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Growth and Maturation > Unit 5: Functional Development of the Heart and Lungs > Flashcards

Unit 5: Functional Development of the Heart and Lungs Flashcards

1
Q

Heart development at 18-21 days

A

-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

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2
Q

What are the three layers of embryonic tissue

A

ectoderm, mesoderm and endoderm

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3
Q

what are the three structures of the mesoderm

A

paraxial, intermediate and lateral plate (made up of somatic and splanchnic)

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4
Q

What is splanchnic portion of the lateral plate made up of and what does it form

A

cardiogenic tissue and it forms the pericardial coelom and the endocardial tubes

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5
Q

What causes the splanchnic lateral mesoderm to differentiate

A

vascular endothelial growth factors

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6
Q

What does the splanchnic lateral mesoderm differentiate into

A

angioblasts (blood vessels) and hemocytoblasts (blood content)

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7
Q

What occurs between 20 and 21 days in heart development

A

-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

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8
Q

What happens at 22 days during heart development

A

-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

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9
Q

What layers does the heart tube consist of at 22 days

A

2 layers
-myocardium (myocytes)
-endocardium( endothelial cells)

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10
Q

6 regions of the heart tube at 22 days

A

distal aortae, truncus arteriosus, bulbus cordis, primitive ventricle, primitive atrium, sinus venosus

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11
Q

What does the distal aortae become

A

the aorta

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12
Q

what does the truncus arteriosus become

A

pulmonary trunk

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13
Q

what does the bulbus cordis become

A

right ventricle and outflow tracts

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14
Q

What does the primitive ventricle become

A

left ventricle

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15
Q

what does the primitive atrium become

A

left and right atria

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16
Q

what does the sinus venosus become

A

SVC, IVC, coronary sinus and conductive system

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17
Q

What directions do contractions pump blood in the heart tube

A

from sinus venosus to truncus arteriosus

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18
Q

What process in heart development occurs at 23-24 days

A

Cardiac looping

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19
Q

What happens during cardiac looping

A

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

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20
Q

What occurs on day 35 of heart development

A

-primitive atrium wraps around truncus arteriosus and is partitioned into L and R atria
-bulbus cordis becomes right ventricle and outflow tract

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21
Q

Internal changes that occur between 28 days and 8 weeks

A

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

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22
Q

What is the septum between the atrioventricular canals called

A

dorsal endocardial cushion/ septum intermedium

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23
Q

Fetal circulation in the heart

A

blood by passes lungs through the foramen ovale and the ductus arteriosus

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24
Q

What is cranial-caudal folding

A

when the embryo folds onto itself directing the heart from the head to the chest cavity

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25
Q

Where is the site of gas exchange in a fetus

A

the placenta

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26
Q

What is the purpose of the ductus venosus in fetal circulation

A

inflow tract for O2 rich blood form placenta - skips liver and goes to heart

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27
Q

What is the purpose of the ductus arteriosus

A

an opening that connects the pulmonary artery to the aorta

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28
Q

Why is the pressure in the right ventricle high

A

hypoxic vasoconstriction - blood doesn’t go to capillaries in lungs because they arent functional

29
Q

What are Lacunae

A

maternal blood pools form arterioles into intervillous spaces within the placenta

30
Q

What are chronic-villi

A

finger-like projections that penetrate the lacunae to facilitate fetal nurtient exchange with maternal blood

31
Q

Placental gas exchange

A

O2, nutrients, vitamins, antibodies and H2O diffuse from lacunae into capillaries in the chronic villi

32
Q

Fetal waste

A

includes CO2, urea and hormones
diffuses from the lacunae into the maternal blood vessels

33
Q

Neonatal circulation

A

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

34
Q

What changes occur in neonatal circualtion

A

-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

35
Q

Difference in fetal blood content compared to regular blood content

A

fetal blood contains 20% more hematocrit than mother, more RBC= greater O2 carrying capacity
-innate ability

36
Q

Fetal hemoglobin

A

-fetal hemoglobin contains gamma subunit
-fetal hemoglobin is slightly less positive than maternal hemoglobin
-fetal hemoglobin has lower affinity for 2,3, DPG binding

37
Q

2, 3 Diphosphoglycerate

A

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

38
Q

Oxyhemoglobin dissociation curve

A

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

39
Q

Fetal shifts in hemoglobin curve

A

left-shift
more O2 uptake and less O2 extraction
essential for the fetus in its hypoxic environment
-persists 2-6 months after birth

40
Q

What does the lungs develop from

A

Endoderm and Splanchnic portion of lateral plate of mesoderm

41
Q

What becomes the epithelial lining of he respiratory tract

A

endoderm

42
Q

What does the splanchnic LP mesoderm form

A

cartilage, blood vessels, connective tissue and muscles of the respiratory tract

43
Q

What are the 5 stages of lung development

A

embryonic, pseudoglandular, canalicular, saccular, alveolar

44
Q

Embryonic folding for lung development

A

lateral and cranial-caudal folding occur simultaneously

45
Q

Where do the lungs develop from

A

they bud off of the foregut, initially forming the diverticulum which is surrounded by splanchnic LP mesoderm

46
Q

Embryonic stage of lung development

A

-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

47
Q

Pseudoglandular stage of lung development

A

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

48
Q

Bronchial divisions

A

primary bronchi - 1R, 1L
secondary bronchi (3R, 2R)
tertiary bronchi (20R, 18L)
terminal bronchioles (n= a lot)

49
Q

At the end of the pesudoglandular stage what does further development entail

A

lengthening, widening, and functional development of existing airway generations

50
Q

Canalicular stage of lung development

A

16 weeks to 25 weeks - functional lung development
-characterized of extensive vascularization and formation of the respiratory zones

51
Q

respiratory zones

A

where O2 from the lungs can diffuse into the capillaries for gas exchange
-includes the respiratory bronchioles, alveolar ducts and primitive alveoli

52
Q

Primitive Alveoli

A

inner surface of alveoli in lined with cuboidal cells
pulmonary capillaries form around the primitive alveoli

53
Q

Saccular stage of lung development

A

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

54
Q

Type 1 pneumocytes

A

squamous cells ideal for gas exchange

55
Q

Type 2 Pneumocytes

A

cuboidal cells ideal for surfactant secretion

56
Q

Surfactant

A

reduces surface tension caused by the air-water interface to prevent atelectasis

57
Q

Surface tension

A

layer of H2O that doesnt interact with gas bu exerts force on each other
tends to compress downwards

58
Q

Laplace’s law

A

collapsing pressure (P)=2T/r

59
Q

How does surfactant work to reduce surface tension

A

moves air-water interface and reduces surface tension by exerting a force upwards
-via hydrophobic/hydrophilic fatty acid composition

60
Q

Alveolar stage of lung development

A

-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

61
Q

When do fetal breathing movements occur around

A

15th week

62
Q

What is the percent increase in fetal breathing movements between 15 and 30 weeks

A

30%

63
Q

What does the fetus breath and why

A

amniotic fluid which helps to prepare the respiratory muscles and lungs for neonatal breathing

64
Q

Pulmonary vasoconstriction before birth

A

-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

65
Q

Changes at babys first breath

A
  • 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
66
Q

Changes after birth in respiratory system

A

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

67
Q

Parallel circualtion

A

both the right and left sides of the heart provide systemic blood flow

68
Q

Series circulation

A

the right side of the heart caries deoxygenated blood to the lungs and the left side of the heart becomes the systemic circualtion

69
Q

Infant respiratory distress syndrome

A

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

Growth and Maturation (8 decks)

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