Anatomy of the Heart - Cardiovascular System

Heart Anatomy

• The heart is approximately the size of a fist
• Located on the superior surface of the diaphragm, left of the midline, and anterior to the vertebral column, posterior to the sternum
• Coverings of the heart:
  • Pericardium: a double-walled sac around the heart
  • Fibrous pericardium: a superficial layer
  • Serous pericardium: a deep two-layer layer (parietal and visceral layers)
  • Pericardial cavity: a fluid-filled space between the parietal and visceral layers

Function of the Pericardium

• Protects and anchors the heart
• Prevents overfilling of the heart with blood
• Allows for the heart to work in a relatively friction-free environment

Heart Wall

• Epicardium: visceral layer of the serous pericardium
• Myocardium: cardiac muscle layer forming the bulk of the heart
• Fibrous skeleton of the heart: a layer of connective tissue
• Endocardium: endothelial layer of the inner surface of the heart

External Heart: Major Vessels

• Vessels returning blood to the heart:
  • Superior and inferior venae cavae
  • Right and left pulmonary veins
• Vessels conveying blood away from the heart:
  • Pulmonary trunk (splits into right and left pulmonary arteries)
  • Ascending aorta

External Heart: Vessels that Supply/Drain the Heart

• Arteries: mainly coronary arteries
• Veins: small cardiac, anterior cardiac, and great cardiac veins

Atria and Ventricles

• Atria: receiving chambers of the heart
• Blood enters right atria from superior and inferior venae cavae and coronary sinus
• Blood enters left atria from pulmonary veins
• Ventricles: discharging chambers of the heart
• Right ventricle pumps blood into pulmonary arteries
• Left ventricle pumps blood into the aorta

Pathway of Blood Through the Heart and Lungs

• Right atrium → tricuspid valve → right ventricle
• Right ventricle → pulmonary semilunar valve → pulmonary arteries → lungs
• Lungs → pulmonary veins → left atrium
• Left atrium → bicuspid valve → left ventricle
• Left ventricle → aortic semilunar valve → aorta
• Aorta → systemic circulation

Coronary Circulation

• Functional blood supply to the heart muscle itself

Heart Valves

• Ensure unidirectional blood flow through the heart
• Atrioventricular (AV) valves: prevent backflow into the atria when ventricles contract
• Semilunar valves: prevent backflow of blood into the ventricles
• Aortic semilunar valve: lies between the left ventricle and the aorta
• Pulmonary semilunar valve: lies between the right ventricle and pulmonary trunk

Blood and Lymph System

• Blood: a fluid consisting of formed elements and plasma
• Produced by bone marrow
• Volume depends on body weight (approximately 5 quarts/liters for a 154-pound individual)
• Functions: transportation of respiratory gases, chemicals, and cells that protect the body from foreign substances

Vascular Tree

• Hierarchical network of arteries, arterioles, capillary beds, veins, and venules
• Characterized by an inner layer of endothelium and an outer layer of basement membrane

Blood Plasma

• Fluid part of the blood (55% of total blood volume)
• Clear or straw-colored
• Composed mostly of water and proteins

Lymph

• Clear, nearly colorless, alkaline fluid
• Occupies the space between all cells of the body (interstitial fluid)
• 95% water
• Seeps in and out through the walls of capillaries
• Mostly fluid from blood plasma

Lymphatic System

• Connected to the circulatory system
• Consists of capillaries, vessels, ducts, and nodes
• Transports lymph one-way back to the bloodstream
• No pump, but lymph moves via skeletal muscle action, respiratory movement, and contraction of smooth muscle in vessel walls

Lymph Nodes

• Filters, slowing down and cleaning the lymph before returning it to the blood

Accessory Organs to the Lymphatic System

• Spleen:
  • Removes old red blood cells from the blood supply
  • Removes, stores, and produces white blood cells
• Tonsils:
  • Filter bacteria and produce white blood cells

Learn about the anatomy of the heart, its location, and coverings. Understand the structure of the pericardium and its layers.