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Unit 8:
Part 2:
Fertilization/Development
and Human Reproduction
Key Questions
1. Why is sexual reproduction advantageous
over asexual reproduction?
2. What structures make up the male and
female reproductive systems?
3. How do offspring of sexually-reproducing
organisms receive their genetic information?
Key Questions
4. Why do the offspring look different from
the parents?
5. What controls human reproduction and
development?
6. How does a zygote develop and what
factors can affect its development?
Question???
• Why is sexual reproduction advantageous
over asexual reproduction?
Reproductive Systems
• Goal of male and female reproductive
systems is to create gametes, deliver
them, and in females, to allow for
embryonic and fetal development.
Compare the Gametes
EGGS
SPERM
Non-Motile
Motile
Large
Small
Nucleus
Neck
Tail
Yolk/Cytopla
sm
Head/
Nucleus
Human Egg Cell
Bat sperm
(mitochondria)
Human Sperm
Human Reproduction
Comparison of male and female
reproductive anatomy
Female Reproductive System
• 2 Functions of the female reproductive
system:
1.
2.
To produce eggs.
To provide an environment for
internal fertilization and
development of embryo.
Female Reproductive System
• FYI:
– Facts:
• Females have about 2 million eggs at
birth.
• 400,000 eggs survive to puberty.
• Only 450 – 500 eggs mature and
leave the ovaries.
Female Reproductive System
Structure
Ovaries
Function
1. Produce eggs
1. Secrete sex hormones
(estrogen and progesterone)
Follicles
1. Tiny egg sacs where eggs
mature within the ovaries.
Female Reproductive System
Structure
Fallopian Tubes
(Oviduct)
Uterus
Function
1. Tube that egg travels
through from ovary to
uterus.
2. Where fertilization occurs!!!
(within 48 hrs of egg release)
1. Thick muscular organ
2. Where fertilized egg
develops until birth
Female Reproductive System
Structure
Function
Cervix
1. Muscular tube
between uterus and
vagina
Vagina
1. Also called birth
canal
2. Connects uterus to
outside the body.
Male Reproductive System
• Main function of the male reproductive
system:
1.
Produce and deliver sperm.
Male Reproductive System
Structure
Testes
Function
1. Has small coiled tubes-seminiferous
tubules – where sperm cells are produced.
2. Produce testosterone-necessary for sperm
production.
Scrotum
1. Contains the testes
2. Temperature is 1-2 degrees cooler than
body – provides “optimal” environment for
sperm production.
Male Reproductive System
Structure
Function
Epididymis
1. Where sperm mature (takes about
18 hours) after leaving seminiferous
tubules and are stored.
Vas Deferens
1. Tubes that leave each of the testes
and join the urethra.
Male Reproductive System
Structure
Function
Urethra
1. Tube leading to outside of male
body.
2. Both semen and urine pass
through this tube.
3. Semen traveling through penis =
land adaptation for internal
fertilization.
Male Reproductive System
System
Function
Prostate gland
Seminal Vesicles
Cowper’s Gland
1. Secrete fluids into the urethra when
sperm pass through - transport
medium for sperm.
Semen
1. Mixture of sperm + seminal fluids =
semen
1. 3.5 mL of semen released-contains
400 million sperm.
Reproductive System
• Spermatogenesis Video
– (on server-40 sec.)
• What is the role of the menstrual cycle???
Human Menstrual Cycle
• Feedback mechanism regulated by
interaction of various glands and
hormones
• Cycle begins at puberty (around age 1014)
• Cycle stops during pregnancy and at
menopause (age 45-55)
Human Menstrual Cycle
• Egg is prepared matures and released
from ovary; uterus prepares to receive it (if
fertilized)
• There are 4 stages of the menstrual cycle
Human Menstrual Cycle
Stage 1
Follicle
Stage
FSH –
Follicle
stimulating
hormone
1. FSH is secreted by pituitary
gland to stimulate 1 follicle to
mature an egg.
1. Estrogen is secreted by the
follicle.
Estrogen
2. Causes vascularization (uterine
lining thickens with a rich
supply of blood vessels)
Human Menstrual Cycle
Stage 2
Ovulation
LH –
1. High level of estrogen (from
Luteinizing
follicle makes pituitary
Hormone
gland decrease FSH level
2. As level of FSH decreases,
pituitary gland secretes LH
(luteinizing hormone).
3. Ovulation – high level of LH
causes the release of an egg
from follicle in ovary
Human Menstrual Cycle
Stage 3
Corpus
Luteum
Stage
Progesterone
1. Corpus luteum (empty
follicle that fills in
with fluid/cells)
secretes progesterone
2. Progesterone
maintains the
vascularization of the
uterus.
Human Menstrual Cycle
Stage 4
Menstruation
1. Occurs when fertilization
does NOT take place.
2. Shedding of the uterine
lining caused by decrease in
progesterone levels
3. Low progesterone levels
cause pituitary to start with
FSH production – starts all
over again
Menstrual Cycle
• http://www.abpischools.org.uk/page/modul
es/hormones/horm4.cfm?age=Age%20ran
ge%2014-16&subject=Biology
Golden Ticket
• Name the female reproductive system
structures the sperm need to travel through
to get to an egg (hint: there are 4).
The joining of the gametes…
Reproduction
• Fertilization: Fusion of of
gametes to produce a zygote.
• Zygote: A fertilized egg
Fertilization
fertilization
+
1n
1n
2n Zygote
• Fertilization RESTORES the
chromosome number (2n)
Zygote
Fertilization
• Eggs are NON-MOTILE (don’t move
on their own), so sperm must find the
egg.
–A fluid environment is necessary so
sperm can swim to the egg.
Internal Fertilization
• Gametes fuse inside the female’s body.
• Occurs in terrestrial (land) environment.
FYI – External Fertilization
• Gametes join outside of the female’s body
in an water environment so sperm can
swim to eggs
• Large number of gametes (eggs) released
to be sure some will survive (No parental
care after birth)
External Fertilization
Embryonic Development:
• Define Development:
–Orderly series of changes that
occur in an organism.
–In humans, development occurs
inside the female’s body
Development
Zygotes undergo a series of early mitotic
cell divisions called CLEAVAGE. Once
cleavage begins, the zygote is considered
a developing embryo.
Development
2 cells
4 cells
8 cells
Development
• Early stages of cleavage results in a solid ball of
cells called a MORULA.
• Draw:
A solid ball
of cells
Development
• They are re-arranged into a HOLLOW BALL of
cells 1 cell thick called a BLASTULA.
• Draw:
The middle
has been
‘blasted out’
Stem Cells
• Up until this point in the embryo’s
development, the cells are referred to as
stem cells.
• The cells have not become specialized yet
– they are all the same.
Stem Cells Video (13:40)
• (on server – stem cell research)
– http://www.pbs.org/wgbh/nova/body/stemcells-research.html
Development
• When the blastula reaches hundreds of cells,
1 side indents to form a 2-layered embryo
called a GASTRULA.
Development
The process of indentation is called
GASTRULATION.
• Outer layer is called ectoderm
• Inner layer is endoderm
Draw:
ectoderm
endoderm
Video Clips
• Fertilization (on server-1 min.)
• Differentiation (on server-2 min.)
Development
• After the endoderm and ectoderm form, a
middle layer forms between them called
the MESODERM.
ectoderm
Draw:
mesoderm
endoderm
Development
FYI• Endoderm, mesoderm, and ectoderm are
embryonic layers, or GERM LAYERS.
Development
• Differentiation: Occurs during
gastrulation.
– Cells become special kinds of cells to do
certain jobs (specialization) (no longer stem
cells) – genes turn on/off
– The 3 germ layers give rise to various tissues,
organs, and systems.
Differentiated Cells
Development
FYI:
• Ectoderm – hair, skin, nails, nervous
system
• Mesoderm – bones, muscles,
circulatory system, excretory system,
reproductive system
• Endoderm – Digestive system,
respiratory system, liver, pancreas
Development
• For proper development, the embryo
needs nourishment, oxygen, proper
temperature, protection, and waste
removal.
FYI
• Many organisms have external
development.
– Occurs outside the female’s body.
• Nourishment comes from yolk in egg.
• Little or no protection.
• Example: frogs, fish
Jawfish
Male jawfish care for
eggs in his mouth
until they hatch
Chick - 9 days
• 1. The clear fluid
surrounding the
chick is the
amnion.
• 2. The yellow
area covered with
a blood system is
the yolk.
• 3. The blood
system in the
piece of egg shell
is the allantois.
• 4. The milky,
clear material to
the right of the
shell is albumen.
Human Embryonic
Development
• Human females have specialized structures
to allow for internal development.
Internal Development
– After fertilization, the dividing by mitosis
embryo travels from fallopian tube to uterus
– Implantation - embryo embeds itself in think
uterine lining (marks beginning of pregnancy
– occurs 5-10 days after fertilization)
• Differentiation begins to occur – cluster of cells
from inner cell mass becomes embryo rest
becomes surrounding tissues
• Pregnancy tests test for HCG
Internal Development
• Special structure forms called a
PLACENTA – formed to nourish embryo
and remove wastes.
• Allows for exchange of nutrients, wastes,
gases between mom and embryo by
process of DIFFUSION.
Internal Development
• There is NO DIRECT CONNECTION
between mom and embryo’s blood
streams.
• UMBILICAL CORD – structure that
attaches embryo to placenta.
– Blood vessels (2 arteries and 1 vein) in cord
transports blood back and forth from embryo
and placenta
Placenta
Umbilical Cord Blood Banking
• http://www.cordblood.com/benefits-cordblood/umbilical-cord-stem-cells
Problems…
• Placenta previa
Internal Development
• Amniotic Fluid –
– Liquid within a membrane that protects
embryo/fetus (water, salts, cells, urine
from baby).
– Gives it a stable environment and
absorbs shock
Early Development
• The early stages of development are very
important – external factors can disrupt
development at this time
– Environmental factors such as inadequate
diet, use of alcohol/drugs/tobacco, other
toxins, infections can harm embryonic
development
Fetal Development
• After 8 weeks of development = fetus
• During months 4-6, fetus becomes more
complex and specialized
• Last 3 months – systems mature and fetus
grows in size and mass
• Gestation
– length of time from fertilization to birth
(40 weeks in humans – about 9 months)
Fetal Development
Internal Development
• Child Birth
– About 9 months after fertilization
– Complex factors trigger process
• Hormones released by pituitary gland (oxytocin)
triggers uterus to contract
– Causes cervix to open
– Amniotic sac may break
– Labor –
• Baby is delivered head first
• Umbilical cord is clamped and cut
• Mother delivers placenta
Problem…
• Cesarean section
• Umbilical cord around baby’s neck (25%)
After Birth
• After birth, mother produces a hormone
(prolactin) which stimulates production of
milk in mother’s breast tissues
• The nutrients found in breast milk have
everything the baby needs for growth and
development in early life
Internal Development
FYI-
b. Non-Placental Mammals
– Internal fertilization and development in uterus
(no placenta).
– Young are born prematurely – then crawl into
pouch-attach to mammary glands.
Internal Development
• Development is completed in pouch
• “Survival of the fittest.”
• Examples – Marsupials (pouched
mammals) kangaroo, opossum
Non-placental mammals: marsupials
Wombat
Other - Twins
• Identical
• Fraternal
Other-Twins
• Siamese/Conjoined Twins
Other
• Reproductive Technologies
Applicable NYS Learning
Standards
• 2.1e, 3.1g, 4.1c, 4.1d, 4.1e, 4.1f, 4.1g,
4.1h