Embryology Of The Respiratory System Flashcards
What to do first
Look at the power point
What develops before the lungs
Cardiac tubes
Vascular network present from very early in development
What is stage 1 in histological embryology
Embryonic
Stages up until the formation of segmental (tertiary) bronchi
Endoderm develops into epithelium with mucosal and submucosal glands
Splanchnic mesoderm forms smooth muscle cartilage and connective tissue
What is stage 2 of histological embryology
Pseudoglandular
Lungs extended developing conducting branches of bronchial tree and vascularisation begins
What is stage 3 in histological embryology
Canalicular
Airways lumen enlarge respiratory bronchioles form
Capillaries come into contact with epithelium
What is stage 4 in histological embryology
Terminal sac
Respiratory bronchioles give off sacs lines with cuboidal epithelium which organises into type 1 and type 2 alveolar cells
Production of surfactant begins
What is stage 5 of histological embryology
Alveolar
Capillaries associated closely with alveolar lining
Surfactant production increases
Incomplete at birth continues post natally
How does gas exchange occur in the foetus
Early embryo - diffusion
Placentation (see reproduction notes) brings maternal and foetal circulations into close apposition
What to do next
Check PowerPoints for diagrams
What state does the foetus exist in
Relative hypoxia
Oxygenated and deoxygenated blood mix at points in the circulation
Carotid bodies relatively insensitive to hypoxia in the foetus
How does the foetus cope with this
Higher cardiac output than a adult animal
Higher affinity of foetal Hb for oxygen
What three factors increase a foetuses Hb for oxygen
Related to 2,3 DPG
Ruminants foetal Hb unresponsive to 2,3 DPG
Primates foetal Hb has a reduced interaction with 2,3 DPG
Horses/pigs no foetal Hb just adult but foetal erythrocytes contain a lower 2,3 DPG
What is pulmonary circulation like before birth
Largely shut down as lung is collapsed. Most of blood shunted into systemic circulation
Moves via ductus arteriosus
High pressure in the collapsed lung facilitates this shunting
What changes occur at birth
Alveoli expand as foetus develops due to fluid in alveoli
Respiratory muscles start contracting from first trimester
The process of birth squeezes some fluid out of the lungs and the remainder is reabsorbed into the lymphatic and blood vessels
What happens before and during the first breath
Due to hypoxia hypercapnia lowering body temperature and increased sensory stimulation
Huge effort - intra-alveolar pressure of 60mmHg below atmospheric pressure necessary
This inflates the lungs and pulls open the pulmonary vessels
Reduces pulmonary vascular resistance so blood no longer diverted
