Cardiovascular System Overview

Overview of the Cardiovascular System

• Cardiology studies the heart and its disorders.
• The cardiovascular system includes the heart and blood vessels.
• The heart is a pump that keeps blood flowing.
• Vessels deliver blood to body tissues and return it.
• Arteries carry blood away from the heart.
• Veins carry blood toward the heart.
• Capillaries are microscopic vessels connecting small arteries to small veins.
• The circulatory system includes the heart, vessels, and blood.
• All arteries carry oxygenated blood, except for the pulmonary arteries.
• All veins carry deoxygenated blood, except for the pulmonary veins.

Pulmonary and Systemic Circuits

• The cardiovascular system has two major divisions: pulmonary and systemic circuits.
• The pulmonary circuit carries blood to the lungs for gas exchange and back to the heart, using the right side of the heart.
• The systemic circuit supplies oxygenated blood to all body tissues and returns it to the heart, using the left side of the heart.
• The superior vena cava (above the diaphragm) and inferior vena cava (below the diaphragm) are part of the right side pulmonary circuit.
• The right and left atria are the top chambers of the heart.
• The right and left ventricles are the bottom chambers of the heart.
• The tricuspid valve is located between the right atrium and right ventricle.
• The pulmonary semilunar valve is below the right ventricle.
• The pulmonary semilunar trunk comes out of the pulmonary valve.
• The right and left pulmonary arteries branch out of the trunk and carry blood to the lungs.
• Clean blood travels through the left and right pulmonary arteries to connect to the left atrium
• The bicuspid (mitral) valve is located between the left atrium and left ventricle.
• The aortic semilunar valve is below the left ventricle.
• The aorta branches out of the aortic semilunar valve.
• The right side of the heart supplies the pulmonary circuit.
• Oxygen-poor blood arrives from the body tissues.
• Blood is sent to the alveoli of the lungs via the pulmonary trunk and pulmonary arteries, picks up oxygen, and returns to the heart via the pulmonary veins.
• The left side of the heart supplies the systemic circuit.
• Fully oxygenated blood is sent to the body tissues via the aorta, which branches into smaller vessels.
• Blood releases oxygen at the tissues; deoxygenated blood returns to the heart via the superior and inferior vena cava.
• The major arteries and veins entering and leaving the heart are called the great vessels.

Position, Size, and Shape of the Heart

• The heart is located in the mediastinum, which is the space between the lungs.
• The base is the wide, superior portion of the heart where large vessels attach.
• The apex is the tapered inferior end that tilts to the left.
• The adult heart weighs 10 ounces and measures 3.5 inches wide at the base and 5 inches from base to apex.
• At any age, the heart is approximately the size of a fist.

The Pericardium

• The heart is enclosed by the pericardium, which is a double-walled sac.
• The pericardium allows the heart to beat without friction, provides room to expand, and resists excessive expansion.
• The pericardium is anchored to the diaphragm inferiorly and the sternum anteriorly.
• The structure of the pericardium includes the fibrous pericardium and the serous pericardium.
• The fibrous pericardium is the outermost layer and is a tough, fibrous sac.
• The serous pericardium has two layers - the parietal layer, which lines the fibrous pericardium, and the visceral layer (epicardium), which adheres to the heart surface.
• The pericardial cavity is the space between the parietal and visceral layers of the serous pericardium and contains 5 to 30 mL of pericardial fluid.
• Pericarditis is the inflammation of the pericardium, which may result in a friction rub.
• The epicardium is the outside layer of the heart.
• The myocardium is the middle layer of the heart.
• The endocardium is the innermost layer of the heart.

The Chambers

• The heart has four chambers: two atria and two ventricles.
• The right and left atria are the two superior chambers that receive blood returning to the heart and are separated by the interatrial septum.
• Each atrium has an auricle, which is an earlike flap that increases the chamber volume.
• The right atrium and both auricles contain pectinate muscles, which are internal ridges of the myocardium.
• The atria have thin, flaccid walls and pump blood to the ventricles.
• The right and left ventricles are the two inferior chambers that eject blood into the arteries and are separated by the interventricular septum.
• The left ventricle wall is 2-4x thicker than the right ventricle because it has a greater workload in pumping blood to the entire body versus only to the lungs.
• Both ventricles contain trabeculae carneae, which are internal muscular ridges that help the chambers expand and refill more easily.

Valves

• Atrioventricular valves control blood flow between the atria and ventricles.
• The right AV valve is the tricuspid valve.
• The left AV valve is the mitral valve.

General Anatomy of the Blood Vessels

• The three principal categories of blood vessels are arteries, veins, and capillaries.
• Arteries carry blood away from the heart.
• Veins carry blood back to the heart.
• Capillaries connect the smallest arteries to the smallest veins to create a circuit.

The Vessel Wall

• The walls of arteries and veins have three layers called tunics.
• The tunica interna (tunica intima) lines the blood vessel and is exposed to blood.
• The tunica interna consists of the endothelium, which is simple squamous epithelium.
  • The endothelium is the selectively permeable barrier.
  • The endothelium secretes chemicals that stimulate dilation or contraction.
  • The endothelium normally repels blood cells and platelets to prevent clotting.
  • When tissues around the vessel are inflamed, the endothelial cells produce cell-adhesion molecules.
  • Cell adhesion causes leukocytes to congregate in tissues where their defensive actions are needed.
• The tunica media is the middle layer.
  • The tunica media consists of smooth muscle, collagen, and elastic tissue.
  • The tunica media strengthens vessels and prevents blood pressure from rupturing them.
  • Contraction of muscles controls blood vessel diameter
• The tunica externa (tunica adventitia) is the outermost layer.
• The tunica externa consists of loose connective tissue that often merges with that of neighboring vessels, nerves, or other organs.
• The tunica externa anchors the vessel and provides passage for small nerves and lymphatic vessels.
• The vasa vasorum are small vessels that supply blood to the outer half of the walls in the larger vessels.

Arteries

• Arteries are divided into three classes: conducting (elastic or large) arteries, distributing (muscular or medium) arteries, and resistance (small) arteries.
• Examples of conducting arteries include the aorta, common carotid, subclavian, pulmonary trunk, and common iliac arteries.
  • Conducting arteries expand during systole and recoil during diastole.
  • Expansion takes pressure of smaller downstream vessels
  • Recoil maintains pressure during relaxation and keeps blood flowing.
• Distributing arteries distribute blood to specific organs.
  • Examples of distributing arteries include the branchial, femoral, renal, and splenic arteries.
  • Smooth muscle layers constitute three-fourths of the wall thickness.
  • Internal and external elastic laminae are thick.
• Resistance arteries are small arteries.
  • Resistance arteries have a thicker tunica media in proportion to their lumen than large arteries and little tunica externa.
• Arterioles are the smallest of the resistance arteries.
  • Arterioles have a diameter of 200 mm and only 1 to 3 layers of smooth muscles.
  • Arterioles control the amount of blood to various organs.