Entry of more than one sperm into a single oocyte, which the fast and slow blocks prevent, is called polyspermy.
Missing Word
polyspermy
Polyspermy is fertilization of an oocyte by more than one sperm. It would produce a triploid zygote that cannot survive, so membrane depolarization and the cortical reaction prevent it.
Category: Fertilization
Question 2
A solid ball of about 16 cells produced by cleavage of the zygote is the morula.
Missing Word
morula
The morula is the compacted cluster of blastomeres formed by early cleavage. It reaches the uterus and then develops a fluid-filled cavity to become a blastocyst.
Category: Embryonic Development
Question 3
The outer layer of cells of the blastocyst, which forms the chorion and the fetal portion of the placenta, is the trophoblast.
Missing Word
trophoblast
The trophoblast is the outer shell of the blastocyst. It invades the endometrium during implantation, secretes hCG, and develops into the chorion and fetal side of the placenta.
Category: Embryonic Development
Question 4
The innermost embryonic membrane, which surrounds the embryo in a cushioning fluid-filled cavity, is the amnion.
Missing Word
amnion
The amnion encloses the embryo in amniotic fluid, which protects it from mechanical injury and temperature change and allows free movement.
Category: Embryonic Development
Question 5
Formation of the three primary germ layers from the two-layered embryonic disc is called gastrulation.
Missing Word
gastrulation
Gastrulation converts the bilaminar disc into ectoderm, mesoderm, and endoderm as cells migrate inward through the primitive streak.
Category: Embryonic Development
Question 6
The embryonic process in which the ectoderm folds into a hollow tube that becomes the brain and spinal cord is called neurulation.
Missing Word
neurulation
Neurulation is the folding of the neural plate into the neural tube, which forms the central nervous system. Failure of the tube to close causes defects such as spina bifida.
Category: Embryonic Development
Question 7
The fine, silky hair that covers the skin of the fetus and is usually shed before birth is lanugo.
Missing Word
lanugo
Lanugo is the fine fetal body hair. It is normally lost before birth, though very premature infants may still have some.
Category: Fetal Development
Question 8
The dark first feces of a newborn, formed from swallowed amniotic fluid, cell debris, mucus, and bile, is called meconium.
Missing Word
meconium
Meconium accumulates in the fetal intestine and is normally passed after birth. Passage before birth can signal fetal distress, and inhaling it can cause breathing problems.
Category: Fetal Development
Question 9
The phospholipid-rich secretion of type II alveolar cells that lowers surface tension so the lungs of a newborn can inflate is surfactant.
Missing Word
surfactant
Surfactant reduces surface tension in the alveoli so they do not collapse. Premature infants who lack enough of it can develop respiratory distress syndrome.
Category: Fetal Development
Question 10
The shrinking of the uterus back toward its pre-pregnancy size after childbirth is called involution.
Missing Word
involution
Involution is the return of the uterus to its nonpregnant size through continued contractions. Breastfeeding helps by stimulating oxytocin release.
Category: Pregnancy and Labor
Question 11
The vaginal discharge of blood, mucus, and uterine tissue in the weeks after childbirth is called lochia.
Missing Word
lochia
Lochia is the postpartum discharge as the uterine lining heals. It changes from red to pinkish to whitish over the following weeks.
Category: Pregnancy and Labor
Question 12
The thick, yellowish milk secreted in the first few days after birth, rich in protein and immunoglobulins, is called colostrum.
Missing Word
colostrum
Colostrum is the first secretion of the mammary glands. It is lower in fat than mature milk and supplies antibodies that help protect the newborn's gut.
Category: Lactation
Question 13
The physical, behavioral, and biochemical traits that an individual's genes express make up the phenotype.
Missing Word
phenotype
Phenotype is the set of observable or measurable characteristics produced by the genes. It differs from the genotype, which is the genetic makeup itself.
Category: Patterns of Inheritance
Question 14
A person whose two alleles for a particular gene are different from each other is heterozygous for that gene.
Missing Word
heterozygous
Heterozygous means carrying two different alleles of a gene. In such a person a dominant allele usually masks a recessive one.
Category: Patterns of Inheritance
Question 15
Failure of homologous chromosomes or sister chromatids to separate properly during meiosis, a common cause of Down syndrome, is called nondisjunction.
Missing Word
nondisjunction
Nondisjunction leaves one gamete with an extra chromosome and another missing one. Fertilization by a gamete with an extra chromosome 21 produces trisomy 21.
Category: Patterns of Inheritance