Anatomy Of The Cardiovascular System

Lecture 1

Abbas A. A. ShawkaMedical student

1st stage

Subjects

• Mediastinum• Middle mediastinum• Surface anatomy• Pericardium

Mediastinum• The mediastinum is a broad

central partition that separates the two laterally placed pleural cavities.

• It extends from the sternum to the bodies of the vertebrae, and from the superior thoracic aperture to the diaphragm

• The mediastinum contains the thymus gland, the pericardial sac, the heart, the trachea, and the major arteries and veins.

• Additionally, the mediastinum serves as a passageway for structures such as the esophagus , thoracic duct, and various components of the nervous system as they traverse the thorax on their way to the abdomen.

• For organizational purposes, the mediastinum is subdivided into several smaller regions. A transverse plane extending from the sternal angle (the junction between the manubrium and the body of the sternum) to the intervertebral disc between vertebrae TIV and TV separates the mediastinum into the:

1- superior mediastinum 2- inferior mediastinum, which is further partitioned into the anterior, middle, and posterior mediastinum by the pericardial sac.

Middle Mediastinum• The middle mediastinum i s centrally located

in the thoracic cavity. It contains the pericardium, heart, origins of the great vessels, various nerves, and smaller vessels .

Surface Anatomy

Pericardium• The pericardium is a fibroserous

sac surrounding the heart and the roots of the great vessels.

• It consists of two components 1- the fibrous pericardium 2- the serous pericardium• The parietal and visceral layers of

serous pericardium are continuous at the roots of the great vessels .

• The narrow space created between the two layers of serous pericardium, containing a small amount of fluid, is the pericardial cavity. This potential space allow for the relatively uninhibited movement of the heart.

Fibrous pericardium• The fibrous pericardium is a cone-shaped bag with its• base on the diaphragm and its apex continuous with the

adventitia of the great vessels• The base is attached to the central tendon of the diaphragm

and to a small muscular area of the diaphragm on the left side. Anteriorly, it is attached to the posterior surface of the sternum by sternopericardial ligaments.

• The phrenic nerves, which innervate the diaphragm and originate from spinal cord levels C3 to CS, pass through the fibrous pericardium and innervate the fibrous pericardium as they travel from their point of origin to their final destination.

• The Trachea pericardiacophrenic vessels are also located within and supply the fibrous pericardium as they pass through the thoracic cavity.

Serous pericarium• The parietal layer of serous pericardium is continuous with the

visceral layer of serous pericardium around the rootsof the great vessels.

• These reflections of serous pericardium occur in two locations: 1- superiorly, surrounding the arteries , the aorta, and the pulmonary trunk 2- the second more posteriorly, surrounding the veins, the superior and inferior vena cava, and the pulmonary veins.• The zone of reflection surrounding the veins is J-shaped, and

the cul-de-sac formed within the J, posterior to the left atrium, is the oblique pericardial sinus. A passage between the two sites of reflected serous pericardium is the transverse pericardial sinus. This sinus lies posterior to the ascending aorta and the pulmonary trunk, anterior to the superior vena cava, and superior to the left atrium.

When the pericardium is opened anteriorly during surgery, a finger placed in the transverse sinus separates arteries from veins. A hand placed under the apex of the heart and moved superiorly slips into the oblique sinus

• The location of the transverse pericardial sinus is:

Posterior to the ascending aorta and pulmonary trunk. Anterior to the superior vena cava. Superior to the left atrium.• In this position, the transverse

pericardial sinus separates the arterial vessels (aorta, pulmonary trunk) and the venous vessels (superior vena cava, pulmonary veins) of the heart.

• This can be used to identify and subsequently ligate (to tie off) the arteries of the heart during coronary artery bypass grafting.

• The oblique pericardial sinus lies posterior to the heart in the pericardial sac. Lift the apex of the heart and place your fingers posterior to the heart to identify the oblique pericardial sinus and examine its borders.

• On the right side, the oblique sinus is bounded by the lines of reflection of the serous pericardium onto the inferior vena cava and the right pulmonary veins.

• On the left, the sinus is bounded only by the lines of reflection of serous pericardium onto the left pulmonary veins. Observe that the two sinuses are not continuous with one another.

• The oblique sinus of the pericardial cavity is a blind ending passage posterior to the heart formed by the reflections of the visceral and parietal pericardium onto the vessels traversing the space.

• With the heart in its anatomical position and the dorsal pericardium intact, it forms an inverted U-shaped recess that can be probed to reveal the structures forming its walls:

• anterior: left atrium• posterior: parietal serous pericardium• right and inferior: visceral peritoneum on inferior vena cava• right: 2 right pulmonary veins• left: 2 left pulmonary veins• superior: reflection of visceral pericardium onto wall of

pericardial sac• inferior: opening of sinus

• The pericardium is supplied by branches from the internal thoracic, pericardiacophrenic, musculophrenic, and inferior phrenic arteries , and the thoracic aorta.

• Veins from the pericardium enter the azygos system of veins and the internal thoracic and superior phrenic veins.

• Nerves supplying the pericardium arise from the vagus nerve [X] . the sympathetic trunks, and the phrenic nerves.

• It is important to note that the source of somatic sensation (pain) from the parietal pericardium is carried by somatic afferent fibers in the phrenic nerves. For this reason, "pain" related to a pericardia! problem may be referred to the supraclavicular region of the shoulder or lateral neck area dermatomes for spinal cord segments C 3 , C4, and C 5.

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