenesis, on the other hand, refers to the process of formation and maturation of an ovum or the female gamete from the primordial germ cell. This process transpires through meiosis and is very important since it leads to production of mature eggs. This process occurs in all sexually reproductive species and includes all immature stages of the ovum. During its maturation, the ovum in mammals - oogonium, primary oocyte, secondary oocyte, ootid, and finally the ovum - is formed. The ovum formed contains half of the genetic composition of a mature individual.
Whereas in oogenesis only one mature ovum is produced, in spermatogenesis there occurs a production of four mature sperms from a single spermatocyte (Johnson 2008). It follows, that the fundamental purpose of spermatogenesis is to turn every diploid spermatogonium into four haploid sperm cells. This is usually achieved during the course of the meiotic cell division. In the process of oogenesis the production of a single egg cell usually occurs only once per month, starting from a period of puberty till menopause.
The Menstrual Cycle
The connection between menstrual cycle and women's cognitive and emotional state has captivated scientists’ attention for more than a century. Menstrual cycle is the physiological revolutionization that takes place in a fertile woman for the purposes of reproduction and fertilization. It can also be defined as the series of processes that occur in women with the intention of preparation for pregnancy. This cycle is divided into three stages, which lead to the completion of the cycle (Jerrold & Conklin 2010). These are follicular phase, ovulation phase, and the luteal phase. There are several hormones that usually are actively involved in the menstrual cycle.
Follicle stimulating hormone is involved in the follicular phase. The main purpose of this phase is to develop a viable follicle with a capability of undergoing ovulation (Mordecai 2006). During this time, the intensity of oestrogen hormone increases. This causes the liner of the uterus called the endometrium to thicken. In addition, follicle-stimulating hormone causes follicles in ovaries to grow. Only one of the follicles developing forms a fully mature egg.
Processes in this phase are stimulated by the follicle stimulating hormone. Increase in the level of the follicle stimulating hormone is linked to either a decrease or increase in the progesterone and oestrogen levels at the end of preceding cycle. Usually, under normal conditions, a single follicle should evolve into the dominant follicle, which is destined for ovulation. In the ovulation stage, luteinizing hormone (LH) is responsible for the process. Due to the influence of this hormone, primary oocyte enters the end stage of the meiotic division. Then the luteinizing hormone induces the release of proteolytic enzyme, which eventually degrades cells at the float up of the follicle. These effects of the LH lead to distension and rupturing of the follicle. At the ovulation phase, oocyte and corona radiate are expelled into peritoneal cavity. Oocyte then sticks to the ovary. Strong retrenchment of the fallopian tube leads to its contact with tubal epithelium and hence a migration through the oviduct begins.
Luteal stage takes place between 15th to the 28th day of the cycle. After the release of the ovum trough fallopian tube, the level of progesterone increases to aid in preparation of the uterine wall for pregnancy. In case of fertilization, the egg sticks to the uterine wall. Otherwise, oestrogen and progesterone levels decrease and the thickened uterine wall is shed during the menstrual period. After ovulation FSH and LH cause remaining parts of the dominant follicle to transform into corpus luteum, which produces progesterone. Increased production of progesterone induces oestrogen production. It is, therefore, diminishing levels of progesterone that lead to menstruation and the commencement of subsequent cycle.
The Role of hCG In Pregnancy and Testing
The human Chorionic Gonadotropin (hCG) also known as the ‘pregnancy hormone’ is a hormone that is produced in the pregnancy period. This hormone is produced by the embryo developing in the womb after conception and later by the placental element. This hormone can also be produced by some cancerous tumours, hence high levels of this hormone in a non-pregnant patient can lead to diagnosis of cancer (Mordecai 2006).
This hormone, through interaction with LHCG receptor, upholds the maintenance of corpus luteum at the beginning of pregnancy, triggering it to produce progesterone. Hormone progesterone provides uterus with a thick lining of capillaries and blood vessels hence enabling it to hold the growing foetus. In a normal pregnancy, the intensity of the hCG doubles about every two or three days during the first ten weeks of pregnancy. It is, therefore, the work of this hormone to maintain oestrogen and progesterone hormones at their normal levels until placenta is fully developed to take over the function of these two hormones.
The hCG is also responsible for increased blood supply to pelvis, which leads to a increased frequency of bladder emptying (Jerrold & Conklin 2010). This condition, however, ends after the first trimester and may appear again as the baby continues developing and growing within the womb. This hormone is also responsible for nausea that occurs in early stages of pregnancy, also known as morning sickness.
Since hCG is secreted by emerging placental tissue, it is a very trustworthy sign of whether the woman is pregnant or not. The intensity of hCG may be measured in urine or blood. There exist special tests that are carried out to detect the presence of any embryo in the womb. Blood and most responsive urine tests usually detect hCG within 6 to 12 days after ovulation. However, it should be understood that the level of this hormone may vary during the first four weeks. Therefore, it may lead to false results during that period.
Contraception is the means used to prevent fertilization. There are various contraception methods that are currently in use in the contemporary world. Contraception includes barrier methods which function to ensure prevention of any possible meeting between the sperm and the egg (Mordecai 2006). These methods include use of condom or diaphragm, hormonal contraception, which is also known as the oral contraception, and the injectable contraceptives. However, the widely used contraceptive methods are pills and condoms. Other contraceptive methods are intrauterine devices (IUD), intrauterine system (IUS), natural family planning, vaginal rings (Johnson 2008), progesterone-only pill, contraceptive patch withdrawal, and the caps.
Some methods of contraception are more effective than others in the prevention of pregnancy. While condom is only known to offer a protection against sexually transmitted infections, it should be noted that none of methods gives a hundred percent guarantee against pregnancy. Therefore, the only method that guarantees prevention of pregnancy is the abstinence from sex. Other methods such as vaginal rings are not recommended as a high risk is posed by its continued use. Just like the pill, this contraception method contains two hormones. Researchers warn about long term effects of using these contraception methods which include cancer. Several side effects have since been detected, which include the presence of intense vaginal discharge, headache, nausea, and very rampant mood changes that usually affect normal functioning of the person who is using these methods.
Others, such as intrauterine devices, IUD, are usually circumstanced with health threats. This method has reaching effects on those who use these methods as a control for pregnancy. Proponents of the contraception process have advocated for the use of a combined contraception. According to these advocates, combination of contraception methods, for instance the use of a condom and any other birth control method, have led to a decrease in chances of pregnancy (Johnson 2008). It should, however, be understood that opponents of these methods think differently and view these methods as unethical. Therefore, their continued influence on the human body should be halted.
Features of Embryonic and Foetal Development
Prenatal development is commonly regarded to have two stages: the embryonic and the foetal stage. During the first trimester, most of embryo’s physiological systems and body parts begin to form. Within the first month, three cell layers have already formed. These layers include ectoderm, from which the skin and sense organs develop, mesoderm, from which muscular, circulatory, and excretory systems develop, and endoderm, from which digestive system and lungs emerge. By the second month, embryo’s head represents almost half of its total weight (Jerrold & Conklin 2010). Facial features that include nose, ears, eyes, and tongue become visible and the size of forehead is big due to the brain size.
At the beginning of the third month the developing embryo is known as the foetus. It is at this period that the foetus is able to float in the amniotic fluid. It can also move, though it is too early for the mother to feel these moves at this period. Nails on fingers and toes emerge. So do the genitals, making it is easy to tell the sex of the foetus. Therefore, by the end of the first trimester the foetus is a miniature human. During subsequent two trimesters organs mature and the general growth occurs.
Placenta and Its Role
Placenta is the tissue that facilitates the exchange of nutrients between the embryo and the mother. The structure of placenta is highly related to the role it plays in exchange of nutrients between the embryo and the mother (Johnson 2008). It, therefore, nourishes and aids in the transmission of endocrine signals between the mother and the foetus. Therefore, it is the centre for nutrient and waste exchange.
For a perfect adaptation to its function, placenta has numerous highly specialized cells that aid in regulation of intrauterine development in humans. Therefore, it performs the function of several adult organs in the foetus (Harding, & Bocking 2007). Placenta is also known to have the sensory ability to maternal and foetal environment. Therefore, it is able to provide optimal environment for the growth and development of the foetus.
In placenta there are imprinted genes that help regulate adaptive responses to stressors. These genes are of great help to the developing foetus as they are capable to control the amount of nutrients that pass all the way to the foetus. They also manipulate physiology that can be in conflict with mother’s own interests.
Foetal changes at birth are important in that they prepare the foetus to adapt in the new environment. In the circulation, placental blood ceases and lungs respiration begins. The pulmonary resistance is drastically reduced. The abrupt fall in right arterial pressure forces the septum primum away from the septum secundum hence closing the foramen ovale. Failure of this closure can cause heart disease to the foetus during its growth (Harding & Bocking 2007). At birth, lungs of the baby are not inflated but are full of amniotic fluid. Within first 10 seconds after delivery the baby takes the first breath. The sudden change of environment and temperature makes newborn's central nervous system react.
In foetus, the liver functions as a storage of sugar and iron. Changes occur in foetus’ liver at birth. Later liver functions to produce substances that help in blood clotting and breaking down waste products such as excess erythrocytes. The liver also supports production of protein, which helps to break down bilirubin, failure of which can lead to newborn jaundice.
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