Animal Reproduction

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Animal Reproduction
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Chapter 32 Animal Reproduction

• Key Concepts
• 32.1 Reproduction Can Be Sexual or Asexual
• 32.2 Gametogenesis Produces Haploid Gametes
• 32.3 Fertilization Is the Union of Sperm and Ovum

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Chapter 32 Animal Reproduction

• Key Concepts
• 32.4 Human Reproduction Is Hormonally Controlled
• 32.5 Humans Use a Variety of Methods to Control
  Fertility

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Chapter 32 Opening Question

• How does the pill prevent contraception?

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Concept 32.1 Reproduction Can Be Sexual or Asexual

• Asexual reproduction requires no mating but does
  not result in genetic diversity.
• Asexually reproducing species are mostly
  invertebrates, sessile, and live in constant
  environments.
• Three types of asexual reproduction are budding,
  regeneration, and parthenogenesis.

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Concept 32.1 Reproduction Can Be Sexual or Asexual

• Budding produces new individuals that form from
  the bodies of older animals.
• A bud grows by mitotic cell divisioncells
  differentiate before the bud breaks away.
• The bud is genetically identical to the parent.
• Regeneration can replace damaged tissue or form a
  complete individual.
• Example Echinoderms.

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Figure 32.1 Three Forms of Asexual Reproduction
(Part 1)
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Figure 32.1 Three Forms of Asexual Reproduction
(Part 2)
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Concept 32.1 Reproduction Can Be Sexual or Asexual

• Parthenogenesis is the development of offspring
  from unfertilized eggs.
• Parthenogenesis may determine the sex of the
  offspring.
• In some species, females can act as males
  depending on cyclic states of estrogen and
  progesterone.

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Figure 32.1 Three Forms of Asexual Reproduction
(Part 3)
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Concept 32.1 Reproduction Can Be Sexual or Asexual

• In sexual reproduction two haploid cells,
  gametes, form a diploid individual.
• Three fundamental steps of sexual reproduction
• Gametogenesismaking haploid gametes
• Spawning or matinggetting gametes together
• Fertilizationfusing gametes to form a diploid

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Concept 32.1 Reproduction Can Be Sexual or Asexual

• Sexual reproduction has a big advantage the
  generation of genetic diversity.
• Meiosis allows genetic diversity through crossing
  over between homologous chromosomes and
  independent assortment.

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Concept 32.2 Gametogenesis Produces Haploid
Gametes

• Gametogenesis occurs in the gonadsthe testes in
  males and ovaries in females
• Male gametes, the sperm, move by flagella.
• The larger gametes of females are the ova, or
  eggs, and are nonmotile.
• Gametes are produced from germ cellspresent
  early in development and distinct from other
  (somatic) cells of the body.

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Concept 32.2 Gametogenesis Produces Haploid
Gametes

• Germ cells migrate to the gonads when they begin
  to form.
• Embryonic germ cells divide by mitosis to form
  diploid spermatogonia in males and oogonia in
  females.
• These multiply by mitosis, producing primary
  spermatocytes and primary oocytesthese enter
  meiosis and produce haploid gametes, sperm and
  ova.

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Concept 32.2 Gametogenesis Produces Haploid
Gametes

• The production of sperm is spermatogenesisof ova
  is oogenesis.
• The first meiotic division of a primary
  spermatocyte results in two secondary
  spermatocytes.
• The second division produces four haploid
  spermatids, which will each become a sperm.

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Figure 32.2 Gametogenesis (Part 1)
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Concept 32.2 Gametogenesis Produces Haploid
Gametes

• Oogenesis
• A primary oocyte immediately begins prophase I of
  meiosis. Here, development stops in many species.
  
• The primary oocyte grows larger and acquires
  nutrients.
• When meiosis resumes, the nucleus of the oocyte
  divides into two daughter cells of unequal sizes.
• The cell with more cytoplasm is the secondary
  oocytethe smaller one is the first polar body.

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Concept 32.2 Gametogenesis Produces Haploid
Gametes

• The second meiotic division forms daughter cells
  of unequal sizes.
• One is a large ootid, which differentiates to
  become a mature ovum.
• The other forms the second polar body.

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Figure 32.2 Gametogenesis (Part 2)
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Concept 32.2 Gametogenesis Produces Haploid
Gametes

• Few primary oocytes complete all meiotic
  stagesfemales produce far fewer gametes than
  males.
• The average woman has about 450 menstrual cycles
  and releases on ovum each time, until
  menopausethe end of fertility.
• A man produces over 100 million sperm per day.

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Concept 32.2 Gametogenesis Produces Haploid
Gametes

• In hermaphroditic species such as earthworms, a
  single individual may produce sperm and ova
  simultaneously.
• An anemone fish produces sperm and ova
  sequentially and may function as a male or a
  female at different times.

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Concept 32.3 Fertilization Is the Union of Sperm
and Ovum

• Fertilization is the union of a haploid sperm and
  a haploid egg.
• It creates a single diploid cell, called a
  zygote, which will develop into an embryo.
• Fertilization involves a complex series of
  events.

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Concept 32.3 Fertilization Is the Union of Sperm
and Ovum

• Steps in fertilization
• Recognition and binding of sperm and ovum
• Activation of sperm
• Plasma membranes fuse
• Additional sperm entry blocked
• Activation of ovum
• Ovum and sperm nuclei fuse

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Concept 32.3 Fertilization Is the Union of Sperm
and Ovum

• Aquatic animals bring gametes together through
  spawninggamete release before external
  fertilization occurs.
• Internal fertilization occurs when sperm is
  released directly into the female reproductive
  tract.
• Internal fertilization requires accessory sex
  organs, such as penis and vagina.
• Copulation is the joining of the male and female
  accessory organs.

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Concept 32.3 Fertilization Is the Union of Sperm
and Ovum

• Species-specific sperm and ovum interactions are
  controlled by specific recognition molecules.
• Ova of aquatic species release chemical
  attractants to cause sperm to swim toward the
  ovum.
• Sperm must go through two protective layers to
  reach an ovuma jelly coat and the vitelline
  envelope.

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Figure 32.3 Fertilization of Sea Urchin Egg
(Part 1)
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Concept 32.3 Fertilization Is the Union of Sperm
and Ovum

• The acrosome is a membrane-enclosed structure on
  the sperm head.
• Egg and sperm contact causes substances in the
  jelly coat to trigger an acrosomal reaction.
• Membranes in the sperm head and acrosome break
  down enzymes are released and digest the jelly
  coat.

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Figure 32.3 Fertilization of Sea Urchin Egg
(Part 2)
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Concept 32.3 Fertilization Is the Union of Sperm
and Ovum

• An acrosomal process extends from the head of the
  sperm.
• The acrosomal process is coated with
  bindinspecific recognition molecules.
• Bindin acts on bindin receptors in the vitelline
  envelope.
• Sperm and egg plasma membranes fuse to form a
  fertilization cone.

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Concept 32.3 Fertilization Is the Union of Sperm
and Ovum

• Internal fertilization involves species-specific
  mating behaviors and ovum-sperm recognition
  mechanisms.
• The ovum is surrounded by the cumulus, cells in a
  gelatinous matrix.
• The zona pellucida, or zona, is a glycoprotein
  envelope beneath the cumulus.

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Concept 32.3 Fertilization Is the Union of Sperm
and Ovum

• When sperm make contact with the zona,
  species-specific glycoproteins bind to
  recognition molecules on the sperm.
• Binding triggers the acrosomal reaction, and
  enzymes digest the zona pellucida.
• When sperm reaches ovum membrane other proteins
  facilitate membrane fusion.

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Figure 32.4 Barriers to Mammalian Sperm
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Concept 32.3 Fertilization Is the Union of Sperm
and Ovum

• Fusion and entry of a sperm into the ovum lead
  to
• Blocks to polyspermymechanisms to prevent more
  than one sperm from entering an ovum

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Concept 32.3 Fertilization Is the Union of Sperm
and Ovum

• Fast block to polyspermy
• Transient
• Caused by change in membrane potential as sodium
  ions (Na) enter plasma membrane of ovum after
  contact with a sperm

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Concept 32.3 Fertilization Is the Union of Sperm
and Ovum

• Slow block to polyspermy
• Initiated by release of calcium ions (Ca2)
• Cortical granules fuse with plasma membrane and
  release enzymes, dissolving bonds between
  vitelline envelope and ovum plasma membrane.
• H2O is absorbed and the vitelline envelope rises
  to form a fertilization envelope.
• Enzymes remove sperm-binding receptors and cause
  envelope to harden.

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Concept 32.3 Fertilization Is the Union of Sperm
and Ovum

• In mammals sperm entry does not cause membrane
  depolarization.
• Ca2 influx occurs, and cortical granules fuse
  with the ovum plasma membrane.
• No fertilization envelope forms, but cortical
  granule enzymes destroy the sperm-binding
  molecules in the zona pellucida.

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Concept 32.3 Fertilization Is the Union of Sperm
and Ovum

• Fertilized ova may be released into the
  environment or retained
• Oviparityegg laying
• Oviparous animals lay eggs in the environment,
  and embryos develop outside the mothers body.
• Viviparitylive bearing
• Viviparous animals retain the embryo in the
  mothers body during early development.

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Concept 32.3 Fertilization Is the Union of Sperm
and Ovum

• Viviparity differs in mammals as they have a
  specialized female reproductive tract
• Uterus (or womb)holds the embryo
• Placentadevelops in the uterus and enables
  exchange of nutrients and waste

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Concept 32.4 Human Reproduction Is Hormonally
Controlled

• Sperm are produced in the paired male gonads, or
  testes.
• The testes are located in the scrotum, outside of
  the body, to maintain optimal temperature for
  sperm production.
• Semen is made up of sperm and other fluids and
  molecules.

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Figure 32.5 Reproductive Organs of the Human
Male (Part 1)
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Figure 32.5 Reproductive Organs of the Human
Male (Part 2)
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Concept 32.4 Human Reproduction Is Hormonally
Controlled

• Spermatogenesis occurs in the seminiferous
  tubules in each testis.
• Between the tubules are Leydig cells, which
  produce testosterone.
• Spermatogonia reside in the outermost regions of
  the tubules, near Sertoli cells, which provide
  nutrients.

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Figure 32.6 Spermatogenesis Takes Place in the
Seminiferous Tubules (Part 1)
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Figure 32.6 Spermatogenesis Takes Place in the
Seminiferous Tubules (Part 2)
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Figure 32.6 Spermatogenesis Takes Place in the
Seminiferous Tubules (Part 3)
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Concept 32.4 Human Reproduction Is Hormonally
Controlled

• Immature sperm cells are shed in the lumen of the
  seminiferous tubule.
• They move into the epididymis, mature, and become
  motile.
• Sperm travel in the vas deferens which joins with
  the semen-carrying ejaculatory duct.
• This joins the urethra, the common final duct, at
  the base of the penis and opens to the outside at
  the tip of the penis.

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Concept 32.4 Human Reproduction Is Hormonally
Controlled

• Besides sperm, semen contains seminal fluidsthe
  products of several accessory glands
• The paired seminal vesicles, the prostate gland,
  and the bulbourethral glands
• The prostate gland produces a fluid that is
  alkaline and reduces acidity in male and female
  reproductive tracts.
• The fluid also contains enzymes to thicken semen
  and later to dissolve it.

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Concept 32.4 Human Reproduction Is Hormonally
Controlled

• The bulbourethral glands produce an alkaline
  secretion that
• Neutralizes acidity in the urethra
• Provides lubrication and facilitates sperm
  movement during climax
• These secretions precede climax yet carry
  residual sperm capable of fertilization.
• Pregnancy can occur even when the penis is
  withdrawn prior to ejaculation (coitus
  interruptus).

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Concept 32.4 Human Reproduction Is Hormonally
Controlled

• Male copulatory organ is the penis.
• The sensitive tip of the penis, the glans penis,
  is covered by the foreskinremoval of the
  foreskin is circumcision.
• Sexual stimulation triggers the nervous system to
  produce penile erection.
• Nitric oxide (NO) acts on blood vessels by
  stimulating production of cGMP.
• cGMP causes dilation of blood vessels so that
  spongy erectile tissue fills with blood.

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Concept 32.4 Human Reproduction Is Hormonally
Controlled

• At the climax of copulation, semen is ejaculated
  through the vasa deferentia and urethra.
• Ejaculation is accompanied by feelings of intense
  pleasure called orgasm.
• After ejaculation NO release decreases and
  enzymes break down cGMPblood vessels are no
  longer compressed, and erection declines.

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Concept 32.4 Human Reproduction Is Hormonally
Controlled

• Erectile dysfunction (ED), or impotence, is the
  inability to achieve or sustain an erection.
• Drugs used in treatment inhibit the breakdown of
  cGMP, enhancing the effect of NO on blood vessels.

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Concept 32.4 Human Reproduction Is Hormonally
Controlled

• Hormones control male sexual function
• GnRH (gonadotropin-releasing hormone)released by
  the hypothalamus at puberty
• GnRH increases the release of LH (luteinizing
  hormone) and FSH (follicle-stimulating hormone)
  by the anterior pituitary.

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Figure 32.7 Male Reproductive Hormones
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Concept 32.4 Human Reproduction Is Hormonally
Controlled

• LH increases testosterone
• Increases growth rate and starts development of
  secondary sexual characteristics
• FSH and testosterone control spermatogenesis in
  the Sertoli cells.
• Sertoli cells also produce inhibin, which exerts
  negative feedback on cells that produce and
  secrete FSH.

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Concept 32.4 Human Reproduction Is Hormonally
Controlled

• In females, the ovary releases an ovum into one
  of the oviducts, or Fallopian tubes, where it may
  be fertilized.
• The ovum is propelled towards the uterus where it
  will develop if fertilized.
• The bottom of the uterus is the narrow cervix,
  which opens into the vagina.

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Figure 32.8 Reproductive Organs of the Human
Female (Part 1)
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Concept 32.4 Human Reproduction Is Hormonally
Controlled

• In humans, two sets of skin folds surround the
  opening of the vagina and the urethra
• Labia minorathe inner folds
• Labia majorathe outer folds. At the anterior tip
  is the clitoris, erectile tissue that is
  important in sexual response.
• The labia and clitoris become engorged with blood
  in response to sexual stimulation.

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Figure 32.8 Reproductive Organs of the Human
Female (Part 2)
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Concept 32.4 Human Reproduction Is Hormonally
Controlled

• The female reproductive cycle is about 28 days
  and consists of two linked cycles
• The ovarian cycle that produces mature ova and
  hormones
• The uterine, or menstrual, cycle that prepares
  the uterus for the arrival of an embryo.

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Concept 32.4 Human Reproduction Is Hormonally
Controlled

• Each primary oocyte and its surrounding ovarian
  cells constitute a follicle.
• At the beginning of a cycle, the anterior
  pituitary increases FSH and LH.
• 6 to 12 follicles grow in the first two weeks of
  the cyclethe follicular phase.
• Follicles increase estrogen production until the
  largest follicle matures completely and others
  die (atresia).

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Figure 32.9 The Ovarian Cycle (Part 1)
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Figure 32.9 The Ovarian Cycle (Part 2)
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Concept 32.4 Human Reproduction Is Hormonally
Controlled

• Estrogen exerts negative feedback on the
  pituitary early in the ovarian cycle.
• During days 1214 estrogen becomes a positive
  feedback signal and causes a surge of LH and FSH.
• The LH surge triggers ovulationthe follicle
  ruptures and the oocyte is released from the
  ovary.

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Concept 32.4 Human Reproduction Is Hormonally
Controlled

• Follicle has two types of cells
• Granulosa cells surround the developing oocyte
  and are stimulated by FSH.
• Thecal cells enclose the whole follicle, produce
  androgens when stimulated by LH.
• Levels of circulating estrogen increase, which
  feeds back negatively to the hypothalamus and
  anterior pituitary.
• FSH and LH levels then fall.

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Figure 32.10 The Ovarian and Uterine Cycles
(Part 1)
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Figure 32.10 The Ovarian and Uterine Cycles
(Part 2)
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Figure 32.10 The Ovarian and Uterine Cycles
(Part 3)
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Figure 32.10 The Ovarian and Uterine Cycles
(Part 4)
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Concept 32.4 Human Reproduction Is Hormonally
Controlled

• The follicle with the most FSH receptors
  survives.
• The other follicular cells form the corpus
  luteum, which remains in the ovary.
• The corpus luteum functions as an endocrine gland
  and produces estrogen and progesterone for about
  two weeksthe luteal phase.
• Progesterone causes the uterine lining, the
  endometrium, to thicken.

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Figure 32.11 Hormones Control the Female
Reproductive Cycles
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Concept 32.4 Human Reproduction Is Hormonally
Controlled

• If an embryo does not arrive within 2 weeks after
  ovulation, then endometrium breaks down.
• Menstruation is the sloughing off of the
  endometrium through the vagina.
• In other mammals, estrus, or sexual receptivity,
  corresponds to ovulation.
• Most other mammals do not menstruate the uterine
  lining is reabsorbed.

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Concept 32.4 Human Reproduction Is Hormonally
Controlled

• Different hormones control pregnancy.
• After fertilization, the zygote divides and moves
  toward the uterus.
• It attaches to the endometrium as a blastocyst
  and burrows inimplantation.
• A new cover layer of cells secretes human
  chorionic gonadatropin (hCG).
• hCG causes the corpus luteum to continue to
  produce estrogen and progesterone, and
  endometrium is maintained.

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Concept 32.4 Human Reproduction Is Hormonally
Controlled

• Pregnancy tests use an antibody to detect hCG in
  urine.
• The placenta forms from combined maternal and
  embryonic tissues and secretes progesterone and
  estrogen.
• Both hormones prevent the pituitary from
  releasing gonadotropins, so the ovarian cycle
  ceases during pregnancy.

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Concept 32.4 Human Reproduction Is Hormonally
Controlled

• The onset of labor is triggered by hormonal and
  mechanical stimuli
• Progesteroneinhibits uterine contractions
• Estrogenstimulates contractions
• The ratio shifts in favor of estrogen near the
  end of pregnancy.
• The onset of labor is marked by an increase in
  oxytocina powerful stimulant of uterine
  contractionby mother and fetus.

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Concept 32.4 Human Reproduction Is Hormonally
Controlled

• Mechanical stimuli
• Uterine stretching by fully grown fetus
• Pressure on the cervix by the head
• These stimuli create a positive feedback
  loopcause release of oxytocin which increases
  contractions and puts more pressure on the cervix.

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Concept 32.4 Human Reproduction Is Hormonally
Controlled

• Between contractions in early labor, hormonal and
  mechanical stimuli cause the cervix to dilate.
• It becomes large enough for the baby to pass
  through, about 10 cm.
• Contractions then become more frequent and
  intense.
• The head enters the vagina and passage is
  assisted by mother bearing down and pushing
  with abdominal muscles.

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Concept 32.4 Human Reproduction Is Hormonally
Controlled

• If the baby suckles at the breast immediately
  after birth, additional oxytocin is secreted.
• This causes the uterus to continue to contract
  and reduce in size and helps stop bleeding.
• Oxytocin also promotes bonding between mother and
  infant.

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Concept 32.5 Humans Use a Variety of Methods to
Control Fertility

• Ways to prevent fertilization or implantation
  (conception) are referred to as contraception.
• The only failure-proof methods of preventing
  pregnancy are complete abstinence from sexual
  activity or gonad removal.
• Other methods vary in their failure rate.

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Table 32.1 Methods of Contraception (Part 1)
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Table 32.1 Methods of Contraception (Part 2)
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Table 32.1 Methods of Contraception (Part 3)
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Concept 32.5 Humans Use a Variety of Methods to
Control Fertility

• An abortion is a termination of the pregnancy
  once the fertilized egg is implanted in the
  uterus.
• A spontaneous abortion is a miscarriage, and may
  occur before the pregnancy is known.
• Abortions through medical intervention may be for
  therapeutic reasons or for fertility controlthe
  embryo and some of the endometrium are removed.

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Concept 32.5 Humans Use a Variety of Methods to
Control Fertility

• Infertility is the inability of a couple to
  conceive a childseveral treatments exist.
• Artificial inseminationphysician positions sperm
  in womans reproductive tract
• Assisted reproductive technologies (ARTs)remove
  unfertilized eggs, combine them with sperm
  outside the body, and return them for
  implantation
• In vitro fertilization (IVF)the first ART.

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Answer to Opening Question

• Birth control pills prevent contraception by
  creating a hormonal condition similar to
  pregnancy.
• Most pills contain synthetic hormones resembling
  estrogen and progesterone.
• Higher levels of these hormones exert negative
  feedback on the hypothalamus and anterior
  pituitary, so no follicles mature and ovulation
  does not occur.