Reproduction-and-Development of Human Beings

Developmental biology lesson

2. 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?
KEY QUESTIONS FOR THIS UNIT

3. 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.

4. 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)

5. 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

6. 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.

8. Zygote (approximately 16-20 hours after
insemination)
Two-cell embryo (approximately 24 hours after
insemination).
Four-cell embryo (approximately 45 hours after
insemination). Eight-cell embryo (approximately 72 hours after insemination).

9. 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

10. Blastula-development of hollow center filled with
fluid-blastocoel
On the 4th day after insemination an epithelial cellular
layer forms, thicker towards the outside, and its cells
flatten out and become smaller.
Yolk filled end
Fluid filled inside sphere
opening

11. 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.

12. 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.

13. 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

14. Ectoderm
Mesoderm
Endoderm
Nervous system, epidermis, sweat glands, hair and
nails, lining of mouth, nostrils and anus
Bones & muscles, blood, blood vessels & heart,
reproductive and excretory systems, inner layer of
skin
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

15. 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.

17. Which came first?
https://www.youtube.com/watch?v=1a8pI65emDE

18. 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

19. yolk
(Part of white)
chorion
2.shell-
prevents bacteria from entering, porous
enough for oxygen and carbon dioxide to
exchange, slows rate of evaporation.

20. 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.
b. Umbilical cord-attaches the embryo to the
placenta of the mother in the uterus
** 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.

22. 2. Non placental mammals- 2 types
a. egg laying mammals (monotremes) -
duckbill platypus, spiny anteater

23. b. marsupials- pouched mammals-kangaroo, opossum

24. 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

26. 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

27. 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.

28. 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

29. Female Secondary Male Secondary
Sex CharacteristicsSex Characteristics
•Development of
breasts
•Changes in body form
•Growth of body hair
•Growth of beard and
body hair
•Changes in body
form
•Lowered voice pitch

30. 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.

31. 1. Testes: make and store sperm
(scrotum)
-- saclike pouch which houses the testes, is 1-2
degrees Celsius below normal body
temperature
Just before birth (and sometimes just after) the testes
descend through a canal into an external sac called the
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

32. The haploid
sperm cell is
produced in
the
seminiferous
tubules and
move to the
epididymis
until they are
fully mature.

33. 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

34. 6. Urethra: opening through the penis
7. Penis: releases the semen
SEMEN:
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.
liquid loaded with sperms
About 2 to 6 milliliters of semen, containing more than 200 to 600
million sperm, are released in an average ejaculation.

36. 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

37. 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.

38. 2. Ovaries also secrete estrogen (hormones)
responsible for secondary sex characteristics
B. Fallopian tubes or Oviduct - leads from each
ovary (neither in contact)
1. Site for fertilization
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

39. 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

41. 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.

42. 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.
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..
Fertilization occurs in the upper portion of the
oviduct (Fallopian Tube)

43. Sometimes - for varying reasons (blocked oviduct,
infertile husband) – A technique known as in Vitro
Fertilization is used
Test-Tube Baby

44. 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

45. 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

47. Third Phase - Embryonic Period
Period of primary organ differentiation
Ends at about the 8
th
week
Last phase – a.k.a. Fetal Period
Characterized by rapid growth, changes in body parts
& the final preparation for birth

48. 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.

49. The Placenta also acts as a barrier for most
microorganisms.
However, certain viruses
AIDS
German measles
chicken pox
encephalitis
Can pass through

51. http://
www.med.upenn.edu/
meded/public/berp/
overview.mov

52. 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.

53. 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

54. 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).

55. 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.

56. 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.

58. 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.

59. Some important human reproductive disorders:
•Sexually Transmitted Disease (STD)
•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
Ex.: syphilis, gonorrhea, genital herpes, AIDS
ohttp://www.cdc.gov/std/
ohttp://www.plannedparenthood.org/health-
topics/stds-hiv-safer-sex-101.htm
ohttp://www.webmd.com/sexual-conditions/
default.htm

60. 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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a.BIOLOGY 2012-2013\POWER POINTS\HUMAN REPRODUCTION\US Breast
Cancer Stats 2011 to 2012.pdf

61. 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