PLEASE READ EVERYTHING AND ANSWER IN DETAIL. Consider the process of conception,
ID: 195834 • Letter: P
Question
PLEASE READ EVERYTHING AND ANSWER IN DETAIL.
Consider the process of conception, where 200 million sperm have an incredible upstream race “like space voyagers approaching a huge planet 85,000 times their own size” (Myers, p. 137). The egg, once pierced by the fastest sperm, shuts out all others, and soon fuses with it to begin something new. Take a good look at the progression from zygote to embryo to fetus.
How might genetics and environment come into play even this early? (Consider teratogens in your comments.)
How do behaviors like rooting, sucking, crying, and gazing at face-like patterns 8-12 inches away work to help newborns survive and develop?
What instinctual behaviors on the part of parents might help babies develop? (Think of evolutionary processes in how these behaviors came to be.)
Explanation / Answer
The process of fusion of a sperm [male gamete] with an ovum [female gamete] is called fertilisation.
During coitus, semen is released into the female's body . The motile sperms swim rapidly through the cervix, enter into the uterus and reach the ampullary isthmic junction of the oviduct.
A sperm comes in contact with the zona pellucida of the ovum. The acrosome in the head of the sperm helps it to enter the ovum by secreting enzymes which dissolve the zona pellucida and the cell membrane. After penetrating the ovum, the sperm induces changes in the zona pellucida to block the entry of other sperms.
The nuclei of the sperm and ovum fuse to form a diploid zygote.
The zygote divides rapidly by mitotic division. This is called cleavage. As a result 2, 4, 8 and 16 daughter cells are produced which remain together and are called blastomeres. This stage is called morula.
The cells in morula divide further to form a large mass of cells called blastocyst. Blastomeres in the blastocyst are arranged into an outer layer called trophoblast and an inner group of cells attached to the trophoblast called inner cell mass.
The trophoblast layer gets attached to the cells of the endometrium of the uterine wall. The inner cell mass gives rise to the embryo.
The cells of the endometrium divide rapidly and cover the blastocyst. Thus the blastocyst gets embedded in the endometrium of the uterus. This is called implantation.
Meanwhile, the cells of the trophoblast divide rapidly to form an inner and an outer layer. The outer layer, called chorion, develops finger like projections which penetrate into the endometrium. These projections are called chorion villi and they form an intimate connection with the uterine tissue and form the placenta which is the main structural and functional unit connecting the fetus to the mother.
An umbilical cord connects placenta with the embryo that helps in transport of nutrients, oxygen etc to the fetus from mother and discharge of waste from the fetus for excretion.
The inner cell mass of blastocyst develops into three layers :
i] outer layer called ectoderm
ii] middle layer called mesoderm, and
iii] inner layer called endoderm
Inner cell mass contain certain cells called stem cells which have the potency to give rise to all the tissues and organs.
After one month of pregnancy , the fetal heart is formed.
By the end of the second month, the fetus develops limbs and digits.
By the end of the third month, most of the organ systems are formed.
Appearance of hair on the head and fetal movement is observed during the fifth month of pregnancy.
After six months, the body is covered with fine hair , eyelids separate and eyelashes are formed.
By the end of the ninth month, the fetus is completely developed and can survive as an individual outside of its mother's body. It is ready for delivery.
The average duratin of uman pregnancy is about 9 months which is called gestation period.
The act of expelling a fully formed fetus from the mother's uterus is called parturition.
A mother has to be extremely careful in her lifestyle, eating habits, sleep cycles in fact almost everything to bear a healthy child . Sometimes, a child is born with congenital defects like sickle cell anemia, colour blindness etc. but many a times external factors also play a crucial role in congenial abnormalities. Example is due to teratogens.
Teratogens are drugs, chemicals, alcohol or even infections that can cause abnormal fetal development. Malformations like cleft lip, premature birth , mental retardation and even death of the newborn are possible side effects of teratogens.
Newborns are said to recognise their mother's feel and voice as soon as they are born. Since, the only way babies can express themselves is by crying, it is very important for their survival. They express hunger, pain or any other form of discomfort by crying and this makes the parents react to their call. Suckling comes instinctively to newborns ; nobody teaches them to suckle milk. Within a couple of months of their birth, the babies begin to recognise faces. Familiar face, touch, sound and environment makes them feel secure and safe. They react to unfamiliar things by crying and respond to all things that are familiar to them. This helps in their healthy growth.
As we all know, instinctive behaviour of parents towards their offsprings, is not restricted only to humans. In fact all mammals and even birds show care and protection towards their newborns. There is nothing more fierce in the world than an angry mother who senses any danger to her babies ! Understanding the need of their newborn comes naturally to mothers. Human mothers can understand the need of their child just by the way the baby cries i.e whether the cry is due to hunger, pain or any other factor. So, the bond between a mother and her baby is instinctive, inborn and psychic--- it goes beyond all explanations. Perhaps this is necessary for generations to go on and on.
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