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Chapter 46. Animal Reproduction. Figure 46.1. Overview: Doubling Up for Sexual Reproduction The two earthworms in this picture are mating Each worm produces both sperm and eggs, which will fertilize And in a few weeks, new worms will hatch. A population transcends finite life spans

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Chapter 46

Chapter 46

Animal Reproduction


Chapter 46

Figure 46.1

  • Overview: Doubling Up for Sexual Reproduction

  • The two earthworms in this picture are mating

  • Each worm produces both sperm and eggs, which will fertilize

    • And in a few weeks, new worms will hatch


Chapter 46

  • A population transcends finite life spans

    • Only by reproduction


Chapter 46

  • Concept 46.1: Both asexual and sexual reproduction occur in the animal kingdom

  • Asexual reproduction is the creation of new individuals

    • Whose genes all come from one parent


Chapter 46

  • Sexual reproduction is the creation of offspring

    • By the fusion of male and female gametes to form a zygote

  • The female gamete is the egg

  • The male gamete is the sperm


Mechanisms of asexual reproduction

Mechanisms of Asexual Reproduction

  • Many invertebrates reproduce asexually by fission

    • The separation of a parent into two or more individuals of approximately the same size

Figure 46.2


Chapter 46

  • Also common in invertebrates is budding

    • In which two new individuals arise from outgrowths of existing ones

  • Another type of asexual reproduction is fragmentation, which

    • Is the breaking of the body into several pieces, some or all of which develop into complete adults

    • Must be accompanied by regeneration, the regrowth of lost body parts


Reproductive cycles and patterns

Reproductive Cycles and Patterns

  • Most animals exhibit cycles in reproductive activity

    • Often related to changing seasons

  • Reproductive cycles

    • Are controlled by hormones and environmental cues


Chapter 46

  • Animals may reproduce exclusively asexually or sexually

    • Or they may alternate between the two

  • Some animals reproduce by parthenogenesis

    • A process in which an egg develops without being fertilized


Chapter 46

(a) Both lizards in this photograph are C. uniparensfemales. The one on top is playing the role of a male. Every two or three weeks during the breeding season, individuals switch sex roles.

Ovarysize

Ovulation

Ovulation

Progesterone

Estrogen

Hormones

(b) The sexual behavior of C. uniparens is correlated with the cycle of ovulation mediated by sex hormones. As blood levels of estrogen rise, the ovaries grow, and the lizard behaves like a female. After ovulation, the estrogen level drops abruptly, and the progesterone level rises; these hormone levels correlate with male behavior.

Time

Behavior

Female-like

Male-like

Female-like

Male-like

Figure 46.3a, b

  • Among vertebrates, several genera of fishes, amphibians, and lizards, including whiptail lizards

    • Reproduce exclusively by a complex form of parthenogenesis


Chapter 46

  • Sexual reproduction presents a special problem for certain organisms

    • That seldom encounter a mate

  • One solution to this problem is hermaphroditism

    • In which each individual has both male and female reproductive systems


Chapter 46

Figure 46.4

  • Another remarkable reproductive pattern is sequential hermaphroditism

    • In which an individual reverses its sex during its lifetime


Chapter 46

  • Concept 46.2: Fertilization depends on mechanisms that help sperm meet eggs of the same species

  • The mechanisms of fertilization, the union of egg and sperm

    • Play an important part in sexual reproduction


Chapter 46

Eggs

Figure 46.5

  • Some species have external fertilization, in which

    • Eggs shed by the female are fertilized by sperm in the external environment


Chapter 46

  • Other species have internal fertilization, in which

    • Sperm are deposited in or near the female reproductive tract, and fertilization occurs within the tract


Chapter 46

  • In either situation, fertilization requires critical timing

    • Often mediated by environmental cues, pheromones, and/or courtship behavior

  • Internal fertilization

    • Requires important behavioral interactions between male and female animals

    • Requires compatible copulatory organs


Ensuring the survival of offspring

Ensuring the Survival of Offspring

  • All species produce more offspring than the environment can handle

    • But the proportion that survives is quite small


Chapter 46

  • The embryos of many terrestrial animals

    • Develop in eggs that can withstand harsh environments

  • Instead of secreting a shell around the embryo

    • Many animals retain the embryo, which develops inside the female


Chapter 46

Figure 46.6

  • Many different types of animals

    • Exhibit parental care to ensure survival of offspring


Gamete production and delivery

Gamete Production and Delivery

  • To reproduce sexually

    • Animals must have systems that produce gametes


Chapter 46

  • The least complex systems

    • Do not even contain distinct gonads, the organs that produce gametes in most animals


Chapter 46

  • The most complex reproductive systems

    • Contain many sets of accessory tubes and glands that carry, nourish, and protect the gametes and the developing embryos


Chapter 46

2

2

3

1

4

3

1

Genitalpore

(Digestive tract)

Female organs:

Male organs:

Uterus

Yolk gland

Yolk duct

Sperm duct(vas deferens)

Seminalvesicle

Oviduct

Testis

Ovary

Vas efferens

Seminal

receptacle

Figure 46.7

(Excretory pore)

  • Many animals with relatively simple body plans

    • Possess highly complex reproductive systems


Chapter 46

Vagina

2

5

4

1

1

3

3

Accessorygland

Ovary

  • Most insects

    • Have separate sexes with complex reproductive systems

Ejaculatoryduct

Testis

Oviduct

Spermatheca

Penis

Vas deferens

Accessorygland

Seminalvesicle

(a) Male honeybee. Sperm form in the testes, pass through the sperm duct (vas deferens), and are stored in the seminal vesicle. The male ejaculates sperm along with fluidfrom the accessory glands. (Males of somespecies of insects and other arthropods haveappendages called claspers that grasp thefemale during copulation.)

(b) Female honeybee. Eggs develop in the ovaries and then pass through the oviducts and into the vagina. A pair of accessory glands (only one is shown)add protective secretions to the eggs in the vagina. After mating, sperm are stored in the spermatheca, a sac connected to the vagina by a short duct.

Figure 46.8a, b


Chapter 46

  • Concept 46.3: Reproductive organs produce and transport gametes: focus on humans


Female reproductive anatomy

Female Reproductive Anatomy

  • The female external reproductive structures include

    • The clitoris

    • Two sets of labia


Chapter 46

  • The internal organs are a pair of gonads

    • And a system of ducts and chambers that carry gametes and house the embryo and fetus


Chapter 46

Uterus

(Urinary bladder)

Oviduct

(Pubic bone)

Ovary

(Rectum)

Cervix

Vagina

Urethra

Shaft

Bartholin’s gland

Glans

Clitoris

Prepuce

Labia minora

Vaginal opening

Labia majora

Figure 46.9

  • Reproductive anatomy of the human female


Chapter 46

Oviduct

Ovaries

Follicles

Endometrium

Uterine wall

Uterus

Cervix

Corpus luteum

Vagina


Ovaries

Ovaries

  • The female gonads, the ovaries

    • Lie in the abdominal cavity


Chapter 46

  • Each ovary

    • Is enclosed in a tough protective capsule and contains many follicles

  • A follicle

    • Consists of one egg cell surrounded by one or more layers of follicle cells


Chapter 46

  • The process of ovulation

    • Expels an egg cell from the follicle

  • The remaining follicular tissue then grows within the ovary

    • To form a solid mass called the corpus luteum, which secretes hormones, depending on whether or not pregnancy occurs


Oviducts and uterus

Oviducts and Uterus

  • The egg cell is released into the abdominal cavity

    • Near the opening of the oviduct, or fallopian tube

  • Cilia in the tube

    • Convey the egg to the uterus


Vagina and vulva

Vagina and Vulva

  • The vagina is a thin-walled chamber

    • That is the repository for sperm during copulation

    • That serves as the birth canal through which a baby is born


Chapter 46

  • The vagina opens to the outside at the vulva

    • Which includes the hymen, vestibule, labia minora, labia majora, and clitoris


Mammary glands

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


Male reproductive anatomy

Male Reproductive Anatomy

  • In most mammalian species

    • The male’s external reproductive organs are the scrotum and penis

  • The internal organs

    • Consist of the gonads, which produce sperm and hormones, and accessory glands


Chapter 46

(Urinarybladder)

Seminal

vesicle

(behind

bladder)

Prostate gland

Bulbourethral gland

Urethra

Erectile tissue

of penis

Scrotum

Vas deferens

Epididymis

Glans penis

Testis

Figure 46.10

  • Reproductive anatomy of the human male


Chapter 46

(Urinary

bladder)

Seminal vesicle

(Rectum)

(Pubic bone)

Erectile

tissue of

penis

Vas deferens

Ejaculatory duct

Prostate gland

Urethra

Bulbourethral gland

Glans penis

Vas deferens

Epididymis

Testis

Prepuce

Scrotum


Testes

Testes

  • The male gonads, or testes

    • Consist of many highly coiled tubes surrounded by several layers of connective tissue

  • The tubes are seminiferous tubules

    • Where sperm form


Chapter 46

  • Production of normal sperm

    • Cannot occur at the body temperatures of most mammals

  • The testes of humans and many mammals

    • Are held outside the abdominal cavity in the scrotum, where the temperature is lower than in the abdominal cavity


Ducts

Ducts

  • From the seminiferous tubules of a testis

    • The sperm pass into the coiled tubules of the epididymis

  • During ejaculation

    • Sperm are propelled through the muscular vas deferens, the ejaculatory duct, and exit the penis through the urethra


Glands

Glands

  • Three sets of accessory glands

    • Add secretions to the semen, the fluid that is ejaculated

  • A pair of seminal vesicles

    • Contributes about 60% of the total volume of semen


Chapter 46

  • The prostate gland

    • Secretes its products directly into the urethra through several small ducts

  • The bulbourethral gland

    • Secretes a clear mucus before ejaculation that neutralizes acidic urine remaining in the urethra


Semen in the female reproductive tract

Semen in the Female Reproductive Tract

  • Once in the female reproductive tract

    • A number of processes, including contractions of the uterus, help move the sperm up the uterus


Penis

Penis

  • The human penis

    • Is composed of three cylinders of spongy erectile tissue

  • During sexual arousal

    • The erectile tissue fills with blood from the arteries, causing an erection


Human sexual response

Human Sexual Response

  • Two types of physiological reactions predominate in both sexes

    • Vasocongestion, the filling of tissue with blood

    • Myotonia, increased muscle tension


Chapter 46

  • The sexual response cycle can be divided into four phases

    • Excitement, plateau, orgasm, and resolution


Chapter 46

  • Concept 46.4: In humans and other mammals, a complex interplay of hormones regulates gametogenesis

  • The process of gametogenesis

    • Is based on meiosis, but differs in females and males


Chapter 46

Ovary

Primary germ cell in embryo

Differentiation

Oogonium

in ovary

Oogonium

2n

Mitotic

division

Primary

oocyte

within

follicle

Primary oocyte,

arrested in prophase

of meiosis I

(present at birth)

2n

Growing

follicle

Completion of meiosis I

and onset of meiosis II

n

First

polar

body

Secondary oocyte,

arrested at meta-

phase of meiosis II

n

Ovulation

Mature follicle

Entry of

sperm triggers

completion of

meiosis II

n

n

Ruptured

follicle

Ovum

Ovulated

secondary oocyte

Corpus luteum

Degenerating

corpus luteum

Figure 46.11

  • Oogenesis is the development of mature ova


Chapter 46

  • Spermatogenesis is the production of mature sperm

Epididymis

Seminiferous tubule

Testis

Cross section

of seminiferous

tubule

Spermatogonium

2n

Mitotic division,

producing large numbers

of spermatogonia

Sertoli cell

nucleus

Differentiation andonset of meiosis I

Primary spermatocyte

(in prophase of meiosis I)

2n

Meiosis I completed

n

n

Secondary spermatocyte

Meiosis II

Lumen of

Seminiferous tubule

Early

spermatids

Spermatids

(at two stages of

differentiation)

n

n

n

n

Differentiation

(Sertoli cells provide

nutrients)

Sperm cells

Neck

n

n

n

n

Head

Midpiece

Tail

Plasma membrane

Mitochondria

Nucleus

Acrosome

Figure 46.12


Chapter 46

  • Oogenesis differs from spermatogenesis

    • In three major ways


Chapter 46

  • First, during the meiotic divisions of oogenesis

    • Cytokinesis is unequal, with almost all the cytoplasm monopolized by a single daughter cell, the secondary oocyte


Chapter 46

  • Second, sperm are produced continuously throughout a male’s life

    • Which is not the case in oogenesis

  • Third, oogenesis has long “resting” periods

    • While spermatogenesis produces sperm in uninterrupted sequence


The reproductive cycles of females

The Reproductive Cycles of Females

  • In females

    • The secretion of hormones and the reproductive events they regulate are cyclic


Menstrual versus estrous cycles

Menstrual Versus Estrous Cycles

  • Two different types of cycles occur in females


Chapter 46

  • Humans and other primates have menstrual cycles

    • While other mammals have estrous cycles

  • In both cases ovulation occurs at a time in the cycle

    • After the endometrium has started to thicken in preparation for implantation


Chapter 46

  • In menstrual cycles

    • The endometrium is shed from the uterus in a bleeding called menstruation

    • Sexual receptivity is not limited to a specific timeframe

  • In estrous cycles

    • The endometrium is reabsorbed by the uterus

    • Sexual receptivity is limited to a “heat” period


The human female reproductive cycle a closer look

The Human Female Reproductive Cycle: A Closer Look

  • The female reproductive cycle

    • Is one integrated cycle involving two organs, the uterus and ovaries


Chapter 46

  • Cyclic secretion of GnRH from the hypothalamus

    • And of FSH and LH from the anterior pituitary orchestrates the female reproductive cycle

  • Five kinds of hormones

    • Participate in an elaborate scheme involving both positive and negative feedback


Chapter 46

Control by hypothalamus

Inhibited by combination of

estrogen and progesterone

Hypothalamus

Stimulated by high levels

of estrogen

GnRH

(a)

Anterior pituitary

Inhibited by low levels of

estrogen

LH

FSH

1

Pituitary gonadotropins

in blood

2

(b)

6

LH

FSH

FSH and LH stimulate

follicle to grow

LH surge triggers

ovulation

Ovarian cycle

3

(c)

7

8

Corpus

luteum

Degenerating

corpus luteum

Growing follicle

Mature

follicle

Ovulation

Luteal phase

Follicular phase

Progesterone and

estrogen secreted

by corpus luteum

Estrogen secreted

by growing follicle in

increasing amounts

Peak causes

LH surge

4

Ovarian hormones

in blood

(d)

5

Progesterone

Estrogen

10

Progesterone and estro-

gen promote thickening

of endometrium

Estrogen level

very low

9

Uterine (menstrual) cycle

(e)

  • Endometrium

Secretory phase

Menstrual flow phase

Proliferative phase

Figure 46.13a–e

25

28

5

14

15

0

20

10

Days

  • The reproductive cycle of the human female


The ovarian cycle

The Ovarian Cycle

  • In the ovarian cycle

    • Hormones stimulate follicle growth, which results in ovulation

  • Following ovulation

    • The follicular tissue left behind transforms into the corpus luteum


The uterine menstrual cycle

The Uterine (Menstrual) Cycle

  • Cycle after cycle

    • The maturation and release of egg cells from the ovary are integrated with changes in the uterus

  • If an embryo has not implanted in the endometrium by the end of the secretory phase

    • A new menstrual flow commences


Menopause

Menopause

  • After about 450 cycles, human females undergo menopause

    • The cessation of ovulation and menstruation


Hormonal control of the male reproductive system

Hormonal Control of the Male Reproductive System

  • Testosterone and other androgens

    • Are directly responsible for the primary and secondary sex characteristics of the male


Chapter 46

Stimuli from other

areas in the brain

Hypothalamus

GnRH from the

hypothalamus reg-

ulates FSH and LH

release from the

anterior pituitary.

Anterior

pituitary

Negative

feedback

FSH acts on the

Sertoli cells of the

seminiferous

tubules, promoting

spermatogenesis.

LH stimulates the

Leydig cells to make

testosterone, which

in turn stimulates

sperm production.

Leydig cells

make

testosterone

Primary and

secondary sex

characteristics

Sertoli cells

Spermatogenesis

Testis

Figure 46.14

  • Androgen secretion and sperm production

    • Are both controlled by hypothalamic and pituitary hormones


Chapter 46

  • Concept 46.5: In humans and other placental mammals, an embryo grows into a newborn in the mother’s uterus


Conception embryonic development and birth

Conception, Embryonic Development, and Birth

  • In humans and most other placental mammals

    • Pregnancy, or gestation, is the condition of carrying one or more embryos in the uterus


Chapter 46

Cleavage (cell division)

begins in the oviduct

as the embryo is moved

toward the uterus

by peristalsis and the

movements of cilia.

Cleavage continues.

By the time the embryo

reaches the uterus,

it is a ball of cells.

It floats in the uterus for

several days, nourished by

endometrial secretions. It

becomes a blastocyst.

3

4

Ovary

Fertilization occurs. A sperm

enters the oocyte; meiosis of

the oocyte finishes; and the

nuclei of the ovum and sperm

fuse, producing a zygote.

2

The blastocyst implants

in the endometrium

about 7 days after conception.

5

Uterus

Ovulation releases a

secondary oocyte, which

enters the oviduct.

1

Endometrium

(a)

From ovulation to implantation

Endometrium

Inner cell mass

Cavity

Trophoblast

Blastocyst

Figure 46.15a, b

(b)

Implantation of blastocyst

  • Fertilization of an egg by a sperm, conception

    • Occurs in the oviduct


Chapter 46

  • After fertilization

    • The zygote undergoes cleavage and develops into a blastocyst before implantation in the endometrium


First trimester

First Trimester

  • Human gestation

    • Can be divided into three trimesters of about three months each

  • The first trimester

    • Is the time of most radical change for both the mother and the embryo


Chapter 46

  • During its first 2 to 4 weeks of development

    • The embryo obtains nutrients directly from the endometrium

  • Meanwhile, the outer layer of the blastocyst

    • Mingles with the endometrium and eventually forms the placenta


Chapter 46

Maternal

veins

Maternal

arteries

Placenta

Maternal portion

of placenta

Umbilical cord

Chorionic villus

containing fetal

capillaries

Fetal portion of

placenta (chorion)

Maternal blood

pools

Uterus

Umbilical arteries

Fetal arteriole

Umbilical vein

Fetal venule

Umbilical cord

Figure 46.16

  • Blood from the embryo

    • Travels to the placenta through arteries of the umbilical cord and returns via the umbilical vein


Chapter 46

(a) 5 weeks. Limb buds, eyes, theheart, the liver, and rudimentsof all other organs have startedto develop in the embryo, whichis only about 1 cm long.

(b) 14 weeks. Growth anddevelopment of the offspring,now called a fetus, continueduring the second trimester.This fetus is about 6 cm long.

(c) 20 weeks. By the end of thesecond trimester (at 24 weeks),the fetus grows to about 30 cmin length.

Figure 46.17a–c

  • The first trimester is the main period of organogenesis

    • The development of the body organs


Second trimester

Second Trimester

  • During the second trimester

    • The fetus grows and is very active

    • The mother may feel fetal movements

    • The uterus grows enough for the pregnancy to become obvious


Third trimester

Third Trimester

  • During the third trimester

    • The fetus continues to grow and fills the available space within the embryonic membranes


Chapter 46

Estrogen

Oxytocin

from fetus

and mother's

posterior pituitary

from

ovaries

Positive feedback

Induces oxytocin

receptors on uterus

Stimulates uterus

to contract

Stimulates

placenta to make

Prostaglandins

Stimulate more

contractions

of uterus

Figure 46.18

  • A complex interplay of local regulators and hormones

    • Induces and regulates labor, the process by which childbirth occurs


Chapter 46

  • Birth, or parturition

    • Is brought about by a series of strong, rhythmic uterine contractions


Chapter 46

Placenta

Umbilical

cord

Uterus

Cervix

Dilation of the cervix

1

Expulsion: delivery of the infant

2

Uterus

Placenta

(detaching)

Umbilical

cord

Delivery of the placenta

Figure 46.19

3

  • The process of labor has three stages


The mother s immune tolerance of the embryo and fetus

The Mother’s Immune Tolerance of the Embryo and Fetus

  • A woman’s acceptance of her “foreign” offspring

    • Is not fully understood

    • May be due to the suppression of the immune response in her uterus


Contraception and abortion

Contraception and Abortion

  • Contraception, the deliberate prevention of pregnancy

    • Can be achieved in a number of ways


Chapter 46

  • Some contraceptive methods

    • Prevent the release of mature eggs and sperm from gonads

    • Prevent fertilization by keeping sperm and egg apart

    • Prevent implantation of an embryo


Chapter 46

Female

Male

Event

Event

Method

Method

Production of

viable sperm

Production of

viable oocytes

Vasectomy

Combination

birth control

pill (or injection,

patch, or

vaginal ring)

Ovulation

Sperm transport

down male

duct system

Abstinence

Abstinence

Condom

Coitus

interruptus

(very high

failure rate)

Sperm

deposited

in vagina

Capture of the

oocyte by the

oviduct

Tubal ligation

Spermicides;

diaphragm;

cervical cap;

progestin alone

(minipill, implant,

or injection)

Transport

of oocyte in

oviduct

Sperm

movement

through

female

reproductive

tract

Meeting of sperm and oocyte

in oviduct

Morning-after

pill (MAP)

Union of sperm and egg

Progestin alone

Implantation of blastocyst

in properly prepared

endometrium

Figure 46.20

Birth

  • Mechanisms of some contraceptive methods


Modern reproductive technology

Modern Reproductive Technology

  • Recent scientific and technological advances

    • Have made it possible to deal with many reproductive problems


Chapter 46

  • Amniocentesis and chorionic villus sampling

    • Are invasive techniques in which amniotic fluid or fetal cells are obtained for genetic analysis


Chapter 46

Head

Body

Head

Body

Figure 46.21

  • Noninvasive procedures

    • Usually use ultrasound imaging to detect fetal condition


Chapter 46

  • Modern technology

    • Can help infertile couples by in vitro fertilization


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