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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. CHAPTER 53.

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Presentation on theme: "Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. CHAPTER 53."— Presentation transcript:

1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. CHAPTER 53

2 Reproductive Strategies Most animals reproduce sexually –Requires meiosis to produce haploid gametes (sperm and eggs) –Gametes united by fertilization to produce the diploid zygote –Zygote develops by mitosis into a new multicellular organism 2

3 Reproductive Strategies Asexual reproduction –Genetically identical cells are produced from a single parent cell through mitosis –Single-celled organisms utilize fission –Cnidarians reproduce by budding 3

4 Novel Reproductive Strategies Parthenogenesis –Females produce offspring from unfertilized eggs Hermaphroditism –One individual has both testes and ovaries –May be sequential – change sex Protogyny – female-to-male change Protandry – male-to-female change 4

5 Sex Determination Temperature-sensitive –In many fish and reptiles –Has evolved many times Genetic –XX or XY –Humans Embryonic gonads indifferent for first 40 days SRY gene on Y converts gonads to testes Testosterone promotes male development 5

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7 Vertebrate Fertilization Internal fertilization has led to three strategies for development 1.Oviparity Fertilized eggs are deposited outside mothers body to complete their development 2.Ovoviviparity Fertilized eggs are kept within mother to complete development, young obtain food from egg yolk 3.Viviparity Young develop within mother and obtain nourishment from her blood 7

8 Vertebrate Fertilization Fishes –In most species of bony fish, fertilization is external –Thousands of eggs are fertilized, but only a few individuals grow to maturity –In most species of cartilaginous fish, fertilization is internal Development of young is viviparous Gives birth to a few, well-developed offspring 8

9 Vertebrate Fertilization Amphibians –In most species fertilization is external –Eggs of most species develop in water –With some interesting exceptions 9

10 a)Male carries tadpoles on his back b)Froglets develop in brood pouches c)Female carries developing larvae on her back d)Male holds developing froglets in his vocal pouch 10

11 Vertebrate Fertilization Reptiles –Amniotic egg Extraembryonic membranes Adaptation for life on land –Most oviparous reptiles lay eggs and abandon them Leathery shell on egg 11

12 Vertebrate Fertilization Birds –Amniotic egg Extraembryonic membranes Adaptation for life on land –All birds practice internal fertilization –Hard calcareous shell on egg –Birds are endotherms Must incubate eggs to keep them warm 12

13 Vertebrate Reproductive Cycles Female reproductive cycles involve periodic release of a mature ovum (ovulation) Females sexually receptive to males only around time of ovulation (estrus) Primates have menstrual cycles –Females bleed when shedding inner lining of the uterus (menstruation) –Can copulate at any time in their cycle 13

14 Reproduction in Mammals Mammals are of three types –Monotremes are oviparous Lay eggs –Marsupials are viviparous Give birth to incompletely developed fetuses, which mature in mothers pouch –Placentals are viviparous Retain young in uterus for long period of development Nourished by placenta from mothers blood 14

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16 Human Male Reproductive System Seminiferous tubules –Sites of sperm production Leydig cells produce testosterone –Converts indifferent external genitalia into penis and scrotum Shortly before birth, the testes descend into the scrotum because sperm need cooler temperature to develop 16

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18 Human Male Reproductive System Gamete production –Spermatogonium (germ cells) divides by mitosis to produce two diploid cells One later undergoes meiosis, the other remains as a spermatogonium –Primary spermatocyte – diploid cell that begins meiosis –Primary spermatocyte undergoes meiosis I to produce two haploid secondary spermatocytes –Each secondary spermatocyte undergoes a second meiotic division to produce 2 haploid spermatids –Total of 4 haploid spermatids produced 18

19 Human Male Reproductive System Seminiferous tubules also contain supporting cells called Sertoli cells –Nurse developing germ cells –Help convert spermatids into spermatozoa (sperm) by engulfing their extra cytoplasm 19

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21 Human Male Reproductive System Sperm structure –Head – contains a nucleus Capped by the acrosome, which aids in penetration of the egg –Body – consists of many mitochondria Provide energy Centriole acts as a basal body for the flagellum –Tail – consists of a flagellum Provides locomotion 21

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23 Human Male Reproductive System Sperm are delivered into the epididymis for storage and maturation From there sperm enter vas deferens Then to the urethra 23

24 Human Male Reproductive System Semen –Complex mixture of fluids and sperm –Seminal vesicles Produce a fructose-rich fluid, which makes up 60% of semen volume –Prostate gland Contributes about 30% of the bulk of semen –Bulbourethral glands Add secretions to make up the last 10% of semen Also lubricate the tip of the penis 24

25 Human Male Reproductive System Penis –Consists of erectile tissue columns Two corpora cavernosa on dorsal side One corpus spongiosum on ventral side During erection, these tissues fill with blood –Parasympathetic nerves release nitric oxide (NO), which stimulates dilation of arteries –Ejaculation is the ejection from the penis of about 2–5 mL of semen containing an average of 300 million sperm 25

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27 Human Male Reproductive System Hormonal control –Hypothalamic GnRH stimulates anterior pituitary to secrete FSH and LH –FSH stimulates the Sertoli cells to facilitate sperm development –LH stimulates the Leydig cells to secrete testosterone –Controlled by negative feedback 27

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29 Human Female Reproductive System Ovaries develop more slowly than the testes Female embryo develops a clitoris and labia majora –In the absence of testosterone –Homologous structures to penis and scrotum Ovaries contain microscopic structures called ovarian follicles –Each follicle contains a potential egg cell called a primary oocyte 29

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31 Human Female Reproductive System At puberty, granulosa cells secrete estrogen –Triggers menarche, first menstrual cycle –Stimulates secondary sexual characteristics At birth, ovaries contain about 1 million follicles –Each contains a primary oocyte that is arrested in prophase of meiosis I The human menstrual cycle lasts ~ 1 month –Divided into follicular phase, ovulation, and luteal phase 31

32 Human Female Reproductive System Ovarian events –Follicular phase Several follicles are stimulated to grow under FSH stimulation But only one achieves full maturity as a tertiary, or Graafian, follicle Estrogen causes growth of the endometrium –Proliferative phase of the endometrium Primary oocyte completes meiosis I –Produces one large secondary oocyte and one tiny polar body 32

33 33 Ovarian events –Follicular phase Secondary oocyte begins meiosis II However, its progress is arrested in metaphase II Does not complete the second meiotic division unless it becomes fertilized in the Fallopian tube

34 Human Female Reproductive System Ovarian events –Ovulation Estrogen stimulates the anterior pituitary to secrete LH about midcycle LH surge causes the Graafian follicle to burst, releasing its secondary oocyte into the Fallopian tube If oocyte is not fertilized, it disintegrates If it is fertilized, it completes meiosis II, forming a mature ovum and second polar body Fusion of the nuclei from the ovum and the sperm produces a diploid zygote 34

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37 Human Female Reproductive System Ovarian events –Luteal phase LH stimulation transforms the Graafian follicle into the corpus luteum Corpus luteum secretes estrogen and progesterone Exert negative feedback on FSH and LH Cause endometrium to become more vascular and glandular –Secretory phase of endometrium –Prepare uterus for embryo implantation 37

38 Human Female Reproductive System Ovarian events –Luteal phase In the absence of fertilization, the corpus luteum degenerates due to decreasing levels of FSH and LH Built-up endometrium is sloughed off with accompanying bleeding –Menstrual phase of endometrium 38

39 Human Female Reproductive System Ovarian events –Luteal phase If ovulated oocyte is fertilized, the corpus luteum is maintained by human chorionic gonadotropin (hCG) Keeps high levels of estrogen and progesterone, and so prevents menstruation until placenta takes over hCG is produced by the embryo –Tested for in all pregnancy tests 39

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42 Female Accessory Sex Organs Fallopian tubes (uterine tubes or oviducts) Uterus – muscular pear-shaped organ Cervix – narrow opening Vagina – initially covered by a membrane called the hymen Bartholins glands secrete lubricant that facilitates penetration by penis During sexual arousal, external genitalia become engorged with blood 42

43 Contraception Prevention of ovulation –Birth control pills or oral contraceptives Contain analogues of progesterone, sometimes with estrogens Prevent follicle development Hormone-containing capsules can also be implanted beneath the skin –Prevention of embryo implantation Intrauterine devices (IUD) Morning-after pill, or Plan B 43

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