Test: Thorax - NEET PG MCQ

At lower border of T4, a ridge of cartilage is present called carina, which marks the bifurcation of trachea into two bronchi.

• At sternal angle of Louis arch of aorta begins (anteriorly) and ends (posteriorly), crosses from right to left.
• Azygos vein arches over the root of right lung to end in the superior vena cava at this level.

Cardiac jelly is secreted by the cardiac myocytes (myocardium) around the endothelial lining of heart tube and transforms into the connective tissue of endocardium.

• Heart beat begins by day 22 post-ovulation and can be detected by Doppler ultrasound.
• It is week 4 post-ovulation (or fertilization) and week 6 from LMP (Last Menstrual Period).

• Sinus venosus is the venous end of the heart tube having right and left horns.
• Each horn receives blood from following three pair of veins. Vitelline veins (from yolk sac), Umbilical veins (from placenta) and common cardinal veins (from body wall).

• Sinus venosus is a paired structure but shifts towards right associating only with the right atrium as the embryonic heart develops.
• The left portion shrinks in size and eventually forms the coronary sinus and oblique vein of the left atrium, whereas the right part becomes incorporated into the right atrium to form the sinus venarum (smooth part of right atrium).

• Right horn of sinus venosus contributes to sinus venarum (posterior smooth part of right atrium).
• Anterior part of right atrium is rough (derived from the primitive atrium).

Septum secundum grows down from the roof of the common atrium toward the atrioventricular endocardial cushions.

Fossa ovalis is an oval depression on the interatrial portion consisting of the valve of the fossa ovalis (a central sheet of thin fibrous tissue) which is a remnant of septum primum, and the limbus of the fossa ovalis (a horseshoe-shaped muscular rim), which is a remnant of the septum secundum.

Limbus (annulus) fossa ovalis is a horseshoe-shaped muscular rim, situated above fossa ovalis. It is a remnant of the septum secundum.

• Limbus fossa ovalis is the margin of foramen ovale (present in septum secundum).
• As viewed from right atrium, the floor of fossa ovalis is formed by septum primum.

• According to some authorities, pulmonary veins develop from the left atrial wall.
• There is no consensus about whether the pulmonary vein as a branch from the left atrium obtains a connection to the lung plexus or the pulmonary vein forms as a solitary vessel in the dorsal mesocardium and is only secondarily incorporated into the atrium.

• If the AP septum is not spiral, the great vessels are not spiral, and they open in the opposite ventricles (transposition of great vessels).
• The aorta arises from the right ventricle, and the pulmonary artery emerges leftward and posteriorly from the LV (two separate parallel circulations).

In tetralogy of Fallot infundibular stenosis occurs due to anterior deviation of the infundibular septum causing hypoplasia of the sub-pulmonary infundibulum, leading to narrowing of RVOT (Right Ventricular Outflow Tract).

• Patent ductus arteriosus carries the blood towards the lungs and promotes oxygenation thus, reduces cyanosis.
• AP septum anomalies like PTA, TGV and TOF present with right to left shunt, blood reaches systemic circulation without proper oxygenation, hence leading to cyanosis.

The pentalogy of Fallot is a variant of the more common tetralogy of Fallot, comprising the classical four features with the addition of an atrial septal defect/patent foramen ovale or patent ductus arteriosus.

• Anatomical closure of ductus arteriosus occurs within 2–12 postnatal weeks (1 month to 3 months).
• DA is closed by 8 weeks in 88% of children with a normal cardiovascular system.
• Authorities consider the patent ductus to be abnormal only after 3 months (12 weeks) of age.

• In fetal circulation, ductus venosus shunts a portion of the left umbilical vein blood flow directly to the inferior vena cava.
• It allows oxygenated blood from the placenta to bypass the liver.
• The only related option appears to be choice c.

• Scalenus posterior attaches to second rib.
• Other attachments on first ribs are: Subclavius, serratus anterior, costoclavicular ligament.

• Thoracic duct passes through superior thoracic aperture, but not between apex of lung and first rib.
• SVAN structures are present between first rib and apex of lung (medial to lateral): S - Sympathetic trunk, V- Vein (intercostal), A - Artery (superior intercostal), N – Nerve (T1 nerve).

• 10th rib do not articulate with sternum anteriorly (false rib).
• The first seven ‘true’ ribs connect to the sternum by costal cartilages, whilst the remaining lower five ‘false’ ribs either join the suprajacent (upper) costal cartilage (8–10) or ‘float’ free at their anterior ends as relatively small and delicate structures tipped with cartilage.

• Ribs 8 –10 are vertebro-chondral with no direct articulation to sternum.
• Their costal cartilages articulate with each other and with 7th costal cartilage.
• Ribs 11 and 12 have free anterior ends (floating ribs) and definitely they are never going to reach the sternum., but this statement is never mentioned in textbooks.

• Ribs directly articulate with vertebral body by costovertebral joint, with transverse process by costotransverse joint and with costal cartilage by costochondral joint.
• It is the costal cartilage which attaches the ribs to the sternum, hence the costosternal joint is a misnomer, and correctly should be mentioned as chondrosternal joint.

The first sterno-costal joint is an unusual variety of synarthrosis (fibrous) and is often inaccurately called a 1° cartilaginous (synchondrosis).

• Phrenic nerve arises from the anterior (ventral) primary rami of C-2, 3, 4, descends lying between the mediastinal pleura and fibrous pericardium.
• It provides motor supply to diaphragm and carries sensations from central portion of the diaphragm.
• Additionally, it also carries sensations from mediastinal pleura, pericardium and peritoneum.