Understanding Human Reproductive Systems: Anatomy, Processes, and Development
This chapter covers the intricate systems of human reproduction, highlighting similarities across species and the anatomical differences in male and female reproductive structures. It details sperm and egg production, copulation, fertilization processes, and the hormonal regulation involved. The stages of spermatogenesis and oogenesis are explored, along with the menstrual cycle and embryo development. The text emphasizes the importance of various hormones and the complex sequence of developmental stages from fertilization through gestation.
Understanding Human Reproductive Systems: Anatomy, Processes, and Development
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Presentation Transcript
Chapter 44 Human Reproduction
Reproductive Systems • Many similarities between species • Most similar within order • Basics of initial sperm & egg production, copulation, fertilization the same.
Male Reproductive Anatomy • Testes—Sperm & testosterone • Seminiferous tubules—Sperm production • Epididymis—Sperm storage & maturing • Vas deferens—Moves sperm from dpididymis • Urethra—Moves sperm & urine outside of body • Scrotum—Skin sac that contains testes • Penis—Male copulatory organ
Male Reproductive Anatomy • Seminal vesicles—Nutrient fluid • Prostate gland—Alkaline fluid, prolongs sperm lifespan in female • Bulbourethral glands—Lubricating fluid • Semen—combination of sperm & glandular fluids
Spermatogenesis • Begins at 12-14 years old • Continues through entire life • Under hormonal control • Gonadotropin-releasing hormone (GnRH)—stimulates other hormones to be released; produced by hypothalamus • Follicle-stimulating hormone (FSH)—enhances spermatogenesis, not fully understood; anterior pituitary • Lutenizing hormone (LH)—controls testosterone release; anterior pituitary • Testosterone—Sexual characteristics & behavior, sperm production • Inhibin—Released when high sperm count, suppresses other hormones, therefore sperm production.
Spermatogenesis • Occurs in seminiferous tubules in testes • Spermatogonia cells • Leydig cells—release testosterone • Germ cells undergo meiosis • 1 diploid (2n) 4 haploid (n) cells • Sertoli cells—release inhibin
Spermatogenesis • Most flagellated (including some plants) • Nematodes—amoeboid • Head • Nucleus—contains genetic material • Acrosome—enzymes to penetrate egg • Midpiece • Mitochondria • Tail
Female Reproductive Anatomy • Ovaries—produce ovum, reproductive hormones • Oviducts (Fallopian tubes)—moves ovary to uterus, fertilization • Uterus—houses embryo • Endometrium—lining of uterus, supports developing fetus • Cervix—opening to uterus • Vagina—birth canal, copulatory organ
Oogenesis • Begins before birth • Continues until menopause • Eggs develop to primary oocyte, stopping in prophase I • At puberty, oocyte develops into primary follicle • Develops to metaphase II and stops (secondary oocyte) • Secondary oocyte released during ovulation • Remaining follicle becomes corpus luteum, secretes progesterone • Secondary oocyte only develops further if fertilized
Oogenesis • Numerous hormones! • GnRH—triggers release of LH and FSH; hypothalamus • FSH—stimulates primary oocytes to develop to next stage; anterior pituitary • LH—stimulates ovulation, estrogen production; anterior pituitary • Estrogen—female reproductive tract development, sex characteristics; ovary, corpus luteum • Progesterone—maintains endometrium; corpus luteum
Menstrual Cycle • Mestruation—Day 1-5 • Low estrogen & progesterone • Follicular Phase—Day 6-13 • Estrogen increases • Endometrium thickens • Ovulation—Day 14 • LH & FSH released just prior • Mature egg released • Luteal Phase—Day 15-28 • Corpus luteum increases progesterone • Endometrium thickness doubles • If no pregnancy, CL degenerates
Fertilization • 150-350 million sperm deposited • Only a few hundred reach oviduct • Acrosome dissolves outer coating of egg (zonapellucida) • Sperm penetrates to egg cell membrane • Sperm nucleus enters egg
Fertilization • Once sperm penetrates zonapellucida, cortical granules are released, and move into zonapellucida • Zonapellucida hardens, becoming impermeable to any more sperm
Embryo Development • Conceptus—First 2 weeks • Embryo—3rdthrough 8th weeks • Fetus—After 8 weeks • Gestation averages 38 weeks (266 days) • Rabbits—31 days • Dogs & Cats—63 days • Horses—335-340 days • Bottlenose Dolphins—364-378 days • Elephants—630-660 days (22 months)
Embryo Development • Zygote—fertilized egg, diploid • Undergoes cleavage (mitosis) multiple times • Travels down oviduct • Morula—solid ball of cells
Embryo Development • Morula develops into blastula • Blastocoel—fluid-filled center • Implants in endometrium in later stages • Some cells of blastula migrate inside • This is where embryo will form • Is now a gastrula • Ectoderm, endoderm, mesoderm form
Embryo Development • Week 4 • Notochord forms • Primitive heart tube forms • Week 5 • Heart develops, begins to beat • Limb buds form • Earliest stages of organs • Week 6 • Blood begins flowing • Hands and feet developing • Week 8 • Nipples & hair follicles form • Limb movements noticeable
Fetal Development • Weeks 10-13 • Face well formed • Tooth buds appear • Fetus able to make a fist • Genitals well differentiated • Weeks 14-17 • Sucking motions with mouth • Lanugo (fine hair) begins to form • Week 20 • Eyebrows, eyelashes, nails develop • Fetal heartbeat heard with stethoscope • Mother feels fetus move • Lanugo hair covers body
Fetal Development • Week 24 • All eye structures developed • Fingerprints forming • Alveoli forming • Responds to sounds • Week 28 • Respiratory system can exchange gasses • Brain growing rapidly • Nervous system controlling body functions • Premature birth high risk, but possible • Opens & closes eyes • Week 32 • Rhythmic breathing • Thalamic connections in brain • Bones fully developed
Fetal Development • Weeks 37-40 • Considered full term
