Embryonic Development: Key Processes and Disorders

Sperm Capacitation

Final maturation stage enabling sperm to fertilize.

Erection

Physiological response enabling penetration during intercourse.

Orgasm

Rhythmic contractions facilitating sperm entry.

Refractory Period

Time after orgasm where males cannot achieve another.

Uterine Tube

Site where fertilization and early cleavage occur.

Zona Pellucida

Glycoprotein layer surrounding the oocyte.

Peristaltic Contractions

Muscle contractions moving zygote through uterine tube.

Embryonic Period

Stage of development from fertilization to organ formation.

Fetal Period

Stage of development after embryonic period.

Hormonal Changes

Alterations in hormone levels during pregnancy.

Inner Cell Mass

Develops into the embryo during early development.

First Cleavage

Occurs on day one, resulting in two cells.

Four Cell Stage

Occurs on day two of embryonic development.

Early Morula

16-18 compact cells by day three.

Advanced Morula

16-32 cells preparing for differentiation.

Apposition

First stage of implantation; loose alignment with endometrium.

Fertilization

Process where sperm and egg unite to form zygote.

Zygote

Fertilized egg that begins mitotic divisions.

Acrosome Reaction

Sperm enzymes digest layers surrounding the oocyte.

Implantation

Blastocyst embeds into the uterine wall.

Blastocyst

Stage of embryo with inner cell mass and trophoblast.

Gastrulation

Formation of three primary germ layers.

Neurulation

Development of neural structures from ectoderm.

Placenta

Organ providing nutrients and gas exchange for fetus.

Amniotic Sac

Fluid-filled cavity protecting the developing embryo.

Umbilical Cord

Structure connecting fetus to placenta for nutrient exchange.

Cleavage Division

Rapid mitotic divisions without cell growth.

Morula

Solid ball of cells formed after several cleavage divisions.

Compaction

Cells adhere closely, preparing for differentiation.

Blastocoel

Fluid-filled cavity in the blastocyst.

Inner Cell Mass (ICM)

Cluster of cells forming the embryo proper.

Trophoblast

Outer layer of blastocyst forming the placenta.

Human Chorionic Gonadotropin (hCG)

Hormone produced by trophoblast sustaining pregnancy.

Oocyte

Female gamete involved in fertilization.

Adhesion

Blastocyst establishes firmer contact with endometrium.

Cytotrophoblast

Mononuclear cell layer supporting further invasion.

Syncytiotrophoblast

Multinucleated layer facilitating deeper implantation.

Invasion

Critical phase where blastocyst burrows into endometrium.

Decidualization

Endometrial cells transform to support embryo.

Human Chorionic Gonadotropin (HCG)

Hormone signaling corpus luteum to maintain pregnancy.

Implantation Bleeding

Mild spotting occurring 7-10 days post-fertilization.

Embryonic Development Period

Spans from day 15 to week eight post-fertilization.

Ectoderm

Outer layer developing into skin and nervous system.

Mesoderm

Middle layer forming muscles and cardiovascular system.

Endoderm

Inner layer forming gastrointestinal tract and organs.

Histogenesis

Formation of tissues from germ layers.

Organogenesis

Development of internal organs from germ layers.

Somatogenesis

Formation of somites from mesoderm.

Primitive Streak

Marks future site for spine and symmetry.

Neural Plate

Thickened ectoderm forming above the notochord.

Notochord

Rod-like structure providing axial support.

Neuroplate

Thickened ectoderm forming above the notochord.

Neural folds

Elevated edges of the neural plate during development.

Neural groove

Central depression formed between neural folds.

Neural crest cells

Specialized cells that differentiate into various cell types.

Neural tube

Precursor to the central nervous system.

Anterior neuropore

Front end of the neural tube that closes first.

Posterior neuropore

Back end of the neural tube that closes last.

Anencephaly

Condition from anterior neuropore closure failure.

Spina bifida

Condition from posterior neuropore closure failure.

Heart tube

Primitive structure that develops into the heart.

Cardiac mesoderm

Precursor cells forming the heart during embryogenesis.

Aortic roots

Future arterial outflow tracks in the heart.

Truncus arteriosus

Single outflow track separating into aorta and pulmonary artery.

Bulbus cordis

Part of heart tube contributing to right ventricle.

Primitive ventricle

Develops into the left ventricle of the heart.

Primitive atrium

Divides to form left and right atria.

Sinus venosus

Inflow region of the heart receiving venous blood.

Aortic arches

Paired structures that develop into major arteries.

Septum primum

Thin wall partitioning the atria during heart development.

Endocardial cushions

Tissue masses aiding in heart partitioning.

Fetal circulation

Blood flow system established during early gestation.

Neural tube fusion

Process completing neural tube formation by day 28.

Week five development

Heart forms two chambers; limbs begin to develop.

Week six development

Heart pumps; red blood cells produced by liver.

Week seven development

Fetal heart rate becomes detectable with Doppler.

Week eight development

Facial features develop; baby resembles a human.

Atrial Separation

Formation of septum premium in heart.

Septum Premium

Thin wall partitioning left and right atria.

Osteum Premium

Temporary opening for blood flow between atria.

Osteum Secundum

Second opening in septum premium after closure.

Foramen Ovale

Shunt allowing blood from right to left atrium.

Ventricular Separation

Muscular growth completing interventricular septum.

Endocardial Cushions

Tissue masses aiding heart partitioning.

Aortic Pulmonary Septum

Divides outflow into aorta and pulmonary arteries.

Fetal Circulation

Blood bypasses non-functional organs before birth.

Ductus Arteriosus

: Connects pulmonary artery to aorta in fetus.

Ductus Venosus

Directs blood from umbilical vein to inferior vena cava.

Umbilical Vein

Carries oxygenated blood from placenta to fetus.

Cleft Lip

Result of interrupted fusion of primary palate.

Cleft Palate

Result of interrupted fusion of secondary palate.

Palatogenesis

Development of the palate in two stages.

Primary Palate

Forms from frontonasal and medial nasal prominences.

Secondary Palate

Forms from palatine shelves during weeks 8-12.

Facial Prominences

Structures forming distinct facial features.

Cranial Neural Crest Cells

Cells migrating to form facial structures.

Kidney Development

Progresses through pro-, meso-, and metanephros stages.

Pronephros

Primitive non-functional kidney structure in early gestation.

Mesonephros

Primitive kidney producing small urine amounts.

Metanephros

Permanent functional kidney developing from week five.