Chapter 6: Conception and Prenatal Development Flashcards
1
Q
explain oogenesis
A
- formation of female gametes
- Begins during prenatal life
- Primary oogonium begins first meiotic division but does not complete the process until puberty
- Shortly before ovulation, the primary oocyte completes its first meiotic division–>secondary oocyte (23 chromosomes)
- At ovulation, the secondary oocyte undergoes a second meiotic division to form a mature ovum with 23 chromosomes
- During the 2nd meiotic division, the oocyte is suspended in metaphase until fertilization takes place.
- When ovum released from ovary, it is surrounded by zona pellucida and corona radiata which protect the ovum and prevent fertilization by more than one sperm
2
Q
explain spermatogenesis
A
- Begins during puberty, requires 70 days to be completes
- Male continues to produce new spermatogonia that can reach maturity throughout his lifetime
- 50% of the 4 spermatids that result from the 2 meiotic divisions of the spermatogonium carry an X and 50% carry a Y
3
Q
how long can an ovum survive after its release?
how long can a sperm survive in the female reproductive tract?
A
- ovum can survive no longer than 24 hours after its release
- male sperm can survive no longer than 24 in the female’s reproductive tract, but some can live up to 80 hours
4
Q
preparation for conception in the female
A
- before ovulation, many oocytes begin to mature d/t the release of FSH and LH–>the maturing oocytes form Graafian follicles which produce estrogen and progesterone to prepare the endometriumàeventually, only follicle outgrows the others
- release of the ovum:
- ovulation: 14 days before next menstrual period
- follicle develops a weak spot and ruptures
- collapsed follicle becomes the corpus luteum which secretes high levels of progesterone and estrogen
- ovum transport:
- ovum picked up by fimbriae of fallopian tube and transported along the tube
- fertilization normally occurs in the distal 1/3 of the fallopian tube (ampulla) near the ovary
- ovum, fertilized or not, enters uterus 3 days after release from ovary
- release of the ovum:
5
Q
preparation for conception in the male
A
- ejaculation:
- sperm suspended in seminal fluid which nourishes and protects them
- transport of sperm:whiplike movement of the tails propels the sperm
- uterine contractions (induced by PGs in the seminal fluid) enhance the movement of the sperm
- only sperm cells enter the cervix, seminal fluid stays in vagina
- preparation of sperm for fertilization:
- during trip to the ovum, the sperm undergoes capacitation–>glycoprotein coat and seminal proteins are removed from the acrosome on the sperm head
- so now can better penetrate the corona radiata and zona pellucida
- sperm then undergo an acrosomal rxn to penetrate the ovum by releasing hyaluronidase and acrosin
- during trip to the ovum, the sperm undergoes capacitation–>glycoprotein coat and seminal proteins are removed from the acrosome on the sperm head
6
Q
explain the process of fertilization
A
- entry of one spermatozoa can cause 3 things:
- zona reaction—zona pellucida changes and prevents a second sperm from entering
- cell membranes of the ovum and sperm fuse and break down which allows the contents of the sperm head to enter the cytoplasm of the ovary
- ovum completes its 2nd meiotic division
- fusion of nuclei:
- once the sperm has entered the ovum, the head enlarges and the tail degenerates and the nuclei start to fuse and move toward the center of the ovum
7
Q
when does implantation typically occur?
A
b/w 6-10 days after conception (average about 9 days after ovulation)
8
Q
what does implantation and survival of the conceptus require and how does the body get that?
A
- Implantation and survival of the conceptus requires a supply of estrogen and progesterone, so the zygote secretes human chorionic gonadotropin (hCG) to tell the body pregnancy has begun and to make the corpus luteum continue to produce estrogen and progesterone
9
Q
where does implantation occur most favorably? why?
A
- Normally occurs at the upper uterus slightly more on the posterior wall—this is b/c:
- Upper uterus has a rich blood supply for gas exchange, nutrition, waste
- Uterine lining is thick, so placenta won’t go too deep into muscle and placenta is easily expelled after birth
- Limits blood loss after birth b/c strong interlacin muscle fibers compress open endometrial vessels after placenta detaches
10
Q
what does the placenta look like?
A
- Thick disc-shaped organ that has a maternal and fetal component
- Fetal side is smooth, with branching vessels covering membrane-covered surface with the umbilical cord inserted near the center
- Maternal side is rough where it attaches to uterus
11
Q
explain the maternal component of the placenta
A
- when conception occurs, cells of endometrium undergo changes to provide nutrition to the early embryo and to convert to decidua
- exchange of substance b/w mom and fetus occurs within the intervillous space
12
Q
explain the fetal component of the placenta
A
- develops from the outer cell layer of the blastocyst and the primary chorionic villi
- umbilical cord contains the umbilical arteries and vein to transport bloodchorionic villi are bathed by oxygen and nutrient rich blood in the intervillous spaces
- each chorionic villous is supplied by a tiny fetal artery carring deoxygenated blood and waste products from the fetus
- vein of the chorionic villous returns oxygenated blood and nutrients to the fetus
- membranes of the villous separate the mother’s blood from contact with the fetal blood—good for compatibility problems
13
Q
what are the metabolic functions of the placenta?
A
- makes glycogen, cholesterol, fatty acids for the placenta
14
Q
what are the transfer functions of the placenta?
A
- Exchange of oxygen, nutrients, and waste products across the chorionic villi occurs through several methods
- Placental transfer of harmful substances also may occur
- Oxygen and carbon dioxide pass through the placental membrane by simple diffusion
- Nutrients – glucose, fatty acids, vitamins, and electrolytes pass readily across placenta
- Waste – carbon dioxide, urea, uric acid, and bilirubin are transferred from fetus to mother for disposal
- Antibody – IgG antibodies are passed from mother to fetus through the placenta, which confers passive immunity to fetus against diseases to which mother is immune
- Beneficial because newborn doesn’t produce antibodies for several months after birth
- Not always beneficial in the case of Rh antibodies
15
Q
What are the hormones the placenta can produce?
A
- hCG
- human placental lactogen
- estrogen
- progesterone
