Circulatory System I

Circulatory System I

• The circulatory system comprises the heart, blood vessels, and blood. This is also called the cardiovascular system
• The circulatory system transports substances throughout the body via blood.
• Blood is the liquid that carries materials.
• Blood vessels direct blood flow to specific destinations.
• The heart is the pump that keeps blood moving.
• Without valves, more effort is needed to circulate blood.

Functions of the Circulatory System

• The circulatory system's primary function is transporting substances throughout the body.
• Blood serves as the medium for transport.
• Blood vessels direct blood flow.
• The heart acts as the pump for blood circulation.

Pulmonary and Systemic Circuits

• The cardiovascular system has two main divisions: the pulmonary and systemic circuits.
• The pulmonary circuit carries blood to the lungs for oxygenation and returns oxygenated blood to the heart.
• The systemic circuit carries oxygenated blood to the body and returns deoxygenated blood to the heart.

The Right Half of the Heart

• The right half of the heart is responsible for the pulmonary circuit.
• It receives deoxygenated blood from the body and pumps it to the lungs via the pulmonary trunk.
• In the lungs, the blood releases carbon dioxide and picks up oxygen.
• Oxygenated blood returns to the left side of the heart via pulmonary veins.

The Left Half of the Heart

• The left half pumps oxygenated blood throughout the body from the heart via the aorta.
• The aorta branches into smaller vessels to deliver oxygen to all body parts.
• The blood picks up carbon dioxide and other waste products from the body tissues.
• Deoxygenated blood returns to the right side of the heart via the superior and inferior vena cava.

Position, Size, and Shape of the Heart

• The heart sits in the mediastinum, between the lungs behind the sternum.
• Most of the heart is on the left side of the body's midline.
• The heart's broadest part is superior and is called the base
• The heart narrows to a point called the apex, which is near the diaphragm.

The Pericardium

• The heart is encased in a double-walled sac called the pericardium.
• The outer layer is a tough fibrous layer.
• The inner layer, which forms the epicardium, is a serous membrane.
• The space between these layers is the pericardial cavity.

The Heart Wall

• The heart wall has three layers:
  • Epicardium (outer layer)
  • Myocardium (middle, thick muscular layer)
  • Endocardium (inner layer)

The Chambers of the Heart

• The heart has four chambers: two atria and two ventricles.
• Atria (singular: atrium) are thin-walled, receiving chambers.
• Ventricles are thick-walled, pumping chambers.
• Blood enters the atria, then moves to the ventricles to be pumped out of the heart.

Heart Valves

• The heart has four valves that regulate blood flow.
  • Atrioventricular (AV) valves (tricuspid and mitral)
  • Semilunar valves (pulmonary and aortic)
• AV valves prevent backflow from the ventricles to the atria.
• Semilunar valves prevent backflow from the arteries to the ventricles.

Pathway of Blood Flow Through the Heart

• Blood flows through the heart in a specific pathway.
• Deoxygenated blood enters the right atrium, then the right ventricle, then to the lungs for gas exchange.
• Oxygenated blood returns to the heart in the left atrium, then the left ventricle, and finally is pumped to the body throughout the systemic circulation.

Coronary Circulation

• The coronary arteries supply blood to the heart muscle.
• The coronary veins collect deoxygenated blood.
• The coronary sinus is a large vein that collects blood from the heart and drains into the right atrium.

The Conduction System

• The conduction system coordinates the heart's pumping action.
• Specialized cells in the heart generate and spread electrical signals to trigger contraction of the heart chambers.
• The sinoatrial (SA) node serves as the pacemaker and initiates the heart's contraction sequence.