Chapter 5 Flashcards
How many chromosomes results from meiosis?
23 (22 autonomies and 1 sex chromosome)
What is crossing over?
Each chromosome exchanges some material with its mate to allow variation in genetic material
What are primary follicles?
A layer of follicular cells that surround primary oocytes
Throughout childhood, what stage are a females eggs at?
The primary follicle and its oocyte, which still contains 46 chromosomes remain dormant
When are primary germ cells produced in females?
During about 30th week of fetal life
when are primary germ cells produced in males?
Continuously after puberty
Number of mature germ cells that develop from each primary cell in males and females?
Females: 1
Males: 4
When does the primary oocyte complete its first meiotic division, which began in fetal life?
Shortly before ovulation (the result is a secondary oocyte containing 23 chromosomes)
When does the second meiotic division of an oocyte occur?
Is prolonged and remains suspended in metaphase until fertilization occurs
Two layers that surround the mature ovum when it’s released from the ovary
Zona pellucida
The cells of the corona radiata
How long does spermatogenesis take?
Approx 70 days
Hormones that cause oocytes to begin to mature before ovulation
FSH & LH
Sac the maturing oocyte is contained in before ovulation
Graafian follicle
Hormones the Graafian follicle produces
Why?
Estrogen and progesterone
To prepare the endometrium for a possible pregnancy
After the mature ovum and its surrounding cells are released onto the surface of the ovary, what does the collapsed follicle transform into and what is its purpose?
Corpus luteum
Maintains high estrogen and progesterone secretion which is necessary to finish preparing uterine lining for fertilized ovum
Where does fertilization normally occur?
In the distal third of the Fallopian tube (ampulla) near the ovary
How long after release from the ovary does it take for the ovum to enter the uterus?
4 days
Function of seminal fluid
Nourishes and protects sperm from acidic environment of the vagina
What is capacitation?
Changes sperm undergo to enable one of them to penetrate the protective layers surrounding the ovum
When has fertilization officially occurred?
When one spermatozoon enters the ovum and the two neuclei containing the parents’ chromosomes merge
When is the preembryonic period?
First 2 weeks after conception
What occurs during the preembryonic period?
Initiation of cell division (conceptus)
Zygote enters the uterus (4th day after fertilization)
Implantation in the decidua (what the endometrium is now called)
Zygote secretes hCG to signal woman’s body that pregnancy has begun
Cells and membranes resulting from fertilization of the ovum
Conceptus
When the conceptus is a solid ball of 16 cells
Morula
After the blastocyst enters the uterus, how long does it stay before it implants?
Approx 2-4 days
Another name for implantation
Nidation
When does implantation occur?
Approx 6-10 days after fertilization
How is the decidua maintained?
Zygote secretes hCG to signal pregnancy to woman’s body
Production of hCG by conceptus causes corpus luteum to continue secretion of estrogen and progesterone until placenta takes over this function
Why is the upper uterus the best place for implantation?
Richly supplied with blood
Lining is thicker, preventing placenta from attaching too deeply
Limits blood loss after birth because of strong interlacing muscle fibers in this area
What are primary chorionic villi?
Tiny projections of surface of the conceptus that extend into the endometrium (the decidua now) and eventually form the fetal side of the placenta
What forms the maternal side of the placenta?
Decidua basalis (what the endometrium was)
When is the embryonic period?
From the beginning of the 3rd week through the 8th week after conception
What occurs during the embryonic period?
Basic structures of all major body organs are completed
When is the fetal period?
Begins 9 weeks after conception and ends with birth
Define embryo
Developing baby from the beginning of the third week through the 8th week after conception
When are structures of the baby most vulnerable to damage from teratogens and why?
During the embryonic period (3rd - 8th week) because structures are developing so rapidly
What is considered full term?
36-40 weeks of fertilization age
38-42 weeks of gestational age
Major developments during weeks 9-12
Eyes close at 9 weeks
Intestines move from umbilical cord to abdomen at 11 weeks
Blood formation shifts form the liver to the spleen by end of week 12
Fetus begins producing urine
Fetal gender can be determined by end of week 12
Developments during weeks 13-16
Head becomes more proportionate to body as body grows rapidly in length
Movements strengthen, mother may be able to detect them
Ears become in line with the eyes
Developments during weeks 17-20
Fetal movements feel like fluttering
Vernix covers skin
Lanugo covers body
Brown fat deposited
Developments during weeks 21-24
Skin is still translucent
Lungs begin to produce surfactant (actually begins at 20 weeks and continues throughout)
Capillary network surrounding alveoli increasing
Developments during weeks 25-28
Lungs, pulmonary capillaries, and CNS more mature, survival is more likely
Subcutaneous fat deposited under skin
Skin gradually becomes less red
Eyes reopen
Head hair is abundant
Blood formation shifts from spleen to bone marrow
*Fetus usually assumes head down position
Developments during weeks 29-32
Skin is pigmented according to race
Toenails present, fingernails extend to fingertips
More subcutaneous fat which rounds body contours
Chances of survival are good, esp with specialized neonatal care
Developments during weeks 33-38
Fetus mainly gaining weight
Lanugo may be present on forehead, upper back, upper arms
Vernix remains in major creases
Testes in scrotum
Breast tissue palpable b/c of maternal hormone effects
List the auxiliary structures that sustain pregnancy and permit normal prenatal development
Placenta
Umbilical cord
Fetal membranes
Which side of the placenta is which?
Smooth side is toward fetus
Rough side is toward uterus
What are the intervillous spaces of the placenta?
Where exchange of substances between mother and fetus occurs
Maternal blood washes over chorionic villi containing fetal vessels and returns to maternal circulation
3 reasons that explain how the fetus can thrive in the low-oxygen environment
- fetal hemoglobin can carry more oxygen
- fetus has higher hemoglobin level so can cherry more oxygen
- low carbon dioxide partial pressure (Pco2) levels allow hemoglobin to carry more oxygen
Major energy source for fetal growth
Glucose
Functions of the placental hormone, human placental lactogen
Promotes normal nutrition and growth of the fetus
Promotes maternal breast development for lactation
Decreases maternal insulin sensitivity and glucose use, making more glucose available for the fetus
Steroid hormones secreted by the placenta
Progesterone and estrogen
Two fetal membranes
Amnion (inner membrane)
Chorion (outer membrane)
How does the amniotic fluid protect the fetus
- cushions against impacts
- maintains stable temperature
- promotes normal prenatal development
(Symmetric development, prevents membranes from adhering to developing fetal parts, allows movement)
Abnormally small amount of amniotic fluid
Oligohydramnios
Too much amniotic fluid
Hydramnios
Functions of the arteries in the umbilical cord
Carry deoxygenated blood and waste products away from the fetus to the placenta
Function of the vein in the umbilical cord
Carries oxygenated blood and nutrients from the placenta back to the fetus
What is Wharton’s jelly?
Soft substance in umbilical cord that prevents obstruction
Three shunts in the fetal circulatory system
Ductus venous
Foramen ovale
Ductus arteriosus
Function of the three shunts in the fetal circulatory system
Allow blood with the highest oxygen concentration to be sent to the fetal heart and brain
What does the ductus venous connect to?
The inferior vena cava (skips the liver)
What is the Foramen ovale?
Flap valve in septum between right and left atria of fetal heart
What does the ductus arteriosus connect to?
Connects the pulmonary artery and the descending aorta during fetal life
What happens to the Foramen ovale after birth?
When the infant breathes air, the Foramen ovale closes
What happens to the ductus arteriosus after birth?
It constricts as the arterial oxygen levels rise
What happens to the ductus venous after the baby is born?
It constricts when the flow of blood from the umbilical cord stops
Becomes a ligament
How are monozygotic twins conceived?
By a single ovum and spermatozoon that divide into two
How are dizygotic twins conceived?
Arise from two ova fertilized by different sperm
