Cytology · MU Sofia

71. Gametes and gametogenesis. Gonad development.

Covers how gametes form through gametogenesis, comparing spermatogenesis in the testes with oogenesis in the ovary, including sperm structure and the timing of oocyte meiosis. It then describes fertilisation in five steps, from acrosomal penetration to zygote formation, and ends with gonad development from the indifferent stage, sex determination by SRY, and the fate of the genital ducts in each sex.

Inside: 7 sections · 2 labelled pictures · 14 flashcards · 9 min

Topic 71 of 127 in the MU Sofia syllabus for Cytology (Dental Medicine, Year 1). The free AceMed note covers it in 7 sections, about 1,231 words (9 min of reading), with 14 flashcards.

In this note

  1. Gametes and Gametogenesis. Gonad Development.
  2. I. Gametes (Sex Cells)
  3. II. Gametogenesis (Formation of Gametes)
  4. C. Fertilization
  5. III. Gonad Development (Male and Female)
  6. A. Male Gonad Development (Testis)
  7. B. Female Gonad Development (Ovary)

Gametes and Gametogenesis. Gonad Development.

This topic covers the formation of reproductive cells (gametes) and the development of the organs that produce them (gonads).

I. Gametes (Sex Cells)

  • Definition: Gametes are biological cells that give rise to the reproductive cells of an organism that reproduces sexually. In humans, these are sperm cells (male gametes) and mature oocytes/egg cells (female gametes).
  • Genetic Content: Gametes are haploid cells, meaning they contain half the diploid number of chromosomes (23 in humans), with each pair of chromosomes having been separated during meiosis. In males, all four resulting cells from meiosis become sperm, while in females, one becomes an egg with two polar bodies.
  • Origin: Gametes arise from primordial germ cells.

II. Gametogenesis (Formation of Gametes)

  • Definition: Gametogenesis is the process by which humans develop spermatozoa and oocytes. It involves DNA replication followed by two rounds of cell division (meiosis) to produce four daughter cells, each with half the genetic information of the parent cell.

Gametogenesis is the general process by which an organism produces gametes, which are the reproductive cells. In humans, this involves the development of spermatozoa (sperm) in males (spermatogenesis) and oocytes (eggs) in females (oogenesis).

Gametogenesis

  • Gametogenesis is the process by which humans develop spermatozoa and oocytes (spermatogenesis and oogenesis).
  • Germ cells, which give rise to gametes, originate in the primitive streak of the embryonic disk and migrate to the developing gonads where they undergo meiosis and cellular differentiation into mature gametes.

Spermatogenesis

  • Definition: Spermatogenesis is the process by which spermatozoa are produced from male primordial germ cells through mitosis and meiosis.
  • Location: This process occurs in the seminiferous tubules of the male testes.

Process:

  • It begins with spermatogonia, which divide by mitosis to produce primary spermatocytes.
  • Primary spermatocytes then undergo Meiosis I to form two secondary spermatocytes.
  • Each secondary spermatocyte divides by Meiosis II to produce spermatids.
  • These spermatids then mature into spermatozoa (sperm cells) through a process called spermiogenesis.
  • The entire process from spermatogonia to spermatids takes about two months.
  • Spermatozoon Structure: Spermatozoa are structured with a head, middle section, and tail.
  • Head: Contains lytic enzymes (e.g., hyaluronidase and acrosin) in the acrosome to digest the egg's outer membrane, allowing penetration during fertilization. It also holds a single X or Y chromosome.
  • Mid-section: Located behind the head, it contains mitochondria that respire sugars in the semen to generate ATP for tail movement.
  • Tail: A basic flagellum with nine outer and two central microfilaments, responsible for sperm movement.

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