Anatomy and Embryology: Sympathetic Chain, Cardiac Development, Respiratory System, and Diaphragm

Flashcards covering the course and anatomy of the thoracic duct and sympathetic chain, embryology and anomalies of the heart, respiratory development, and diaphragm anatomy.

Where does the thoracic duct originate, and through which opening does it enter the thorax?

The thoracic duct begins at the upper end of the cisterna chyli at the lower border of $T12$ and enters the thorax through the aortic opening.

At what vertebral level does the thoracic duct incline to the left, and where does it terminate?

It inclines to the left opposite $T5$ and terminates at the root of the neck in the angle formed by the junction of the left subclavian and internal jugular veins.

Which body region is drained by the right lymphatic duct rather than the thoracic duct?

The right upper quadrant of the body.

How many ganglia are in the thoracic sympathetic trunk, and how is the Stellate ganglion formed?

The thoracic part contains $12$ ganglia (sometimes $11$ due to fusion of ganglia $11$ and $12$). In $75\%-80\%$ of people, the first thoracic ganglion fuses with the inferior cervical ganglion to form the Stellate ganglion.

What are the segmental spinal origins of the greater, lesser, and least splanchnic nerves?

Greater splanchnic nerve: $T5-T9$; Lesser splanchnic nerve: $T10-T11$; Least splanchnic nerve: $T12$.

What four clinical signs characterize Horner syndrome resulting from sympathetic chain injury?

$1.$ Ptosis (eyelid drop), $2.$ Myosis (constriction of the pupil), $3.$ Anhydrosis, and $4.$ Enophthalmos.

Which three constrictions subdivide the primary heart tube, and what four chambers do they create?

Three constrictions subdivide the primary heart tube into the sinus venosus, primitive atrium, primitive ventricle, and bulbus cordis.

Which embryonic origins give rise to the endocardium/myocardium versus the great vessel septa/smooth muscle?

Cardiogenic mesoderm gives rise to the endocardium and myocardium, while neural crest gives rise to the septa that separate the great vessels and the smooth muscle of the great arteries.

What adult cardiac structures develop from the left horn, right horn, and median part of the sinus venosus?

The left horn forms the coronary sinus, while the right horn and median part are absorbed into the primitive common atrium to form the sinus venarum.

What structures derive from the upper and lower parts of the right venous valve of the sinoatrial orifice?

The upper part forms the lower part of the crista terminalis, while the lower part forms the valves of the inferior vena cava ($IVC$) and coronary sinus.

How is the septum intermedium formed during heart development?

It is formed by two mesenchymal proliferations called endocardial cushions (ventral and dorsal) in the atrioventricular canal that grow toward each other and fuse.

How do the septum primum and septum secundum interact to close the foramen ovale at birth?

At birth, pressure increases in the left atrium, pushing the septum primum against the septum secundum, thereby closing the foramen ovale.

What adult ventricular structures derive from the middle part (conus cordis) and proximal part of the bulbus cordis?

The middle part (conus cordis) forms the infundibulum (pulmonary infundibulum) of the right ventricle and the aortic vestibule of the left ventricle; the proximal part forms most of the right ventricle.

On what timeline does the human embryonic heart begin beating, and when is it fully formed?

The heart begins to beat $22-23\text{ days}$ after fertilization and becomes fully formed in the $9\text{th}-10\text{th}\text{ weeks}$.

What cardiac positioning anomaly occurs if the heart tube bends to the left instead of the right?

Dextrocardia, in which all chambers of the heart and associated blood vessels are reversed as a mirror image.

What percentage of individuals exhibit a probe patent foramen ovale?

$20\%-25\%$ of people.

What four characteristic cardiac defects define Tetralogy of Fallot?

Pulmonary stenosis, right ventricular hypertrophy, ventricular septal defect ($VSD$), and an overriding aorta.

What embryological defect causes Transposition of the Greater Arteries (TGA)?

The conotruncal septum fails to follow its normal spiral course and instead runs straight down, causing the aorta to connect to the right ventricle and the pulmonary trunk to connect to the left ventricle.

What distinguishes preductal coarctation of the aorta from postductal coarctation?

In preductal coarctation, the narrow segment of the aortic arch is proximal to the ductus arteriosus ($DA$) entrance and the $DA$ persists; in postductal coarctation, the narrow segment is distal to the $DA$ entrance and the $DA$ usually obliterates.

When and where does the lung bud arise during embryogenesis?

The lung bud arises at the $4\text{th}\text{ week}$ as an outgrowth from the ventral wall of the foregut.

Which germ layers form the epithelium versus the cartilaginous and muscular components of the respiratory tree?

The epithelium of the larynx, trachea, bronchi, and lungs develops from foregut endoderm, whereas the cartilaginous, muscular, and connective tissue components derive from surrounding splanchnic mesoderm.

How many generations of bronchial tree subdivisions form before and after birth?

$17$ generations of subdivisions occur before birth, and $6$ additional generations form after birth.

What causes neonatal Respiratory Distress Syndrome?

Failure of the alveoli to ventilate due to the absence of surfactant.

What four mesodermal structures unite to form the diaphragm?

$1.$ Septum transversum and cervical myotomes, $2.$ The two pleuro-peritoneal membranes, $3.$ Mesoderm of the chest wall, and $4.$ Mesentery of the esophagus and mesoderm around the aorta.

What is the origin, sphincteric role, and vertebral level of the right crus of the diaphragm?

The right crus arises from the upper $3$ lumbar vertebral bodies and intervertebral discs; some of its fibers encircle the esophageal opening at $T10$ and act as a sphincter.

What structures pass through the aortic opening of the diaphragm, and what is its vertebral level?

Located in the midline behind the median arcuate ligament at the $T12$ level, it transmits the aorta (to the left), thoracic duct (in between), and azygos vein (to the right).

What structures pass through the esophageal opening of the diaphragm, and what is its vertebral level?

Located $1\text{ inch}$ to the left of the midline in the right crus at the $T10$ level, it transmits the esophagus, $2$ vagi, and esophageal branches of the left gastric vessels.

What structures pass through the inferior vena cava (IVC) opening of the diaphragm, and what is its vertebral level?

Located $1\text{ inch}$ to the right of the midline in the central tendon at the $T8$ level, it transmits the $IVC$, right phrenic nerve, and lymphatics.

Which embryological structure forms the central tendon of the diaphragm, and what is its motor innervation?

The central tendon is formed by the septum transversum (invaded by myotomes from $C3, C4, C5$ somites), and it receives motor supply from the right and left phrenic nerves ($C3, C4, C5$).

What developmental failure leads to Congenital Diaphragmatic Hernia of Bockdalek?

Failure of the pleuro-peritoneal membranes to close the pericardio-peritoneal canals.