APR Module 9: Cardiovascular Dissection Thorax Arteries-Anterior Apex of Heart

Heart Location and Pericardium

• The heart is located within the mediastinum of the thoracic cavity between the lungs.
• The heart is enclosed in three layers, collectively called the pericardium.
• The pericardium consists of: • Fibrous pericardium (outer layer): dense irregular connective tissue that encloses the heart but does not attach to it. • Parietal layer of the serous pericardium (middle layer): simple squamous epithelium and an underlying delicate layer of areolar connective tissue; adheres to the inner surface of the fibrous pericardium. • Visceral layer of the serous pericardium (inner layer): also composed of simple squamous epithelium and an underlying delicate layer of areolar connective tissue; adheres directly to the heart, forming the visceral pericardium (or epicardium).

Cardiac Muscle and Energy Needs

• Cardiac muscle has features that support its great demand for energy, including: • Extensive blood supply • Numerous mitochondria • Myoglobin (globular protein that binds oxygen) • Creatine kinase (catalyzes the transfer of Pi from creatine phosphate to ADP, yielding ATP and creatine)
• Cardiac muscle relies almost exclusively on aerobic cellular respiration.
• Cellular structures and metabolic processes support this, including: • Large number of mitochondria (approximately 25% of cardiac muscle cell volume) • Ability to use different types of fuel molecules (fatty acids, glucose, lactate, amino acids, and ketone bodies)

Heart Chambers and Blood Circulation

• The four heart chambers are involved in the continuous process of blood circulation.
• The right atrium: • Has a smooth posterior surface and muscular ridges (pectinate muscles) on its anterior wall and within the auricle. • Has an oval depression called the fossa ovalis, which occupies the former location of the fetal foramen ovale. • Receives deoxygenated blood from the coronary sinus, superior vena cava, and inferior vena cava.
• The right atrioventricular opening contains the right AV valve, allowing deoxygenated blood to flow into the right ventricle.

Cardiac Muscle Cells and Intercalated Discs

• Cardiac muscle cells are unique in having intercalated discs, which link cells together mechanically and electrically.
• Intercalated discs contain: • Desmosomes (protein filaments that anchor into a protein plaque located on the internal surface of the sarcolemma) • Gap junctions (protein pores between the sarcolemma of adjacent cardiac muscle cells)
• Gap junctions allow for the flow of ions between cardiac cells, resulting in synchronous contraction of the chamber.

Fibrous Skeleton

• The fibrous skeleton is composed of dense irregular connective tissue that provides both mechanical support and electrical insulation within the heart.
• Cardiac muscle cells are arranged in spiral bundles around the heart chambers, attached to the fibrous skeleton.
• When the atria contract, they compress the wall of the chambers inward, moving blood inferiorly into the ventricles.

Learn about the location of the heart within the mediastinum of the thoracic cavity and its relationship to other organs, as well as the layers of the pericardium. This quiz covers anatomical details of the heart and great vessels.