Development of heart and respiratory system

ByDr. Abdul Waheed Ansari

Chairperson &Prof. Anatomy, RAKCODS. RAKMHSU.

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The learning outcomes for this embryology topics are

• Formation of primitive heart tube from the mesoderm.

• Five different chambers of embryonic heart and their transformation in to 4 chambers of adult heart.

• Common congenital forms of heart development- ASD, VSD, & Fallot’s Tetralogy.

• Development of larynx, trachea and lungs.

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Primitive heart tube

• The heart is the first organ to form within the embryo and this complex developmental process begins during the fourth week.

• Heart developmental abnormalities affect 8-10 of every 1000 births in the United States.

• The heart initially forms from two tubes located bilaterally of the trilaminar embryo in the cranial region.

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The image below shows the primitive tubes

developing in an embryo approximately 18 days

after conception

At the most cranial end of the embryonic disc these blood islands (splanchnic mesenchymal cells) are forming the primitive heart tube.

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Two endothelial heart tubes come together and fuse in

the midthoracic region to form the primordial

cardiac\heart tube- 22 days embryo

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There are five chambers in the primitive heart

From venous end to arterial end the five chambers are as follows:-

1. Sinus venosus

2. Primitive atrium

3. Primitive ventricle

4. Bulbus cordis

5. Truncus arteriosus

• The primitive heart begins to beat on22nd day of intrauterine life.

• The circulation does not start until days 27-29.

• The sinus venosus will transform into right atrium-smooth part.

• The primitive atrium will split and form rough parts of right and left atria of adult.

• The primitive ventricle develops into right and left ventricle in adult.

• The bulbus cordis get absorbed into smooth part of right and left ventricle.

• The truncus arteriosus will form the aorta and pulmonary trunk.

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Common congenital heart diseases

• This abnormality is Ventricular Septal Defect.

• There will be a hole between right and left ventricles

• 25% of CHD are VSD.

• VSD is more frequent in males.

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Tetralogy of Fallot’s

• The incidence of this abnormality is 9-14% of CHD.

• There are 4 components for this syndrome:-

1. pulmonary stenosis, 2. VSD, 3.dextroposition of aorta, 4. RV hypertrophy. • Results in cyanosis.

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Transposition of the Great Vessels

• It occurs in 10-11% of CHD.

• Aorta arises from the RV with the pulmonary trunk arising from the left.

• Most common cause of cyanotic heart disease in newborns

• This can be surgically corrected.

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Atrial Septal Defect

• This defect occurs in 6-10% of CHD.

• This defect is more common in females.

• Most commonly patent foramen ovale; can also be an ostium secundum defect, an endocardial cushion defect with ostium primum defect, sinus venosus defect, common atrium.

• Results in cyanosis due to right-to-left shunt.

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Development of larynx• The larynx is first seen as an outgrowth from the foregut during week 4 of

fetal development.

• The outgrowth of tissue is called the lung bud or the respiratory

diverticulum, which is a ventral diverticulum of endoderm that arises from

the floor of the foregut caudal to the pharynx.

• The lung bud forms a groove in the floor of the pharynx called the

laryngotracheal groove.

• The lung bud mesenchyme gives rise to the smooth muscles of the lower

respiratory system.

• The lung bud initially is in open communication with the foregut, but

eventually they become separated by indentations of mesoderm called the

tracheoesopheageal (or esophagotracheal) folds.

• In the 4th week of development, the tracheoesophageal folds fuse in the

midline to form the tracheoesopheageal septum, and it is here where the

foregut divides into the trachea ventrally and esophagus dorsally.

• The opening of the respiratory diverticulum into the foregut becomes the

laryngeal orifice.

•

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Development of cartilages and muscles of larynx

• The pharyngeal arches or branchial arches are the ridges like structures developing below the head region of the embryo during the 5th – 6th weeks of I.U.L.

• There are 6 branchial arches developing on either sides of primitive pharyngeal cavity.

• Each pharyngeal arch is covered by ectoderm, having a central core of mesoderm and lined internally by endoderm. In addition to mesenchyme derived from paraxial and lateral plate mesoderm, the core of each arch receives substantial numbers of neural crest cells, which migrate into the arches to contribute to skeletal components of the face.

• Each arch contains an artery, cartilage, nerve, & muscular component.

• Arches and Pouches form the face, tongue, lips, jaws, palate, pharynx and neck cranial nerves, sense organ components,& glands. 12/18/2014 13

Each arch will give rise to muscles,

cartilages, bones and ligaments

• The laryngeal cartilages and intrinsic muscles of larynx develops from 4th & 6th pharyngeal arches.

• The nerve of 4th arch is external laryngeal nerve.

• The cricothyroid muscle of larynx is the only intrinsic muscle visible outside the larynx and it is supplied by external laryngeal nerve, a branch of vagus nerve

• All intrinsic muscles of larynx are supplied by recurrent laryngeal nerve, branch of vagus. It is the nerve of 6th pharyngeal arch.

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Pharyngeal arches-1,2,3,4

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Pharyngeal arches that contributes to larynx

Pharyngeal Arch 4

• Associated with aortic arch 4, which contributes to the proximal segment of the right subclavian artery and the arch of the aorta.

• Innervated by CN X (superior laryngeal branch of the vagus nerve).

• The thyroid, cricoid, arytenoid,

corniculate and cuneiformcartilagesdevelop from mesoderm of4th arch.

The cricothyroideus muscledevelops from 4th arch.

Pharyngeal Arch 6

• Associated with aortic arch 6, which contributes to the proximal segments of the pulmonary arteries and ductus arteriosus (which becomes the ligamentum arteriosum in the adult).

• Innervated by CN X (recurrent laryngeal branch of the vagus nerve).

• Epiglottis develops from hypobranchial eminence.

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Oral cavity structures during embryonic development

• 1. Lateral lingual swelling

• 2. Tuberculum impar

• 3. Foramen cecum

• 4. Copula of His

• 5. Epiglottis swelling/Hypobranchialeminence

• 6. Laryngeal orifice

• 7. Arytenoid swellings

• 8. Pharyngeal arches

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References

• http://php.med.unsw.edu.au/embryology/index.php?title=Basic_Cardiac_Embryology

• http://php.med.unsw.edu.au/embryology/index.php?title=Intermediate_-_Primordial_Heart_Tube

• http://php.med.unsw.edu.au/embryology/index.php?title=Intermediate_-_Cardiac_Abnormalities

• http://www.cram.com/flashcards/embryology-cvs-1647352

• http://respiratory-system.weebly.com/larynx.html

• https://musom.marshall.edu/anatomy/grosshom/allppt/pdf/BranchialArchesLectureff.pdf

• https://web.duke.edu/anatomy/embryology/craniofacial/craniofacial.html

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