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What is the diploid number of chromosomes in a normal human body cell?
Which type of cell division reduces the chromosome number by half?
What is the process of gamete formation in males called?
At what point in development does a female have all the ova she will ever have?
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Each sperm contains how many autosomes?
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How many sperm are produced from one primary spermatocyte during spermatogenesis?
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What type of cell division is primarily responsible for growth and cell replacement in the body?
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What is the primary function of human placental lactogen during pregnancy?
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What is the correct structure of the umbilical cord in terms of its vessels?
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Which shunt in the fetal circulatory system diverts most blood from the right atrium to the left atrium?
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What physiological change occurs to the foramen ovale after birth?
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What is true about the ductus venosus after the umbilical cord is cut?
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How many mature ova are formed from each primary oocyte during oogenesis?
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What is the composition of sex chromosomes in an ovum?
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When does ovulation typically occur in relation to a woman's menstrual cycle?
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What process occurs when a sperm penetrates an ovum?
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What is the role of the corpus luteum after ovulation?
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What primarily determines the sex of the child?
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How long can sperm remain viable in the female reproductive tract?
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What happens to the corpus luteum if fertilization does not occur?
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What is the likelihood of pregnancy if a couple has unprotected sex three days before ovulation?
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What is the name of the solid ball that forms after cleavage and before the zygote implants?
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What structure develops from the trophoblast and eventually forms the fetal portion of the placenta?
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What happens to the size of the zygote during cleavage?
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Which layer of cells becomes the inner mass of the blastocyst?
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Which part of the uterus is typically where the zygote implants?
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What is a function of the amniotic fluid during fetal development?
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Which germ layer is responsible for the development of muscles and bones?
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When does the yolk sac begin to form after fertilization?
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What type of membrane surrounds and protects the embryo?
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How much amniotic fluid is typically present at 20 weeks of pregnancy?
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At what week of gestation are the external genitalia visible by ultrasound examination?
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Which hormone is primarily responsible for maintaining the uterine lining for implantation of the zygote?
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What occurs at around week 20 of gestation regarding fetal development?
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Which of the following events occurs at week 17 of gestation?
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What is the primary function of the placenta during pregnancy?
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What significant development occurs during week 25 of gestation?
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What role does Human Chorionic Gonadotropin (hCG) play early in pregnancy?
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At what stage is the fetal position considered stable within the uterus?
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Which week marks the establishment of maternal-fetal circulation?
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What is the age of viability for a fetus in gestation?
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Study Notes
Cellular Development
- Chromosomes occur in pairs, one from the mother and one from the father.
- Each body cell contains 46 chromosomes, 22 pairs of autosomes and one pair of sex chromosomes.
- Mitosis is cell division for body growth and development, as well as replacing dead cells.
- Meiosis is cell division that reduces the number of chromosomes to 23 in the reproductive cells (gametes).
- Gametogenesis is the development of sperm and ova:
- Oogenesis is the formation of ova (female gametes).
- Each ovum contains 23 chromosomes including one X sex chromosome.
- A female has all the ova she will ever have by the 30th week of gestation.
- Spermatogenesis is the formation of sperm (male gametes).
- Four sperm develop from a single spermatocyte.
- Each sperm contains 23 chromosomes, either X or Y.
- Spermatogenesis begins during puberty.
Fertilization
- Ovulation typically occurs 14 days before menstruation begins.
- One ovum among several matures, releasing estrogen and progesterone to prepare the uterus, which is then absorbed by the corpus luteum.
- Upon ejaculation, sperm can reach the fallopian tube within 5 minutes and remain viable for up to 5 days.
- Fertilization occurs when a sperm penetrates the ovum in the outer third of the fallopian tube, restoring the chromosome count to 46.
- The fertilized ovum (zygote) begins rapid mitotic division, forming a blastomere.
- The male determines the sex of the child depending on the sperm's sex chromosome.
- The fertilized egg, after reaching the uterus, proceeds through stages of further development and implantation.
Implantation of the Zygote
- The ovum is transported through the fallopian tube by muscular action and cilia.
- Fertilization occurs in the ampulla (distal third of the fallopian tube).
- The zygote undergoes rapid cell division, forming a morula.
- The morula enters the uterus and implants in the upper section of the posterior uterine wall.
- The zygote burrows into the endometrium, which is now called the decidua. The decidua basalis is the area under the blastocyst and forms the maternal part of the placenta.
Prenatal Development
- The zygote differentiates into the chorion, amnion, yolk sac, and three primary germ layers.
- Chorion: Develops from the trophoblast and envelops the amnion, embryo, and yolk sac. The chorion forms the fetal portion of the placenta.
- Amnion: A thin sac that encloses the embryo and is filled with amniotic fluid.
- Yolk Sac: Forms on the ninth day and initially functions as the site of red blood cell production.
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Germ Layers:
- Ectoderm: Outer layer of skin, hair follicles, nails, sense organs, mouth, and anus.
- Mesoderm: True skin, skeleton, muscle, blood, kidneys, and gonads.
- Endoderm: Lining of respiratory system, digestive system, bladder, and urethra.
- Prenatal development includes three periods:
- Zygote: The first two weeks, where the zygote grows and develops.
- Embryo: Weeks 2-8, where basic structures are formed.
- Fetus: Weeks 9-40, where growth and maturation take place.
Accessory Structures of Pregnancy
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Placenta: A temporary organ for respiration, nutrition, and excretion for the fetus. It also produces hormones.
- It forms from the chorionic villi extending into the maternal decidua basalis.
- Maternal and fetal blood do not mix.
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Placental Functions:
- Transfers oxygen and nutrients to the fetus.
- Removes waste products from the fetus.
- Produces hormones:
- Progesterone: Maintains uterine lining, reduces uterine contractions, prepares breasts for lactation.
- Estrogen: Stimulates uterine growth, increases blood flow to uterine vessels, stimulates breast duct development.
Human Chorionic Gonadotropin (hCG)
- Signals the corpus luteum that conception has occurred
- Causes the corpus luteum to continue producing estrogen and progesterone for pregnancy
- Detectable in maternal blood after implantation (7-9 days after fertilization)
- Basis for most pregnancy tests
Human Placental Lactogen
- Decreases maternal insulin sensitivity and glucose use
- Makes more glucose available for fetal nutrition
Umbilical Cord
- Develops with the placenta and fetal blood vessels
- Lifeline between fetus and placenta
- Contains two arteries and one vein
- Vein carries oxygenated blood to the fetus
- Arteries carry deoxygenated blood and waste from the fetus to the placenta
- Vessels coiled for movement and stretching without restricting circulation
- Cushioned by Wharton's jelly to prevent obstruction from pressure
- Normal length is about 22 inches
Fetal Circulatory Circuit
- Established after the 4th week of gestation
- Requires three shunts because the fetus does not breathe and the liver does not process most waste products
- Ductus venosus diverts blood away from the liver
- Foramen ovale diverts blood from the right atrium to the left atrium, bypassing the lungs
- Ductus arteriosus diverts blood from the pulmonary artery to the aorta
- Oxygenated blood enters the fetus through the umbilical vein
- About half of the blood flows through the liver, the rest bypasses it and enters the inferior vena cava via the ductus venosus
- Blood enters the right atrium and mixes with deoxygenated blood
- Most blood passes directly into the left atrium via the foramen ovale, mixing with a small amount of blood from the lungs
- Blood is pumped from the left ventricle to the aorta to nourish the body
- A small amount of blood from the right ventricle circulates to the lungs
- The rest of the blood from the right ventricle joins oxygenated blood in the aorta via the ductus arteriosus
- Deoxygenated blood returns to the placenta via the umbilical arteries
Circulation Changes at Birth
- Fetal circulatory shunts are not needed after birth because the infant oxygenates blood in the lungs and is not circulating blood to the placenta
- As the infant breathes, blood flow to the lungs increases, pressure in the right side of the heart falls, and the foramen ovale closes
- The ductus arteriosus constricts as arterial oxygen level rises
- The ductus venosus constricts when flow of blood from the umbilical cord stops
Closure of Fetal Circulatory Shunts
- Foramen ovale closes functionally within 2 hours and permanently by age 3 months
- Ductus arteriosus closes functionally within 15 hours and permanently in about 3 weeks
- Ductus venosus closes functionally when the cord is cut and permanently in about 1 week
- The ductus arteriosus and ductus venosus become ligaments after permanent closure
Fetal Lung Preparation for Birth
- Lung fluid decreases during labor for transition to extrauterine breathing
- Hormones increase in the fetus during labor to decrease lung fluid production and increase reabsorption, preparing the lungs to accept air
Multifetal Pregnancy
- Twins occur 33.5/1000 pregnancies in the US
- Hormone therapy for ovulation increases twinning and other multifetal births
- Monozygotic twins
- Begin development at the end of the first week after fertilization
- Share identical genetic complements (conceived from a single egg and sperm)
- Same gender
- Any physical differences are caused by prenatal environmental factors
- Two amnions (inner membranes) but a single chorion (outer membrane) and share a placenta
- Dizygotic twins
- Called fraternal twins
- Arising from two eggs fertilized by different sperm
- Can be the same or different genders
- Don't always have similar physical traits
- Always have two amnions, two chorions, and two placentas, although chorions and placentas sometimes fuse
- May be hereditary
- Incidence increases with maternal age
- Many twins and higher multiples are born prematurely because the uterus becomes overly distended
- The placenta may not be able to supply sufficient nutrition to both fetuses, resulting in one or both twins being smaller than average
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Description
Explore the intricate processes of cellular development, including mitosis, meiosis, and gametogenesis. This quiz covers key concepts such as the structure and function of chromosomes and the roles of sperm and ova in fertilization.
