A skin disorder caused by blockage and inflammation of sebaceous glands.
acrosome reaction
The opening of a sperm’s acrosome, releasing enzymes necessary for penetration of the zona pellucida of the ovum.
activational effect
The influence of a sex hormone on the function of brain circuitry in adulthood.
amnion
The membranous sac containing amniotic fluid and the fetus.
amniotic fluid
The fluid within which the fetus develops.
anal fold
The posterior portion of the urethral fold, which gives rise to the anus.
androgen insensitivity syndrome (AIS)
An intersexed condition caused by absent or nonfunctional androgen receptors.
anti-Müllerian hormone (AMH)
A peptide hormone secreted by Sertoli cells of the testis that prevents the development of the female internal reproductive tract.
blastocyst
A conceptus shortly before implantation, when it takes the form of a sphere of cells with a central cavity.
breast bud
The first stage of breast development at puberty.
capacitation
A chemical change in the surface of a sperm within the female reproductive tract that allows it to swim more forcefully and respond to the presence of the ovum.
cloaca
The common exit of the gastrointestinal and urogenital systems; in humans it is present only in embryonic life.
conception
Fertilization of the ovum.
conceptus
The developing organism from the 2-cell stage onward, including both embryonic and extraembryonic tissues.
congenital adrenal hyperplasia (CAH)
An intersexed condition caused by a genetic defect in corticosteroid synthesis.
cryptorchidism
Failure of one or both testicles to descend into the scrotum by 3 months of postnatal age.
DAX-1
A gene that promotes development of the ovaries.
delayed puberty
Failure of onset of puberty by some criterion age, usually 13 or 14 in girls and 14 in boys.
diethylstilbestrol (DES)
A synthetic estrogen receptor agonist that was once used to prevent miscarriage but that caused cancer and fertility problems in some of the daughters born of these pregnancies.
disorders of sex development
An alternative term for intersexed conditions.
ectoderm
The upper, outermost layer of embryonic cells, which will give rise to the skin and most of the nervous system.
embryo
The portion of the conceptus that develops into the fetus. Used loosely to describe the entire conceptus from the 2-cell stage onward.
embryonic stem cell
A cell found in the inner cell mass of the blastocyst, capable of developing into any type of cell.
endoderm
The lower, innermost layer of embryonic cells, which will give rise to the digestive system and lungs.
fertilization
The entry of a sperm into an ovum, thus transforming the ovum into a genetically unique diploid organism capable of development (conceptus).
fetus
The developing organism between the time when the main anatomical structures of the body have been established (in humans, 6 weeks after conception) and birth.
genital ridge
One of two bilateral clusters of cells in the embryo that give rise to the gonads.
genital swelling
Regions of the genitalia in the embryo that give rise to the labia majora (in females) or the scrotum (in males).
genital tubercle
A midline swelling in front of the cloaca, which gives rise to the glans of the clitoris (in females) or penis (in males).
gonadal intersexuality
The existence of ovarian and testicular tissue in the same individual. Also called true hermaphroditism.
gubernaculum
Either of two bilateral fibrous bands that are involved in the descent of the gonads in the fetus.
gynecomastia
Enlargement of one or both breasts in a male.
human chorionic gonadotropin (hCG)
A gonadotropin secreted by the conceptus and by the placenta; it prevents regression of the corpus luteum.
hypospadias
An abnormal location of the urethral meatus on the underside of the glans, the shaft of the penis, or elsewhere.
idiopathic
Lacking an identifiable cause.
intersexed
Having a biological sex that is ambiguous or intermediate between male and female.
Kallmann syndrome
A developmental syndrome characterized by delayed puberty, inability to smell, and other problems.
kisspeptin
A hormone produced in the hypothalamus that is involved in the initiation of puberty.
leptin
A hormone secreted by fat cells that may play a role in triggering puberty.
lordosis
In female rodents, an inverse arching of the back that exposes the vulva for intromission by a male.
Müllerian duct
One of two bilateral ducts in the embryo that give rise to the female reproductive tract.
masculinize
Cause to become male or male-like.
masturbation
Sexual self-stimulation. Sometimes also used to refer to manual stimulation of another person’s genitalia.
medial preoptic area
A region of the hypothalamus involved in the regulation of sexual behaviors typically shown by males.
menarche
The onset of menstruation at puberty.
mesoderm
The middle layer of embryonic cells, which will give rise to bone, muscle, connective tissue, and cardiovascular system.
mesonephros
A transitory embryonic kidney that provides tissue to the gonads.
micropenis
A penis shorter than about 2 cm (0.8 inches) in stretched length at birth.
morula
The conceptus when it consists of about 16 to 32 cells arranged in a compact spherical mass.
mounting
A male-typical sexual behavior: climbing onto the female to reach a position in which intromission is possible. (Used mostly for nonhuman animals.)
nocturnal emission
Ejaculation during sleep.
organizational effect
The influence of a sex hormone on the development of brain circuitry.
placenta
A vascular organ, partly of fetal and partly of maternal origin, by which gases, nutrients, hormones, and waste products are exchanged between the fetus and its mother.
precocious puberty
Puberty that begins early enough to be considered a medical problem.
pregnancy
The state of carrying a living, implanted conceptus, embryo, or fetus.
primary amenorrhea
Failure to commence menstruation at puberty.
primordial germ cells
The cells that give rise to oocytes and to the progenitors of sperm.
pronucleus
A nucleus containing a haploid set of chromosomes derived from a sperm or ovum.
pseudohermaphroditism
Outdated term for intersexed conditions involving structures other than the gonads.
puberty
The biological transition to sexual maturity.
raphe
The midline ridge of the perineum.
recessive trait
An inherited trait that shows itself only when the responsible gene is present on both homologous chromosomes.
sebaceous glands
Oil-secreting glands associated with hair follicles.
second polar body
A small body containing the chromosomes discarded during the second meiotic division of an ovum.
secondary amenorrhea
Absence of menstruation in a woman who has previously menstruated normally.
sensitive period
A period of development during which the survival or growth of a biological system depends on the presence of some factor, such as a hormone.
sexually dimorphic nucleus of the preoptic area (SDN-POA)
A cell group in the medial preoptic area of the hypothalamus of rodents that is larger in males than females.
SRY (Sex-determining Region of the Y chromosome)
A gene located on the Y chromosome that causes the embryo to develop as a male.
third interstitial nucleus of the anterior hypothalamus (INAH3)
A sexually dimorphic cell group in the medial preoptic area of the human hypothalamus.
transcription factor
A protein that regulates gene expression.
true hermaphroditism
Outdated term for gonadal intersexuality.
umbilical cord
The vascular cord that runs from the umbilicus (navel) of the fetus to the placenta.
urethral folds
Folds of ectodermal tissue in the embryo that give rise to the labia minora (in females) or the shaft of the penis (in males).
urogenital sinus
The common opening of the urinary and genital systems in the embryo.
Wolffian duct
One of two bilateral ducts in the embryo that give rise to the male reproductive tract.
yolk sac
A transient, early extraembryonic structure; the source of primordial germ cells.
zona pellucida
The capsule surrounding an ovum that must be penetrated by the fertilizing sperm.
zygote
A cell formed by the fusion of gametes: a fertilized ovum.
