Question

(c) diagram below shows the sequence of events which take place when the nucleu of an animal sperm enters the cytoplasm of the egg. Zona pellucida Egg cell membrane Cytoplasm i) Name the part of the reproductive tract in which these events take place. [1] Use the information in the diagram to explain the role of in the process. Pl

Answer 1

Ques-c:

Part-1:

Answer: Fallopian tube

Reason: The fallopian tube is the specific section of the oviduct in uterus where fertilization occurs, there are total 4 layers of fallopian tube such as serosa, subserosa, lamina propria and innermost mucosa. The inner mucosa and subsera layers composed of peg cell, which are having "nuclear receptors" to get stimulated via "action of estrogens". Finally, numbers of cilia are going to increase in peg cells on visceral peritoneum. This location of hormone receptors in the cells, internal cellular responses to estrogen binding to its receptor and the result of estrogen stimulation of the oviductal cell trigger movement of oocyte to meet with sperm cells. ​Fertilization of the ovum occurs, if the ovum meets with the sperm and results in the formation of a zygote.

Part-2: acrosome

Reason:

Inside the female uterus, ampulla of fallopian tube, fertilization initiates due to acrosomal reaction takes place due to secretion of hyalurinidase fluids at the penetration of sperm cell into the secondary oocyte using acrosome. Sperm cells uses whip like flagella movement to penetrate into the ovum (chemotaxis) zona pellucida layer finally sperm cells uses hyalurinidase enzyme to penetrate inside the egg through corona radiata.

The fusion of plasma membranes of egg and sperm during the process of fertilization triggers a series of changes in the egg, which blocks polyspermy. Fusion of plasma membranes of sperm and egg cells triggers depolarization of the membrane. Now, this membrane causes “fast block to polyspermy,” which temporarily blocks the sperm penetration. This occurs prior to the cortical reaction.

Ques-2:

Estrogen has mainly available in humans in three forms and they are

Estrone (E1) - it is produced during the menopause

Estradiol (E2) - it is produced from the ovary

Estriol (E3) - it is majorly produced during pregnancy, this hormone is normally at low levels during follicular and luteal phase & mid-cycle of menstruation phase. The normal lab values of serum and urine of estriol has described below

During follicular phase, the FSH (follicle stimulating hormone) released by the anterior pituitary help maturation of the ovum, and the surge of luteinising hormone is essential for the release of matured ovum. At 14 or 15th day of menstrual cycle ovulation occurs, and the follicular sac develops into corpus luteum that secretes progesterone (luteal phase).

In the uterine cycle, during the preovulatory stage (6 to 15 days), estrogens promote the proliferation of uterine wall and increase the vascular supply.

The concentration of FSH and LH decreases after ovulation, the progesterone concentration increases with little estrogen. During this phase of the uterine cycle (16 to 28 days), the vasculature of endometrium is increased by progesterone and estrogen.

Thus, if the corpus luteum fails to secrete progesterone, the endometrial vasculature does not develop, which is must for am ovum to survive after implantation. Mean, though implantation occurs in this case, full term pregnancy is not possible.

High testosterone levels in women may leads to development of sterility and male secondary sexual features & there will be no menstrual cycle. Therefore, low level of testosterone in women is going to promote “menstrual cycle” & this testosterone is going to maintain equilibrium level of balancing estrogen and progesterone hormones during the menstrual cycle as explained below.

Estrogens and progesterone have negative feedback regulation on FSH and LH through the anterior pituitary. The FSH and LH cause the increased secretion of estrogen and progesterone from the ovaries.

Ovulation takes place on day 14 due to the stimulus given by leutinizing hormone.

Higher levels of estrogen are during the last follicular phase produces a positive feedback mechanism on leutinizing hormone and gonadotrophic hormone and further leading to formation of corpus luteum.

Hormones such as gonadotrophins (FSH, LH) released from the anterior pituitary are responsible for the regulation of ovarian and uterine menstruation cycle further leading to elevated levels of gonadotrophin enable release of egg and leading to corpus luteum. Graffian follicle is at maturity during menstrual cycle therefore, higher levels of LH observed just prior to ovulation. Here hCG usually signals corpus luteum to further release of secondary sexual hormones such as progesterone and estrogen to avoid the endometrium as of sloughing off.

After ovulation, the primitive corpus luteum produced from the old remnant tissue of the Graffian follicle followed by formation of follicular cavity from remnants of corpus hemorrhages. Corpus luteum possess histologically highly vascularised and has two types of cell and these are acts as temporary endocrine glands and releases progesterone, a female secondary sexual hormone that stimulates luteal phase finally enable secretory activity of endometrium. If fertilization does not occur this corpus luteum become calpus albicans and releases via sloughed off tissues in the menstruation.