Question

1. Describe the pathway of a mature egg through ovulation and menstruation. What structures does the oocyte pass through and what interactions occur?

2. Describe the pathway of a mature sperm cell during ejaculation. What structures does the sperm cell pass through and what interactions occur?

Answer 1

(1)The figure shown is of an ovary where in an oocyte is getting matured and finally is released from the ovary. The Primary follicle matures to become secondary follicle by developing more layers of granulosa cells around it ; the secondary gets transformed into tertiary wherein a fluid filled cavity is formed in it and more granulosa cells surround it; and tertiary follicle then finally matures into the graafian follicle.

  The release of egg(secondary oocyte from graafian follicle) from ovary is termed as ovulation. Ovulation occurs when luteinizing hormone(LH) is secreted(generally within 24 to 36 hours after secretion of LH).

During fertilization, the released ovum goes to ampullary- isthmic junction (via infundibulum) of the fallopian tube where sperm is already waiting for it and thus the ovum gets fertilized. But, not every time is the case that sperm waits for ovum. In that case, Menstruation occurs.

Menstruation: when the ovum is not fertilized, endometrial lining of uterus and blood vessels breakdown and comes out in the liquid form through vagina. This is a monthly process that occurs in every 28-30 days. The menstrual flow is of 3-5 days.

Menstrual cycle has 3 phases:

1. Menstruation- As we now know that egg is released due to LH secretion, this LH also stimulate secretion of Progesterone which is a hormone that helps maintain the uterus endometrium lining to support pregnancy. But when the egg is not fertilized, corpus luteum gets signals of rupturing and thus no more LH is secreted which hence does'nt stimulate the secretion of progesterone and as a result the uterus endometrial lining breaks off and menstruation takes place. It lasts for 3-5 days.

2. Follicular Phase- After 3-5 days , again in ovary the process of oocyte maturation starts ; eventually graafian follicle is formed , uterus lining builds up again. During this phase the LH and Follicle stimulating hormone(FSH) secretion increases that stimulate follicle growth and development; as well as secretion of estrogen. When LH reaches at its peak ovulation occurs. This phase lasts for 9-10 days.

3. Luteal Phase- After ovulation , the graafian follicle which is left in the ovary is now called corpus luteum, it stimulates the secretion of progesterone (that maintains the endometium which is necessary for implantation of fertilized egg) and its levels are maintained during pregnancy, that time no menstruation occurs(for 9 months; in case of humans). But otherwise, corpus luteum degenerates and leads to shedding of endometrial lining of uterus. This phase lasts till 14 days. After that new cycle starts.

(2)

Sperms are formed inside the testes in the seminiferous tubules.

(a) Spermatogonium divide mitotically to from primary spermatocyte which then divide meiotically to form secondary spermatocyte , then the secondary spermatocyte undergo second meiotic division to form (haploid)spermatids.These spermatids mature into the spermatozoa which embed themselves into sertoli cells (present in the seminiferous tubules) to obtain nutrition.

(b) On the top of testes , epididymis is present where sperms migrate from seminiferous tubules and get matured while residing there for a few days. On stimulation , sperms are ejected from epididymis and reach vas deferens.

(c) Vas deferens is a muscular duct that is directed towards abdomen by crossing over the urinary bladder. It pushes the sperm forward after which the sperm reaches ampulla where it gets mixed with the secretions(seminal fluid) of seminal vesicle.

(d) The seminal fluid along with sperms is then passed through the prostate gland wherein a milky fluid is added to this and finally forms SEMEN which is ejaculted through the urethera and finally ejacultes out..