Pregnancy Flashcards
Define fertilization
Fertilization occurs when the chromosomes from the male & female gametes come together in the ovum
When does fertilization usually occur?
Usually occurs around day 14 of female ovarian cycle
When does the embryo enter the uterus?
Day 4-6 after fertilization
Define implantation
Act of burrowing into endometrium
When is an embryo called a blastocyte?
During implantation
What structures are present in the blastocyte?
1. Inner cell mass A. Future embryo 2. Trophoblast A. Outer layer B. Provides nourishment for embryo C. Becomes placenta
What cells contribute to the placental development?
- Both embryonic & maternal tissues contribute to placenta
A. Trophoblastic and blastocyst cells proliferate
B. Trophoblastic cells, with endometrial cells, form placenta
Where does the embryo get nutrition for the first 8 weeks of pregnancy?
- As trophoblastic cells invade endometrium, stored nutrients in endometrium are used by embryo for growth and development
- Embryo continues to obtain nutrients as above until week 8 when placenta begins to form
Where does the mesoderm of the placenta develop from?
Trophoblast gives rise to formation of mesoderm
What two cells layers form chorionic villi?
Inner cell mass and trophoblast
What is the chorionic villi?
- Chorionic villi are intricate network of blood vessels
- come into direct contact with maternal blood
A. Microscopic projections that line the chorion, the outermost layer of the embryonic sac
Why are the chorionic villi important?
- Surgeons sample these projections for genetic testing because they contain the same genetic material as a fetus (>90% accuracy)
- Able to be sampled before amniotic fluid
- Very low risk of miscarriage
How does the umbilical cord form?
- Embryo connects to the chorion through small stalk that carries blood to and from placenta
- Stalk becomes umbilical cord when embryonic vessels form over the next 2 weeks
- Once vascular connection is formed, nutrients, wastes, & other substances begin diffusing between mom’s blood & embryo’s blood across chorionic villi
How long does it take the umbilical cord to form?
usually occurs by the end of the first month of pregnancy
What is the chorion?
The outermost layer of the embryonic sac
When is the placenta formed by? How is this related to growth of the chorionic villi?
- Chorionic villi continue to grow in complexity until placenta is formed, usually about the beginning of the fourth month of pregnancy
- Chorionic villi are the precursor to the placenta
What is the flow of blood through the placenta?
- Blood flows to placenta through paired umbilical arteries & away from placenta through umbilical vein
What hormones does the placenta produce?
- Human Chorionic Gonadotropin
- Estrogens
- Progesterone
What is HCG secreted by?
- Secreted by fetal tissues
2. Occurs coincidentally with the development of trophoblast
What vessels of the placenta carry oxygenated blood?
umbilical vein carries oxygenated blood & nutrients to fetus
What vessels of the placenta carry deoxygenated blood and wastes?
Umbilical arteries carry wastes & deoxygenated blood to placenta
When can HCG be measured? How does secretion rates change during pregnancy?
- Can be measured 8 days after ovulation
A. Ovum implants in endometrium - Rate of secretion rises rapidly over first 8 weeks
- Decreases to low values at 16-20 weeks
What is the function of HCG?
- Stimulates corpus luteum to produce greater quantities than usual of progesterone and estrogen
A. Causes endometrium to thicken and store nutrients
When does the placenta begin to secrete estrogen and progesterone?
After 7 weeks gestation, placenta begins to secrete sufficient quantities of progesterone and estrogen to maintain pregnancy
What is the concentration of estrogen production by the placenta?
Increases to approximately 30x normal by end of pregnancy
What are the functions of estrogen in a pregnant woman?
- Enlargement of uterus
- Enlargement of breast stromal tissue and growth of breast ductal tissue
- Relax pelvic ligaments
A. Facilitate passage of baby through birth canal
What is the concentration of progesterone production by the placenta?
Increases ten-fold by end of pregnancy
What are the functions of progesterone in a pregnant woman?
- Causes decidual cells to develop in endometrium
A. Important role in nutrition of embryo - Decreases contractility of pregnant uterus
A. Prevents spontaneous abortions - Prepares mom’s breasts for lactation
A. Growth of lobules and alveoli
define parturition
Expulsion of fetus
When does normal parturition occur?
Occurs approximately 266 days after fertilization & 280 days after last menstrual period
What hormonal changes occur at the end of gestation?
1. Estrogen levels rise A. From placenta 2. Oxytocin levels rise A. Stimulated by high estrogen levels & distortion of cervix 3. Prostaglandin production A. Stimulated by estrogen & oxytocin
What is the dilation stage of labor?
cervix dilates & fetus descends into birth canal
What is the expulsion stage of labor?
cervix fully dilated, fetus emerges from birth canal
What is the placental stage of labor?
- connection between uterus & placenta breaks, allowing delivery of placenta
A. Afterbirth
What is lactation stimulated by?
Milk formation: Prolactin secreted by anterior pituitary
When do prolactin levels begin to rise?
- Secretion rises steadily from 5th week gestation until birth
A. Level 10x normal by delivery
When does milk begin to be released after birth?
- Promotes secretion of milk
A. Within 2-3 days after birth, breasts begin to secrete milk
Define colostrum
- Colostrum contains more proteins & less fat than breast milk
- Infant ingests this in first 2 or 3 days of life
- High levels of IgGs
When does colostrum secretion begin?
By the end of 6th month pregnancy, mammary glands secrete colostrum
When does milk production begin to occur?
As colostrum production drops, mammary glands produce breast milk
What is the composition of breast milk?
Consists of water, proteins, amino acids, lipids, sugars, salts, & lysozymes
Describe the milk let down reflex
- Mammary gland secretion triggered when infant sucks on nipple
- Tactile receptors stimulate neurons in paraventricular nucleus of mom’s hypothalamus
- These neurons release oxytocin at post pituitary gland
- When oxytocin reaches mammary gland, myoepithelial cells of lactiferous ducts & sinuses contract, resulting in milk ejection
