- Development of human lung
The development of human lung arises from the laryngotracheal groove.
The larynx, trachea, bronchi and lungs begin to form during the fourth week of embryonic development. At this time, the respiratory diverticulum (lung bud) appears ventrally to the caudal portion of the foregut. The location of the diverticulum along the gut tube is directed by various signals from the surrounding mesenchyme, including fibroblast growth factors. As the lung bud grows, its distal end enlarges to form the tracheal bud. At the same time the future trachea separates from the foregut through the formation of tracheoesophageal ridges, which fuse to form the tracheoesophageal septum.
The tracheal bud divides into two primary bronchial buds. During the fifth week of development, the bronchial buds enlarge to form right and left main bronchi. These continue to develop into secondary and tertiary bronchi.
The maturation of the lungs occurs in several phases:
Period Time Description Pseudoglandular period (also known as "glandular period") weeks 6 to 16 The developing lung resembles an endocrine gland at this time. By the end of this period, all of the major lung elements, except those required for gas exchange (e.g. alveoli), have appeared. Respiration is not possible during this phase, and fetuses born during this period are unable to survive. Canalicular period weeks 16 to 26 The lumens of the bronchi enlarge and lung tissue becomes highly vascularized during the canalicular period. By week 24, respiratory bronchioles and alveolar ducts have developed from the terminal bronchioles. Respiration is possible towards the end of this period, but few fetuses born during this time will survive. Terminal saccular period week 26 to birth The important blood-air barrier is established during the terminal saccular period. Specialized cells of the respiratory epithelium appear at this time, including type I alveolar cells across which gas exchange occurs, and type II alveolar cells which secrete pulmonary surfactant. This surfactant is important in reducing the surface tension at the air-alveolar surface, allowing expansion of the terminal saccules. During this time, the lungs are rock-like and will sink if placed in water but will expand after the first breath, a trait which is used to determine if babies were born alive. Alveolar period birth to 8 years of age During this stage the terminal saccules, alveolar ducts, and alveoli increase in number.
At birth, the baby's lungs are filled with fluid secreted by the lungs and are not inflated. When the newborn is expelled from the birth canal, its central nervous system reacts to the sudden change in temperature and environment. This triggers it to take the first breath, within about 10 seconds after delivery.
- ^ Moore KL, Persaud TVN (2002). The Developing Human: Clinically Oriented Embryology (7th ed. ed.). Saunders. ISBN 0-7216-9412-8.
- ^ Sadler T (2003). Langman's Medical Embryology (9th ed. ed.). Lippincott Williams & Wilkins. ISBN 0-7817-4310-9.
- ^ Kyung Won, PhD. Chung (2005). Gross Anatomy (Board Review). Hagerstown, MD: Lippincott Williams & Wilkins. pp. 156. ISBN 0-7817-5309-0.
- ^ "U.S. v. Nelson". http://www.armfor.uscourts.gov/opinions/2000Term/00-0010.htm. Retrieved 2007-11-22.
- ^ About.com > Changes in the newborn at birth Review Date: 27 November 2007. Reviewed By: Deirdre OReilly, MD
Prenatal development/Mammalian development of respiratory system (overview) (GA 11.1071, TE E5.5) Upper LowerLaryngotracheal groove · Respiratory bud
Wikimedia Foundation. 2010.
Look at other dictionaries:
Lung cancer — Classification and external resources Cross section of a human lung. The white area in the upper lobe is cancer; the black areas are discoloration due to smoking. ICD 10 C … Wikipedia
Lung transplantation — Intervention ICD 9 CM 33.5 MeSH … Wikipedia
Lung — For other uses, see Lung (disambiguation). Lunged redirects here. For other uses, see Lunge. The lungs of a pig … Wikipedia
human rights — fundamental rights, esp. those believed to belong to an individual and in whose exercise a government may not interfere, as the rights to speak, associate, work, etc. [1785 95] * * * Rights that belong to an individual as a consequence of being… … Universalium
Human T-lymphotropic virus — Taxobox name = PAGENAME virus group = vi familia = Retroviridae subfamilia = Orthoretrovirinae genus = Deltaretrovirus species = Simian T lymphotropic virus subdivision ranks = Serotypes subdivision = Human T lymphotropic virus Human T… … Wikipedia
human aging — ▪ physiology and sociology Introduction physiological changes that take place in the human body leading to senescence, the decline of biological functions and of the ability to adapt to metabolic stress. In humans the physiological… … Universalium
human disease — Introduction an impairment of the normal state of a human being that interrupts or modifies its vital functions. health versus disease Before human disease can be discussed, the meanings of the terms health, physical fitness, illness … Universalium
human cardiovascular system — ▪ anatomy Introduction organ system that conveys blood through vessels to and from all parts of the body, carrying nutrients and oxygen to tissues and removing carbon dioxide and other wastes. It is a closed tubular system in which the… … Universalium
Human nutrition — For aspects of nutrition science not specific to humans, see Nutrition. Human nutrition is the provision to humans to obtain the materials necessary to support life. In general, humans can survive for two to eight weeks without food, depending on … Wikipedia
human body — Introduction the physical substance of the human organism, composed of living cells and extracellular materials and organized into tissues, organs, and systems. Human anatomy and physiology are treated in many different articles. For… … Universalium