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Anatomy > Embryology of the Respiratory System and clinical implications > Flashcards

Embryology of the Respiratory System and clinical implications Flashcards

1
Q

Stages of early respiratory system development

A

formation of trachea and bronchi
lung development
formation of pleural cavities
diaphragm development

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2
Q

What is the respiratory diverticulum?

A

lung bud

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3
Q

When and where does the respiratory diverticulum form?

A

around the 4th week
forms as blind-ending outgrowth from ventral wall of foregut
endodermal origin

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4
Q

When does the trachea develop?

A

during the 4th week

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5
Q

What happens for the trachea to form?

A

oesophagotracheal ridges fuse to form oesophagotracheal septum
laryngotracheal tube and oesophagus is separate

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6
Q

What does the laryngotracheal tube develop into?

A

larynx and trachea

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7
Q

Describe the structure of the laryngotracheal tube

A

inner lining: endoderm

outer lining: splanchnic mesoderm

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8
Q

What does the endoderm of the laryngotracheal tube give rise to?

A

epithelium and glands of trachea and pulmonary epithelium

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9
Q

What does the splanchnic mesoderm of the laryngotracheal tube give rise to?

A

cartilage, connective tissue and muscles

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10
Q

Stages of lung maturation

A
  1. pseudoglandular stage
  2. canalicular period
  3. terminal sac period
  4. alveolar period
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11
Q

When is the pseudoglandular stage?

A

5-16 weeks

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12
Q

What occurs in the pseudoglandular stage?

A

terminal bronchioles form
by the end: all major components of the lung has formed, except those needed for gas exchange
development of pleural cavities

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13
Q

Development of pleural cavities

A

pericardioperitoneal canals are connected to pericardial (primitive thoracic) and peritoneal (primitive abdominal) cavities
pericardioperitoneal canals become separated from the pericardial cavity by pleuropericardial folds

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14
Q

When do the pericardioperitoneal canals become completely separated?

A

remain connected to peritoneal (abdominal) cavity until closed by fusion of the peritoneal folds during formation of the diaphragm

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15
Q

When is the canalicular period?

A

16-26 weeks

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16
Q

What happens in the canalicular period?

A

lumens of bronchi and terminal bronchi enlarge
tissue becomes vascularised
by 24 weeks: each terminal bronchiole has formed 2 or more respiratory bronchioles
towards end: 1st terminal sacs form at end of resp. bronchioles

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17
Q

What are respiratory bronchioles characterised by?

A

cuboidal epithelium

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18
Q

When is the terminal sac period?

A

26 weeks - birth

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19
Q

What happens in the terminal sac period?

A

many terminal sacs form (primordial alveoli)
type 1 alveolar epithelial cells form
capillaries come into close contact with flat epithelial cells - start to blge into primordial alveoli
type 2 alveolar cells begin to form

20
Q

Type 1 alveolar cells

A

epithelial cells of the terminal sacs become flat and thin squamos cells from cuboidal
line alveolar sacs
allows efficient gas exchange

21
Q

Type 2 alveolar epithelial cells

A

rounded, secretory epithelial cells
line alveolar sacs
formed from end of 6th month
produce surfactant

22
Q

What is surfactant

A

produced by type II alveolar epithelial cells
phospholipid-rich fluid
forms monomolecular film over internal walls of the terminal sace and mature alveoli
lowers surface tension at the air-alveolar interface so alveoli don’t collapse due to change in pressure

23
Q

When is the alveolar period?

A

8 months - childhood

24
Q

What happens in the alveolar period?

A

increased production of surfactant
primordial alveoli increase in size
type I cells thinner and capillaries even closer association
postnatal increase in lung size: increased divisions to form repiratory bronchioles and continued prmordial alveoli production

25
Q

Changes in lungs before birth

A

amount of surfactant produced increases, mostly in last two weeks
breathing movements occur to stimulate lung development and respiratory muscles
amniotic fluid aspirated

26
Q

Changes in lungs at birth

A

lungs half-filled with liquid, removed by:

  1. pressure on thorax during delivery
  2. absorbed into circulation via pulmonary circulation
  3. absorbed into lymphatics

thin coating of surfactant left lining alveolar cell membranes

27
Q

Lungs of a stillborn

A

1st breath not taken, lungs have no air and are full of fluid and baby will sink in water

28
Q

What is the diaphragm?

A

musculotendinous dome-shaped partition that separates the thoracic and abdominal cavities

29
Q

What are the embryonic components of the formation of the diaphragm?

A

transverse septum
pleuroperitoneal membranes
dorsal mesentery of oesophagus
muscular ingrowth from lateral body walls

30
Q

What is the transverse septum?

A

sheet of non-continuous tissue (mesodermal in origin)

primordium of central tendon of diaphragm (non-muscular)

31
Q

Where and when does the transverse septum grow?

A

4th week
grows dorsally from ventrolateral body wall
forming liver is embedded in tissue
caudal to pericardial cavity, partially separating it from peritoneal cavity
ventral and lateral, not posterior

32
Q

When and where do the pleuroperitoneal membranes form?

A

5th week

form from the lateral wall of pleural and peritoneal cavities

33
Q

What do the pleuroperitoneal membranes form

A

forms posterior and lateral parts of the diaphragm

fuses with the transverse septum and dorsal mesentery in the 7th week

34
Q

What does the dorsal mesentery form?

A

medial region of the diaphragm
muscle bundles anterior to the aorta (in adults: Crura of the diaphragm)
not yet mature/muscularised

35
Q

What is the dorsal mesentery derived from?

A

myoblasts that have previously migrated into the dorsal mesentery of oesophagus

36
Q

Formation of the mature diaphragm

A

muscular ingrowth from lateral body walls
contributes muscle to peripheral region of diaphragm external to the region that is derived from the pleuroperitoneal membranes
by 12th week

37
Q

Give examples of defects and problems of the lungs and diaphragm

A

premature and Respiratory Distress Syndrome
oesophageal atresia and tracheoesophageal fistula
congenital cysts of the lung
congenital diaphragmatic hernia

38
Q

Premature baby

A

not enough surfactant
high surface tension at blood-air interface
risk of alveoli collapsing during expiration
RDS

39
Q

RDS

A

2% of newborns
rapid, laboured breathing
treatments (if known in advance): artificial surfactant and treatment with glucocorticoids to stimulate surfactant production

40
Q

Oesophageal atresia and tracheoesophageal fistula

A

abnormal separation of the oesophagus and trachea by the oesophagotracheal septum
more common in males
associated with other defects like congenital heart disease
most common: proximal blind end of oesophagus

41
Q

Atresia meaning

A

narrowing/withering away

42
Q

Fistula meaning

A

abnormal opening or passage

43
Q

Problem of most common oesophageal atresia and tracheoesophageal fistula

A

XS amounts of fluid in mouth/upper RT, gastric contents may reflux - into trachea and lungs
coughing and choking
pneumonia

44
Q

Congenital cysts of the lungs

A

terminal bronchi abnormally dilated, usually at periphery
small and numerous/few and large
problems: drain poorly, chronic lung infections

45
Q

Congenital diaphragmatic hernia

A

congenital absence of large area of diaphragm
due to: failure of fusion of pleuroperitoneal membrane with other components, posterolateral defect
problems: abdominal contents hemiated, hypoplastic lung, pressure on heart

Anatomy (9 decks)

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