1. Human Development: From Conception to Birth
Biology DAY 2
Reproductive System
Human Development: From Conception to Birth

2. What are we learning today?
Benchmark
Objectives
SC.912.L …Describe the process of human development from fertilization to birth and major changes that occur in each trimester of pregnancy.
I will describe the process of human development from the zygotic stage to the end of the third trimester and birth.

3. What is the essential question?
Summarize that changes that occur each trimester during the development of the embryo or fetus.
Answer:
First trimester
Organ systems begin to form (cell differentiation)
Nervous system begins forming
Heart begins beating
Embryo begins to move
Ears, eyelids, and teeth buds are formed
Second trimester
Mostly growth
Fetal skeleton forms
Mother can feel the fetus moves
Fetus can now hear.
Hair forms on the body
Third trimester
Fetus turn into a head-down position.
Fat is deposited beneath the skin
A greasy substance forms on the fetus skin.
Lungs mature
Fetus can see light and react to sounds.

4. What cellular processes make it all happen?
Growth or the increase in the number of cells.
Development or the arrangement of the cells into specific organs.
Differentiation or the specialization of cells to perform specific tasks and functions.
To the Teacher: Use the frog diagram to explain cellular processes.

5. Occurs in upper third of Fallopian tube
What is fertilization?
Fertilization is the union of a sperm cell and an egg cell to form a zygote.
Occurs in upper third of Fallopian tube
Only 1 sperm can fertilize an egg
To the Teacher:

6. Fertilization
During sexual intercourse, sperm are released when semen is ejaculated through the penis into the vagina, a point just below the cervix.
300 million sperm are released in about 4 ml of sperm.
Sperm swim actively through the uterus into the Fallopian tubes.

7. Fertilization
The egg is surrounded by a protective layer that contains binding sites to which sperm can attach.
When a sperm attaches to a binding site, a sac in the sperm head releases powerful enzymes that break down the protective layer of the egg.
The sperm nucleus then enters the egg, and chromosomes from the sperm and egg are brought together.
The process of a sperm joining and egg is called fertilization.
The fertilized egg is called a zygote.

8. Fertilization
What prevents more than one sperm from fertilizing an egg?
Egg cell contains a series of granules just beneath its outer surface.
When a single sperm enters the egg, the egg reacts by releasing the contents of these granules outside the cell.
The material in the granules coats the surface of the egg, forming a barrier that prevents other sperm from attaching to an entering the egg.
Early in the 20th Century, cell biologist Ernest Everett found the answer.

9. Early Development
While still in the Fallopian tube, the zygote begins to undergo mitosis.

10. Early Development
Four days after fertilization, the embryo is a solid ball of about 64 cells called a morula.
The stages of early development include implantation, gastrulation, and neurulation.

11. What is implantation?
Zygote divides several times to form a solid ball of cells called a morula.
More cellular divisions result in a blastocyst, a ball of cells with a large fluid cavity.
Blastocyst burrows into the lining of the uterus during implantation.
Describe the process of fertilization and implantation?

12. Implantation
As the morula grows, a cavity forms in the center transforming the morula into a hollow structure with an inner cavity called a blastocyst.
About 6-7 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 in a process called implantation.

13. Implantation
At this point, cells in the blastocysts begin to specialize as a result of the activation of genes in a process called differentiation.
Differentiation is responsible for the development of the various types of tissue in the body.
An inner cell mass develops within the inner cavity of the blastocyst from a which the embryo will develop.

14. What happens after implantation?
Implanted blastocyst gradually sorts itself into three layers forming a gastrula.
All the organs and tissues of the embryo will be formed from these three layers by cell differentiation.

15. What is neurulation?
Neurulation is the development of the nervous system.
Neural folds create neural tube.
One end of the neural tube will develop into the brain, the other end develops into the spinal cord.

16. Neurulation Neurulation is the development of the nervous system.
A block of mesodermal tissue differentiates into a notochord.
Ectoderm near the notochord thickens and forms the neural plate.
The raise edges of the neural plate forms the neural folds.
Gradually, these folds move together to create a neural tube.
One end of the neural tube will develop into the brain, the other end develops into the spinal cord.
Cells of the neural crest migrate to other locations and develop into nerves.

17. What are some important extraembryonic structures?
Placenta is the structure through which the mother nourishes the embryo
Umbilical cord contains arteries and veins that carry blood between the embryo and the placenta C
Amniotic sac is a membrane that surrounds the embryo
Amniotic fluid keeps cushions the embryo from injury and keeps it moist

18. Extraembryonic Membranes
As the embryo develops, membranes form to protect and nourish the embryo.
The amnion develops into a fluid-filled amniotic sac, which cushions and protects the developing embryo within the uterus.

19. Extraembryonic Membranes
The chorion, the outermost of the extraembryonic membranes forms by the end of the 3rd week.
Small, fingerlike projections called chorionic villi form on the outer surface of the chorion and extend into the uterine wall.

20. Placenta Previa
Condition where the placenta lies low in the uterus and partially or completely covers the cervix.
Affects about 1 in 200 pregnant women in the third trimester of pregnancy.
Most common symptom is painless bleeding during the third trimester.
Premature contractions
Baby is breech, or in transverse position
Uterus measures larger than it should according to gestational age.

21. Placenta Abruptio Separation of the placenta from the uterine lining.
Usually occurs in the 3rd trimester, but can occur any time after the 20th week of pregnancy.
Only about 1% of all pregnant women will experience placental abruption
Most can be successfully treated depending on what type of separation occurs.

22. What are the major milestones of the first trimester?
All organ systems begin to form (cell differentiation)
Nervous system begins forming
Heart begins beating
Embryo begins to move
Ears, eyelids, and teeth buds are formed

23. Why is Early Development so Important?
Early development can be disrupted by a number of external factors.
Many substances can penetrate the placenta.
AIDS and German measles.
Alcohol and other addictive substances.
Medications.

24. What are the major milestones of the second trimester?
Tissues of the fetus become more complex and specialized, and begin to function.
Mostly growth
Fetal skeleton forms (bone replaces cartilage)
Mother can feel the fetus moves
the The fetal heart becomes large enough so that it can be heard with a stethoscope.
Fetus can now hear.
Soft hair forms on the body

25. What are the major milestones of the third trimester?
Organ systems mature.
Fetus grows in size and mass.
The lungs and other organs undergo a series of changes to prepare them for life outside the uterus.
Fetus turns into a head-down position.
Fat is deposited beneath the skin
A greasy substance forms on the fetus skin.
Fetus can see light and react to sounds.
Regulates its body temperature.
What are the major milestones of the third trimester?

26. Muscles in the vagina and cervix relax allowing them to enlarge
What is birth?
Takes place about 38 weeks after fertilization
Muscles in the vagina and cervix relax allowing them to enlarge
Uterine contractions force fetus through birth canal
Once umbilical cord is cut, baby functions independently

27. Childbirth
These contractions expand the cervix until it is large enough for the head of the baby to pass through it.
Once the amniotic sac breaks, contractions of the uterus force the baby out.
In a final series of contractions, the placenta itself and the empty amniotic sac are expelled from the uterus as the afterbirth.

28. Caesarean Section
Operation in which a baby is removed from a mother’s body through incisions in her abdominal wall and uterus.
Name came from a Roman law, under Julius Caesar, that required all women dying in childbirth to undergo the procedure in order to save the offspring.

29. What is the essential question?
Summarize that changes that occur each trimester during the development of the embryo or fetus.
Answer:
First trimester
Organ systems begin to form (cell differentiation)
Nervous system begins forming
Heart begins beating
Embryo begins to move
Ears, eyelids, and teeth buds are formed
Second trimester
Mostly growth
Fetal skeleton forms
Mother can feel the fetus moves
Fetus can now hear.
Hair forms on the body
Third trimester
Fetus turn into a head-down position.
Fat is deposited beneath the skin
A greasy substance forms on the fetus skin.
Lungs mature
Fetus can see light and react to sounds.

30. The Miracle of Life