MCAT Biology: Embryogenesis and the Nervous System

Comprehensive practice flashcards covering vocabulary from Embryogenesis, Development, and the Nervous System transcript for MCAT preparation.

Fertilization

The union of a sperm and an ovum to form a diploid zygote.

Ampulla

The widest part of the fallopian tube where fertilization usually occurs.

Acrosomal enzymes

Substances released by sperm to penetrate the corona radiata and zona pellucida of the oocyte.

Acrosomal apparatus

A tube-like structure formed by the first sperm to contact the secondary oocyte's cell membrane, allowing the pronucleus to enter.

Cortical reaction

The release of calcium ions after sperm penetration that depolarizes the ovum membrane.

Fertilization membrane

The depolarized and impenetrable membrane of the ovum formed after the cortical reaction.

Dizygotic (fraternal) twins

Twins formed from the fertilization of two different eggs by two different sperm during one ovulatory cycle.

Monozygotic (identical) twins

Twins formed when a single zygote splits into two, sharing identical genetic material.

Monochorionic/monoamniotic twins

Identical twins that share both the same amnion and chorion.

Monochorionic/diamniotic twins

Identical twins that each have their own amnion but share the same chorion.

Dichorionic/diamniotic twins

Identical twins that each have their own amnion and chorion.

Conjoined twins

Offspring that are physically attached due to incomplete division of a single zygote.

Cleavage

The process of rapid mitotic cell divisions of the zygote as it moves toward the uterus.

Embryo

The developmental stage starting after the first cleavage, marked by the loss of unicellularity.

Nuclear-to-cytoplasmic (N:C) ratio

One of two ratios increased during early cleavage to enhance area for gas and nutrient exchange.

Surface area-to-volume ratio

A ratio increased during cleavage as cells divide into progressively smaller units.

Indeterminate cleavage

Cell division resulting in cells that can still develop into complete organisms; source of monozygotic twins.

Determinate cleavage

Cell division resulting in cells with fates that are already committed to a specific cell line.

Morula

A solid mass of cells resulting from several divisions after fertilization; named after the Latin word for mulberry.

Blastulation

The process that follows the morula stage, forming the blastula.

Blastula

A hollow ball of cells with a fluid-filled inner cavity known as a blastocoel.

Blastocoel

The fluid-filled inner cavity of the blastula.

Blastocyst

The mammalian term for a blastula, consisting of the trophoblast and inner cell mass.

Trophoblast

The outer group of cells in a blastocyst that surround the blastocoel and give rise to the chorion and placenta.

Inner cell mass

The group of cells in the blastocyst that protrude into the blastocoel and give rise to the organism itself.

Implantation

The process where the blastula burrows into the endometrium of the uterus.

Chorion

An extraembryonic membrane that develops from trophoblast cells into the placenta.

Chorionic villi

Microscopic finger-like projections from the trophoblast that penetrate the endometrium to support maternal–fetal gas exchange.

Umbilical cord

The connection between the embryo and the placenta, consisting of two arteries and one vein.

Umbilical vein

Vessel that carries oxygenated blood rich with nutrients from the placenta to the embryo.

Umbilical arteries

Vessels that carry deoxygenated blood and waste from the embryo to the placenta.

Yolk sac

The structure that supports the embryo until the placenta is functional and serves as the site of early blood cell development.

Allantois

Structure involved in early fluid exchange between the embryo and the yolk sac; its remnants help form the umbilical cord.

Amnion

A thin, tough, extraembryonic membrane filled with fluid that surrounds the developing embryo.

Amniotic fluid

The fluid within the amnion that acts as a shock absorber for the fetus during pregnancy.

Amniocentesis

A procedure to aspirate amniotic fluid to examine fetal cells for chromosomal abnormalities or sex determination.

Gastrulation

The generation of three distinct germ layers in the embryo: ectoderm, mesoderm, and endoderm.

Archenteron

The membrane invagination into the blastocoel during gastrulation that eventually develops into the gut.

Blastopore

The opening of the archenteron.

Deuterostomes

Organisms (including humans) in which the blastopore develops into the anus.

Protostomes

Organisms in which the blastopore develops into the mouth.

Ectoderm

The outermost germ layer giving rise to the epidermis, hair, nails, nervous system, lens of the eye, and inner ear.

Mesoderm

The middle germ layer giving rise to the musculoskeletal, circulatory, and excretory systems, as well as the gonads and adrenal cortex.

Endoderm

The innermost germ layer giving rise to epithelial linings of the digestive and respiratory tracts, lungs, pancreas, and thyroid.

Selective transcription

The process where only specific genes needed for a particular cell type are transcribed, allowing cell specialization.

Induction

The ability of one group of cells to influence the differentiation of nearby cells, mediated by chemical inducers.

Inducer

Chemical substances that diffuse from organizing cells to responsive cells to guide development.

Adrenal cortex origin

Derived from the mesoderm.

Adrenal medulla origin

Derived from the ectoderm (contains nervous tissue).

Neurulation

The development of the nervous system, beginning after the formation of the three germ layers.

Notochord

A rod of mesodermal cells along the long axis that induces the formation of neural folds from overlying ectoderm.

Neural folds

Ectodermal structures that slide inward during induction by the notochord to surround the neural groove.

Neural tube

Formed by the fusion of neural folds, this structure gives rise to the central nervous system.

Neural crest cells

Cells at the tip of neural folds that migrate to form the peripheral nervous system and other specialized tissues like melanocytes.

Peripheral nervous system components from neural crest

Sensory ganglia, autonomic ganglia, adrenal medulla, and Schwann cells.

Spina bifida

A defect resulting from the failure of the neural tube to close, exposing parts of the spinal cord.

Anencephaly

A fatal defect where the brain fails to develop due to incomplete neural tube closure.

Folate (folic acid)

A vitamin recommended for women of childbearing age to prevent neural tube defects.

Teratogens

Substances such as alcohol or prescription drugs that interfere with development, causing defects or death.

Organogenesis

The production and development of organs within the embryo.

Hyperglycemia prenatal effect

High maternal blood glucose can lead to a fetus that is too large and suffers from hypoglycemia after birth.

Specification

The initial, reversible stage of cell specialization where a cell is designated as a specific type.

Determination

The irreversible commitment of a cell to a particular functional lineage.

Morphogens

Secreted molecules that diffuse through the environment to cause determination of neighboring cells.

Differentiation

The process following determination where a cell undergoes structural and biochemical changes to match its cell type.

Stem cells

Cells that have not yet differentiated or that give rise to other cells that will differentiate.

Potency

A spectrum defining the range of tissue types into which a stem cell can differentiate.

Totipotent stem cells

Cells with the greatest potency, able to differentiate into any cell type including placental structures.

Pluripotent stem cells

Cells able to differentiate into any germ layer except for placental structures.

Multipotent stem cells

Cells that can differentiate into multiple types of cells within a specific group (e.g., hematopoietic stem cells).

Adult stem cells

Multipotent cells found in adults that can be induced to increase potency using transcription factors.

Knockout mice

Mice created using stem cells lacking a particular gene to study its function.

Autocrine signals

Signals that act on the same cell that secreted them.

Paracrine signals

Signals that act on cells in the local area via diffusion.

Juxtacrine signals

Direct stimulation of receptors on an adjacent cell without diffusion.

Endocrine signals

Secreted hormones that travel through the bloodstream to distant target tissues.

Growth factors

Peptides that promote differentiation and mitosis in specific tissues based on cell competence.

Reciprocal development

A process where one tissue induces another, which then induces the original tissue (e.g., lens and optic vesicle).

Gradients (signaling)

The use of varying concentrations of morphogens to induce specific cell types based on distance from the source.

Sonic hedgehog (Shh)

A common morphogen involved in developmental signaling and determination.

Cell migration

The movement of cells from their origin to their final location (e.g., anterior pituitary moving from oral ectoderm).

Apoptosis

Programmed cell death characterized by the formation of contained blebs that are digested without leaking substances.

Apoptotic blebs

Self-contained protrusions of a cell undergoing apoptosis that are broken into apoptotic bodies.

Necrosis

Cell death caused by injury, resulting in the leaking of internal substances and potential tissue irritation.

Complete regeneration

Replacing lost or damaged tissues with identical tissues, seen in species like salamanders.

Incomplete regeneration

Regrowth resulting in tissue that is not identical in structure or function to the lost tissue, common in humans.

Liver regenerative capacity

High; the liver can undergo extensive regeneration even after 50% loss.

Heart regenerative capacity

Virtually non-existent; injury often results in permanent scarring.

Senescence

Biological aging resulting in molecular and metabolic disruption and the failure of cells to divide.

Telomeres

Ends of chromosomes with high guanine and cytosine content that prevent DNA unraveling but shorten during replication.

Telomerase

A reverse transcriptase enzyme that synthesizes telomeres, preventing senescence in germ, fetal, and tumor cells.

Fetal hemoglobin (HbF)

A form of hemoglobin in fetal blood with a greater affinity for oxygen than adult hemoglobin ($HbA$).

Placental barrier function

Facilitates nutrient/waste exchange while preventing maternal and fetal blood mixing and providing immune protection.

TORCHES infections

Pathogens capable of crossing the placental barrier, including Syphilis and Toxoplasma gondii.

Endocrine functions of placenta

Produces progesterone, estrogen, and human chorionic gonadotropin ($hCG$).

Foramen ovale

A fetal shunt connecting the right atrium to the left atrium, bypassing the lungs.

Ductus arteriosus

A fetal shunt that directs blood from the pulmonary artery to the aorta, bypassing the lungs.

Ductus venosus

A fetal shunt that connects the umbilical vein to the inferior vena cava, bypassing the liver.

Right vs Left heart pressure in fetus

The right side of the heart is at a higher pressure than the left side in the fetus.

Gestation length

Approximately $280\,days$ in humans, divided into three trimesters.