development of the respiratory system Flashcards

1
Q

when does implantation occur?

what are the 2 layers that form and from where?

A
  • implantation occurs by days 7/9
  • two layers of cells form from the inner cell mass - epiblast and hypoblast (bi-laminar disc)
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2
Q

describe the process of gastrulation?

where do all 3 layers arise from?

A

formation of the 3 germ layers

  • all 3 layers arise from the epiblast via gastrulation that starts on day 17
  • ectoderm, endoderm and mesoderm
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3
Q

what are the 3 main things that the ectoderm gives rise to?

A
  • surface ectoderm (skin, tooth enamel)
  • neural tube (CNS)
  • neural crest (cranial and sensory ganglia)
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4
Q

what 3 things will mesoderm give rise to?

A

1) paraxial mesoderm (somites)

2) intermediate mesoderm (urogenital system)

3) lateral plate mesoderm (smooth muscle/connective tissue)

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5
Q

what will the endoderm give rise too?

A

gut tube
liver
pancreas
bladder
liver

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6
Q

describe the development of the body cavities and the role of mesoderm?

what does the parietal and visceral layers form?

what day does the happen?

A
  • the mesoderm develops into 3 parts, paraxial, intermediate and lateral plate mesoderm.
  • the lateral plate is divided into parietal (somatic) and visceral (splanchnic) by the development of the intra embryonic coelom.
  • parietal layer forms the body walls
  • visceral layers form connective tissue of respiratory system
  • day 21
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7
Q

what does the intra embryonic coelom form?

A

the intra embryonic coelom will form a horse shoe shape around the developing head (this is entrapped during folding)

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8
Q

what are the 2 folding planes of the embryonic disc?

A

1) cranio-caudally
2) laterally

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9
Q

what does lateral folding cause?

what will this cavity be lined with?

A
  • causes the closing of the body walls and the “entrapment” of intra-embryonic coelom into closed body cavity.
  • the cavity will be lined by somatic lateral plate mesoderm, gut tube/mesentery by visceral lateral plate mesoderm.
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10
Q

What do the 2 layers of the lateral plate mesoderm cover/fuse with during lateral folding?

What movement occurs during lateral folding?

What ends up being pinched?

What lines the yolk sac?

What does this form?

What 3 things will the primitive yolk sack form during development?

A

During lateral folding, the parietal layer of lateral plate mesoderm fuses with the ectoderm to form the surface ectoderm

  • The visceral layer of lateral plate mesoderm coves the endoderm
  • During lateral folding, the lateral parts of the tri-laminar disk start to move anteriorly and medially towards each other, with them both eventually meeting and fusing In the midline
  • This results in the primitive yolk sack being pinched (the yolk sac is lined by endoderm)
  • This process forms a gut tube from the endoderm/yolk sac, and a connection between the gut tube and the yolk sac called the vitelline duct

During development, the primitive yolk sack will form:
1) The gut tube
2) GU systems
3) Respiratory systems

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11
Q

When is lateral folding complete?

What has happened to the surface ectoderm?

What will the CNS develop from?

What will the surface endoderm end up forming?

What does the parietal layer of lateral plate mesoderm form?

What does the intraembryonic coelom form?

A

Lateral folding is complete when the lateral foldings have met anteriorly in the midline and fused

The surface ectoderm has detached itself from the neural groove to become the neural tube
The CNS will develop from the neural tube

The surface ectoderm will eventually form the serous membranes e.g pericardium, pleura, peritoneum

The parietal layer of lateral plate mesoderm will fuse with the ectoderm to form the thoracic wall/body walls (and parietal pleura)

The intraembryonic coelom forms body cavities (thoracic, abdominal, pelvic) in between the visceral and parietal lateral plate mesoderm
The diagram has been takin from a transverse section above the vitelline duct, so it can’t be seen

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12
Q

What is the dorsal mesentery?

What does the dorsal mesentery do?

What is inside the dorsal mesentery?

A

The dorsal mesentery is part of the visceral lateral plate mesoderm that extends between the posterior abdominal wall and the gut tube

The dorsal mesentery serves as the root of gut tube, and suspends the gut tube through attachment to the posterior abdominal wall

In the dorsal mesentery, we have the arteries that supply various parts of the gut tube

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13
Q

What is the diverticulum?

When does is appear?

What does the diverticulum develop into?

When do the tracheo-oesophageal ridges/folds grow?

How do they move as they grow?

What does the respiratory diverticulum divide into?

How is the gut tube divided up?

What does the foregut form?

A

The diverticulum is a growth that appears anterior to the gut tube in the midline

  • It appears at about week 4
  • The diverticulum develops into part of the respiratory system
  • The tracheo-oesophageal ridges/folds grow as the diverticulum grows
  • As these ridges/folds grow, they start to move towards each other, with the aim being to separate the gut tube from the respiratory diverticulum (with the exception of the laryngeal orifice – comes later)
  • The respiratory diverticulum will divide into 2 lung buds, which will grow, expand, and dilate to become part of the lungs
  • The gut tube is divided into the foregut, midgut, and hindgut
  • The foregut developed into the oesophagus, stomach, and part of the duodenum
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14
Q

what does the 2 plane folding cause?

A

the 2 lane folding will cause the development of the heart and septum transverse and the associated intra-embryonic coelom will move caudally

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15
Q

what happens to these primitive body cavities?

A
  • the continuous primitive body cavities must under go partitioning.
  • lung buds invaginate into pericardioperitoneal canals forming pleural cavities and pleuropericadial folds
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16
Q

what is septum transverse?

A

plays a role in the development of the diaphragm

17
Q

what does the pleuropericardial fold form?

A

it will form the fibrous pericardium

18
Q

what separates the pericardial and pleural cavities?

A

a ridge of mesenchyme = embryonic connective tissue

19
Q

describe the development of the diaphragm?

A
  • the diaphragm forms to seperate thoracic and abdominopelvic cavities
  • pleuroperitoneal membranes grow medially
  • fuse with mesentery of oesophagus (forms crura of diaphragm)
  • continue growth over septum transverse.
20
Q

what creates the central tendon?

what nerve accompanies?

what is it composed off?

A

you get a fusion area, so septum transverse will have the pleural peritoneal membranes growing over it.

  • peripherally a central tendon scaffold with migrating myoblasts (C3,4,5 somites)
  • phrenic nerve accompanies
  • composed of septum transversum, pleuroperitoneal membranes, mesentery of oesophagus and the body wall (myoblasts)
21
Q

what happens around day 28?

what do the tracheosophageal ridges do?

A

respiratory diverticulum (lung bud) develops

  • it is an out pouching of the forgot, this is the endoderm and visceral lateral plate mesoderm origin.
  • tracheoesophageal ridges fuse to form tracheoesophageal septum
  • separating the trachea and oesophagus (maintains communication via laryngeal orifice)
22
Q

what pharyngeal arches will contribute to the larynx?

what does each arch have?

A
  • pharyngeal arches 4 and 6
  • each arch will have a mesenchymal core with neural crest cells (giving rise to cartilage), ectoderm outer layer and endoderm inner layer
23
Q
A
24
Q

where is the internal epithelium of the larynx from?

what does the laryngeal muscles and cartilage come from?

A
  • the endoderm
  • the laryngeal muscles and cartilage will come from fungi of mesenchyme from arches 4 and 6
25
Q

hoe dow you get he lung segments?

what divisions take place for create the bronchial tree?

A

primary bronchial buds undergo divisions- lobar and bronchopulmonary segments

this rapidly fills the pericardial peritoneal canals

generational divisions take place to create the bronchial tree

26
Q

what are the 4 phases of lung development?

A

1) pseudo glandular period 5-16 weeks

2) canalicular period 16-26 weeks

3) saccular period 26 weeks to birth

4) alveolar period 8 months to childhood (8 years)

27
Q

what is the earliest time a baby can be born?

A

week 24 is the earliest the baby can be born prematurely and survive (lung development Is a major factor in survival) because development continuous after birth (6 more generations, tripling number in alveoli)

28
Q

phase 1 lung development

A

phase 1= pseudoglandular

weeks 5-16

branching up to terminal bronchioles (no respiratory bronchioles or alveoli)

28
Q

Why can embryos not survive in the first 2 stages of development?

When does surfactant start to be produced?

What is it produced by?

From what time onwards can the foetus survive?

Why can some babies that are delivered between 20-28 weeks survive while others cannot?

A

Embryos can’t survive during the first 2 stages of development since surfactant is required for breathing and has not been produced during these stages

From 20 weeks, type 2 pneumocytes (type II alveolar cells) begin to secrete surfactant

From 28 weeks and onwards the foetus can survive, as there is now enough surfactant to support life

Between 20 – 28 weeks, some babies delivered during this period can survive depending on the amount of surfactant produced, which comes down to anatomical variation and will differ from case to case

29
Q

phase 2 lung development

A

phase 2 = canalicular

week 16-26

form primitive alveoli with cuboidal epithelium, capillaries also start developing

30
Q

phase 3 lung development

A

phase 3 = saccular stage

week 26 - birth

increased alveoli and respiratory bronchioles and capillaries, epithelial changes, formation of type 1 and type 2 pneumocytes, surfactant production.

31
Q

phase 4 lung development

A

phase 4= alveolar phase

birth to 8 years

  • increased number of alveoli, divisions/partitions within alveoli increasing surface area
32
Q

what are pneumocystes?

A

alveolar epithelium

33
Q

what are the 6 types of congenital abnormalities?

A

1- congenital diaphragmatic hernia

2- oesophageal atresia and tracheosophageal fistula

3- respiratory distress syndrome

4- congenital pulmonary airway malformation

5- supernumerary lobules

6- ectopic lobules

34
Q

what is a congenital diaphragmatic hernia?

describe the treatment?

A
  • posterolateral (Bochdalek) in 95% of cases
  • parasternal (morgagni) in 2% of cases
  • abdominal organs can enter thoracic cavity, preventing lungs from developing fully

intervention is through fetoscope end-liminal tracheal occlusion

35
Q

describe oesophageal atresia and a tracheosophageal fistula?

what other defects may it accompany?

A

1 in 3000 births have a defect in partitioning of the trachaeosopheal septum

  • can be diagnosed in utero by having excess amniotic fluid
  • surgical correction after birth

may accompany other defects like:
- VACTERL association:
vertebral anomalies
anal atresia
cardiac defects
traclaesopheal fistula
oesophageal atresia
renal anomalies
limb defects

36
Q

what is respiratory distress syndrome
how is it managed

A
  • premature birth with insufficient surfactant
  • alveoli are therefore in a collapsed state
    20% mortality

managed by artificial surfactant or giving mother glucocorticoids to stimulate surfactant.

37
Q

what is congenital pulmonary airway malformation

A

1 in 30,000

  • a lobe is replaced by non functioning cystic tissue
  • often asymptomatic (75%)
  • surgical removal after birth
38
Q

What is a fistula?

What is the most common tracheooesophageal defect?

What are tracheooesophageal fistulas caused by?

What will happen to the trachea with the most common defect?

What will happen if the baby tries to feed?

What are other common fistulas?

A

A fistula is an abnormal connection between two body parts, such as an organ or blood vessel and another structure

The most common tracheooesophageal defect is a tracheooesophageal fistula, where there is no connection to the proximal gut tube (oesophagus), and an abnormal connection between the distal gut tube and the trachea (A on diagram)

This type of fistula accounts for 90% of tracheooesophageal defects

Tracheooesophageal fistulas are formed by the failure of the fusion of the tracheooesophageal ridge while separating the trachea from the gut tube

With the most common defect, contents can move back up into the trachea, causing chemical pneumonitis, as the acid from the stomach will damage the respiratory epithelium lining the trachea

If the baby tries to feed, it will reflux/vomit the food back up