In the head/neck region, the pharynx forms a major arched cavity within the phrayngeal arches. The lungs go through 4 distinct phases of development and late in foetal development respiratory motions and amniotic fliud are thought to have a role in lung maturation. Development of this system is not completed until the last weeks of Fetal development, just before birth. Therefore premature babies have difficulties associated with insufficient surfactant (end month 6 alveolar cells type 2 appear and begin to secrete surfactant).
Week 4 - laryngotracheal groove forms on floor foregut.
Week 5 - left and right lung buds push into the pericardioperitoneal canals (primordia of pleural cavity)
Week 6 - descent of heart and lungs into thorax. Pleuroperitoneal foramen closes.
Week 7 - enlargement of liver stops descent of heart and lungs.
Month 3-6 - lungs appear glandular, end month 6 alveolar cells type 2 appear and begin to secrete surfactant.
Month 7 - respiratory bronchioles proliferate and end in alveolar ducts and sacs.
Lung Development 4 histological periods
Diaphragm 5 elements contribute to the diaphragm (More? Respiratory - Diaphragm | Musculoskeletal System - Muscle)
Blood Supply
Clicking on the section number will open the full image.
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B1,B2: Pharynx. Crest in ventral floor of pharynx formed by fusion of 3rd pharyngeal arches = hypopharyngeal eminence (precursor of root of tongue). Rathke's pouch = rudimentary adenohypophysis. |
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B3: Rudimentary thyroid ventral to aortic sac (also seen in B2, ventral to the hypopharyngeal eminence). |
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B4: Caudal pharynx compressed dorsoventrally. |
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B6: Further compression of ventral part of pharynx to form a fused epithelial lamina, the vocal fold. Note surrounding dense mesenchyme. Nasal placode. (not shown) |
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B7: Glottis drawn off from pharyngeal foregut. Nasal placodes. Pulmonary arteries. (not shown) |
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C1,C2: Commencement of trachea and oesophagus with dense mesenchyme. R. nasal pit. (not shown) |
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C2: Commencement of trachea and oesophagus with dense mesenchyme. R. nasal pit. |
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C3,C4: Common cardinal vein in the posterior wall of the intraembryonic coelom - the pleuropericardial folds which contribute later to the formation of the pleura and pericardium. L. nasal pit. In C4, junction of R common cardinal vein with dorsal wall of sinus venosus. |
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C4: Common cardinal vein in the posterior wall of the intraembryonic coelom - the pleuropericardial folds which contribute later to the formation of the pleura and pericardium. L. nasal pit. In C4, junction of R common cardinal vein with dorsal wall of sinus venosus. |
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C5: Smaller oesophagus, expanding trachea. Note ventral anchoring of attachment site is at the most cranial extension of the septum transversum. Note also that this attachment now divides the intraembryonic coelom around the trachea into two canals, the L and R pleuro (pericardio-peritoneal) canals. (Canals are lined by coelomic mesothelium and are continuous with whole I-E coelom - they will be referred to hereafter simply as coelomic canals). Note the pleuroperitoneal fold on the medial side of the R common cardinal vein - this fold will form part of the diaphragm. |
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C5,C6: Lateral extension of pulmonary mesenchyme is moulded to shape of coelomic canals. R common cardinal draining directly into sinus venosus; L common cardinal vein with prominent L pleuropericardial fold. Oesophagus lumen obliterated (common site of oesophageal atresia and/or tracheo-oesophageal fistula). Prominent R pleuroperitoneal fold. |
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C7: Bifurcation of trachea into L, R lung buds. Junction of L common cardinal vein and L; of sinus venosus. Note dorsal extent of coelomic canals. Oesophagus lumen reappears caudal to bifurcation. Distinct R (smaller on L) pleuroperitoneal fold below the common cardinal vein. |
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Dl: R lung bud prominent. (L lung bud is more cranial, therefore R primary bronchus is more vertical than the left - cf. Gross Anatomy). note ventral anchoring of pulmonary mesenchyme to the septum transversum, in which is also embedded the sinus venous. |
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D2 R and L lung buds. Note beginning of GIT expansion for stomach in midline. |
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D3: Liver embedded in septum transversum (ventral border of septum transversum contributes to diaphragm). |
G7: Rathke's pouch. Floor of pharynx with foramen caecum (remains of thyroglossal duct), and caudally to it, the hypopharyngeal eminence. L lungbud caudal to L atrium with attachment of pulmonary mesenchyme to septum transversum. |
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G6: Pharynx, initially compressed dorsoventrally then more caudally, compressed mediolaterally in region of dense mass of mesenchyme (cf B6). Tracheal bifurcation dorsal to sinus venosus. Attachment of pulmonary mesenchyme to septum transversum. |
An overview of the Stage 22 Embryo respiratory system from trachea to developing lungs and diaphragm.
Page Links: Introduction | Trachea | Lungs | Embryo Sections | Glossary
Clicking on the section numbers below will open the full image.
A5: Bridge of nose. R and L olfactory bulbs from forebrain (cf. A4). A6: Nose. Nasal septum. Nasal capsule. Olfactory epithelium lining roof of nasal cavity. Orbital part of the developing sphenoid bone (intramembranous ossification). A7: Conchae. Nasal capsule and septum. B1: Conchae. Optic nerve. B2: Perpendicular plate of ethmoid cartilage. Adenohypophysis. Neurohypophysis. Ant. and post. walls of hypopophysial fossa. Lesser wings of sphenoid cartilage. Internal carotid arteries. B4: Dorsum of tongue. Oropharynx communicating with naso-pharynx (cf. B3 - palatal processes not fused). B5: Tongue with palatal processes at either side. Transverse (intrinsic) muscle of tongue. Pharyngotympanic tubes. |
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B6: Tongue with transverse muscle, genioglossus muscle (medial) and hyoglossus muscle (lateral). Meckel's cartilage. Palatal processes. Note teeth enamel organs (dark masses at sides of tongue attachment). |
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B7: Transverse caudal pharynx. epiglottis. Hyoid musculature. Pharyngeal constrictor muscle. Submandibular gland. |
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C2: Pharynx. Thyroid cartilage. Smaller laryngeal caecum (cf.C1). Carotid neurovascular bundle. |
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C3: Pharynx with its inferior constrictor muscle. Glottis region. |
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C4: (Section damaged) Oesophagus with muscle layer and trachea with thyroid gland laterally. Common carotid arteries. Vagus nerve. Internal jugular veins. |
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C5: Oesophagus, smaller than in C4. Trachea. Thyroid gland (isthmus). Clavicle. Small dark masses near posterolateral borders of thyroid gland are the parathyroid glands from the caudal part of 3rd pharyngeal pouch. |
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C6: Clavicles. Dark connecting stalk between parathyroid gland and thymus (rostral end of 3rd pharyngeal pouch). Trachea. Common carotid artery. |
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C7: Sternum. Thymus gland. L brachiocephalic vein. Brachiocephalic trunk. Trachea. Oesphagus. Apex of R lung in pleural cavity |
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Dl: Sternum. Thymus. Lungs. Visceral and parietal pleurae. Pleural cavities. Other contents of superior mediastinum. |
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D3: Tracheal bifurcation. |
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D4: R primary bronchus (torn) and R superior lobe bronchus. L primary bronchus. L, R pulmonary arteries. Ribs joining to sternum. |
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D5: R, L primary bronchi. R anterior and posterior segmental bronchi coming off R superior lobe bronchus. L, R pulmonary arteries. Hilar attachments of lungs to mediastinal tissues - note extent of R, L pleural cavities. |
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D6: R, L primary bronchi (note left still has not branched). R pulmonary artery. |
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D7: R, L primary bronchi: note distinct horizontal course of L, vertical course of R, L pulmonary veins (L empty). R pulmonary artery. |
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E1,E2: Pulmonary veins. Azygos, hemiazygos veins. Ribs. Intercostal muscles. |
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E2: Pulmonary veins. Azygos, hemiazygos veins. Ribs. Intercostal muscles. |
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E3: R dome of diaphragm. Liver. R long middle and inferior lobes. L long superior and inferior lobes. Xiphoid process. |
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E4: Diaphragm (note costal attachment). R lung inferior lobe. Inferior vena cava, dorsal to diaphragm. |
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E5: Liver. Diaphragm with sternal attachments. Inferior vena cava, now ventral to diaphragm (vena caval foramen). Inferior lobes of lungs. |
E6: Liver. Thoracic aorta. Large adrenal glands. E7: Lumbar diaphragm. Thoracic aorta. Note ribs 11 and 12 on L and three layers of abdominal muscles extending ventrally. Fl: Lumbar diaphragm. Thoracic aorta. F2: Attachment of lumbar diaphragm near L 1 on R with psoas muscle dorsal to it. Note abdominal aorta giving rise to superior mesenteric artery. |
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The diaphragm is a muscular structure, though covered in respiration the notes on musculoskeletal development should also be read. (More? Musculoskeletal System)
Adult Diaphragm
Page Links: Introduction | Diaphragm Components | Adult Diaphragm | Abnormalities | Congenital Diaphragmatic Hernia | Glossary
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Five elements contribute to the diaphragm. septum transversum - central tendon 3rd to 5th somite - musculature of diaphragm (More? Somites) ventral pleural sac - connective tissue mesentry of oesophagus - connective tissue around oesophasus and IVC (More? Gastrointestinal Tract) pleuroperitoneal membranes - connective tissue around central tendon |
Congenital Diaphragmatic Hernia (International Classification of Diseases code 756.6)
Failure of the pleuroperitoneal foramen (foramen of Bochdalek) to close allows viscera into thorax. Intestine, stomach or spleen can enter the pleural cavity, compressing the lung.
Australian national rate (1982-1992) 2.1 - 3.8 /10,000 births. (Congenital Malformations Australia 1981-1992 P. Lancaster and E. Pedisich ISSN 1321-8352)
Search Now: Pubmed - Congenital Diaphragmatic Hernia | OMIM - Congenital Diaphragmatic Hernia
Lecture 10 - Respiratory Development Thu 13:00 - 14:00 Australian School Business 119 (K-E12-119)
Laboratory 06 - Thu 10:00 - 12:00 Wallace Wurth 106/108 (K-C27-106)
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atresia - (Greek, a = without + tresis = perforation) Term used for anatomical closing or absence of a cavity or opening that should exist. Used as an antomical, pathological and clinical term: esophageal atresia, biliary atresia, duodenal atresia, jejunal atresia, choanal atresia, urethral atresia, bronchial atresia.
biliary cells - The liver epithelial cell formed from hepatoblast differentiation (hepatoblasts form from endoderm). (More? Gastrointestinal Tract - Liver)
buccal (Latin, bucca = cheek) term used to relate to the mouth (oral cavity). (More? GIT Notes)
buccopharyngeal membrane - (oral membrane) (Latin, bucca = cheek) Forms the external upper membrane limit (cranial end) of the early gastrointestinal tract (GIT). This membrane is formed during gastrulation by ectoderm and endoderm without a middle (intervening) layer of mesoderm. The membrane breaks down to form the initial "oral opening" of the gastrointestinal tract. (see also cloacal membrane)
cloacal membrane - Forms the external lower membrane limit (caudal end) of the early gastrointestinal tract (GIT). This membrane is formed during gastrulation by ectoderm and endoderm without a middle (intervening) layer of mesoderm. The membrane breaks down to form the initial "anal opening" of the gastrointestinal tract. (More? buccopharyngeal membrane | GIT Notes)
enteroendocrine cells - Endocrine cells found within the epithelium of the gastrointestinal tract. (More? Endocrine Notes)
extrahepatic bile ducts - (EHBDs) is used to describe the hepatic, cystic, and common bile ducts. (More? GIT Notes - Gall Bladder)
foregut - The first of the three part/division (foregut - midgut - hindgut) of the early forming gastrointestinal tract. The foregut runs from the buccopharyngeal membrane to the midgut and forms all the tract (esophagus and stomach) from the oral cavity to beneath the stomach. In addition, a ventral bifurcation of the foregut will also form the respiratory tract epithelium. (More? Gastrointestinal Tract - Stomach | Gastrointestinal Tract Notes | Respiratory Notes)
gall bladder - The septum transversum differentiates to form the hepatic diverticulum and the hepatic primordium, these two structures together will go on to form different components of the mature liver and gall bladder. In the adult, the gall bladder is a site of bile salt storage and concentration, to then be released into the small intestine where they act to solubilize dietary lipids by their detergent effect. Bile salts are a cholesterol derivative (breakdown product). (More? Gastrointestinal Tract - Gall Bladder | Liver Notes)
greater omentum - The greater omentum is the peritoneal fold extending from the greater curvature of the stomach and hanging down "like an apron" ventrally over the small intestine. It forms initially in the embryo and fetus as a loop of the dorsal mesentery, which later fuses to form a single sheet attached to the posterior body wall. The lesser omentum is a smaller ventral peritoneal fold extending from lesser curvature of the stomach to liver. (More? GIT Notes)
hepatic - (Greek, hepato = liver) relates to the liver and its associated structures. (More? Gastrointestinal Tract - Liver)
hepatic duct - the liver excretory duct, joins with gall bladder cystic duct to form the common bile duct. (More? Gastrointestinal Tract - Liver)
hepatoblast - The undifferentiated liver progenitor cell formed initially from endoderm, which willlater form both hepatocytes and biliary cells. (More? Gastrointestinal Tract - Liver)
hepatocyte - The functional liver cell formed from hepatoblast differentiation (hepatoblasts form from endoderm). (More? Gastrointestinal Tract - Liver)
hindgut - The last of the three part/division (foregut - midgut - hindgut) of the early forming gastrointestinal tract. The hindgut forms all the tract from the distral transverse colon to the cloacal membrane and extends into the connecting stalk (placental cord) as the allantois. In addition, a ventral of the hindgut will also form the urinary tract (bladder, urethra) epithelium. (More? Gastrointestinal Tract Notes | Urogenital Notes)
interstitial cells of Cajal - (ICC) Neural cells located in the gastrointestinal tract (enteric nervous system) located within the smooth muscle wall (tunica muscularis) that act as electrical pacemakers to coordinate muscular slow wave contraction propagation. (More? Neural Crest Notes)
insulin - A protein hormone, produced by specialized cells of the pancreas, that regulates glucose uptake; a signal for the absorptive state; promotes the synthesis of glycogen and inhibits its breakdown. (More? Endocrine Development - Pancreas)
intestinal immune system - consists of a system of functional regions and cells including: Peyer's patches, isolated lymphoid follicles, cryptopatches and mesenteric lymph nodes.
lesser omentum - The smaller of two splanchnic mesoderm peritoneal folds (lesser/greater), the lesser extends from lesser curvature of the stomach to liver. The greater omentum extends from the greater curvature of the stomach and hanging down "like an apron" ventrally over the small intestine. (More? GIT Notes)
meconium - The gastrointestinal contents that accumulate in the intestines during the fetal period. This material is a mixture of liver and glandular secretions, amniotic fluid, and cellular debris. Meconium is also used to describe the first postnatal rectal discharge from the neonate. Fetal stress in the third trimester or at parturition can lead to premature meconium discharge into the amniotic fluid, ingestion by the fetus and damage to respiratory function. Damage to placental vessels meconium myonecrosis may also occur. (More? Birth)
mesogastrium - The developmental term for the splanchnic mesoderm forming early mesenteries (dorsal and ventral) that support the developing gastrointestinal tract. The majority of the ventral mesentery is developmentally lost at the level of the midgut and the dorsal mesentery remains in the adult, through which blood vessels, nerves and lymph connects to the gastrointestinal wall. Note that specific visceral organs also develop within each mesogastrium. (More? GIT Notes)
midgut - The middle of the three part/division (foregut - midgut - hindgut) of the early forming gastrointestinal tract. The midgut is initially connected on the ventral embryo surface to the external yolk sac by a yolk stalk, a narrow tubular connection. The midgut forms all the tract from beneath the stomach (duodenum, small intestine and large intestine) to the distral transverse colon. The midgut develops as an external loop "herniated" ventrally, until early fetal growth of the body wall recaptures this external loop, which also undergoes a rotation about the superior mesenteric artery to establish the adult anatomical position. (More? Gastrointestinal Tract - Intestine | Gastrointestinal Tract Notes)
neural crest - cell region at edge of neural plate, then atop the neural folds, that remains outside and initially dorsal to the neural tube when it forms. These paired dorsal lateral streaks of cells migrate throughout the embryo and can differentiate into many different cell types (= pluripotential). Those that remain on the dorsal neural tube form the sensory spinal ganglia (DRG). Neural crest cells also migrate into the mesoderm to form the enteric nervous system of the gut. (More? Neural Crest Notes)
pancreas - The gastrointestinal tract associated organ with both exocrine (pH change and digestive enzyme secretion) and endocrine (hormone secretion) functions. In humans, the pancreas develops at the foregut/midgut junction (the septum transversum) and initially form connected to the gastrointestinal tract as two pancreatic buds (dorsal and ventral endoderm) which later fuse to form a single organ. The pancreas exocrine function (alkylate acidic stomach contents and amylase protein digestion) begins mainly fter birth. The endocrine function (alpha cell - glucagon, delta cell - somatostatin, beta cell - insulin) can be measured from 10 to 15 weeks onward. (More? Gastrointestinal Tract - Pancreas | Endocrine Development - Pancreas)
parenchymal - (parenchyma) Histological term used to describe the functional cells of an organ, tissue or structure. The term is often paired with stromal (stroma), which describes the supportive cells within an organ, tissue or structure.
peritoneal cavity - Anatomical body cavity in which the lower body organs lie: intestines, liver, bladder, uterus, ovary. The peritoneal cavity forms initially from two separate regions of the early intraembryonic coelom (formed in the lateral plate mesoderm), which with embryo folding, fuse to form a single cavity. Note the single intraembryonic coelom forms all three major body cavities: pericardial, pleural, peritoneal. (More? Coelomic Cavity Notes)
pleuroperitoneal membrane - An early embryonic membrane that forms inferiorly at the septum transversum to separate peritoneal cavity from pleural cavity.
septum transversum (transverse septum) A mesodermal region in the early embryo. Identified externally as the junctional site between amnion and yolk sacs, and internally (within the embryo) lying directly beneath the heart and at the foregut/midgut junction. This ventro-dorsal "plate" of mesoderm contributes several structures including: the central tendon of diaphragm and some of the liver. The transverse septum has an important structural role in early embryonic development and is pierced by the gastrointestinal tract. (More? Gastrointestinal Tract Notes | Liver Notes | Respiratory Development - Diaphragm)
splanchnic mesoderm - Gastrointestinal tract (endoderm) associated mesoderm formed from the splitting of the lateral plate mesoderm. This mesoderm is the embryonic origin of the gastrointestinal tract connective tissue, smooth muscle, blood vessels and contribute to organ development (pancreas, spleen, liver). The same lateral plate mesoderm lying above the buccopharygeal membrane will form the heart. The cavity in the lateral plate mesoderm (intraembryonic coelom) will form the three major body cavities including the peritoneal cavity of the gut. The other half of the lateral plate mesoderm (somatic mesoderm) is associated with ectoderm and the body wall.
spleen - The spleen develops within the gastrointestinal tract dorsal mesogastrium mesenchyme. With folding it is located on the left side of the abdomen and has a role initially in blood (haematopoisis, blood cell formation) and later immune system development. The spleen's haematopoietic function is lost with fetal development and lymphoid precursor cells migrate into the developing organ. (More? Spleen Notes
stenosis - Term used to describe an abnormal narrowing, usually in relation to a tube. For example, in a blood vessel or in the gastrointestinal tract. (More? Gastrointestinal Tract Abnormalities)
stomach - Gastrointestinal tract (GIT) foregut organ that has a major function in digestion. In humans, during week 4 initially as a dilatation of the foregut lying behind the heart. Differential growth of the ventral and dorsal walls establishes the greater curvature of the stomach and second rotation (of 90 degrees) occurs on the longitudinal axis establishing the adult anatomical orientation of the stomach. (More? Gastrointestinal Tract - Stomach)
stomadeum - (stomadeum) A ventral surface depression on the early embryo head surrounding the buccopharyngeal membrane, which lies at the floor of this depression. This surface depression lies between the maxillary and mandibular components of the first pharyngeal arch. (More? Gastrointestinal Tract Notes | Head Notes)
stromal - (stroma) Histological term used to describe supportive cells within an organ, tissue or structure. The term is often paired with parenchymal, which describes the functional cells of an organ, tissue or structure.
(septum transversum) see septum transversum a mesodermal region in the early embryo.
atresia - (Greek, a = without + tresis = perforation) Term used for anatomical closing or absence of a cavity or opening that should exist. Used as an antomical, pathological and clinical term: esophageal atresia, biliary atresia, duodenal atresia, jejunal atresia, choanal atresia, urethral atresia, bronchial atresia.
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