## Lesson 4.3: Menstrual Cycle The menstrual cycle is a complex interplay of three levels: neuroendocrine, ovarian, and uterine, all occurring simultaneously. ### I. Neuroendocrine Level: The Communication Hub This level involves the constant communication between the nervous and endocrine systems to regulate the reproductive system. The hypothalamus, a brain structure, acts as the command center. Think of the hypothalamus as the CEO of the endocrine system, directing all hormonal activities. * **Hypothalamus:** Secretes GnRH (Gonadotropin-releasing Hormone), which communicates with the pituitary gland. * **Pituitary Gland (Hypophysis):** The "master gland," releasing stimulating hormones. * **Neurohypophysis (posterior pituitary):** Controls 2 hormones. * **Adenohypophysis (anterior pituitary):** Controls 7 hormones, including FSH (Follicle-stimulating Hormone) and LH (Luteinizing Hormone), crucial for sex hormone regulation and gamete release. The hypothalamus and pituitary gland work in a coordinated dance to orchestrate the menstrual cycle. * **Follicle-stimulating Hormone (FSH):** Responsible for follicle maturation, preparing the egg for fertilization. A mature follicle is called a Graafian follicle. If fertilization doesn't occur, FSH contributes to menstruation. * **Luteinizing Hormone (LH):** Responsible for ovulation, the release of the egg from the Graafian follicle. LH triggers the release of prostaglandins, which help rupture the follicle. A common misconception is that FSH and LH work independently. In reality, they have an inverse relationship during ovulation: FSH decreases as LH increases. Imagine a seesaw: as FSH goes down, LH goes up, and vice versa. This balance is crucial for a healthy cycle. **Key Takeaway:** The neuroendocrine level sets the stage for the ovarian and uterine cycles through the precise regulation of hormones. ### II. Ovarian Level: The Egg's Journey The ovarian cycle has three phases: follicular, ovulation, and luteal. * **1. Follicular Phase:** Egg maturation. Estrogen, secreted by maturing follicles (stimulated by FSH), prepares the egg for release and stimulates the cervix to produce fertile mucus. Ovulation occurs at the end of this phase. * **2. Ovulation Phase:** Egg release. During the follicular phase, estrogen suppresses LH (negative feedback). As estrogen levels reach a threshold, they stimulate LH release (positive feedback), triggering ovulation. * **3. Luteal Phase:** Corpus luteum development. After ovulation, the remaining follicle forms the corpus luteum, which produces significant amounts of progesterone. Progesterone prepares the endometrium for implantation. Remember the acronym EPOR for the phases of sexual response: Excitation, Plateau, Orgasm, Resolution. * **Fertilization Occurs:** Progesterone (P4) levels remain high to support a potential pregnancy. * **No Fertilization:** Estrogen (E2) levels rise, and progesterone levels fluctuate, leading to menstruation. **Key Takeaway:** The ovarian cycle focuses on the egg's development and release, driven by the interplay of FSH, LH, estrogen, and progesterone. ### III. Uterine Level: Preparing the Womb The uterine cycle has four phases: menstruation, proliferative, ovulation, and secretory. These phases are coordinated with the ovarian cycle. * **1. Menstrual Phase (Days 1-4):** Shedding of the uterine lining. Low estrogen levels stimulate FSH release, initiating the next cycle. Prostaglandins cause uterine contractions, potentially causing pain. * **2. Proliferative Phase (Days 5-13):** Increased estrogen from developing follicles thickens the endometrium. * **3. Ovulation (Days 13-16):** Corresponds to ovulation in the ovarian cycle. * **4. Secretory Phase (Days 17-28):** Progesterone from the corpus luteum further thickens the endometrium, preparing it for implantation. The menstrual cycle and menstrual phase are not interchangeable terms. The menstrual phase is one part of the menstrual cycle. **Key Takeaway:** The uterine cycle prepares the uterus for potential pregnancy, reflecting the hormonal changes of the ovarian cycle. ## Lesson 4.4: Sexual Intercourse Sexual intercourse, also known as copulation or coitus, involves the rhythmic movement of the erect penis into the vagina. Its purpose can be for pleasure, reproduction, or both. ### I. Physiology of Sexual Response (Masters & Johnson) The four phases are: Excitation, Plateau, Orgasm, Resolution (EPOR). * **1. Excitation:** Vasocongestion (blood flow to genitals), increased vital signs (heart rate, blood pressure, etc.), and myotonia (muscle tension). This phase can last from minutes to hours. * **2. Plateau:** Intensification of changes from the excitation phase. Libido increases. Copious perspiration and increased myotonia. * **3. Orgasm:** The climax, characterized by very high heart rate, blood pressure, and breathing. Intense myotonia. Males experience ejaculation; females experience contractions of the orgasmic platform and uterus. * **4. Resolution:** The body returns to its normal state. Males enter a refractory period (1-4 hours). Understanding the physiological changes in each phase helps appreciate the complexity of sexual response. **Key Takeaway:** The physiology of sexual response involves a coordinated series of physiological changes in both males and females. ## Lesson 4.5: Pregnancy Pregnancy is the period of fetal development in the uterus, lasting approximately 40 weeks. ### I. Key Terms * **Conception:** The meeting of sperm and egg in the fallopian tube. * **Fertilization:** The union of sperm and egg, resulting in a diploid zygote. * **Implantation:** The attachment of the blastocyst to the uterine wall. * **Pregnancy:** The entire process from conception to delivery. ### II. Developmental Milestones * **First Trimester:** Organogenesis (formation of organs). * **Second Trimester:** Organ function development. Fetal sex can be determined. * **Third Trimester:** Fetal growth and preparation for delivery. ### III. Important Hormones * **Human Chorionic Gonadotropin (hCG):** A pregnancy hormone detected in blood or urine tests. * **Prolactin:** A hormone that stimulates breast tissue growth and milk production. **Key Takeaway:** Pregnancy is a dynamic process involving significant developmental changes and hormonal shifts. ## Lesson 5: The Philippine Reproductive Health Program Reproductive health is a state of complete physical, mental, and social well-being related to the reproductive system. It encompasses sexual life, reproduction, and the freedom to decide if, when, and how often to reproduce. ### I. Reproductive Health in the Philippines The Philippine Reproductive Health Program aims to improve the reproductive health of Filipinos through responsible parenthood and access to reproductive health care. ### II. Family Planning Family planning programs aim to empower individuals and couples to make informed choices about family size and spacing. This involves various methods, including natural and artificial methods. **Key Takeaway:** The Philippine Reproductive Health Program strives to improve the well-being of Filipinos by promoting responsible parenthood and access to comprehensive reproductive health services.