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Chapter 46 Animal Reproduction PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Overview: Doubling Up for Sexual Reproduction • The two earthworms in this picture are mating • Each worm produces both sperm and eggs, which will fertilize – And in a few weeks, new worms will hatch Figure 46.1 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Concept 46.1: Both asexual and sexual reproduction occur in the animal kingdom • Asexual reproduction is the creation of new individuals – Whose genes all come from one parent • Sexual reproduction is the creation of offspring – By the fusion of male and female gametes to form a zygote • The female gamete is the egg • The male gamete is the sperm Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Mechanisms of Asexual Reproduction • Many invertebrates reproduce asexually by fission – The separation of a parent into two or more individuals of approximately the same size Figure 46.2 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Also common in invertebrates is budding – In which two new individuals arise from outgrowths of existing ones • Another type of asexual reproduction is fragmentation, which – Is the breaking of the body into several pieces, some or all of which develop into complete adults – Must be accompanied by regeneration, the regrowth of lost body parts Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Reproductive Cycles and Patterns • Most animals exhibit cycles in reproductive activity – Often related to changing seasons • Reproductive cycles – Are controlled by hormones and environmental cues Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Animals may reproduce exclusively asexually or sexually or they may alternate between the two • Some animals reproduce by parthenogenesis – A process in which an egg develops without being fertilized – Among vertebrates, several genera of fishes, amphibians, and lizards, including whiptail lizards Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Sexual reproduction presents a special problem for certain organisms – That seldom encounter a mate • One solution to this problem is hermaphroditism – In which each individual has both male and female reproductive systems Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Another remarkable reproductive pattern is sequential hermaphroditism – In which an individual reverses its sex during its lifetime Figure 46.4 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Concept 46.2: Fertilization depends on mechanisms that help sperm meet eggs of the same species • The mechanisms of fertilization, the union of egg and sperm – Play an important part in sexual reproduction Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Some species have external fertilization, in which – Eggs shed by the female are fertilized by sperm in the external environment Eggs Figure 46.5 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Other species have internal fertilization, in which – Sperm are deposited in or near the female reproductive tract, and fertilization occurs within the tract Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • In either situation, fertilization requires critical timing – Often mediated by environmental cues, pheromones, and/or courtship behavior • Internal fertilization – Requires important behavioral interactions between male and female animals – Requires compatible copulatory organs Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Ensuring the Survival of Offspring • All species produce more offspring than the environment can handle – But the proportion that survives is quite small Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • The embryos of many terrestrial animals – Develop in eggs that can withstand harsh environments • Instead of secreting a shell around the embryo – Many animals retain the embryo, which develops inside the female Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Many different types of animals – Exhibit parental care to ensure survival of offspring Figure 46.6 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Gamete Production and Delivery • To reproduce sexually – Animals must have systems that produce gametes • The least complex systems – Do not even contain distinct gonads, the organs that produce gametes in most animals • The most complex reproductive systems – Contain many sets of accessory tubes and glands that carry, nourish, and protect the gametes and the developing embryos Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Many animals with relatively simple body plans – Possess highly complex reproductive systems Genital pore (Digestive tract) Female organs: Male organs: 3 Uterus 4 Seminal vesicle Yolk gland Yolk duct 3 Sperm duct (vas deferens) 2 Oviduct 1 Ovary 2 Vas efferens 1 Testis Seminal receptacle Figure 46.7 (Excretory pore) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Most insects – Have separate sexes with complex reproductive systems 1 Ovary Accessory gland 1 Testis 4 Ejaculatory duct 2 Vas deferens 5 Penis 3 Seminal vesicle (a) Male honeybee. Sperm form in the testes, pass through the sperm duct (vas deferens), and are stored in the seminal vesicle. The male ejaculates sperm along with fluid from the accessory glands. (Males of some species of insects and other arthropods have appendages called claspers that grasp the Figure 46.8a, b female during copulation.) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Oviduct Spermatheca 3 Vagina Accessory gland (b) Female honeybee. Eggs develop in the ovaries and then pass through the oviducts and into the vagina. A pair of accessory glands (only one is shown) add protective secretions to the eggs in the vagina. After mating, sperm are stored in the spermatheca, a sac connected to the vagina by a short duct. Female Reproductive Anatomy • The female external reproductive structures include – The clitoris – Two sets of labia • The internal organs are a pair of gonads – And a system of ducts and chambers that carry gametes and house the embryo and fetus Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Reproductive anatomy of the human female Uterus Oviduct (Urinary bladder) (Pubic bone) Ovary (Rectum) Cervix Vagina Urethra Shaft Glans Bartholin’s gland Prepuce Vaginal opening Figure 46.9 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Labia minora Labia majora Clitoris Ovaries Oviduct Follicles Uterus Uterine wall Endometrium Corpus luteum Cervix Vagina Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Ovaries • The female gonads, the ovaries – Lie in the abdominal cavity • Each ovary – Is enclosed in a tough protective capsule and contains many follicles • A follicle – Consists of one egg cell surrounded by one or more layers of follicle cells Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • The process of ovulation – Expels an egg cell from the follicle • The remaining follicular tissue then grows within the ovary – To form a solid mass called the corpus luteum, which secretes hormones, depending on whether or not pregnancy occurs Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Oviducts and Uterus • The egg cell is released into the abdominal cavity – Near the opening of the oviduct, or fallopian tube • Cilia in the tube – Convey the egg to the uterus Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Vagina and Vulva • The vagina is a thin-walled chamber – That is the repository for sperm during copulation – That serves as the birth canal through which a baby is born Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • The vagina opens to the outside at the vulva – Which includes the hymen, vestibule, labia minora, labia majora, and clitoris Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Mammary Glands • The mammary glands are not part of the reproductive system – But are important to mammalian reproduction • Within the glands – Small sacs of epithelial tissue secrete milk Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Male Reproductive Anatomy • In most mammalian species – The male’s external reproductive organs are the scrotum and penis • The internal organs – Consist of the gonads, which produce sperm and hormones, and accessory glands Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Reproductive anatomy of the human male Seminal vesicle (behind bladder) (Urinary bladder) Prostate gland Urethra Scrotum Glans penis Figure 46.10 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Bulbourethral gland Erectile tissue of penis Vas deferens Epididymis Testis (Urinary bladder) Seminal vesicle (Rectum) (Pubic bone) Erectile tissue of penis Vas deferens Ejaculatory duct Prostate gland Bulbourethral gland Urethra Vas deferens Epididymis Glans penis Testis Scrotum Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Prepuce Testes • The male gonads, or testes – Consist of many highly coiled tubes surrounded by several layers of connective tissue • The tubes are seminiferous tubules – Where sperm form Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Production of normal sperm – Cannot occur at the body temperatures of most mammals • The testes of humans and many mammals – Are held outside the abdominal cavity in the scrotum, where the temperature is lower than in the abdominal cavity Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Ducts • From the seminiferous tubules of a testis – The sperm pass into the coiled tubules of the epididymis • During ejaculation – Sperm are propelled through the muscular vas deferens, the ejaculatory duct, and exit the penis through the urethra Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Glands • Three sets of accessory glands – Add secretions to the semen, the fluid that is ejaculated • A pair of seminal vesicles – Contributes about 60% of the total volume of semen • The prostate gland – Secretes its products directly into the urethra through several small ducts • The bulbourethral gland – Secretes a clear mucus before ejaculation that neutralizes acidic urine remaining in the urethra Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Semen in the Female Reproductive Tract • Once in the female reproductive tract – A number of processes, including contractions of the uterus, help move the sperm up the uterus Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Penis • The human penis – Is composed of three cylinders of spongy erectile tissue • During sexual arousal – The erectile tissue fills with blood from the arteries, causing an erection – How does nitric oxide work again? Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Human Sexual Response • Two types of physiological reactions predominate in both sexes – Vasocongestion, the filling of tissue with blood – Myotonia, increased muscle tension • The sexual response cycle can be divided into four phases – Excitement, plateau, orgasm, and resolution Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Concept 46.4: In humans and other mammals, a complex interplay of hormones regulates gametogenesis • The process of gametogenesis – Is based on meiosis, but differs in females and males Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Oogenesis is the development of mature ova Ovary Primary germ cell in embryo Differentiation Oogonium in ovary Oogonium 2n Mitotic division Primary oocyte within follicle Primary oocyte, arrested in prophase of meiosis I (present at birth) 2n Growing follicle Completion of meiosis I and onset of meiosis II n First polar body n Secondary oocyte, arrested at metaphase of meiosis II Ovulation n n Entry of sperm triggers completion of meiosis II Mature follicle Ruptured follicle Ovum Ovulated secondary oocyte Corpus luteum Figure 46.11 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Degenerating corpus luteum • Spermatogenesis is the production of mature sperm Epididymis Seminiferous tubule Testis Cross section of seminiferous tubule Spermatogonium 2n Mitotic division, producing large numbers of spermatogonia Sertoli cell nucleus Differentiation and onset of meiosis I Primary spermatocyte (in prophase of meiosis I) 2n Meiosis I completed n n Secondary spermatocyte Meiosis II n n n n Early spermatids Lumen of Seminiferous tubule Spermatids (at two stages of differentiation) Differentiation (Sertoli cells provide nutrients) n n n Sperm cells n Neck Head Midpiece Tail Plasma membrane Mitochondria Nucleus Figure 46.12 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Acrosome Oogenesis differs from spermatogenesis in three major ways • First, during the meiotic divisions of oogenesis – Cytokinesis is unequal, with almost all the cytoplasm monopolized by a single daughter cell, the secondary oocyte • Second, sperm are produced continuously throughout a male’s life – Which is not the case in oogenesis • Third, oogenesis has long “resting” periods – While spermatogenesis produces sperm in uninterrupted sequence Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Reproductive Cycles of Females • In females – The secretion of hormones and the reproductive events they regulate are cyclic Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Menstrual Versus Estrous Cycles • Two different types of cycles occur in females Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Humans and other primates have menstrual cycles – While other mammals have estrous cycles • In both cases ovulation occurs at a time in the cycle – After the endometrium has started to thicken in preparation for implantation Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • In menstrual cycles – The endometrium is shed from the uterus in a bleeding called menstruation – Sexual receptivity is not limited to a specific timeframe • In estrous cycles – The endometrium is reabsorbed by the uterus – Sexual receptivity is limited to a “heat” period Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • The female reproductive cycle – Is one integrated cycle involving two organs, the uterus and ovaries • Cyclic secretion of GnRH from the hypothalamus – And of FSH and LH from the anterior pituitary orchestrates the female reproductive cycle • Five kinds of hormones – Participate in an elaborate scheme involving both positive and negative feedback – Know these 5 hormones and their roles! Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • The reproductive cycle of the human female (a) Control by hypothalamus Inhibited by combination of estrogen and progesterone Hypothalamus 1 Stimulated by high levels of estrogen GnRH Anterior pituitary LH FSH 2 (b) Inhibited by low levels of estrogen Pituitary gonadotropins in blood 6 LH 3 (c) FSH FSH and LH stimulate follicle to grow Ovarian cycle 7 Growing follicle Mature follicle 8 Corpus luteum Ovulation Follicular phase 4 (d) LH surge triggers ovulation 5 Estrogen Peak causes LH surge 10 Progesterone Estrogen level very low (e) Luteal phase Progesterone and estrogen secreted by corpus luteum Estrogen secreted by growing follicle in increasing amounts Ovarian hormones in blood Degenerating corpus luteum 9 Progesterone and estrogen promote thickening of endometrium Uterine (menstrual) cycle Endometrium Days Menstrual flow phase Figure 46.13a–e 0 5 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Proliferative phase 14 15 10 Secretory phase 20 25 28 The Ovarian Cycle • In the ovarian cycle – Hormones stimulate follicle growth, which results in ovulation • Following ovulation – The follicular tissue left behind transforms into the corpus luteum Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Uterine (Menstrual) Cycle • Cycle after cycle – The maturation and release of egg cells from the ovary are integrated with changes in the uterus • If an embryo has not implanted in the endometrium by the end of the secretory phase – A new menstrual flow commences Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Menopause • After about 450 cycles, human females undergo menopause – The cessation of ovulation and menstruation Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Hormonal Control of the Male Reproductive System • Testosterone and other androgens – Are directly responsible for the primary and secondary sex characteristics of the male Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Androgen secretion and sperm production – Are both controlled by hypothalamic and pituitary hormones Stimuli from other areas in the brain Hypothalamus GnRH from the hypothalamus regulates FSH and LH release from the anterior pituitary. FSH acts on the Sertoli cells of the seminiferous tubules, promoting spermatogenesis. Figure 46.14 Anterior pituitary Negative feedback LH stimulates the Leydig cells to make testosterone, which in turn stimulates sperm production. Leydig cells make testosterone Sertoli cells Spermatogenesis Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Primary and secondary sex characteristics Testis Conception, Embryonic Development, and Birth • Concept 46.5: In humans and other placental mammals, an embryo grows into a newborn in the mother’s uterus • In humans and most other placental mammals – Pregnancy, or gestation, is the condition of carrying one or more embryos in the uterus Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Fertilization of an egg by a sperm, conception – Occurs in the oviduct 3 Cleavage (cell division) begins in the oviduct as the embryo is moved toward the uterus by peristalsis and the movements of cilia. 4 Cleavage continues. By the time the embryo reaches the uterus, it is a ball of cells. It floats in the uterus for several days, nourished by endometrial secretions. It becomes a blastocyst. Ovary 2 Fertilization occurs. A sperm enters the oocyte; meiosis of the oocyte finishes; and the nuclei of the ovum and sperm fuse, producing a zygote. 5 The blastocyst implants in the endometrium about 7 days after conception. Uterus 1 Ovulation releases a secondary oocyte, which enters the oviduct. (a) From ovulation to implantation Endometrium Endometrium Inner cell mass Cavity Blastocyst Figure 46.15a, b (b) Implantation of blastocyst Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Trophoblast • After fertilization – The zygote undergoes cleavage and develops into a blastocyst before implantation in the endometrium Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings First Trimester • Human gestation – Can be divided into three trimesters of about three months each • The first trimester – Is the time of most radical change for both the mother and the embryo Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • During its first 2 to 4 weeks of development – The embryo obtains nutrients directly from the endometrium • Meanwhile, the outer layer of the blastocyst – Mingles with the endometrium and eventually forms the placenta Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Blood from the embryo – Travels to the placenta through arteries of the umbilical cord and returns via the umbilical vein Maternal arteries Maternal veins Placenta Maternal portion of placenta Umbilical cord Chorionic villus containing fetal capillaries Fetal portion of placenta (chorion) Maternal blood pools Uterus Figure 46.16 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Fetal arteriole Fetal venule Umbilical cord Umbilical arteries Umbilical vein • The first trimester is the main period of organogenesis – The development of the body organs (a) 5 weeks. Limb buds, eyes, the (b) 14 weeks. Growth and heart, the liver, and rudiments development of the offspring, of all other organs have started now called a fetus, continue to develop in the embryo, which during the second trimester. is only about 1 cm long. This fetus is about 6 cm long. Figure 46.17a–c Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings (c) 20 weeks. By the end of the second trimester (at 24 weeks), the fetus grows to about 30 cm in length. Second Trimester • During the second trimester – The fetus grows and is very active – The mother may feel fetal movements – The uterus grows enough for the pregnancy to become obvious Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Third Trimester • During the third trimester – The fetus continues to grow and fills the available space within the embryonic membranes Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • A complex interplay of local regulators and hormones – Induces and regulates labor, the process by which childbirth occurs Oxytocin from ovaries from fetus and mother's posterior pituitary Induces oxytocin receptors on uterus Stimulates uterus to contract Stimulates placenta to make Prostaglandins Figure 46.18 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Stimulate more contractions of uterus Positive feedback Estrogen • Birth, or parturition – Is brought about by a series of strong, rhythmic uterine contractions Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • The process of labor has three stages Placenta Umbilical cord Uterus Cervix 1 Dilation of the cervix 2 Expulsion: delivery of the infant Uterus Placenta (detaching) Umbilical cord Figure 46.19 3 Delivery of the placenta Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Mother’s Immune Tolerance of the Embryo and Fetus • A woman’s acceptance of her “foreign” offspring – Is not fully understood – May be due to the suppression of the immune response in her uterus Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Contraception and Abortion • Contraception, the deliberate prevention of pregnancy – Can be achieved in a number of ways Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Some contraceptive methods – Prevent the release of mature eggs and sperm from gonads – Prevent fertilization by keeping sperm and egg apart – Prevent implantation of an embryo Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Mechanisms of some contraceptive methods Female Male Method Event Event Production of viable sperm Method Production of viable oocytes Vasectomy Ovulation Sperm transport down male duct system Abstinence Combination birth control pill (or injection, patch, or vaginal ring) Abstinence Condom Coitus interruptus (very high failure rate) Sperm deposited in vagina Capture of the oocyte by the oviduct Tubal ligation Sperm movement through female reproductive tract Transport of oocyte in oviduct Spermicides; diaphragm; cervical cap; progestin alone (minipill, implant, or injection) Meeting of sperm and oocyte in oviduct Union of sperm and egg Morning-after pill (MAP) Progestin alone Implantation of blastocyst in properly prepared endometrium Figure 46.20 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Birth Modern Reproductive Technology • Recent scientific and technological advances – Have made it possible to deal with many reproductive problems Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Amniocentesis and chorionic villus sampling – Are invasive techniques in which amniotic fluid or fetal cells are obtained for genetic analysis Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Noninvasive procedures – Usually use ultrasound imaging to detect fetal condition Head Head Body Figure 46.21 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Body • Modern technology – Can help infertile couples by in vitro fertilization Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings