28.9: Key Terms

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Words (or words that have the same definition)	The definition is case sensitive	(Optional) Image to display with the definition [Not displayed in Glossary, only in pop-up on pages]	(Optional) Caption for Image	(Optional) External or Internal Link	(Optional) Source for Definition
(Eg. "Genetic, Hereditary, DNA ...")	(Eg. "Relating to genes or heredity")		The infamous double helix	https://bio.libretexts.org/	CC-BY-SA; Delmar Larsen

Glossary Entries

Word(s)	Definition	Image	Caption	Link	Source
acrosomal reaction	release of digestive enzymes by sperm that enables them to burrow through the corona radiata and penetrate the zona pellucida of an oocyte prior to fertilization
acrosome	cap-like vesicle located at the anterior-most region of a sperm that is rich with lysosomal enzymes capable of digesting the protective layers surrounding the oocyte
afterbirth	third stage of childbirth in which the placenta and associated fetal membranes are expelled
allantois	finger-like outpocketing of yolk sac forms the primitive excretory duct of the embryo; precursor to the urinary bladder
allele	alternative forms of a gene that occupy a specific locus on a specific gene
amnion	transparent membranous sac that encloses the developing fetus and fills with amniotic fluid
amniotic cavity	cavity that opens up between the inner cell mass and the trophoblast; develops into amnion
autosomal chromosome	in humans, the 22 pairs of chromosomes that are not the sex chromosomes (XX or XY)
autosomal dominant	pattern of dominant inheritance that corresponds to a gene on one of the 22 autosomal chromosomes
autosomal recessive	pattern of recessive inheritance that corresponds to a gene on one of the 22 autosomal chromosomes
blastocoel	fluid-filled cavity of the blastocyst
blastocyst	term for the conceptus at the developmental stage that consists of about 100 cells shaped into an inner cell mass that is fated to become the embryo and an outer trophoblast that is fated to become the associated fetal membranes and placenta
blastomere	daughter cell of a cleavage
Braxton Hicks contractions	weak and irregular peristaltic contractions that can occur in the second and third trimesters; they do not indicate that childbirth is imminent
brown adipose tissue	highly vascularized fat tissue that is packed with mitochondria; these properties confer the ability to oxidize fatty acids to generate heat
capacitation	process that occurs in the female reproductive tract in which sperm are prepared for fertilization; leads to increased motility and changes in their outer membrane that improve their ability to release enzymes capable of digesting an oocyte’s outer layers
carrier	heterozygous individual who does not display symptoms of a recessive genetic disorder but can transmit the disorder to their offspring
chorion	membrane that develops from the syncytiotrophoblast, cytotrophoblast, and mesoderm; surrounds the embryo and forms the fetal portion of the placenta through the chorionic villi
chorionic membrane	precursor to the chorion; forms from extra-embryonic mesoderm cells
chorionic villi	projections of the chorionic membrane that burrow into the endometrium and develop into the placenta
cleavage	form of mitotic cell division in which the cell divides but the total volume remains unchanged; this process serves to produce smaller and smaller cells
codominance	pattern of inheritance that corresponds to the equal, distinct, and simultaneous expression of two different alleles
colostrum	thick, yellowish substance secreted from a mother’s breasts in the first postpartum days; rich in immunoglobulins
conceptus	pre-implantation stage of a fertilized egg and its associated membranes
corona radiata	in an oocyte, a layer of granulosa cells that surrounds the oocyte and that must be penetrated by sperm before fertilization can occur
cortical reaction	following fertilization, the release of cortical granules from the oocyte’s plasma membrane into the zona pellucida creating a fertilization membrane that prevents any further attachment or penetration of sperm; part of the slow block to polyspermy
dilation	first stage of childbirth, involving an increase in cervical diameter
dominant	describes a trait that is expressed both in homozygous and heterozygous form
dominant lethal	inheritance pattern in which individuals with one or two copies of a lethal allele do not survive in utero or have a shortened life span
ductus arteriosus	shunt in the pulmonary trunk that diverts oxygenated blood back to the aorta
ductus venosus	shunt that causes oxygenated blood to bypass the fetal liver on its way to the inferior vena cava
ectoderm	primary germ layer that develops into the central and peripheral nervous systems, sensory organs, epidermis, hair, and nails
ectopic pregnancy	implantation of an embryo outside of the uterus
embryo	developing human during weeks 3–8
embryonic folding	process by which an embryo develops from a flat disc of cells to a three-dimensional shape resembling a cylinder
endoderm	primary germ layer that goes on to form the gastrointestinal tract, liver, pancreas, and lungs
epiblast	upper layer of cells of the embryonic disc that forms from the inner cell mass; gives rise to all three germ layers
episiotomy	incision made in the posterior vaginal wall and perineum that facilitates vaginal birth
expulsion	second stage of childbirth, during which the mother bears down with contractions; this stage ends in birth
fertilization	unification of genetic material from male and female haploid gametes
fertilization membrane	impenetrable barrier that coats a nascent zygote; part of the slow block to polyspermy
fetus	developing human during the time from the end of the embryonic period (week 9) to birth
foramen ovale	shunt that directly connects the right and left atria and helps divert oxygenated blood from the fetal pulmonary circuit
foremilk	watery, translucent breast milk that is secreted first during a feeding and is rich in lactose and protein; quenches the infant’s thirst
gastrulation	process of cell migration and differentiation into three primary germ layers following cleavage and implantation
genotype	complete genetic makeup of an individual
gestation	in human development, the period required for embryonic and fetal development in utero; pregnancy
heterozygous	having two different alleles for a given gene
hindmilk	opaque, creamy breast milk delivered toward the end of a feeding; rich in fat; satisfies the infant’s appetite
homozygous	having two identical alleles for a given gene
human chorionic gonadotropin (hCG)	hormone that directs the corpus luteum to survive, enlarge, and continue producing progesterone and estrogen to suppress menses and secure an environment suitable for the developing embryo
hypoblast	lower layer of cells of the embryonic disc that extend into the blastocoel to form the yolk sac
implantation	process by which a blastocyst embeds itself in the uterine endometrium
incomplete dominance	pattern of inheritance in which a heterozygous genotype expresses a phenotype intermediate between dominant and recessive phenotypes
inner cell mass	cluster of cells within the blastocyst that is fated to become the embryo
involution	postpartum shrinkage of the uterus back to its pre-pregnancy volume
karyotype	systematic arrangement of images of chromosomes into homologous pairs
lactation	process by which milk is synthesized and secreted from the mammary glands of the postpartum female breast in response to sucking at the nipple
lanugo	silk-like hairs that coat the fetus; shed later in fetal development
let-down reflex	release of milk from the alveoli triggered by infant suckling
lightening	descent of the fetus lower into the pelvis in late pregnancy; also called “dropping”
lochia	postpartum vaginal discharge that begins as blood and ends as a whitish discharge; the end of lochia signals that the site of placental attachment has healed
meconium	fetal wastes consisting of ingested amniotic fluid, cellular debris, mucus, and bile
mesoderm	primary germ layer that becomes the skeleton, muscles, connective tissue, heart, blood vessels, and kidneys
morula	tightly packed sphere of blastomeres that has reached the uterus but has not yet implanted itself
mutation	change in the nucleotide sequence of DNA
neural fold	elevated edge of the neural groove
neural plate	thickened layer of neuroepithelium that runs longitudinally along the dorsal surface of an embryo and gives rise to nervous system tissue
neural tube	precursor to structures of the central nervous system, formed by the invagination and separation of neuroepithelium
neurulation	embryonic process that establishes the central nervous system
nonshivering thermogenesis	process of breaking down brown adipose tissue to produce heat in the absence of a shivering response
notochord	rod-shaped, mesoderm-derived structure that provides support for growing fetus
organogenesis	development of the rudimentary structures of all of an embryo’s organs from the germ layers
parturition	childbirth
phenotype	physical or biochemical manifestation of the genotype; expression of the alleles
placenta	organ that forms during pregnancy to nourish the developing fetus; also regulates waste and gas exchange between mother and fetus
placenta previa	low placement of fetus within uterus causes placenta to partially or completely cover the opening of the cervix as it grows
placentation	formation of the placenta; complete by weeks 14–16 of pregnancy
polyspermy	penetration of an oocyte by more than one sperm
primitive streak	indentation along the dorsal surface of the epiblast through which cells migrate to form the endoderm and mesoderm during gastrulation
prolactin	pituitary hormone that establishes and maintains the supply of breast milk; also important for the mobilization of maternal micronutrients for breast milk
Punnett square	grid used to display all possible combinations of alleles transmitted by parents to offspring and predict the mathematical probability of offspring inheriting a given genotype
quickening	fetal movements that are strong enough to be felt by the mother
recessive	describes a trait that is only expressed in homozygous form and is masked in heterozygous form
recessive lethal	inheritance pattern in which individuals with two copies of a lethal allele do not survive in utero or have a shortened life span
sex chromosomes	pair of chromosomes involved in sex determination; in males, the XY chromosomes; in females, the XX chromosomes
shunt	circulatory shortcut that diverts the flow of blood from one region to another
somite	one of the paired, repeating blocks of tissue located on either side of the notochord in the early embryo
syncytiotrophoblast	superficial cells of the trophoblast that fuse to form a multinucleated body that digests endometrial cells to firmly secure the blastocyst to the uterine wall
trait	variation of an expressed characteristic
trimester	division of the duration of a pregnancy into three 3-month terms
trophoblast	fluid-filled shell of squamous cells destined to become the chorionic villi, placenta, and associated fetal membranes
true labor	regular contractions that immediately precede childbirth; they do not abate with hydration or rest, and they become more frequent and powerful with time
umbilical cord	connection between the developing conceptus and the placenta; carries deoxygenated blood and wastes from the fetus and returns nutrients and oxygen from the mother
vernix caseosa	waxy, cheese-like substance that protects the delicate fetal skin until birth
X-linked	pattern of inheritance in which an allele is carried on the X chromosome of the 23rd pair
X-linked dominant	pattern of dominant inheritance that corresponds to a gene on the X chromosome of the 23rd pair
X-linked recessive	pattern of recessive inheritance that corresponds to a gene on the X chromosome of the 23rd pair
yolk sac	membrane associated with primitive circulation to the developing embryo; source of the first blood cells and germ cells and contributes to the umbilical cord structure
zona pellucida	thick, gel-like glycoprotein membrane that coats the oocyte and must be penetrated by sperm before fertilization can occur
zygote	fertilized egg; a diploid cell resulting from the fertilization of haploid gametes from the male and female lines