This article is about the development of embryos in animals. For the development of plant embryos, see Sporophyte.
|
This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (July 2007) |
1 - blastula,
2 - gastrula with blastopore;
orange - ectoderm,
red - endoderm.
Dissection of human embryo, 38 mm - 8 weeks
Embryology (from Greek ἔμβρυον, embryon, "the unborn, embryo"; and -λογία, -logia) is the branch of biology that deals with the development of an embryo from the fertilization of the ovum to the fetus stage.
Contents
- 1 Embryonic development of animals
- 2 History of embryology
- 2.1 After 1827
- 2.2 After 1950
- 3 Vertebrate and invertebrate embryology
- 4 Modern embryology research
- 5 See also
- 6 Notes
- 7 References
- 8 Further reading
- 9 External links
Embryonic development of animals
After cleavage, the dividing cells, or morula, becomes a hollow ball, or blastula, which develops a hole or pore at one end.
Bilaterals
In bilateral animals, the blastula develops in one of two ways that divides the whole animal kingdom into two halves (see: Embryological origins of the mouth and anus). If in the blastula the first pore (blastopore) becomes the mouth of the animal, it is a protostome; if the first pore becomes the anus then it is a deuterostome. The protostomes include most invertebrate animals, such as insects, worms and molluscs, while the deuterostomes include the vertebrates. In due course, the blastula changes into a more differentiated structure called the gastrula.
The gastrula with its blastopore soon develops three distinct layers of cells (the germ layers) from which all the bodily organs and tissues then develop:
- The innermost layer, or endoderm, gives a rise to the digestive organs, the gills, lungs or swim bladder if present, and kidneys or nephrites.
- The middle layer, or mesoderm, gives rise to the muscles, skeleton if any, and blood system.
- The outer layer of cells, or ectoderm, gives rise to the nervous system, including the brain, and skin or carapace and hair, bristles, or scales.
Embryos in many species often appear similar to one another in early developmental stages. The reason for this similarity is because species have a shared evolutionary history. These similarities among species are called homologous structures, which are structures that have the same or similar function and mechanism, having evolved from a common ancestor.
Humans
Humans are bilaterals and deuterostomes.
In humans, the term embryo refers to the ball of dividing cells from the moment the zygote implants itself in the uterus wall until the end of the eighth week after conception. Beyond the eighth week after conception (tenth week of pregnancy), the developing human is then called a fetus.
History of embryology
Human embryo at six weeks gestational age
Histological film 10 day mouse embryo
As recently as the 18th century, the prevailing notion in western human embryology was preformation: the idea that semen contains an embryo — a preformed, miniature infant, or "homunculus" — that simply becomes larger during development. The competing explanation of embryonic development was epigenesis, originally proposed 2,000 years earlier by Aristotle. Much early embryology came from the work of the great Italian anatomists: Aldrovandi, Aranzio, Leonardo da Vinci, Marcello Malpighi, Gabriele Falloppio, Girolamo Cardano, Emilio Parisano, Fortunio Liceti, Stefano Lorenzini, Spallanzani, Enrico Sertoli, Mauro Rusconi, etc.[1] According to epigenesis, the form of an animal emerges gradually from a relatively formless egg. As microscopy improved during the 19th century, biologists could see that embryos took shape in a series of progressive steps, and epigenesis displaced preformation as the favoured explanation among embryologists.[2]
After 1827
Karl Ernst von Baer and Heinz Christian Pander proposed the germ layer theory of development; von Baer discovered the mammalian ovum in 1827.[3][4][5] Modern embryological pioneers include Charles Darwin, Ernst Haeckel, J.B.S. Haldane, and Joseph Needham. Other important contributors include William Harvey, Kaspar Friedrich Wolff, Heinz Christian Pander, August Weismann, Gavin de Beer, Ernest Everett Just, and Edward B. Lewis.
After 1950
After the 1950s, with the DNA helical structure being unravelled and the increasing knowledge in the field of molecular biology, developmental biology emerged as a field of study which attempts to correlate the genes with morphological change, and so tries to determine which genes are responsible for each morphological change that takes place in an embryo, and how these genes are regulated.
-
A study of embryos by Leonardo da Vinci
Vertebrate and invertebrate embryology
Many principles of embryology apply to invertebrates as well as to vertebrates.[6] Therefore, the study of invertebrate embryology has advanced the study of vertebrate embryology. However, there are many differences as well. For example, numerous invertebrate species release a larva before development is complete; at the end of the larval period, an animal for the first time comes to resemble an adult similar to its parent or parents. Although invertebrate embryology is similar in some ways for different invertebrate animals, there are also countless variations. For instance, while spiders proceed directly from egg to adult form, many insects develop through at least one larval stage.
Modern embryology research
Currently, embryology has become an important research area for studying the genetic control of the development process (e.g. morphogens), its link to cell signalling, its importance for the study of certain diseases and mutations, and in links to stem cell research.
See also
- Cell signalling
- Deuterostomes
- Developmental biology
- Embryo drawing
- Embryogenesis
- Embryology of digestive system and the body cavities
- Epigenesis (biology)
- French flag model
- Germ layers
- Hedgehog signaling pathway
- Hox gene
- Morphogens
- Ontogeny
- Plant embryogenesis, the development of a plant embryo from a fertilized ovum
- Plant physiology
- Prenatal development
- Protostomes
- Recapitulation theory
Notes
- ^ Massimo De Felici, Gregorio Siracus, The rise of embryology in Italy: from the Renaissance to the early 20th Century, Int. J. Dev. Biol. 44: 515-521 (2000).
- ^ Campbell et al. (p. 987)
- ^ K. J. Betteridge (1981). "An historical look at embryo transfer" (PDF). Reproduction. the Journal of the Society for Reproduction and Fertility 62 (1): 1–13. doi:10.1530/jrf.0.0620001.
Three years later, the Estonian, Karl Ernst von Baer, finally found the true mammalian egg in a pet dog (von Baer, 1827).
- ^ Lois N. Magner (2005). History of the Life Sciences. New York. Basel: Marcel Dekker. p. 166. ISBN 9780824743604.
- ^ Alex Lopata (2009). "History of the Egg in Embryology". Journal of Mammalian Ova Research 26: 2–9. doi:10.1274/jmor.26.2.
- ^ Parker, Sybil. "Invertebrate Embryology," McGraw-Hill Encyclopedia of Science & Technology (McGraw-Hill 1997).
References
- Embryology - History of embryology as a science." Science Encyclopedia. Web. 06 Nov. 2009. <http://science.jrank.org/pages/2452/Embryology.html>.
- "Germ layer." Encyclopædia Britannica. 2009. Encyclopædia Britannica Online. 06 Nov. 2009 <http://www.britannica.com/EBchecked/topic/230597/germ-layer>.
Further reading
- Apostoli, Pietro; Catalani, Simona (2011). "Chapter 11. Metal Ions Affecting Reproduction and Development". In Astrid Sigel, Helmut Sigel and Roland K. O. Sigel. Metal Ions in Toxicology. Metal Ions in Life Sciences 8. RSC Publishing. pp. 263–303. doi:10.1039/9781849732116-00263.
- Scott F. Gilbert. Developmental Biology. Sinauer, 2003. ISBN 0-87893-258-5.
- Lewis Wolpert. Principles of Development. Oxford University Press, 2006. ISBN 0-19-927536-X.
External links
|
Wikimedia Commons has media related to Embryology. |
- Online course in embryology
- Indiana University's Human Embryology Animations
- UNSW Embryology Large resource of information and media.
- What is a human admixed embryo?
- Definition of embryo according to Webster
- Embryonews _ resource for IVF and embryology articles
Human embryogenesis in the first three weeks
|
|
Week 1 |
- Fertilization
- Oocyte activation
- Zygote
- Cleavage
- Blastomere
- Morula
- Blastocoele
- Blastocyst
- Blastula
- Inner cell mass
|
|
Week 2
(Bilaminar) |
|
|
Week 3
(Trilaminar) |
Germ layers |
- Archenteron/Primitive streak
- Primitive pit
- Primitive knot/Blastopore
- Primitive groove
- Gastrula
- Regional specification
- Embryonic disc
|
|
Ectoderm |
- Surface ectoderm
- Neuroectoderm
- Somatopleuric mesenchyme
- Neurulation
- Neural crest
|
|
Endoderm |
- Splanchnopleuric mesenchyme
|
|
Mesoderm |
- Axial mesoderm
- Paraxial
- Intermediate
- Lateral plate
- Intraembryonic coelom
- Splanchnopleuric mesenchyme
- Somatopleuric mesenchyme
|
|
|
Index of developmental medicine
|
|
Description |
- Embryology
- Cell lines
- endoderm
- mesoderm
- ectoderm
|
|
Disease |
- Due to toxins
- Syndromes
- Chromosomal
- Neonate
- Twins
|
|
|
Development of the head and neck
|
|
Face |
- Nasal placode
- Nasal pit
- Nasal prominences
- Intermaxillary segment
- Frontonasal prominence
- Maxillary prominence
- Mandibular prominence
|
|
Oral cavity |
Palate |
- Primary palate
- Secondary palate
|
|
Tongue |
- Lateral lingual swelling
- Tuberculum impar
- Copula linguae
- Hypopharyngeal eminence
- Gustatory placode
|
|
General |
- Branchial apparatus
- Pharyngeal groove
- Pharyngeal arch
- Pharyngeal pouch
|
|
|
Index of the mouth
|
|
Description |
|
|
Disease |
- Congenital
- face and neck
- cleft
- digestive system
- Neoplasms and cancer
- Other
- Symptoms and signs
|
|
Treatment |
|
|
|
Development of bone
|
|
Ossification |
- Triradiate cartilage
- Limb development
- Apical ectodermal ridge
- Zone of polarizing activity
- Sclerotome
- Myotome
- Septum transversum
|
|
Index of bones and cartilage
|
|
Description |
- Anatomy
- bones
- skull
- face
- neurocranium
- compound structures
- foramina
- upper extremity
- torso
- pelvis
- lower extremity
- Physiology
- Development
- Cells
|
|
Disease |
- Congenital
- Neoplasms and cancer
- Trauma
- Other
- Symptoms and signs
|
|
Treatment |
|
|
|
Development of the circulatory system
|
|
Heart |
Tubular heart |
- Truncus arteriosus
- Bulbus cordis
- Primitive ventricle
- Primitive atrium
- Sinus venosus
|
|
Septa |
- Atrioventricular cushions/Septum intermedium
- Primary interatrial foramen
- Septum primum
- Septum secundum
- Aorticopulmonary septum
|
|
Other |
- Atrioventricular canal
- Primary interventricular foramen
- Protein signalling in heart development
|
|
|
Vessels |
Arteries |
- Dorsal aorta
- Aortic arches
- Aortic sac
|
|
Veins |
- Anterior cardinal vein
- Posterior cardinal vein
- Common cardinal veins
|
|
Lymph vessels |
|
|
|
Extraembryonic
hemangiogenesis |
- Blood islands
- Chorion
- Connecting stalk
- Yolk sac
- Placenta
|
|
Fetal circulation |
- umbilical cord: Umbilical vein → Ductus venosus → Inferior vena cava → Heart → Pulmonary artery → Ductus arteriosus → Aorta → Umbilical artery
- yolk sac: Vitelline veins
- Vitelline arteries
|
|
Index of the heart
|
|
Description |
- Anatomy
- Physiology
- Development
|
|
Disease |
- Injury
- Congenital
- Neoplasms and cancer
- Other
- Symptoms and signs
- Blood tests
|
|
Treatment |
- Procedures
- Drugs
- glycosides
- other stimulants
- antiarrhythmics
- vasodilators
|
Index of the circulatory system
|
|
Description |
- Anatomy
- Arteries
- head and neck
- arms
- chest
- abdomen
- legs
- Veins
- head and neck
- arms
- chest
- abdomen and pelvis
- legs
- Development
- Cells
- Physiology
|
|
Disease |
- Congenital
- Neoplasms and cancer
- Lymphatic vessels
- Injury
- Vasculitis
- Other
- Symptoms and signs
|
|
Treatment |
- Procedures
- Drugs
- beta blockers
- channel blockers
- diuretics
- nonsympatholytic vasodilatory antihypertensives
- peripheral vasodilators
- renin–angiotensin system
- sympatholytic antihypertensives
- vasoprotectives
|
|
|
Development of the nervous system
|
|
Neurogenesis |
General |
- neural development
- neurulation
- neurula
- Notochord
- Neuroectoderm
- Neural plate
- Neural fold
- Neural groove
- Neuropoiesis
|
|
Neural crest |
- Cranial neural crest
- Cardiac neural crest complex
- Truncal neural crest
|
|
Neural tube |
- Rostral neuropore
- Neuromere / Rhombomere
- Cephalic flexure
- Pontine flexure
- Alar plate
- Basal plate
- Glioblast
- Neuroblast
- Germinal matrix
|
|
|
Eye |
- Neural tube
- Optic vesicle
- Optic stalk
- Optic cup
- Surface ectoderm
|
|
Ear |
|
|
Index of the central nervous system
|
|
Description |
- Anatomy
- meninges
- cortex
- association fibers
- commissural fibers
- lateral ventricles
- basal ganglia
- diencephalon
- mesencephalon
- pons
- cerebellum
- medulla
- spinal cord
- Physiology
- Development
|
|
Disease |
- Cerebral palsy
- Meningitis
- Demyelinating diseases
- Seizures and epilepsy
- Headache
- Stroke
- Sleep
- Congenital
- Injury
- Neoplasms and cancer
- Other
- Symptoms and signs
- head and neck
- eponymous
- lesions
- Tests
|
|
Treatment |
- Procedures
- Drugs
- general anesthetics
- analgesics
- addiction
- epilepsy
- cholinergics
- migraine
- Parkinson's
- vertigo
- other
|
Index of the eye
|
|
Description |
- Anatomy
- Physiology
- Phenomena
- appearance
- visual
- optical illusions
- proteins
- Development
|
|
Disease |
- Congenital
- Corneal dystrophy
- Neoplasms and cancer
- Other
- Symptoms and signs
|
|
Treatment |
- Procedures
- Drugs
- infection
- glaucoma and miosis
- mydriatics
- vascular
|
Index of the ear
|
|
Description |
- Anatomy
- Physiology
- Development
|
|
Disease |
- Congenital
- Other
- Symptoms and signs
|
|
Treatment |
|
|
|
Development of the respiratory system
|
|
Upper |
|
|
Lower |
- Lungs
- Laryngotracheal groove
- Respiratory bud
|
|
Index of the respiratory system
|
|
Description |
- Anatomy
- Physiology
- Development
|
|
Disease |
- Congenital
- Neoplasms and cancer
- Chest trauma
- Infection
- common cold
- pneumonia
- tuberculosis
- Other
- Symptoms and signs
|
|
Treatment |
- Procedures
- Drugs
- nasal
- throat
- obstructive airway diseases
- cough and cold
- histaminergics
- pulmonary arterial hypertension
- other
- Surgery
|
|
|
Development of the digestive system
|
|
Gut |
Foregut |
- Stomodeum
- Buccopharyngeal membrane
- Rathke's pouch
- Tracheoesophageal septum
- Accessory digestive glands
- Pancreatic bud
- Hepatic diverticulum
|
|
Midgut |
|
|
Hindgut |
- Urorectal septum
- Proctodeum
- Cloaca
|
|
|
Other |
Mesentery |
|
|
Thoracic diaphragm |
|
|
Cavities |
- Intra-embryonic coelom
- Extra-embryonic coelom
|
|
|
Index of digestion
|
|
Description |
- Anatomy
- Physiology
- Development
|
|
Disease |
- Congenital
- Neoplasms and cancer
- Inflammatory bowel disease
- Gluten sensitivity
- Other
- Symptoms and signs
- Blood tests
|
|
Treatment |
- Procedures
- Drugs
- anabolic steroids
- antacids
- diarrhoea and infection
- bile and liver
- functional gastrointestinal disorders
- laxatives
- peptic ulcer and reflux
- nausea and vomiting
- other
- Surgery
|
|
|
Development of the urinary and reproductive systems
|
|
Common |
- Mesoderm
- Intermediate mesoderm
- Lateral plate mesoderm ("LPM")
- Endoderm → Cloaca → Urogenital sinus ("US")
- Endoderm+Ectoderm → Cloacal membrane
|
|
Urinary system |
- Nephrogenic cord → Kidney
- Mesonephros (Mesonephric tubules)
- Mesonephric duct → Ureteric bud + Metanephrogenic blastema
- US → Urinary bladder + Urethra + Primary urethral groove + Urachus
|
|
Reproductive system |
Internal |
- Gonadal ridge → Indifferent gonad → Gonadal cord (Cortical cords, Testis cords)
- Pronephric duct → Mesonephric (Wolffian) duct + Paramesonephric (Müllerian) duct (Vaginal plate)
- Urogenital sinus → Prostate or Skene's gland
|
|
External |
- LPMGenital tubercle → Labioscrotal swelling → Scrotum or Labia majora
- LPM → Genital tubercle → Primordial phallus → Penis or Clitoris
- Peritoneum → Processus vaginalis or Canal of Nuck
|
|
|
See also |
- List of homologues of the human reproductive system
- Prenatal development
- Embryogenesis
|
|
Index of the urinary system
|
|
Description |
- Anatomy
- Physiology
- Development
- Cells
|
|
Disease |
- Electrolyte and acid-base
- Congenital
- Neoplasms and cancer
- Other
- Symptoms and signs
- Urine tests
- Blood tests
|
|
Treatment |
- Procedures
- Drugs
- Intravenous fluids
|
Index of reproductive medicine
|
|
Description |
- Anatomy
- Physiology
- Development
- sex determination and differentiation
|
|
Disease |
- Infections
- Congenital
- Neoplasms and cancer
- male
- female
- gonadal
- germ cell
- Other
- Symptoms and signs
|
|
Treatment |
- Procedures
- Drugs
- benign prostatic hypertrophy
- erectile dysfunction and premature ejaculation
- sexual dysfunction
- infection
- hormones
- androgens
- estrogens
- progestogens
- GnRH
- prolactin
- Assisted reproduction
- Birth control
|
|
|
Authority control |
- GND: 4014562-1
- NDL: 00562996
|
|