Topics 6.6 & 11.4
Fertilization
 For sexual reproduction to take place, the male gamete
(sperm) must fertilize the female gamete (ovum)
Somatic Cells vs Gametes
 Somatic cells (body cells)
 Diploid (2n)
 In humans = 46 chromosomes
 Contain 2 copies of each of the 22 autosomes and 1 pair
of sex chromosomes
 (XX if it’s a girl; XY if it’s a boy)
Gametes
 Gametes: sex cells
 Haploid
 In humans = 23 chromosomes
 Made in the gonads (reproductive organs)


Male gonad = the testes
Female gonad = the ovaries
Zygote
 During fertilization, a male gametes and a female
gamete combine their chromosomes to create the
zygote – the fertilized egg – which will be the first cell
of the new organism.
 The zygote will have a complete
genome – 46 chromosomes
Male Reproductive System
Male Reproductive System
Male Reproductive System
 The purpose of the male reproductive system is to
produce sperm to fertilize an ovum
 Sperm is made in the testes through the process of
spermatogenesis.
 The testes are located in a sac called the scrotum,
outside the main body cavity because a cooler
temperature is required for healthy sperm
development.
Testes
 Inside the testes are tiny, twisting tubes called the
seminiferous tubules
Seminiferous Tubules
 Outside the seminiferous
tubules are Leydig cells
(which secrete hormones)
and blood capillaries
Lumen
(the center of a seminiferous
tubules) where the sperm
will travel
Seminiferous Tubules
 Sperm is made from the walls of the seminiferous
tubules, from cells called spermatogonia (plr)
(singular = spermatogonium)
 Each spermatogonium is diploid and is capable of
undergoing mitosis or meiosis
Spermatogonia
 If a spermatogonium undergoes meiosis, it will
produce 4 haploid spermatozoa (that will develop into
sperm cells)
 If a spermatogonium undergoes mitosis, 2 new
diploid daughter cells, identical to the original
spermatogonium will be produced
 Mitosis occurs to replenish cells
 (If all the spermatogonia underwent meiosis, the
individual would run out of sperm)
Spermatogenesis
 The creation of sperm
 A spermatogonium that undergoes meiosis is called a
primary spermatocyte
1 diploid
primary spermatocyte
4 haploid
spermatids
Spermatogenesis
1 diploid primary spermatocyte (46 single stranded chrom.)
INTERPHASE
1 diploid primary spermatocyte (46 double stranded chrom)
MEIOSIS I
2 haploid secondary spermatocytes (23 double stranded chrom)
MEIOSIS II
4 haploid spermatids (23 single stranded chrom.)
Spermatogenesis
Spermatogenesis
 After meiosis, the spermatids stay within the interior of
the seminiferous tubules to develop into fully functioning,
motile sperm cells/ spermatozoa
 As they develop they move through the seminiferous
tubules to the epididymis
 As they develop, they require nutrients.
 Sertoli cells, are cells in the seminiferous tubules that
provide nourishment as the spermatozoa develop
Animations
 Spermatogenesis
 http://highered.mheducation.com/sites/0072943696/
student_view0/chapter19/animation__spermatogenesi
s__quiz_1_.html
Sperm Cell
 Singular: spermatozoon; Plural: spermatozoa
 Head: contains haploid nucleus
 Acrosome: contain enzymes to penetrate egg cell
 Body: contains mitochondria to provide energy for
sperm to move
Route of Sperm
1.
Develops in the seminiferous tubules of the testes
(within the scrotum)
2. Sperm is stored in the epididymis (finishes
development here)
3. During ejaculation, sperm leaves the epididymis via
the vas deferens
4. The vas deferens circles around the bladder and joins
the urethra.
Route of Sperm
(The urethra carries both urine and semen out of the
body – but not at the same time!)
5. The seminal vesicles and prostate gland and
Cowper’s gland will add fluid to the urethra.
“milky-white” fluid + sperm = semen
6. Semen will travel through the urethra and leave the
male via the penis
Semen
 Seminal Vesicles
 produce most of the fluid in semen
 Fluid rich in sugars (fructose) to provide energy for
sperm
 Also contains prostaglandins which cause contractions
in the female productive system to help move sperm to
the egg
Semen
 Prostate Gland
 The female reproductive tract is too acidic (pH 4) for
sperm cells
 The prostate gland adds an alkaline fluid, providing an
optimal pH (of 6) for the sperm
 Cowper’s Gland/Bulbo-urethral gland
 Produce a clear fluid that will lubricate the urethra
allowing sperm to pass through
 Fluid will neutralize any residual acidic urine
Additional Info….
 It takes several weeks for spermatozoa to be produced
 100 million sperm are produced daily
 300-700 million are released in a single ejaculation
 Unreleased sperm will die, be broken down, and
reabsorbed to make new sperm
Ejaculation
 During sexual arousal, the blood vessels in the penis
dilate to allow for increased blood flow to the penis.
 This causes the penis to become erect.
 This will also cause the sphincter at the base of the
bladder to close, preventing urine from leaving the
bladder during ejaculation
Male Reproductive Hormones
 FSH & LH – both produced by the anterior pituitary
gland
 FSH: Follicle Stimulating Hormone
 Stimulates spermatogenesis
 Stimulates maturation of Sertoli cells
 LH: Luteinizing Hormone
 Stimulates Leydig cells to produce testosterone
Male Reproductive Hormones
 Note: FSH and LH are released by the anterior
pituitary gland when the hypothalamus releases GnRH
(gonadotropin releasing hormone).
 GnRH is released secreted and released at the on set of
puberty
 Males will continue to release GnRH throughout their
life and thus have the potential to make sperm from
puberty till death
Male Reproductive Hormones
 Testosterone
 Promotes the maturation of spermatids to spermatazoa
 Promotion of male secondary sexual characteristics:



Facial, chest and pubic hair
Broadening of shoulders
Deepening of the voice
 Promotes growth and activity of male reproductive
organs
 Increased sexual desire
 Increases immune response
Animations
 http://www.pennmedicine.org/encyclopedia/em_Disp
layAnimation.aspx?gcid=000120&ptid=17
 http://www.pennmedicine.org/encyclopedia/em_Disp
layAnimation.aspx?gcid=000121&ptid=17
 Vasectomy
 http://www.pennmedicine.org/encyclopedia/em_Disp
layAnimation.aspx?gcid=000139&ptid=17
Female Reproductive System
Animations
 Interactive Female Anatomy
 http://www.pennmedicine.org/encyclopedia/em_Disp
layAnimation.aspx?gcid=000055&ptid=17
Female Reproductive System
 The female reproductive system and gamete is more
complicated than the male’s because it is designed to
nourish and support a developing embryo
Route of Sperm – In Female
Reproductive System
1.
Sperm is released into the vagina (muscular passage
way)
2. Sperm travels up through the cervix to the uterus
(pear shaped womb)
3. Travels through one of the 2 oviducts (also called
fallopian tubes) to attempt to fertilize a waiting egg
Female Reproductive System
 Ova (eggs cells) are produced by the 2 ovaries
 The production of gametes and regulation of the
female reproductive cycle is controlled by hormones.
Female Reproductive Hormones
 At the onset of puberty, the hypothalamus produces
gonadotropin-releasing hormone (GnRH) which
signals the anterior pituitary to produce and release
FSH and LH.
 FSH (Follicle Stimulating Hormone)
 Made and stored in the anterior pituitary gland
 Released when signaled by the hypothalamus (by
GnRH)
 Stimulates ovarian follicle growth

Follicle releases estrogen
Female Reproductive Hormones
 Estrogen
 Made by follicles in the ovary
 Causes the endometrium (the uterine lining) to thicken
(preparing for implantation of a potential embryo)
 A buildup of estrogen causes inhibits FSH (negative
feedback!)
 A buildup of estrogen stimulates the secretion of LH by
the pituitary gland.
Female Reproductive Hormones
 LH (Luteinizing Hormone)
 Stimulates OVULATION (the release of an ovum by
the ovary)
 Stimulates the formation of the corpus luteum
 CORPUS LUTEUM – a temporary endocrine structure
that develops in the ovary from an ovarian follicle after
the ovary has released an ovum (ovulation)
 Produces progesterone
Female Reproductive Hormones
 Progesterone
 Hormone which keeps the endometrium intact
 Inhibits FSH and LH secretion
 And thus inhibits ovulation
 If fertilization does not occur….
the corpus luteum degenerates  progesterone levels
decrease  endometrium will break down
(menstruation)
GnRH
Animations
 Ovulation
 http://www.pennmedicine.org/encyclopedia/em_Disp
layAnimation.aspx?gcid=000094&ptid=17
Ovary
 In the ovary, the follicles will develop to produce the
female gamete – the ovum (plr: ova)
 Several follicles at different stages of development are
present in the ovary.
 During each reproductive cycle, hundreds of follicles
will begin to develop but usually only one will reach
maturity and become an ovum
Oogenesis
 Oogenesis: the development of ova
 Spermatogenesis creates 4 haploid sperm cells
 Oogenesis involves unequal division an will produce
only 1 haploid ovum.
Oogenesis -Pre-birth
 Oogenesis starts prenatal!
 Within the ovaries of the female fetus, cells called
oogonia undergo mitosis repeatedly to build up the
number of oogonia in the ovaries.
 These oogonia grow into larger cells called primary
oocytes.
 (Oogonia and the primary oocytes are diploid cells)
Oogenesis - pre-birth
 The large primary oocytes begin the early steps of
meiosis but the process stops during prophase I.
 Also within the ovaries, cells called follicle cells
repeatedly undergo mitosis.
 A single layer of these follicle cells surround each
primary oocyte and the entire structure is called a
primary follicle.
Oogenesis - pre-birth
 Initially, a female fetus will have ~7 million primary
oocytes, but only about ½ million at birth!
 These primary follicles remain unchanged and paused
in meiosis until the female reaches puberty and begins
her menstrual cycles
Oogenesis – Menstrual cycle
 Each menstrual cycle, a few primary follicle finish
meiosis I.
 For each primary follicle, 2 haploid cells are produced
at end of meiosis I:
 1 large haploid cell = the secondary oocyte which will go
on to meiosis II
 1 small haploid cell = a polar body which will
disintegrate
Oogenesis – Menstrual cycle
 Only 1 secondary oocyte will begin meiosis II
 However, meiosis will pause during prophase II
 Meiosis II will not actually continue again unless
fertilization occurs.
 When a female ovulates, people say that she releases
an “ovum”, but really it’s a secondary oocyte
 Meanwhile, as the secondary oocyte develops, the
other follicle cells grow (because of FSH) and produce
estrogen
 When a female ovulates, the follicle cells surrounding
the secondary oocyte burst open and release the
secondary oocyte into the oviduct)
Oogenesis – post ovulation
 When meiosis II is continues again, another unequal
division will occur, resulting 2 haploid cells:
 1 large haploid cell = Ootid  which will become the
gamete (the ovum)
 1 small haploid polar body  which will disintegrate
 The ovum is large and packed with nutrients so that
when it is fertilized it can undergo rapid cell divisions
Animations
 Egg Cell Production
 http://www.pennmedicine.org/encyclopedia/em_Disp
layAnimation.aspx?gcid=000045&ptid=17
Ovulation - Fertilization
 After ovulation, the “egg” moves along the oviduct and
awaits fertilization by a sperm cell.
 Cilia (hair-like structures in the oviduct) sweep the egg
cell down the oviduct
Egg Cell / Ovum
 Much larger than the sperm cell
 The egg cell that is released from the ovary during
ovulation is technically still a secondary oocyte paused
in meiosis II (and a first polar body from meiosis I)
surrounded by a layer of follicle cells.
 (This “egg” may also be referred to as a “mature
follicle”
“Egg” Cell Structure
 CORONA RADIATA: layer of
Plasma
Membrane
follicle cells
 ZONA PELLUCIDA: a “jelly”
coat of glycoproteins
First polar
body
Coritcal Granule
 CORITCAL GRANULES: special
lysosomes that contain special
enzymes to thicken the zona
pellucida after fertilization (to
prevent another sperm from
entering)
Animations
 Follicle Development
 http://highered.mheducation.com/sites/0072943696/
student_view0/chapter19/animation__maturation_of_
the_follicle_and_oocyte.html
Fertilization
 The fusion of the male and female gametes (in the oviduct)
to create a diploid zygote
 In order for the 2 nuclei to fuse and combine their
chromosomes, the sperm must penetrate the “egg cell”
 Many sperm cells will attempt to penetrate the egg, but
only 1 can be successful
 The egg cell has 2 barriers – the corona radiata and the
zona pellucida – which the sperm must penetrate through.
Fertilization
1.
When sperm cell reach the mature follicle, the sperm
first must push its way through the corona radiata to
reach the zona pellucida
2. Acrosome Reaction
 When the sperm makes contact with the zona
pellucida, the enzymes in the acrosome are released.
 This allows the sperm to force their way through by
vigourously beating their tails.
Fertilization
3. The first sperm cell to get through the zona pellucida
to the cell membrane (of the secondary oocyte) will
fuse with the membrane of the secondary oocyte.
4. The fused membranes open allowing the haploid
sperm nucleus to enter the cytoplasm of the
secondary oocyte. (The tail and body will be left
behind)
Fertilization
5. The fusion of the 2 membranes causes the Cortical
Reaction:
 The cortical granules in the cytoplasm of the secondary
oocyte will immediately release enzymes that will
thicken the zona pellucida and create an impenetrable
membrane (fertilization membrane)
 This prevents other sperm cells from penetrating the
egg.
 This will also protect the developing embryo during the
first days of life
Fertilization
6. The fusion of the 2 membranes signals the
secondary oocyte to complete meiosis II and
produce a second polar body (which will
disintegrate) and an ootid that will almost
immediately mature into an ovum.
7. It will actually take a couple of hours for the sperm
and ovum nuclei to actually fuse together. When
they do we will now have a diploid zygote!
Animations
 Conception
 http://www.pennmedicine.org/encyclopedia/em_DisplayAnimation.aspx?gcid=000032&
ptid=17
 Twins!
 http://www.pennmedicine.org/encyclopedia/em_DisplayAnimation.aspx?gcid=000058&
ptid=17
 Egg Development
 http://highered.mheducation.com/sites/0072943696/student_view0/chapter19/animati
on__maturation_of_the_follicle_and_oocyte.html
Post - Fertilization
 ~24 hours after fertilization, the zygote will now undergo a
series of rapid mitotic divisions, forming a 2-cell embryo,
then a 4-cell embryo…. (all within the fertilization
membrane)
 These divisions are rapid – no periods of cell growth like in
somatic cells of an adult.
 A solid “ball of cells” called the morula is formed.
 As mitosis is occurring, the morula moves through the
oviduct toward the uterus.
Post-Fertilization: The Blastocyst
 It takes ~4 days for the
morula to reach the
uterus.
 By day 7 it is a mass of
~100 cells called a
blastocyst which can
implant itself in the
endometrium
Post Fertilization - Implantation
 By day 7-8 the blastocyst implants itself in the uterine
wall (the endometrium)
 The trophoblast will grow villi (trophoblastic villi)
which will absorb nutrients from the endometrium
 In this way, the developing embryo will receive
nourishment until the placenta takes over
Trophoblast
 Also secretes the hormone HCG (human chorionic
gonadotrophin) which maintains the corpus luteum
(in the ovary), thus continuing progesterone
production
 (remember, progesterone keeps the endometrium
intact)
 After ~10 weeks when the placenta has developed, it
will produce progesterone and the corpus luteum will
no longer be required
Animations
 Cell Division (after fertilization)
 http://www.pennmedicine.org/encyclopedia/em_Disp
layAnimation.aspx?gcid=000025&ptid=17
Pregnancy
 http://www.pennmedicine.org/encyclopedia/em_Disp
layAnimation.aspx?gcid=000103&ptid=17
HCG & Pregnancy Tests
 HCG is excreted into urine and is detected during a
pregnancy test.
 Proteins on HCG will bind to antibodies (proteins)
with pigments in the tester causing a “line” to appear if
you are pregnant
Placenta
 This is where oxygen and nutrients will diffuse from the
mother’s blood into the baby’s blood.
 Also, waste products from the baby’s blood will diffuse to
the mothers’ to be expelled by the mother.
 Materials are exchanged, but fetal and maternal blood do
not mix.
 Fetus and the placenta are connected by the umbilical cord.
Animations
 Placenta:
http://www.pennmedicine.org/encyclopedia/em_Disp
layAnimation.aspx?gcid=000101&ptid=17
 Amniotic Sac:
http://www.pennmedicine.org/encyclopedia/em_Disp
layAnimation.aspx?gcid=000130&ptid=17
Amniotic Sac
 The amniotic sac is a membrane filled with amniotic
fluid that surrounds the fetus
 Amniotic fluid protects the fetus from infection,
buffers shocks, provides protection, prevents cells
from growing together.
 The fetus will ingest amniotic fluid (practicing using
its digestive and excretory systems) and will also
urinate in the fluid
Pregnancy Hormones
 Estrogen - in high levels
 Stimulates the growth of uterine muscles (important for
labour) and the growth of mammary glands (important
for lactation)
 Progesterone – high
 After ~38 weeks of gestation, progesterone levels drop
 This causes the endometrium to detach and the mother
to go into labour
 It also allows for lactation
Animations
 Fetal Development:
http://www.pennmedicine.org/encyclopedia/em_Disp
layAnimation.aspx?gcid=000056&ptid=17
 Face Development:
http://www.pennmedicine.org/encyclopedia/em_Disp
layAnimation.aspx?gcid=000071&ptid=17
Gestation
 Differentiation: is when the cells become specialized
to perform the different tasks of various tissues and
organs in the body.
 Ex: certain cells become heart cells, others become
blood cells etc.
 Human gestation (the length of pregnancy) is about 38
weeks. It is divided into 3 blocks of time called a
trimester.
FIRST TRIMESTER
 (weeks 1- 12 or 1st-3rd months)
 The limbs, eyes and spine begin to form
 8-9 weeks: embryo forms its first bone cells – now we
call it a FETUS
 By 12 weeks: the fetus has the beginnings of its liver,
stomach, brain, and heart
First Trimester
 Has noticeable head (with developing facial features)
and limbs (arms and legs)
 Arms and legs begin to move
 It’s 100mm long (10 cm)
 The gender can be determined with an ultrasound
Sex Determination
 Remember, that females have 2 X chromosomes and
males have an X and a Y chromosome (XY)
 The Y chromosome, is important in the embryonic
development of a male as it contains the SRY gene
 Initially, the development of the embryo is the same in
all embryos (male or female)
Sex Determination
 Around the 8th week the embryo starts sexual
differentiation
 The gene SRY causes the production of androgens
from the adrenal cortex which leads to the
development of male gonads (testes)
 Since females do not have a Y chromosome, they will
not have the SRY gene and their gonads will continue
development into female ovaries
Animation
 Sexual Differentiation:
http://www.pennmedicine.org/encyclopedia/em_Disp
layAnimation.aspx?gcid=000110&ptid=17
Androgen Insensitivity Syndrome
 This condition results in genetic males (XY) when a
cell is insensitive to androgens.
 As a result, despite having a Y chromosomes and being
a genetic male, these individuals will not develop male
genitalia and will continue to develop external female
genitalia and appear female.
 However, because the individual only has one X
chromosome, they will not by fertile. (Similar to
Turner’s Syndrome)
SECOND TRIMESTER
 (weeks 12-24 or 4th-6th months)
 16 weeks: the placenta is too small to surround the
fetus, so it moves to one side.
 Skeleton begins to form and brain grows rapidly
 The mother can feel movements of fetus and it flexes
its new muscles.
Second Trimester
 20 weeks: may start sucking its thumb
 By 24 weeks: most organs are formed.
 Eyelids and eyelashes form.
 Soft hair covers the entire body
 It’s about 300 mm in length
 If it were born now, it would have little chance of
surviving
THIRD TRIMESTER
 (week 24-38 or 6th -9th months)
 Fetus rapidly increases in overall size and moves a lot
more stretching and kicking.
 Organ systems begin to function properly
 8th month: fetus opens its eyes
Third Trimester
 Fetus about 500 mm in length and 2700-4100g in mass
 Nutrition important because the building of vital
brain tissue in fetus. But nutrition is also important for
the mother. An improper diet may cause serious
problems in some women.
Risk Factors
 The developing fetus receives all its nutrients and
oxygen from its mother’s bloodstream.
 Whatever the mother eats, drinks, or inhales will end
up in her blood and then passed to the fetus.
 Some substances can be harmful to the development
of the fetus such as cigarette smoke, alcohol, and other
drugs.
 It can result in birth defects
Birth
 38-40 weeks after conception, the fetus is ready to be born
and progesterone levels drop
 This will initiate the birthing process which includes 3
phases:
Dilation Phase
2) Expulsion Phase
3) Placental Phase
1)
1) Dilation Phase
 Lasts 2 -20 hours
 Prostaglandins, hormones made and released in
the uterus, initiate contractions of the uterine wall
and push the fetus again the cervix
 This causes the cervix to dilate
 Usually causes the amniotic sac to rupture – the
amniotic fluid lubricates the birth canal.
Birth – Dilation Phase
 Dilation of the cervix sends a message to the brain and
the pituitary gland to release oxytocin from the
posterior pituitary gland.
 Oxytocin increase the contractions of the uterus.
 This is an example of positive feedback: the presence
of contractions results in the increase in strength and
duration of contractions
2) Expulsion Phase
 Lasts 0.5 – 2 hours
 When the cervix is fully dilated to 10 cm, powerful
contractions will expel the baby.
3) Placental Phase
 Occurs 10-15 minutes after the baby is born
 After the baby is born, the afterbirth (the placenta)
will also have to be expelled.
 The umbilical cord is cut and tied off
 (After the baby is expelled, since there is no longer
anything pushing against the cervix, oxytocin release
will be inhibited and the contractions stop)
Problems during Childbirth
 Mother’s pelvis can be too small for the baby to pass
through
 The baby may not be in the correct position
 Often, the baby is delivered through a Cesarean
section (when the mother’s abdomen and uterus are
cut open to remove the baby)
LACTATION
 During pregnancy, high levels of estrogen and
progesterone prepare the mother’s breasts for milk
production.
 At birth, the mother’s pituitary gland makes the
hormone prolactin which stimulates the production of
milk.
 Milk production is also stimulated by the baby’s
sucking action and removal of milk.
Breast Milk
 Breast milk helps the develop the baby’s immune
system.
 A woman can produce 1.5 L of milk each day.
 A mother producing that much milk would need
about 50 g of fat,100 g of lactose, and 3 g of calcium
phosphate each day.
Animations
 vaginal delivery:
http://www.pennmedicine.org/encyclopedia/em_Disp
layAnimation.aspx?gcid=000138&ptid=17
 Cervix Dilation:
http://www.pennmedicine.org/encyclopedia/em_Disp
layAnimation.aspx?gcid=000027&ptid=17
 C-Section:
http://www.pennmedicine.org/encyclopedia/em_Disp
layAnimation.aspx?gcid=000028&ptid=17