Answers, BIO 2320, Pregnancy

Objectives – 4, BIO 2320, Pregnancy and DevelopmentAnswers


1.Oviduct; joining of egg & sperm. Fertilization is the point where the sex of the baby is determined. If the sperm was carrying a Y chromosome it is a boy and if the sperm was carrying an X chromosome it is a girl.

2.Change in head of sperm weakening the acrosomal cap so that it may release its enzymes upon the layers around the egg.

3.Fertilized egg, diploid

4. Dizygotic are fraternal and are 2 different eggs fertilized by 2 different sperm. Monozygotic are identical with one egg plus one sperm forming one zygote that then splits into two.

5.Egg wall changes so that no other sperm may enter. Nucleus of egg and sperm unite, then cleavage begins

6.Cleavage is mitosis as zygote travels down oviduct. A ball of identical cells formed from cleavage is a morula. Once in the uterus, the cells rearrange to become a blastocyst.

7.When the blastocyst burrows its way into the mom’s endometrium on day 7 or 8, this is implantation.

8.Gastrulation is the stage where the germ layers form. Depending which layer a cell ends up in determines which organ it will become. Neurulation is the formation of the neural tube which will become brain cranially and spinal cord, organogenesis is the beginning of the formation of all major organs in the body and is occurring at about week 4.

9.Ectoderm becomes skin & nervous system, Mesoderm becomes cardiovascular system, muscles, bone, connective tissues, Endoderm becomes digestive structures and lungs

10.At the end of the second month of gestation, the embryo distinctly has human characteristics and at that point is called a fetus.

11.HCG is made by the embryo from about week 2-12. It is the hormone that is tested for in do-it-yourself pregnancy tests. It keeps the corpus luteum alive so that the endometrium won’t be sloughed as with a non-pregnant menstrual cycle. By keeping the corpus luteum alive, estrogen & progesterone continue to be produced.

12.By week 12, the placenta takes over the role of making estrogen & progesterone and continues to do so throughout the rest of pregnancy. The placenta is where mom’s blood meets baby’s blood without the blood actually mixing. However, diffusion allows nutrients and oxygen to travel from mom’s blood to baby’s and diffusion allows waste and carbon dioxide to travel from baby’s blood to mom’s.

13.Mom’s endometrium (=decidua basalis) plus baby’s chorion

14.Decidua basalis is mom’s endometrium, trophoblast cells are the outer cells of the blastocyst stage of the embryo that develop into an outer membrane called the chorion. The chorion is vascular and has finger-like extensions digging into mom’s endometrium called villi. Here is the location of diffusion. The Umbilical arteries & vein comprise the umbilical cord and connect baby to the placenta. The fetal membrane immediately surrounding the fetus is the amnion and it is filled with the fetus plus fluid called amniotic fluid. The fluid allows movement, is a protective cushion and keeps a constant temperature for the fetus.

15.40 full weeks = 280 days.

16.The uterus has weak contractions due to the very high levels of estrogen towards the end of pregnancy. When these contractions are about every 30 minutes, labor has begun. A contraction will finally be strong enough to break the amnion and thus releasing the amniotic fluid (water breaking).

17.As the weak contractions force baby’s head into the cervix, the cervix is stretched. This stretching causes the hypothalamus to make oxytocin which is released from the post pituitary gland. Oxytocin causes a uterine contraction which forces baby’s head more into the cervix and the stretching causes more oxytocin –>stronger contraction –>more stretching of cervix –>more oxytocin –>bigger contraction…

18.Oxytocin covered above. Relaxin is made by the placenta and “relaxes” mom’s pelvic structures making it easier for a baby to pass through.

19.After delivery of baby, the oxytocin is still causing uterine contractions which in an empty uterus causes a shearing and passing of the placenta.

Urinary, Reproduction and Development flash cards: