Chapter 27
REPRODUCTION
Asexual versus Sexual Reproduction
Asexual Reproduction: A single parent gives rise to
two or more offspring by:
 Fission
(Splitting): One individual splits into two or
more of about equal size.

E.g.: Bacteria, sea anemone.
 Budding:
New individual(s) are generated from a
portion of the parent and are smaller than parent.

E.g.: Many plants, budding yeast.
 Fragmenting:

Can regenerate body parts.
E.g.: Sea stars when cut into several pieces will regenerate
into several new star fish.
“Virgin development”. Unfertilized
egg develops into an adult animal. Adaptation for
stressful times.
 Parthenogenesis:


Whiptail lizard
Several insects
Asexual versus Sexual Reproduction
Sexual Reproduction:
 The
most common type of animal reproduction.
 Occurs through the fusion of gametes (sperm and egg).


Male: Produces sperm cells. Small and motile, propels itself
by whiplike flagellum.
Female: Produces eggs (ova). Large and nonmotile.
 Zygote:
Egg cell fertilized by a sperm cell.
Fertilization: Creation of zygotes by fusion of ova
and sperm cells. Two types:
 Internal
Fertilization: Gametes fuse inside the female’s
body.


Usually requires copulation (intercourse) in which male
delivers sperm directly into body of female.
Practiced by most terrestrial animals, aquatic reptiles, birds,
and mammals.
Asexual versus Sexual Reproduction
 External
Fertilization: Gametes fuse outside the
female’s body.



Mating partners release eggs and sperm simultaneously into the
water.
Practiced by most aquatic animals: fish, amphibians.
Many eggs are lost and eaten by predators. Therefore, many
must be made and released for a few to survive.
Hermaphroditism:
 A single
individual produces both sperm and eggs.
 Some such as the tapeworm are capable of selffertilization.
 Others (e.g.: earthworm) must mate with other animals.
 In some species self-fertilization is prevented by
development of testis and ovaries at different times.
 Used by “solitary” animals.
Advantages of Sexual Reproduction:
 Genetic
diversity among offspring.
 If environment changes drastically, the population
may survive if a few individuals have genetic traits
that allow them to adapt to changes.
Disadvantages of Sexual Reproduction:
 Need
to invest considerable time, resources, and
energy searching for suitable mate.
 Only pass on 50% of your genetic material to each
offspring.
Advantages of Asexual Reproduction:
 Don’t
need to invest time and energy searching for
suitable mate.
 Replicates a given genotype rapidly and precisely.
 Pass on 100% of your genetic makeup to each
offspring.
 Useful for organisms well adapted to a stable
environment.
Disadvantages of Asexual Reproduction:
 No
genetic diversity among offspring.
 If environment changes drastically, the entire
population may die out.
Reproductive System of Humans
Reproductive Functions of Female:
 Produces
eggs (ova)
 Receives sperm
 Incubates and nourishes the embryo and fetus
 Gives birth
 Produces milk for young
All of these processes are regulated and coordinated
by hormones secreted by:
 Hypothalamus
 Pituitary
 Ovaries
gland (anterior portion)
Endocrine Glands Regulate Sexual Functions
Reproductive System of Humans
Major Organs of Female Reproductive System:
 Ovaries: Produce ova (oogenesis) and sex
hormones.
 Size
and shape of large almonds.
 Located close to lateral walls of pelvic cavity and held
in place by connective tissue.
 Mainly connective tissue containing scattered eggs
(ova) in different stages of development.
 Follicles: A single egg with surrounding cells that
nourish and protect it.


Women are born with all of their follicles (40,000 to 400,000).
Only a fraction of follicles release eggs during a woman’s
reproductive life.
Frontal View of Female Reproductive System
Side View of Female Reproductive System
Female Reproductive System:
 Ovulation & Oogenesis: After puberty, each month
one immature egg (oocyte), is released from ovary.
 Each
follicle contains a primary oocyte, arrested in
prophase I of meiosis.
 Pituitary hormones FSH (follicle stimulating hormone)
and LH (luteinizing hormone) cause a follicle to enlarge
and complete meiosis I.
 One large cell (secondary oocyte) and a tiny cell (polar
body) are produced.
 LH (luteinizing hormone) causes the secondary oocyte to
be released by the ovary during ovulation.
 Oocyte will not finish meiotic division, until fertilized.
 In the end, one large ovum (egg) and 3 small polar bodies
are made from oogenesis.
Oogenesis and Ovary Structure
Major Organs of Female Reproductive System:
 Oviducts (Fallopian Tubes): Transport the egg
from the ovary to the uterus.
 Peristalsis
of smooth muscle in oviduct and beating of
cilia, help the egg move along.
 Fertilization occurs in the first third of oviduct.
 Scarring of oviducts is a common consequence of
sexually transmitted diseases: chlamydia and
gonorrhea.
 Ectopic Pregnancy: Fertilized egg does not reach the
uterus. Usually starts to develop in oviduct.




Usually due to a blocked oviduct.
Occurs in 1% of all pregnancies in the U.S.
Must be surgically removed.
May cause death and severe hemorrhage.
Fertilization Occurs in the Oviducts
Ectopic Pregnancy of Twins
Ectopic pregnancies occur in about 1% of pregnancies in U.S.
and usually require surgical removal of embryos.
Reproductive System of Humans
Major Organs of Female Reproductive System:
 Uterus: Incubates the embryo/fetus.
 Size
of a fist, in center of pelvic cavity.
 Oviducts open into upper corners of uterus.
 Has thick walls of smooth muscle (myometrium)
responsible for uterine contractions and cramps.
 Endometrium: Inner mucous lining, which thickens
each month in preparation for pregnancy.
 If fertilization does not occur, endometrium breaks
down and is discharged during menstruation.
 If fertilization occurs, the egg implants in the
endometrium which supports its growth until the
placenta develops.
The Uterus Incubates and Nourishes the Fetus
Reproductive System of Humans
Major Organs of Female Reproductive System:
 Cervix: Lower portion of the uterus, which
projects into the vagina.
 Pap
smear: Examination of cervical tissue to detect
abnormalities. Recommended yearly.
 Cervical cancer: Most cases caused by a viral
infection with human papillomavirus.
 Women are infected through intercourse with
asymptomatic male.
 Takes about 20 to 30 years to develop.
 Men don’t appear to be affected.
Reproductive System of Humans
Major Organs of Female Reproductive System:
 Vagina: Thin walled, muscular chamber.




Vulva: External structures.






Receives the sperm and penis
Acid pH kills bacteria and sperm cells
Part of birth canal
Clitoris: Equivalent to male penis.
Labia minora: Skin folds that border vaginal opening.
Labia majora: Protect entire genital region.
Hymen: Ring of tissue that forms a border around vaginal
entrance. No known function.
Bartholin’s gland: Secrete lubricating fluid during sexual arousal.
Breasts: Lactation
Female Hormones Controlling Reproduction

Follicle Stimulating Hormone (FSH)



Luteinizing Hormone (LH)





Secreted by pituitary gland
Stimulates growth of follicle and completion of meiosis I
Induces ovulation
Promotes development of corpus luteum and hormone secretion.
Estrogen





Secreted by pituitary gland
Stimulates growth of ovarian follicle
Secreted by ovarian follicle
Low levels inhibit FSH and LH secretion
High levels stimulate FSH and LH secretion
Promotes growth of endometrium
Progesterone and Estrogen



Secreted by corpus luteum
Maintain endometrium, sharp drop causes menstruation
High levels inhibit inhibit FSH and LH secretion
Female Menstrual Cycle: Approximately 28 days.
 Menstruation: Day 1 of cycle.




Pre-Ovulatory phase: Starts around day 5 of cycle.


Rising estrogen levels cause the endometrium to start thickening.
Ovulation: Occurs around day 14 of cycle.




Walls of endometrium break down.
Caused by falling levels of progesterone and estrogen.
Lasts 3 to 7 days.
FSH stimulates growth of ovarian follicle.
LH causes follicle to finish meiosis I (secondary oocyte) and to be
released by ovary.
Corpus luteum: Starts to secrete estrogen and progesterone.
Post-ovulatory Phase: Starts around day 15.



Endometrium continues to grow in response to rising estrogen and
progesterone.
If no fertilization occurs, corpus luteum degenerates and
menstruation occurs.
If fertilization occurs, embryo maintains corpus luteum.
Stages of Female Reproductive Cycle
Reproductive System of Humans
Reproductive Functions of Male:
 Produces
sperm
 Delivers sperm to female reproductive tract
All of these processes are regulated and coordinated
by hormones secreted by:
 Hypothalamus
 Pituitary
gland (anterior portion)
 Testes (Sing. Testis)
Side View of Male Reproductive System
Front View of Male Reproductive System
Major Organs of Male Reproductive System:
 Testes: Paired male gonads.
 Produce
sperm through spermatogenesis, which
produces four sperm cells of equal size.
 Spermatogenesis occurs in a vast system of hollow
tubes called seminiferous tubules.
 Each mature sperm has a head, a midpiece, and a
flagellum.
 Sperm head has an acrosome, which produces
enzymes that help it penetrate the egg.
 Human sperm cannot develop at body temperature.
 Testicles descend from abdominal cavity into scrotum,
a skin covered sac, about two months before birth.
 Undescended testicles (cryptorchidism) may cause
infertility.
Spermatogenesis Occurs in Seminiferous
Tubules of Testes
Sperm Cell Structure
Reproductive System of Humans
Major Organs of Male Reproductive System:
 Epididymus:
 Large
coiled tube (23 ft long) that surrounds testes.
 Stores sperm while they develop fertilizing ability and
motility (about 20 days).
 During ejaculation, sperm cells are propelled from
epididymus.

Vas Deferens:
 Long
muscular ducts from scrotum to back of bladder.
 During ejaculation, the sperm pass from epididymus
into these two ducts.
 Vasectomy: Each vas deferens is cut to prevent sperm
from entering urethra.
Reproductive System of Humans
Major Organs of Male Reproductive System:
 Ejaculatory Duct:
 Short

duct after two vas deferens ducts unite.
Urethra:
 Deliver sperm
to the exterior.
 In males, urine and sperm pass through the urethra.
 Females have a separate urethra from the
reproductive system.
Reproductive System of Humans
Major Organs of Male Reproductive System:
Accessory Glands: Produce semen.
 Functions
of semen:
 Activate sperm cells
 Provide nutrients for motility
 Counteract acidity of vagina and male urethra
 Stimulate contractions of female reproductive tract
 Antimicrobial action
 Ejaculation volume 4 to 5 ml.
 One ejaculation has 50-500 million sperm cells
 Sperm cells account for less than 5% of semen volume.
 Secretions from 3 different accessory glands make up
the rest of the volume: Seminal vesicles (2), prostate,
and bulbourethral glands (2).
Major Organs of Male Reproductive System:
Accessory Glands:
A. Seminal vesicles (2): Secrete fluid that nourishes
sperm.
 Contribute
about 60% of semen volume.
 Thick, clear, alkaline fluid.
 Contains:



Fructose: Provides energy for sperm motility.
Prostaglandins: Stimulate smooth muscle contractions of
female and male reproductive tracts.
Fibrinogen: Forms temporary clot in vagina.
 Sperm
cells become highly motile when mixed with
this fluid.
Accessory Glands:
B. Prostate gland: Produces a thin milky secretion.
 Largest
of semen secreting glands.
 Contributes 30% of semen volume.
 Produces an antibiotic that may prevent urinary tract
infections in men.
 Benign (noncancerous) prostate enlargement is
common among older men.


50% of men over 40.
Almost all men over 70.
 Prostate
cancer is the second leading cause of cancer
and cancer deaths in men.




Over 330,000 new cases/year and 40,000 deaths.
Average age at diagnosis: 72
Detected by blood test or digital rectal exam.
Treated surgically or with drugs to reduce prostate size or
activity.
Benign Prostate Enlargement Usually
Procedes Prostate Cancer
Normal prostate is 2 to 3 cm in diameter
Major Organs of Male Reproductive System:
Accesory Glands:
C. Bulbourethral glands (2): Release a mucous
secretion that lubricates penis and facilitates its
entry into vagina.
 Pair
of small glands below the prostate.
 Contribute 5-10% of semen volume.
 Before ejaculation secrete a clear mucus that
neutralizes acid from remaining urine in urethra.
 Bulbourethral fluid also carries some sperm that is
released before ejaculation. One cause of high failure
rate of withdrawal method.
Major Organs of Male Reproductive System:
 Penis: Copulatory organ that delivers sperm to
female body.
 Composed
of three cylinders of erectile tissue.
 During sexual arousal, the penis fills with blood from
the arteries.
 Erection is essential for penetration.
 Impotence is the inability to maintain an erection.


May be caused by alcohol, drugs, illness, and/or emotional
problems.
Viagra acts by relaxing smooth muscle of penis blood vessels,
allowing blood to enter erectile tissue.
 Penis


structure:
Shaft: Long cylinder with thick skin.
Glans: Enlarged tip of penis. Thin skin, covered by prepuce
or foreskin.
Fertilization: Sperm Cell Penetrates
Egg with Acrosomal Enzymes
Fertilization and Early Embryonic
Development
Developing Embryo is Nourished by
Placenta
Pregnancy and Human Development
 Gestation:
In humans starts at conception and
lasts approximately 38 weeks (266 days).
 Due date typically 40 weeks after last
menstruation.
 First Trimester: By the end of week 13
 Sex
distinguished externally
 Fetus weighs about 150 grams
 Second


Trimester: By the end of week 26
Fetus weighs about 1000 g
May survive if born at this point.
 Third
Trimester: By the end of week 38
 Fetus
weighs about 3500 g (7 ½ lb.)
 Testes have descended in males.
Critical Stages of Embryonic and
Fetal Development
Childbirth (Labor) and its Three Stages
Hormonal triggers:
 Rising
estrogen levels causes the formation of oxytocin
receptors on smooth muscle of uterus.
 Oxytocin is secreted by fetal cells and mother’s pituitary.
 Prostaglandins are released by placenta.
Stages of Childbirth
 First


Stage: Dilation
Cervix opens from 1 cm to 10 cm.
Lasts several hours or days.
 Second


Strong uterine contractions every 2 to 3 min push baby through
birth canal.
Lasts 20 min to a couple of hours.
 Third

Stage: Expulsion
Stage: Delivery of placenta (afterbirth)
Usually within 15 minutes of delivery
Labor Contractions Are Induced by
Several Hormones
Birth of Human Child Requires
Dilation of Cervix
Different Contraceptive Methods
1. Prevent Release of Gametes:
 Birth
control pill (combination): Prevents ovulation
2. Prevent Fertilization









Vasectomy: Male sterilization
Tubal ligation: Female sterilization
Minipill: Progestin only, blocks cervical opening
Norplant implant: Releases progestin for 5 years
Rhythm (calendar): Avoid intercourse around ovulation
Withdrawal: Remove penis before ejaculation
Condom: Latex or sheepskin barrier
Diaphragm, cervical cap: Block cervical opening
Spermicide: Kill sperm cells
3. Prevent Implantion


Intrauterine device (IUD)
Morning after pills
Effectiveness of Methods of Contraception
Effectiveness of Methods of Contraception
Incidence (New Cases) of Sexually
Transmitted Diseases in the U.S. (1996)
Reproductive System Diseases
1. Gonorrhea
 Characteristics:
Acute infection of urethra, anus, vagina,
cervix, and fallopian tubes.
Yellow foul discharge (more common in men).
Causes pelvic inflammatory disease (PID) in women.
Major cause of infertility in both men and women.
May also result in throat and eye infections.
In a large percentage of cases, symptoms are mild or
absent.
 Pathogens: Neisseria gonnorrhoea (bacterium).
 Transmission: Direct sexual or mucous membrane
contact.
Mother to infant transmission during childbirth.
 Incubation period: 2 to 7 days.
Gonorrhea: Acute Urethral Infection
Typical discharge in male with gonorrhea.
Source: Tropical Medicine and Parasitology, 1995
Gonorrhea: Eye Infection in Newborn
Ophtalmia neonatorum caused by Neisseria gonorrheae
Source: Microbiology Perspectives, 1999
1. Gonorrhea (Continued)
 Epidemiology
: Up to 500,000 new cases/year in U.S.
 Control:
Use of condoms, avoid sexual contact with
infected individuals.
Vaginal and cervical cultures of pregnant women.
 Treatment:
women.
Antibiotics. Erythromycin for pregnant
2. Syphilis
Characteristics: Disease occurs in three stages:
1. Primary stage: Painless lesion (chancre), which
disappears after several days.
2. Secondary stage: Skin rash with fever and mucous
membrane lesions.
Typically followed by a long latent period.
3. Tertiary stage: Extensive damage to central nervous
system, cardiovascular system, bones, sense organs,
visceral organs, and other sites.
 Pathogens:
Treponema pallidum (bacterium).
Syphilis: Primary and Secondary Stage Lesions
Primary syphilitic chancre and secondary rash.
Source: Tropical Medicine and Parasitology, 1997
Syphilis: Secondary Stage Rash
Secondary syphilitic rash.
Source: Tropical Medicine and Parasitology, 1997
Syphilis: Tertiary Stage Lesions
Syphilis, Gumma: Large rubbery ulceration of anterior tongue
in a patient with tertiary syphilis.
Source: A textbook of oral pathology, 1983.
Syphilis: Advanced Tertiary Stage Lesions
Severe gumma lesions in tertiary syphilis.
Source: Tropical Medicine and Parasitology, 1997
2. Syphilis (Continued)
 Transmission:
Direct contact with lesions, body
secretions, blood, semen, saliva, vaginal discharges;
usually during sexual contact.
Mother to infant transplacental transmission (congenital
syphilis).
Blood transfusions.
 Incubation period: 10 days to several weeks.
 Epidemiology : Over 80,000 new cases/year in U.S.
 Control: Use of condoms, avoid sexual contact with
infected individuals. Blood tests (VDRL) for high risk
individuals.
 Treatment: Antibiotics, long acting penicillin G,
tetracycline, etc.
Congenital Syphilis Causes Teeth and Bone Defects
Congenital Syphilis with Hutchinson incisors.
Source: Physical evaluation of the dental patient, 1982.
3. Chlamydia
 Characteristics:
Painful urination, watery discharge,
salpingitis, and pelvic inflammation in women.
Symptoms may be mild or absent, especially in women.
Common cause of sterility in both men and women.
Newborns may develop eye infections and pneumonia.
 Pathogens: Chlamydia trachomatis.
 Reservoir: Humans.
 Transmission: Direct sexual contact or mother to infant
transmission during childbirth.
 Incubation period: 2 to 3 weeks. May be asymptomatic.
 Epidemiology : Up to 1 million new cases/year in U.S.
Most common sexually transmitted disease in U.S.
 Control: Use of condoms, avoid sexual contact with
infected individuals. Prophylactic treatment of contacts
and pregnant women.
 Treatment: Antibiotics.
Both Chlamydia and Neisseria gonorrhea
Cause Salpingitis
Chlamydia Infections: Inflammation of eyelid
Source: Microbiology Perspectives, 1999
4. Candidiasis (Yeast Infection)
 Characteristics:
Painful irritation and inflammation of
vagina and vulva in women. Redness and intense
itching. White vaginal discharge.
May cause infections of mouth, throat, and rectum in
immunocompromised patients.
 Pathogen:
Candida albicans (yeast), part of normal flora
of mucous membranes.
 Reservoir:
Humans.
 Transmission:
Opportunistic pathogen.

Antibiotic treatment

Weakened host: stress, diet, or illness.
 Incubation
period: 2 to 3 weeks. May be asymptomatic.
 Epidemiology
 Treatment:
: Millions cases/year in U.S.
Antifungal medication.
Oral candidiasis in an AIDS patient
Source: Atlas of Clinical Oral Pathology, 1999
5. Herpes Simplex 1 & 2
Characteristics:
 Herpes
Simplex 1 (Oral Herpes): Recurring painful
blister lesions that form mainly on lips, but may be
found in other areas of body. In immunocompromised
patients may have extensive lesions on tongue and inside
mouth.
 Herpes
Simplex 2 (Genital Herpes): Recurring painful
blister lesions in genital and/or rectal areas.
 Pathogens:

Human Herpes Virus 1: Oral Herpes.

Human Herpes Virus 2: Genital Herpes.
 Reservoir:
Humans.
 Transmission:
Kissing, touching lesions, sexual contact.
Oral Herpes: Recurrent Herpes Labialis
Less than 1 day with
erythema and burning
Same patient 24 h later with multiple
fluid filled vesicles and erythema
Source: Atlas of Clinical Oral Pathology, 1999.
Oral Herpes: Recurrent Herpes Labialis
Recurrent Herpes Labialis: Bilateral vesicles on upper and lower lips.
Source: Atlas of Clinical Oral Pathology, 1999.
Oral Herpes: Chronic Atypical Lesions
Chronic Herpes Simplex infection with lesions on tongue and lips
Source: Atlas of Clinical Oral Pathology, 1999.
Genital Herpes
Herpes simplex 2 infection with fluid filled vesicles on penis.
Source: Mike Remington, University of Washington Viral Disease Clinic
Genital Herpes
Acyclovir resistant peri-rectal HSV2 infection in HIV infected male.
Source: AIDS, 1997
5. Herpes Simplex 1 & 2
 Incubation
period: Several days to weeks. May be
asymptomatic.
 Epidemiology
: Millions cases/year in U.S.

Oral Herpes: Up to 70% of population is infected. Many have
no symptoms.

Genital Herpes: Up to 20% of population is infected. Many
have no symptoms. Others have recurring lesions several times
a year.
 Treatment
and Prevention: No cure. Infection is for
life. Antiviral medications (acyclovir) decrease
frequency and severity of outbreaks.
Women with genital herpes should deliver by cesarean
section to avoid infecting newborn. Neonatal herpes is
very serious and can be deadly.