# Human Reproductive System This section details the structure, function, and hormonal control of the male and female reproductive systems, which become functional at puberty. ### 11.1.1 Male Reproductive System The primary function of the male reproductive system is to *produce and maintain sperm*. #### Structure of the Male Reproductive System The system consists of gonads, accessory ducts, accessory glands, and a copulatory organ. | Component | Structure(s) | Function(s) | | :--- | :--- | :--- | | **Gonads** | **Testes** (singular: testis) | Located in the **scrotum** (skin pouch). Each testis contains 250-300 lobules, with each lobule holding 1-4 **seminiferous tubules** where sperm are produced. | | **Accessory Ducts** | Epididymis, Vas Deferens, Ejaculatory Duct, Urethra | A pathway for sperm transport and maturation. Sperm move from seminiferous tubules -> rete testis -> efferent ductules -> **epididymis** (storage/transport) -> **vas deferens** -> **ejaculatory duct** -> **urethra** (carries both urine and semen). | | **Accessory Glands** | Seminal Vesicles, Prostate Gland, Bulbourethral (Cowper's) Glands | Produce secretions that mix with sperm to form **semen**. Semen provides nutrients, protection, and a transport medium for sperm. | | **Copulatory Organ** | **Penis** | Consists of erectile tissue that fills with blood to cause an erection, facilitating internal fertilization. | *Science Titbit:* The testes are located outside the abdomen in the scrotum because sperm production (spermatogenesis) is most efficient at approximately 35°C, which is 2°C cooler than the normal body temperature. #### Spermatogenesis (Sperm Formation) This is the process of sperm formation occurring in the **seminiferous tubules**. 1. **Spermatogonia** (diploid cells) divide by mitosis to form a **primary spermatocyte**. 2. The primary spermatocyte undergoes *meiosis I* to form two haploid **secondary spermatocytes**. 3. Each secondary spermatocyte undergoes *meiosis II* to produce two **spermatids** (haploid, non-motile cells). 4. Each spermatid matures, elongates, and forms a tail to become a motile, active **sperm**. ### 11.1.2 Hormonal Control of Male Reproductive Function The male reproductive cycle is controlled by hormones from the hypothalamus and anterior pituitary, starting at puberty. - **Hypothalamus:** Releases **Gonadotropin-releasing hormone (GnRH)**. - **Anterior Pituitary:** Stimulated by GnRH to release two key hormones: 1. **Follicle-Stimulating Hormone (FSH):** Acts on **Sertoli cells** in the testes to facilitate spermatogenesis. 2. **Luteinizing Hormone (LH):** Acts on **interstitial cells of Leydig** in the testes to produce and release **testosterone**. - **Testosterone:** A key male hormone responsible for: - Stimulating spermatogenesis. - Development of **secondary sexual characteristics** (e.g., deep voice, growth of facial and body hair). #### Negative Feedback System This system regulates hormone levels and sperm production. - **High Testosterone Levels:** Inhibit the release of GnRH, FSH, and LH from the hypothalamus and pituitary. - **High Sperm Count:** Sertoli cells release the hormone **inhibin**, which inhibits GnRH and FSH release, slowing down spermatogenesis. When the sperm count drops, inhibin release stops, and the process resumes. ### 11.1.3 Female Reproductive System The female reproductive role is complex, involving gamete production and nurturing a developing embryo for approximately nine months. #### Structure of the Female Reproductive System | Component | Structure(s) | Function(s) | | :--- | :--- | :--- | | **Gonads** | **Ovaries** (a pair) | Produce ova (eggs) and female sex hormones. Contain **ovarian follicles**, each with an immature egg (oocyte). **Ovulation** is the monthly release of an oocyte. The ruptured follicle becomes the **corpus luteum**. | | **Duct System** | **Oviducts** (Fallopian tubes) | Receive the ovulated oocyte. This is the primary site of **fertilization**. Transport the developing ovum towards the uterus. | | **Uterus** | Fundus, body, and cervix | A hollow, muscular organ (womb) that receives, retains, and nourishes a fertilized ovum. | | **Uterine Wall** | 1. *Perimetrium:* Outermost thin covering. 2. *Myometrium:* Middle thick, smooth muscle layer that contracts during childbirth. 3. *Endometrium:* Inner spongy lining where the embryo implants. | Protection, muscular contraction during childbirth, and lining for embryo implantation. | | **Vagina** | An 8-10 cm long tube | Extends from the cervix to the body's exterior. Serves as the birth canal and a passageway for menstrual flow. |