Week 1: Zygote - Morula - Blastula/Blastomere/Blastosphere - Archenteron/Primitive streak - Blastopore - Allantois - Trophoblast (Cytotrophoblast - Syncytiotrophoblast - Gestational sac) Mammalian embryogenesis is the process of cell division and cellular differentiation which leads to the development of a mammalian embryo. ... This article or section is in need of attention from an expert on the subject. ... This article or section is in need of attention from an expert on the subject. ... Fetal (U.S. English; Foetal UK English) development is the process in which a fetus (U.S. English; Foetus UK English) develops during gestation, from the times of conception until birth. ... A human fetus A fetus (or foetus, or fœtus – see below) is a developing mammal after the embryonic stage and before birth. ... In embryology, Carnegie stages are a standardized system of 23 stages used to provide a unified developmental chronology of the embryo. ... This article or section does not cite its references or sources. ... Morula is a stage of embryonic development in animals, including the 16-cell phase, the 32-cell phase, and the 64-cell phase. ... Blastulation. ... A blastomere is the structure which results from the divisions of a fertilised egg during embryonic development . ... Blastulation. ... The archenteron is an indentation that forms early on in a developing blastula. ... The primitive streak is a structure that forms during the early stages of avian, reptilian and mammalian embryonic development. ... A blastopore is an opening into the archenteron during the embryonic stages of an organism. ... Allantois is a part of a developing animal embryo. ... The trophoblast (from Greek threphein: to feed) is considered to be the first of all embryonic annexes. ... The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ... Syncytiotrophoblasts are cells found in the placenta of human embryos. ... The gestational sac is the only available intrauterine structure that can be used to determine if an intrauterine pregnancy (IUP) exists, until the embryo is identified. ...

Week 2: Yolk sac - Vitelline duct - Bilaminar disc The yolk sac is the first element seen in the gestational sac during pregnancy, usually at 5 weeks gestation. ... At the end of the fourth week the yolk-sac presents the appearance of a small pear-shaped vesicle (umbilical vesicle) opening into the digestive tube by a long narrow tube, the vitelline duct. ... This article, image, template or category should belong in one or more categories. ...

Week 3: Hensen's node - Gastrula/Gastrulation - Trilaminar embryo Branchial arch (1st) - Branchial pouch - Meckel's cartilage - Somite/Somitomere - Germ layer (Ectoderm, Endoderm, Mesoderm, Chordamesoderm, Paraxial mesoderm, Intermediate mesoderm, Lateral plate mesoderm) Hensens Node is the organizer for gastrulation in birds. ... 1 - blastula, 2 - gastrula; orange - ectoderm, red - endoderm. ... 1 - blastula, 2 - gastrula; orange - ectoderm, red - endoderm. ... It has been suggested that this article or section be merged with Embryogenesis. ... In the development of vertebrate animals, the branchial arches (or pharyngeal arches) develop during the fourth and fifth week in utero as a series of mesodermal outpouchings on the left and right sides of the developing pharynx. ... It has been suggested that this article or section be merged into branchial arch. ... Pharyngeal or branchial pouches form on the endodermal side between the branchial arches, and pharyngeal grooves (or clefts) form from the lateral ectodermal surface of the neck region to separate the arches. ... The cartilaginous bar of the mandibular arch is formed by what are known as Meckel’s cartilages (right and left) ; above this the incus is developed. ... In the developing vertebrate embryo, somites are masses of mesoderm distributed along the two sides of the neural tube and that will eventually become dermis (dermatome), skeletal muscle (myotome), and vertebrae (sclerotome). ... In the developing vertebrate embryo, the somitomeres are loose masses of paraxial mesoderm derived cells that form along each side of the neural tube towards the end of the third gestational week. ... It has been suggested that organogenesis be merged into this article or section. ... The ectoderm is outermost of the three germ layers of the developing embryo, the other two being the mesoderm and the endoderm. ... The endoderm, sometimes refered to as entoderm, is one of the three germ layers of the developing embryo, the other two being the ectoderm and the mesoderm. ... The mesoderm is one of the three germ layers in the early developing embryo, the other two layers being the ectoderm and the endoderm. ... Chordamesoderm is a type of mesoderm that lies along the central axis, under the neural tube. ... Paraxial mesoderm is the area of mesoderm that forms just lateral to the neural tube on both sides. ... Intermediate mesoderm is a type of mesoderm that is located between the paraxial mesoderm and the lateral plate. ... Lateral plate mesoderm (or hypomere) is a type of mesoderm that is found at the periphery of the embryo. ...

Histogenesis and Organogenesis An Introduction to Histogenesis Histogenesis is defined as the formation of tissues and organs from undifferentiated cells (Encarta Dictionary). ... Organogenesis is a stage of animal development where the ectoderm, endoderm, and mesoderm are formed. ...

Circulatory system: Primitive atrium - Primitive ventricle - Bulbus cordis - Truncus arteriosus - Ostium primum - Foramen ovale - Ductus venosus - Ductus arteriosus - Aortic arches - Septum primum - Septum secundum - Cardinal veins Human circulatory system. ... The primitive atrium grows rapidly and partially encircles the bulbus cordis; the groove against which the bulbus cordis lies is the first indication of a division into right and left atria. ... The primitive ventricle becomes divided by a septum, the septum inferius or ventricular septum, which grows upward from the lower part of the ventricle, its position being indicated on the surface of the heart by a furrow. ... When the heart assumes its S-shaped form the bulbus cordis lies ventral to and in front of the primitive ventricle. ... For the medical condition with the same name, see Truncus arteriosus. ... In the developing heart, for a time the atria communicate with each other by an opening, the ostium primum of Born (interatrial foramen primum), below the free margin of the septum. ... In the fetal heart, the foramen ovale allows blood to enter the left atrium from the right atrium. ... In the fetus, the ductus venosus connects the left umbilical vein with the upper inferior vena cava. ... In the developing fetus, the ductus arteriosus (DA) is a shunt connecting the pulmonary artery to the aortic arch that allows much of the blood from the right ventricle to bypass the fetus fluid-filled lungs. ... This article focuses upon the multiple aortic arches present in the embryo. ... The cavity of the primitive atrium becomes subdivided into right and left chambers by a septum, the septum primum, which grows downward into the cavity. ... The septum secundum, semilunar in shape, grows downward from the upper wall of the atrium immediately to the right of the primary septum and foramen ovale. ... During development of the veins, the first indication of a parietal system consists in the appearance of two short transverse veins, the ducts of Cuvier, which open, one on either side, into the sinus venosus. ...

Nervous system: Neural development/Neurulation - Neurula - Neural folds - Neural groove - Neural tube - Neural crest - Neuromere (Rhombomere) - Notochord - Optic vesicles - Optic stalk - Optic cup The nervous system of an animal coordinates the activity of the muscles, monitors the organs, constructs and also stops input from the senses, and initiates actions. ... The study of neural development draws on both neuroscience and developmental biology to describe the cellular and molecular mechanisms by which complex nervous systems emerge during embryonic development and throughout life. ... Neurulation is a part of organogenesis in vertebrate embryos. ... A Neurula is an embryo at the early stage of development in which neurulation occurs. ... In front of the primitive streak two longitudinal ridges, caused by a folding up of the ectoderm, make their appearance, one on either side of the middle line. ... Between the neural folds is a shallow median groove, the neural groove. ... In the developing vertebrate nervous system, the neural tube is the precursor of the central nervous system, which comprises the brain and spinal cord. ... The neural crest, a component of the ectoderm, is one of several ridgelike clusters of cells found on either side of the neural tube in vertebrate embryos. ... Neuromeres are transient segments during the early development of the human brain. ... In the vertebrate embryo, a rhombomere is a segment of the developing rhombencephalon. ... The notochord is a flexible, rod-shaped body found in embryos of all chordates. ... The eyes begin to develop as a pair of diverticula from the lateral aspects of the forebrain. ... The optic vesicles project toward the sides of the head, and the peripheral part of each expands to form a hollow bulb, while the proximal part remains narrow and constitutes the optic stalk. ... The outer wall of the bulb of the optic vesicles becomes thickened and invaginated, and the bulb is thus converted into a cup, the optic cup (or ophthalmic cup), consisting of two strata of cells). ...

Digestive system: Foregut - Midgut - Hindgut - Proctodeum - Rathke's pouch - Septum transversum For the Physics term GUT, please refer to Grand unification theory The gastrointestinal or digestive tract, also referred to as the GI tract or the alimentary canal or the gut, is the system of organs within multicellular animals which takes in food, digests it to extract energy and nutrients, and... The foregut is the anterior part of the alimentary canal, from the mouth to the intestine, or to the entrance of the bile duct. ... The midgut is the portion of the embryo from which most of the intestines are derived. ... Hindgut is the posterior (caudal) part of the alimentary canal. ... A proctoduem is the back ectodermal part of an alimentary canal. ... The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ... The liver arises in the form of a diverticulum or hollow outgrowth from the ventral surface of that portion of the gut which afterward becomes the descending part of the duodenum. ...

Urinary/Reproductive system: Urogenital folds - Urethral groove - Urogenital sinus - Kidney development (Pronephros - Mesonephros - Ureteric bud - Metanephric blastema) - Fetal genital development (Wolffian duct - Müllerian duct - Gubernaculum - Labioscrotal folds) The urinary system is the organ system that produces, stores, and carries urine. ... A reproductive system is the ensembles and interactions of organs and/or substances within an organism that strictly pertain to reproduction. ... The urogenital folds are an embryological structure which give rise to a portion of the external genitalia. ... The urethral groove is a temporary linear indentation on the underside (ventral side) of the male penis during embryonic development. ... The urogenital sinus (also known as the persistent cloaca) is a part of the human body while it is an embryo. ... In humans, the metanephros (adult kidney) begins as an aggregate of mesenchymal cells that are detectable by the fifth gestational week as two small areas in the intermediate mesoderm close to the pelvic aorta. ... Pronephros the most primitive of the three excretory organs that develop in vertebrate, corresponding to the first stage of kidney development. ... The mesonephros (Latin for middle kidney) is one of three excretory organs that develop in vertebrates. ... The Ureteric bud is a portion of the mesonephric duct. ... The Metanephric blastema (or metanephric mesenchyme) is one of the two embryological structures that give rise to the kidney (the other is the ureteric bud. ... This article or section is in need of attention from an expert on the subject. ... The Wolffian duct (also known as archinephric duct, Leydigs duct, and the mesonephric duct) is an paired organ found in mammals including humans during embryogenesis. ... The Müllerian ducts are paired ducts of the embryo which empty into the cloaca, and which in the female develop into the upper vagina, cervix, uterus and oviducts; in the male they disappear except for the vestigial vagina masculina and the appendix testis. ... The gubernaculum is a fold of peritoneum which attaches to the caudal end of the testes. ... The labioscrotal folds (or labioscrotal swellings) are paired embryonic structures that represent the final stage of development of the caudal end of the external genitals before sexual differentiation. ...

Glands: Thyroglossal duct A gland is an organ in an animals body that synthesizes a substance for release such as hormones, often into the bloodstream (endocrine gland) or into cavities inside the body or its outer surface (exocrine gland). ... The thyroglossal duct is an embryological anatomical structure which forms the connection between the initial area of development of the thyroid gland and its final position. ...

Uterine support: Placenta - Umbilical cord (Umbilical artery, Umbilical vein, Wharton's jelly) - Amniotic sac (Amnion, Chorion) The uterus or womb is the major female reproductive organ of most mammals, including humans. ... The placenta is an ephemeral (temporary) organ present only in female placental vertebrates during gestation (pregnancy). ... In placental mammals, the umbilical cord is a tube that connects a developing embryo or fetus to its placenta. ... Umbilical arteries carry deoxygenated blood from the fetus to the placenta in the umbilical cord. ... Fetal circulation; the umbilical vein is the large, red vessel at the far left The umbilical vein is a blood vessel present during fetal development that carries oxygenated blood from the placenta to the growing fetus. ... Whartons jelly is a gelatinous substance within the umbilical cord. ... Amnion. ... For the alien race in Stephen Donaldsons The Gap Cycle, see Amnion (Gap Cycle). ...

Limb development: Limb bud - Apical Ectodermal Ridge/AER The vertebrate limb arises out of a general morphogenetic area called a limb field. ... In embryology, the limb bud is a structure formed by the developing limb, derived from lateral plate mesoderm[citation needed]. It is intimately related with the apical ectodermal ridge, which secretes factors inducing the initial differentiation of the limb bud. ... There are very few or no other articles that link to this one. ...