KEY QUESTIONS FOR THIS UNIT
What effects do estrogens and testosterone have
on males and females?
What are the main functions of the male
reproductive system?
What are the main functions of the female
reproductive system?
What are some of the most common STDs?
What takes place during fertilization and early
human development?
What important events occur during the later
stages of human development?
After fertilization, embryonic development in animals
begins. It follows a well-defined pattern of growth
and differentiation.
It is controlled – most part – by genes – the hereditary
material from the parent cells.
In some animals, development is external.
Yet, in others – like humans – it occurs
within the body of a parent.
After fertilization of an egg, the zygote is formed.
This is the first in a series of complex events that
conclude with the birth of a full-grown organism.
Following fertilization, the zygote begins a series of
mitotic cell divisions know as cleavage.
Cleavage- Cells don't grow, just divide; therefore, cell
size decreases
1. Series of cell divisions after fertilization
2. Mitosis
3. Embryo-development of the zygote (one cell)
Stages of Cleavage- the number of cells doubles at
each division but no growth occurs.
1. Morula-developing embryo is solid ball of cells
2. Blastula-development of hollow center filled
with fluid-blastocoel
3. Gastrulation-"horse shoe stage" when blastula
reaches several hundred cells
1. Morula-developing embryo is solid ball of cells
The process begins when the zygote divides into two
identical cells by mitosis.
The two cells then divide into four smaller cells,
which in turn divide into eight smaller cells.
This process continues and a solid ball of cells called
the morula is formed.
Zygote (approximately 16-20 hours after
insemination)
Four-cell embryo (approximately 45 hours after
insemination).
Two-cell embryo (approximately 24 hours after
insemination).
Eight-cell embryo (approximately 72 hours after
insemination).
The morula, a collection of around 30 cells (blastomere), is created at about 96
hours. Because these cells arise only through the cleavage, no growth is seen.
Every new cell is thus only half as large as the cell from which it derives. The name
of this stage comes from its resemblance to a mulberry, since it really looks like a
collection of spherical cells
Blastula-development of hollow center filled with fluidblastocoel
On the 4th day after insemination an epithelial cellular
layer forms, thicker towards the outside, and its cells
flatten out and become smaller.
Fluid filled inside sphere
Yolk filled end
opening
The blastula stage is followed by the formation
of the gastrula.
During the formation of the gastrula, one side of
the blastula pushes inward forming a second, inner,
layer of cells.
The inner cell layer is called the endoderm.
The outer cell layer is called the ectoderm.
A third cell layer, the mesoderm, then forms
between the endoderm and ectoderm.
The endoderm, ectoderm and mesoderm layers
continue dividing and form all the tissues, organs and
organ systems of the animal.
The process is called differentiation.
Growth and Differentiation
1.Differentiation-series of changes that transforms the
unspecialized embryonic cells into specialized cells,
tissues, and organs
2. Growth-increasing number of cells
Ectoderm
Nervous system, epidermis, sweat glands, hair and
nails, lining of mouth, nostrils and anus
Mesoderm
Bones & muscles, blood, blood vessels & heart,
reproductive and excretory systems, inner layer of
skin
Endoderm
Lining of the digestive tract, lining of the trachea,
bronchi and lungs, liver & pancreas, thyroid,
parathyroid, and thymus, urinary bladder
https://www.youtube.com/watch?v=k_9MTZgAhv0
Control of Development
A. Nucleus
1. DNA-contains hereditary information.
a. Controls cellular activity
b. encodes for the production of cellular proteins
B. Cytoplasm
-receives instructions from the DNA in the nucleus.
Which came first?
https://www.youtube.com/watch?v=1a8pI65emDE
DEVELOPMENT
A. External in water
1. Nourishment is supplied by the yolk stored in the egg
2. No parental care
B. External on land- production of egg and shell, some
parental care
1. Extra embryonic membranes- 4 membranes outside
of the embryo
a. Chorion-outermost membrane-aids in gas exchange
b.allantois-exchange of oxygen and carbon dioxide,
stores wastes until egg hatches
c. amnion-fluid filled sac that surrounds the embryo
cushion, shock absorber
d. yolk sac- surrounds the yolk- source of food for embryo
Example of organism-lizards, birds, and snakes
yolk
(Part of white)
chorion
2.shellprevents bacteria from entering, porous enough
for oxygen and carbon dioxide to exchange,
slows rate of evaporation.
C. Internal Development
1. Placental mammals-blood vessels of embryo
are in close contact with the mother's blood
a. Placenta-structure produced by the uterus of
the mother, which supplies nutrients to the
embryo and removes wastes from the embryo.
** Gas & food exchange is accomplished between the
mother and the embryo by diffusion and active transport
through the placenta. No direct blood link exists between
the mother and the fetus.
b. Umbilical cord-attaches the embryo to the
placenta of the mother in the uterus
2. Non placental mammals- 2 types
a. egg laying mammals (monotremes) -duckbill
platypus, spiny anteater
b. marsupials- pouched mammals-kangaroo, opossum
Aging: complex series of developmental
changes which occur with the passage of
time -- caused by both heredity &
environment
Death: irreversible cessation (end) of all brain
functions
Reproduction is the formation of new individuals
The reproductive system could be thought of as the
single most important system for the continuation of a
species—without it, no species could produce another
generation
In humans, as in other vertebrates, the reproductive
system produces, stores, and releases specialized sex
cells known as gametes.
These cells are released in ways that make possible the
fusion of sperm and egg to form a zygote, the single
cell from which all cells of the human body develop
For the first six weeks of development, human male
and female embryos are identical in appearance. Then,
during the seventh week, major changes occur.
The primary reproductive organs—the testes in males
and the ovaries in females—begin to develop.
The testes produce testosterone, a male sex hormone.
Testosterone is required for sperm production and the
development of male physical characteristics.
The ovaries produce the female sex hormones estrogen
and progesterone.
Estrogen is required for the development of eggs and
for the formation of female physical characteristics.
Progesterone prepares the uterus for the arrival of a
developing embryo
Female Secondary
Male Secondary
Sex Characteristics
Sex Characteristics
•Development of breasts
•Growth of beard and
body hair
•Changes in body form
•Growth of body hair
•Changes in body
form
•Lowered voice pitch
The Male Reproductive
System
The main structures of the male reproductive
system are the testes, the epididymis, the vas
deferens, the urethra, and the penis.
These structures work together to produce and
deliver sperm.
1. Testes: make and store sperm
Just before birth (and sometimes just after) the testes
descend through a canal into an external sac called the
(scrotum)
-- saclike pouch which houses the testes, is 1-2
degrees Celsius below normal body temperature
2. Within each testis, are hundreds of tiny tubules
called seminiferous tubules: carries/stores sperm
from the testes
3. Epididymis: temporary storage organ for sperm at
the beginning of the Vas Deferens
The haploid
sperm cell is
produced in
the
seminiferous
tubules and
move to the
epididymis
until they are
fully mature.
4. Vas Deferens: tube which carries the sperm
past 3 lubricating glands
5. Cowper's gland, Seminal vesicle, prostate
gland:
-- 3 lubricating glands
-- prostate produces an alkaline fluid which
neutralizes the urine in the urethra
-- prostate cancer kills many over 70 males
-- treated with radiation and estrogen
6. Urethra: opening through the penis
7. Penis: releases the semen
SEMEN: liquid loaded with sperms
EJACULATION:
Sperm are ejected from the penis by the
contractions of smooth muscles lining the
glands in the reproductive tract.the release
of semen
Note: because ejaculation is regulated by the
autonomic nervous system, it is not completely
voluntary.
About 2 to 6 milliliters of semen, containing more than 200 to 600
million sperm, are released in an average ejaculation.
Puberty in females starts when the hypothalamus signals the pituitary
gland to release FSH and LH. FSH stimulates cells within the ovaries to
produce estrogen, the female steroid sex hormone. Interactions of
estrogen with target cells produce female secondary sex characteristics.
Female Reproductive System
The main structures of the female reproductive
system are the:
ovaries
Fallopian tubes
uterus
vagina.
In addition to producing eggs, the female
reproductive system prepares the female’s body to
nourish a developing embryo
A. Ovaries - female gonads
1. Each ovary contains about 400,000 follicles
(tiny egg sacs), which contain an immature egg
Although a female is born with about 400,000
immature eggs (primary follicles)—and does not
produce any new eggs during her lifetime—only about
400 eggs will actually be released.
Roughly once a month, under the influence of FSH, a follicle gets larger
and the egg passes through the early stages of meiosis. When meiosis is
complete, a single large haploid egg and three smaller cells called polar
bodies will be produced. The polar bodies have very little cytoplasm and
soon disintegrate.
2. Ovaries also secrete estrogen (hormones)
responsible for secondary sex characteristics
1. Site for fertilization
B. Fallopian tubes or Oviduct - leads from each
ovary (neither in contact)
When a follicle has completely matured, its egg is
released in a process called ovulation. The follicle
breaks open, and the egg is swept from the surface of
the ovary into the opening of one of the two Fallopian
tubes.
2. Eggs are not motile; they get pushed along the
fallopian tube by cilia
C. Uterus or Womb - site where the egg implants
it's self if fertilized
After a few days, the egg passes from the Fallopian
tube into the cavity of an organ known as the uterus.
The lining of the uterus is ready to receive a fertilized
egg, if fertilization has occurred.
The outer end of the uterus is called the cervix.
D. Vagina - birth canal, leads to the outside of the
body
IMPLANTATION, DEVELOPMENT
If an egg is to become fertilized, sperm must be
present in the Fallopian tube.
Sperm swim actively through the uterus into the
Fallopian tubes.
FYI: Although hundreds of millions of sperm are released during an
ejaculation, only about one percent will reach the upper region of each
Fallopian tube.
If the egg and sperm meet in the Fallopian tube, the
egg and sperm cell may fuse.
The fusion of the sperm nucleus and egg cell nucleus
is fertilization.
Fertilization occurs in the upper portion of the
oviduct (Fallopian Tube)
The fertilized egg is known a a zygote (a newly
formed diploid cell)
If the egg is not fertilized within about 24 hours after
ovulation, it breaks down and passes through the
uterus, through the vagina in a process known as
menstruation..
Sometimes - for varying reasons (blocked oviduct,
infertile husband) – A technique known as in Vitro
Fertilization is used
Test-Tube Baby
Cleavage of the zygote begins while the fertilized egg
is still in the oviduct – about 36 hrs. after fertilization.
Division continues & four days after fertilization, the
embryo is a solid ball of about 50 cells called a morula
Cells rearrange and about six or seven days after
fertilization, the blastocyst attaches itself to the wall of
the uterus.
The embryo secretes enzymes that digest a path into
the soft tissue. This process is known as implantation.
This is the first phase of pregnancy
The second phase – gastrulation and formation – is
about 2 weeks after fertilization.
The marks the actual beginning of pregnancy.
Keep in mind events leading up to birth are sequential
and follow a definite timeline.
If the embryo implants somewhere other than the
uterus – i.e.: oviduct, ovaries, cervix - this is
termed an ectopic pregnancy
Third Phase - Embryonic Period
Period of primary organ differentiation
Ends at about the 8th week
Last phase – a.k.a. Fetal Period
Characterized by rapid growth, changes in body parts
& the final preparation for birth
By the end of the third week of development, the
nervous and digestive systems have begun to form.
The chorion has grown into the uterine tissue to
form a vital organ called the placenta.
The placenta is the connection between mother and
developing embryo.
The developing embryo needs a supply of nutrients
and oxygen. It also needs a means of eliminating
carbon dioxide and other metabolic wastes.
The Placenta also acts as a barrier for most
microorganisms.
However, certain viruses
AIDS
German measles
chicken pox
encephalitis
Can pass through
http://www.med.upenn.edu/
meded/public/berp/overvie
w.mov
Birth – Human gestation period is ~ 9 months
(length of pregnancy .
Development does not end but continues until death
Aging is the term that is applied to the developmental
changes that occur in an organism from birth until
death.
The causes of aging are not fully understood. It
appears that aging involves both hereditary and
environmental factors.
1. Multiple Birth.
a. Identical - formed when 1 egg is fertilized and splits
during the first division.
b. Fraternal - formed when 2 eggs are fertilized at the
same time
The Human Menstrual Cycle
A mature egg develops & is released approximately 28
days
There are 4 stages to the menstrual cycle:
1. Follicle Stage - FHS (follicle stimulating hormone)
secreted by pituitary causes follicles to develop in the
ovaries. As follicle develops, it releases estrogen,
which stimulates the uterine lining to thicken with
blood (10-14 days).
2. Ovulation - FHS decreases, LH (lutenizing
hormone) from the pituitary gland increases which
causes a mature egg to release from the follicle &
from the ovary. Occurs in the middle of the cycle (14
day).
3. Corpus Luteum Stage (yellow body stage) After ovulation the follicle fills with cells forming
the corpus luteum. Corpus luteum secretes
progesterone that maintains the continued growth
of the uterine lining.
4. Menstruation - if fertilization does not occur,
secretion of the LH decreases & the corpus
luteum breaks down. Progesterone levels
decrease & the lining of the uterus breaks down &
is given off. Lasts 3-5 days.
Menopause - The permanent cessation of the
menstrual cycle that occurs approximately
between 45-50 years of age.
The menstrual cycle is regulated by something
called a negative feedback mechanism.
In its simplest terms, in a negative feedback
mechanism, the level of one hormone in the blood
stimulates or inhibits the production of another
hormone.
Some important human reproductive disorders:
•Sexually Transmitted Disease (STD)
Ex.: syphilis, gonorrhea, genital herpes, AIDS
o http://www.cdc.gov/std/
o http://www.plannedparenthood.org/healthtopics/stds-hiv-safer-sex-101.htm
o http://www.webmd.com/sexualconditions/default.htm
•Epidemic in some geographic areas
•May be transmitted by both males and females
•Can cause sterility or death if not treated
•Early treatment leads to recovery
Prostate Enlargement – enlargement of prostate gland
– common in males over 40
Breast Cancer – cancerous growth in both male in
female breast tissue.
Major cause of death in women 25 – 45 year old.
Early detection and treatment very important in
identifying and curing.
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Documents\a.BIOLOGY 2012-2013\POWER POINTS\HUMAN
REPRODUCTION\US Breast Cancer Stats 2011 to 2012.pdf
Cervical Cancer - caused by several types of a
virus called human papillomaviruses (HPV)
•spreads through sexual contact
•sometimes the virus leads to cancer
•At higher risk if you smoke, have many children,
use birth control pills for a long time, or have HIV
infection.
•A vaccine for girls and young women protects
against the four types of HPV that cause most
cervical cancers
http://www.nlm.nih.gov/medlineplus/cervicalcancer.
html