Female Reproductive System free essay sample

When a girl reaches the age of 13-15, she begins to ovulate or starts her period. This is the age of her sexual maturity, the age of sexual maturity in both male and female is called puberty. The female reproductive system is a complex and important system. The system serves three main functions: to store ova, to produce ova, and to keep a fertilized egg until it is ready to live on its own. What happens in this age? Puberty is marked by changes in the body for example, in the female the breasts start developing, pubic hairs also grow and you become way more moody. The first menstruation in the life of a girl is called menarche. In the female, the internal genitals are the ovaries, the fallopian tubes, the uterus and the vagina. The ovary it is a paired organ. Each ovary of the adult female is an oval body and weight 2-8 grams. We will write a custom essay sample on Female Reproductive System or any similar topic specifically for you Do Not WasteYour Time HIRE WRITER Only 13.90 / page The ovum drops into the body cavity. The process is called ovulation; the ovum which is released in to abdominal cavity is pushed towards the oval funnel. The ovum finally enters the funnel and starts coming down the duct. The ovum is very small the size of a pinhead. The ovary releases one ovum every 28 days. Next comes the uterus or womb, it is a hollow, pear-shaped muscular structure. Its upper broader portion is called the corpus uteri and the narrow portion is the cervix. The cavity of the womb is 7-8 centimeter long. The external genital parts of the female include the outer and the inner lips and the clitoris. The outer and inner lips close the openings of the vaginal tube, the vestibule. The clitoris is found in the pubic cleft. In menstruation eggs will never be implanted in the uterus in the unfertilized state. After about two weeks of ovulation the uterus begins to contract. This sign is of undoing the preparations it had made to receive to have a baby. Upon the contraction of uterus, the blood capillaries rupture, and the blood flows out through the vagina. The blood along with tissue debris is called menses. Menstruation lasts for 3-4 days. Menstruation takes place 14 days after the ovulation. Again 14 days after menstruation, there is fresh ovulation. Both these processes stop once pregnancy had set in. There are post-fertilization changes like, mplantation after fertilization the reproductive organs are directed towards a different set of activities. As the fertilized egg goes down the oviduct, it going through mitotic cell division, it is a nonstop process, but for our convenience we divide the post-fertilization events in to a number of stages. When the cell forms a mass of cells there is no space within the group, it’s called the morula stage. The cells of morula rearrange in a manner to leave some space. This stage is called blastula; therefore it is blastula which is embedded in the uterus. This process is called implantation. The wall of the uterus is thick and its wall has muscles, glands and blood capillaries. As the fertilized egg erodes into the uterine wall, there is some erosion of blood capillary. As a result the blood comes out and the blastula gets nutrition from that blood. This will develop in to fetus and finally a baby. When the blastula implanted in the uterus of the mother, it continues to grow by cell division. There important layers of cells develop. These are the germ layers. Membranes are developed and the outermost membrane of the embryo is formed and now called chorion. The second covering of the embryo is amnion, which immediately surrounds the fetus and protects it. Within this covering there is an amniotic fluid which protects the embryo from shocks as well as any major trauma. There is an intimate contact between the blood vessels of the uterus and that of the fetus through the placenta. Umbilical cord serves as a link between the fetus and maternal circulation. When the embryonic development is completed, the baby is born. The baby is pushed out by the contraction of the uterine muscles; this is called birth. Somewhere between 45-55 years the ovary stops releasing the egg. We can say that the ovary has become nonfunctional. Menopause is a normal part of a womans aging process. The ovaries stop releasing eggs, and menstrual periods stop. Most women experience menopause around age 50. Before to menopause, menstrual cycles often become off. The ovaries are less active to stimulating hormone and luteinizing hormone. To try to make up for the decreased response, the body produces MORE of these hormones. The level of these hormones will decrease. The hormones produced by the ovaries include the different forms of estrogen, progesterone, and prolactin. The ovaries continue to produce small amounts of testosterone and some estrogen. The hormones produced by the pituitary gland are also decreased. Because hormone levels fall, changes occur in the entire reproductive system. The vaginal walls become less elastic, thinner, and less rigid. The vagina becomes smaller and shorter. When menstruation stops in a woman, it is taken for granted that she will not be able to have a child any more. Ending of menstruation is called menopause.

The selfish gene theory Essay Example

The selfish gene theory Essay Example The selfish gene theory Paper The selfish gene theory Paper Therefore, if people acted purely in their self-interest as relayed in the often misunderstood purest form of the selfish gene theory, this person would not contribute to the common account in the first place and would reap the rewards of everyone else’s contribution. Contributions to the common fund started at approximately 50% of the total points of each player but this decreased over the course of the game as some people put less in the common account. Justifications for the decline in cooperation were that the only way to punish people who were not contributing to the common account was to decline to contribute to that account also. It begs the question as to how sustainable cooperative and social behaviours are without a significant deterrent to behaving selfishly. When this game was conducted with opportunity to heavily punish non contributors by using their own points to deduct from those of the non-contributing players this was consistently selected. This pattern of behaviour meant that cooperation no longer decreased over the rounds so cooperative behaviour was maintained by reward and punishment as it often is in society. More recent neurobiological evidence supports the notion that even this seemingly altruistic behaviour by the actor is selfish at a genetic level, De Quervain et al (2004) found that when a person punishes another for non-cooperative behaviour the dorsal striatum is stimulated and as this is the circuitry involved in reward-related activity there is a direct fitness benefit being bestowed by this behaviour to the actor. Additionally, there are indirect benefits for the group to which the actor belongs as this behaviour increases their survival chances and productivity. Therefore the overall fitness benefits to the person’s genes through the ultimate maintenance of the group and societal norms which help to preserve that group outweighs the personal sacrifices made to maintain this system of cooperative and social fairness which has fitness benefits for those who engage in it (Hamilton, 1964, 1975). If selfish behaviour increases a persons’ overall fitness then it would seem obvious that genes which promote selfishness should increase their presence in the gene pool and that altruistic genes would therefore be outbred. This would mean that Dawkins (1976) explanation for cooperative and social behaviour would be fundamentally flawed. However, game theory has shown how important the combination of those who behave selfishly and those who behave in a seemingly altruistic way is to the evolution of the genes that promote these behaviours. A game called ‘prisoners dilemma’ demonstrates that when two people behave altruistically they increase the overall fitness of both parties and hence the gene that promotes this behaviour is likely to survive and be replicated. When both parties behave selfishly both decrease their overall fitness which makes the gene responsible less likely to survive and be replicated and when one partner behaves selfishly it is their own fitness that will increase but if there is discrimination from those who have the altruistic genes in their willingness to interact with those carrying the selfish gene then this explains why the population is not overcome by those carrying the selfish gene. Dawkins purports that consciousness has evolved to be able to override the influence of the genes and that the more executive decisions are made at the helm of this consciousness. It is the relationship between the genes and consciousness that determine how a person will behave and the influence of the environment and its culture shapes consciousness more than genes do. Dawkins acknowledged a meme as a unit of culture that can be passed from person to person at a much faster rate than genes would be and therefore memes create rules for cooperative and social behaviour and these rules help to maintain systems of cooperation by punishing those who do not engage fairly in social interactions. Therefore where behaviours cannot be explained by genes they are explained by memes and Cartesian-dualism. Because ultimately genes are primarily concerned with their own replication, they influence people to behave in ways that are most likely to meet this need; altruistic and cooperative behaviour has evolved as a consequence of its success at replicating itself and therefore cooperative and social behaviour is explained by the SGT as having evolved at the level of the genes through selfish means. Cooperative and social behaviour at the level of the organism is therefore only a mechanism to ensure that the needs of the genes are being met. The survival of the fittest is therefore not a competition for resources and advantageous selfish behaviour but it is an enhanced chance of survival and reproduction bestowed on those who behave in efficient ways such as through cooperative and social behaviours (Margulis Lovelock, 1974) Conclusively, Dawkins SGT appears to be able to offer adequate explanations for cooperative and social behaviours that enhance the fitness of the actor and those who share the same genes. If the fitness is not directly or indirectly enhanced with an immediate effect then this can be explained as having a lifetime fitness benefit by this same theory but it is worth noting that measuring lifetime fitness benefits is difficult to do which limits this explanation. The weaker the genetic connection between the actor and the recipient the weaker the theory becomes when offering explanations for cooperative and social behaviours, especially as the behaviour of the actor becomes increasingly altruistic. Therefore from the perspective of the SGT even apparently cooperative and social behaviour at the level of the organism is always one of selfish motivation at the level of the genes; put succinctly, ‘scratch an altruist and watch a hypocrite bleed’ (Ghiselin, 1974). References Dawkins, R. (1976). The selfish gene. New York: Oxford University Press. Hamilton, W. D. (1964). The genetical evolution of social behaviour. I II. Journal of Theoretical Biology. 7, pp. 1-52. Hamilton, W. D. (1975). Innate social aptitudes of man: An approach from evolutionary genetics. In R. Fox (Ed. ), Biosocial anthropology (pp. 133-155). New York: Wiley. Sachs, J. L. , Mueller, U. G. , Wilcox, T. P. , Bull, J. J. (2004). The evolution of cooperation. Quarterly Review of Biology, 79, pp. 135-160. Trivers, R. L. (1971) Evolution of reciprocal altruism. Q. Rev. Biol. 46, pp. 35-7. Gardner, A. , and West, S. A. 2004. Spite and the scale of competition. J. Evol. Biol. 17, pp. 1195–1203. Gardner, A. and West, S. A. 2006. Demography, altruism, and the benefits of budding. Journal of Evolutional Biology. 19, pp. 1707–1716. West, S. A. , Gardner, A. , Barton, N. H. (2007). The relation between multilocus population genetics and social evolution theory. 169, pp. 207–226. Maynard Smith, J. (1964). Group selection and kin selection. Nature, 20, pp. 1145-1147. Johannsen, W. (1911). The genotype conception of heredity, Amer. Natur. , 1911. 95. 1911-10005-00110. 1086/279202. Krebs, J. R. , Davies, N. B. (1993). An introduction to behavioral ecology. (3rd ed. ). Oxford, england: blackwell. de Quervain, D. J. , Fischbacher, U. , Treyer, V. , Schellhammer, M. , Schnyder, U. , Buck, A. , Fehr, E. (2004, August 27). The neural basis of altruistic punishment. Science, 305, 1254-1258. West, S. A. , A. S. Griffin, and A. Gardner. 2007. Social semantics: altruism, cooperation, mutualism, strong reciprocity and group selection. J. Evol. Biol. 20, pp. 415–432. West, S. A. , A. S. Griffin, A. Gardner, and S. P. Diggle. 2006. Social evolution theory for microorganisms. Nat. Rev. Microbiol. 4, pp. 597–607. Griffin, A. S. , and S. A. West. 2002. Kin selection: fact and fiction. Trends Ecol. Evol. 17, pp. 15–21. Frank, S. A. (2003). Perspective: repression of competition and the evolution of cooperation. Evolution 57. pp. 693–705. Lehmann, L. , and L. Keller. 2006. The evolution of cooperation and altruism- a general framework and a classification of models. J. Evol. Biol. 19 pp. 1365–1376. Kummerli, R. , Gardner, R. , West, S. A. , Griffin, A. S. (2008) Limited dispersal, budding dispersal and cooperation: an experimental study. Ghiselin, M. (1974). A radical solution to the species problem. Systematic Zoology, 23, 536-554. Van Baalen M. and Jansen V. A. A. (2006) Kinds of kindness: classifying the causes of altruism and cooperation. Journal of Evolutionary Biology 19: 1377-1379 Heylighen F. (1992) Selfish Memes and the Evolution of Cooperation, Journal of Ideas , 2. pp 77-84.