L10 Development of the Respiratory System

Question 1

Around what day does implantation of the embryo take place?

Answer 1

Day 6

Question 2

Around day 8, the cell mass differentiates into 2 distinct layers. What are these layers called?

Answer 2

The hypoblast and epiblast.

Together these layers form the bilaminar embryonic disc.

Question 3

True or false: When the blastocyst binds to the wall of the endometrium of uterus (circa 6 days), it binds on the side that contains the inner cell mass.

Answer 3

True

Question 4

Why does the blastocyst always bind to the endometrium on the side where the inner cell mass is located?

Answer 4

The inner cell mass secretes hormones that promote the activation of specific binding proteins in the adjacent trophoblasts. These binding receptors are not active in the other trophoblasts.

Question 5

By day 9, the hypoblast cells have flattened and migrated to form a membrane around the inner surface of the blastocyst. What is this membrane called?

Answer 5

Exocoelomic membrane

Question 6

Gastrulation takes place in which week of gestation?

Answer 6

Week 3

Question 7

True or false: Cells in the yolk sac develop into the gonads and parts of the GI tract

Answer 7

True

Question 8

What occurs during gastrulation?

Answer 8

The bilaminar disc develops into trilaminar structure made up of the three primary germ layers:

Ectoderm
Mesoderm
Endoderm

Question 9

What does each primitive germ layer give rise to?

Answer 9

Ectoderm: skin and nervous system

Mesoderm: Muscle and bone

Endoderm: Epithelial lining of GI tract and many organs

Question 10

In week three of gestation, what forms on the dorsal surface of the anterior region of the embryo?

Answer 10

Oropharyngeal membrane

Question 11

In week three of gestation, what forms on the dorsal surface of the posterior (tail) region of the embryo?

Answer 11

Cloacal membrane

Question 12

What occurs in week 4 to connect the oral cavity (mouth) to the pharynx and the GI tract?

Answer 12

Oropharyngeal membrane breaks down

Question 13

What occurs in week 4 to form the openings of the anal, urinary and reproductive tracts?

Answer 13

Cloacal membrane breaks down

Question 14

Why does embryonic folding occur?

Answer 14

The various regions of the embryo grow at different rates.

Folding in the medial plane gives rise to the head and tail, whilst lateral folds give rise to the coelom and pinch off the yolk sac to form the primitive gut.

Question 15

What are the three regions of the primitive gut?

Answer 15

Foregut, midgut, and hindgut.

Question 16

At the time of embryonic folding several arches develop on either side of the head, as do internal pharyngeal pouches. From where does the respiratory system develop?

Answer 16

Ventral wall of the foregut, and fourth and sixth pharyngeal arches.

Question 17

During week 4, __1__ bud or __2__ diverticulum appear as outgrowths from the ventral wall of the foregut.

Answer 17

1) lung

2) respiratory

Question 18

Initially, the lung bud and foregut share a common opening, but they become separated by what structure(s)?

Answer 18

Oesophagotracheal ridges

Question 19

Oesophagotracheal ridges fuse to form what structure, that divides the foregut into the oesophagus (dorsal) and trachea (ventral)?

Answer 19

Oesophagotracheal septum

Question 20

True or false: The lining of the larynx is endodermal in origin, but the muscles and cartilages are mesodermal.

Answer 20

True.

The muscles and cartilages of the larynx arise from the mesenchyme (mesoderm) of the fourth and sixth pharyngeal arches.

Question 21

What are the embryonic origins of the thyroid cartilage, cricoid cartilage and arytenoid cartilage?

Answer 21

These cartilages arise from the mesenchyme (mesoderm) of the fourth and sixth pharyngeal arches.

Question 22

How do the true and false vocal cords form?

Answer 22

As the laryngeal cartilages form the laryngeal epithelium proliferates and temporarily blocks the lumen of the of the diverticulum. This is followed by vascularisation and recanalisation resulting in the formation of the laryngeal ventricles, which in turn give rise to the true and the false vocal cords.

Question 23

Following development of the left and right primary bronchi in week 5, the left develops and forms how many secondary bronchi?

Answer 23

2

Question 24

Following development of the left and right primary bronchi in week 5, the right develops and forms how many secondary bronchi?

Answer 24

3

Question 25

How many tertiary bronchi are formed as each secondary bronchus extends into the body cavity?

Answer 25

10 on the right, 8 on the left.

These tertiary bronchi give rise to the bronchopulmonary segments of the lungs.

Question 26

True or false: The bronchial tree continues to develop postnatally, with an additional 6 divisions taking place.

Answer 26

True.

Question 27

What are pericardioperitoneal canals?

Answer 27

Narrow structures either side of the foregut and developing heart. They develop into the pleural cavities and fill with pleural fluid.

Question 28

From where do the parietal and visceral pleura arise?

Answer 28

Visceral pleura is derived from the mesoderm covering the outside of each developing lung.

Parietal pleura is derived from the mesoderm covering the inner surface of the body wall.

Question 29

What changes do the respiratory epithelial cells undergo in month seven?

Answer 29

Month seven the epithelial cells start to flatten into type I alveolar epithelial cells and become closely associated with blood and lymph capillaries, and gas exchange is possible. At same time type II cells secrete surfactant. Lungs are filled with fluid.

Question 30

What happens to the lung fluid at birth?

Answer 30

It is reabsorbed

Question 31

True or false: The lungs usually stop growing around 4 years old.

Answer 31

False.

The lungs continue to grow until about year 10 of postnatal life.

Question 32

What is oesphageal atresia?

Answer 32

Developmental disorder that results in the oesophagus terminating in a blind-ended passage.

Question 33

What is tracheoesophageal fistula?

Answer 33

Developmental disorder that results in an abnormal opening between the oesophagus and the trachea.

Question 34

True or false: Oesophageal atresia and tracheoesophageal fistula occur together in 90% of cases where at least one is present.

Answer 34

True.

They occur in about 1/3000 births, and usually together.

Question 35

Developmental abnormalities usually occur in association with other conditions. What does the acronym VACTERL stand for?

Answer 35

Vertebral
Anal atresia
Cardiac
Traceoesophageal fistual
Esophageal atresia
Renal
Limb

Question 36

Congenital cysts arise due to abnormal budding of the diverticulum and results in dilated, poorly vascularised terminal or larger bronchioles.

How do these appear on a radiograph?

Answer 36

Gives the lung a honeycomb appearance

Question 37

Congenital cysts arise due to abnormal budding of the diverticulum and results in dilated, poorly vascularised terminal or larger bronchioles.

Treatment involves respiratory support, antibiotics, and surgery to remove the bad lobe. Why is it possible to remove a lung lobe?

Answer 37

Each lobe has its own vascular and nervous supply.

Question 38

Why does respiratory distress syndrome occur? Who is at most risk?

Answer 38

Occurs because of insufficient surfactant in the lungs.

Premature babies (not enough time to produce the type II alveolar cells and make surfactant) and babies from diabetic mothers (beta-corticoids stimulate alveolar type II cells, and diabetes lowers b-corticoid levels) are at higher risk.

Question 39

From what does the respiratory system develop?

Answer 39

At the time