The eight videos on the site depict the process of human reproduction and the scientific principles governing the reproductive process (www.pbs.org). The videos are placed in a sequential manner; one following the other with a total viewing time of one hour during which the birth of a new baby and the intricacies involved in it is shown.
The first video ‘Passing on your DNA’ introduces the viewer to the process of human reproduction. It begins by explaining how each individual begins life as a single cell and how different molecules and forces bring about the transformation of single cells to the multi-cellular human baby. The urge to reproduce in living beings is introduced as an effect of hormones and frenzy of activities within our body.
The DNA is the building block of all living species and carries the chemical instruction for building bodies of various living beings. The DNA of simpler life forms like bacteria makes copies of itself through a process called cloning. Reproduction in higher life forms including humans is not as simple as clones would be identical and susceptible to disease attack by a single organism. Higher forms reproduce by sexual means which allows the incorporation of DNA from different individuals which results in variety which is necessary for survival. The man’s sexual organ, the testicles contain miles of tubules in which almost a100 million new sperms are formed every day.
Each sperm is one of a kind. The human DNA has 46 chromosomes. 23 are from the mother and the other 23 from the father. Chromosomes occur in pairs and they divide through meiosis, a process of cell division. During reproduction, the chromosome undergoing meiosis makes an exact copy of itself and the resultant 4 sections (from either parent) embrace and exchange material. The sperm as well as the egg carry 23 chromosomes and the gene shuffling when they exchange material results in diversity which is essential for survival.
The second video entitled ‘The Eggs Journey’ elaborates about the actual process of reproduction. The female creates all her eggs as a fetus in the womb in millions but the figure reduces to as less as 1000 by age 31. Every month, one egg is selected and released from the ovary into the fallopian tube from where it is swept into the uterus by muscular contractions and movement of cilia. This egg needs DNA from a sperm in the absence of which it will die.
Partner choice among humans is a complicated process and influenced by natural hormones from the brain. Love causes dramatic changes in both sexes which result in increased glucose production and release of hormones which result in the man and woman indulging in sexual activity. Millions of sperms along with secretions from prostrate and seminal vesicles gush out but only a single sperm fertilizes the egg. Successful fertilization is controlled by changes within a woman’s body. Cervix mucus becomes watery and forms channels to guide the sperms. Undulations of uterine muscles propel the sperms towards the fallopian tube.
Sperms are chaperoned by Stuart cells and a successful sperm must pierce the Zona layer on the egg for fertilization. The zona dissolves under the influence of enzymes, allowing the sperm to push through membranes of two cells to fuse with the egg to form the embryo. 24 hours later the egg moves towards uterus and the fused cells divide resulting in formation of 4, 8, 16 and subsequently increasing number of cells.
Occasionally it splits and 2 embryos are created resulting in identical twins. 5 days after fertilization, the embryo arrives in the uterus at an approximately 100 cell stage and is now called the blastocyst. The cells within zona blastocyst must break out and find a place of nourishment in the mother’s uterus by overcoming yet another barrier – the mother’s immune system. Chemicals are now produced to suppress the immune cells and the embryo in its search for food and oxygen burrows into the tissue of the uterine lining. The mother usually feels nauseous at this stage.
The subsequent videos show the details of embryo development. The embryo takes shape 2 weeks after conception. This is followed by gastrulation in which some cells dive inwards to form three layers. The lowermost layer differentiates into organs such as the liver, the digestive tract, the middle layer gives rise to heart muscles, bones and blood and the topmost layer differentiates into the nervous system, skin and hair. This differentiation occurs three weeks after fertilization under the instructions of the DNA. The DNA instructs the formation of particular proteins like collagen, actin, myosin and Hemoglobin which are essential for life. The DNA accomplishes this task by loosening up specific portions of its highly coiled structure under the influence of molecules to synthesize the essential proteins.
The sixth video shows how ultrasound can be utilized to visualize the body of the fetus at twenty weeks time. Boys and girls look alike and the gonads can become testes or ovaries under the influence of the SRY gene which turns on a set of chemical reactions for sex determination.
The seventh video shows how the fetus takes nutrition from the mother’s blood through the placenta. The placenta has villi which lie in the pool of mother’s blood and grab food and oxygen through the umbilicus. The eyes and retina are formed by the 9th week. By the 4th month, the hard bones are formed after 5 months the process of complete body formation is complete.
The last video shows the processes taking place in the third trimester when all organ systems are well in place main job is the growth of myelin sheaths around the neurons for rapid brain development. When the fetus develops to a stage where the mother can no longer cater to its nutritional requirements, it is time for birth which is an amazing but painful experience. The cervix opens and uterus contracts and the vaginal passage widens to almost 4 inches to accommodate the baby’s head.
The videos show good graphical depiction of human reproduction with well-illustrated diagrams and videotaped movies. The narrative is excellent as well as informative.
Works Cited
Life’s Greatest Miracle, Informative videos showing the human reproductive process. Web.