Embryonic Development and Gametogenesis
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Questions and Answers

What characterizes the primary or preantral follicle stage in terms of its cellular composition?

  • It contains both granulosa and theca cells.
  • It lacks any surrounding glycoprotein layers.
  • It is comprised solely of flat follicular cells. (correct)
  • It includes mature oocytes ready for fertilization.

Which function does the zona pellucida serve during the early stages of fertilization?

  • It facilitates the transfer of nutrients from maternal blood.
  • It acts as a barrier to prevent polyspermy. (correct)
  • It provides protective support to the oocyte during cleavage.
  • It assists in the production of hcG for early pregnancy signaling.

During the implantation process, which cell type is primarily responsible for invading the endometrial lining?

  • Granulosa cells
  • Theca externa cells
  • Flat follicular cells
  • Syncytiotrophoblast cells (correct)

What is the primary role of the placenta once it is formed?

<p>To facilitate gas exchange and nutrient transfer between mother and fetus. (B)</p> Signup and view all the answers

Which statement correctly describes the composition of a secondary or antral follicle?

<p>It includes theca interna and externa layers with a fluid-filled antrum. (B)</p> Signup and view all the answers

What structure forms after the syncytiotrophoblast burrows into the endometrium and vacuoles fuse?

<p>Lacunae (A)</p> Signup and view all the answers

Which germ layer is primarily produced from the epiblast during gastrulation?

<p>Mesoderm (A)</p> Signup and view all the answers

What is a primary function of the zona pellucida?

<p>Protecting the oocyte (C)</p> Signup and view all the answers

In which week of embryonic development does gastrulation occur?

<p>Third week (B)</p> Signup and view all the answers

What is an example of an abnormal site of implantation?

<p>Ectopic pregnancy (C)</p> Signup and view all the answers

Which component of the placenta is formed due to the fusion of maternal blood supply and the syncytiotrophoblast?

<p>Lacunae (C)</p> Signup and view all the answers

What role does the hypoblast play during early embryonic development?

<p>Develops the yolk sac (C)</p> Signup and view all the answers

What type of tissue primarily composes the syncytiotrophoblast?

<p>Epithelial tissue (B)</p> Signup and view all the answers

What is the primary role of the zona pellucida during fertilization?

<p>To prevent polyspermy. (C)</p> Signup and view all the answers

During the initial stages of cleavage, what structure do the cells form as they divide?

<p>Morula. (A)</p> Signup and view all the answers

What is the main function of the syncytiotrophoblast during implantation?

<p>To invade the endometrium and create spaces for maternal blood. (B)</p> Signup and view all the answers

What two structures arise from the inner cell mass of the blastocyst?

<p>Hypoblast and epiblast. (A)</p> Signup and view all the answers

What is restored during the process of fertilization?

<p>Diploid number of chromosomes. (B)</p> Signup and view all the answers

Which layer of the blastocyst eventually forms the placenta?

<p>Trophoblast. (C)</p> Signup and view all the answers

What triggers the corpus luteum to continue producing progesterone after implantation?

<p>Beta-hCG secretion. (D)</p> Signup and view all the answers

Which of the following marks the transition from morula to blastocyst?

<p>Formation of trophoblast. (C)</p> Signup and view all the answers

Which barrier do spermatozoa face first during fertilization?

<p>Corona radiata. (C)</p> Signup and view all the answers

What is NOT a role of the zona pellucida during fertilization?

<p>Nourishing the developing embryo. (C)</p> Signup and view all the answers

What is the main function of the zona pellucida during fertilization?

<p>It prevents multiple sperm from fertilizing the same egg. (A)</p> Signup and view all the answers

Which event occurs during the cortical reaction following sperm binding to the egg?

<p>Cortical granules release enzymes that harden the zona pellucida. (A)</p> Signup and view all the answers

What triggers the menstrual cycle after the corpus luteum breaks down?

<p>Decrease in progesterone levels. (B)</p> Signup and view all the answers

What role does capacitation play in the fertilization process?

<p>It ensures the sperm can penetrate the zona pellucida. (C)</p> Signup and view all the answers

During which phase does the corpus luteum form?

<p>Luteal phase. (D)</p> Signup and view all the answers

What occurs after the sperm successfully penetrates the zona pellucida?

<p>The oocyte completes its second meiotic division. (A)</p> Signup and view all the answers

What is a primary function of the placenta after formation?

<p>To facilitate nutrient exchange between mother and fetus. (C)</p> Signup and view all the answers

How do cortical granules contribute to preventing polyspermy?

<p>By releasing enzymes that harden the zona pellucida. (B)</p> Signup and view all the answers

What is the first binding mechanism involved in the fast block to polyspermy?

<p>Binding to ZP3 receptors on zona pellucida. (A)</p> Signup and view all the answers

Which factor signals the end of the corpus luteum's secretory activity?

<p>Lack of implantation. (D)</p> Signup and view all the answers

Flashcards

Syncytiotrophoblast function

The syncytiotrophoblast produces enzymes to penetrate the uterine lining.

Lacunae formation

Syncytiotrophoblast vacuoles fuse to create spaces filled with maternal blood.

Epiblast germ layer

The epiblast forms the three germ layers (ectoderm, mesoderm, endoderm) that develop into the embryo.

Placenta development

The fusion of the syncytiotrophoblast with maternal blood vessels creates the placenta.

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Hypoblast function

The hypoblast forms the yolk sac and lines the chorionic cavity.

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Tubal pregnancy

Ectopic pregnancy in the fallopian tube.

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Ectopic pregnancy definition

Blastocyst implants outside the uterus, e.g., fallopian tube.

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Implantation site

Normal implantation occurs in the uterus.

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Polyspermy

Fertilization of an ovum by more than one sperm.

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Zonal Reaction

The process hardening the zona pellucida to prevent further sperm entry.

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Blastocyst

Stage of embryonic development after the morula, containing an inner cell mass and outer trophoblast.

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Trophoblast

Outer layer of cells in the blastocyst, forming the placenta.

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Cytotrophoblast

Inner layer of trophoblast cells, with clear cell boundaries.

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Syncytiotrophoblast

Fused trophoblast cells with multiple nuclei, no distinct cell boundaries.

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Implantation

Embedding of the blastocyst into the uterine wall.

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Embryoblast

Inner cell mass of the blastocyst, forming the embryo.

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Beta-hCG

Hormone secreted after implantation, maintaining corpus luteum.

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Bilaminar Germ Disc

Embryonic structure formed during the second week of development, composed of epiblast and hypoblast.

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Primary follicle development

A primary follicle contains a primary oocyte surrounded by a single layer of flat cells.

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Secondary follicle development

The primary follicle becomes a secondary follicle with multiple fluid-filled spaces called antra.

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Corpus luteum of menstruation

The corpus luteum forms after ovulation and produces progesterone to prepare the uterus for pregnancy. If fertilization doesn't occur, it breaks down after 9 days, leading to lower progesterone levels and menstruation.

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Capacitation

A process that occurs in the uterine tube where sperm undergo changes to remove their glycoprotein coat and become hypermotile, ready to fertilize the egg.

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Acrosomal Reaction

The process where the sperm's acrosome releases enzymes that break down the zona pellucida, allowing the sperm to penetrate the egg.

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Fast Block to Polyspermy

A rapid mechanism that prevents multiple sperm from fertilizing the same egg by creating a positive charge across the oocyte membrane.

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Cortical Reaction

A process initiated by sperm binding to the oocyte membrane, triggering the release of cortical granules that harden the zona pellucida to prevent additional sperm from entering.

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What happens during the second meiotic division?

The secondary oocyte completes its second meiotic division and becomes an ovum (mature egg) after the cortical reaction.

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What is the function of the corona radiata?

The corona radiata is a layer of cells surrounding the oocyte, providing protection and facilitating sperm guidance.

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What is ZP3 and why is it important?

ZP3 is a receptor molecule located on the zona pellucida that binds to sperm and initiates the acrosomal reaction.

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What is the role of the beta subunit of the oocyte membrane?

The beta subunit on the oocyte membrane binds to the sperm, initiating the fast block to polyspermy by allowing Na+ to flow into the oocyte, creating a positive charge.

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What is the role of the alpha subunit of the oocyte membrane?

The alpha subunit binds to the sperm, triggering the cortical reaction, which hardens the zona pellucida.

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Study Notes

Early Embryonic Development

  • Spermatogenesis: Produces spermatozoa in seminiferous tubules (ST) within the testes. Sertoli cells surround primordial germ cells, which become spermatogonia. Leydig cells are in the interstitial space between ST. Spermiogenesis transforms immature spermatids into motile sperm. Key steps include acrosomal cap formation, nuclear condensation, and tail development. Sperm structure includes an acrosome (enzymes), mitochondria (energy), a neck, middle piece, and tail. This process is continuous throughout a male's reproductive life.

  • Hormones Involved in Spermatogenesis: GnRH from the hypothalamus stimulates LH and FSH release from the anterior pituitary. LH acts on Leydig cells to produce testosterone. FSH and testosterone act on Sertoli cells for androgen-binding protein and inhibin production, supporting sperm maturation.

Oogenesis

  • Oogenesis Overview: Occurs in ovarian follicles. Begins before birth and arrests in prophase I until puberty, where it resumes cyclically. It ends at fertilization. Errors in meiosis (nondisjunction, anaphase lag) can lead to chromosomal abnormalities like Down syndrome (trisomy 21) and Turner syndrome (monosomy X).

  • Follicle Development: Primordial follicles are present at birth. Primary, secondary, and pre-ovulatory (Graafian) follicles develop during a menstrual cycle, one of which releases an ovum during ovulation. The primary oocyte completes meiosis I, producing a secondary oocyte and a polar body. The secondary oocyte arrests in metaphase II until fertilization.

  • Hormonal Regulation of Oogenesis: LH stimulates theca cells to produce androgens, which granulosa cells convert to estrogen. FSH stimulates granulosa cells to convert androgens to estrogen.

Ovarian Cycle

  • Ovulation & Corpus Luteum: Follicle development leads to ovulation when estrogen production from the increasing dominant follicle induces a LH surge. This ruptures the dominant follicle, releasing the ovum. After ovulation, the ruptured follicle forms the corpus luteum which produces progesterone and estrogen. The corpus luteum functions for pregnancy or menstruation.

  • Endometrial Cycle: The endometrial lining of the uterus thickens (proliferative phase) under the influence of rising estrogen, preparing for potential implantation. Progesterone from the corpus luteum maintains this lining (secretory phase). If fertilization doesn't occur, the corpus luteum degrades, progesterone levels fall, and the lining sheds (menstruation).

Fertilization and Implantation

  • Fertilization: Sperm undergo capacitation to prepare for fertilization. The sperm must penetrate the corona radiata and zona pellucida, then fuse with the oocyte membrane to prevent polyspermy. The 2nd meiotic division is completed by the oocyte after fertilization causing it to form mature ovum.

  • Implantation: The fertilized ovum (zygote) undergoes initial cell divisions (cleavage). The resulting blastocyst implants in the uterine wall, embedding into the uterine lining. The trophoblast cells develop into structures that support fetal development within the uterine wall, such as the placenta.

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Description

This quiz covers the processes of spermatogenesis and oogenesis in early embryonic development. It discusses the hormonal regulation involved and the structural features of spermatozoa and oocytes. Dive into the intricacies of male and female gamete formation and their developmental stages.

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