The Pericardium

The pericardium (peri = "around" + cardia = "heart") is the covering around the heart. It is composed of two distinct but continuous layers separated from each other by a potential space containing a lubricating substance called serous fluid. During embryological development, the heart moves from a peripheral location into a space called the celomic cavity. The cavity has

Superior Pericardial Recess Fluid

Fig. 3. The anterior surface of the heart. The atria are positioned superior to (posterior to) and to the right of their respective ventricles. From superior to inferior, down the anterior surface of the heart, runs the anterior interventricular sulcus ("a groove"). This sulcus separates the left and right ventricles. The base of the heart is defined by a plane, called the atrioventricular groove or sulcus, that separates the atria from the ventricles. Note that the great arteries, aorta, and pulmonary trunk arise from the base of the heart. The right and left atrial appendages appear as extensions hanging off each atria. The anterior (superior) surface of the heart is formed primarily by the right ventricle. The right lateral border is formed by the right atrium, and the left lateral border by the left ventricle. The posterior surface is formed by the left ventricle and the left atrium, which is centered equally on the midline.

Fig. 3. The anterior surface of the heart. The atria are positioned superior to (posterior to) and to the right of their respective ventricles. From superior to inferior, down the anterior surface of the heart, runs the anterior interventricular sulcus ("a groove"). This sulcus separates the left and right ventricles. The base of the heart is defined by a plane, called the atrioventricular groove or sulcus, that separates the atria from the ventricles. Note that the great arteries, aorta, and pulmonary trunk arise from the base of the heart. The right and left atrial appendages appear as extensions hanging off each atria. The anterior (superior) surface of the heart is formed primarily by the right ventricle. The right lateral border is formed by the right atrium, and the left lateral border by the left ventricle. The posterior surface is formed by the left ventricle and the left atrium, which is centered equally on the midline.

a serous fluid-secreting lining. As the heart migrates into the cavity, the serous lining wraps around the heart. This process can be described as similar to a fist pushed into a balloon (Fig. 4). Note that the fist is surrounded by balloon; however, the fist does not enter the balloon, and the balloon is still one continuous layer of material. These same properties are true for the pericardium.

Furthermore, although it is one continuous layer, the pericardium is divided into two components. The part of the pericardium that is in contact with the heart is called the visceral pericardium (viscus = "internal organ") or epicardium (epi = "upon" + "heart"). The free surface of the epicardium is covered by a single layer of flat-shaped epithelial cells called mesothelium. The mesothelial cells secrete a small amount of serous fluid to lubricate the movement of the epicardium on the parietal pericardium. The epicardium also includes a thin layer of fibroelastic connective tissue, which supports the mesothelium, and a broad layer of adipose tissue, which serves to connect the fibroelastic layer to the myocardium. The part of the pericardium forming the outer border is called the parietal pericardium (parietes = "walls"). The parietal pericardium, in addition to a serous layer, also contains a fibrous or epipericardial layer, referred to as the fibrous pericardium. These layers contain collagen and elastin fibers to provide strength and some degree of elasticity to the parietal pericardium.

Parietal Pericardium

Fig. 4. The pericardium. The pericardium is the covering around the heart. It is composed of two distinct but continuous layers separated from each other by a potential space containing a lubricating serous fluid. During embryological development, the heart migrates into the celomic cavity, and a serous lining wraps around it, a process similar to a fist pushed into a balloon. Note that the balloon and the pericardium are one continuous layer of material. The pericardium can be divided into the visceral pericardium (epicardium) and the parietal pericardium. A small amount of serous fluid is secreted into the pericardial space to lubricate the movement of the epicardium on the parietal pericardium. The parietal pericardium contains an epipericardial layer called the fibrous pericardium.

Fig. 4. The pericardium. The pericardium is the covering around the heart. It is composed of two distinct but continuous layers separated from each other by a potential space containing a lubricating serous fluid. During embryological development, the heart migrates into the celomic cavity, and a serous lining wraps around it, a process similar to a fist pushed into a balloon. Note that the balloon and the pericardium are one continuous layer of material. The pericardium can be divided into the visceral pericardium (epicardium) and the parietal pericardium. A small amount of serous fluid is secreted into the pericardial space to lubricate the movement of the epicardium on the parietal pericardium. The parietal pericardium contains an epipericardial layer called the fibrous pericardium.

Inferiorly, the parietal pericardium is attached to the diaphragm. Anteriorly, the superior and inferior pericardiosternal ligaments secure the parietal pericardium to the manubrium and the xiphoid process, respectively. Laterally, the parietal pericardium is attached to the parietal pleura (the covering of the lungs). In the space between these layers, the phrenic nerve (motor innervation to the diaphragm) and the pericardiac-ophrenic artery and vein (supplying the pericardium and diaphragm) are found running together.

Under normal circumstances, only serous fluid exists between the visceral and parietal layers in the pericardial space or cavity. However, the accumulation of fluid (blood from trauma, inflammatory exudate following infection) in the pericardial space leads to compression of the heart. This condition, called cardiac tamponade ("heart" + tampon = "plug"), occurs when the excess fluid limits the expansion of the heart (the fibrous pericardium resists stretching) between beats and reduces the ability to pump blood, leading to hypoxia (hypo = "low" + oxygen") (Fig. 5).

Superiorly, the parietal pericardium surrounds the aorta and pulmonary trunk (about 3 cm above their departure from the heart) and is referred to as the arterial reflections or arterial mesocardium; the superior vena cava, inferior vena cava, and pulmonary veins are referred to as the venous reflections or venous mesocardium. The outer fibrous/epipericardial layer merges with the outer adventitial layer of the great vessels. The inner serous layer becomes continuous with the visceral pericardium. The result of this reflection is that the heart hangs "suspended" within the pericardial cavity.

Within the parietal pericardium, a blind-ended saclike recess called the oblique pericardial sinus is formed from the venous reflections of the inferior vena cava and pulmonary veins (Fig. 6). A space called the transverse pericardial sinus is formed between the arterial reflections above and the venous reflections of the superior vena cava and pulmonary veins below. This sinus is important to cardiac surgeons in procedures such as coronary artery bypass grafting, for which it is important to stop or divert the circulation of blood from the aorta and pulmonary trunk. By passing a surgical clamp or ligature through the transverse sinus and around the great vessels, the tubes of a circulatory bypass machine can be inserted. Cardiac surgery is then performed while the patient is on car-diopulmonary bypass. (For more details on the pericardium, see Chapters 5 and 7.)

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

Get My Free Ebook


Post a comment