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Encyclopedia > Fetal development

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. American English (AmE) is the dialect of the English language used mostly in the United States of America. ... Diagram showing the geographical locations of selected languages and dialects of the British Isles. ... Fetus at eight weeks Foetus redirects here. ... U.S. English, Inc. ... Diagram showing the geographical locations of selected languages and dialects of the British Isles. ... Gestation is the carrying of an embryo or fetus inside a female viviparous animal. ... The term conception can refer to more than one meaning: Concept Fertilisation This is a disambiguation page — a navigational aid which lists pages that might otherwise share the same title. ... Birth is the process in animals by which an offspring is expelled from the body of its mother. ...

Contents


Human fetal development

Fertilization and Embryogenesis

Main article: Fertilization
A sperm fertilizing an ovum
Enlarge
A sperm fertilizing an ovum

When semen is deposited in the vagina, the spermatozoa travel through the cervix and body of the uterus and into the Fallopian tubes. Fertilization of the ovum (egg cell) usually takes place in the Fallopian tube. Many sperm must cooperate to penetrate the thick protective shell-like barrier that surrounds the ovum. The first sperm that penetrates fully into the egg donates its genetic material (DNA). The resulting combination is called a zygote. The term "conception" refers variably to either fertilization or to formation of the conceptus, which occurs after uterine implantation. Categories: Biology stubs ... Image File history File links Sperm-egg. ... Image File history File links Sperm-egg. ... Human semen collected on a glass surface during ejaculation process. ... The vagina, (from Latin, literally sheath or scabbard ) is the tubular tract leading from the uterus to the exterior of the body in female placental mammals and marsupials, or to the cloaca in female birds, monotremes, and some reptiles. ... Schematic diagram of a sperm cell, showing the (1) acrosome, (2) cell membrane, (3) nucleus, (4) mitochondria, and (5) flagellum (tail) A sperm cell, or spermatozoon ( spermatozoa) (in Greek: sperm = semen and zoon = alive), is the haploid cell that is the male gamete. ... Schematic frontal view of female anatomy The cervix (from Latin neck) is the lower, narrow portion of the uterus where it joins with the top end of the vagina. ... Female internal reproductive anatomy The Fallopian tubes or oviducts are two very fine tubes leading from the ovaries of female mammals into the uterus. ... Categories: Biology stubs ... A human ovum An ovum (from Latin, loosely, egg or egg cell) is a female sex cell or gamete. ... Cells in culture, stained for keratin (red) and DNA (green). ... Genetic material is the material used to store genetic information for a living organism. ... The general structure of a section of DNA Deoxyribonucleic acid (DNA) is a nucleic acid — usually in the form of a double helix — that contains the genetic instructions or genocode monitoring the biological development of all cellular forms of life, and many viruses. ... This article or section does not cite its references or sources. ... Conceptus (latin is conceptio, derivatives of zygote) The embryo and its adnexa (appendages or adjunct parts) or associated membranes (i. ...


Like every cell in the body, the zygote contains all of the genetic information unique to an individual. Half of the genetic information came from the mother's egg, and the other half from a single sperm. The zygote spends the next few days traveling down the Fallopian tube. Meanwhile it divides several times to form a ball of cells called a morula. Further cellular division is accompanied by the formation of a small cavity between the cells. This stage is called a blastocyst. Up to this point there is no growth in the overall size of the embryo, so each division produces successively smaller cells. The signifier sperm can refer to: (mass noun, from Greek sperma = seed) a substance which consists of spermatozoa and which is a component of semen (mass noun) semen itself (informally, count noun with plural sperm or sperms) a single spermatozoon (= sperm cell) sperma ceti (Latin ceti, genitive of cetus = whale... Morula is a stage of embryonic development in animals, including the 16-cell phase, the 32-cell phase, and the 64-cell phase. ... Cell division is the process by which a cell (called the parent cell) divides into two cells (called daughter cells). ... Embryogenesis is the process of cell division and cellular differentiation which leads to the development of an embryo. ...


The blastocyst reaches the uterus at roughly the fifth day after fertilization. The embryo "hatches" from its zona pellucida, a glycoprotein shell. It then adheres to the uterine lining and becomes embedded in the endometrial cell layer. This process is also called "implantation". In most successful human pregnancies, the conceptus implants 8 to 10 days after ovulation (Wilcox et al 1999). The inner cell mass forms the embryo, while the outer cell layers form the membranes and placenta. Together, the embryo and its membranes are referred to as a conceptus, or the "products of conception". Embryogenesis is the process of cell division and cellular differentiation which leads to the development of an embryo. ... The uterus or womb is the major female reproductive organ of most mammals, including humans. ... The zona pellucida is a glycoprotein membrane surrounding the plasma membrane of an oocyte. ... The endometrium is the inner uterine membrane in mammals which is developed in preparation for the implantation of a fertilized egg upon its arrival into the uterus. ... Embryos (and one tadpole) of the wrinkled frog (Rana rugosa). ... The placenta is an ephemeral (temporary) organ present only in female placental mammals during gestation (pregnancy). ...


Rapid growth occurs and the embryo's main external features begin to take form. This process is called differentiation, which produces the varied cell types (such as blood cells, kidney cells, and nerve cells). A spontaneous abortion, or miscarriage, in the first trimester of pregnancy is usually due to major genetic mistakes or abnormalities in the developing embryo. During this critical period (most of the first trimester), the developing fetus is also susceptible to toxic exposures, such as: Cellular differentiation is a concept from developmental biology describing the process by which cells acquire a type. The morphology of a cell may change dramatically during differentiation, but the genetic material remains the same, with few exceptions. ... Miscarriage or spontaneous abortion is the natural or accidental termination of a pregnancy at a stage where the embryo or the fetus is incapable of surviving, generally defined at a gestation of prior to 20 weeks. ... For the term trimester used in academic settings, see Academic term The human gestation period of approximately 40 weeks between the time of the last menstrual cycle and delivery is traditionally divided into three periods of three months, or trimesters. ...

In chemistry, an alcohol is any organic compound in which a hydroxyl group (-OH) is bound to a carbon atom of an alkyl or substituted alkyl group. ... A psychoactive drug or psychotropic substance is a chemical that alters brain function, resulting in temporary changes in perception, mood, consciousness, or behavior. ... For a list of biologically injurious substances, including toxins and other materials, as well as their effects, see poison. ... A congenital disorder is a medical condition or defect that is present at or before birth (for example, congenital heart disease). ... An infection is the detrimental colonization of a host organism by a foreign species. ... Rubella (also known as epidemic roseola, German measles, liberty measles or three-day measles) is a disease caused by the Rubella virus. ... Species see text Cytomegalovirus (CMV), is a genus of Herpes viruses; in humans the species is known as Human herpesvirus 5 (HHV-5). ... Radiation in physics is a process of emission of energy or particles. ... In the NATO phonetic alphabet, X-ray represents the letter X. An X-ray picture (radiograph) taken by Röntgen An X-ray is a form of electromagnetic radiation with a wavelength approximately in the range of 5 pm to 10 nanometers (corresponding to frequencies in the range 30 PHz... Clinac 2100 C accelerator Radiation therapy (or radiotherapy) is the medical use of ionizing radiation as part of cancer treatment to control malignant cells (not to be confused with radiology, the use of radiation in medical imaging and diagnosis). ... Many diseases in humans are thought to be directly or indirectly related to nutrition, These include, but are not limited to, deficiency diseases, caused by a lack of essential nutrients. ... Folic acid (the anion form is called folate) is a B-complex vitamin (once called vitamin M) that is important in preventing neural tube defects (NTDs) in the developing human fetus. ...

Fetal Development

From the 9th week until birth (around 38 weeks), the developing human is called a fetus. The fetus is not as sensitive to damage from environmental exposures as the embryo. The majority of structures are already formed in the fetus, but they continue to grow and become functional.


Changes by weeks of age (and weeks of pregnancy)

The following list describes specific changes in human development by week. "Weeks of pregnancy" are dated by obstetricians from the start of the last menstrual period which means that ovulation occurs at the end of the 2nd week.


Pre-implantation

Toxic exposures may cause prenatal death but do not cause developmental defects

  • Week 1 (3rd week of pregnancy)
    • Fertilization of the ovum to form a zygote which undergoes mitotic cellular division, but does not increase in size. A hollow cavity forms marking the blastocyst stage.
    • The blastocyst contains only a thin rim of trophoblast cells and a clump of cells at one end known as the "embryonic pole" which include embryonic stem cells.
    • The blastocyst hatches from its protein shell (zona pellucida) and implants onto the endometrial lining of the mother's uterus.
    • If the zygote is going to separate into identical twins, 1/3 of the time it will happen before day 5.[1]
  • Week 2 (4th week of pregnancy)
    • Trophoblast cells surrounding the embryonic cells proliferate and invade deeper into the uterine lining. They will eventually form the placenta and embryonic membranes.
    • Formation of the yolk sac.
    • The embryonic cells flatten into a disk, two-cells thick.
    • If the zygote is going to separate into identical twins, 2/3 of the time it will happen between days 5 and 9. If it happens after day 9, there is a significant risk of the twins being conjoined.

Overview of the major events in mitosis In biology, mitosis is the process of chromosome segregation and nuclear division that follows replication of the genetic material in eukaryotic cells. ... Cell division is the process by which a cell (called the parent cell) divides into two cells (called daughter cells). ... Embryogenesis is the process of cell division and cellular differentiation which leads to the development of an embryo. ... The trophoblast (from Greek threphein: to feed) is considered to be the first of all embryonic annexes. ... Mouse embryonic stem cells. ... The zona pellucida is a glycoprotein membrane surrounding the plasma membrane of an oocyte. ... The endometrium is the uterine membrane in mammals which is thickened in preparation for the implantation, of a fertilized egg upon its arrival into the uterus. ... The uterus or womb is the major female reproductive organ of most mammals, including humans. ... Fraternal twin boys in the tub The term twin most notably refers to two individuals (or one of two individuals) who have shared the same uterus (womb) and usually, but not necessarily, born on the same day. ... The placenta is an ephemeral (temporary) organ present only in female placental mammals during gestation (pregnancy). ... Modern, healthy, living 15-year-old conjoined twins Abigail and Brittany Hensel. ...

Embryonic Period

Toxic exposures often cause major congenital malformations A congenital disorder is a medical condition that is present at birth. ...

  • Week 3 (5th week of pregnancy - first missed menstrual period)
    • A notochord forms in the center of the embryonic disk.
    • A neural groove (future spinal cord) forms over the notochord with a brain bulge at one end.
    • Heart tubes begin to fuse.
  • Week 4 (6th week of pregnancy)
    • The embryo measures 4 mm (1/8 inch) in length and begins to curve into a C shape.
    • Somites, the divisions of the future vertebra, form.
    • The heart bulges, further develops, and begins to beat in a regular rhythm.
    • Branchial arches, grooves which will form structures of the face and neck, form.
    • The neural tube closes.
    • The ears begin to form as otic pits.
    • Arm buds and a tail are visible.
  • Week 5 (7th week of pregnancy)
    • The embryo measures 8 mm (1/4 inch) in length.
    • Lens pits and optic cups form the start of the developing eye.
    • A primitive mouth and nasal pits form.
    • The brain divides into 5 vesicles, including the early telencephalon.
    • Leg buds form and hands form as flat paddles on the arms.
    • Rudimentary blood moves through primitive vessels connecting to the yolk sac and chorionic membranes.
  • Week 6 (8th week of pregnancy)
    • The embryo measures 13 mm (1/2 inch) in length.
    • Lungs begin to form.
    • The brain continues to develop.
    • Arms and legs have lengthened with foot and hand areas distinguishable.
    • The hands and feet have digits, but may still be webbed.
  • Week 7 (9th week of pregnancy)
    • The embryo measures 18 mm (3/4 inch) in length.
    • Nipples and hair follicles begin to form.
    • Location of the elbows and toes are visible.
    • Spontaneous limb movements may be detected by ultrasound.
    • All essential organs have at least begun formation.
  • Week 8 (10th week of pregnancy)
    • Embryo measures 30 mm (1.2 inches) in length.
    • Intestines rotate.
    • Facial features continue to develop.
    • the eyelids are more developed.
    • the external features of the ear begin to take their final shape.

The notochord is a flexible, rod-shaped body found in embryos of all chordates. ... Cross-section through cervical spinal cord. ... Comparative brain sizes In animals, the brain, or encephalon (Greek for in the head), is the control center of the central nervous system. ... The heart and lungs, from an older edition of Grays Anatomy. ... 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). ... A diagram of a thoracic vertebra. ... The face of Leonardo da Vincis Mona Lisa, one of the most recognized faces in the world A human face The face is the front part of the head, in humans from forehead to chin including the head, hair, forehead, eyebrow, eyes, nose, cheek, mouth, lips, teeth, skin, and... The neck is the part of the body on many limbed vertebrates that distinguishes the head from the torso or trunk. ... The neural tube is the embryonal structure that gives rise to the brain and spinal cord. ... A human ear An ear is the organ used by a human or an animal to detect sound waves. ... In anatomy, an arm is one of the upper limbs of a two-legged animal. ... 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). ... Closeup of a blue-green human eye. ... Sagittal section of nose mouth, pharynx, and larynx. ... In cell biology, a vesicle is a relatively small and enclosed compartment, separated from the cytosol by at least one lipid bilayer. ... The telencephalon (te-len-seff-a-lon) is the technical name for a large region within the brain which is attributed many functions, which some groups would class as unique features which make humans stand out from other species. ... Leg has multiple meanings: For the limbs of animals that support them above the ground: in the case of the legs of humans, see Human leg; in the case of the legs of horses, see Equine leg; in the case of the legs of crabs, lobsters, and their close relatives... Alternate meanings: Hand (disambiguation) A human left hand The hand (med. ... Human blood smear: a - erythrocytes; b - neutrophil; c - eosinophil; d - lymphocyte. ... The yolk sac is the first element seen in the gestational sac during pregnancy, usually at 5 weeks gestation. ... The lungs flank the heart and great vessels in the chest cavity. ... A human foot - Enlarge to view legend For other uses, see Foot (disambiguation). ... A human hand typically has four fingers and a thumb. ... The udder of a cow with nipples showing In its most general form, a nipple is an appurtenance from which a fluid emanates, in this instance breast milk, to nurture a mothers young. ... A hair follicle is part of the skin that grows hair by packing old cells together. ... Elbow redirects here. ... Toes on foot. ... In biology, an organ (Latin: organum, instrument, tool) is a group of tissues that perform a specific function or group of functions. ... The intestine is the portion of the alimentary canal extending from the stomach to the anus and, in humans and other mammals, consists of two segments, the small intestine and the large intestine. ... An eyelid is a thin fold of skin and muscle that covers and protects an eye. ...

Fetal Period

During the fetal period, toxic exposures often cause physiological abnormalities or minor congenital malformation

  • Weeks 9 to 12 (11th to 14th week of pregnancy)
    • The fetus reaches a length of 8 cm (3.2 inches).
    • The head comprises nearly half of the fetus' size.
    • The face is well formed and develops a human appearance.
    • The eyelids close and will not reopen until about the 28th week.
    • Tooth buds, which will form the baby teeth, appear.
    • The limbs are long and thin.
    • The fetus can make a fist with its fingers.
    • Genitals appear well differentiated.
    • Red blood cells are produced in the liver.
  • Weeks 13 to 16 (15th to 18th week of pregnancy)
    • The fetus reaches a length of about 15 cm (6 inches).
    • A fine hair called lanugo develops on the head.
    • Fetal skin is almost transparent.
    • More muscle tissue and bones have developed, and the bones become harder.
    • The fetus makes active movements.
    • Sucking motions are made with the mouth.
    • Meconium is made in the intestinal tract.
    • The liver and pancreas produce fluid secretions.
  • Week 18 (20th week of pregnancy)
    • The fetus reaches a length of 20 cm (8 inches).
    • Lanugo covers the entire body.
    • Eyebrows and eyelashes appear.
    • Nails appear on fingers and toes.
    • The fetus is more active with increased muscle development.
    • "Quickening" usually occurs (the mother can feel the fetus moving).
    • The fetal heartbeat can be heard with a stethoscope.
  • Week 22 (24th week of pregnancy)
    • The fetus reaches a length of 28 cm (11.2 inches).
    • The fetus weighs about 725 g (1 lb 10 oz).
    • Eyebrows and eyelashes are well formed.
    • All of the eye components are developed.
    • The fetus has a hand and startle reflex.
    • Footprints and fingerprints continue forming.
    • Alveoli (air sacs) are forming in lungs.
  • Weeks 23 to 26 (25th to 28th week of pregnancy)
    • The fetus reaches a length of 38 cm (15 inches).
    • The fetus weighs about 1.2 kg (2 lb 11 oz).
    • The brain develops rapidly.
    • The nervous system develops enough to control some body functions.
    • The eyelids open and close.
    • The respiratory system, while immature, has developed to the point where gas exchange is possible.
    • A baby born prematurely at this time may survive, but the possibilities for complications and death remain high.
  • Weeks 27 to 31 (29th to 33rd week of pregnancy)
    • The fetus reaches a length of about 38-43 cm (15-17 inches).
    • The fetus weighs about 2 kg (4 lb 6 oz).
    • The amount of body fat rapidly increases.
    • Rhythmic breathing movements occur, but lungs are not fully mature.
    • Thalamic brain connections, which mediate sensory input, form.
    • Bones are fully developed, but are still soft and pliable.
    • The fetus begins storing iron, calcium, and phosphorus.
  • Week 34 (36th week of pregnancy)
    • The fetus reaches a length of about 40-48 cm (16-19 inches).
    • The fetus weighs about 2.5 to 3 kg (5 lb 12 oz to 6 lb 12 oz).
    • Lanugo begins to disappear.
    • Body fat increases.
    • Fingernails reach the end of the fingertips.
    • a baby born at 36 weeks has a high chance of survival, but may require medical interventions.
  • Weeks 35 to 38 (37th to 40th week of preganancy)
    • The fetus is considered full-term at the 37th week of pregnancy.
    • It may be 48 to 53 cm (19 to 21 inches) in length.
    • The lanugo is gone except on the upper arms and shoulders.
    • Fingernails extend beyond fingertips.
    • Small breast buds are present on both sexes.
    • Head hair is now coarse and thicker

This article or section does not cite its references or sources. ... A limb (from the Old English lim) is a jointed appendage of the human or animal body; a large or main branch of a tree; a representative, branch or member of a group or organization. ... Future Infantry Soldier Technology is the British Ministry of Defences program as part of the Future Soldier project. ... Fingers of the human left hand The finger is any of the digits of the hand in humans and other species such as the great apes. ... Human red blood cells Red blood cells are the most common type of blood cell and are the vertebrate bodys principal means of delivering oxygen from the lungs or gills to body tissues via the blood. ... The liver is the largest internal organ of the human body. ... Lanugo are hairs that grow on the body to attempt to insulate it because of lack of fat. ... A close-up of human skin. ... Meconium from 12-hour-old newborn — the babys third bowel movement. ... The pancreas is an organ in the digestive system that serves two major functions: exocrine - it produces pancreatic juice containing digestive enzymes. ... Stethoscope The stethoscope (Greek στηθοσκόπιο, of στήθος, stéthos - chest and σκοπή, skopé - examination) is an acoustic medical device for auscultation, i. ... ... A footprint is an impression left by a foot or shoe, for example an indentation in soft ground or snow, or a mark left by mud etc from the sole of the foot. ... A fingerprint is an impression normally made by ink or contaminants transferred from the peaks of friction skin ridges to a relatively smooth surface such as a fingerprint card. ... The alveoli (singular:alveolus), tiny hollow sacs which are continuous with the airways, are the sites of gas exchange with the blood. ... 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. ... Premature birth (also known as preterm birth, or premie) is defined medically as childbirth occurring earlier than 37 completed weeks of gestation. ... Please wikify (format) this article as suggested in the Guide to layout and the Manual of Style. ... General Name, Symbol, Number iron, Fe, 26 Chemical series transition metals Group, Period, Block 8, 4, d Appearance lustrous metallic with a grayish tinge Atomic mass 55. ... General Name, Symbol, Number calcium, Ca, 20 Chemical series alkaline earth metals Group, Period, Block 2, 4, s Appearance silvery white Atomic mass 40. ... This article is about the chemical element. ...

References

  • "MedlinePlus Medical Encyclopedia"
  • Moore, Keith L. The Developing Human: 3rd Edition. W.B. Saunders Company, Philadelphia PA
  • Wilcox AJ, Baird DD, Weinberg CR. Time of implantation of the conceptus and loss of pregnancy. 1999 N Engl J Med. 340(23):1796-9. PMID 10362823
  • Ljunger, E, Cnattingius, S, Lundin, C, & Annerén, G. 2005 Chromosomal anomalies in first-trimester miscarriages. Acta Obstetricia et Gynecologica Scandinavica 84(11):1103-1107. PMID 10362823

External links

Mammalian embryogenesis/Embryology and Fetal development - edit

Embryo/Carnegie stages: Zygote | Morula | Blastula/Blastomere/Blastosphere | Gastrula/Gastrulation | Neurula | Fetus Mammalian embryogenesis is the process of cell division and cellular differentiation which leads to the development of a mammalian embryo. ... Embryology is the branch of developmental biology that studies embryos and their development. ... Embryos (and one tadpole) of the wrinkled frog (Rana rugosa). ... 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 . ... The hollow globe or sphere formed by the arrangement of the blastomeres on the periphery of an impregnated ovum. ... 1 - blastula, 2 - gastrula; orange - ectoderm, red - endoderm. ... 1 - blastula, 2 - gastrula; orange - ectoderm, red - endoderm. ... A Neurula is an embryo at the early stage of development in which neurulation occurs. ... Fetus at eight weeks Foetus redirects here. ...


General: Archenteron/Primitive streak | Blastopore | Hensen's node | Germ layer (Ectoderm, Endoderm, Mesoderm) | Histogenesis | Organogenesis | Branchial arch (1st) | Branchial pouch | Meckel's cartilage | Somite/Somitomere | Thyroglossal duct | Vitelline duct 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. ... Hensens Node is the organizer for gastrulation in birds. ... 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. ... 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. ... 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. ... 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. ... 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. ... 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. ... 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. ...


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 | Neural folds | Neural groove | Neural tube | Neural crest | Neuromere | 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. ... 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. ... The neural tube is the embryonal structure that gives rise to 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. ... 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. ... It has been suggested that this article or section be merged into sex organ. ... 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. ...


Uterine support: Placenta | Umbilical cord (Umbilical artery, Umbilical vein, Wharton's jelly) | Amniotic sac (Amnion, Chorion) | Yolk sac | Allantois | Trophoblast (Cytotrophoblast | Syncytiotrophoblast | Gestational sac) 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 mammals during gestation (pregnancy). ... A newborn at 45 seconds. ... 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. ... amniotic sac The amniotic sac is a tough but thin transparent pair of membranes, which hold a developing embryo (and later fetus) until shortly before birth. ... The amnion is a membranous sac which surrounds and protects the embryo. ... Chorion can refer to the following things: Chorion is the outer membrane of the amniotic sac. ... The yolk sac is the first element seen in the gestational sac during pregnancy, usually at 5 weeks gestation. ... 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. ...


  Results from FactBites:
 
Fetal development - Wikipedia, the free encyclopedia (1449 words)
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 spontaneous abortion, or miscarriage, in the first trimester of pregnancy is usually due to major genetic mistakes or abnormalities in the developing embryo.
The fetal heartbeat can be heard with a stethoscope.
Fetal Alcohol Syndrome (979 words)
Fetal alcohol syndrome (FAS) is a serious health problem that tragically affects its victims and their families, but that is completely preventable.
Victims of fetal alcohol syndrome often experience mental health problems, disrupted school experience, inappropriate sexual behavior, trouble with the law, alcohol and drug problems, difficulty caring for themselves and their children, and homelessness.
Not a single case of fetal alcohol syndrome occurred and no adverse effects on children were found when consumption was under 8.5 drinks per week.
  More results at FactBites »

 
 

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