Chapter 29:
Reproductio
n
and
Development
Asexual Reproduction
Asexual Reproduction: a mode of
reproduction by
which offspring arise from a single parent, and inherit
the genes
of that parent only, it is
reproduction
which does not
involve meiosis or
fertilization
o
Budding: a new individual grows from another
EX: yeast
o Fragmentation and regeneration: an organism is split
into fragments and gives rise to new individuals from
those fragments
EX: Sea star
http://en.wikipedia.org/wiki/Asexual_reproduction
Sexual Reproduction
Sexual Reproduction
Parthenogenesis: modified
sexual reproduction in
which an unfertilized egg
develops into a complete
individual
EX: In honeybees, the queen is
the only fertile female
•
The queen can allow eggs to
be fertilized or unfertilized
•
The fertilized eggs become
diploid female (workers)
•
The unfertilized eggs
become haploid males
(drones)
•
Worker bees are unable to
mate & drones can only
mate w/a queen
Produced gametes (sperm,
eggs) in GONADS (testes,
ovaries)
Zygote results from the
fertilization of an egg by a
sperm
Copulation: sexual union to
facilitate the reception of
sperm by a female
External fertilization: egg and
sperm join outside the body
Oviparous vs Viviparous
Oviparous: egg-laying animals
•
Ovoviviparous: eggs are retained in the body until they
hatch (releasing fully developed offspring)
Viviparous: produce living young
•
These animals have placenta, which allows the exchange
of materials with the mother internally
Male Reproductive System
Testes: developed inside abdominal cavity and descend
during puberty
o
o
•
Sterility by body temperature if not descend (2-3°
lower than body temperature)
•
Sperm development only after puberty
Semen (seminal fluid): a thick, whitish fluid that contains
sperm and secretions from 3 glands
•
-
•
Epididymis: maturation of sperm in coiled tubule
Vas deferens: a tube on both testis that propels sperm
from the epididymis to the urethra
•
o
Penis: a cylindrical organ consists of spongy, erectile tissue
•
Increased blood flow fills the blood spaces and
causes erection
•
Drugs such as Viagra, Cialis, and Levitra work by
increasing blood flow to the penis to achieve
erection
Seminal vesicles is found at the base of the
bladder
Prostate gland is found just below the bladder
-
Secretes a milky alkaline fluid to activate or
increase motility of the sperm
-
Also, neutralize the acidic environment of the
vagina
Bulboerethral glands are a plair of small glands
found on either side of the urethra and below
the prostate
-
o
Secrete a thick, viscous fluid containing
nutrients for use by the sperm
Produce mucous secretions with a lubricating
effect
Phases of ejaculation:
1.
Emission: muscular contractions causing sperm
to enter the ejaculatory duct
•
2.
Brought about by nerve impulses from the
spinal cold to the epididymides and vas
deferentia
Expulsion: rhythmic contractions of muscles at
the base of the penis and within the urethral wall
expel semen in spurts from the urethra
•
The contractions that expel semen from the
penis are a part of male orgasm
•
No multiple orgasm due to refractory period
Testes
Spermatogenesis: the process of sperm cell development involving the
reduction of chromosome number from diploid (2n) to haploid (n)
•
•
o
Occurs in the seminiferous tubules of the testes
Spermatogonium (2n)  primary spermatocyte (2n)  secondary
spermatocyte (n)  spermatids (n) ------ sperm
Sertoli cells are also found in the testes
•
They support, nourish, and regulate the production of sperm
o
A sperm has a head (capped by an acrosome), a middle piece
(containing many mitochondria), and a tail (a flagellum that allows
sperm to swim).
o
In a normal human male, ejaculated semen contains 40 million
sperm per milliliter, but only one sperm normally enters an egg.
Hormonal Regulation
The hypothalamus control the testes
by secreting gonadotropin-releasing
hormone (GnRH), which stimulate
the anterior pituitary to produce
gonadotropic hormones: LH and FSH
Luteinizing hormone (LH) controls
the production of testosterone by
stimulating the interstitial cells
scattered between the seminiferous
tubules.
•
The interstitial cells produce
testosterone
Follicle-stimulating hormone (FSH)
promotes spermatogenesis in the
seminiferous tubules.
Testosterone: the main sex hormones
in males
•
•
•
Essential for the normal
development and functioning of
sex organs
Necessary for the maturation of
sperm
Maintains secondary sex
characteristics during puberty
•
Growth in height, broader
shoulders, longer legs, deeper
voice due to larger larynx with
longer vocal cords, facial hair,
body hair, and greater muscular
development.
Female Reproductive System
Oviducts aka Fallopian tubes
•
•
•
o
Extend from the ovaries to the uterus
(not attached to ovaries)
Fimbrae (finger-like projections) of
the oviducts sweep over the ovaries
Ovulation: secondary oocyte is
expelled and fimbrae sweep it into
the oviduct to the site of fertilization
in the ampulla)
Uterus: thick-walled organ the size and
shape of an inverted pear
•
Embryo completes its development
after implantation in the uterine
lining (endometrium)
Ovaries: responsible for the production
of eggs
•
•
•
•
•
Oogenesis starts with an oogonium
(2n)  primary oocyte
(2n)secondary oocyte (n)  egg (n)
The oogonium undergoes mitosis to
make a primary oocyte
Primary oocyte undergoes meiosis I to
give secondary oocyte
Secondary oocyte undergoes meiosis
II and combining with fertilization to
arrive at an egg
An ovary contains many primary
follicles (2 million but will reduce to
300,000-400,000 by puberty)
-
o
Vagina: 45° angle w/ the body’s vertical
axis
•
Muscular lining of the vagina lies in
folds and vagina can expand (serves as
birth canal)

Only 400 primary follicles will ever
mature and produce secondary oocyte
A follicle that has lost its oocyte
develops into a CORPUS LUTEUM
-
Corpus luteum will degenerate if not
pregnant
Ovarian Cycle
Follicular Phase
•
•
•
FSH promotes the
development of follicles that
secrete estrogen
The increase in estrogen will
cause an LH spike, which
induce ovulation at day 14
High estrogen also feedback
inhibit FSH so that FSH
levels will decrease
Luteal Phase
•
•
•
LH promotes the
development of the corpus
luteum, which secretes
progesterone
Progesterone promotes and
maintain thickness of the
endometrium (preparing for
the implantation of the
embryo)
If no pregnancy, the corpus
luteum degenerate bc there
is no hCG to maintain the
corpus luteum as the level of
LH decline due to feedback
inhibition from the high
level of progesterone
Menstrual Cycle
Days 1-5: female sex hormones at low level causing the endometrium to
disintegrate and blood vessels rupture
•
o
Menstruation occurs
Days 6-13: increased production of estrogen by ovarian follicles causes
endometrium to thicken and become vascular
•
Proliferative phase of the menstrual cycle
o
Day 14: Ovulation
o
Days 15-28: increased production of progesterone by the corpus luteum causes
endometrium to double in thickness and the uterine glands to mature
•
•
Secretory phase: producing thick mucoid secretion in preparation for receiving the
embryo
No fertilization: LH will decrease due to feedback inhibition by progesterone and
corpus luteum degenerate (leading to decreased progesterone)
Control of Reproduction and
Infertility
Abstinence
Contraceptive Vaccines
1.
Oral contraception
o
•
E and P pills shut down anterior pituitary
from making LH and FSH
•
No follicle development in ovary and no
ovulation
Synthetic progesterone capsule prevent
ovulation
Barrier methods
•
o
P and E injections have the same effect as
the pills
o
Preven: kit of 4 synthetic progesterone to
prevent implantation
•
Mifepristone: RU-486 blocking
progesterone receptor proteins to prevent
implantation
Infertility
•
Lack of pregnancy after 1 yr of unprotected
sex
•
Due to low sperm count, abnormal sperm
Contraceptive implants
•
o
•
Contraceptive injections
•
o
2.
Vaccine against hCG (hormone necessary
for maintaining endometrial thickness and
implantation)
Morning After
Condoms, cervical cap, and diaphragms
prevent fertilization of an egg by a sperm
Intrauterine device
•
Insertion of a device into the uterus and
alter the environment of uterus or oviducts
to prevent fertilization and implantation
(caused by sedentary lifestyle, smoking, etc.)
•
Female infertility can be caused by
1.
Polycystic Ovary Syndrome: many cysts
but no functioning follicles and no
ovulation
2.
Pelvic inflammatory disease: damage to
oviducts and blocking fertilization or
causing ectopic pregnancy
Assisted Reproductive
Technologies
Artificial Insemination
•
Sperm are collected, concentrated, and deposited in vagina
In vitro fertilization
•
•
Immature eggs are brought to maturity before concentrated sperm are
added
Conception outside of the body
Intracytoplasmic Sperm Injection
•
A single sperm injected into an egg and transferred to uterus to be
implanted
Gamete Intrafallopian Transfer (GIFT)
•
Eggs and sperm are placed in oviducts and fertilization occurs there
S.2 Phases of HIV infection
Phases of HIV infection
Category A:
Asymptomatic but highly infectious
CD4 count above 500 cells/mm3
Drug therapy can keep patients in this phase indefinitely (Magic Johnson)
Category B:
One or more related to an impaired immune system
•
Swollen lymph nodes, weight loss, fever, fatigue, night sweat, thrush, herpes recur
CD4 count between 200-499 cells/mm3
Patient dies 6-8 yrs after infection
Category C:
Full-blown AIDS
At this point the person has AIDS in which they have one or more of the AIDS
opportunistic infections that eventually is the cause of death
CD4 count has fallen below 200 cells/mm3
Patient dies 7-9 yrs after infection
S.2 Phases of HIV infection
Phases of HIV infection
S.3 HIV structure and life cycle
Structure of HIV
Two single strands of RNA
Enveloped with spikes
(Gp120)
Carries 3 enzymes
Reverse transcriptase
Integrase
Protease
S.3 HIV structure and life cycle
Transmission and prevention of HIV
Transmission is through sexual contact, dirty
needles, a blood transfusion or to a baby from their
mother
Globally heterosexual sex is the most common
mode of transmission
HIV is not passed through casual contact
Prevention is through abstinence, sex with only one
uninfected partner and proper, consistent use of
condoms
Bacterial Infections
• Chlamydia.
– Leading sexually transmitted disease in
the US.
•Usually asymptomatic to mild burning
sensation on urination.
– Risk of spreading from the cervix to the
oviducts and into pelvic inflammatory disease.
» Usually treated with a single dose of
antibiotics.
Bacterial Infections
• Gonorrhea.
– Affected individuals often have a secondary infection
with Chlamydia.
•Asymptomatic to pain on urination and milky urethral
discharge within 3-5 days.
– Usually cured with antibiotics.
– If a pregnant woman has gonorrhea, she may give the
infection to her baby as the baby passes through the
birth canal during delivery. This can cause blindness,
joint infection, or a life-threatening blood infection in
the baby.
Pelvic Inflammatory
Disease
In women, gonorrhea is a common cause of pelvic inflammatory
disease (PID).
When symptoms are present, they can be very severe and can include
abdominal pain and fever.
PID can lead to internal abscesses (pus-filled “pockets” that are hard to
cure) and long-lasting, chronic pelvic pain.
PID can damage the fallopian tubes enough to cause infertility or
increase the risk of ectopic pregnancy.
Ectopic pregnancy is a life-threatening condition in which a fertilized egg
grows outside the uterus, usually in a fallopian tube.
In men, gonorrhea can cause epididymitis, a painful condition of the
testicles that can lead to infertility if left untreated.
Gonorrhea can spread to the blood or joints. This condition can be
life threatening.
Some of these complications are also seen in Chlamydia
Bacterial Infections
• Syphilis.
– Three stages.
•Primary stage - Hard chancre
•Secondary stage - Rash
•Tertiary stage - Weakened arterial walls
– Prompt and adequate treatment is critical for control
» Treatment is a form of penicillin
Viral Diseases
Herpes.
Herpes Simplex Virus Type 1
Cold sores and fever blisters around the mouth
Herpes Simplex Virus Type 2
Herpes infection of the genitals
Asymptomatic to tingling and itching prior to
blistering
May be reccurring due to stressors. Both type I and type
II viruses hide in nerves until stimulated
Presently no cure
Varicella-zoster Virus. Also hides in nervous
system
Causes chicken pox –vaccine is avaliable
can later remerge as shingles
Genital Warts
• Human papillomaviruses cause many forms of
warts, including genital warts
– Commonly seen on the penis and near vaginal
opening
•Associated with cervical cancer
– Presently no cure
» Effective treatment relies on various forms of wart removal
•Vaccine is now avaliable
Other STDs
Trichomoniasis
•
•
o
Caused by a protozoan
Asymtomatic male is usually the reservoir of infection
Yeast infection
•
•
•
•
Caused by candida albicans
Normal organism in vagina
Birth control increases yeast infections
Use of antibiotics elsewhere can alter normal balance of
organism
Fertilization
Fertilization requires the sperm and secondary oocyte to interact
Results in a ZYGOTE
Zona pellucida surrounds the secondary oocyte; follicle cells
surround the zona pellucida and secondary oocyte
Acrosomal enzymes on the sperm’s head digest the zona pellucida
and it binds and fuses to the secondary oocyte’s plasma membrane
•
o
The nucleus enters and the secondary oocyte completes meiosis
II and become an egg
Zona pellucida hardens to prevent the binding and penetration of
additional sperm
Early Embryonic Development
1st 2 mos. are considered the embryonic period
•
6 days of development occur in oviducts before implantation into the uterine lining (endometrium)
Following fertilization, the zygote undergoes cleavage (cell division without growth)
•
•
•
DNA replication and mitotic division occur repeatedly and cells get smaller w/ each division
Cleavage only increase the number of cells not the original volume of the egg cytoplasm
A MORULA (tightly packed ball of cells) is form
o
The cells of the morula divide and secrete fluid, resulting in the formation of a BLASTOCYST (a
hollow ball of cells)
o
Cells in the inner cell mass will become the embryo
o
The outer cell mass becomes the chorion, which will help in the development of the placenta
o
The PLACENTA forms and secretes hCG
•
•
hCG maintains the corpus luteum, which produces progesterone to maintin the endometrium
No ovulation and menstruation during pregnancy
Later Embryonic Development
3rd week: primitive streak appears
Gastrulation produces the 3 germ layers
•
•
•
o
Endoderm: epithelial lining of GI, respiratory tract, and urinary
bladder
Mesoderm: cardiovascular, skeletal, muscular, reproductive,
urinary, respiratory, and digestive systems
Ectoderm: nervous system, parts of the eye, epidermis of skin
and epithelial lining of oral and rectum
Amnion: embryonic membrane that surrounds the developing
embryo and later fetus
•
Encloses amniotic fluid which offers protection from sudden
blows, allows freedom of fetal movement, maintains constant
temperature, prevents drying out and assists in lung development
Neurulation
CNS (central nervous system) is the first to develop
Mesoderm forms a supporting rod, the NOTOCHORD
•
•
The notochord induce the thickening of cells (neural plate) from
midline ectoderm
Neural folds develop on either side of neural groove and fuse to form a
NEURAL TUBE
-
•
•
•
Anterior becomes brain
Posterior become spinal cord
Midline mesoderm cells not contributing to notochord gives rise to
somites, later become vertebrae and muscles associated with axial
skeleton
Neural crest cells migrate and form skin, adrenal medulla, and ganglia
Embryo is 2mm long at 3rd week
Organ Formation
5th wk: limb buds appear, head enlarges, and sense organs become
more prominent
(can make out ears, eyes, and nose)
o
Umbilical cord developed from a bridge of mesoderm called BODY
STALK
•
•
o
Umbilical cord connects the developing embryo to the placenta
Allantois is also contained w/in this stalk and its blood vessels become
the umbilical blood vessels
6-8 wks: brain development, neck region develop (making the head
distinct from the body)
•
•
The nervous system is developed well enough to permit the reflex
actions, such as a startle response to touch
Embryo weighs about an aspirin and 38mm long
Placenta
The placenta inner membrane faces the chorion and outer
membrane faces the uterine tissues
Chorionic villi are surrounded by maternal blood
•
•
Maternal and fetal blood never mix because exchange always
takes place across the walls of villi
Umbilical cord stretches between placenta and fetus
•
•
Umbilical blood vessels take fetal blood to and from the
placenta
Harmful chemicals can cross the placenta
•
•
E.g. alcohol, drugs, tobacco
These can alter the normal development and cause birth
defects
Fetal Development and Birth
3rd-9th months
Extreme increase in size, weight increase by 600x and 50 cm in length
Genitalia appear in 3rd mos
Hair, eyebrows, eye lashes, fingernails and toenails
10 wks: fetal heartbeat can be heard using a stethoscope
Movements occur at about 4th month
5th month: fine downy hair covers limbs and trunk
Vernix caseosa (cheese-like substance) covers and protects the wrinkly skin from amniotic
fluid
Baby can survive if born at 22wks, although lungs still under-developed
Stages of Birth
Fetal hypothalamus causes pituitary to stimulate adrenal cortex to produce
androgen
Placenta uses androgens as precursors for estrogen
Estrogen then stimulate the production of oxytocin and prostaglandins
Estrogen, oxytocin, and prostaglandins cause uterus to contract and expel the
fetus
Stages:
1.
Cervix dilates to allow the passage of the fetus
(amnion bursts at the same time…water breaks)
2.
3.
Baby is born, umbilical cord is cut
Placenta (afterbirth) is delivered (expelled)