Chapter 27 Reproduction and Embryonic Development 0 0

Chapter 27 Reproduction and Embryonic Development 0

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

0 a. Fertility drugs a. Are sometimes too effective

ASEXUAL AND SEXUAL REPRODUCTION 27. 1 Sexual and asexual reproduction are both common among animals a. In asexual reproduction o One parent produces genetically identical offspring 0

0 a. Modes of asexual reproduction include a. Budding, fission, or fragmentation/regeneration LM 25 Figure 27. 1 A, B

0 a. Asexual reproduction a. Enables an individual to produce many offspring rapidly

0 a. Sexual reproduction involves the fusion of gametes from two parents a. Resulting in genetic variation among offspring “Head” Intestine Ovary Eggs LM 210 Figure 27. 1 C

0 a. Some animals exhibit hermaphroditism a. In which each individual has both female and male reproductive systems Figure 27. 1 D

0 a. Reproduction in some animals is accomplished through external fertilization a. In which the parents release their gametes into the environment where fertilization occurs Eggs Figure 27. 1 E

0 a. Sexual reproduction a. May enhance reproductive success in changing environments

HUMAN REPRODUCTION 0 27. 2 Reproductive anatomy of the human female a. Both sexes in humans o Have a set of gonads where gametes are produced o Have ducts for delivery of the gonads and structures for copulation

0 a. A woman’s ovaries a. Contain follicles that nurture eggs and produce sex hormones Ovaries Oviduct Follicles Corpus luteum Wall of uterus Uterus Endometrium (lining of uterus) Cervix (“neck” of uterus) Vagina Figure 27. 2 A

0 a. Oviducts convey eggs to the uterus a. Where the eggs develop Egg cell Ovary LM 200 Figure 27. 2 B

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

0 a. Other structures of the female reproductive system include a. Labia, the clitoris, Bartholin’s glands, and the cervix Oviduct Ovary Uterus Rectum (digestive system) Urinary bladder (excretory system) Pubic bone Cervix Urethra (excretory system) Vagina Shaft Glans Bartholin’s gland Prepuce Labia minora Anus (digestive system) Labia majora Vaginal opening Figure 27. 2 C Clitoris

0 27. 3 Reproductive anatomy of the human male a. A man’s testes o Produce sperm Rectum (digestive system) Urinary bladder (excretory system) Seminal vesicle Vas deferens Ejaculatory duct Pubic bone Erectile tissue of penis Prostate gland Bulbourethral gland Figure 27. 3 A Vas deferens Urethra (excretory system) Epididymis Glans of penis Testis Scrotum Prepuce Penis

0 a. Several glands a. Contribute to the formation of fluid that nourishes and protects sperm Urinary bladder (excretory system) Seminal vesicle (behind bladder) Prostate gland Bulbourethral gland Erectile tissue of penis Urethra Vas deferens Scrotum Epididymis Testis Figure 27. 3 B Glans of penis

0 a. During ejaculation a. Sperm and the nourishing fluid, called semen, are expelled through the penis Contractions of vas deferens Sphincter contracts Urinary bladder Urethra region here expands and fills with semen Contractions of seminal vesicle Contractions of prostate gland Sphincter contracts Contractions of epididymis First stage Sphincter remains contracted Semen expelled Contractions of muscles around base of penis Sphincter relaxes Figure 27. 3 C Second stage Contractions of urethra

0 a. A negative feedback system of hormones a. Controls sperm production Stimuli from other areas in the brain Hypothalamus Releasing hormone Anterior pituitary Negative feedback FSH Testis LH Androgen production Sperm production Figure 27. 3 D

0 27. 4 The formation of sperm and ova requires meiosis a. Spermatogenesis, the formation of sperm cells o Takes about 65– 75 days in the human male

0 a. Primary spermatocytes, which are diploid, are made continuously in the testes a. And undergo meiosis to produce haploid sperm Epididymis Testis Scrotum 2 n Diploid cell Differentiation and onset of Meiosis I 2 n Primary spermatocyte (in prophase of Meiosis I) Penis Testis Seminiferous tubule Cross section of seminiferous tubule Meiosis I completed n Secondary spermatocyte n (haploid; double chromatids) Meiosis II n n Developing sperm cells (haploid; single chromatids) Differentiation n Figure 27. 4 A n n n Sperm cells (haploid) Center of seminiferous tubule

0 a. Each month one primary oocyte a. Matures to form a secondary oocyte, which can be fertilized b. Completes meiosis and becomes a haploid ovum Diploid cell In embryo 2 n Differentiation and onset of Meiosis I Primary oocyte (arrested in prophase of Meiosis I) 2 n Present at birth Completion of Meiosis I and onset of Meiosis II Secondary oocyte n (arrested at metaphase of Meiosis II; released from ovary) n First polar body Entry of sperm triggers completion of Meiosis II Ovum (haploid) Figure 27. 4 B n Second n polar body

0 a. The development of an ovarian follicle a. Involves many different processes Degenerating corpus luteum Start: Corpus luteum Primary oocyte within follicle Growing follicles Mature follicle Ovary Secondary oocyte Ovulation Figure 27. 4 C Ruptured follicle

0 27. 5 Hormones synchronize cyclic changes in the ovary and uterus a. The ovarian cycle includes o Changes in the ovary that occur about every 28 days • The menstrual cycle o Involves changes that occur in the uterus

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

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

0 a. Five hormones a. Synchronize the events in the ovarian cycle Table 27. 5

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

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

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

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

0 Control of the Menstrual Cycle a. The menstrual cycle o Is directly controlled by estrogen and progesterone

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

a. The ovarian and menstrual cycles A Control by hypothalamus Inhibited by combination of estrogen and progesterone Stimulated by high levels Releasing hormoneof estrogen Hypothalamus Anterior pituitary FSH 1 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 Degenerating luteum corpus luteum Mature Ovulation follicle Pre-ovulatory phase Post-ovulatory phase Growing follicle Progesterone and estrogen Estrogen D Ovarian hormones in blood 3 7 8 Estrogen Progesterone and estrogen E Menstrual cycle Endometrium 0 Figure 27. 5 5 Menstruation 10 14 15 Days 20 25 28

0 27. 6 The human sexual response occurs in four phases a. The excitement phase o Prepares the sexual organs for coitus • The plateau phase o Is marked by increases in breathing and heart rate

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

CONNECTION 27. 7 Sexual activity can transmit disease a. Sexual intercourse o Carries the risk of exposure to sexually transmitted diseases (STDs) 0

0 a. STDs common in the United States Table 27. 7

CONNECTION 27. 8 Contraception can prevent unwanted pregnancy a. Contraception o Is Table 27. 8 the deliberate prevention of pregnancy 0

0 a. Contraception can be accomplished a. Through various methods Skin patch Condom Diaphragm Spermicide Birth control pills Figure 27. 8

PRINCIPLES OF EMBRYONIC DEVELOPMENT 0 27. 9 Fertilization results in a zygote and triggers embryonic development a. Embryonic development begins with fertilization o The union of sperm and egg to form a diploid zygote

0 The Properties of Sperm Cells a. Only one sperm o Fertilizes an egg Colorized SEM 500 Figure 27. 9 A

0 a. During fertilization a. A sperm releases enzymes from the acrosome that pierce the egg’s coat Plasma membrane Middle piece Neck Head Tail Mitochondrion (spiral shape) Nucleus Acrosome Figure 27. 9 B

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

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

a. The process of fertilization 1 The sperm approaches the egg Sperm 2 The sperm’s acrosomal enzymes digest the egg’s jelly 3 Proteins on the sperm head bind to coat egg receptors 4 The plasma membranes of sperm and egg fuse Nucleus Sperm head Acrosome Plasma membrane 5 The sperm nucleus enters the egg cytoplasm Acrosomal enzymes 6 A fertilization envelope forms Receptor protein molecules Plasma membrane Vitelline layer Egg nucleus Jelly coat Egg cell Figure 27. 9 C Cytoplasm Sperm nucleus 7 The nuclei of sperm and egg fuse Zygote nucleus

0 27. 10 Cleavage produces a ball of cells from the zygote a. Cleavage is a rapid series of cell divisions o That results in a blastula, a ball of cells Zygote 2 cells 4 cells 8 cells Blastocoel Many cells (solid ball) Figure 27. 10 Blastula Cross section (hollow ball) of blastula

0 27. 11 Gastrulation produces a three-layered embryo a. In gastrulation o Cells migrate inward and form a rudimentary digestive cavity • The resulting gastrula o Has three layers of cells

a. Development of the frog gastrula Animal pole 1 Blastocoel The blastula 1 Blastula Vegetal pole 2 Blastopore formation Gastrulation 2 Blastopore forming 3 Blastocoel shrinking Cell migration to form layers Archenteron 3 Archenteron 4 Completion of gastrulation Ectoderm Mesoderm Endoderm 4 Yolk plug Figure 27. 11 Yolk plug Gastrula

0 27. 12 Organs start to form after gastrulation Neural a. After gastrulation fold three embryonic tissue layers give rise to specific organ systems Neural plate o The Notochord Ectoderm Mesoderm Endoderm Archenteron Neural folds Figure 27. 12 A 15

0 a. A structure known as the neural plate a. Forms the neural tube, which will become the spinal cord Neural fold Neural plate Outer layer of ectoderm Neural tube Figure 27. 12 B

0 a. After neural tube formation a. The somites and the coelom form Neural tube Notochord Somite Coelom Archenteron (digestive cavity) Somites Tail bud Eye SEM 15 Figure 27. 12 C

0 a. During one stage of frog development, a tadpole forms a. Which eventually develops into an adult frog Figure 27. 12 D

0 a. The three embryonic tissue layers a. Develop into a number of different organs and tissues in an adult Table 27. 12

0 27. 13 Changes in cell shape, cell migration, and programmed cell death give form to the developing animal a. Cells of the ectoderm Ectoderm o Fold inward during neural tube formation Figure 27. 13 A

0 a. Programmed cell death, or apoptosis a. Is a key developmental process in which cells die Apoptosis Dead cell engulfed and digested by adjacent cell Figure 27. 13 B

0 27. 14 Embryonic induction initiates organ formation a. In a process called induction o Adjacent cells and cell layers influence each other’s differentiation via chemical signals

a. Induction during eye development Lens ectoderm Optic cup Cornea Future brain 1 Figure 27. 14 Lens Optic vesicle Optic stalk Future retina 2 3 4

0 27. 15 Pattern formation organizes the animal body a. Pattern formation o Is the emergence of the parts of a structure in their correct relative positions

0 a. Involves the response of genes to spatial variations of chemicals in the embryo Anterior Bird embryo Ventral Limb bud develops Distal Dorsal Proximal Posterior Figure 27. 15 A Normal wing

0 a. Experimental evidence has revealed a. That vertebrate limbs have zones of cells that provide positional information to other cells Donor limb bud Graft of cells from patternforming zone Donor cells Figure 27. 15 B Host limb bud Graft Host limb bud develops Host patternforming zone Wing with duplication

HUMAN DEVELOPMENT 0 27. 16 The embryo and placenta take shape during the first month of pregnancy a. Pregnancy, or gestation o Is the carrying of developing young within the female reproductive tract

0 An Overview of Developmental Events a. Human development o Begins with fertilization in the oviduct Cleavage starts Fertilization of ovum Ovary Oviduct Secondary oocyte Ovulation Blastocyst (implanted) Endometrium Uterus Figure 27. 16 A

0 a. Cleavage produces a blastocyst a. Whose inner cell mass becomes the embryo Endometrium Inner cell mass Cavity Trophoblast Figure 27. 16 B

0 a. The blastocyst’s outer layer, the trophoblast a. Implants in the uterine wall Endometrium Blood vessel (maternal) Future embryo Multiplying cells of trophoblast Future yolk sac Trophoblast Uterine cavity Figure 27. 16 C

0 a. Meanwhile, the four extraembryonic membranes develop a. The amnion, the chorion, the yolk sac, and the allantois Amniotic cavity Amnion Chorionic villi Amnion Embryo: Ectoderm Mesoderm Endoderm Allantois Mesoderm cells Chorion Yolk sac Figure 27. 16 D, E Yolk sac

0 Roles of the Extraembryonic Membranes a. About a month after conception o The extraembryonic membranes are fully formed Placenta Mother’s blood vessels Allantois Yolk sac Amniotic cavity Amnion Embryo Chorionic villi Figure 27. 16 F

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

0 a. The allantois a. Forms part of the umbilical cord

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

0 27. 17 Human development from conception to birth is divided into three trimesters a. Human development is divided into three trimesters o Each about three months in length

0 The First Trimester a. The most rapid changes o Occur Figure 27. 17 A during the first trimester

0 a. By 9 weeks a. The embryo is called a fetus Figure 27. 17 B

0 Second Trimester a. The second trimester o Involves an increase in size and general refinement of the human features Figure 27. 17 C

0 a. At 20 weeks a. The fetus is about 19 centimeters long, and weighs half a kilogram Figure 27. 17 D

0 Third Trimester a. The third trimester o Is Figure 27. 17 E a time of rapid growth, which ends in birth

0 27. 18 Childbirth is hormonally induced and occurs in three stages a. The birth of a child o Is brought about by a series of strong, rhythmic contractions of the uterus, called labor

0 a. Estrogen makes the uterus more sensitive to oxytocin a. Which acts with prostaglandins to initiate labor Estrogen from ovaries Oxytocin from fetus and pituitary Induces oxytocin receptors on uterus Stimulates uterus Positive feedback to contract Stimulates placenta to make Prostaglandins Stimulate more contractions of uterus Figure 27. 18 A

a. Labor occurs in three stages a. Dilation, expulsion, and delivery of the placenta Placenta Umbilical cord Uterus Cervix 1 Dilation of the cervix 2 Expulsion: delivery of the infant Uterus Placenta (detaching) Umbilical cord Figure 27. 18 B 3 Delivery of the placenta

CONNECTION 27. 19 Reproductive technology increases our reproductive options a. New techniques o Can Figure 27. 19 provide help to infertile couples 0

0 a. Some of these methods a. Raise important ethical and legal questions