Chapter 1 Fetal Lung Development

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Three stages of FETAL development

1 OVUM 2 EMBRYO 3 FETUS

OVUM Stage

0-2 weeks after gestation...Fertilized egg(Zygote) implants into uterine wall

EMBRYO Stage

2-8 weeks after gestation..Tissue layers begin to form.

FETUS Stage

8-40 weeks after gestation..Interanl Development begins and tissue function becomes more specialized.

Five stages of FETAL LUNG development

1 Embryonal 2 Pseudoglandular 3 Canalicular 4 Saccular
5 Alveolar

EMBRYONAL STAGE

Days 26-52 Lungs begin to emerge from pharynx as a "BUD" Trachea and 2 broncial buds forming the mainstem bronchi branching to segmental and subsegmental bronchi. Tracheosophageal septum form, Smooth muscle, veins and arteries develop AW epithelim begins to differentiate with influence from mesenchyme , Diaphragm begins to develop, seperating thoracic from abdominal cavities

PSEUDOGLANDULAR STAGE

Days 52-week 16.Lung resembles a gland, hence the name. .Conducting AW continue to develop, repeated subdivisions and branching thats sets pattern for the adult lungs.(only size will increase), Terminal bronchioles form, Respiratory portion of the AW is laid down and almost complete.(Pulmonary Acinus or respiratory bronchioles Type II cells develop(surfactant), cilia, goblet cells, submucosal glands cartilage and lymphaticus all begin to appear...AW, arteries and veins matching the adult pattern are established by the end of this stage.

Cilia, goblet &submucosal glands, cartilage and lymphaticus all begin to appear in this stage

PSEUDOGLANDULAR STAGE

what is established at the end of thePseudoglandular stage?

AW, arteries and veins mathing the adult pattern.

Canalicular Stage

Week 17-26...Development of vascular bed(capillaries) form around the alveoli for LIMITED gas exchange by week 22.,Type I(alveolar structural cells), Type II cells can be identified..Fetus can survive week 22-24, as lungs are beginning to be capable of gas exchange.

Saccular Stage

Week 26-36...terminal bronchioles widen to form smooth walled cylindrical structures(saccules) , Subdivide via secondary crests and form alveoli..second type of surfactant (Phosphocholine) is produced.
Alveoli form as early as 32 weeks, increasing gas exchange area potential.

Alveolar Stage

week 36-term Continuation of saccular stage
At birth, 20-150 million alveoli(50 average)
15-20% of adult alveoli present at birth
3-4mSquared of gas exchanging surface area at birth

Adult Lung

300 million alveoli,
70-80 msquared surface area..
most lung growth occurs in first 1.5 years of life...
alveoli continue to develop up to age 8.

Factors affecting prenatal lung growth...

Maternal starvation..Fetal hyoxia..High FiO2 causing BPF and hyaline membrane disease..Maternal Smoking..Diaphragmatic hernia, Diminished Respirations

Oligohydroamnious

reduced amniotic fluid, causing lung compression and lung hypoplasia

Tracheoesohageal fistula

an abnormal opening between the trachea and esophagus, this can occur during the embryonal stage caused by teratogens ( drugs, infections or chemicals.)

pulmonary hypoplasia

underdevelopment of the lung, again caused by teratogens.

congenital diaphragmatic hernia

failure of the diaphragm to completely from, allowing abdominal organs to enter the pleural cavity and compress the lungs, resulting in severe underdevelopment or hypoplasia of the lung.

Acinus

functional respiratory (gas exchanging) unit of lung, all alveoli are contained in the acinus.

Terminal bronchioles

part of the conducting airway, does not exchange gas....

respiratory bronchioles

continuation from each terminal bronchioles,. This marks the start of the gas exchange, because alveoli first appear in the respiratory bronchioles

Type I cells

important in the development of alveolar capillary membrane

Type II cells

involved with surfactant production

Type III cells

Microphage...WBC's clean the lung...

Leprechaunism

Abnormal lung development caused by abnormal carbohydrate metabolism

Down Syndrome

Fetal lung growth is normal, but Postnatal lung growth is abnormal, larger and fewer alveoli.

Fetal Lung Liquid

Essential for normal lung development...high in chloride and low in bicarb.
Fetal Lungs=secretory organs, produce 250-300 ml/day
80ml constantly fill the lungs, 15ml/hr move oud of the lung
Fluid produced during canalicular period
Removal of liquid essential after birth..lymphaticus will drain it away in several hrs.

Role of surfactant

Decrease alveoli surface tension, increasing compliance

Synthetic Surfactant

Exosurf

Animal Derived Surfactant

Curosurf, Infasurf, Survanta

DPPC

Dipalmitoyl Phosphatidyl Choline...Natural Surfactant, chemical compound, we all have.

Conditions that delay surfactant production

Acidosis, Hypoxia, Shock, Over/underinflation, mech. ventilation, Pulmonary edema, Hypercapnia

Conditions that accelerate fetal surfactatn production

Heroin addiction, premature rupture of membranes, placenta insufficiency, Maternal hypertension,

Diminished respirations

has a severe effect on lung growth, due to lack of stretch to lung.

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