BSC2086 A&P II Final Exam Study Guide – Lesson 21 1 Lesson 21: The Reproductive System Part I Introduction to the Reproductive System • Reproductive System o ONLY system that is NOT essential to the life of the individual o Reproductive Structures: Gonads: Organs that produce gametes & hormones Ducts: Receive & transport gametes Accessory Glands: Secrete fluids into ducts External Genitalia: Perineal structures • Male & Female Reproductive Systems… o Are functionally different o Secrete hormones that play major roles in the maintenance of normal sexual function o Produce & store specialized reproductive cells that combine to form new individuals Female produces one (1) gamete per month • Retains & nurtures zygote – formed after fertilization Male produces large quantities of gametes • Produces ½ billion sperm per day Male Reproductive System • Testes: Male gonads o Secrete male sex hormones – androgens o Produce male gametes – spermatozoa (sperm) • Accessory Organs: Secrete fluids into ejaculatory ducts & urethra o Seminal glands (vesicles) o Prostate gland o Bulbo-urethral glands • External Genitalia o Penis: Erectile organ containing distal portion of urethra o Scrotum: Encloses testes Has two chambers – scrotal cavities Each testis lies in a separate scrotal chamber Raphe: Raised thickening in scrotal surface • Marks partition of two scrotal chambers Dartos Muscle: Layer of smooth muscle in the dermis of scrotum • Resting muscle tone causes characteristic wrinkling of scrotal surface & elevates testes Cremaster Muscle: Layer of skeletal muscle deep to dermis that can contact or relax to move the scrotum • Contraction tenses scrotum & pulls testes closer to body o Occurs during temperature regulation, sexual arousal o Normal sperm development in testes requires temperatures 1.1° C (2° F) lower than body temperature • Spermatic Cords: Extend between abdominopelvic cavity & testesBSC2086 A&P II Final Exam Study Guide – Lesson 21 2 o Consist of layers of fascia & muscle o Enclose ductus deferens, blood vessels, nerves, & lymphatic vessels of testes o Pass into the scrotum through the inguinal canal – passageways through abdominal musculature Form during development as testes descend into scrotum Cryptorchidism: Testes do not descend into scrotum & remain in abdomen • May cause sterility, testicular cancer o The cells in the testes are exposed to a higher temperature & begin dying off o 10% experience testicular cancer Male Inguinal Hernias: Protrusions of visceral tissues into inguinal canal • Spermatic cord causes weak point in abdominal wall • Common in males (not in females) because… o Abdominal wall is nearly intact in females o Female inguinal canals are very small Contains ilioinguinal nerves & round ligaments of uterus • Histology of the Testes o Septa subdivide testis into lobules Lobules: Contain about 800 slender & tightly coiled seminiferous tubules Seminiferous Tubules: Produce sperm • Each testis contains ~1/2 of tightly coiled seminiferous tubules o Form a loop connected to rete testis – network of passageways that connects to the epididymisBSC2086 A&P II Final Exam Study Guide – Lesson 21 3 • Connective Tissue Capsules – surround seminiferous tubules o Within those spaces, there are: Blood vessels Interstitial Cells (Leydig Cells): Large cells that produce androgens – dominant male sex hormones • Testosterone – most important androgen Meiosis • Meiosis is a special form of cell division involved only in production of gametes o Spermatozoa in males o Oocytes in females • Gametes contain 23 chromosomes – half the normal amount (46) • Fusion of male & female gametes produces zygote with 46 chromosomes • Occurs at seminiferous tubules in males o Begins with primary spermatocytes o Produces spermatids – undifferentiated male gametes • Meiosis I: Reductional division – number of chromosomes is halved from 46 23 o Prophase I Chromosomes condense Synapsis: Maternal & paternal chromosomes come together to form a tetrad • Crossing Over: Exchange of genetic material that increases genetic variation among offspring o Metaphase I Tetrads line up along metaphase plate o Anaphase I Maternal & paternal chromosomes separate Each tetrad splits Maternal & paternal components are randomly distributed to the daughter cell o Telophase I Ends with formation of two (2) daughter cells with unique combinations of chromosomesBSC2086 A&P II Final Exam Study Guide – Lesson 21 4 Both cells contain 23 chromosomes with two (2) chromatids each • Not the same as a diploid cell • Interphase – separates meiosis I & meiosis II Very brief DNA is NOT replicated • Meiosis II: Equational division – chromosome number is not changed o Prophase II o Metaphase II o Anaphase II Duplicate chromatids separate o Telophase II Yields four (4) cells Each contains 23 chromosomes Cytoplasm may not be distributed evenly Male Reproductive Function • Spermatogenesis: The process of sperm production o Begins at outermost cell layer in seminiferous tubules o Proceeds toward lumen of seminiferous tubules o Spermatogonia (Stem Cells): Divide by mitosis to produce two (2) daughter cells Both daughter cells have identical info One remains as a spermatogonium Second differentiates into primary spermatocyte o Primary Spermatocyte: Begins meiosis & creates two secondary spermatocytes Secondary spermatocytes formed by the end of meiosis I • Do NOT have the same genetic information o Secondary Spermatocytes: Undergo meiosis II and form spermatids by the end of telophase IIBSC2086 A&P II Final Exam Study Guide – Lesson 21 5 o Spermatids: Immature gametes that will differentiate/mature into spermatozoa o Spermatozoa: Mature gametes Lose contact with wall of seminiferous tubule • Enter fluid in lumen of seminiferous tubules o Spermiogenesis: Last step of spermatogenesis Each spermatid matures into one spermatozoon (sperm) • Attached to cytoplasm of nurse cells At spermiation… • Spermatozoon loses attachment to nurse cell & enters lumen of seminiferous tubule o Spermatogonial division to spermiation takes ~9 weeksBSC2086 A&P II Final Exam
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