Ga2 - Development Of The Respiratory System

Front 1

The respiratory system develops from 2 different entities

Back 1

the respiratory diverticulum (lung bud) and the splanchnic mesoderm

Front 2

Respiratory diverticulum arises as a what and what does it expand into?

Back 2

Respiratory diverticulum arises as a mid-line evagination of foregut

Respiratory diverticulum expands into surrounding SPLANCHNIC MESODERM (It grows away from the midgut into the surrounding mass of mesenchyme (embryonic connective tissue) which is the splanchnic mesoderm)

*Remember the splanchinic mesoderm is everything else that isn’t luminal lining of glands

Front 3

Spanchnic Mesoderm gives rise to what (2)

Back 3

The splanchnic mesoderm is important because it gives rise to the mural structures (“in the wall of”) and visceral organs in the thorax and abdomen

Front 4

Embryological Origins in Respiratory System

Back 4

STUDY CHART ON SLIDE 6!

Notes:
• The respiratory diverticulum and the splanchnic mesoderm are the main players in respiratory system formation, but the bone marrow and neural crest also contribute
• The foregut is lined by endoderm, so we can think of the lungs/trachea as a glandular diverticulum off of the gut tube (think of the lungs as a surfactant secreting “gland”)
• All the cells in the entire airway and gas exchange surfaces within respiratory system are derived from endoderm
• The splanchnic mesoderm gives rise to everything else you find in the wall outside the respiratory epithelium
• The neural crest makes a minor contribution to the respiratory system, but significant because the regulatory APUD cells/Kulchitsky cells are derived from it

Front 5

What Main Structures Arise from Respiratory Diverticulum (2)

Back 5

Respiratory Diverticulum:
-Airway epithelium, including glands
-Alveolar epithelium

Front 6

What Main Structures Arise from Splanchnic Mesoderm (6)

Back 6

Splanchnic Mesoderm:
-Lamina propria
-Mural cartilage
-Mural smooth muscle
-CT, blood vessels, lymphatics

Front 7

tracheoesophageal septum - forms between what and does what to those 2 things

Back 7

The tracheoesophageal septum forms in between the trachea and esophagus to eventually separate them so that the respiratory and GI system are separated

Front 8

The respiratory diverticulum will bifurcate into what

Back 8

The respiratory diverticulum forms as a blind-ending sac that will bifurcate into LUNG BUDS as shown in the last structure

Front 9

Lung buds are the precursor to what

Back 9

The lung buds are the precursor to the mainstem bronchi and the lungs themselves

Front 10

Traceoesophageal Fistula (TEF) - what is it, what does infant with TEF do, inflammation where, how is it corrected?, how is it caused?

Back 10

-A fistula (pl. fistulae) is defined as an abnormal connection from one epithelial surface to another, derived from Latin word for “pipe”

-Infant with most common kind of TEF will vomit undigested milk soon after feeding – there won’t be bile present because there is no digestion

-May have inflammation of trachea and lungs because of gastric reflux into respiratory system.

-Corrected surgically.

-TEF caused when the tracheoesophageal septum formation is abnormal (many ways).

Front 11

Types of Traceoesophageal Fistula - blind-ending esophageal pouch: what happens to child, surgically repaired how?

Back 11

(most common type) blind-ending esophageal pouch proximally with the distal portion of esophagus connected to the respiratory system
-this child will vomit easily and have pulmonary and tracheal inflammation because of acid reflux from the stomach
-surgically, you would disconnect the distal portion of the esophagus from the trachea and reconnect it with the upper portion and close up the trachea

Front 12

Types of Traceoesophageal Fistula - disconnected esophagus: what happens to child, surgically repaired how?

Back 12

disconnected proximal and distal portions of the esophagus, no connection to respiratory system
-this child will vomit easily (undigested milk), but will not have pulmonary inflammation
-surgically, just reattach the proximal and distal portions of the esophagus

Front 13

Types of Traceoesophageal Fistula - esophagus connected to the respiratory system: what happens to child

Back 13

proximal and distal portions of esophagus connected to the respiratory system
-this case is especially bad because milk will enter the respiratory system which will induce gagging/coughing and vomiting of undigested milk

Front 14

What type of milk will the child be vomiting?

Back 14

• The hallmark of this disease is that the child will be vomiting undigested, non-bile stained milk

Front 15

There are other types of abnormalities

Back 15

the food the infant will vomit will be bile-stained if there was a constriction downstream from bile duct and pancreatic duct.

• If there is a constriction in the pyloric area upstream from bile duct, the infant will still vomit, but partially digested food that is non-bile stained

Front 16

Reciprocal Inductive Interaction - what does the Respiratory diverticulum cause?

Back 16

Respiratory diverticulum causes region-specific splanchnic mesodermal differentiation

Front 17

Reciprocal Inductive Interaction - what does the Splanchnic Mesoderm cause? Both of them working together leads to what?

Back 17

Splanchnic mesoderm causes region-specific branching and epithelial differentiation.
Splanchnic mesoderm sends out message to respiratory diverticulum to branch (series of dichotomous branchings).

• These two structures need to work together by reciprocal inductive interaction, they cause region-specific differentiation in each other

Front 18

What do the proximal and istal portions include when splanchnic mesoderm causes epithelial differentiation

Back 18

Splanchnic mesoderm will cause epithelial differentiation too – the proximal portion will induce PCC epithelium while the distal portion will induce Type I and II cell

Front 19

Lungs Expand into what and how, leading to creation of what, what 2 pleura cover what surfaces

Back 19

-Lung buds branch and expand into intraembryonic coelom (a precursor to the body cavity)

-As they do so, they carry splanchnic mesoderm with them

-Lung buds expand into coelom, leading to creation of thoracic cavities

-Visceral pleura covers surface of developing lungs

-Parietal pleura covers thoracic wall

-Space between them is thoracic cavity

Front 20

Respiratory Diverticulum - from what, branches how many times to form what

Back 20

-Simple bud from FOREGUT

-Branches first time to form main stem bronchi

-Braches again to form lobar bronchi (3 on right, 2 on left)

-Branches about 20 more times to form about 22 generations of branches to alveoli = 2^22 alveoli -> huge surface area for gas exchange and many alveoli

Front 21

Histogenesis of Lungs - Pseudoglandular Period: how many weeks in, what is formed (2)

Back 21

5-16 weeks, up to terminal bronchioles (TB) , no respiratory bronchioles (RB) or alveoli (A) , few blood vessels (BV)

Front 22

Histogenesis of Lungs - Canalicular Period: how many weeks in, what is formed (2)

Back 22

16-26 weeks, terminal bronchioles form respiratory bronchioles and alveolar ducts (AD), blood vessels distant

Front 23

Histogenesis of Lungs - Terminal Sac Period: how many weeks in, what is formed (2)

Back 23

26-40 weeks, more alveolar ducts, alveolar sacs (AS) form, some type II cells (tII), BV close

Front 24

Histogenesis of Lungs - Alveolar Period: how many weeks in, what is formed

Back 24

32-childhood, alveoli (A) present, many tII, BV protrude into A

Front 25

Respiratory Distress Syndrome I - most common cause of what?, due to what?, born before what types of cells differentiate?

Back 25

-Most common cause of death in premature infants

-Due to functional immaturity of lungs

-Born before type II cells differentiate

-Severe prior to 28 weeks

-Declining severity with increasing gestational age after 28 weeks

(When born before Type II cell differentiation begins, the alveoli are collapsed due to lack of surfactant. There is a rapid decline in severity post 28 weeks because Type II cell differentiation begins.)

Front 26

Respiratory Distress Syndrome II - also known as what, premature infants show what symptoms?

Back 26

-AKA Hyaline Membrane Disease

-Premature infant showing:
--Cyanosis, low pO2, high pCO2
Tachycardia,
--Grunting noises from effort to breath
--Clavicular depression
--Dense lungs on chest x-ray, atelectasis

Front 27

Lipids in Amniotic Fluid - what are the 2 main lipids found, what is their ratio relationship to type II cell maturation

Back 27

-Fetal breathing mixes contents of alveoli with amniotic fluid

**Lecithin (L) is chief phospholipid in surfactant

-Lecithin values begin to increase rapidly at 28 weeks as type II cells begin to secrete surfactant

-Another lipid, Sphingomyelin (S) remains low and constant during gestation

-Therefore, as type II cells mature, L/S ratio increases

Front 28

Prenatal Diagnosis of RDS - what needs to be found where, how can the ratio be measured and what does this value tell?

Back 28

-Lecithin in amniotic fluid
-L/S ratio can be measured by amniocentesis
-This value tells you about state of fetal lung maturity and therefore risk of RDS

Front 29

Prevention - 2 things prescribed, what does each thing do for prevention?

Back 29

-If L/S ratio low and delivery is threatened, treat mother with bed rest and glucocorticoids

-BED REST reduces chances of premature delivery and thus risk of RDS

-GLUCOCORTICOIDS accelerate type II differentiation and thus reduce risk of RDS

-Check L/S ratio during bed rest period – when high enough, perform an immediate Caesarean section

Front 30

Treatment of RDS - supply what 2 things to patient and how do they help

Back 30

-Supply Artificial Surfactant in aerosol
-Supply Extra O2
-Inflation of lungs and air in alveoli triggers type II cell differentiation
-First day is most critical for newborn’s survival