Cytology · MU Pleven

Topic 46 Sex cells – female sex cells.

Covers female gametes: the process of gametogenesis and how germ cells become sperm or ova, with the ovum's structure, including its zona pellucida and corona radiata, and how fertilisation proceeds. It then traces the embryonic origin of germ cells and gonocytes, their migration to the developing gonads, and the oocyte stages and follicular cells, from primordial to Graafian follicles.

Inside: 3 sections · 2 labelled pictures · 14 flashcards · 3 min

Topic 46 of 59 in the MU Pleven syllabus for Cytology (Medicine, Year 1). The free AceMed note covers it in 3 sections, about 482 words (3 min of reading), with 14 flashcards.

In this note

  1. Topic 46 Sex cells – female sex cells.
  2. Ovum (ova – plural)
  3. Oocytes (female sex cells)

Topic 46 Sex cells – female sex cells.

Gametogenesis – conversion of germ cells into male and female gametes

  • Two types of gametogenesis – spermatogenesis, oogenesis
  • Meiosis – cell division in germ cells to produce male and female gametes
  • Cytodifferentiation – development of specialised structures and functions in embryonic cells
  • Gamete – sex cell that fuses with another during fertilisation in sexually reproducing organisms
  • Two types of gametes – sperm, ovum
  • Diploid somatic cells have one chromosome set from sperm and one from ovum
  • Sperm and ovum are haploid cells
  • Gametes are produced in reproductive organs called gonads
  • Gonads produce sex hormones needed for the growth and development of primary and secondary reproductive organs and structures

Ovum (ova – plural)

  • Ovum – largest cell in the body; only cell visible by naked eye
  • Sperm are mobile; ova are immobile
  • Ova contain only X chromosome; sperm contain X or Y → sperm determines sex
  • Ova are produced by follicle cells of the ovaries
  • Structure: nucleus, large cytoplasm, zona pellucida, corona radiata
  • – Plasma membrane (vitelline membrane) – secreted by ovum; thin, transparent
  • – Cytoplasm (ooplasm) – rich in yolk
  • – Zona pellucida – membrane covering the ovum; binds sperm and aids fertilisation; secreted by follicular cells and oocyte; thick, transparent, non-cellular
  • – Corona radiata – outer protective layers of radially elongated follicular cells surrounding zona pellucida
  • During discharge from Graafian follicle, several layers of epithelial cells adhere to zona pellucida, forming corona radiata
  • Previtelline space – between vitelline membrane and zona pellucida
  • Fertilisation: sperm use acrosomal enzyme hyaluronidase to disperse corona radiata, enter perivitelline space, and contact oocyte nucleus

Embryonic origin

  • Germ cells – give rise to gametes
  • Primordial germ cells – still need to reach gonads (testes or ovaries)
  • Precursor germ cells/gonocytes – divide repeatedly during migration through gut to developing gonads

Gonocyte

  • Germ cell responsible for gametogenesis
  • Includes: gametogonia (divide into gametocytes – spermatogonia and oogonia), oocytes (female gametocyte), ootids (immature ovum), ova
  • Gametocyte – divides by mitosis into other gametocytes or by meiosis into gametids
  • Often excludes short-lived spermatocytes, spermatids, or sperm
  • Formed in epiblast during 2nd week of gestation
  • Moves to yolk sac wall during 3rd week
  • Migrates to developing gonads in 5th week
  • Primary sex cords form → testis cords (males) & cortical cords (females)
  • – Testis cords – precursors to rete testis (network of tubules carrying sperm)
  • – Cortical cords – precursors to ovarian follicles (contain a single oocyte)

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