BIOL 221 Lecture Notes - Lecture 13: Oocyte, Meiosis, Endometrium
4 Mar 2020
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Oogenesis
● Oogonium → primary oocyte
● Primary oocyte goes through meiosis I to form secondary oocyte and 1 polar
body
● Secondary oocyte is released during ovulation
○ IF secondary oocyte is fertilized, THEN it will go through meiosis II to
form ovum and second polar body
○ The oogonium gives rise to the primary oocyte. All of the oogonia
become primary oocytes before birth.
○ Once per month, a primary oocyte goes through meiosis I as the
follicle develops around it to form one secondary oocyte and one
polar body.
○ The secondary oocyte is released during ovulation.
○ If the secondary oocyte is fertilized, then it will go through meiosis
II to form an ovum whose haploid nucleus will unite with the
haploid nucleus of the sperm and a second polar body.
○ The second polar body may or may not divide.
○ The newly formed diploid cell, called a zygote, undergoes rapid
cell division in a process called cleavage (Topic 14).
Menstrual (Uterine) Cycle
● Cyclical changes in the endometrium
● prepare it for implantation of a fertilized ovum
● Three phases:
● Menstrual
● Proliferative
● Secretory
○ The menstrual (uterine) cycle refers to the cyclical changes that
occur in the endometrium to prepare it for implantation of a
fertilized ovum.
○ The three phases are the menstrual phase, the proliferative and
the secretory phase.
Document Summary
Primary oocyte goes through meiosis i to form secondary oocyte and 1 polar body. If secondary oocyte is fertilized, then it will go through meiosis ii to form ovum and second polar body. The oogonium gives rise to the primary oocyte. All of the oogonia become primary oocytes before birth. Once per month, a primary oocyte goes through meiosis i as the follicle develops around it to form one secondary oocyte and one polar body. The secondary oocyte is released during ovulation. If the secondary oocyte is fertilized, then it will go through meiosis. Ii to form an ovum whose haploid nucleus will unite with the haploid nucleus of the sperm and a second polar body. The second polar body may or may not divide. The newly formed diploid cell, called a zygote, undergoes rapid cell division in a process called cleavage (topic 14). Prepare it for implantation of a fertilized ovum.
