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Encyclopedia > Prenatal development

Prenatal development is the process in which an embryo or fetus (or foetus) gestates during pregnancy, from fertilization until birth. Often, the terms fetal development, foetal development, or embryology are used in a similar sense. Mammalian embryogenesis is the process of cell division and cellular differentiation which leads to the development of a mammalian embryo. ... For other uses, see Embryo (disambiguation). ... “Unborn child” redirects here. ... Gestation is the carrying of an embryo or fetus inside a female viviparous animal. ... A pregnant woman near the end of her term Pregnancy is the carrying of one or more offspring in an embryonal or fetal stage of development by female mammals, including humans, inside their bodies, between the stages of conception and birth. ... Categories: Biology stubs ... Birth is the process in animals by which an offspring is expelled from the body of its mother. ... This article or section is in need of attention from an expert on the subject. ...


After fertilization the embryogenesis starts. In humans, when embryogenesis finishes, by the end of the 10th week of gestational age, the precursors of all the major organs of the body have been created. Therefore, the following period, the fetal period, is described both topically on one hand, i.e. by organ, and strictly chronologically on the other, by a list of major occurrences by weeks of gestational age. Gestational age is age of a fetus (or newborn infant) from presumed conception. ...

Contents

Fertilization

Main article: Fertilization
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 after uterine implantation, and this terminology is controversial. Categories: Biology stubs ... Image File history File links Sperm-egg. ... Image File history File links Sperm-egg. ... Horse semen being collected for breeding purposes. ... 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. ... The cervix (from Latin neck) is the lower, narrow portion of the uterus where it joins with the top end of the vagina. ... The Fallopian tubes, also known as oviducts, uterine tubes, and salpinges (singular salpinx) are two very fine tubes leading from the ovaries of female mammals into the uterus. ... Categories: Biology stubs ... A human ovum Sperm cells attempting to fertilize an ovum An ovum (plural ova) is a haploid female reproductive cell or gamete. ... Drawing of the structure of cork as it appeared under the microscope to Robert Hooke from Micrographia which is the origin of the word cell being used to describe the smallest unit of a living organism Cells in culture, stained for keratin (red) and DNA (green) The cell is the... Genetic material is used to store the genetic information of an organic life form. ... The structure of part of a DNA double helix Deoxyribonucleic acid, or DNA, is a nucleic acid molecule that contains the genetic instructions used in the development and functioning of all known living organisms. ... It has been suggested that Biparental zygote be merged into this article or section. ... Conceptus (latin is conceptio, derivatives of zygote) The embryo and its adnexa (appendages or adjunct parts) or associated membranes (i. ... Controversy over the beginning of pregnancy usually occurs in the context of the abortion debate. ...


Like every cell in the body, the zygote contains all of the genetic information unique to an individual. Half of the genetic information residing in the zygote's nucleus comes from the mother's egg nucleus, and the other half from the nucleus of a single sperm. However, the mitochondrial genetic information of the zygote is in its totality contributed by the mother's egg. HeLa cells stained for DNA with the Blue Hoechst dye. ... A spermatozoon or spermatozoan ( spermatozoa), from the ancient Greek σπέρμα (seed) and (living being) and more commonly known as a sperm cell, is the haploid cell that is the male gamete. ... In cell biology, a mitochondrion is an organelle found in the cells of most eukaryotes. ...


Embryonic period

Main article: Human embryogenesis

The embryonic period in humans begins at fertilization (2nd week of gestation) and continues until the end of the 10th week of gestation (8th week of development). Human embryogenesis is the process of cell division and cellular differentiation of the human embryo during early prenatal development. ... Categories: Biology stubs ...


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. 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). ... The blastocyst is the structure formed in early mammalian embryogenesis, after the formation of the blastocele, but before implantation. ... For other uses, see Embryo (disambiguation). ...


The blastocyst reaches the uterus at roughly the fifth day after fertilization. It is here that lysis of the zona pellucida, a glycoprotein shell, occurs. This is required so that the trophectoderm cells of the blastocyst can come into contact with the luminal epithelial cells of the endometrium. (Contrast this with zona hatching, an event that occurs in vitro by a different mechanism, but with a similar result). It then adheres to the uterine lining and becomes embedded in the endometrial cell layer. This process is also called implantation. In most successful 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". The blastocyst is the structure formed in early mammalian embryogenesis, after the formation of the blastocele, but before implantation. ... This article is about female reproductive anatomy. ... The zona pellucida (or zona striata in older texts) is a glycoprotein membrane surrounding the plasma membrane of an oocyte. ... Zona hatching is a phenomenon occuring during prenatal development. ... Wiktionary has a definition of: In vitro In vitro (Latin: within glass) means within a test tube, or, more generally, outside a living organism or cell. ... The endometrium is the inner membrane of the mammalian uterus. ... Implantation is a phenomenon in prenatal development, i. ... The placenta is an ephemeral (temporary) organ present in female placental vertebrates during gestation (pregnancy), but a placenta has evolved independently also in other animals as well, for instance scorpions and velvet worms. ...


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 embryo 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. ...

Generally, if a structure pre-dates another structure in evolutionary terms, then it often appears earlier than the other in an embryo; this general observation is sometimes summarized by the phrase "ontogeny recapitulates phylogeny."[1] For example, the backbone is a common structure among all vertebrates such as fish, reptiles and mammals, and the backbone also appears as one of the earliest structures laid out in all vertebrate embryos. The cerebrum in humans, which is the most sophisticated part of the brain, develops last. The concept of recapitulation is not absolute, but it is recognized as being partly applicable to development of the human embryo.[1] This article does not cite any references or sources. ... An assortment of psychoactive drugs A psychoactive drug or psychotropic substance is a chemical substance that acts primarily upon the central nervous system where it alters brain function, resulting in temporary changes in perception, mood, consciousness and 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). ... Fetal alcohol syndrome or FAS is a disorder of permanent birth defects that occurs in the offspring of women who drink alcohol during pregnancy. ... An infection is the detrimental colonization of a host organism by a foreign species. ... Rubella, commonly known as German measles, is a disease caused by the rubella virus. ... Species see text Cytomegalovirus (CMV) (from the Greek cyto-, cell, and -mega-, large) is a viral genus of the Herpesviruses group: in humans it is commonly known as human herpesvirus 5 (HHV-5). ... Radiation as used in physics, is energy in the form of waves or moving subatomic 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 C100 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. ... The theory of recapitulation, also called the biogenetic law or ontogeny recapitulates phylogeny, is a theory in biology which attempts to explain apparent similarities between humans and other animals. ... For other uses, see Fish (disambiguation). ... Reptilia redirects here. ... Subclasses & Infraclasses Subclass †Allotheria* Subclass Prototheria Subclass Theria Infraclass †Trituberculata Infraclass Metatheria Infraclass Eutheria Mammals (class Mammalia) are warm-blooded, vertebrate animals characterized by the production of milk in female mammary glands and by the presence of: hair, three middle ear bones used in hearing, and a neocortex region in... For other articles about other subjects named brain see brain (disambiguation). ... The human brain controls the central nervous system (CNS), by way of the cranial nerves and spinal cord, the peripheral nervous system (PNS) and regulates virtually all human activity. ...


Changes by weeks of gestational age

See also: embryo and Human embryogenesis
A 10mm embryo from an ectopic pregnancy, still in the oviduct. This embryo is about five weeks old (or from the seventh week of menstrual age).
This embryo is also from an ectopic pregnancy, this one in the cornu (the part of the uterus to which the Fallopian tube is attached). The features are consistent with a developmental age of seven weeks (reckoned as the ninth week of pregnancy).
  • Week 2 (week of fertilization)
  • Week 3 (1 week following fertilization)
    • 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 separation into identical twins occurs, 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.
    • Primitive streak develops. [3]
    • Primary stem villi appear. [3]
  • Week 4 (2 weeks from fertilization - 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. Neuromeres appear.
    • Heart tubes begin to fuse.
    • Gastrulation commences. [3]
    • Somites, the divisions of the future vertebra, form. [3]
    • Primitive heart tube is forming. Vasculature begins to develop in embryonic disc. [3]
Embryo at 4 weeks after fertilization.[4]
  • Week 6 (4th week of development)
    • The embryo measures 8 mm (1/4 inch) in length.
    • Lens pits and optic cups form the start of the developing eye.
    • 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 7 (5th week of development)
    • 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.
    • The gonadal ridge begins to be perceptible
  • Week 8 (6th week of development)
    • 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.

For other uses, see Embryo (disambiguation). ... Human embryogenesis is the process of cell division and cellular differentiation of the human embryo during early prenatal development. ... Image File history File links Download high-resolution version (1874x2000, 1514 KB) This image was selected as a Featured Picture on the English language Wikipedia on 29 November 2006. ... Image File history File links Download high-resolution version (1874x2000, 1514 KB) This image was selected as a Featured Picture on the English language Wikipedia on 29 November 2006. ... Image File history File links Size of this preview: 400 × 600 pixelsFull resolution (683 × 1024 pixel, file size: 242 KB, MIME type: image/jpeg) The size and anatomic features suggest development equivalent to a nine-week pregnancy (or seven weeks post ovulation). ... Image File history File links Size of this preview: 400 × 600 pixelsFull resolution (683 × 1024 pixel, file size: 242 KB, MIME type: image/jpeg) The size and anatomic features suggest development equivalent to a nine-week pregnancy (or seven weeks post ovulation). ... Female internal reproductive anatomy The Fallopian tubes, also known as oviducts, uterine tubes, and salpinges (singular salpinx), are two very fine tubes leading from the ovaries of female mammals into the uterus. ... 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). ... In embryology, cleavage is the division of cells in the early embryo. ... The blastocyst is the structure formed in early mammalian embryogenesis, after the formation of the blastocele, but before implantation. ... The trophoblast (from Greek threphein: to feed) is considered to be the first of all embryonic annexes. ... Mouse embryonic stem cells. ... The zona pellucida (or zona striata in older texts) 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. ... This article is about female reproductive anatomy. ... 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 in female placental vertebrates during gestation (pregnancy), but a placenta has evolved independently also in other animals as well, for instance scorpions and velvet worms. ... This article or section does not cite any references or sources. ... The primitive streak is a structure that forms during the early stages of avian, reptilian and mammalian embryonic development. ... Chorionic villi are villi that sprout from the chorion, in order to give a maximum area of contact with the maternal blood. ... The notochord is a flexible, rod-shaped body found in embryos of all chordates. ... The Spinal cord nested in the vertebral column. ... In animals, the brain or encephalon (Greek for in the head), is the control center of the central nervous system, responsible for behaviour. ... Neuromeres are transient segments during the early development of the human brain. ... The heart and lungs, from an older edition of Grays Anatomy. ... It has been suggested that epiboly be merged into this article or section. ... 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 cavity of the primitive atrium becomes subdivided into right and left chambers by a septum, the septum primum, which grows downward into the cavity. ... 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. ... For other uses, see Face (disambiguation). ... A human neck. ... In the developing vertebrate nervous system, the neural tube is the precursor of the central nervous system, which comprises the brain and spinal cord. ... For other uses, see Ear (disambiguation). ... The first rudiment of the internal ear appears shortly after that of the eye, in the form of a patch of thickened ectoderm, the auditory plate, over the region of the hind-brain. ... Look up ARM in Wiktionary, the free dictionary. ... Human respiratory system The lungs flank the heart and great vessels in the chest cavity. ... The liver is an organ present in vertebrates and some other animals. ... Over the crescentic masses of the mesoderm the ectoderm and endoderm come into direct contact with each other and constitute a thin membrane, the buccopharyngeal membrane (or oropharyngeal membrane), which forms a septum between the primitive mouth and pharynx. ... The gallbladder (or cholecyst, sometimes gall bladder) is a pear-shaped organ that stores about 50 ml of bile (or gall) until the body needs it for digestion. ... The pancreas is a gland organ in the digestive and endocrine systems of vertebrates[2]. It is both exocrine (secreting pancreatic juice containing digestive enzymes) and endocrine (producing several important hormones, including insulin, glucagon, and somatostatin). ... The rectum (from the Latin rectum intestinum, meaning straight intestine) is the final straight portion of the large intestine in some mammals, and the gut in others, terminating in the anus. ... The anterior horn is the anterior division of the lateral ventricle of the brain. ... The posterior horn of the spinal cord is dorsal(more towards the back) to the anterior horn. ... The Spinal cord nested in the vertebral column. ... The spleen is an organ located in the abdomen, where it functions in the destruction of old red blood cells and holding a reservoir of blood. ... The Ureteric bud is a portion of the mesonephric duct. ... Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... 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). ... For other uses, see Eye (disambiguation). ... 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. ... Diagram of an insect leg A leg is the part of an animals body that supports the rest of the animal above the ground and is used for locomotion. ... 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. ... Human respiratory system The lungs flank the heart and great vessels in the chest cavity. ... For other uses, see Foot (disambiguation). ... For other uses, see Hand (disambiguation). ... In embryology, the gonadal ridge (or genital ridge) is the precursor to the gonads. ... This article is about anatomical structure. ... A hair follicle is part of the skin that grows hair by packing old cells together. ... Elbow redirects here. ... Toes on foot. ... Ş:For other uses, see Organ (disambiguation) In biology, an organ (Latin: organum, instrument, tool) is a group of tissues that perform a specific function or group of functions. ...

Fetal period

See also: Fetus

The fetal period begins at the end of the 10th week of gestation (8th week of development). Since the precursors of all the major organs are created by this time, the fetal period is described both by organ and by a list of changes by weeks of gestational age. “Unborn child” redirects here. ...


Because the precursors of the organs are formed, fetus also is not as sensitive to damage from environmental exposures as the embryo. Instead, toxic exposures often cause physiological abnormalities or minor congenital malformation.


By organ

Each organ has its own development.

  • Development of circulatory system
  • Development of digestive system
  • Development of endocrine system
  • Development of integumentary system
  • Development of lymphatic system
  • Development of muscular system
  • Development of nervous system
  • Development of the urinary and reproductive system
  • Development of respiratory system

The heart is the first functional organ in a vertebrate embryo. ... Radiograph of lower right (from left to right) third, second, and first molars in different stages of development. ... The human lymphatic system The lymphatic system is a complex network of lymphoid organs, lymph nodes, lymph ducts, lymphatic tissues, lymph capillaries and lymph vessels that produce and transport lymph fluid from tissues to the circulatory system. ... 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. ... The development of the urinary and reproductive organs is a part of the prenatal development, and concerns the urinary system and sex organs. ... The development of the reproductive system is a part of the prenatal development, and concerns the sex organs. ... The prenatal development of the gonads is a part of the development of reproductive system and sultimately forms the testes in males and ovaries in females. ... The prenatal development of the suspensory ligament of the ovary is a part of the development of the reproductive system. ... The Respiratory System Among quadrupeds, the respiratory system generally includes tubes, such as the bronchi, used to carry air to the lungs, where gas exchange takes place. ...

Changes by weeks of gestational age

See also: Fetus

From the 8th week until birth (around 38 weeks), the developing organism is called a fetus. The fetus is not as sensitive to damage from environmental exposures as the embryo, and toxic exposures often cause physiological abnormalities or minor congenital malformation. All major structures are already formed in the fetus, but they continue to grow and develop. “Unborn child” redirects here. ...

Fetus at 8 weeks after fertilization.[5]
  • Week 9 (7th week of development)
    • 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.
  • Weeks 10 to 13 (8th to 11th week of development)
    • 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
    • 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 14 to 17 (12th to 15th week of development)
    • 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.
Fetus at 18 weeks after fertilization.[6]
  • Week 20 (18th week of development)
    • 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 24 (22nd week of development)
    • 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.
  • Week 28 (26th week of development)
    • 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 cochleae are now developed, though the myelin sheaths in neural portion of the auditory system will continue to develop until 18 months after birth.
    • 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 32 (30th week of development)
    • 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 36 (34th week of development)
    • 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.
Fetus at 38 weeks after fertilization.[7]
  • Weeks 37 to 40 (35th to 38th week of development)
    • The fetus is considered full-term at the 37th week of gestational age.
    • 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 thickest.
Human fetus at eight weeks after fertilization.

Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... In anatomy, the intestine is the segment 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 (or colon). ... An eyelid is a thin fold of skin and muscle that covers and protects an eye. ... A humans visible teeth. ... Look up Limb in Wiktionary, the free dictionary. ... Fist can refer to the following: A hand that has the fingers curled into the palm and the thumb retracted. ... This article does not cite any references or sources. ... “Red cell” redirects here. ... The liver is an organ present in vertebrates and some other animals. ... Lanugo are hairs that grow on the body to attempt to insulate it because of lack of fat. ... Beyond overall skin structure, refer below to: See-also. ... Meconium from 12-hour-old newborn — the babys third bowel movement. ... The pancreas is a gland organ in the digestive and endocrine systems of vertebrates[2]. It is both exocrine (secreting pancreatic juice containing digestive enzymes) and endocrine (producing several important hormones, including insulin, glucagon, and somatostatin). ... Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Lanugo are hairs that grow on the body to attempt to insulate it because of lack of fat. ... Stethoscope The stethoscope (Greek στηθοσκόπιο, of στήθος, stéthos - chest and σκοπή, skopé - examination) is an acoustic medical device for auscultation, or listening, to internal sounds in a human or animal body. ... ... 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 macro shot of a palm and the base of several fingers; as seen here, debris can gather between the ridges. ... 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. ... In most systems of human pregnancy, the condition, premature birth (also known as a preterm birth), occurs when the baby is born within sooner than 36 weeks of completed gestation. ... The thalamus (from Greek θάλαμος = bedroom, chamber, IPA= /ˈθælÉ™mÉ™s/) is a pair and symmetric part of the brain. ... For other uses, see Iron (disambiguation). ... General Name, Symbol, Number calcium, Ca, 20 Chemical series alkaline earth metals Group, Period, Block 2, 4, s Appearance silvery white Standard atomic weight 40. ... General Name, Symbol, Number phosphorus, P, 15 Chemical series nonmetals Group, Period, Block 15, 3, p Appearance waxy white/ red/ black/ colorless Standard atomic weight 30. ... Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Thelarche is the first stage of secondary (postnatal) breast development, usually occurring at the beginning of puberty in girls. ... From Henry Gray (1821–1865). ... From Henry Gray (1821–1865). ... “Unborn child” redirects here. ...

References

  1. ^ a b Stephen Jay Gould,. Ontogeny and Phylogeny. Cambridge, Mass: Belknap Press, 206. ISBN 0-674-63941-3. 
  2. ^ Scott F. Gilbert; with a chapter on plant development by Susan R. Singer (2000). Developmental biology. Sunderland, Mass: Sinauer Associates. ISBN 0-87893-243-7. 
  3. ^ a b c d e f g h i j k l m n William J. Larsen (2001). Human embryology. Edinburgh: Churchill Livingstone. ISBN 0-443-06583-7. 
  4. ^ 3D Pregnancy (large image of fetus at 4 weeks after fertilization). Retrieved 2007-08-28. A rotatable 3D version of this photo is available here, and a sketch is available here.
  5. ^ 3D Pregnancy (large image of fetus at 10 weeks after fertilization). Retrieved 2007-08-28. A rotatable 3D version of this photo is available here, and a sketch is available here.
  6. ^ 3D Pregnancy (large image of fetus at 18 weeks after fertilization). Retrieved 2007-08-28. A rotatable 3D version of this photo is available here, and a sketch is available here.
  7. ^ 3D Pregnancy (large image of fetus at 38 weeks after fertilization). Retrieved 2007-08-28. A rotatable 3D version of this photo is available here, and a sketch is available here.
  • "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

Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... is the 240th day of the year (241st in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... is the 240th day of the year (241st in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... is the 240th day of the year (241st in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... is the 240th day of the year (241st in leap years) in the Gregorian calendar. ...

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