1. Fertilization and Development
11.4 Reproduction
Fertilization and Development

2. I. Fertilization
A. As a result of sexual intercourse (copulation), millions of sperm are ejaculated into the female’s vagina.
1. The sperm cells swim within the fructose rich semen through the narrow cervix and into the uterus.
2. A few of the sperm cells are able to actively swim against a fluid current generated by the cilia that line the oviducts (fallopian tubes).
3. Should this coincide with an egg being inside at least one of the oviducts then a fertilization is possible.

3. Pregnant Elephant (Mammal) Internal fertilization and Development
After a twenty-two-month pregnancy, the mother will give birth to a calf that will weigh about 113 kg (250 lb) and stand over 76 cm (2.5 ft) tall.

4. B. In the Oviduct
1. A small number of sperm (10’s) actually make it to the egg.
2. These few sperm will try to penetrate the follicle layer (corona) surrounding the secondary oocyte.
3. Several sperm will gain access to receptors on the zona pellucida (glycoprotein gel layer) and release hydrolytic enzymes contained in their ACROSOME.
Acrosome Reaction

5. Fertilization: Sperm Cell Penetrates Egg with
Acrosomal Enzymes

6. 4. These enzymes dissolve a route to the plasma membrane.
5. ONE sperm reaches the plasma membrane first and fuses membranes to initiate the CORTICAL REACTION.
CORTICAL REACTION.
Release of Ca++ causes cortical granules to fuse with the oocytes cell membrane and release their enzymes by EXOCYTOSIS to the outside.
These enzymes result in a raising of the egg membrane and a chemical change of the zona pellucida making it impermeable to any more sperm.
Ensures that only one sperm cell actually fertilizes the egg.

8. 6. The sperm releases the nuclei into the oocyte.
7. The fertilized oocyte now contain two haploid nuclei forming a diploid ZYGOTE.

9. II. Pregnancy A. Early Human Embryonic Development
1. Fertilization triggers the zygote to divide by mitosis. (first division occurs about 24 hour after fertilization)
2. The embryo continues to divide and increase in number of cells not size as it moves through the fallopian tubes moving towards the uterus for implantation.
At this stage of about 100 cells the embryo is called a BLASTOCYST.

10. Structure of the BLASTOCYST: (no change in size just number of cells)
a. TROPOBLAST- outer layer of cells help form the fetal portion of the placenta.
b. INNER CELL MASS- forms the body of the embryo.
c. Fluid- filled cavity.

11. Fertilization Occurs in the Oviducts

12. B. Secretion of Human Chorionic Gonadotrophin:
1. The implantation of the blastocyst into the uterine lining begins the secretion of human chorionic gonadotrophin (HCG) by the blastocyst.

13. 2. HCG enters the bloodstream of the mother to target the CORPUS LUTEUM in the ovaries.
HCG maintains the corpus luteum to continue secreting PROGESTERONE and ESTROGEN to maintain the uterine lining for the early part of pregnancy.
This process is taken over by the placenta later in the pregnancy.

16. III. Role of Placenta
A. About a week after fertilization, the embryo implants itself into endometrial lining of the uterus to start the formation of the placenta.
1. The placenta forms from the trophoblast layer of the blastocyst.
2. The placenta allows for the exchange of material between the mother and the fetus.

17. Material passed from fetus to mother.
Material passed from mother to fetus.
Carbon dioxide
Oxygen
Urea (waste)
Nutrients (ex) glucose- passive transport, amino acids- active transport
Water
Hormones
Vitamins and Minerals
Alcohol, drugs, nicotine
Some Viruses (HIV and German measles)

18. B. Structure of the Placenta
(a) Umbilical cord- attaches the fetus to the placenta
(b) Umbilical arteries- carry deoxygenated blood to the maternal blood to be re-oxygenated. The fetal blood has a much stronger affinity for oxygen than maternal blood
(c) Umbilical vein- carries the oxygenated blood back to the circulatory system of the fetus.
(d) Placental tissue- embedded deep within the maternal endometrium.

20. (e) Myometrium- strong muscular wall
(f) Endometrium- thick vascular tissue.
(g) Maternal blood supply.
(h) open ended arterioles forming pools of maternal blood (i)
(j) Chorionic villi- embedded deep in the endometrium and in close association with maternal blood

23. C. The placenta also acts as an endocrine organ in the second half of pregnancy.
1. The corpus luteum degenerates and stops the production of estrogen and progesterone at about 20 weeks of development.
2. The placenta takes over the production of estrogen and progesterone in order to maintain the uterine lining for the remainder of the pregnancy.

24. IV Role of Amniotic Fluid
A. Some of the tissue of the developing embryo is used to create the AMNIOTIC SAC.
1. The amniotic sac forms around the embryo and is filled with AMNIOTIC FLUID.
2. Functions of the amniotic fluid:
a. Cushions and protects floating fetus.
b. Environment for free movement for growth and development.
c. Thermal stability.

25. Amniocentesis

26. V. Hormones associated with Birth
A. The physiological events associated with the body’s preparation for birth is called PARTURATION.
1. PROGESTERONE levels significantly drop.
2. At about the same time the OXYTOCIN is secreted from the POSTERIOR PITUITARY gland of the mother.
3. Studies have shown that the decrease in PROGESTERONE near the end of pregnancy may be associated with the production of OXYTOCIN receptor on the uterus.

27. 4. POSITIVE FEEDBACK-
a. The production of low levels of OXYTOCIN in the beginning of labor stimulate the first contractions of the MYOMETRIUM of the UTERUS.
b. Each contraction sends signals back to the POSTERIOR PITUITARY to produce MORE OXYTOCIN causing the contractions to INTENSIFY and become more FREQUENT.
c. The child is passes though the cervix and vagina to be born
d. Contractions continue for a further period until the placenta is delivered (after birth).

29. 5. Major Events of Childbirth
a. The cervix softens and opens to 10 cm.
b. Baby is engaged in the pelvis head- first and face down.
c. The shoulders are the widest part of the baby to pass through the birth canal.
d. The afterbirth or placenta is expelled from the uterus.
e. Lactation begins soon after childbirth.
Child Birth Animation

30. http://www.youtube.com/watch?v=F4MzcpX3viY Elephant Birth