Introduction to thorax

some very basics information about thorax. anatomy of ribs and sternum is excluded in this pdf.

1. Dr.Ritika Dixit BAMS, MD (AYU .) Associate proffessor dept. of Rachana Sharir Introduction to the Thorax

2. INTRODUCTION The trunk of the body is divided by the diaphragm into an upper part called the Thorax , and a lower part called the Abdomen. The thorax is supported by a skeletal framework, thoracic cage. The thoracic cavity contains the principal organs of respiration – the lungs and of circulation- the heart.

3. S keleton of Thorax It is also known as thoracic cage. Thoracic Cage is a skeletal framework which supports the thorax. It’s nature is osseocartilaginous and elastic. – It gives protection for the internal organs of the thoracic cavity and supports the superior trunk, pectoral girdle, and upper limbs .

4. Bony wall of the thorax is formed by: – Anteriorly by : sternum - posteriorly by: 12 thoracic vertebrae and intervening intervertebral discs. - on each side by :12 ribs with their cartilages.

5. Each rib articulates posteriorly with the vertebral column. A nteriorly , only the upper 7 ribs articulate with sternum and these are called true ribs. The costal cartilages of 8 th 9 th 10 th ribs end by joining the next higher costal cartilage, these ribs are called vertebrochondral ribs. Anterior ends of 11 th and 12 th ribs are free these are called floating ribs. Last 5 ribs are also called as false ribs.

6. S hape The thorax resembles a truncated cone, which is narrow above and broad below. The narrow upper end is continuous with the root of neck. Upper end is partly separated from root of the neck by suprapleural membrane or sibson’s fascia. The broad lower end is completely separated from abdomen by diaphragm. In transverse section, the thorax is reniform . The transverse diameter is greater than the anteroposterior diameter.

7. In infants it is circular. In infants the ribs are horizontal. In adults the thorax is oval, and the ribs are oblique, and their movements alternately increase and decrease the diameters of the thorax. This results in the drawing in of air into the thorax called inspiration and its expulsion is called expiration.

8. T horacic wall Superficial structures: • Skin • Superficial fascia – Superficial A. – Superficial V. • Thoracoepigastric v . • Lateral thoracic v. – Superficial N. • Supraclavicular N. • Anterior and lateral cutaneous branches of intercostal n.

9. Deep structures • Deep fascia – Superficial layer – Deep layer— clavipectoral fascia • Muscles of thorax – Subclavius – Pectoralis major – Pectoralis minor – Serratus anterior – Intercostales externi – Intercostales interni – Intercostales intimi • Endothoracic fascia

10. The superior aperture/ inlet of the thorax The narrow upper end of thorax,continous with the neck is called the inlet of thorax. It is kidney shaped. It’s transverse diameter is 10-12.5cm. The anteroposterior diameter is about 5cm. Boundaries: Antriorly : upper border of manubrium sterni . Posteriorly : superior surface of the body of the first thoracic vertebra. On each side: first rib with its costl cartilage. The plane of the inlet is directed downwards and forwardswith an obliquity of about 45 degrees.

11. Partition at the inlet of the thorax : The diaphragm is in two halves, right and left with a cleft in between. Each half is also known as sibson’s fascia or suprapleural membrane,it partly separates the thorax from the neck. -the membrane is triangular in shape -its apex is attached to the tip of the transverse process of the 7 th cervical vertebra and the base to the inner border of the first rib and its cartilage. It is regarded as the flattened tendon of the scalenus minimus muscle. Functionally it provides rigidity to the thoracic inlet.

12. Structures passing through the inlet of thorax: Viscera – Trachea Oesophagus apices of lungs with pleura remains of the thymus Vessels: Brachiocephalic artery on right side. Left common carotid artery & the left subclavian artery on left side. Right and left brachiocephalic veins. Nerves : Rt.& lt.phrenic nerves Rt.& lt.vagus nerves Rt.& lt. sympathetic trunks

13. ` Muscles : Sternohyoid Sternothyroid Longus coli

14. The inferior aperture/ outlet of thorax The inferior aperture is the broad end of of the thorax which surrounds the upper part of the abdominal cavity, but is separated from it by the diaphragm. Boundaries: - anteriorly : infrasternal angle between the two costal margins. posteriorly : inferior surface of the body of the 12 th thoracic vertebra. On each side: costal margin formed by the cartilages of seventh to 12 th ribs.

15. Diaphragm at the outlet of thorax The outlet is closed by a large musculotendinous partition , called the diaphragm- the thoracoabdominal diaphragm, which separates the thorax from abdomen. Structures passing through the diaphragm:3 large and several small openings in diaphragm which allow passage to structures from thorax to abdomenor vice versa. large openings : Aortic opening the oesophageal opening The venacaval opening

16. A . The Aortic opening: lies at the lower border of the T12. -it transmits:- i . the aorta, ii. thoracic duct iii. The azygous vein B. The oesophageal opening: lies in the muscular part of the diaphragm, at the level of T10. It transmits : i . the oesophagus ii. The Gastric ( vagus ) nerves iii. The oesophageal branches of the lt. gastric artery, with some oesophageal veins that accompany the arteries. C. The venacaval opening: lies in the central tendon of the diaphragm at the level of the T8. It transmits: i . the inferior venacava ii.branches of right phrenic nerve.

17. Small openings in the diaphragm 1. Each crus of diaphragm is pierced by- greater and lesser splanchnic nerves. The left crus is pierced by hemiazygous vein. 2. The sympathetic chain passes from the thorax to the abdomen behind the medial arcuate ligament. 3. The subcostal nerve and vessels pass behind the lateral arcuate ligamnet . 4. The superior epigastric vessels and some lymphatics pass between the xiphoid and costal origin of diaphragm. 5. The musculophrenic vessels pierce the diaphragm at the level of 9 th costal cartilage. 6. Several small veins pass through minute apertures in the central tendon.

18. Applied aspect / clinical anatomy In adults, the ribs may be fractured by direct or indirect violence. In indirect violence like crushing injuries, the rib fractures at its weakest point located at the angle. The upper 2 ribs and lower 2 ribs are least commonly injured. A cervical rib is a rib attached to vertebra C7. In coarctation or narrowing of the aort , the posterior intercostl arteries get enlarged greatly to provide a collateral circulation.