allantois - One of four extraembryonic membranes that form during embryonic development. It functions in early blood formation and development of the urinary bladder.
alpha fetoprotein - A protein of fetal origin that is found in the maternal circulatory system during gestation. Abnormally high levels indicate abnormal fetal development.
amnion- One of four extraembryonic membranes that becomes fluid-filled, and in which the embryo and fetus can grow, move freely, and be protected from sudden temperature shifts and impact.
antibody - A protein with binding sites for specific antigens. Only B lymphocytes produce antibodies and subsequently secrete them into the circulatory system to provide protection against foreign antigens.
antigen - Any molecule that is recognized as foreign to the body and that triggers an immune response (e.g., antibody production).
atresia - The loss (death) of ovarian follicles prior to final development. Greater than 99% of ovarian follicles present at birth will be lost via atresia before the end of the female's reproductive life span.
antral follicles - Ovarian follicles at the tertiary (as yet immature) stage of development characterized by the presence of an antrum (the fluid-filled space in the developing follicle).
artherosclerosis - Condition in which an artery's wall thickens and loses elasticity, and the vessel becomes clogged with lipid deposits. In the artery wall, abnormal smooth muscle cells accumulate, and there is an increase in connective tissue. Plaques consisting of lipids, calcium salts, and fibrous material disrupt blood flow.
blastocyst - The stage of embryo development prior to implantation consisting of a hollow ball of surface cells around a fluid-filled blastocoel.
bromocriptine - A drug used to treat hyperprolactinemia (excessive secretion of prolactin, leading to infertility) in both men and women.
capacitation - The process whereby the acrosome region of sperm wears away to enable the release of enzymes which will facilitate fertilization of the egg.
cholesterol - A common steroid which is the precursor for the sex steroids, progesterone, androgen and estrogen.
chorion- One of four extraembryonic membranes that becomes a major component of the placenta. Absorptive structures (chorionic villi) that develop at its surface are crucial for the passive transfer of substances between the embryo and mother.
chromosomes - A DNA molecule with many associated proteins. Many hundreds/thousands of genes are present on each chromosome.
clomiphene citrate - An estrogen-like substance used to induce multiple ovulations prior to in vitro fertilization. Acts by stimulating gonadotropin secretion.
colostrum - The first milk produced by the mother within the first few days after parturition which contains IgA antibodies responsible for providing protective immunity until the neonates own immune system begins to function.
corpus luteum - A glandular structure; it develops from cells of a ruptured ovarian follicle and secretes progesterone, relaxin and some estrogen. During non-fertile cycles, the CL will regress after 7-14 days.
cortical reaction - A change in the structure of the egg's zona pellucida following penetration by the first sperm that makes the egg impermeable to any additional sperm, thus preventing polyspermy.
corticotropin releasing factor (CRF) - A hormone produced both by the hypothalamus and the placenta which is responsible for stimulation of adrenal function. A rise in CRF levels during late pregnancy is thought to trigger the onset of parturition.
cortisol - A steroid produced by the adrenal gland of the adult which is responsible for mobilizing energy under stressful conditions (a corticosteroid). Cortisol is also important for breast development during gestation and for milk production.
cryptorchidism - A condition characterized by the retention of testes within the abdominal cavity, and the failure to descend into the scrotal sac before or shortly after birth.
deoxyribonucleic acid (DNA) - For all cells, the molecule of inheritance. A category of nucleic acids, each usually consisting of two nucleotide strands twisted together helically and held together by hydrogen bonds. The nucleotide sequence encodes the instructions for assembling proteins, and, ultimately, a new individual.
diploid - For many sexually reproducing species, the chromosome number of somatic cells and of germ cells prior to meiosis. Such cells have two chromosomes of each type (that is, pairs of homologous chromosomes).
ectoderm - Outermost tissue layer of the embryo which gives rise to such things as the skin and tissues of the nervous system.
ectopic pregnancy - Implantation of a fertilized egg in a location outside the uterus. Such 'pregnancies' may be life-threatening and usually require surgical intervention.
endoderm - The inner tissue layer of the embryo that gives rise to such tissues as the inner lining of the gut and organs derived from it.
endometrium - The cell layer of the uterus which borders the uterine lumen; strongly influenced by the estrogen:progesterone environment.
endorphins - Natural chemicals produced by the body that act to minimize pain during stress; morphine also will bind to the endorphin receptors to act similarly.
enzymes - One class of protein that greatly speeds up (catalyzes) reactions between specific substances. The substances that each enzyme acts upon are called its substrate.
estrogen - A sex hormone that helps oocytes mature, induces changes in the uterine lining during the menstrual cycle and pregnancy, and maintains secondary sexual traits; also influences body growth and development. In almost all non-human species, it is responsible for inducing behavior indicative of sexual receptivity. Conjugated estrogens are those that carry a water-soluble component such as a sugar or a sulphate group covalently linked to it. Such estrogens are commonly used to clinically treat menopause, and are typically less potent than unconjugated estrogens. Estriol is another form of estrogen that is produced in large amounts during pregnancy.
follicle-stimulating hormone (FSH) - The name is derived from its function in the female, to stimulate growth and differentiation of ovarian follicles. A gonadotropin produced by the anterior lobe of the pituitary. In males it acts on the testes as part of a sequence to stimulate sperm production.
gamete - (also called germ cell) A haploid cell that functions in sexual reproduction. Sperm and eggs are examples.
gene - A unit of information about a heritable trait that is passed on from parents to offspring. Each gene has a specific location on a chromosome.
gonadotropin releasing hormone (GnRH) - A neuroendocrine hormone (a decapeptide) produced within the hypothalamus of the brain which stimulates both LH and FSH secretion from the pituitary gland.
gonadotropins - Protein hormones produced by the pituitary which include luteinizing hormone and follicle-stimulating hormone.
Graafian follicles - Fully mature, preovulatory follicles.
granulosa cells - The cells that immediately surround the oocyte in a developing ovarian follicle; a major steroid product of these cells is estrogen.
growth hormone - A protein hormone secreted by the pituitary that induces muscle mass and skeletal growth. Recent clinical studies have shown that elderly men which receive GH treatment increase their lean body mass, decrease adipose tissue and increase vertebral bone density! Growth hormone also plays a role in breast development during gestation.
haploid - The chromosome number of a gamete that, as an outcome of meiosis, is only half that of the parent germ cell (it has only one of each pair of homologous chromosomes).
high density lipoproteins (HDL) - Lipids circulating in the blood that are generally thought to be beneficial in preventing heart disease.
human chorionic gonadotropin (hCG) - A protein hormone secreted by the implanting blastocyst and by the placenta. It is highly similar in structure to LH, and is one of the signals following a successful fertilization. The measurement of this hormone is the basis of many pregnancy tests.
human menopausal gonadotropin (hMG) - hMG is a purified gonadotropin preparation (consisting of equal amounts of LH and FSH) extracted from the urine of postmenopausal women, and used to induce ovulation/multiple ovulations.
inhibin - A protein hormone produced by both the ovary and testis which is capable of suppressing FSH secretion from the pituitary gland.
insulin - A protein hormone that induces the uptake of glucose into cells. Insulin is also important for breast development and lactation.
Leydig cells - The testosterone-secreting cell found in interstitial tissue of the testes. Cells most sensitive to LH.
low density lipoproteins (LDL) - Lipids circulating in the blood that, when in excess, are generally thought to be a causative factor in promoting heart disease.
luteinizing hormone (LH) - Secreted by the anterior lobe of the pituitary gland; a gonadotropin. In males, it acts on interstitial cells of the testes to stimulate them to secrete testosterone.
meiosis - Two-stage nuclear division process in which the chromosome number of a germ cell is reduced by half, to the haploid number. (Each daughter nucleus ends up with one of each type of chromosome.) Meiosis is the basis of gamete formation.
menarche - The initiation of menstrual cycles at puberty. The initiation of menarche does not necessary indicate the initiation of regular ovulations, as this may not occur for several more years.
menopause - End of the period of a human female's reproductive potential characterized by the cessation of menses.
mesoderm - The embryonic tissue layer that gives rise to muscle, organs of circulation,reproduction and excretion, most of the internal skeleton and connective tissue.
Mullerian inhibiting substance - A hormone produced by the embryo, produced in response to the SRY gene product, which induces the regression of the female reproductive tract.
myometrium - The inner, muscular layer responsible for uterine motility, especially for expulsion of the fetus at parturition.
mitosis - Type of nuclear division that maintains the parental chromosome number for daughter cells. It is the basis of embryonic and normal body growth.
oocyte - The female gamete.
oxytocin - A neuropeptide produced in the hypothalamus and secreted from the posterior pituitary (neurohypophysis). Stimulates uterine contractions at the time of parturition and causes milk ejection during lactation.
pampiniform plexus - A series of blood vessels in the testes that serves to cool blood coming from the body cavity to the testes, and to rewarm blood leaving the testes and returning to the body cavity. The decrease in blood temperature is important for optimal sperm production.
placental lactogen - A hormone produced by the placenta that has fetal growth-promoting activity.
polycystic ovaries - A syndrome consisting of amenorrhea, hirsutism and obesity associated with enlarged ovaries and the overproduction of androgen. Etiology may be undetermined, but can be caused by elevated estrogen secretion. Frequently results in infertility.
polyspermy - Fertilization of an egg by more than one sperm; these zygotes may initiate cleavage, but are not viable. Normally, polyspermy is blocked by the zona reaction.
primordial germ cells - Primitive sex cells (male or female) that arise from the yolk sac during embryonic development. They will eventually form the eggs and sperm.
primordial follicle - A newly organized ovarian follicle characterized by being surrounded by a single layer of cells; these cells eventually differentiate into granulosa cells.
progesterone - Female steroid sex hormone secreted by the ovary. Important for the preparation of the uterus for implantation and critical for maintaining pregnancy.
prolactin - A pituitary protein hormone that, among other things, stimulates breast milk production. Hyperprolactinemia (which occurs during lactation) can interfere with gonadotropin secretion and directly inhibit ovarian function.
prostaglandin - A lipid hormone/signaling factor which causes smooth muscle to contract or relax, as in stimulating strong contractions of the uterine myometrium at the time of parturition, in altering respiratory pathways or the diameter of blood vessels.
prostate - Gland in male reproductive tract that wraps around the urethra and ejaculatory ducts; its secretions, including prostaglandins, become part of semen. In men (especially over the age of 50), the prostate may become enlarged, causing urinary tract obstruction or bladder infections, or become cancerous.
protein - Large organic compound composed of one or more chains of amino acids held together by peptide bonds. Proteins have unique sequences of different kinds of amino acids in their polypeptide chains; such sequences are the basis of a protein's three-dimensional structure and chemical behavior.
ribonucleic acid (RNA) - A category of single-stranded nucleic acids that function in processes by which genetic instructions are used to build proteins.
scrotum - The tissue sac holding the testes outside the body cavity to lower the temperature of the testes and provide optimal sperm production.
Sertoli cells - Cells in seminiferous tubules that nourish and otherwise aid in the development of sperm (nurse cells).
spermatogonia - Immature sperm that replicate by mitosis (they are 2N in chromosomal number).
spermatozoa - Mature sperm, with a chromosomal number of N.
SRY gene - The gene located on the Y (male) chromosome that is responsible for the expression of Mullerian inhibiting substance (MIH). Activation of this gene results in a male phenotype.
steroid - A type of lipid-soluble hormone synthesized from cholesterol. Many steroid hormones move into the nucleus and bind to a receptor; others bind to a receptor in the cytoplasm, and the entire complex moves into the nucleus. (Examples of steroid classes: progestins, androgens, estrogens.)
teratogen - Any substance that interferes with fetal development and results in fetal malformations.
theca cells - The layer of cells lying outside the granulosa layer of a developing follicle; a major steroid product of these cells is androgen, which is used as a precursor for estrogen production by the granulosa layer.
totipotent cells from the embryo - Cells which are undifferentiated, and thus have the capacity to become any type of cell (e.g., liver, lung, heart, nerve... cell).
trophoblast - The surface layer of cells of the blastocyst that secretes enzymes that break down the uterine lining where the embryo will implant.
very low-density lipoproteins (VLDL) - Lipids circulating in the blood that, when in excess, are generally thought to be a causative factor in promoting heart disease.
yolk sac- One of four extraembryonic membranes that becomes a site of blood cell formation, and some of its cells give rise to germ cells, the predecessors of male and female gametes.
zona pellucida - An acellular layer that separates the oocyte from the granulosa cell layer in a preovulatory follicle. Following ovulation, sperm must pass through the zona to fertilize the egg; once fertilization occurs, the zona reaction blocks all other sperm from entering (e.g., prevents polyspermy).
zygote - The first cell of a new individual, formed by the fusion of a sperm nucleus with the nucleus of an egg (fertilization).