- 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 his or her 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