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

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

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

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

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

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

5 Sex Determination Temperature-sensitive Genetic
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


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

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

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

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

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

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

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

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 mother’s pouch Placentals are viviparous Retain young in uterus for long period of development Nourished by placenta from mother’s blood


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


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

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


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


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

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

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


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


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


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

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

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



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

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

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



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 Bartholin’s glands secrete lubricant that facilitates penetration by penis During sexual arousal, external genitalia become engorged with blood

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


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