The thoracic structure refers to the anatomical components of the thorax, which is the region of the body between the neck and the abdomen, also known as the chest. It includes the thoracic vertebrae, ribs, sternum (breastbone), and associated muscles, ligaments, and organs such as the heart and lungs. The thoracic structure plays a crucial role in protecting vital organs, supporting the upper body, and facilitating respiration. The thoracic structure encompasses the anatomical elements of the chest region, including the thoracic vertebrae, ribs, sternum, associated muscles, and vital organs such as the heart and lungs. It provides protection, support, and facilitates respiration, highlighting its critical role in overall bodily function and health.The thoracic structure comprises the chest's anatomical components, including vertebrae, ribs, sternum, muscles, and vital organs like the heart and lungs, crucial for protection, support, and respiration..The thoracic structure includes the chest's bones, muscles, and organs, vital for breathing and protecting the heart and lungs. 1. **Thoracic Vertebrae:** The thoracic spine consists of twelve vertebrae (T1-T12) that form the posterior aspect of the thoracic structure. These vertebrae are larger than those in the cervical or lumbar regions and articulate with the ribs, providing stability and support for the upper body. 2. **Ribs:** There are twelve pairs of ribs that attach posteriorly to the thoracic vertebrae and curve anteriorly to meet the sternum. Ribs play a vital role in protecting the internal organs of the thoracic cavity, such as the heart and lungs. The upper seven pairs are true ribs, while the lower five pairs are false ribs (some of which do not directly attach to the sternum) or floating ribs. 3. **Sternum:** The sternum is a flat bone located in the center of the anterior thoracic wall. It consists of three parts: the manubrium, body, and xiphoid process. The sternum serves as an attachment point for the ribs and provides structural support to the chest. 4. **Muscles:** Several muscles surround the thoracic cavity, contributing to breathing and movement of the chest wall. These include the intercostal muscles (external, internal, and innermost), which are located between the ribs and aid in respiration, as well as muscles such as the diaphragm, which separates the thoracic and abdominal cavities and plays a primary role in breathing. 5. **Organs:** The thoracic cavity houses important organs such as the heart and lungs. The heart is situated in the mediastinum, a central compartment of the thoracic cavity, while the lungs occupy the lateral portions. The thoracic structure provides protection and support for these vital organs while allowing for their necessary movements during respiration and circulation. Understanding the anatomy and function of the thoracic structure is essential for various medical disciplines, including anatomy, physiology, orthopedics, cardiology, and res

1. Thymus, Thoracic Duct
&
Blood Vessels Of Thorax

2. Thymus
• The thymus is one of the two primary lymphoid organs,
the other being the bone marrow.
• The thymus is a flattened , bilobed organ.
• The two lobes (right & left) are joined in the midline by
connective tissue that merges with the capsule of each
lobe.
• The thymus plays an important role in the development
and maintenance of the immune system.
• The thymus is located in the lower part of the neck and the
anterior part of the superior mediastinum
• It lies posterior to the manubrium and extends into the
anterior mediastinum where it lies between the sternum
and the pericardium.

3. • In the newborn infant, it reaches its largest size relative to the
size of the body.
• The thymus continue to grow until puberty but after puberty, the
thymus undergoes gradual involution and is largely replaced by
fat & connective tissue.

5. Relations Of Thymus
• Anteriorly –
– Sternohyoid, sternothyroid and fascia (in the neck),
the manubrium sterni, internal thoracic vessels and
upper three costal cartilages (in the thorax).
• Laterally –
– The pleurae
• Anterolaterally –
– The phrenic nerves
• Posteriorly –
– The thymus is in contact with the vessels of the
superior mediastinum , the upper part of the thoracic
trachea and the anterior surface of the heart.

7. Blood supply of thymus
Arterial supply to the thymus is derived
mainly from
–The inferior thyroid artery,
–Anterior intercostal and the anterior mediastinal
branches of the internal thoracic arteries.
The veins of the thymus end in the left
brachiocephalic, internal thoracic, and inferior
thyroid veins.

8. Blood Vessels Of Thorax
The Aorta
• This is a great arterial trunk which
receives oxygenated blood from the
left ventricle & distributes to the
whole of the body
• It is consists of 3 parts
1) Ascending aorta
2) The arch of aorta and
3) Descending aorta

9. The Ascending Aorta
• This arises from the upper
end of the left ventricle
• It is about 5 cm long & is
enclosed in the pericardium
• It begins at the level of 3rd
costal cartilage, behind the
left border of the sternum
• At the root of aorta there
are 3 dilatations called the
aortic sinuses
• They are anterior aortic
sinus, left posterior aortic
sinus and right posterior
aortic sinus.
Branches
• Right coronary artery
arising from the anterior
aortic sinus
• Left coronary artery
arising from the left
posterior aortic sinus

10. Arch Of Aorta
• It is the continuation of the
ascending aorta
• It is situated in the superior
mediastinum behind the lower
half of the manubrium sterni.
Course
• It begins behind the upper border
of the 2nd right sternochondral
joint.
• It runs upwards backwards & to
the left across the bifurcation of
the trachea.
• It ends at the lower border of the
body of the 4th thoracic vertebra
& continues as descending aorta
– Thus Begining & End Of Arch Of
Aorta Is At The Same Level

11. Branches –
 Brachiocephalic
artery
 It divides in to
right common
carotid artery and
right subclavian
arteries
 Left common
carotid artery
 Left subclavian
artery
 Occasionally
 Thyroidia ima
artery or arteria
thyroidia ima
 Vertebral artery
may arise from
arch of aorta.

13. Descending Thoracic Aorta
• It is the continuation of the arch of aorta
• It arises in the posterior mediastinum
Course –
1. It begins on the left side of the lower border of the body of
the 4th thoracic vertebra
2. It descends with an inclination to the right & terminates
at the lower border of the 12th thoracic vertebra.
Branches –
• 9 posterior intercostal arteries on each side for 3rd to 11th
inter costal spaces
• The sub costal artery on each side
• 2 left bronchial arteries.
• Esophageal branches, to the middle 1/3rd of esophagus
• Pericardial branches to the posterior surface of the
pericardium
• Mediastinal branches, to Lymph nodes & aerolar tissue of
the posterior mediastinum
• Superior phrenic arteries, to posterior part of the diaphragm

15. Superior Vena Cava
• The superior vena cava is
about 7 cm long
• It is formed by the union of
right & left brachiocephalic
veins behind the lower
border of the 1st right costal
cartilage close to the
sternum.
• It begins behind the lower
border of the sternal end of
the 1st right costal cartilage,
pierces the pericardium
opposite the 2nd right costal
and terminates by opening
in to the upper part of the
right atrium behind the 3rd
costal cartilage.
Tributaries
•The azygos vein
–It arches over the root of the right
lung & opens in to the superior vena
cava at the level of the 2nd costal
cartilage just before the latter enters
the pericardium.

16. Brachiocephalic Veins
• The right
brachiocephalic vein is
formed at the root of
the neck by the union of
the right subclavian
and the right internal
jugular veins.
• The left brachiocephalic
vein has a similar
origin.
• The LBV passes
obliquely downward
and to the right behind
the manubrium sterni
and in front of the large
branches of the aortic
arch.
• It joins the right
brachiocephalic vein to
form the superior vena
cava

17. Azygos Venous system
• The azygos veins
consist of
– The azygos vein,
– The hemiazygos
vein
– The accessory
hemiazygos vein.
• They drain blood
from the posterior
parts of the
intercostal spaces,
the posterior
abdominal wall,
the pericardium,
the diaphragm,
the bronchi, and
the esophagus.

18. Azygos Vein
• It is formed by the union of the right ascending
lumbar vein and the right subcostal vein.
• It ascends through the aortic opening in the
diaphragm on the right side of the aorta to the
level of the upper border of fifth thoracic
vertebra.
• Here it arches forward above the root of the
right lung to empty into the posterior surface of
the superior vena cava.
• Tributaries
– The eight lower right intercostal veins,
– The right superior intercostal vein,
– The hemiazygos vein
– The accessory hemiazygos vein
– Numerous mediastinal veins.

20. • Hemiazygos Vein
– The hemiazygos vein is often formed by
the union of the left ascending lumbar vein
and the left subcostal vein.
– It ascends through the left crus of the
diaphragm and, at about the level of the
eighth thoracic vertebra, turns to the right
and joins the azygos vein.
– It receives as tributaries some lower left
intercostal veins and mediastinal veins.
• Accessory Hemiazygos Vein
– It is formed by the union of the fourth to
the eighth intercostal veins.
– It joins the azygos vein at the level of the
seventh thoracic vertebra.

21. Thoracic duct
• The thoracic duct is the principal channel through which lymph from
most of the body is returned to the venous system
• The thoracic duct begins below in the abdomen as a dilated sac called
as the cisterna chyli.
• It ascends through the aortic opening in the diaphragm, on the right
side of the descending aorta.
• It gradually crosses the median plane behind the esophagus and
reaches the left border of the esophagus at the level of the sternal
angle.
• It then runs upward along the left edge of the esophagus to enter the
root of the neck.
• Here, it bends laterally behind the carotid sheath and in front of the
vertebral vessels.
• It turns downward in front of the left phrenic nerve and crosses the
subclavian artery to enter the beginning of the left brachiocephalic
vein.
• At the root of the neck, the thoracic duct receives the left jugular,
subclavian, and bronchomediastinal lymph trunks, although they may
drain directly into the adjacent large veins.
• The thoracic duct thus conveys to the blood all lymph from the lower
limbs, pelvic cavity, abdominal cavity, left side of the thorax, and left
side of the head, neck, and left arm.

23. Sympathetic trunks
• They are an important
component of the
sympathetic part of the
autonomic division of the
PNS and are usually
considered a component of
the posterior mediastinum
as they pass through the
thorax.
• This portion of the
sympathetic trunks consists
of two parallel cords
punctuated by 11 or 12
ganglia.
• The ganglia are connected to
adjacent thoracic spinal
nerves by white and gray
rami communicantes.
• The sympathetic trunks leave
the thorax by passing
posterior to diaphragm under
the medial arcuate ligament
or through the crura of the
diaphragm

24. • The medial branches from the ganglia joins together & forms
three thoracic splanchnic nerves
– The greater splanchnic nerves
– The lesser splanchnic nerves
– The least splanchnic nerves
• The greater splanchnic nerve
– It arises from the fifth to ninth or tenth thoracic ganglia.
– It descends across the vertebral bodies moving in a medial
direction, passes into the abdomen through the crus of the
diaphragm, and ends in the celiac ganglion.
• The lesser splanchnic nerve
– It arises from the ninth and tenth, or tenth and eleventh thoracic
ganglia.
– It descends across the vertebral bodies moving in a medial
direction, and passes into the abdomen through the crus of the
diaphragm to end in the aorticorenal ganglion.
• The least splanchnic nerve (lowest splanchnic nerve)
– It arises from the twelfth thoracic ganglion.
– It descends and passes into the abdomen through the crus of the
diaphragm to end in the renal plexus

25. Applied Anatomy
1. When the superior vena cava is obstructed
above the opening of the azygos vein, the
venous blood of the upper half of the body
is returned through the azygos vein
2. When the SVC is obstructed below the
opening of the azygos vein, the blood is
returned through the inferior vena cava via
the femoral vein, & the superficial veins are
dilated on both the chest & abdomen up to
the saphenous opening in the thigh.
3. In cases of the mediastinal syndrome the
signs of superior venacaval obstructions
are the 1st to appear.