Animal Reproduction - Houston Community College

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

PowerPoint® Lecture Presentations for

BiologyEighth Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp

Chapter 46

Animal Reproduction

Fig. 46-1


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

• Sexual reproduction is the creation of an

offspring by fusion of a male gamete (sperm)

and female gamete (egg) to form a zygote

• Asexual reproduction is creation of offspring

without the fusion of egg and sperm


Mechanisms of Asexual Reproduction

• In budding, new individuals arise from

outgrowths of existing ones

• Fragmentation is breaking of the body into

pieces, some or all of which develop into adults

• Fragmentation must be accompanied by

regeneration, regrowth of lost body parts

• Parthenogenesis is the development of a new

individual from an unfertilized egg

Fig. 46-2

Many invertebrates reproduce asexually by

fission, separation of a parent into two or

more individuals of about the same size

Asexual reproduction of a sea anemone (Anthopleura

elegantissima)


Sexual Reproduction

• Sexual reproduction results in genetic

recombination, which provides potential

advantages:

– An increase in variation in offspring, providing

an increase in the reproductive success of

parents in changing environments

– An increase in the rate of adaptation

– A shuffling of genes and the elimination of

harmful genes from a population


Sexual Reproduction

Sexual reproduction methods: fusion of

gametes produced by meiosis

• Hermaphroditism

• Separate sexes

• External fertilization

• Internal fertilization


• Individuals of some species undergo sex

reversals

• Some species exhibit male to female reversal

(for example, certain oysters), while others

exhibit female to male reversal (for example,

a coral reef fish)

Fig. 46-5

Eggs

External fertilization


• In internal fertilization, sperm are deposited

in or near the female reproductive tract, and

fertilization occurs within the tract

• All fertilization requires critical timing, often

mediated by environmental cues, pheromones,

and/or courtship behavior

10/48

Fig. 46-8

Genitalpore

(Digestive tract)

Male organs:

Seminalvesicle

Sperm duct(vas deferens)

Vas efferens

Testis

Female organs:

Uterus

Yolk gland

Yolk duct

Oviduct

Ovary

Seminalreceptacle

(Excretory pore)

4

3

2

1

3

2

1

Even animals with simple body plans can have

complex reproductive systems, for example

parasitic flatworms

Reproductive anatomy of a hermaphrodite


Concept 46.3: Reproductive organs produce and transport gametes

• The following section focuses

on the human reproductive

system


Female Reproductive Anatomy

• The female external reproductive structures

include the clitoris and two sets of labia

• The internal organs are a pair of gonads and

a system of ducts and chambers that carry

gametes and house the embryo and fetus

Fig. 46-10a

(Rectum)

Cervix

Vagina

Vaginal opening

Oviduct

Ovary

Uterus

(Urinary bladder)

(Pubic bone)

Urethra

ClitorisShaftGlans

Prepuce

Labia minora

Labia majora

e x

t e

r n

a l

Fig. 46-10b

OvariesOviduct

Follicles

Corpus luteumUterine wallUterus

Cervix

Endometrium

Vagina


Female reproductive anatomy

• Ovaries: produce ova (eggs)

• Ovarian follicles: contain immature ova

• Uterine tube (oviduct): captures ovulated

ova; site of fertilization

• Uterus: site of embryo development

• Endometrium: lining of uterus

• Cervix: opens into vagina



• Vagina: from cervix to vestibule

• Hymen: membrane covering vaginal

opening

• Vulva: external genitalia

• Labia: skin folds on exterior

• Vestibule: common area where urethra and

vagina open

• Clitoris: contains erectile tissue,

homologous to penis

• Mammary glands: secrete milk


Female reproductive anatomy: oogenesis

Oogenesis: production of ova

• Oogonia: ova stem cells

• Become oocyte and begin meiosis

• Each oocyte surrounded by follicle

• After puberty one oocyte (ovum) is ovulated

each month

• Through meiosis one oogonium produces one

ovum and 2 polar bodies; polar bodies

degenerate


Fig. 46-12g

Primordial germ cell

Mitotic divisions

Oogonium

Mitotic divisions

Primary oocyte(present at birth), arrestedin prophase of meiosis I

Completion of meiosis Iand onset of meiosis II

Secondary oocyte,arrested at metaphase of meiosis II

Firstpolarbody

Ovulation, sperm entry

Completion of meiosis II

Secondpolarbody

Fertilized egg

2n

2n

nn

n

n

In embryo

Human

gametogenesis


Female reproductive anatomy: ovarian cycle

Ovarian cycle: maturation of follicle and release

of ovum every month

• Follicular phase

Follicle grows

Oocyte grows within follicle

• Ovulation

Ovary wall ruptures expelling ovum

• Luteal phase

Corpus luteum: forms from ruptured follicle

If no pregnancy, degenerates in 10 days

If pregnancy: corpus luteum persists

until placenta develops

Maintains early pregnancy

20/48


Fig. 46-12f

Ovary

Primaryoocytewithinfollicle

Rupturedfollicle

Growingfollicle

Mature follicle

Ovulatedsecondary oocyte

Corpus luteum

Degeneratingcorpus luteum

Human

gametogenesis


Female reproductive anatomy: Hormonal regulation

• Hormonal regulation• Follicle stimulating hormone (FSH): stimulates ovarian

follicle to grow

• Luteinizing hormone (LH): stimulates secretion of estrogen

by follicle

LH triggers ovulation and causes development of

corpus luteum

Stimulates secretion of progesterone by corpus luteum

• Estrogen: stimulates proliferative phase of uterine cycle

Stimulates reproductive tract to grow larger and

become functional at puberty

Stimulates development of secondary sex

characteristics at puberty

• Progesterone: stimulates secretory phase of uterine cycle,

maintains pregnancy


Fig. 46-14aControl by hypothalamus Inhibited by combination of

estradiol and progesterone

Stimulated by high levelsof estradiol

Inhibited by low levels of estradiol

Hypothalamus

GnRH

Anterior pituitary

FSH LH

Pituitary gonadotropinsin blood

LH

FSH

FSH and LH stimulatefollicle to grow

LH surge triggersovulation

Ovarian cycle

Growing follicle Maturingfollicle

Corpusluteum

Degeneratingcorpus luteum

Follicular phase Ovulation Luteal phase

(a)

(b)

(c)

Da

ys

0 5 10 14 15 20 25 28| | | | | | | |

–

–

+

The reproductive

cycle of the

human female



Uterine cycle (menstrual cycle): changes in

endometrium each month

• Menstrual phase

Endometrium shed, eliminated from body via vagina

• Proliferative phase

Endometrium rebuilds

Cervical mucus thins, allows passage of

sperm into uterus

Ovulation occurs at end of phase

• Secretory phase

Endometrium prepares for implantation

Uterine glands secrete nutrients for

embryo until implantation

Cervical mucus thickens forming plug

If no pregnancy, endometrium

deteriorates and is shed (menstruation)


Fig. 46-14b

Ovarian hormones in blood

Peak causesLH surge

Estradiol level very low

Estradiol Progesterone

Ovulation Progesterone and estra-diol promote thickeningof endometrium

Uterine (menstrual) cycle

Endometrium

0 5 10 14 20 25 28| | | | | | | |

Days

15

Menstrual flow phase Proliferative phase Secretory phase

(d)

(e)

The reproductive cycle of the human female


Female reproductive anatomy: estrous cycle

• Estrous cycle: • Majority of mammals

In the absence of a pregnancy, the uterus

reabsorbs the endometrium and no extensive

fluid flow occurs

• Mammals with estrous cycle typically copulate

only during the period of estrus (sometimes

called heat), when female is receptive to

mating


Menstrual Versus Estrous Cycles

• Menstrual cycles are characteristic of humans

and some other primates:

– The endometrium is shed from the

uterus in a bleeding called

menstruation

– Sexual receptivity is not limited to a timeframe


• Estrous cycles are characteristic of most

mammals:

– The endometrium is reabsorbed by the

uterus

– Sexual receptivity is limited to a “heat” period

– The length and frequency of estrous cycles

varies from species to species


Menopause

• After about 500 cycles, human females

undergo menopause, the cessation of

ovulation and menstruation

• Menopause is very unusual among

animals

• Menopause might have evolved to allow a

mother to provide better care for her children

and grandchildren - ?


Male Reproductive Anatomy

• The male’s external reproductive organs are

the scrotum and penis

• Internal organs are the gonads, which produce

sperm and hormones, and accessory glands

30/48

Fig. 46-11a

Seminalvesicle(behindbladder)

Urethra

Scrotum

(Urinarybladder)

Prostate gland

Bulbourethralgland

Erectile tissueof penis

Vas deferens

Epididymis

Testis

Fig. 46-11b

Seminal vesicle

(Rectum)

Vas deferens

Ejaculatory duct

Prostate gland

Bulbourethral gland

Vas deferens EpididymisTestisScrotum

(Urinarybladder)

(Urinaryduct)

(Pubic bone)

Erectiletissue

Urethra

Glans

Prepuce

Penis



• Testes: produce sperm

Seminiferous tubules: site of sperm

production

Interstitial cells (Leydig cells): produce

testosterone

• Scrotum: contains testes

• Epididymis: site of sperm maturation, storage

• Ductus deferens (vas deferens): conveys

sperm from epididymis to urethra

• Seminal vesicles: secrete fluid for semen;

contains nutrients



• Prostate gland: contains enzymes, activates

sperm

• Bulbourethral glands: secrete mucus

• Penis: contains urethra and erectile tissue

Glans penis: enlarged tip

Prepuce: loose collar of skin around glans

• Erectile tissue: connective tissue and smooth

muscle with vascular spaces

Vascular spaces fill with blood during erection



• Spermatogenesis: production of sperm

• Spermatogonia: sperm stem cells

After puberty some spermatogonia

become spermatocytes and undergo

meiosis to produce spermatozoa

Through meiosis one spermatogonium

produces 4 spermatozoa


Fig. 46-12b

Epididymis

Seminiferous tubuleSertoli cellnucleus

Testis

Cross sectionof seminiferoustubule

Spermatogonium

Primary spermatocyte

Secondary spermatocyte

Spermatids(two stages)

SpermLumen ofseminiferous tubule

Human gametogenesis


Fig. 46-12cPrimordial germ cell in embryo

Mitotic divisions

Spermatogonialstem cell

Mitotic divisions

Spermatogonium

Mitotic divisions

Primary spermatocyte

Meiosis I

Secondary spermatocyte

Meiosis II

Earlyspermatid

Differentiation (Sertolicells provide nutrients)

Sperm

2n

2n

2n

n n

n n n n

n n n n

Human

gametogenesis


Male Reproductive Anatomy: Hormonal regulation

• Hormonal regulation

• Follicle-stimulating hormone: stimulates

spermatogenesis

• Luteinizing hormone: stimulates interstitial cells to

secrete testosterone

• Testosterone: stimulates spermatogenesis

Stimulates accessory organs to grow and

function

Stimulates development of secondary sex

characteristics at puberty

Responsible for sex drive in males and

females


Fertilization, development, and parturition

• Fertilization: union of sperm and ova producing

zygote

• Cleavage: rapid mitosis following fertilization

Blastocyst formed

Trophoblasts: contribute to placenta formation

Inner cell mass: forms embryonic disc

• Implantation: when embryonic disc reaches

uterus

Trophoblasts adhere to endometrium

Blastocyst burrows in and becomes covered by

endometrial cells


Fig. 46-15

Ovary

Uterus

Endometrium(a) From ovulation to implantation

(b) Implantation of blastocyst

Cleavage

Fertilization

Ovulation

Cleavage continues

The blastocystimplants

Trophoblast

Inner cell mass

Cavity

Blastocyst

Endo-metrium

1

2

3

4

5

40/48


Fertilization, development, and partutrition

• Development: major events

• 1st trimester

Organ systems develop

Limbs develop and ossification begins

Embryo becomes fetus at 8 weeks

• 2nd trimester

Fetus grows

Movement felt by mother

• 3rd trimester

Continued growth


Fig. 46-17

(a) 5 weeks (b) 14 weeks (c) 20 weeks

Human fetal development


Fertilization, development, and partutrition

• Parturition (labor)

• 1. Dilation of cervix

Stretching of uterus causes release of

oxytocin: stimulates uterine contractions

Amnion ruptures, releasing fluid

• 2. Expulsion: delivery of baby

Strong contractions of uterus

• 3. Delivery of placenta

Contractions cause placenta to detach, is

expelled from uterus

Fig. 46-19-1

Placenta

Umbilical cord

Uterus

Cervix

Dilation of the cervix1

Fig. 46-19-2

Expulsion: delivery of the infant2

Fig. 46-19-3

Delivery of the placenta

Uterus

Placenta

(detaching)

Umbilicalcord

3


Lactation

• Lactation

• Prolactin: stimulates milk production to begin

• Oxytocin: stimulates expression of milk


• Spermatogenesis differs from oogenesis:

– In oogenesis, one egg forms from each cycle

of meiosis; in spermatogenesis four sperm

form from each cycle of meiosis

– Oogenesis ceases later in life in females;

spermatogenesis continues throughout the

adult life of males

– Oogenesis has long interruptions;

spermatogenesis produces sperm from

precursor cells in a continuous sequence



Thank you for your attention and participation!


You should now be able to:

1. Distinguish between asexual and sexual reproduction

2. Explain how hermaphroditism may be advantageous to animals that have difficulty encountering a member of the opposite sex

3. Using diagrams, identify and state the function of each component of the male and female reproductive systems

4. Describe oogenesis and spermatogenesis; describe three major differences between them


5. Explain how the uterine and ovarian cycles are synchronized and describe the functions of the hormones involved

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Animal Reproduction - Houston Community College