Human Reproduction

Human eggs are alecithal. It is also called microlecithal eggs. It has a very small or negligible amount of yolk. Yolk is present in order to provide nourishment to the developing embryo. Examples of animals with alecithal eggs are frogs, toads etc.

In human female, the blastocyte Gets implanted in endometrium by trophoblast cells. Following fertilization, a process known as cleavage occurs in which the cytoplasm of the zygote is evenly split among multiple smaller cells or morulas.

• A morula is reached in humans after the fourth day after fertilization.
• The blastula stage comes after the morula stage. The blastula is made up of blastomeres, which are organized in an inner cell mass and an outside layer termed trophoblast, respectively.
• The trophoblast cells implant the blastula in the uterine endometrial lining 7-9 days or around one week after ovulation.
• An embryo's sustenance is given by the nutrients released by the uterine cavity prior to implantation, such as iron and fat-soluble vitamins.
• Implantation in the endometrial uterine wall takes place at the blastocyst stage of embryonic development.
• Before implantation, the blastomeres of early blastocyst get arranged into an outer layer called trophoblast and an inner group of cells attached to the trophoblast called inner cell mass.
• It is the trophoblast layer through which the blastocyst gets attached to the endometrium and the inner cell mass gets differentiated as the embryo.

The release of the ovum, or female gamete, from the ovary, is known as ovulation. The isthmus region of the fallopian tube is where the male gamete, or sperm, and the female gamete, or fertilization, fuse. A zygote is created by this union. A multicellular fetus will develop inside the body of the mother from a diploid unicellular cell.

• After fertilisation, the zygote is separated.
• The zygote is changed into a morula through cleavage. It is distinguished by a dense clump of cells that contains 16–32 cells.
• A blastula stage or hollow mass of cells will result from this.
• The blastocoel, a hollow filled with fluid inside the cell ball, is encircled by an inner cell mass and trophoblast on the outside.
• The trophoblast layer expands into the uterine endometrial lining by dissolving endometrium molecules during about one week, or 7-9 days, following ovulation.
• This is followed by the gastrulation stage, during which the three germ layers—endoderm, mesoderm, and ectoderm—are formed through cell rearrangement.
• And this collection of cells is called a gastrula.
• The placenta develops after implantation.

Discover more from this chapter: Human Reproduction

The correct answer is Option 1: Is produced by granulosa cells in ovary and inhibits the secretion of FSH.

Explanation:

Inhibin is a glycoprotein hormone that plays a key role in regulating the reproductive system.

In females, inhibin is produced primarily by the granulosa cells in the ovaries. It inhibits the secretion of FSH (Follicle Stimulating Hormone) from the anterior pituitary gland, helping to regulate the menstrual cycle and follicular development.

In males, inhibin is produced by the Sertoli cells in the testes and serves to inhibit the secretion of FSH, not LH.

Breakdown of Options:

Option 1: Correct. Inhibin is produced by the granulosa cells in the ovaries and inhibits the secretion of FSH.

Option 2: Incorrect. Inhibin inhibits FSH, not LH.

Option 3: Incorrect. While inhibin is produced by nurse (Sertoli) cells in testes in males, it inhibits FSH, not LH.

Option 4: Incorrect. Inhibin specifically inhibits FSH secretion, not LH and prolactin.

Conclusion:

Option 1 is the correct statement about inhibin.

• In human reproduction, fertilization generally occurs at the ampullary-isthmic junction of the fallopian tube.
• For successful fertilization, both the ovumsperms (deposited in the vagina) must reach this site at the same time.
• This ensures that the sperm can penetrate and fertilize the ovum before it degenerates (typically viable for 24 hours).

Incorrect options:

• Option 2: Cervix is not the site of fertilization.
• Option 3: Fertilization occurs in the fallopian tube, not uterus.
• Option 4: Vaginal deposition is normal, but timing must match ovulation, and fertilization doesn’t happen in the vagina.

Therefore, the correct condition for fertilization is when both ovum and sperm meet at the ampullary-isthmic junction of the fallopian tube.

Sperm Transport Route

Sperms are produced in the testis and transported out of the testis through the following route:

• Rete testis: The network of tubules in the testis where sperm begins to collect.
• Efferent ductules (Vasa efferentia): These small ducts carry sperm from the rete testis to the epididymis.
• Epididymis: A coiled tube where sperm matures and is stored before ejaculation.
• Vas deferens: The tube that carries mature sperm from the epididymis to the urethra during ejaculation.

Capacitation is a phenomenon of activation of sperm by which it develops the ability to fertilize ova in mammals. The secretions of the female reproductive tract lead to the removal of the coating substances that are deposited on the surface of the sperms, especially on acrosomes, therefore exposing the receptor sites and activating the sperm to penetrate the egg.

Therefore, Capacitation is an increase in fertilizing capacity of sperms that occurs in the female reproductive tract.

The correct Answer is option (a); Release of Prolactin

To determine the correctness of the given statements, we will analyze each statement separately:

• Statement I: The release of sperms into the seminiferous tubules is called spermiation.
  In human biology, spermiation refers to the process of releasing mature spermatozoa from the Sertoli cells into the lumen of the seminiferous tubules. Hence, Statement I is correct.
• Statement II: Spermiogenesis is the process of formation of sperms from spermatogonia.
  Spermiogenesis is actually the transformation of spermatids into mature spermatozoa. The process begins after the formation of spermatids and concludes with the development of mature sperm, whereas the transformation of spermatogonia to spermatids involves several stages such as mitosis and meiosis, which are collectively termed as spermatogenesis. Therefore, Statement II is incorrect.

Thus, in light of the analysis, the correct answer is: Statement I is correct but statement II is incorrect.

1. Embryonic Development Stage: Oogenesis begins during the fetal development in the ovaries of the female fetus. Here, primordial germ cells undergo mitosis to form oogonia.
2. Arrest in Prophase I: These oogonia then enter meiosis but pause in Prophase I, becoming primary oocytes. This pause persists until puberty.
3. Reactivation at Puberty: During puberty, hormonal changes stimulate some primary oocytes to resume meiosis, eventually leading to the formation of a mature ovum.

• FSH or Follicle Stimulating Hormone is primarily known to stimulate ovarian follicles in females, leading to the production of estrogen. In males, however, FSH mainly acts on the Sertoli cells in the testes, which aid in sperm maturation. Leydig cells, on the other hand, are stimulated by LH (Luteinizing Hormone) rather than FSH. Therefore, Assertion A is incorrect regarding Leydig cells.
• Reason R accurately describes that growing follicles in females secrete estrogen and that interstitial (Leydig) cells in males produce androgens (such as testosterone). Thus, the stated reason is true.