Embryology

The pharyngeal arches are structures seen in the development of vertebrates, are recognisable precursors for numerous structures.

In embryogenesis, the sex cords, (primitive sex cords or gonadal cords) are structures that develop from the gonadal ridges.

Anti-Müllerian hormone (AMH), also known by , is a protein that in humans is encoded by the AMH gene.

In biology, a blastomere is a type of cell produced by cleavage (cell division) of the zygote after fertilization and is an essential part of blastula formation.

A blastocoel is a fluid-filled cavity that forms in the animal hemisphere of early amphibian and echinoderm embryos, or between the epiblast and hypoblast of avian, reptilian, and mammalian blastoderm-stage embryos.

The urachus is a fibrous remnant of the allantois, a canal that drains the urinary bladder of the fetus that joins and runs within the umbilical cord.

An egg is the organic vessel containing the zygote in which an animal embryo develops until it can survive on its own, at which point the animal hatches.

The egg cell, or ovum, is the female reproductive cell (gamete) in oogamous organisms.

An embryo is an early stage of development of a multicellular diploid eukaryotic organism.

A germ layer is a primary layer of cells that form during embryogenesis.

In all bilaterian animals, the mesoderm is one of the three primary germ layers in the very early embryo.

The placenta (also known as afterbirth) is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, provide thermo-regulation to the fetus, waste elimination, and gas exchange via the mother's blood supply, fight against internal infection and produce hormones to support pregnancy.

Twins are two offspring produced by the same pregnancy.

In placental mammals, the umbilical cord (also called the navel string, birth cord or funiculus umbilicalis) is a conduit between the developing embryo or fetus and the placenta.

A zygote (from Greek ζυγωτός zygōtos "joined" or "yoked", from ζυγοῦν zygoun "to join" or "to yoke"), is a eukaryotic cell formed by a fertilization event between two gametes.

Allantois (/əˈlæntɔɪs/; plural allantoides or allantoises) is a sac-like structure that forms part of a developing amniote's conceptus (which consists of all embryonic and extra-embryonic tissues).

In the fetal heart, the foramen ovale (/fəˈreɪmən oʊˈvæli, -mɛn-, -ˈvɑː-, -ˈveɪ-/), also foramen Botalli, ostium secundum of Born or falx septi, allows blood to enter the left atrium from the right atrium.

The zona pellucida (plural zonae pellucidae, also egg coat or pellucid zone) is a glycoprotein layer surrounding the plasma membrane of mammalian oocytes.

In humans and most mammals, the chorion is one of the membranes that exist during pregnancy between the developing fetus and mother (the fetal membranes).

Neural crest cells are a temporary group of cells unique to vertebrates that arise from the embryonic ectoderm cell layer, and in turn give rise to a diverse cell lineage—including melanocytes, craniofacial cartilage and bone, smooth muscle, peripheral and enteric neurons and glia.

The amnion is a membrane that closely covers the embryo when first formed.

In the developing fetus, the ductus arteriosus, also called the ductus Botalli, is a blood vessel connecting the pulmonary artery to the proximal descending aorta.

In amniote animal embryology, the epiblast is one of two distinct layers arising from the inner cell mass in the mammalian blastocyst or from the blastodisc in reptiles and birds.

The hypoblast is a tissue type that forms from the inner cell mass.

A morula (Latin, morus: mulberry) is an early stage embryo consisting of cells (called blastomeres) in a solid ball contained within the zona pellucida.

In biology, placentation refers to the formation, type and structure, or arrangement of placentas.

Drosophila embryogenesis, the process by which Drosophila (fruit fly) embryos form, is a favorite model system for genetics and developmental biology.

Prenatal or antenatal development is the process in which a human embryo and later fetus (or foetus) develops during pregnancy, from fertilization until birth.

The yolk sac is a membranous sac attached to an embryo, formed by cells of the hypoblast adjacent to the embryonic disk.

The blastocyst is a structure formed in the early development of mammals.

Gametogenesis is a biological process by which diploid or haploid precursor cells undergo cell division and differentiation to form mature haploid gametes.

Oogenesis, ovogenesis, or oögenesis /ˌoʊ.

Paramesonephric ducts (or Müllerian ducts) are paired ducts of the embryo that run down the lateral sides of the urogenital ridge and terminate at the sinus tubercle in the primitive urogenital sinus.

Pronephros the most basic of the three excretory organs that develop in vertebrates, corresponding to the first stage of kidney development.

The chorioallantoic membrane — also called the chorioallantois or abbreviated to CAM — is a vascular membrane found in eggs of some amniotes, such as birds and reptiles.

A spermatogonium (plural: spermatogonia) is an undifferentiated male germ cell.

In the inguinal crest a peculiar structure, the gubernaculum testis, makes its appearance.

Trabecular cartilages (trabeculae cranii, sometimes simply trabeculae) are paired, rod-shaped cartilages, which develop in the head of the vertebrate embryo.

Axial mesoderm, or chordamesoderm, is a type of mesoderm that lies along the central axis under the neural tube.

During Human embryogenesis the mandibular arch and hyoid arch grow more rapidly than those behind them, with the result that the latter become, to a certain extent, telescoped within the former, and a deep depression, the cervical sinus, is formed on either side of the neck.

The cytotrophoblast (or layer of Langhans) is the inner layer of the trophoblast.

In the development of the human embryo the intraembryonic coelom (or somatic coelom) is a portion of the conceptus forming in the mesoderm during the third week of development.

The laryngotracheal groove is a precursor for the larynx and trachea.

The metanephrogenic blastema or metanephric blastema (or metanephric mesenchyme, or metanephric mesoderm) is one of the two embryological structures that give rise to the kidney, the other being the ureteric bud.

By the upgrowth of the surrounding parts the olfactory areas are converted into pits, the nasal pits or olfactory pits, which indent the fronto-nasal process and divide it into a medial and two lateral nasal processes.

A pharyngeal groove (or branchial groove, or pharyngeal cleft) is made up of ectoderm unlike its counterpart the pharyngeal pouch on the endodermal side.

In the embryonic development of vertebrates, pharyngeal pouches form on the endodermal side between the pharyngeal arches.

Paraxial mesoderm, also known as presomitic or somitic mesoderm is the area of mesoderm in the neurulating embryo that flanks and forms simultaneously with the neural tube.

Around the fifth week, the intermaxillary segment arises as a result of fusion of the two medial nasal processes and the frontonasal process within the embryo.

The septum transversum is a thick mass of cranial mesenchyme, formed in the embryo, that gives rise to parts of the thoracic diaphragm and the ventral mesentery of the foregut in the developed human being.

A stigma in mammalian reproductive anatomy refers to the area of the ovarian surface where the Graafian follicle will burst through during ovulation and release the ovum.

In the anatomy of an embryo, the splanchnopleuric mesenchyme is a structure created during embryogenesis when the lateral mesodermal germ layer splits into two layers.

The surface ectoderm (or external ectoderm) forms the following structures: * Skin (only epidermis; dermis is derived from mesoderm) (along with glands, hair, and nails) * Epithelium of the mouth and nasal cavity salivary glands, and glands of mouth and nasal cavity * Tooth enamel (as a side note, dentin and dental pulp are formed from ectomesenchyme which is derived from ectoderm (specifically neural crest cells and travels with mesenchmyal cells) * Epithelium of anterior pituitary * Lens, cornea, lacrimal gland, tarsal glands and the conjunctiva of the eye * Apical ectodermal ridge inducing development of the limb buds of the embryo. * Sensory receptors in epidermis

The thyroglossal duct is an embryological anatomical structure forming an open connection between the initial area of development of the thyroid gland and its final position.

During the third week of embryogenesis there appears, immediately behind the ventral ends of the two halves of the first pharyngeal arch, a rounded swelling named the tuberculum impar or median tongue bud, which was described by His as undergoing enlargement to form the buccal part of the tongue.

In the human embryo, the vitelline duct, also known as the omphalomesenteric duct, is a long narrow tube that joins the yolk sac to the midgut lumen of the developing fetus.

The vitelline membrane is a structure surrounding the outer surface of the plasma membrane of an ovum.

The ultimopharyngeal body or ultimobranchial body or ultimobranchial gland is a small organ found in the neck region of many animals.

The respiratory bud is an embryological structure of endodermal origin that develops into organs of the respiratory system, such as the larynx, trachea and lungs.

The mandibular prominence is an embryological structure which gives rise to the lower portion of the face.

Embryogenesis is the process by which the embryo forms and develops.

Conceptus (Latin: conceptio, meaning derivatives of zygote) denotes the embryo and its adnexa (appendages or adjunct parts) or associated membranes (i.e. the products of conception).

Syncytiotrophoblast (from the Greek 'syn'- "together"; 'cytio'- "of cells"; 'tropho'- "nutrition"; 'blast'- "bud") is the epithelial covering of the highly vascular embryonic placental villi, which invades the wall of the uterus to establish nutrient circulation between the embryo and the mother.

The thyroid pouch or thyroid diverticulum is the embryological structure of the second pharyngeal arch from which thyroid follicular cells derive.

Bilaminar blastocyst or Bilaminar disc refers to the epiblast and the hypoblast, evolved from the embryoblast.

Chorionic villi are villi that sprout from the chorion to provide maximum contact area with maternal blood.

Heuser's membrane (or the exocoelomic membrane) is a short lived combination of hypoblast cells and extracellular matrix.

In the developing vertebrate embryo, the somitomeres (or somatomeres)are cells that are derived from the loose masses of paraxial mesoderm that are found alongside the developing neural tube.

The development of the secondary palate commences in the sixth week of human embryological development.

Aplasia (from Greek a (Not, no); plasis (molding) is defined in general as "defective development or congenital absence of an organ or tissue." In the field of hematology, the term refers to "incomplete, retarded, or defective development, or cessation of the usual regenerative process."

In the anatomy of an embryo, the somatopleuric mesenchyme is a structure created during embryogenesis when the lateral mesoderm splits into two layers.

The fetal membranes are membranes associated with the developing fetus.

During pregnancy changes in the placenta involve the disappearance of the greater portion of the stratum compactum, but the deeper part of this layer persists and is condensed to form what is known as the basal plate.

The floor of the amniotic cavity is formed by the embryonic disc (or embryonic disk) composed of a layer of prismatic cells, the embryonic ectoderm, derived from the inner cell-mass and lying in apposition with the endoderm.

The medial nasal prominence (nasomedial) is an embryological structure that forms the upper lip and nose.

In the development of vertebrate animals, during the 6th Carnegie Stage, the proximal part of the notochordal canal persists temporarily as the neurenteric canal (also known as the "axial canal"), which forms a transitory communication between the amniotic sac and the yolk sac cavities.

The Zone of Polarizing Activity (ZPA) is an area of mesenchyme that contains signals which instruct the developing limb bud to form along the anterior/posterior axis.

The connecting stalk is a yolk sac diverticulum.

Foetal cerebral redistribution or 'brain-sparing' is a diagnosis in foetal medicine.