Back to: ZOOLOGY 400 Level
Welcome to class!
Hello there, my brilliant friend! It’s always a pleasure to have you here, learning and growing every step of the way. Today’s class is a really special one because we’re focusing on how female reproductive systems work — particularly Oogenesis and the Menstrual/Estrous Cycles. This is how female animals (including humans) prepare for reproduction, and it’s an amazing process filled with purpose and precision.
Oogenesis, Menstrual/Estrous Cycles
Oogenesis
Oogenesis is the process by which egg cells (ova) are formed in the ovaries of females. It begins even before a girl is born and continues in phases throughout her life until menopause.
Here’s how it happens:
It starts with oogonia, the original cells in the ovary. These multiply by mitosis during fetal development and then develop into primary oocytes.
Each primary oocyte begins meiosis but stops at a certain stage until puberty.
From puberty, during each menstrual cycle, one primary oocyte completes meiosis and becomes a secondary oocyte.
The secondary oocyte is released during ovulation. If fertilisation occurs, it completes meiosis to form a mature ovum and a polar body (a small non-functional cell).
Unlike spermatogenesis, oogenesis is uneven — one large egg and tiny polar bodies are produced.
Menstrual and Estrous Cycles
These are the reproductive cycles in female animals that prepare the body for pregnancy.
Menstrual Cycle (in humans and some primates):
It is around 28 days and has four main phases:
Menstrual Phase: Shedding of the uterine lining (menstruation or period).
Follicular Phase: Follicles in the ovary develop; the uterus lining begins to rebuild.
Ovulation: A mature egg is released around day 14.
Luteal Phase: The uterus prepares for pregnancy; if no fertilisation occurs, hormones drop and menstruation begins again.
Estrous Cycle (in most non-primate mammals):
Similar purpose but no bleeding occurs. Instead, animals show signs of being “in heat” (oestrus), meaning they are ready to mate. The cycle varies in length depending on the species.
Example: Think of oogenesis as preparing a single golden ticket each month — the ovum. The menstrual or estrous cycle is like preparing the venue (the uterus) for a guest (the fertilised egg). If the guest doesn’t show up, the decorations are taken down, and the cycle starts again.
Summary
- Oogenesis is the process of egg production in females, beginning before birth.
- It involves meiosis, producing one mature ovum and polar bodies.
- The menstrual cycle in humans has four stages: menstrual, follicular, ovulation, and luteal.
- The estrous cycle occurs in non-primate mammals, with visible signs of oestrus.
- Both cycles prepare the body for potential pregnancy.
Evaluation
- What is oogenesis and where does it occur?
- What are the differences between spermatogenesis and oogenesis?
- Describe the four phases of the menstrual cycle.
- How is the estrous cycle different from the menstrual cycle?
- What happens during ovulation?
You’re truly growing into a powerhouse of knowledge! Every lesson you complete takes you closer to your dreams. Keep believing in yourself — with Afrilearn supporting you all the way, there’s absolutely nothing you can‘t achieve. You’ve got this, champ!