ANSWER
Part A: Physical and Hormonal Factors That Cause the Functional Layer to Shed During Menstruation
Hormonal and physical factors controlled by the ovarian and uterine cycles cause the endometrium’s functional layer to shed during menstruation.
Hormonal Elements:
Decline in Progesterone and Oestrogen Levels: The corpus luteum generates progesterone and oestrogen throughout the luteal phase of the ovarian cycle in order to preserve the endometrium’s functional layer. These hormones sharply fall if fertilisation fails because the corpus luteum degenerates. The functioning layer breaks down as a result of this hormone withdrawal.
Release of Prostaglandins: When progesterone levels fall, prostaglandins are produced in response. This leads to ischemia and vasoconstriction in the spiral arteries that supply the endometrium. The functional layer sheds and tissue necrosis results from this ischemia.
Physical Aspects:
Ischemia and Necrosis: The endometrial tissue experiences hypoxia and necrosis as a result of reduced blood supply brought on by prostaglandin-induced vasoconstriction, which makes it easier for the tissue to separate.
Prostaglandins also cause the uterus’s myometrium to contract, which aids in the removal of blood and necrotic tissue through the vagina during menstruation.
Section B: The Impact of Fertilisation
1. The Fertilisation Process
A zygote is formed at the end of a complicated series of activities called fertilisation, which involves both the sperm and the egg.
Procedures Concerning the Egg:
Oocyte Maturation: The secondary oocyte is stopped in metaphase II of meiosis after being liberated after ovulation. Meiosis II is only finished when sperm penetrate.
Zona Pellucida Interaction: The acrosome response is started when glycoproteins in the egg’s zona pellucida attach to certain receptors on the sperm head.
Procedures Concerning the Sperm:
Capacitation: In the female reproductive system, sperm experience metabolic alterations that boost their motility and allow them to pass through the zona pellucida.
Acrosome Reaction: The sperm can access the egg plasma membrane when the zona pellucida is broken down by enzymes released by the sperm’s acrosome.
Fusion: The sperm nucleus enters the egg’s cytoplasm after the membranes of the sperm and egg merge.
Final Occurrences:
After a sperm penetrates, the egg’s cortical granules release enzymes that alter the zona pellucida and stop polyspermy.
Meiosis II Completion: The egg completes its second meiotic division, developing a polar body and a haploid ovum.
Pronuclear Fusion: This process restores the diploid chromosome number by fusing the haploid pronuclei of the sperm and egg.
2. Fertilization’s Effects
Restoration of Diploid Chromosome Number: A diploid zygote (46 chromosomes in humans) is created during fertilisation by fusing the haploid sets of chromosomes from the egg and sperm.
Egg Activation: The metabolic processes of the egg are triggered by fertilisation, which starts the development of the embryo.
Creation of Genetic Variation: Offspring that have their maternal and paternal genomes mixed together have more genetic diversity.
Cell Division Initiation: A multicellular blastocyst is formed when the zygote initiates fast mitotic divisions, or cleavage.
Offspring Sex Determination: The sperm contributes either an X or Y chromosome, which determines the embryo’s sex (XY for males, XX for females).
Development of Embryonic Structures: The processes that lead to implantation and the creation of extra-embryonic structures, like the placenta, are initiated by fertilisation.
These procedures guarantee the development of a viable embryo that can mature into a fully developed organism.
QUESTION
Part A:
In menstruation, the functional layer is shed from the endometrium. Explain the hormonal and physical factors responsible for this shedding.
Part B:
Fertilization involves much more than a mere restoration of the diploid chromosome number.
- What does the process of fertilization entail on the part of both the egg and sperm?
- What are the effects of fertilization?