chapter 27 reproduction and embryonic development
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0. Chapter 27 Reproduction and Embryonic Development. 0. Baby Bonanza The increased use of fertility drugs Has caused an increase in the number of multiple births in the United States. 0. Fertility drugs Are sometimes too effective. ASEXUAL AND SEXUAL REPRODUCTION. 0. - PowerPoint PPT PresentationTRANSCRIPT
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Chapter 27
Reproduction and Embryonic Development
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Baby Bonanza
• The increased use of fertility drugs
– Has caused an increase in the number of multiple births in the United States
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• Fertility drugs
– Are sometimes too effective
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
ASEXUAL AND SEXUAL REPRODUCTION
27.1 Sexual and asexual reproduction are both common among animals
• In asexual reproduction
– One parent produces genetically identical offspring
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• Asexual reproduction
– Enables an individual to produce many offspring rapidly
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• 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
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• Sexual reproduction
– May enhance reproductive success in changing environments
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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
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• A woman’s ovaries
– Contain follicles that nurture eggs and produce sex hormones
OviductOvaries
Follicles
Corpus luteumWall of uterus Uterus
Endometrium(lining of uterus)
Cervix(“neck” of uterus)
Vagina
Figure 27.2A
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• Oviducts convey eggs to the uterus
– Where the eggs develop
Eggcell
Ovary
LM
20
0
Figure 27.2B
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• The uterus opens into the vagina
– Which receives the penis during intercourse and forms the birth canal
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• 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)
ShaftGlans
Prepuce
Clitoris
Labia minora
Labia majora
Vaginal opening
Anus(digestive system)
Bartholin’s gland
Vagina
Cervix
Rectum(digestive system)
Figure 27.2C
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27.3 Reproductive anatomy of the human male
• A man’s testes
– Produce sperm
Rectum(digestive system)
Seminal vesicle
Vas deferens
Ejaculatoryduct
Prostate gland
Bulbourethral gland
Vas deferens
Epididymis
TestisScrotum
Urinary bladder(excretorysystem)
Pubic bone
Erectiletissue ofpenis
Urethra(excretorysystem)
Glans of penis
Prepuce
Penis
Figure 27.3A
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• Several glands
– Contribute to the formation of fluid that nourishes and protects sperm
Urinary bladder(excretorysystem)
Prostate gland
Bulbourethralgland
Erectile tissueof penis
Vas deferens
Epididymis
Testis
Seminalvesicle(behindbladder)
Urethra
Scrotum
Glans ofpenis
Figure 27.3B
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• During ejaculation
– Sperm and the nourishing fluid, called semen, are expelled through the penis
Sphinctercontracts
Urinarybladder
Urethra region hereexpands and fillswith semen
Contractionsof vas deferens
Contractionsof prostategland
Contractionsof seminalvesicle
Sphinctercontracts
Contractionsof epididymis
First stage
Sphincter remainscontracted
Contractionsof musclesaround baseof penis
Sphincterrelaxes
Contractions of urethra
Second stage
Semen expelled
Figure 27.3C
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• A negative feedback system of hormones
– Controls sperm productionStimuli from other areas in the brain
Hypothalamus
Releasing hormone Anterior
pituitary
Neg
ativ
e fe
edba
ck
FSH LH
Androgenproduction
Sperm production
Testis
Figure 27.3D
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• Primary spermatocytes, which are diploid, are made continuously in the testes
– And undergo meiosis to produce haploid sperm
Primary spermatocyte
Differentiation andonset 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 ofseminiferous tubule
n n n n
n n n n
n n
2n
2n
TestisScrotum
Penis
Epididymis
TestisSeminiferous tubule
Cross section ofseminiferoustubule
Diploid cell
Figure 27.4A
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• 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 embryo2n
Differentiation andonset of Meiosis I
Primary oocyte
(arrested in prophaseof Meiosis I)
2n Present at birth
Completion of Meiosis Iand onset of Meiosis II
Secondary oocyte
(arrested at meta-phase of Meiosis II;
released from ovary)
n n
Entry of sperm triggerscompletion of Meiosis II
Ovum
(haploid) n nSecondpolar body
Firstpolar body
Figure 27.4B
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• The development of an ovarian follicle
– Involves many different processes
Corpus luteum
Degeneratingcorpus luteum
Start: Primary oocyte
within follicle
Growingfollicles
Mature follicle
Ovary
Ruptured follicleOvulation
Secondaryoocyte
Figure 27.4C
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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
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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
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• 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
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• Five hormones
– Synchronize the events in the ovarian cycle
Table 27.5
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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
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• As the follicle grows, it secretes estrogen
– Which causes a burst in FSH and LH levels, leading to ovulation
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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
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• 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
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Control of the Menstrual Cycle
• The menstrual cycle
– Is directly controlled by estrogen and progesterone
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• If fertilization of an egg occurs
– A hormone from the embryo maintains the uterine lining and prevents menstruation
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• The ovarian and menstrual cycles
A
B
Control by hypothalamus
Hypothalamus
Releasing hormone
Anterior pituitary
Inhibited by combination ofestrogen and progesteroneStimulated by high levelsof estrogen
FSH LH
Pituitary hormonesin blood
LH
FSH
FSH LH
LH peak triggersovulation andcorpus luteumformation
Ovarian cycle
Growing follicle
Pre-ovulatory phase
Maturefollicle
Ovulation
Corpusluteum
Post-ovulatory phase
Degeneratingcorpus luteum
Estrogen Progesterone and estrogen
Ovarian hormonesin blood
Estrogen
Progesterone
EstrogenProgesterone and estrogen
C
D
E Menstrual cycle
Endometrium
0 5 10 14 15 20 25 28Days
MenstruationFigure 27.5
1
4
6
2
5
3
78
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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
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• Orgasm follows
– Characterized by rhythmic contractions of the reproductive structures
• The resolution phase
– Completes the cycle and reverses the previous responses
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CONNECTION
27.7 Sexual activity can transmit disease
• Sexual intercourse
– Carries the risk of exposure to sexually transmitted diseases (STDs)
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• STDs common in the United States
Table 27.7
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CONNECTION
27.8 Contraception can prevent unwanted pregnancy
• Contraception
– Is the deliberate prevention of pregnancy
Table 27.8
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• Contraception can be accomplished
– Through various methods
Skin patch
Diaphragm
Spermicide
Condom
Birth control pills
Figure 27.8
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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
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The Properties of Sperm Cells
• Only one sperm
– Fertilizes an egg
Co
loriz
ed
SE
M 5
00
Figure 27.9A
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• During fertilization
– A sperm releases enzymes from the acrosome that pierce the egg’s coat
Plasma membrane Middlepiece HeadNeck
Mitochondrion(spiral shape)
Nucleus
Acrosome
Tail
Figure 27.9B
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The Process of Fertilization
• Sperm surface proteins bind to egg receptor proteins
– Sperm and egg plasma membranes fuse, and the two nuclei unite
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• Changes in the egg membrane
– Prevent entry of additional sperm
• The fertilized egg (zygote)
– Develops into an embryo
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Figure 27.9C
• The process of fertilization
Nucleus
Acrosome
Sperm
Plasmamembrane
Spermhead
Acrosomalenzymes
Jellycoat
Vitellinelayer
Plasmamembrane
Receptor proteinmolecules
Spermnucleus
Cytoplasm
Eggnucleus
Egg cell
Zygote nucleus
The spermapproachesthe egg
1
Proteins on thesperm head bind toegg receptors
3
The plasmamembranes of spermand egg fuse
4
The sperm nucleusenters the eggcytoplasm
5
A fertilizationenvelope forms
6
The sperm’sacrosomal enzymesdigest the egg’s jellycoat
2
The nuclei of sperm and egg fuse
7
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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 sectionof blastula
Blastocoel
Figure 27.10
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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
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• Programmed cell death, or apoptosis
– Is a key developmental process in which cells die
Figure 27.13B
Apoptosis
Dead cellengulfed anddigested byadjacent cell
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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
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Futurebrain Optic
vesicle
Lens ectoderm
Opticstalk
Optic cup
Cornea
Lens
Futureretina
Figure 27.14
• Induction during eye development
1 2 3 4
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27.15 Pattern formation organizes the animal body
• Pattern formation
– Is the emergence of the parts of a structure in their correct relative positions
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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
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An Overview of Developmental Events
• Human development
– Begins with fertilization in the oviduct Cleavage starts
Fertilizationof ovum
Oviduct
Secondaryoocyte
Ovulation
Ovary
Blastocyst(implanted)
Endometrium
Uterus
Figure 27.16A
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• Cleavage produces a blastocyst
– Whose inner cell mass becomes the embryo
Endometrium
Inner cell mass
Cavity
Trophoblast
Figure 27.16B
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• The blastocyst’s outer layer, the trophoblast
– Implants in the uterine wall
EndometriumFuture embryo
Futureyolk sac
Blood vessel(maternal)
Multiplying cellsof trophoblast
Trophoblast
Uterine cavity
Figure 27.16C
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• Meanwhile, the four extraembryonic membranes develop
– The amnion, the chorion, the yolk sac, and the allantois
Amnioticcavity Amnion
Mesodermcells Chorion
Yolk sac
Chorion
Amnion
Allantois
Yolk sac
Chorionic villi
Embryo:
EctodermMesodermEndoderm
Figure 27.16D, E
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Roles of the Extraembryonic Membranes
• About a month after conception
– The extraembryonic membranes are fully formed
Mother’s bloodvessels
Allantois
Yolk sac
Placenta
Amnioticcavity
Amnion
Embryo
Chorion
Chorionicvilli
Figure 27.16F
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• 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
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• The allantois
– Forms part of the umbilical cord
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The Placenta
• The placenta’s chorionic villi
– Absorb food and oxygen from the mother’s blood to nourish the embryo
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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
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The First Trimester
• The most rapid changes
– Occur during the first trimester
Figure 27.17A
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• By 9 weeks
– The embryo is called a fetus
Figure 27.17B
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Second Trimester
• The second trimester
– Involves an increase in size and general refinement of the human features
Figure 27.17C
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• At 20 weeks
– The fetus is about 19 centimeters long, and weighs half a kilogram
Figure 27.17D
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Third Trimester
• The third trimester
– Is a time of rapid growth, which ends in birth
Figure 27.17E
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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
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• Estrogen makes the uterus more sensitive to oxytocin
– Which acts with prostaglandins to initiate labor
Estrogen Oxytocin
fromovaries
from fetusand pituitary
Induces oxytocinreceptors on uterus
Stimulates uterusto contract
Stimulatesplacenta to make
Prostaglandins
Stimulate morecontractionsof uterus
Po
sitiv
e f
ee
db
ack
Figure 27.18A
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Placenta
Umbilicalcord
Uterus
Cervix
Uterus
Placenta(detaching)
Umbilicalcord
Figure 27.18B
• Labor occurs in three stages
– Dilation, expulsion, and delivery of the placenta
Dilation of the cervix1
Expulsion: delivery of the infant2
Delivery of the placenta3
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CONNECTION
27.19 Reproductive technology increases our reproductive options
• New techniques
– Can provide help to infertile couples
Figure 27.19
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• Some of these methods
– Raise important ethical and legal questions