Fertilization and Early Development

1
Fertilization and Early Development

• Campbell, N. 1999 Biology. United States
  Benjamin Cummings Publishing Company.

2
Fertilization

• Fertilization or Syngamy
• Union of haploid gametes (egg/ova and sperm) to
  form a zygote takes place in the fallopian tube
• The egg is fertilized in the oviduct, the
  resulting zygote travels down into the uterus.

3
Pregnancy and Development

• Gestation is divided into three trimesters.
• First trimester
• Second trimester
• Third trimester

4
Hormonal Control of Pregnancy

• During the first trimester the embryo secretes a
  hormone indicating its presence, HCG (sometimes
  excreted in the urine-pregnancy tests)
• HCG acts like the pituitary LH maintaining
  progesterone and estrogen secretion through the
  first trimester
• Increased mucus secretion in the cervix
• Growth of placenta
• Cesation of ovulation and menstrual cycle
  (-feedback)

5
First Trimester

• Cleavage begins 24 hrs. after fertilization.
• Blastocyst About after fertilization a mass of
  cells or blastocyst is formed.
• Implantation 7 days after ovulation the
  blastocyst implants in the endometrium. The
  endometrium responds by growing over the
  blastocyst. Tissue grows from the embryo joining
  the endometrium and forming the placenta.
• Organogenesis (fetus) period of extensive
  development and radical change for both mother
  and baby). Example heart beats by the fourth
  week by the end of the eight week all the organs
  are present in rudimentary form

6
Second Trimester

• Rapid growth of fetus
• Movement
• Hormonal levels stabilize as HCG declines.
  Placenta secretes its own progesterone
• Corpus luteum deteriorates

7
Third Trimester

• Fetal activity decreases as fetus fills available
  space in the embryonic membranes
• Mothers abdominal organs become compressed and
  displaced resulting in frequent urination and
  digestive blockage

8
Hormonal Control of Birth

• Progesterone is needed to facilitate implantation
• Birth or parturition occurs through a series of
  strong, rhythmic contraction of the uterus,
  commonly called labor.
• Prostaglandins from the uterus, oxytocin from the
  Posterior Pituitary and nervous reflexes all
  regulate labor contraction

9
Stages of Labor

• First stage of labor. The opening of the cervix
  thins out and dilates. Complete dilation of the
  cervix ends the first stage of labor
• Second stage is birth. The uterus is firmly
  attached to the floor of the abdomen. Continuous
  contractions force the fetus down and out the
  uterus and vagina
• Final stage. Expulsion of the placenta.

10
Fetal Development

• List and describe embryonic membranes
• Explain how the exchange of materials between
  mother and fetus takes place
• Oral Presentation (see due date)
• Genetic screening and assisted fertilization
  techniques (I.e IVF, GIFT)
• Research Paper (TBA)
• Describe four methods of family planning and
  contraception
• Discuss ethical issues associated with family
  planning and contraception