University:
Kentucky State University
Course:
BIO 301 | Human Anatomy
Academic year:

2024
Views:

161

Pages:

19
Author:

FrextWhestembki

Lecture Title : Oogenesis Lecture Date : 30/3/2021 Introduction • • • • Somatic cells have 46 Chromosomes (23 pairs) : 22 pairs of homologous chromosomes (Autosomes). One pair of sex chromosomes. In the Interphase the Chromosomes duplicate so the number of Chromatids become 92. • Each 2 Chromatids are Linked together by Centromere. • Crossing over: interchanging/shuffling of genes between the nonsister chromatids (occurs in Meiosis). completed sheet #1 • Oogenesis starts at the 5th week. • Ovary is divided into two major parts : 1)Outer part (cortex) containing Oocytes at different stages of development. 2)Inner part (Medulla) containing blood vessels and matrix. (inner to the cortex) • Main function of the ovary to produce mature Ovum ready for fertilization , and to produce Estrogen & Progesterone. • Most of Oocytes will degenerate and only few of them will succeed. • We take the Section from adult female who has reached puberty (not from new born) to show all the steps of formation/development of the Ovum or Oocyte. Mature gamete : ‫ ـ‬called Sperm in the male. ‫ ـ‬called Ovum.in the female sheet #2 • In preparation for fertilization, Oogonia (2n) mother cells undergo gametogenesis through Meiosis to reduce the number of chromosomes into (1n) and cytoplasmic changes to complete their maturation. sheet #3 • On the 3rd month: In preparation for fertilization, Oogonia undergo gametogenesis to reduce the number of chromosomes and two unequal daughter cells to complete their maturation. They enter meiosis I but arrested in the Prophase stage and form the 1ry Oocyte. • it’s impossible to find Oogonia in the sixth month, all of them will turn into 1ry Oocytes before this time. sheet #4 • 1ry Oocytes Can not grow further and be ready to fertilization alone , They need nutrition and protection. • flat follicular cells are responsible about nutrition & protection of the Oocytes. sheet #5 • Down Syndrome is an example of chromosomal abnormalities. • The female is exposed to a set of problems from birth to adulthood that comes from external influences such as car smoke, some drugs, radiation … all of these affect her chromosomes. sheet #6 • One 1ry Oocyte is selected from a group (about 20) to complete Meiosis I. • 2ry Oocyte and polar body have the same genome(heredity factors) but they differ in the amount of cytoplasm (larger quantity in the 2ry Oocyte) • At Ovulation: The 2ry Oocyte enter Meiosis II but arrested in Metaphase II and only completed it in Fertilization. • Ovulated ovum enter into uterine tube in anticipation to be fertilized and stay viable only ~ 24 hours. • Sperms stay viable for 48 hours. Average cycle: 28 days / Average ovulation: at day 14. At day 13 : The 2ry Oocyte will enlarge and its size will be about 20-25 mm , this is important for IVF. Pituitary gland in female will secrete a large amount of LH (Luteinizing Hormone) induces the preovulatory growth and Meiosis I is completed, resulting in formation of 2ry Oocyte and 1st polar body

Oogenesis

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