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WEEK 18:
Development of Respiratory System:
| Question | Answer |
|---|---|
| diverticulum | lung bud |
| 4 week old embryo | respiratory diverticulum appears as an outgrowth from ventral wall of foregut |
| features from endodermal origin (4) | internal epithelium lining the larynx, trachea (+ glands), bronchi, and lungs |
| features from splanchnic mesoderm surrounding foregut (3) | cartilaginous, muscular, and connective tissue |
| how does lung bud expand from foregut | caudally |
| two longitudinal ridges | tracheoesophageal |
| tracheoesophageal ridges function | separate lung bud from foregut |
| tracheoesophageal ridges fuse to form | tracheoesophageal septum |
| tracheoesophageal septum function | divide foregut into dorsal part (oesophagus) and ventral part (trachea + lung buds) |
| laryngeal orifice | how respiratory primordium maintains communication with pharynx |
| what happens when lung bud separates from foregut | forms trachea + 2 lateral bronchial buds |
| beginning of 5th week | bronchial buds enlarge to form right and left main bronchi |
| end of 6th month** | 17 generations of subdivisions have been formed |
| postnatal life | 6 divisions form |
| pseudoglandular period | 5-16 weeks: branching continued to form terminal bronchioles |
| canalicular period | 16-26 weeks: each terminal bronchiole divides into 2 or more respiratory bronchioles and these divide into 3-6 alveolar ducts |
| terminal sac period | 26 weeks- birth: terminal sacs (primitive alveoli) + capillaries in close contact form |
| alveolar period | 8 months- childhood: mature alveoli have well developed epithelial endothelial (capillary) contacts |
| type I alveolar epithelial cells (type I pneumocytes) | thin squamous epithelial cells lining alveolar sac |
| type II alveolar epithelial cells (type II pneumocytes) | rounded secretory epithelial cells lining alveolar sac, which were formed at end of 6th month and produce surfactant |
| surfactant forms | monomolecular film over internal walls of terminal sacs and mature alveoli |
| breathing movement before birth are responsible for | conditioning respiratory muscles |
| pericardioperitoneal canals | lie on each side of foregut but are initially connected to pericardial (primitive thoracic) and peritoneal (primitive abdominal) cavities and are gradually filled by expanding lung buds |
| pleuropericardial folds | separate pericardioperitoneal canals from pericardial cavities, where reminaing spaces form primitive pleural cavities |
| pleural caivities remainc onnected to peritoneal (abdominal) cavity until when | until closed by fusion of pleuroperitoneal folds during formation of diaphragm |
| septum transversum | stops at gut tube leaving 2 open passageways on right + left (pericardioperitoneal canals) |
| closing the pericardioperitoneal canals requires | growth from dorsolateral body wall (pleuroperitoneal membranes) |
| defects in separating abdominal + thoracic cavity leads to | CDH (congenital diaphragmatic hernias) where abdominal contents herniate into pleural cavities and interfere with lung development |
| somatic mesoderm | covers body wall inside becoming the parietal pleura |
| splanchnic mesoderm | covers outside of lung becoming the visceral pleura |
| changes in lungs before birth (3) | amount of surfactant increases mostly during last 2 weeks of gestation, breathing movements occur, and amniotic fluid is aspirated |
| changes in lungs at birth | lung are half filled with fluid and removed, and a thin coating of surfactant is left lining alveolar cell membranes |
| how is fluid in the lungs removed at birth (3) | pressure on thorax during delivery expels fluid through mouth + nose, fluid absorbed into circulation via pulmonary circulation, and fluid is absorbed into lymphatics |
| lung of a stillborn | 1st breath isnt taken so lungs are full of fluid and will sink in water during autopsy |
| musculotendinous dome shaped partition | separates thoracic and abdominal cavities |
| embryonic components of diaphragm (4) | transverse septum, pleuroperitoneal membranes, dorsal mesentery of oesophagus, and muscular ingrowth from lateral body walls |
| septum transversum origin | mesoderm |
| how does the septum transversum grow | dorsally from ventrolateral body |
| when does septum transversum form | early in development |
| what does the septum transversum form | liver embedded in tissue |
| where is the septum transversum | caudal to pericardial cavity, partially separating it from peritoneal cavity |
| what is the septum transversum | primordium of central tendon of diaphragm |
| when does the pleuroperitoneal membrane form | start of 5th week |
| what does the pleuroperitoneal membrane form | dorsolateral wall of pleural + peritoneal cavities, dorsal + lateral parts of diaphragm (by fusing with transverse septum + dorsal mesentery in 7th week) |
| when does the pleuroperitoneal membrane fuse with the transverse septum and dorsal mesentery | 7th week |
| what does the dorsal mesentery of oesophagus form | median region of diaphragm, muscles bundles anterior to aorta (crura of diaphragm) |
| what is dorsal mesentery of oesophagus derived from | myoblasts that had previously migrated into dorsal mesentery of oesophagus |
| how does the formation of primordial diaphragm occur | |
| ow does the formation of mature diaphragm occur | |
| diaphragm in newborn | |
| congenital anomalies of respiratory system | |
| congenital diaphragmatic hernia |
Created by:
kablooey
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