Anatomy of the Heart

• Anatomy of the heart is the subject of lecture 1 in the block of hematology.

Objectives

• Define pericardium (fibrous and serous)
• Describe the shape, relations, and function of the fibrous pericardium
• Compare the nerve supply of fibrous, parietal, and visceral pericardium, commenting on referred pain
• Describe the pericardial sinuses (transverse and oblique) and realize their clinical importance
• Describe the shape, borders, surfaces, and external features of the heart

Overview of the heart

• The apex of the heart is pointed forward, downward, and to the left
• The apex is located deep to the left fifth intercostal space, 3.5 inches (9cm) from the median plane

Coverings of The Heart

• The pericardium, or pericardial sac, encloses the heart
• The outer layer is the fibrous pericardium
• The inner layer is the serous pericardium, consisting of two layers: parietal and visceral (epicardium)

Pericardium

• The pericardium is a protective, fluid-filled sac that surrounds heart and aids the operation
• The fibrous pericardium is a conical-shaped sac
• The apex is fused with the roots of the great vessels at the base of the heart
• The pericardial cavity is the space between the parietal and visceral pericardium
• The pericardial cavity normally contains 15-50 mL of serous fluid
• The term pericardium is derived from the Greek words "peri" (around) and "kardia" (heart)

Relations of the fibrous pericardium

• Anterior: Sternum and the pleura, besides the cardiac notch
• Posterior: Descending aorta, esophagus, thoracic duct, and T5-T8 vertebrae
• Diaphragm sits inferiorly
• Lateral: Lung, pleura and the phrenic nerve

Function of The Fibrous Pericardium

• Maintains the central position of the heart
• Keeps large vessels open
• Aids venous return
• Acts as a wall for serous pericardium
• Prevents overdistention of the heart

Nerve supply of the Pericardium

• The fibrous pericardium and the parietal layer of the serous pericardium are supplied by the phrenic nerves
• The visceral layer of the serous pericardium is innervated by branches of the sympathetic trunks and the vagus nerves (parasympathetic) and is not sensitive
• Phrenic nerves are branches of the cervical plexus (C3, 4, 5)
• Phrenic nerves provide sensory supply to the fibrous and parietal pericardium, adjacent parietal pleura, and motor supply to the whole diaphragm
• Pain from the pericardium may be referred to the skin over the shoulder tip, i.e., over the acromion process

Transverse Pericardial Sinus

• The heart has two sinuses: the transverse sinus and the oblique sinus
• These sinuses are formed due to reflection of the serous pericardium
• The transverse pericardial sinus is located posterior to the aorta and pulmonary trunk
• The transverse pericardial sinus is located Anterior to the Superior vena cava
• During cardiac surgery, the transverse pericardial sinus allows a surgeon to isolate the pulmonary trunk and ascending aorta, applying a temporary ligature or clamp

Oblique Sinus

• The oblique sinus is a cul-de-sac extending between the two left pulmonary veins on one side and the two right pulmonary veins on the other
• The oblique sinus provides expansion space for the left atrium

Shape of Heart

• The heart is like an upside-down pear, about the size of one's fist

Borders of the Heart

• The heart has four borders: right, left, inferior, and superior
• The right border consists of the IVC, right atrium, and SVC
• The left border consists of the left ventricle and left auricle
• The inferior border consists of the right ventricle and apical part of the left ventricle
• The superior border consists of the right and left atria, SVC, ascending aorta, and pulmonary trunk

Heart Surfaces

• The heart has five surfaces: base (posterior), diaphragmatic (inferior), sternocostal (anterior), left and right pulmonary surfaces
• The base, or posterior surface, is formed mainly by the left atrium, into which open four pulmonary veins
• This surface lies opposite the apex
• The diaphragmatic surface rests on the surface in anatomical position and consists chiefly of the left ventricle and a small portion of the right ventricle
• The sternocostal surface (anterior) is mostly formed by the right atrium and right ventricle
• The left and right pulmonary surfaces are broad and convex, both facing the lungs
• The left pulmonary surface is mainly formed by the lateral part of the left ventricle, also part of the left atrium
• The right pulmonary surface consists mainly of the lateral portion of the right atrium