CAMPBELL BIOLOGY IN FOCUS Urry Cain

CAMPBELL BIOLOGY IN FOCUS Urry • Cain • Wasserman • Minorsky • Jackson • Reece 36 Reproduction and Development Lecture Presentations by Kathleen Fitzpatrick and Nicole Tunbridge © 2014 Pearson Education, Inc.

Concept 36. 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 § Internal vs external § Asexual reproduction is the creation of offspring without the fusion of egg and sperm § Budding § Fission § Fragmentation § Parthogenesis © 2014 Pearson Education, Inc.

Mechanisms of Asexual Reproduction § Many invertebrates reproduce asexually by budding, in which new individuals arise from outgrowths of existing ones § Also common among invertebrates is fission, the separation of a parent organism into two individuals of approximately equal size § Ex: anemones Video: Hydra Budding © 2014 Pearson Education, Inc.

§ 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 is the development of a new individual from an unfertilized egg © 2014 Pearson Education, Inc.

Figure 36. 3 -1 Sexual reproduction Asexual reproduction Female Generation 1 Female Generation 2

Figure 36. 3 -2 Sexual reproduction Asexual reproduction Female Generation 1 Female Generation 2

Figure 36. 3 -3 Sexual reproduction Asexual reproduction Female Generation 1 Female Generation 2

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 § WHY? ? ? © 2014 Pearson Education, Inc.

§ Sexual reproduction results in genetic recombination § The resulting increased variation among offspring may enhance the reproductive success of parents in changing environments © 2014 Pearson Education, Inc.

Hormone level Ovary size An interesting case of sexual reproduction…. Estradiol Ovulation Progesterone Behavior Time (a) A. uniparens females © 2014 Pearson Education, Inc. Female Male- Female like (b) The sexual behavior of A. uniparens is correlated with the cycle of ovulation. Malelike

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 § Any two hermaphrodites can mate, and some hermaphrodites can self-fertilize © 2014 Pearson Education, Inc.

§ Individuals of some species undergo sex reversals § For example, in a coral reef fish, the bluehead wrasse, a lone male defends a group of females § If the male dies, the largest female in the group transforms into a male § Within a few weeks, this individual can begin to produce sperm instead of eggs © 2014 Pearson Education, Inc.

External and Internal Fertilization § Sexual reproduction requires fertilization, the union of sperm and eggs § In external fertilization, eggs shed by the female are fertilized by sperm in the external environment § What kind of environment is necessary? § Why is timing important? § In internal fertilization, sperm are deposited in or near the female reproductive tract, and fertilization occurs within the tract § What are the advantages? § More or less production of gametes? © 2014 Pearson Education, Inc.

§ A moist habitat is almost always required for external fertilization to prevent gametes from drying out and to allow sperm to swim to eggs § Many aquatic invertebrates simply shed gametes into the surrounding water § In this case, timing of release of gametes is crucial to ensure that sperm and egg encounter one another § If external fertilization is not synchronous across a population, courtship behaviors might lead to fertilization © 2014 Pearson Education, Inc.

Figure 36. 6 © 2014 Pearson Education, Inc.

§ However fertilization occurs, the mating animals may use pheromones, chemicals released by one organism that can influence physiology and behavior of another individual of the same species © 2014 Pearson Education, Inc.

Ensuring the Survival of Offspring § Internal fertilization is typically associated with production of fewer gametes but the survival of a higher fraction of zygotes § Think back to ecology: what kind of survivorship curve would this display? § Internal fertilization is also often associated with mechanisms to provide protection of embryos and parental care of young § What kinds of mechanisms? © 2014 Pearson Education, Inc.

§ 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 © 2014 Pearson Education, Inc.

Parental care in an invertebrate © 2014 Pearson Education, Inc.

Concept 36. 2: Reproductive organs produce and transport gametes § Sexual reproduction in animals

Variation in Reproductive Systems § Many (but not all) animals have gonads, organs that produce gametes § Human male gonad? § Human female gonad? § 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 sometimes developing embryos © 2014 Pearson Education, Inc.

§ Most insects have separate sexes with complex reproductive systems § In many insects,

§ 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 © 2014 Pearson Education, Inc.

Human Male Reproductive Anatomy § The male’s external reproductive organs are the scrotum and penis § The internal organs are gonads that produce sperm and reproductive hormones, accessory glands that secrete products essential to sperm movement, and ducts that carry sperm and glandular secretions Animation: Male Reproductive Anatomy © 2014 Pearson Education, Inc.

Figure 36. 8 (Urinary bladder) Seminal vesicle (Urinary duct) (Rectum) (Pubic bone) Vas deferens Ejaculatory duct Prostate gland Bulbourethral gland © 2014 Pearson Education, Inc. Erectile tissue Urethra Vas deferens Epididymis Testis Scrotum Glans Prepuce Penis

Testes § The male gonads, or testes, produce sperm in highly coiled tubes called seminiferous tubules § The scrotum, a fold of the body wall, maintains testis temperature at about 2 o. C below the core body temperature § Why is this important? © 2014 Pearson Education, Inc.

Ducts § From the seminiferous tubules of a testis, sperm pass into the coiled duct 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 § the urethra is also part of what other human body system? © 2014 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 § What purpose does fructose serve? § The prostate gland secretes its products directly into the urethra through several small ducts § What purpose does the alkaline fluid serve? § The bulbourethral glands secrete a clear mucus before ejaculation that neutralizes acidic urine remaining in the urethra © 2014 Pearson Education, Inc.

Penis § The human penis is composed of three cylinders of spongy erectile tissue § During sexual arousal, erectile tissue fills with blood from the arteries, causing an erection § The head of the penis, or glans, has a thinner skin covering than the shaft § The prepuce, or foreskin, is a fold of skin covering the glans; it is removed when a male is circumcised © 2014 Pearson Education, Inc.

Human 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 Animation: Female Reproductive Anatomy © 2014 Pearson Education, Inc.

Figure 36. 9 Oviduct Ovary Uterus (Urinary bladder) (Pubic bone) (Rectum) (Urethra) Cervix Vagina Body Clitoris Glans Prepuce Major vestibular gland Labia minora © 2014 Pearson Education, Inc. Vaginal opening Labia majora

Ovaries § The female gonads, a pair of 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 © 2014 Pearson Education, Inc.

Oviducts and Uterus § Upon ovulation, a mature egg cell is released § It travels from the ovary to the uterus via an oviduct § Another term for oviduct? § Cilia in the oviduct convey the egg to the uterus, also called the womb § The uterus lining, the endometrium, has many blood vessels § What might endometriosis be? § The neck of the uterus is the cervix, which opens into the vagina © 2014 Pearson Education, Inc.

Vagina and Vulva § The vagina is a muscular but elastic 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 © 2014 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 © 2014 Pearson Education, Inc.

Gametogenesis § Gametogenesis is the production of gametes § There is a close relationship between the structure and function of the gonads Video: Flagella in Sperm Video: Sperm Flagellum © 2014 Pearson Education, Inc.

Figure 36. 10 a Epididymis Seminiferous tubule Testis Primordial germ cell in embryo Cross section of seminiferous tubule Mitotic divisions Spermatogonial stem cell Sertoli cell nucleus 2 n Mitotic divisions Spermatogonium 2 n Mitotic divisions Primary spermatocyte 2 n Meiosis I Secondary spermatocyte Lumen of seminiferous tubule Tail Plasma membrane Neck Midpiece n Meiosis II Spermatids (two stages) Early spermatid n n Differentiation (Sertoli cells provide nutrients) Head Acrosome Nucleus Mitochondria © 2014 Pearson Education, Inc. n Sperm cell n n

Figure 36. 10 aa Epididymis Seminiferous tubule Sertoli cell nucleus Testis Spermatogonium Primary spermatocyte Secondary spermatocyte Cross section of seminiferous tubule Spermatids (two stages) Sperm cell Lumen of seminiferous tubule © 2014 Pearson Education, Inc.

Figure 36. 10 ab Primordial germ cell in embryo Mitotic divisions Spermatogonial stem cell 2 n Mitotic divisions Spermatogonium 2 n Mitotic divisions Primary spermatocyte 2 n Meiosis I Secondary spermatocyte n n Meiosis II Early spermatid Sperm cell © 2014 Pearson Education, Inc. n n Differentiation (Sertoli cells provide nutrients) n n

Figure 36. 10 ac Tail Plasma membrane Neck Midpiece Head Acrosome Nucleus Mitochondria ©

Figure 36. 10 b Ovary Primary oocyte within follicle In embryo Primordial germ cell Mitotic divisions 2 n Oogonium Growing follicle Mature follicle Mitotic divisions Primary oocyte (present at birth), arrested in prophase of meiosis I 2 n Completion of meiosis I and onset of meiosis II First polar n body n Secondary oocyte, arrested at metaphase of meiosis II Ruptured follicle Ovulated secondary oocyte Ovulation, sperm entry Completion of meiosis II Second polar n body n © 2014 Pearson Education, Inc. Fertilized egg Corpus luteum Degenerating corpus luteum

Figure 36. 10 ba Ovary Primary oocyte within follicle Growing follicle Ruptured follicle Ovulated secondary oocyte Mature follicle Corpus luteum Degenerating corpus luteum © 2014 Pearson Education, Inc.

Figure 36. 10 bb In embryo Primordial germ cell Mitotic divisions 2 n Oogonium

Figure 36. 10 bc Completion of meiosis I and onset of meiosis II First polar n body n Secondary oocyte, arrested at metaphase of meiosis II Ovulation, sperm entry Completion of meiosis II Second polar n body n © 2014 Pearson Education, Inc. Fertilized egg

Differences in Meiosis: Male vs Female § 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 © 2014 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 © 2014 Pearson Education, Inc.

Concept 36. 3: The interplay of tropic and sex hormones regulates reproduction in mammals § Human reproduction is coordinated by hormones from the hypothalamus, anterior pituitary, and gonads § What does the hypothalamus release? § What does the anterior pituitary release? © 2014 Pearson Education, Inc.

§ FSH and LH regulate processes in the gonads and the production of sex

§ Sex hormones regulate gamete production both directly and indirectly § They serve many additional functions including sexual behavior and the development of primary and secondary sex characteristics § What is the difference between primary and secondary sex characteristics? © 2014 Pearson Education, Inc.

Figure 36. 11 © 2014 Pearson Education, Inc.

Hormonal Control of the Male Reproductive System § FSH and LH act on different cells in the testes to direct spermatogenesis § Sertoli cells, found in the seminiferous tubules, respond to FSH by nourishing developing sperm § Leydig cells, connective tissue between the tubules, respond to LH by secreting testosterone and other androgens, which promote spermatogenesis Animation: Male Hormones © 2014 Pearson Education, Inc.

Figure 36. 12 Hypothalamus Gn. RH FSH LH Leydig cells Sertoli cells Inhibin Spermatogenesis

§ Two negative feedback mechanisms control sex hormone production in males § Testosterone regulates the production of Gn. RH, FSH, and LH through negative feedback mechanisms § Sertoli cells secrete the hormone inhibin, which reduces FSH secretion from the anterior pituitary © 2014 Pearson Education, Inc.

Hormonal Control of Female Reproductive Cycles § Females produce eggs in cycles § 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 § What is this process called? © 2014 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 Animation: Ovulation Animation: Post-Ovulation © 2014 Pearson Education, Inc.

Figure 36. 13 (a) Control by hypothalamus Inhibited by combination of estradiol and progesterone Hypothalamus Stimulated by high levels of estradiol Gn. RH 1 Anterior pituitary 2 FSH Inhibited by low levels of estradiol LH Pituitary gonadotropins in blood (b) 6 LH FSH and LH stimulate follicle to grow 3 Ovarian cycle 7 Growing follicle (c) Maturing follicle 8 Follicular phase Corpus luteum Ovulation Degenerating corpus luteum Luteal phase Estradiol secreted by growing follicle in increasing amounts 4 (d) LH surge triggers ovulation Progesterone and estradiol secreted by corpus luteum Ovarian hormones in blood Peak causes LH surge (see 6 ) 5 10 9 Estradiol Progesterone Estradiol level very low (e) Progesterone and estradiol promote thickening of endometrium Uterine (menstrual) cycle Endometrium Days Menstrual flow phase © 2014 Pearson Education, Inc. 0 5 Proliferative phase 10 14 15 Secretory phase 20 25 28

Figure 36. 13 a (a) Control by hypothalamus Inhibited by combination of estradiol and progesterone Hypothalamus Stimulated by high levels of estradiol Gn. RH 1 Anterior pituitary 2 FSH Inhibited by low levels of estradiol LH Pituitary gonadotropins in blood (b) 6 LH FSH Days 3 0 © 2014 Pearson Education, Inc. FSH and LH stimulate follicle to grow 5 10 LH surge triggers ovulation 14 15 20 25 28

Figure 36. 13 b (b) Pituitary gonadotropins in blood 6 LH FSH 3 (c) FSH and LH stimulate follicle to grow 7 Growing follicle Days Ovarian cycle LH surge triggers ovulation Maturing follicle 8 Corpus luteum Follicular phase Ovulation Estradiol secreted 4 by growing follicle in increasing amounts 0 © 2014 Pearson Education, Inc. 5 10 14 15 Degenerating corpus luteum Luteal phase Progesterone and estradiol secreted by corpus luteum 20 25 28

Figure 36. 13 c (c) Ovarian cycle 7 Growing follicle Maturing follicle 8 Follicular phase Ovulation Ovarian hormones in blood 5 Degenerating corpus luteum Luteal phase Estradiol secreted by growing follicle in increasing amounts 4 (d) Corpus luteum Progesterone and estradiol secreted by corpus luteum Peak causes LH surge (see 6 ) 10 9 Estradiol Progesterone and estradiol promote thickening of endometrium Days Estradiol level very low 0 © 2014 Pearson Education, Inc. 5 10 14 15 20 25 28

Figure 36. 13 d (d) Ovarian hormones in blood Peak causes LH surge (see 6 ) 5 10 9 Estradiol Progesterone Estradiol level very low (e) Progesterone and estradiol promote thickening of endometrium Uterine (menstrual) cycle Endometrium Days Menstrual flow phase 0 © 2014 Pearson Education, Inc. 5 Proliferative phase 10 14 15 Secretory phase 20 25 28

The Ovarian Cycle § The sequential release of Gn. RH then FSH and LH stimulates follicle growth § Follicle and oocyte growth and an increase in the hormone estradiol characterize the follicular phase of the ovarian cycle § Estradiol causes Gn. RH, FSH, and LH levels to rise through positive feedback § The final result is the maturation of the follicle © 2014 Pearson Education, Inc.

§ At the end of the follicular phase, the follicle releases the secondary oocyte § The follicular tissue left behind transforms into the corpus luteum in response to LH; this is the luteal phase § The corpus luteum disintegrates, and ovarian steroid hormones decrease by negative feedback mechanisms © 2014 Pearson Education, Inc.

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 © 2014 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 © 2014 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 time frame © 2014 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 © 2014 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) © 2014 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 © 2014 Pearson Education, Inc.

Concept 36. 4: Fertilization, cleavage, and gastrulation initiate embryonic development § Across animal species, embryonic development involves common stages occurring in a set order § Fertilization § Cleavage § Gastrulation § Organogensis © 2014 Pearson Education, Inc.

Figure 36. 14 EMBRYONIC DEVELOPMENT Sperm Adult frog ATI ON Zygote FER TIL IZ Egg Metamorphosis CL GA STR UL NO GA OR NESIS GE Larval stages E AG V EA Tail-bud embryo © 2014 Pearson Education, Inc. Blastula AT ION Gastrula

Fertilization § Molecules and events at the egg surface play a crucial role in each step of fertilization § Sperm penetrate the protective layer around the egg § Receptors on the egg surface bind to molecules on the sperm surface § Changes at the egg surface prevent polyspermy, the entry of multiple sperm nuclei into the egg © 2014 Pearson Education, Inc.

Video: Cortical Granule Video: Calcium Release of Egg Video: Calcium Wave of Egg ©

Figure 35. 15 -1 Basal body (centriole) Sperm head Acrosome Jelly coat Spermbinding receptors

Figure 35. 15 -2 Basal body (centriole) Sperm head Acrosome Jelly coat Spermbinding receptors

Figure 35. 15 -3 Sperm nucleus Basal body (centriole) Sperm head Acrosome Jelly coat Spermbinding receptors © 2014 Pearson Education, Inc. Acrosomal process Actin filament Hydrolytic enzymes Vitelline layer Egg plasma membrane

Figure 35. 15 -4 Sperm plasma membrane Sperm nucleus Basal body (centriole) Sperm head Acrosomal process Actin filament Fused plasma membranes Acrosome Jelly coat Spermbinding receptors © 2014 Pearson Education, Inc. Hydrolytic enzymes Vitelline layer Egg plasma membrane

Figure 35. 15 -5 Sperm plasma membrane Sperm nucleus Basal body (centriole) Sperm head Acrosome Jelly coat Spermbinding receptors © 2014 Pearson Education, Inc. Acrosomal process Actin filament Cortical Fused granule plasma membranes Perivitelline Hydrolytic enzymes space Fertilization Vitelline layer envelope Egg plasma membrane

§ The events of fertilization also initiate metabolic reactions that trigger the onset of embryonic development, thus “activating” the egg § Activation leads to events such as increased protein synthesis that precede the formation of a diploid nucleus § Sperm entry triggers a release of Ca 2+, which activates the egg and triggers the cortical reaction, the slow block to polyspermy © 2014 Pearson Education, Inc.

Figure 36. 16 Seconds 1 2 3 4 6 8 10 20 30 40 50 1 Binding of sperm to egg Acrosomal reaction: plasma membrane depolarization (fast block to polyspermy) Increased intracellular calcium level Cortical reaction (slow block to polyspermy) Formation of fertilization envelope complete Minutes 2 3 4 5 Increased protein synthesis 10 20 30 40 60 90 © 2014 Pearson Education, Inc. Fusion of egg and sperm nuclei complete Onset of DNA synthesis First cell division

Cleavage and Gastrulation § Fertilization is followed by cleavage, a period of rapid cell division without growth § Cleavage partitions the cytoplasm of one large cell into many smaller cells § The blastula is a ball of cells with a fluid-filled cavity called a blastocoel § The blastula is produced after about five to seven cleavage divisions Video: Cleavage of Egg © 2014 Pearson Education, Inc.

Figure 36. 17 50 m (a) Fertilized egg © 2014 Pearson Education, Inc. (b)

§ After cleavage, the rate of cell division slows § The remaining stages of embryonic development are responsible for morphogenesis, the cellular and tissue-based processes by which the animal body takes shape © 2014 Pearson Education, Inc.

§ During gastrulation, a set of cells at or near the surface of the blastula moves to an interior location, cell layers are established, and a primitive digestive tube forms § The hollow blastula is reorganized into a two- or three-layered embryo called a gastrula © 2014 Pearson Education, Inc.

§ The cell layers produced by gastrulation are called germ layers § The ectoderm forms the outer layer and the endoderm the inner layer § In vertebrates and other animals with bilateral symmetry, a third germ layer, the mesoderm, forms between the endoderm and ectoderm © 2014 Pearson Education, Inc.

Figure 36. 18 Animal pole Blastocoel Mesenchyme cells Vegetal plate Vegetal pole Blastocoel Filopodia Archenteron Mesenchyme cells Blastopore Key Future ectoderm Future mesoderm Future endoderm 50 m Blastocoel Ectoderm Mouth Mesenchyme (mesoderm forms future skeleton) © 2014 Pearson Education, Inc. Archenteron Blastopore Digestive tube (endoderm) Anus (from blastopore)

Figure 36. 18 a-1 Animal pole Blastocoel Mesenchyme cells Vegetal plate © 2014 Pearson

Figure 36. 18 a-2 Animal pole Blastocoel Mesenchyme cells Vegetal plate Vegetal pole Future

Figure 36. 18 a-3 Animal pole Blastocoel Mesenchyme cells Vegetal plate Vegetal pole Future ectoderm Future mesoderm Future endoderm Filopodia Archenteron Blastocoel Archenteron Blastopore © 2014 Pearson Education, Inc.

Figure 36. 18 a-4 Animal pole Blastocoel Mesenchyme cells Vegetal plate Vegetal pole Future ectoderm Future mesoderm Future endoderm Filopodia Archenteron Blastocoel Ectoderm Mouth Mesenchyme (mesoderm forms future skeleton) © 2014 Pearson Education, Inc. Archenteron Blastopore Digestive tube (endoderm) Anus (from blastopore)

Figure 36. 18 b Blastocoel Filopodia Archenteron Mesenchyme cells Blastopore © 2014 Pearson Education,

§ Cell movements and interactions that form the germ layers vary among species § One distinction is whether the mouth develops at the first opening that forms in the embryo (protostomes) or the second (deuterostomes) § Sea urchins and other echinoderms are deuterostomes, as are chordates © 2014 Pearson Education, Inc.

§ Each germ layer contributes to a distinct set of structures in the adult

Figure 36. 19 ECTODERM (outer layer of embryo) • Epidermis of skin and its derivatives (including sweat glands, hair follicles) • Nervous and sensory systems • Pituitary gland, adrenal medulla • Jaws and teeth • Germ cells MESODERM (middle layer of embryo) • Skeletal and muscular systems • Circulatory and lymphatic systems • Excretory and reproductive systems (except germ cells) • Dermis of skin • Adrenal cortex ENDODERM (inner layer of embryo) • Epithelial lining of digestive tract and associated organs (liver, pancreas) • Epithelial lining of respiratory, excretory, and reproductive tracts and ducts • Thymus, thyroid, and parathyroid glands © 2014 Pearson Education, Inc.

Human Conception, Embryonic Development, and Birth § Conception, fertilization of an egg by a sperm, occurs in the oviduct § The resulting zygote begins cleavage about 24 hours after fertilization and produces a blastocyst after 4 more days § A few days later, the embryo implants into the endometrium of the uterus © 2014 Pearson Education, Inc.

§ The condition of carrying one or more embryos in the uterus is called gestation, or pregnancy § Human pregnancy averages 38 weeks from fertilization § Gestation varies among mammals, from 21 days in many rodents to more than 600 days in elephants § Human gestation is divided into three trimesters of about three months each © 2014 Pearson Education, Inc.

Figure 36. 20 3 Cleavage 4 Cleavage continues. Ovary 2 Fertilization Uterus 1 Ovulation 5 Implantation Endometrium (a) From ovulation to implantation Endometrium Cavity Inner cell mass Blastocyst (b) Implantation of blastocyst © 2014 Pearson Education, Inc. Trophoblast

§ During the first trimester, the embryo secretes hormones that signal its presence and regulate the mother’s reproductive system § Human chorionic gonadotropin (h. CG) acts to maintain secretion of progesterone and estrogens by the corpus luteum through the first few months of pregnancy © 2014 Pearson Education, Inc.

§ How are identical twins formed? § How are fraternal twins formed? § What

§ 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 § Materials diffuse between maternal and embryonic circulation to supply the embryo with nutrients, immune protection, and metabolic waste disposal © 2014 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 Video: Ultrasound of Fetus © 2014 Pearson Education, Inc.

Figure 36. 21 (a) 5 weeks © 2014 Pearson Education, Inc. (b) 14 weeks

§ Childbirth begins with labor, a series of strong, rhythmic contractions that push the fetus and placenta out of the body § Which hormone is responsible in this process? § Is this positive or negative feedback? § Once labor begins, local regulators, prostaglandins and hormones, induce and regulate further contractions of the uterus © 2014 Pearson Education, Inc.

§ Lactation, the production of milk, is an aspect of maternal care unique to mammals § Suckling stimulates the release of prolactin, which in turn stimulates mammary glands to produce milk, and the secretion of oxytocin, which triggers milk release from the glands § What type of feedback is this? © 2014 Pearson Education, Inc.

Contraception § Contraception, the deliberate prevention of pregnancy, can be achieved in a number of ways § Contraceptive methods fall into three categories § Preventing development or release of eggs and sperm § Keeping sperm and egg apart § Preventing implantation of an embryo © 2014 Pearson Education, Inc.

Figure 36. 22 Male Method Female Event Method Production of sperm primary oocytes Vasectomy Sperm transport Oocyte down male development duct system and ovulation Abstinence Condom Coitus interruptus (very high failure rate) Combination birth control pill (or injection, patch, or vaginal ring) Abstinence Female condom 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; progestin alone (as minipill or injection) Meeting of sperm and oocyte in oviduct Union of sperm and egg Implantation of blastocyst in endometrium © 2014 Pearson Education, Inc. Morning-after pill; intrauterine device (IUD)

Figure 36. 22 a Male Method Female Event Production of sperm primary oocytes Vasectomy Abstinence Condom Coitus interruptus (very high failure rate) Oocyte Sperm transport development down male duct system and ovulation Method Combination birth control pill (or injection, patch, or vaginal ring) Abstinence Female condom Sperm deposited in vagina Capture of the oocyte by the oviduct Tubal ligation © 2014 Pearson Education, Inc. Spermicides; diaphragm; progestin alone (as minipill or injection)

Figure 36. 22 b Male Method Female Event Sperm movement through female reproductive tract Event Transport of oocyte in oviduct Method Meeting of sperm and oocyte in oviduct Union of sperm and egg Implantation of blastocyst in endometrium © 2014 Pearson Education, Inc. Morning-after pill; intrauterine device (IUD)

§ The rhythm method, or natural family planning, is temporary abstinence 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 © 2014 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% © 2014 Pearson Education, Inc.

Infertility and In Vitro Fertilization § Infertility, the inability to conceive offspring, affects about one in ten couples in the United States and worldwide § The causes are varied and equally likely to affect men and women § Sexually transmitted diseases (STDs) are the most significant preventable causes of infertility © 2014 Pearson Education, Inc.

§ Some forms of infertility are treatable § Hormone therapy can sometimes increase sperm or egg production § In vitro fertilization (IVF) mixes oocytes with sperm in culture dishes and returns the embryo to the uterus at the eight-cell stage § Sperm may be injected directly into an oocyte as well © 2014 Pearson Education, Inc.