Unit 5: Functional Development of the Heart and Lungs Flashcards
Heart development at 18-21 days
-rapid development of the cardiac tissue (first functional organ in the fetus)
-from 18 days, the mesoderm at the head of the embryo differentiates into endocardial tubes
-about 1 day later, these tubes fuse to form the primitive heart tube
What are the three layers of embryonic tissue
ectoderm, mesoderm and endoderm
what are the three structures of the mesoderm
paraxial, intermediate and lateral plate (made up of somatic and splanchnic)
What is splanchnic portion of the lateral plate made up of and what does it form
cardiogenic tissue and it forms the pericardial coelom and the endocardial tubes
What causes the splanchnic lateral mesoderm to differentiate
vascular endothelial growth factors
What does the splanchnic lateral mesoderm differentiate into
angioblasts (blood vessels) and hemocytoblasts (blood content)
What occurs between 20 and 21 days in heart development
-differentiation of splanchnic lateral mesoderm
-splanchnic portions meet one another resulting in the fusion of the endoderm , the pericardial coelom and the endocardial tubes
-endocardial tube fusion forms the primitive heart tube
What happens at 22 days during heart development
-the primitive heart tube now lies in the center of the pericardial cavity, anchored by the dorsal mesocardium
-fusion of the splanchnic plates results in 1 heart tube and 1 pericardial cavity
What layers does the heart tube consist of at 22 days
2 layers
-myocardium (myocytes)
-endocardium( endothelial cells)
6 regions of the heart tube at 22 days
distal aortae, truncus arteriosus, bulbus cordis, primitive ventricle, primitive atrium, sinus venosus
What does the distal aortae become
the aorta
what does the truncus arteriosus become
pulmonary trunk
what does the bulbus cordis become
right ventricle and outflow tracts
What does the primitive ventricle become
left ventricle
what does the primitive atrium become
left and right atria
what does the sinus venosus become
SVC, IVC, coronary sinus and conductive system
What directions do contractions pump blood in the heart tube
from sinus venosus to truncus arteriosus
What process in heart development occurs at 23-24 days
Cardiac looping
What happens during cardiac looping
truncus arteriosus and bulbus cordis begin to fold down and to the right
primitive ventricle and the primitive atrium begin to fold up and to the left
What occurs on day 35 of heart development
-primitive atrium wraps around truncus arteriosus and is partitioned into L and R atria
-bulbus cordis becomes right ventricle and outflow tract
Internal changes that occur between 28 days and 8 weeks
start with septum primum and interventricular septum and then septum secundum forms creating the hole known as the foramen ovale
-valves and chordae tendineae also form by 8 weeks
What is the septum between the atrioventricular canals called
dorsal endocardial cushion/ septum intermedium
Fetal circulation in the heart
blood by passes lungs through the foramen ovale and the ductus arteriosus
What is cranial-caudal folding
when the embryo folds onto itself directing the heart from the head to the chest cavity
Where is the site of gas exchange in a fetus
the placenta
What is the purpose of the ductus venosus in fetal circulation
inflow tract for O2 rich blood form placenta - skips liver and goes to heart
What is the purpose of the ductus arteriosus
an opening that connects the pulmonary artery to the aorta
Why is the pressure in the right ventricle high
hypoxic vasoconstriction - blood doesn’t go to capillaries in lungs because they arent functional
What are Lacunae
maternal blood pools form arterioles into intervillous spaces within the placenta
What are chronic-villi
finger-like projections that penetrate the lacunae to facilitate fetal nurtient exchange with maternal blood
Placental gas exchange
O2, nutrients, vitamins, antibodies and H2O diffuse from lacunae into capillaries in the chronic villi
Fetal waste
includes CO2, urea and hormones
diffuses from the lacunae into the maternal blood vessels
Neonatal circulation
a change in pressure gradients between the left and right side of the heart results in closure of the foramen ovale
-blood is no longer shunted away from pulmonary circulation as lungs become site of gas exchange
-ductus arteriosus and ductus venosus will close shortly after birth
What changes occur in neonatal circualtion
-increased blood flow to the lungs
-closure of the foramen ovale forming fossa ovalis
-closure of the ductus venosus (IVC caries O2 pour blood from lower half) forming ligamentum venosus
-closure of ductus arteriosus forming ligamentum arteriosum
-% mixed blood in system reduced
Difference in fetal blood content compared to regular blood content
fetal blood contains 20% more hematocrit than mother, more RBC= greater O2 carrying capacity
-innate ability
Fetal hemoglobin
-fetal hemoglobin contains gamma subunit
-fetal hemoglobin is slightly less positive than maternal hemoglobin
-fetal hemoglobin has lower affinity for 2,3, DPG binding
2, 3 Diphosphoglycerate
negatively charged molecule that acts as a allosteric effector of hemoglobin by binding in the center pocket.
-lowers affinity of hemoglobin for oxygen resulting in more off loading of the oxygen at tissues
Oxyhemoglobin dissociation curve
indicates relationship between O2 saturation of hb and the partial pressure of arterial oxygen
-dynamic curve which changes based on 2,3, DPG, temperature and H+
-at higher pressure more O2 binds to hb to form oxyhemoglobin
-at lower pressure more readily offloaded form hb
Fetal shifts in hemoglobin curve
left-shift
more O2 uptake and less O2 extraction
essential for the fetus in its hypoxic environment
-persists 2-6 months after birth
What does the lungs develop from
Endoderm and Splanchnic portion of lateral plate of mesoderm
What becomes the epithelial lining of he respiratory tract
endoderm
What does the splanchnic LP mesoderm form
cartilage, blood vessels, connective tissue and muscles of the respiratory tract
What are the 5 stages of lung development
embryonic, pseudoglandular, canalicular, saccular, alveolar
Embryonic folding for lung development
lateral and cranial-caudal folding occur simultaneously
Where do the lungs develop from
they bud off of the foregut, initially forming the diverticulum which is surrounded by splanchnic LP mesoderm
Embryonic stage of lung development
-occurs 4th week of gestation
-2 bronchial/tracheal buds form off the lung bud- eventually becoming the bronchi and all other lower respiratory structures
-lungs begin to partition from the esophagus
-endoderm invades trachea giving rise to epithelial lining
Pseudoglandular stage of lung development
from 5th week to 16th week
-bronchi begin to replicate from the 2 bronchial buds
-subdivided into left and right bronchi
-splanchnic LP mesoderm encircles the bronchioles
-budding is dependent of the splanchnic LP mesoderm
-by the end of this stage all airway generations are established but have yet to differentiate into respiratory bronchioles
Bronchial divisions
primary bronchi - 1R, 1L
secondary bronchi (3R, 2R)
tertiary bronchi (20R, 18L)
terminal bronchioles (n= a lot)
At the end of the pesudoglandular stage what does further development entail
lengthening, widening, and functional development of existing airway generations
Canalicular stage of lung development
16 weeks to 25 weeks - functional lung development
-characterized of extensive vascularization and formation of the respiratory zones
respiratory zones
where O2 from the lungs can diffuse into the capillaries for gas exchange
-includes the respiratory bronchioles, alveolar ducts and primitive alveoli
Primitive Alveoli
inner surface of alveoli in lined with cuboidal cells
pulmonary capillaries form around the primitive alveoli
Saccular stage of lung development
week 26 to birth
-increase in number of capillaries, alveoli and respiratory bronchioles
-specialization of the alveoli - differentiation of cuboidal cells into type 1 and type 2 pneumocytes
Type 1 pneumocytes
squamous cells ideal for gas exchange
Type 2 Pneumocytes
cuboidal cells ideal for surfactant secretion
Surfactant
reduces surface tension caused by the air-water interface to prevent atelectasis
Surface tension
layer of H2O that doesnt interact with gas bu exerts force on each other
tends to compress downwards
Laplace’s law
collapsing pressure (P)=2T/r
How does surfactant work to reduce surface tension
moves air-water interface and reduces surface tension by exerting a force upwards
-via hydrophobic/hydrophilic fatty acid composition
Alveolar stage of lung development
-begins during late saccular stage and ends in childhood (8y)
-the number of alveoli continue to increase (100 mill to 300 mill)
-the number and complexity of pulmonary capillaries increases - most capillaries are in contact with 2 or more alveoli
-septa form within alveoli to greatly increase the surface area - both types of cells line septa
When do fetal breathing movements occur around
15th week
What is the percent increase in fetal breathing movements between 15 and 30 weeks
30%
What does the fetus breath and why
amniotic fluid which helps to prepare the respiratory muscles and lungs for neonatal breathing
Pulmonary vasoconstriction before birth
-the distribution of pulmonary blood flow is determined by O2 - low PO2 means low blood flow)
-vascular smooth muscle shunts blood away from deoxygenated alveoli
-results in high pulmonary arterial pressure
-blood diverted through the ductus arteriosus
Changes at babys first breath
- the amniotic fluid in baby’s lungs gets absorbed into pulmonary capillaries
-sufficient layer of surfactant must be developed or collapsing pressure is too great to overcome -infant respiratory distress syndrom
-air floods into the alveoli and the lungs become the sole sight of gas exchange
Changes after birth in respiratory system
alveoli replace amniotic fluid with gas, resulting in an increase in alveolar PO2
-increase in oxygen tension causes pulmonary vascular resistance to fall as pulmonary blood vessels dilate
-left atrial pressure increases due to the return of oxygenated blood from the pulmonary veins
-ductus arteriosus, ductus venosus and foramen ovale will close due to increased pressure
Parallel circualtion
both the right and left sides of the heart provide systemic blood flow
Series circulation
the right side of the heart caries deoxygenated blood to the lungs and the left side of the heart becomes the systemic circualtion
Infant respiratory distress syndrome
most commonly caused by a surfactant deficiency and is inversely proportional to gestational age
-common symptoms are hypoxia, hypercapina, cyanosis
-treatment options: corticosteroids in womb and exogenous surfactant either derived from animal or human amniotic fluid, or entirely synthstic surfactant
