Overview
The lesson explains the menstrual cycle and the hormonal feedback mechanisms regulating the female reproductive system for Grade 10 Science, Quarter 3 Module 2.
Learning Competency
- Describe feedback mechanisms controlling the menstrual cycle.
- Identify key hormones and organs involved in regulation.
Female Reproductive System: Quick Review
- Main organs: ovaries, fallopian tubes, uterus, cervix, vagina.
- Uterus lining (endometrium) changes each cycle to prepare for possible implantation.
Important Terms
- Gonad: organ producing gametes; in females, the ovary.
- Endometrium: inner lining of the uterus that thickens and sheds.
- Ovulation: release of a mature egg from the ovary.
- Implantation: embedding of a fertilized egg into the uterine lining.
The Menstrual Cycle: Phases
- Menstrual phase: shedding of the endometrium; bleeding occurs.
- Proliferative phase: endometrium rebuilds and thickens.
- Ovulation: egg released, typically mid-cycle.
- Secretory phase: endometrium further thickens, becomes receptive.
28-Day Cycle Outline
- Days 1–5: menstruation; low estrogen and progesterone; shedding of lining.
- Days 6–13: proliferative; rising estrogen; endometrium thickens.
- Day 14: ovulation; triggered by hormonal changes.
- Days 15–28: secretory; progesterone predominates; uterus prepared.
Hormone Review
- Hypothalamus: releases GnRH to stimulate pituitary.
- Pituitary gland: releases FSH and LH to act on ovaries.
- Ovaries: produce estrogen and progesterone; regulate uterus.
- Estrogen: rebuilds endometrium; influences LH surge.
- Progesterone: stabilizes and maintains endometrium post-ovulation.
Feedback Mechanisms
- Negative feedback: rising estrogen/progesterone suppress GnRH, FSH, LH to prevent overstimulation.
- Positive feedback (mid-cycle): sustained estrogen rise triggers LH surge leading to ovulation.
- Post-ovulation: progesterone dominance reinstates negative feedback; prepares for implantation.
Cycle Structure and Regulation
| Phase | Days (approx.) | Key Hormones | Ovarian Event | Uterine Change | Feedback Type |
|---|
| Menstrual | 1–5 | Low estrogen, low progesterone | Follicles start developing | Shedding of endometrium | Reduced stimulation (low hormones) |
| Proliferative | 6–13 | Rising estrogen | Follicular growth | Endometrium thickens | Negative feedback transitioning |
| Ovulation | ~14 | LH surge (estrogen-driven) | Egg released | Peak receptivity begins | Positive feedback (estrogen → LH) |
| Secretory | 15–28 | High progesterone, moderate estrogen | Corpus luteum active | Endometrium becomes glandular, stable | Negative feedback (suppression of GnRH/FSH/LH) |
Key Terms & Definitions
- GnRH: hypothalamic hormone controlling pituitary release of FSH and LH.
- FSH: stimulates follicle growth in the ovary.
- LH: triggers ovulation and corpus luteum formation.
- Corpus luteum: structure producing progesterone after ovulation.
Action Items / Next Steps
- Practice labeling hormone levels across the 28-day cycle.
- Explain how positive and negative feedback regulate LH and FSH.
- Relate uterine phases to ovarian events and dominant hormones.