Reproduction and Embryonic Development Chapter 27 Reproduction and Embryonic Development

Baby Bonanza The increased use of fertility drugs Baby Bonanza The increased use of fertility drugs Has caused an increase in the number of multiple births in the United States

Fertility drugs Are sometimes too effective

ASEXUAL AND SEXUAL REPRODUCTION 27.1 Sexual and asexual reproduction are both common among animals In asexual reproduction One parent produces genetically identical offspring

Asexual reproduction Enables an individual to produce many offspring rapidly

Reproduction in some animals is accomplished through external fertilization In which the parents release their gametes into the environment where fertilization occurs Eggs Figure 27.1E

Sexual reproduction May enhance reproductive success in changing environments

27.2 Reproductive anatomy of the human female HUMAN REPRODUCTION 27.2 Reproductive anatomy of the human female Both sexes in humans Have a set of gonads where gametes are produced Have ducts for delivery of the gonads and structures for copulation

Contain follicles that nurture eggs and produce sex hormones A woman’s ovaries Contain follicles that nurture eggs and produce sex hormones Oviduct Ovaries Follicles Corpus luteum Wall of uterus Uterus Endometrium (lining of uterus) Cervix (“neck” of uterus) Vagina Figure 27.2A

Oviducts convey eggs to the uterus Where the eggs develop Oviducts convey eggs to the uterus Where the eggs develop Egg cell Ovary LM 200 Figure 27.2B

The uterus opens into the vagina Which receives the penis during intercourse and forms the birth canal

Other structures of the female reproductive system include Other structures of the female reproductive system include Labia, the clitoris, Bartholin’s glands, and the cervix Oviduct Ovary Uterus Urinary bladder (excretory system) Pubic bone Urethra (excretory system) Shaft Glans Prepuce Clitoris Labia minora Labia majora Vaginal opening Anus (digestive system) Bartholin’s gland Vagina Cervix Rectum Figure 27.2C

27.3 Reproductive anatomy of the human male 27.3 Reproductive anatomy of the human male A man’s testes Produce sperm Rectum (digestive system) Seminal vesicle Vas deferens Ejaculatory duct Prostate gland Bulbourethral gland Epididymis Testis Scrotum Urinary bladder (excretory system) Pubic bone Erectile tissue of penis Urethra Glans of penis Prepuce Penis Figure 27.3A

Contribute to the formation of fluid that nourishes and protects sperm Several glands Contribute to the formation of fluid that nourishes and protects sperm Urinary bladder (excretory system) Prostate gland Bulbourethral gland Erectile tissue of penis Vas deferens Epididymis Testis Seminal vesicle (behind bladder) Urethra Scrotum Glans of penis Figure 27.3B

During ejaculation Sperm and the nourishing fluid, called semen, are expelled through the penis Sphincter contracts Urinary bladder Urethra region here expands and fills with semen Contractions of vas deferens of prostate gland of seminal vesicle of epididymis First stage Sphincter remains contracted of muscles around base of penis relaxes Contractions of urethra Second stage Semen expelled Figure 27.3C

A negative feedback system of hormones Controls sperm production A negative feedback system of hormones Controls sperm production Stimuli from other areas in the brain Hypothalamus Releasing hormone Anterior pituitary Negative feedback FSH LH Androgen production Sperm production Testis Figure 27.3D

Developing sperm cells (haploid; single chromatids) Primary spermatocytes, which are diploid, are made continuously in the testes And undergo meiosis to produce haploid sperm Primary spermatocyte Differentiation and onset of Meiosis I Meiosis I completed Meiosis II Differentiation (in prophase of Meiosis I) Secondary spermatocyte (haploid; double chromatids) Developing sperm cells (haploid; single chromatids) Sperm cells (haploid) Center of seminiferous tubule n 2n Testis Scrotum Penis Epididymis Seminiferous tubule Cross section of seminiferous tubule Diploid cell Figure 27.4A

Each month one primary oocyte Each month one primary oocyte Matures to form a secondary oocyte, which can be fertilized Completes meiosis and becomes a haploid ovum Diploid cell In embryo 2n Differentiation and onset of Meiosis I Primary oocyte (arrested in prophase of Meiosis I) Present at birth Completion of Meiosis I and onset of Meiosis II Secondary oocyte (arrested at meta- phase of Meiosis II; released from ovary) n Entry of sperm triggers completion of Meiosis II Ovum (haploid) Second polar body First polar body Figure 27.4B

The development of an ovarian follicle The development of an ovarian follicle Involves many different processes Corpus luteum Degenerating corpus luteum Start: Primary oocyte within follicle Growing follicles Mature follicle Ovary Ruptured follicle Ovulation Secondary oocyte Figure 27.4C

27.5 Hormones synchronize cyclic changes in the ovary and uterus 27.5 Hormones synchronize cyclic changes in the ovary and uterus The ovarian cycle includes Changes in the ovary that occur about every 28 days The menstrual cycle Involves changes that occur in the uterus

An Overview of the Ovarian and Menstrual Cycles An Overview of the Ovarian and Menstrual Cycles Events in the menstrual cycle Are synchronized with the ovarian cycle, which occurs about every 28 days

Uterine bleeding, called menstruation Includes the breakdown of the endometrial lining Usually persists for 3–5 days After menstruation The endometrium, the lining of the uterus, regrows

Synchronize the events in the ovarian cycle Five hormones Synchronize the events in the ovarian cycle Table 27.5

Hormonal Events Before Ovulation Hormonal Events Before Ovulation Approximately every 28 days The hypothalamus signals the anterior pituitary to secrete FSH and LH FSH and LH Trigger the growth of a follicle

As the follicle grows, it secretes estrogen Which causes a burst in FSH and LH levels, leading to ovulation

Hormonal Events at Ovulation and After Hormonal Events at Ovulation and After After ovulation The follicle becomes the corpus luteum The corpus luteum secretes both estrogen and progesterone Which exert negative feedback on the hypothalamus and pituitary, causing a decline in FSH and LH levels

As FSH and LH levels drop The hypothalamus can once again stimulate the pituitary to secrete more FSH and LH, and a new cycle begins

Control of the Menstrual Cycle Control of the Menstrual Cycle The menstrual cycle Is directly controlled by estrogen and progesterone

If fertilization of an egg occurs A hormone from the embryo maintains the uterine lining and prevents menstruation

The ovarian and menstrual cycles Control by hypothalamus Inhibited by combination of estrogen and progesterone Stimulated by high levels of estrogen Hypothalamus Releasing hormone Anterior pituitary 1 FSH LH B Pituitary hormones in blood 4 LH peak triggers ovulation and corpus luteum formation 6 LH FSH 2 FSH LH C Ovarian cycle 5 Corpus luteum Degenerating corpus luteum Growing follicle Mature follicle Ovulation Pre-ovulatory phase Post-ovulatory phase Estrogen Progesterone and estrogen D Ovarian hormones in blood 3 7 Estrogen 8 Progesterone Estrogen Progesterone and estrogen E Menstrual cycle Endometrium 5 10 14 15 20 25 28 Days Figure 27.5 Menstruation

27.6 The human sexual response occurs in four phases 27.6 The human sexual response occurs in four phases The excitement phase Prepares the sexual organs for coitus The plateau phase Is marked by increases in breathing and heart rate

Orgasm follows Characterized by rhythmic contractions of the reproductive structures The resolution phase Completes the cycle and reverses the previous responses

27.7 Sexual activity can transmit disease CONNECTION 27.7 Sexual activity can transmit disease Sexual intercourse Carries the risk of exposure to sexually transmitted diseases (STDs)

STDs common in the United States STDs common in the United States Table 27.7

27.8 Contraception can prevent unwanted pregnancy CONNECTION 27.8 Contraception can prevent unwanted pregnancy Contraception Is the deliberate prevention of pregnancy Table 27.8

Contraception can be accomplished Through various methods Contraception can be accomplished Through various methods Skin patch Diaphragm Spermicide Condom Birth control pills Figure 27.8

PRINCIPLES OF EMBRYONIC DEVELOPMENT 27.9 Fertilization results in a zygote and triggers embryonic development Embryonic development begins with fertilization The union of sperm and egg to form a diploid zygote

The Properties of Sperm Cells The Properties of Sperm Cells Only one sperm Fertilizes an egg Colorized SEM 500 Figure 27.9A

A sperm releases enzymes from the acrosome that pierce the egg’s coat During fertilization A sperm releases enzymes from the acrosome that pierce the egg’s coat Plasma membrane Middle piece Head Neck Mitochondrion (spiral shape) Nucleus Acrosome Tail Figure 27.9B

The Process of Fertilization The Process of Fertilization Sperm surface proteins bind to egg receptor proteins Sperm and egg plasma membranes fuse, and the two nuclei unite

Changes in the egg membrane Prevent entry of additional sperm The fertilized egg (zygote) Develops into an embryo

The process of fertilization The sperm approaches the egg 1 The sperm’s acrosomal enzymes digest the egg’s jelly coat 2 Proteins on the sperm head bind to egg receptors 3 Sperm The plasma membranes of sperm and egg fuse 4 Nucleus Sperm head The sperm nucleus enters the egg cytoplasm 5 Acrosome Plasma membrane Acrosomal enzymes A fertilization envelope forms 6 Receptor protein molecules Plasma membrane Sperm nucleus Vitelline layer Cytoplasm Egg nucleus Jelly coat The nuclei of sperm and egg fuse 7 Egg cell Zygote nucleus Figure 27.9C

27.10 Cleavage produces a ball of cells from the zygote 27.10 Cleavage produces a ball of cells from the zygote Cleavage is a rapid series of cell divisions That results in a blastula, a ball of cells Zygote 2 cells 4 cells 8 cells Many cells (solid ball) Blastula (hollow ball) Cross section of blastula Blastocoel Figure 27.10

27.13 Changes in cell shape, cell migration, and programmed cell death give form to the developing animal Cells of the ectoderm Fold inward during neural tube formation Ectoderm Figure 27.13A

Programmed cell death, or apoptosis Programmed cell death, or apoptosis Is a key developmental process in which cells die Apoptosis Dead cell engulfed and digested by adjacent cell Figure 27.13B

27.14 Embryonic induction initiates organ formation 27.14 Embryonic induction initiates organ formation In a process called induction Adjacent cells and cell layers influence each other’s differentiation via chemical signals

Induction during eye development Future brain Optic vesicle Lens ectoderm Optic stalk Optic cup Cornea Lens Future retina Figure 27.14 1 2 3 4

27.15 Pattern formation organizes the animal body 27.15 Pattern formation organizes the animal body Pattern formation Is the emergence of the parts of a structure in their correct relative positions

HUMAN DEVELOPMENT 27.16 The embryo and placenta take shape during the first month of pregnancy Pregnancy, or gestation Is the carrying of developing young within the female reproductive tract

An Overview of Developmental Events An Overview of Developmental Events Human development Begins with fertilization in the oviduct Cleavage starts Fertilization of ovum Oviduct Secondary oocyte Ovulation Ovary Blastocyst (implanted) Endometrium Uterus Figure 27.16A

Cleavage produces a blastocyst Cleavage produces a blastocyst Whose inner cell mass becomes the embryo Endometrium Inner cell mass Cavity Trophoblast Figure 27.16B

The blastocyst’s outer layer, the trophoblast Endometrium Future embryo Future yolk sac Blood vessel (maternal) Multiplying cells of trophoblast Trophoblast Uterine cavity Figure 27.16C The blastocyst’s outer layer, the trophoblast Implants in the uterine wall

Meanwhile, the four extraembryonic membranes develop Meanwhile, the four extraembryonic membranes develop The amnion, the chorion, the yolk sac, and the allantois Amniotic cavity Amnion Mesoderm cells Chorion Yolk sac Allantois Chorionic villi Embryo: Ectoderm Mesoderm Endoderm Figure 27.16D, E

Roles of the Extraembryonic Membranes Roles of the Extraembryonic Membranes About a month after conception The extraembryonic membranes are fully formed Mother’s blood vessels Allantois Yolk sac Placenta Amniotic cavity Amnion Embryo Chorion Chorionic villi Figure 27.16F

The embryo floats in a fluid-filled amniotic cavity Surrounded by the amnion The chorion and mesoderm cells from the yolk sac Form the embryo’s part of the placenta

The allantois Forms part of the umbilical cord

The Placenta The placenta’s chorionic villi The Placenta The placenta’s chorionic villi Absorb food and oxygen from the mother’s blood to nourish the embryo

27.17 Human development from conception to birth is divided into three trimesters Human development is divided into three trimesters Each about three months in length

The First Trimester The most rapid changes The First Trimester The most rapid changes Occur during the first trimester Figure 27.17A

The embryo is called a fetus By 9 weeks The embryo is called a fetus Figure 27.17B

Second Trimester The second trimester Second Trimester The second trimester Involves an increase in size and general refinement of the human features Figure 27.17C

The fetus is about 19 centimeters long, and weighs half a kilogram At 20 weeks The fetus is about 19 centimeters long, and weighs half a kilogram Figure 27.17D

Third Trimester The third trimester Third Trimester The third trimester Is a time of rapid growth, which ends in birth Figure 27.17E

27.18 Childbirth is hormonally induced and occurs in three stages 27.18 Childbirth is hormonally induced and occurs in three stages The birth of a child Is brought about by a series of strong, rhythmic contractions of the uterus, called labor

Estrogen makes the uterus more sensitive to oxytocin Estrogen makes the uterus more sensitive to oxytocin Which acts with prostaglandins to initiate labor Estrogen Oxytocin from ovaries from fetus and pituitary Induces oxytocin receptors on uterus Stimulates uterus to contract Stimulates placenta to make Prostaglandins Stimulate more contractions of uterus Positive feedback Figure 27.18A

Labor occurs in three stages Dilation, expulsion, and delivery of the placenta Placenta Umbilical cord Uterus Cervix Placenta (detaching) Figure 27.18B Dilation of the cervix 1 Expulsion: delivery of the infant 2 Delivery of the placenta 3

27.19 Reproductive technology increases our reproductive options CONNECTION 27.19 Reproductive technology increases our reproductive options New techniques Can provide help to infertile couples Figure 27.19

Some of these methods Raise important ethical and legal questions