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Chapter 26a

Chapter 26a. Reproduction and Development. About this Chapter. Sex determination and differentiation Gametogenesis and patterns of reproduction Male reproductive development and physiology Female reproductive development and physiology Pregnancy and the birth process

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Chapter 26a

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  1. Chapter 26a Reproduction and Development

  2. About this Chapter • Sex determination and differentiation • Gametogenesis and patterns of reproduction • Male reproductive development and physiology • Female reproductive development and physiology • Pregnancy and the birth process • The reproductive system during growth and aging

  3. Sex Determination • Sexual dimorphism • Females and males are physically distinct • Gonads produce gametes and sex hormones • Male gonads = testes  sperm • Female gonads = ovaries  eggs • Sex hormones direct development of genitalia • Internal genitalia • External genitalia

  4. Sex Determination Is Directed By Our Genome • Humans have 23 pairs of chromosomes • 22 pairs of autosomes • X and Y = 1 pair of sex chromosomes Nondisjunction • XXX superfemale • XXY Klinefelters • X0 Turners • XYY supermale Figure 26-1

  5. X and Y Chromosomes Determine Sex Figure 26-2

  6. Sexual Differentiation • Bipotential tissues have not yet differentiated • SRY protein directs development as a male • Gonadal medulla develops into testis • Testicular hormones direct further development • Absence of SRY protein leads to female development • Gonadal cortex develops into ovarian tissue • Mullerian ducts develop into female organs • Wolffian ducts degenerate

  7. Sexual Differentiation Table 26-1

  8. Development of Internal Reproductive Organs Müllerian duct Wolffian duct Bipotential gonad Kidney Cloacal opening FEMALE MALE Bipotential stage: 6 week fetusThe internal reproductive organshave the potential to develop intomale or female structures 1 1 SRY protein in a maleembryo directs themedulla of thebipotential gonadto develop into testis. Gonadal cortexbecomes ovary in theabsence of SRY protein. Testis Absence of testosteronecauses Wolffian ductto degenerate. 2 2 Anti-Müllerianhormone from testiscauses the Müllerianducts to disappear. Wolffianduct Müllerian duct Uterus 10 WEEKS Ovary 3 Testosterone fromtestis converts Wolffianduct into seminalvesicle, vas deferens,and epididymis. DHTcontrols prostatedevelopment. Prostate Absence of anti-Müllerian hormoneallows theMüllerian ductto become thefallopian tube,uterus, and upperpart of the vagina. 3 Seminal vesicle Fallopian tube(from Müllerianduct) Vas deferens Uterus Testis AT BIRTH Epididymis Vagina (a) DEVELOPMENT OF INTERNAL ORGANS Figure 26-3a

  9. Development of External Genitalia Genital tubercle Urethral groove homologous Labioscrotal swelling Urethral fold Anus FEMALE MALE Bipotential stage(6 week fetus) Clitoris Penis Urethral fold Urethral fold Labioscrotalswelling Labioscrotalswelling Anus Anus 1 DHT causesdevelopmentof male externalgenitalia. 10 WEEKS 1 1 In the absenceof androgens,the external genitaliaare feminized. Glans penis Labiamajora Clitoris Shaft of penis Urethral opening Labiaminora Vaginal opening Scrotum 2 The testes descendfrom the abdominalcavity into thescrotum. Anus Anus AT BIRTH (b) DEVELOPMENT OF EXTERNAL GENITALIA Figure 26-3b

  10. Control of Male Development • SRY gene directs male development Figure 26-4

  11. Control of Female Development • The SRY gene and protein are absent • Gonadal cortex develops into ovarian tissue • Mullerian ducts develop into female organs • Vagina • Uterus • Fallopian tubes • Wolffian ducts degenerate

  12. Gametogenesis Differs in Males and Females FEMALE STAGE OF CELL DIVISION MALE Spermatogonium 1 MITOSIS Oögonium Germ cell proliferation 46 chromosomesper cell (only twoshown here) Embryo Embryo 46(diploid) Oögonia Spermatogonia MEIOSIS 2 DNA replicatesbut no cell division. Primaryoocyte Primaryspermatocyte Sisterchromatids Sisterchromatids 46 chromosomes,duplicated 3 First meioticdivision First polarbody Secondaryoocyte(egg) Reproductive adult Secondaryspermatocytes Primary gamete dividesinto two secondary gametes. 23 chromosomes,duplicated (may notoccur) Reproductive adult 4 Second meioticdivision Spermatids Disintegrates Egg releasedfrom ovary atovulation. Secondary gamete divides. develop into 23 chromosomes(haploid) Sperm FERTILIZATION 6 One primary oocyteyields 1 egg. One primary spermatocyteyields 4 sperm. 5 Secondpolar bodydisintegrates. Unfertilized eggpasses out of body. Zygote Figure 26-5

  13. Mitosis: Germ Cell Proliferation FEMALE STAGE OF CELL DIVISION MALE Spermatogonium 1 MITOSIS Oögonium Germ cell proliferation 46 chromosomesper cell (only twoshown here) Embryo Embryo 46(diploid) Oögonia Spermatogonia Reproductive adult Reproductive adult Figure 26-5, step 1

  14. Meiosis: DNA Replicates FEMALE STAGE OF CELL DIVISION MALE Spermatogonium 1 MITOSIS Oögonium Germ cell proliferation 46 chromosomesper cell (only twoshown here) Embryo Embryo 46(diploid) Oögonia Spermatogonia MEIOSIS 2 DNA replicatesbut no cell division. Primaryoocyte Primaryspermatocyte Sisterchromatids Sisterchromatids 46 chromosomes,duplicated Polar bodies Reproductive adult Reproductive adult Figure 26-5, steps 1–2

  15. First Meiotic Division FEMALE STAGE OF CELL DIVISION MALE Spermatogonium 1 MITOSIS Oögonium Germ cell proliferation 46 chromosomesper cell (only twoshown here) Embryo Embryo 46(diploid) Oögonia Spermatogonia MEIOSIS 2 DNA replicatesbut no cell division. Primaryoocyte Primaryspermatocyte Sisterchromatids Sisterchromatids 46 chromosomes,duplicated Polar bodies 3 First meioticdivision First polarbody Secondaryoocyte(egg) Reproductive adult Secondaryspermatocytes Primary gamete dividesinto two secondary gametes. 23 chromosomes,duplicated Reproductive adult Figure 26-5, steps 1–3

  16. Second Meiotic Division FEMALE STAGE OF CELL DIVISION MALE Spermatogonium 1 MITOSIS Oögonium Germ cell proliferation 46 chromosomesper cell (only twoshown here) Embryo Embryo 46(diploid) Oögonia Spermatogonia MEIOSIS 2 DNA replicatesbut no cell division. Primaryoocyte Primaryspermatocyte Sisterchromatids Sisterchromatids 46 chromosomes,duplicated Polar bodies 3 First meioticdivision First polarbody Secondaryoocyte(egg) Reproductive adult Secondaryspermatocytes Primary gamete dividesinto two secondary gametes. 23 chromosomes,duplicated (may notoccur) Reproductive adult 4 Second meioticdivision Spermatids Disintegrates Egg releasedfrom ovary atovulation. Secondary gamete divides. develop into 23 chromosomes(haploid) Sperm One primary spermatocyteyields 4 sperm. Figure 26-5, steps 1–4

  17. Ovulation Without Fertilization FEMALE STAGE OF CELL DIVISION MALE Spermatogonium 1 MITOSIS Oögonium Germ cell proliferation Embryo 46 chromosomesper cell (only twoshown here) Embryo 46(diploid) Oögonia Spermatogonia MEIOSIS 2 DNA replicatesbut no cell division. Primaryoocyte Primaryspermatocyte Sisterchromatids Sisterchromatids 46 chromosomes,duplicated Polar bodies 3 First meioticdivision First polarbody Secondaryoocyte(egg) Reproductive adult Secondaryspermatocytes Primary gamete dividesinto two secondary gametes. 23 chromosomes,duplicated (may notoccur) Reproductive adult 4 Second meioticdivision Spermatids Disintegrates Egg releasedfrom ovary atovulation. Secondary gamete divides. develop into 23 chromosomes(haploid) Sperm One primary oocyteyields 1 egg. One primary spermatocyteyields 4 sperm. 5 Unfertilized eggpasses out of body. Figure 26-5, steps 1–5

  18. Ovulation with Fertilization Is Followed by Final Step of Meiosis FEMALE STAGE OF CELL DIVISION MALE Spermatogonium 1 MITOSIS Oögonium Germ cell proliferation 46 chromosomesper cell (only twoshown here) Embryo Embryo 46(diploid) Oögonia Spermatogonia MEIOSIS 2 DNA replicatesbut no cell division. Primaryoocyte Primaryspermatocyte Sisterchromatids Sisterchromatids 46 chromosomes,duplicated Polar bodies 3 First meioticdivision First polarbody Secondaryoocyte(egg) Reproductive adult Secondaryspermatocytes Primary gamete dividesinto two secondary gametes. 23 chromosomes,duplicated (may notoccur) Reproductive adult 4 Second meioticdivision Spermatids Disintegrates Egg releasedfrom ovary atovulation. Secondary gamete divides. develop into 23 chromosomes(haploid) Sperm FERTILIZATION 6 One primary oocyteyields 1 egg. One primary spermatocyteyields 4 sperm. 5 Secondpolar bodydisintegrates. Unfertilized eggpasses out of body. Zygote Figure 26-5, steps 1–6

  19. Steroid Synthesis Pathways • Steroid hormones are similar to each other • Production of sex steroids differs between men and women • Ovary • Estrogen and progesterone • Testis • Testosterone and dihydrotestosterone (DHT) • Adrenal gland secretes small amounts of sex steroids

  20. Synthesis Pathways for Steroid Hormones Cholesterol Progesterone Dihydro-testosterone(DHT) * Testosterone aromatase Corticosterone Cortisol Estradiol KEY * 5-reductase Aldosterone Intermediate steps Figure 26-6

  21. Hormonal Regulation of Reproduction • Anterior pituitary • Luteinizing hormone (LH) • Follicle stimulating hormone (FSH) • Gonads produce steroid and peptide hormones • Gonads are the main source of sex steroid

  22. General Pattern of Hormonal Control of Reproduction Internal andenvironmentalstimuli CNS GnRH Hypothalamus Short-loop negative feedback KEY Stimulus Anteriorpituitary Integrating center Efferent pathway Effector Long-loop feedbackmay be negativeor positive Tissue response LH FSH Gonads(ovaries or testes) Females only Endocrinecells Gameteproduction Steroid andpeptide hormones Figure 26-7

  23. Consequences of Feedback Table 26-2

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