Chapter 46 Animal Reproduction.

Chapter 46 Animal Reproduction

Overview: Pairing Up for Sexual Reproduction
Each sea slug produces sperm and eggs; in a few weeks, new individuals will hatch from fertilized eggs Animal reproduction takes many forms A population outlives its member only by reproduction, the generation of new individuals from existing ones © 2011 Pearson Education, Inc.

Figure 46.1 Figure 46.1 How can each of these sea slugs be both male and female?

Concept 46.1: Both asexual and sexual reproduction occur in the animal kingdom
Sexual reproduction is the creation of an offspring by fusion of a male gamete (sperm) and female gamete (egg) to form a zygote Asexual reproduction is creation of offspring without the fusion of egg and sperm © 2011 Pearson Education, Inc.

Mechanisms of Asexual Reproduction
Many invertebrates reproduce asexually by fission, separation of a parent into two or more individuals of about the same size © 2011 Pearson Education, Inc.

Figure 46.2 Figure 46.2 Asexual reproduction of a sea anemone (Anthopleura elegantissima).

In budding, new individuals arise from outgrowths of existing ones
Fragmentation is breaking of the body into pieces, some or all of which develop into adults Fragmentation must be accompanied by regeneration, regrowth of lost body parts Parthenogenesis孤雌生殖 is the development of a new individual from an unfertilized egg © 2011 Pearson Education, Inc.

Sexual Reproduction: An Evolutionary Enigma
Sexual females have half as many daughters as asexual females; this is the “twofold cost” of sexual reproduction Despite this, almost all eukaryotic species reproduce sexually © 2011 Pearson Education, Inc.

Asexual reproduction Sexual reproduction Female Generation 1 Female
Figure Asexual reproduction Sexual reproduction Female Generation 1 Female Figure 46.3 The “reproductive handicap” of sex.

Figure Asexual reproduction Sexual reproduction Female Generation 1 Female Generation 2 Male Figure 46.3 The “reproductive handicap” of sex.

Figure Asexual reproduction Sexual reproduction Female Generation 1 Female Generation 2 Male Generation 3 Figure 46.3 The “reproductive handicap” of sex.

Figure Asexual reproduction Sexual reproduction Female Generation 1 Female Generation 2 Male Generation 3 Figure 46.3 The “reproductive handicap” of sex. Generation 4

Sexual reproduction results in genetic recombination, which provides potential advantages
An increase in variation in offspring, providing an increase in the reproductive success of parents in changing environments An increase in the rate of adaptation A shuffling of genes and the elimination of harmful genes from a population © 2011 Pearson Education, Inc.

Reproductive Cycles Ovulation is the release of mature eggs at the midpoint of a female cycle Most animals exhibit reproductive cycles related to changing seasons Reproductive cycles are controlled by hormones and environmental cues Because seasonal temperature is often an important cue in reproduction, climate change can decrease reproductive success © 2011 Pearson Education, Inc.

Figure 46.4 Figure 46.4 Caribou (Rangifer tarandus) mother and calf.

Some organisms can reproduce sexually or asexually, depending on conditions
Several genera of fishes, amphibians, and lizards reproduce only by a complex form of parthenogenesis that involves the doubling of chromosomes after meiosis Asexual whiptail lizards are descended from a sexual species, and females still exhibit mating behaviors © 2011 Pearson Education, Inc.

(a) A. uniparens females
Figure 46.5 (a) A. uniparens females Ovary size Ovulation Ovulation Progesterone Estradiol Hormone level Figure 46.5 Sexual behavior in parthenogenetic lizards. Time Behavior Female Male- like Female Male- like (b) The sexual behavior of A. uniparens is correlated with the cycle of ovulation.

(a) A. uniparens females
Figure 46.5a Figure 46.5 Sexual behavior in parthenogenetic lizards. (a) A. uniparens females

Ovary size Ovulation Ovulation Estradiol Hormone level Time Behavior
Figure 46.5b Ovary size Ovulation Ovulation Progesterone Estradiol Hormone level Time Figure 46.5 Sexual behavior in parthenogenetic lizards. Behavior Female Male- like Female Male- like (b) The sexual behavior of A. uniparens is correlated with the cycle of ovulation.

Variation in Patterns of Sexual Reproduction
For many animals, finding a partner for sexual reproduction may be challenging One solution is hermaphroditism, in which each individual has male and female reproductive systems Two hermaphrodites can mate, and some hermaphrodites can self-fertilize © 2011 Pearson Education, Inc.

Individuals of some species undergo sex reversals
Some species exhibit male to female reversal (for example, certain oysters), while others exhibit female to male reversal (for example, a coral reef fish) © 2011 Pearson Education, Inc.

Concept 46.2: Fertilization depends on mechanisms that bring together sperm and eggs of the same species The mechanisms of fertilization, the union of egg and sperm, play an important part in sexual reproduction In external fertilization, eggs shed by the female are fertilized by sperm in the external environment © 2011 Pearson Education, Inc.

Video: Hydra Releasing Sperm
© 2011 Pearson Education, Inc.

In internal fertilization, sperm are deposited in or near the female reproductive tract, and fertilization occurs within the tract Internal fertilization requires behavioral interactions and compatible copulatory organs All fertilization requires critical timing, often mediated by environmental cues, pheromones, and/or courtship behavior © 2011 Pearson Education, Inc.

Figure 46.6 Figure 46.6 External fertilization.

Ensuring the Survival of Offspring
Internal fertilization is typically associated with production of fewer gametes but the survival of a higher fraction of zygotes Internal fertilization is also often associated with mechanisms to provide protection of embryos and parental care of young © 2011 Pearson Education, Inc.

Some other animals retain the embryo, which develops inside the female
The embryos of some terrestrial animals develop in eggs with calcium- and protein-containing shells and several internal membranes Some other animals retain the embryo, which develops inside the female In many animals, parental care helps ensure survival of offspring © 2011 Pearson Education, Inc.

Figure 46.7 Figure 46.7 Parental care in an invertebrate.

Gamete Production and Delivery
To reproduce sexually, animals must produce gametes In most species individuals have gonads, organs that produce gametes Some simple systems do not have gonads, but gametes form from undifferentiated tissue More elaborate systems include sets of accessory tubes and glands that carry, nourish, and protect gametes and developing embryos © 2011 Pearson Education, Inc.

Most insects have separate sexes with complex reproductive systems
In many insects, the female has a spermatheca in which sperm is stored during copulation © 2011 Pearson Education, Inc.

Accessory gland Ovary Testis Oviduct Spermatheca Vas deferens
Figure 46.8 Accessory gland Ovary Testis Oviduct Spermatheca Vas deferens Ejaculatory duct Seminal vesicle Uterus Accessory gland Penis and claspers Vulva Figure 46.8 Insect reproductive anatomy. (a) Male fruit fly (b) Female fruit fly

Accessory gland Testis Vas deferens Ejaculatory duct Seminal vesicle
Figure 46.8a Accessory gland Testis Vas deferens Ejaculatory duct Seminal vesicle Figure 46.8 Insect reproductive anatomy. Penis and claspers (a) Male fruit fly

Ovary Oviduct Spermatheca Uterus Accessory gland Vulva
Figure 46.8b Ovary Oviduct Spermatheca Uterus Figure 46.8 Insect reproductive anatomy. Accessory gland Vulva (b) Female fruit fly

A cloaca is a common opening between the external environment and the digestive, excretory, and reproductive systems A cloaca is common in nonmammalian vertebrates; mammals usually have a separate opening to the digestive tract © 2011 Pearson Education, Inc.

Monogamy is relatively rare among animals
Males and/or females of some species have evolved mechanisms to decrease the chance of their mate mating with another individual Females can sometimes influence the relative reproductive success of their mates © 2011 Pearson Education, Inc.

Percentage of females lacking sperm in spermatheca
Figure 46.9 RESULTS 30 20 Percentage of females lacking sperm in spermatheca 10 Figure 46.9 Inquiry: Why is sperm usage biased when female fruit flies mate twice? Control; not remated Remated to wild-type males Remated to “no-sperm” males Remated to “no-ejaculate” males

Concept 46.3: Reproductive organs produce and transport gametes
The following section focuses on the human reproductive system © 2011 Pearson Education, Inc.

Female Reproductive Anatomy
The female external reproductive structures include the clitoris and 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 © 2011 Pearson Education, Inc.

Animation: Female Reproductive Anatomy Right-click slide / select “Play”

Major vestibular (Bartholin’s) gland Labia minora Labia majora
Figure 46.10 Oviduct Ovary Uterus (Urinary bladder) (Pubic bone) (Rectum) Urethra Cervix Body Vagina Glans Clitoris Prepuce Major vestibular (Bartholin’s) gland Labia minora Labia majora Vaginal opening Oviduct Ovaries Figure Reproductive anatomy of the human female. Follicles Corpus luteum Uterus Uterine wall Endometrium Cervix Vagina

Major vestibular (Bartholin’s) gland Labia minora Labia majora
Figure 46.10a Oviduct Ovary Uterus (Urinary bladder) (Pubic bone) (Rectum) Urethra Cervix Body Vagina Glans Clitoris Figure Reproductive anatomy of the human female. Prepuce Major vestibular (Bartholin’s) gland Labia minora Labia majora Vaginal opening

Oviduct Ovaries Follicles Corpus luteum Uterus Uterine wall
Figure 46.10b Oviduct Ovaries Follicles Corpus luteum Uterus Uterine wall Endometrium Cervix Figure Reproductive anatomy of the human female. Vagina

Ovaries The female gonads, the ovaries, lie in the abdominal cavity
Each ovary contains many follicles, which consist of a partially developed egg, called an oocyte, surrounded by support cells Once a month, an oocyte develops into an ovum (egg) by the process of oogenesis © 2011 Pearson Education, Inc.

If the egg is not fertilized, the corpus luteum degenerates
Ovulation expels an egg cell from the follicle, the cells of which produce estradiol prior to ovulation The remaining follicular tissue grows within the ovary, forming a mass called the corpus luteum The corpus luteum secretes estradiol and progesterone that helps to maintain pregnancy If the egg is not fertilized, the corpus luteum degenerates © 2011 Pearson Education, Inc.

Oviducts and Uterus The egg cell travels from the ovary to the uterus via an oviduct, or fallopian tube Cilia in the oviduct convey the egg to the uterus, also called the womb The uterus lining, the endometrium, has many blood vessels The uterus narrows at the cervix, then opens into the vagina © 2011 Pearson Education, Inc.

Vagina and Vulva The vagina is a thin-walled chamber that is the repository for sperm during copulation and serves as the birth canal The vagina opens to the outside at the vulva, which consists of the labia majora, labia minora, hymen, and clitoris © 2011 Pearson Education, Inc.

The clitoris has a head called a glans covered by the prepuce
The vagina, labia minora, and clitoris are rich with blood vessels; the clitoris also has many nerve endings © 2011 Pearson Education, Inc.

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 © 2011 Pearson Education, Inc.

Male Reproductive Anatomy
The male’s external reproductive organs are the scrotum and penis Internal organs are the gonads, which produce sperm and hormones, and accessory glands © 2011 Pearson Education, Inc.

Animation: Male Reproductive Anatomy Right-click slide / select “Play”

Seminal vesicle (behind bladder)
Figure 46.11 Seminal vesicle (behind bladder) (Urinary bladder) Prostate gland Bulbourethral gland Urethra Erectile tissue of penis Scrotum Vas deferens Epididymis Testis (Urinary bladder) Seminal vesicle (Urinary duct) Figure Reproductive anatomy of the human male. (Rectum) (Pubic bone) Vas deferens Erectile tissue Ejaculatory duct Prostate gland Urethra Penis Bulbourethral gland Vas deferens Glans Epididymis Testis Prepuce Scrotum

Seminal vesicle (behind bladder)
Figure 46.11a Seminal vesicle (behind bladder) (Urinary bladder) Prostate gland Bulbourethral gland Urethra Erectile tissue of penis Figure Reproductive anatomy of the human male. Scrotum Vas deferens Epididymis Testis

(Urinary bladder) Seminal vesicle (Urinary duct) (Rectum) (Pubic bone)
Figure 46.11b (Urinary bladder) Seminal vesicle (Urinary duct) (Rectum) (Pubic bone) Vas deferens Erectile tissue Ejaculatory duct Prostate gland Figure Reproductive anatomy of the human male. Urethra Penis Bulbourethral gland Vas deferens Glans Epididymis Testis Prepuce Scrotum

Testes The male gonads, or testes, consist of highly coiled tubes surrounded by connective tissue Sperm form in these seminiferous tubules Leydig cells produce hormones and are scattered between the tubules Production of normal sperm cannot occur at the body temperatures of most mammals © 2011 Pearson Education, Inc.

Ducts From the seminiferous tubules of a testis, sperm pass into the coiled tubules of the epididymis During ejaculation, sperm are propelled through the muscular vas deferens and the ejaculatory duct, and then exit the penis through the urethra © 2011 Pearson Education, Inc.

Accessory Glands Semen is composed of sperm plus secretions from three sets of accessory glands The two seminal vesicles contribute about 60% of the total volume of semen The prostate gland secretes its products directly into the urethra through several small ducts The bulbourethral glands secrete a clear mucus before ejaculation that neutralizes acidic urine remaining in the urethra © 2011 Pearson Education, Inc.

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 The head of the penis has a thinner skin covering than the shaft, and is more sensitive to stimulation © 2011 Pearson Education, Inc.

Gametogenesis Gametogenesis, the production of gametes, differs in male and female, reflecting the distinct structure and function of their gametes Sperm are small and motile and must pass from male to female Eggs are larger, and carry out their function within the female © 2011 Pearson Education, Inc.

Oogenesis, the development of a mature egg, is a prolonged process
Spermatogenesis, the development of sperm is continuous and prolific (millions of sperm are produced per day; each sperm takes about 7 weeks to develop Oogenesis, the development of a mature egg, is a prolonged process Immature eggs form in the female embryo, but do not complete their development until years or decades later © 2011 Pearson Education, Inc.

Spermatogenesis differs from oogenesis in three ways
All four products of meiosis develop into sperm while only one of the four becomes an egg Spermatogenesis occurs throughout adolescence and adulthood Sperm are produced continuously without the prolonged interruptions in oogenesis © 2011 Pearson Education, Inc.

Figure 46.12 Exploring: Human Gametogenesis
Figure 46.12a Epididymis Seminiferous tubule Testis Primordial germ cell in embryo Cross section of seminiferous tubule Mitotic divisions Spermatogonial stem cell 2n Mitotic divisions Sertoli cell nucleus Spermatogonium 2n Mitotic divisions Primary spermatocyte 2n Meiosis I Figure Exploring: Human Gametogenesis Secondary spermatocyte n n Meiosis II Lumen of seminiferous tubule Spermatids (two stages) Early spermatid Neck n n n n Tail Midpiece Head Differentiation (Sertoli cells provide nutrients) Plasma membrane Sperm cell n n Acrosome n n Nucleus Mitochondria

Cross section of seminiferous tubule Secondary spermatocyte
Figure 46.12aa Epididymis Seminiferous tubule Sertoli cell nucleus Spermato- gonium Primary spermatocyte Testis Cross section of seminiferous tubule Secondary spermatocyte Spermatids (two stages) Figure Exploring: Human Gametogenesis Sperm cell Lumen of seminiferous tubule

Primordial germ cell in embryo Mitotic divisions
Figure 46.12ab Primordial germ cell in embryo Mitotic divisions Spermatogonial stem cell 2n Mitotic divisions Spermatogonium 2n Mitotic divisions Primary spermatocyte 2n Meiosis I Secondary spermatocyte n n Meiosis II Figure Exploring: Human Gametogenesis Early spermatid n n n n Differentiation (Sertoli cells provide nutrients) Sperm cell n n n n

Neck Tail Midpiece Head Plasma membrane Acrosome Nucleus Mitochondria
Figure 46.12ac Neck Tail Midpiece Head Plasma membrane Acrosome Nucleus Figure Exploring: Human Gametogenesis Mitochondria

Figure 46.12 Exploring: Human Gametogenesis
Figure 46.12b Primary oocyte within follicle Ovary Growing follicle Primordial germ cell In embryo Mitotic divisions 2n Oogonium Mitotic divisions Primary oocyte (present at birth), arrested in prophase of meiosis I Mature follicle 2n Ruptured follicle Completion of meiosis I and onset of meiosis II First polar body n n Secondary oocyte, arrested at metaphase of meiosis II Ovulated secondary oocyte Figure Exploring: Human Gametogenesis Ovulation, sperm entry Completion of meiosis II Second polar body Corpus luteum n Fertilized egg n Degenerating corpus luteum

Primary oocyte within follicle
Figure 46.12ba Ovary Ruptured follicle Primary oocyte within follicle Ovulated secondary oocyte Growing follicle Figure Exploring: Human Gametogenesis Corpus luteum Mature follicle Degenerating corpus luteum

Primary oocyte (present at birth), arrested in prophase of meiosis I
Figure 46.12bb Primordial germ cell In embryo Mitotic divisions 2n Oogonium Mitotic divisions Primary oocyte (present at birth), arrested in prophase of meiosis I 2n Completion of meiosis I and onset of meiosis II First polar body n n Secondary oocyte, arrested at metaphase of meiosis II Ovulation, sperm entry Figure Exploring: Human Gametogenesis Completion of meiosis II Second polar body n Fertilized egg n

Concept 46.4: The interplay of tropic and sex hormones regulates mammalian reproduction
Human reproduction is coordinated by hormones from the hypothalamus, anterior pituitary, and gonads Gonadotropin-releasing hormone (GnRH) is secreted by the hypothalamus and directs the release of FSH and LH from the anterior pituitary FSH and LH regulate processes in the gonads and the production of sex hormones © 2011 Pearson Education, Inc.

Hormonal Control of the Female Reproductive Cycles
In females, the secretion of hormones and the reproductive events they regulate are cyclic Prior to ovulation, the endometrium thickens with blood vessels in preparation for embryo implantation If an embryo does not implant in the endometrium, the endometrium is shed in a process called menstruation © 2011 Pearson Education, Inc.

Hormones closely link the two cycles of female reproduction
Changes in the uterus define the menstrual cycle (also called the uterine cycle) Changes in the ovaries define the ovarian cycle © 2011 Pearson Education, Inc.

Degenerating corpus luteum
Figure 46.13 (a) Control by hypothalamus Inhibited by combination of estradiol and progesterone Hypothalamus  Stimulated by high levels of estradiol 1 GnRH  Anterior pituitary Inhibited by low levels of estradiol  2 FSH LH (b) Pituitary gonadotropins in blood 6 LH FSH 3 FSH and LH stimulate follicle to grow LH surge triggers ovulation (c) Ovarian cycle 7 8 Growing follicle Corpus luteum Degenerating corpus luteum Maturing follicle Follicular phase Ovulation Luteal phase Estradiol secreted by growing follicle in increasing amounts Progesterone and estradiol secreted by corpus luteum 4 (d) Ovarian hormones in blood Peak causes LH surge (see ) 5 6 Figure The reproductive cycle of the human female. 10 Estradiol 9 Progesterone Estradiol level very low Progesterone and estradiol promote thickening of endometrium (e) Uterine (menstrual) cycle Endometrium Menstrual flow phase Proliferative phase Secretory phase Days 5 10 14 15 20 25 28

Control by hypothalamus
Figure 46.13a (a) Control by hypothalamus Inhibited by combination of estradiol and progesterone Hypothalamus  Stimulated by high levels of estradiol  1 GnRH Anterior pituitary Inhibited by low levels of estradiol  2 FSH LH Figure The reproductive cycle of the human female.

Degenerating corpus luteum
Figure 46.13b (b) Pituitary gonadotropins in blood 6 LH FSH 3 FSH and LH stimulate follicle to grow LH surge triggers ovulation (c) Ovarian cycle 7 8 Figure The reproductive cycle of the human female. Corpus luteum Degenerating corpus luteum Growing follicle Maturing follicle Follicular phase Ovulation Luteal phase Days 5 10 14 15 20 25 28

Estradiol secreted by growing follicle in increasing amounts
Figure 46.13c Estradiol secreted by growing follicle in increasing amounts Progesterone and estradiol secreted by corpus luteum 4 (d) Ovarian hormones in blood Peak causes LH surge (see ) 6 5 10 9 Estradiol Progesterone Estradiol level very low Progesterone and estradiol promote thickening of endometrium (e) Uterine (menstrual) cycle Figure The reproductive cycle of the human female. Endometrium (e) Menstrual flow phase Proliferative phase Secretory phase Days 5 10 14 15 20 25 28

The Ovarian Cycle The sequential release of GnRH then FSH and LH stimulates follicle growth Follicle growth and an increase in the hormone estradiol characterize the follicular phase of the ovarian cycle The follicular phase ends at ovulation, and the secondary oocyte is released © 2011 Pearson Education, Inc.

Animation: Ovulation Right-click slide / select “Play”

The corpus luteum disintegrates, and ovarian steroid hormones decrease
Following ovulation, the follicular tissue left behind transforms into the corpus luteum; this is the luteal phase The corpus luteum disintegrates, and ovarian steroid hormones decrease © 2011 Pearson Education, Inc.

Animation: Post Ovulation Right-click slide / select “Play”

The Uterine (Menstrual) Cycle
Hormones coordinate the uterine cycle with the ovarian cycle Thickening of the endometrium during the proliferative phase coordinates with the follicular phase Secretion of nutrients during the secretory phase coordinates with the luteal phase Shedding of the endometrium during the menstrual flow phase coordinates with the growth of new ovarian follicles © 2011 Pearson Education, Inc.

A new cycle begins if no embryo implants in the endometrium
Cells of the uterine lining can sometimes migrate to an abnormal, or ectopic, location Swelling of these cells in response to hormone stimulation results in a disorder called endometriosis © 2011 Pearson Education, Inc.

Menopause After about 500 cycles, human females undergo menopause, the cessation of ovulation and menstruation Menopause is very unusual among animals Menopause might have evolved to allow a mother to provide better care for her children and grandchildren © 2011 Pearson Education, Inc.

Menstrual Versus Estrous Cycles
Menstrual cycles are characteristic only of humans and some other primates The endometrium is shed from the uterus in a bleeding called menstruation Sexual receptivity is not limited to a timeframe © 2011 Pearson Education, Inc.

Estrous cycles are characteristic of most mammals
The endometrium is reabsorbed by the uterus Sexual receptivity is limited to a “heat” period The length and frequency of estrus cycles vary from species to species © 2011 Pearson Education, Inc.

Hormonal Control of the Male Reproductive System
FSH promotes the activity of Sertoli cells, which nourish developing sperm LH regulates Leydig cells, which secrete testosterone and other androgens, which in turn promote spermatogenesis © 2011 Pearson Education, Inc.

Animation: Male Hormones Right-click slide / select “Play”

 Hypothalamus GnRH   Anterior pituitary FSH LH Negative feedback
Figure 46.14  Hypothalamus GnRH   Anterior pituitary FSH LH Negative feedback Negative feedback Sertoli cells Leydig cells Figure Hormonal control of the testes. Inhibin Spermatogenesis Testosterone Testis

Testosterone regulates the production of GnRH, FSH, and LH through negative feedback mechanisms
Sertoli cells secrete the hormone inhibin, which reduces FSH secretion from the anterior pituitary © 2011 Pearson Education, Inc.

Human Sexual Response Two reactions predominate in both sexes
Vasocongestion, the filling of tissue with blood Myotonia, increased muscle tension The sexual response cycle has four phases: excitement, plateau, orgasm, and resolution Excitement prepares the penis and vagina for coitus (sexual intercourse) © 2011 Pearson Education, Inc.

Direct stimulation of genitalia maintains the plateau phase and prepares the vagina for receipt of sperm Orgasm is characterized by rhythmic contractions of reproductive structures In males, semen is first released into the urethra and then ejaculated from the urethra In females, the uterus and outer vagina contract © 2011 Pearson Education, Inc.

During the resolution phase, organs return to their normal state and muscles relax

Concept 46.5: In placental mammals, an embryo develops fully within the mother’s uterus
An egg develops into an embryo in a series of predictable events © 2011 Pearson Education, Inc.

Conception, Embryonic Development, and Birth
Conception, fertilization of an egg by a sperm, occurs in the oviduct The resulting zygote begins to divide by mitosis in a process called cleavage Division of cells gives rise to a blastocyst, a ball of cells with a central cavity © 2011 Pearson Education, Inc.

(a) From ovulation to implantation
Figure 46.15 3 Cleavage 4 Cleavage continues Ovary 2 Fertilization Uterus 5 Implantation 1 Ovulation Endometrium (a) From ovulation to implantation Figure Formation of the zygote and early postfertilization events. Endometrium Inner cell mass Cavity Blastocyst Trophoblast (b) Implantation of blastocyst

After blastocyst formation, the embryo implants into the endometrium
The embryo releases human chorionic gonadotropin (hCG), which prevents menstruation Pregnancy, or gestation, is the condition of carrying one or more embryos in the uterus Duration of pregnancy in other species correlates with body size and maturity of the young at birth © 2011 Pearson Education, Inc.

Pregnancies can terminate spontaneously due to chromosomal or developmental abnormalities
An ectopic pregnancy occurs when a fertilized egg begins to develop in the fallopian tube © 2011 Pearson Education, Inc.

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 During implantation, the endometrium grows over the blastocyst © 2011 Pearson Education, Inc.

During its first 2 to 4 weeks, the embryo obtains nutrients directly from the endometrium
Meanwhile, the outer layer of the blastocyst, called the trophoblast, mingles with the endometrium and eventually forms the placenta Blood from the embryo travels to the placenta through arteries of the umbilical cord and returns via the umbilical vein © 2011 Pearson Education, Inc.

Maternal portion of placenta
Figure 46.16 Maternal arteries Maternal veins Placenta Umbilical cord Maternal portion of placenta Chorionic villus, containing fetal capillaries Fetal portion of placenta (chorion) Maternal blood pool Figure Placental circulation. Uterus Fetal arteriole Fetal venule Umbilical arteries Umbilical cord Umbilical vein

Splitting of the embryo during the first month of development results in genetically identical twins
Release and fertilization of two eggs results in fraternal and genetically distinct twins © 2011 Pearson Education, Inc.

The first trimester is the main period of organogenesis, development of the body organs
All the major structures are present by 8 weeks, and the embryo is called a fetus © 2011 Pearson Education, Inc.

Changes occur in the mother
Mucus plug to protect against infection Growth of the placenta and uterus Cessation of ovulation and the menstrual cycle Breast enlargement Nausea is also very common © 2011 Pearson Education, Inc.

(a) 5 weeks (b) 14 weeks (c) 20 weeks Figure 46.17
Figure Human fetal development. (a) 5 weeks (b) 14 weeks (c) 20 weeks

Figure 46.17a Figure Human fetal development. (a) 5 weeks

Figure 46.17b Figure Human fetal development. (b) 14 weeks

Figure 46.17c Figure Human fetal development. (c) 20 weeks

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 © 2011 Pearson Education, Inc.

Third Trimester During the third trimester, the fetus grows and fills the space within the embryonic membranes A complex interplay of local regulators and hormones induces and regulates labor, the process by which childbirth occurs © 2011 Pearson Education, Inc.

from fetus and mother’s posterior pituitary
Figure 46.18 Estradiol Oxytocin  from ovaries from fetus and mother’s posterior pituitary Activates oxytocin receptors on uterus Stimulates uterus to contract Positive feedback Stimulates placenta to make  Prostaglandins Figure Positive feedback in labor. Stimulate more contractions of uterus

Labor typically has three stages
Thinning and opening of the cervix, or dilation Expulsion or delivery of the baby Delivery of the placenta © 2011 Pearson Education, Inc.

Expulsion: delivery of the infant
Figure 46.19 Placenta Umbilical cord Uterus Cervix 1 Dilation of the cervix 2 Expulsion: delivery of the infant Figure The three stages of labor. Uterus Placenta (detaching) Umbilical cord 3 Delivery of the placenta

Placenta Umbilical cord Uterus Cervix 1 Dilation of the cervix
Figure 46.19a Placenta Umbilical cord Uterus Cervix Figure The three stages of labor. 1 Dilation of the cervix

Expulsion: delivery of the infant
Figure 46.19b Figure The three stages of labor. 2 Expulsion: delivery of the infant

Delivery of the placenta
Figure 46.19c Uterus Placenta (detaching) Umbilical cord Figure The three stages of labor. 3 Delivery of the placenta

Lactation, the production of milk, is unique to mammals
Delivery of the baby and placenta are brought about by a series of strong, rhythmic uterine contractions Lactation, the production of milk, is unique to mammals © 2011 Pearson Education, Inc.

Maternal Immune Tolerance of the Embryo and Fetus
A woman’s acceptance of her “foreign” offspring is not fully understood It may be due to suppression of the immune response in her uterus © 2011 Pearson Education, Inc.

Contraception and Abortion
Contraception, the deliberate prevention of pregnancy, can be achieved in a number of ways Contraceptive methods fall into three categories Preventing release of eggs and sperm Keeping sperm and egg apart Preventing implantation of an embryo © 2011 Pearson Education, Inc.

Production of primary oocytes
Figure 46.20 Male Female Method Event Event Method Production of sperm Production of primary oocytes Vasectomy Combination birth control pill (or injection, patch, or vaginal ring) Sperm transport down male duct system Oocyte development and ovulation Abstinence Abstinence Condom Female condom Coitus interruptus (very high failure rate) Sperm deposited in vagina Capture of the oocyte by the oviduct Tubal ligation Spermicides; diaphragm; progestin alone (as minipill or injection) Sperm movement through female reproductive tract Transport of oocyte in oviduct Figure Mechanisms of several contraceptive methods. Meeting of sperm and oocyte in oviduct Morning-after pill; intrauterine device (IUD) Union of sperm and egg Implantation of blastocyst in endometrium

Production of primary oocytes
Figure 46.20a Male Female Method Event Event Method Production of sperm Production of primary oocytes Vasectomy Combination birth control pill (or injection, patch, or vaginal ring) Sperm transport down male duct system Oocyte development and ovulation Abstinence Abstinence Condom Female condom Coitus interruptus (very high failure rate) Sperm deposited in vagina Capture of the oocyte by the oviduct Figure Mechanisms of several contraceptive methods. Tubal ligation Spermicides; diaphragm; progestin alone (as minipill or injection)

Sperm movement through female reproductive tract
Figure 46.20b Male Female Method Event Event Method Sperm movement through female reproductive tract Transport of oocyte in oviduct Meeting of sperm and oocyte in oviduct Morning-after pill; intrauterine device (IUD) Figure Mechanisms of several contraceptive methods. Union of sperm and egg Implantation of blastocyst in endometrium

The rhythm method, or natural family planning, is to refrain from intercourse when conception is most likely; it has a pregnancy rate of 10–20% Coitus interruptus, the withdrawal of the penis before ejaculation, is unreliable Barrier methods block fertilization with a pregnancy rate of less than 10% A condom fits over the penis A diaphragm is inserted into the vagina before intercourse © 2011 Pearson Education, Inc.

Intrauterine devices (IUDs) are inserted into the uterus and interfere with fertilization and implantation; the pregnancy rate is less than 1% Female birth control pills are hormonal contraceptives with a pregnancy rate of less than 1% © 2011 Pearson Education, Inc.

Sterilization is permanent and prevents the release of gametes
Tubal ligation ties off the oviducts Vasectomy ties off the vas deferens Abortion is the termination of a pregnancy Spontaneous abortion, or miscarriage, occurs in up to one-third of all pregnancies The drug RU486 results in an abortion within the first 7 weeks of a pregnancy © 2011 Pearson Education, Inc.

Detecting Disorders During Pregnancy
Amniocentesis and chorionic villus sampling are invasive techniques in which amniotic fluid or fetal cells are obtained for genetic analysis Noninvasive procedures usually use ultrasound imaging to detect fetal condition Genetic testing of the fetus poses ethical questions and can present parents with difficult decisions © 2011 Pearson Education, Inc.

Treating Infertility Modern technology can provide infertile couples with assisted reproductive technologies In vitro fertilization (IVF) mixes eggs with sperm in culture dishes and returns the embryo to the uterus at the 8-cell stage Sperm are injected directly into an egg in a type of IVF called intracytoplasmic sperm injection (ICSI) © 2011 Pearson Education, Inc.

Video: Ultrasound of Human Fetus 1

Video: Ultrasound of Human Fetus 2

Secondary spermatocytes Secondary oocyte
Figure 46.UN01 Human gametogenesis Spermatogenesis Oogenesis Primary spermatocyte Primary oocyte 2n 2n n Polar body Secondary spermatocytes Secondary oocyte n n n n n n n Spermatids Sperm n n n n Figure 46.UN01 Summary figure, Concept 46.3 n Polar body n Fertilized egg

Figure 46.UN02 Figure 46.UN02 Appendix A: answer to Test Your Understanding, question 9

Chapter 46 Animal Reproduction.

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Chapter 46 Animal Reproduction.

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Presentation on theme: "Chapter 46 Animal Reproduction."— Presentation transcript:

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