Fetal Growth and Development

Vocabulary flashcards covering the stages of early pregnancy, placental development, germ layers, and fetal physiologic systems.

Corona radiata

The outermost layer of cells surrounding an ovum that must be penetrated for fertilization to occur.

Zygote

The single cell resulting from the fusion of a sperm and an egg, marking the beginning of the first cell division.

Morula

A developmental stage occurring around day $3$ consisting of a solid ball of cells produced by early cleavage.

Blastocyst

A hollow structure formed about day $4$ that contains an inner cell mass and an outer layer of cells intended for implantation.

Trophoblast cells

The outer layer of the blastocyst that eventually develops into the placenta and associated fetal membranes.

Implantation

The process where the blastocyst attaches to and embeds within the uterine lining, typically occurring $8$ to $10$ days after fertilization.

Placenta previa

A condition where the blastocyst implants low in the uterus, causing the placenta to potentially obstruct the cervical opening.

Human chorionic gonadotropin (hCG)

A hormone produced by trophoblast cells that sustains the corpus luteum to ensure continued production of estrogen and progesterone.

Decidua

The name for the uterine lining during pregnancy, which is shed after childbirth.

Decidua basalis

The specific area of the uterine lining located directly beneath the implanted embryo where maternal-fetal communication is established.

Decidua capsularis

The portion of the uterine lining that grows over and encapsulates the developing embryo.

Decidua vera

The remaining section of the uterine lining that is not in direct contact with the embryo.

Chorionic villi

Protrusions from the trophoblast that extend into the uterine lining to establish the early circulatory connection for the placenta.

Syncytiotrophoblast

The outer layer of the chorionic villi responsible for producing essential pregnancy hormones like hPL, estrogen, and progesterone.

Cytotrophoblast

Also known as Langhans' layer, this middle cellular layer provides an early protective barrier against certain infections until roughly the $20th$ to $24th$ week.

Cotyledons

Segmented sections on the maternal side of a mature placenta, numbering as many as $30$, providing a complex network for blood exchange.

Diffusion

The movement of substances like oxygen and carbon dioxide across the placenta from areas of high concentration to areas of low concentration.

Facilitated diffusion

The transport of nutrients, such as glucose, across the placenta using a carrier system to speed up the process.

Active transport

An enzyme-dependent process used to move essential amino acids and water-soluble vitamins to the fetus against a concentration gradient.

Pinocytosis

The cellular absorption of tiny droplets and large molecules, such as gamma globulin and certain viruses, into the fetal system.

Progesterone

A hormone critical for maintaining the uterine lining and reducing uterine contractions to help prevent premature labor.

Human placental lactogen (hPL)

A protein hormone that aids in breast development for lactation and regulates maternal nutrient levels for fetal use.

Amniotic fluid

The liquid that surrounds and protects the fetus, regulates temperature, and aids in musculoskeletal development.

Hydramnios

A condition characterized by an excessive amount of amniotic fluid, typically exceeding $2000\,mL$.

Oligohydramnios

A deficiency in the volume of amniotic fluid, defined as less than $300\,mL$, often indicating fetal renal issues.

Wharton's jelly

A specialized gelatinous substance within the umbilical cord that protects the internal blood vessels from compression.

Totipotent stem cells

Highly undifferentiated cells present during the first $4$ days of life with the capacity to develop into a complete human being.

Pluripotent stem cells

Cells that have begun differentiation and can become various specific types of body cells but not a whole organism.

Ectoderm

The primary germ layer that gives rise to the central nervous system, skin, hair, and various sense organs.

Mesoderm

The germ layer responsible for forming supporting structures like bone and muscle, as well as the heart and kidneys.

Entoderm

The innermost germ layer from which the linings of the respiratory and digestive tracts, as well as the bladder, are derived.

Teratogens

Environmental factors or substances, such as tobacco or certain drugs, that can cause abnormalities in a developing embryo or fetus.

Ductus venosus

A fetal circulatory shunt that directs oxygenated blood from the umbilical vein toward the liver and the inferior vena cava.

Foramen ovale

An opening in the fetal heart's atrial septum that allows blood to bypass the lungs by moving from the right atrium to the left atrium.

Ductus arteriosus

A vessel in the fetus that connects the pulmonary artery to the aorta, shunting blood away from the lungs.

Surfactant

A phospholipid mixture that prevents the collapse of fetal alveoli by reducing surface tension during expiration.

L/S ratio

The proportion of lecithin to sphingomyelin used to determine fetal lung maturity, with a mature ratio typically being $2:1$.

Meconium

The dark green or black sticky waste product that accumulates in the fetal intestines starting around the $16th$ week.

Vernix caseosa

A thick, cream-like substance that coats the fetal skin to provide lubrication and prevent maceration from amniotic fluid.

Lanugo

Fine, downy hair covering the fetal body that helps provide insulation while in the uterus.

Passive immunity

Temporary protection granted to the fetus through the transfer of maternal IgG antibodies across the placenta starting around week $20$.