King Faisal University College of Applied Medical Sciences

Respiratory Care DepartmentMSRT411: Perinatal and Pediatric Respiratory Care

Embryonic Development of Pulmonary System

Ghazi Alotaibi, PhD, RRT

Lec01-Sep13

The Beginning of Human Life

• Fertilization (union of perm and ovum) occurs in the fallopian tube.

• Duration of pregnancy is 9 calendar months (40 wks).

• Three Stages of Human Development:

a. Period from conception to complete implantation (about 2 wks)--- OVUM

b. End of ovum stage to around 55 days-EMBRYO.

-- major organ systems are developed in this stage.

-- drug, infections, radiation can affect embryo in this sage.

c. End of embryonic period to end of pregnancy -- FETUS.

-- major organs continue to grow

• The fertilized ovum starts cellular division as it travels through the fallopian tube toward the uterus.

• Enter the uterus when it reaches 16-50 cells.

• Fluid starts to gather around the ovum

• Ovum attaches to the lining of the uterus (endometrium) to start implantation.

• Cells start to grow and differentiate.

Development of Pulmonary System

• Five Stages of Lung Development:1. Embryonic Stage.

2. Pseudoglandular Stage.

3. Canalicular Satge.

4. Saccular Stage.

5. Alveolar stage.

1. Embryonic Stage.

• From day 26- day 52.

• At day 26 following conception, lung emerges as a bud from the pharynx.

• Lung bud elongates and forms 2 bronchial buds and trachea.

• Separated from Esophagus.

• More divisions continue.

## By the end of Embryonic Stage:• Major airways have developed (how many

branches in R and L?)

• Pulmonary arteries and veins start to develop.

• Diaphragm start to develop.

2. Pseudoglandular Stage• From day 52- day week 16.• Further divisions leads to completion of the entire

conducting system. • Once complete, they grow in size.• Cilia appear in the trachea, main bronchi, and peripheral

airways. • Goblet cells and submucosal glands start to grow. (what is

the function of Goblet cells?)• Smooth muscles surrounding the airways start to grow.• Cartilages start to develop.• Lymphatic system appears in lung and hilar region.

3. Canalicular Stage

• From Wk 17- Wk 28.• Capillaries (vascular channels) begin to approximate airway

passages and form a capillary network.• The acinar unit (What are they?) start to develop.• Type I and Type II cells start to appear. (What are their

functions?).• Surfactant is produced (immature at this stage)• By the end of this period: the air-blood barrier is thin

enough to support gas exchange.

During Canalicular Stage, a terminal bronchiole leads to a prospective acinus.

4. Saccular Stage

• Wk 29- Wk 36.• Small sacs (saccules) appears and subdivide by crests

into subsaccules.

5. Alveolar Stage

• Wk 36 –term• Subsaccules develop into alveoli.• !! Alveoli can be present at the end of stage 4.• Mature Surfactant is produced.

• At Birth:• Average 50 million alveoli present. (reported number varies!)

• Represents only 15-20% of adult alveoli.

Lung Growth After Delivery

• Lungs continue to grow during infancy and childhood (up to 8 years).

• After Birth Lung Development:• Alveoli increase 6-fold• Lung weight increases 20-fold• Alveolar surface area increases 21-fold

Surface Tension and the Role of Surfactant

• When a liquid-gas interface exist, the liquid molecules are strongly attracted to each other.

• This cohesive force at the liquid-gas interface is called “Surface Tension”.

• Surface tension leads to collapse of alveoli.

• Surfactant lowers surface tension by lining at the liquid-gas interface and reducing cohesive forces.

Fetal Lung Fluid

• Fetal lungs produce 250-300 ml of liquid per day.• Fluid also flows from lung microcirculation into airspaces. • Lung fluid is produced during intrauterine life until shortly

before delivery. • Fetal lung fluid flows from terminal respiratory units through

conducting airways to pharynx.• Then, it is swallowed or excreted to the amniotic fluid.• Function: To maintain airway open• (What is the composition of Feral Lung Fluid?)

Fetal Lung Fluid

• It is important that the lung fluid is completely evacuated from lungs at birth (why?)

• During vaginal delivery, 1/3 of fluid is removed out by squeezing effect. Lymphatic system absorbs the remaining.

• What happen to fetal lung fluid in neonates who are delivered by cesarean section??

Important Terms

• Neonates: from delivery to first month of life.

• Infant: 1 month to 1 year of life.

• Child: above 1 year to puberty.

Reading Assignment

• Chapter 1 in Czervinske and Barnhart