The Cardiovascular System: Cardiac Function

Cardiovascular System: Cardiac Function

Chapter Outline

• 13.1 Overview of the Cardiovascular System
• 13.2 The Path of Blood Flow Through the Heart and Vasculature
• 13.3 Anatomy of the Heart

Learning Objectives

• Identify the major components of the cardiovascular system, and briefly describe their functions.
• Identify the major structures of the heart, and describe the path of blood flow through the heart and vasculature.

13.1 Overview of the Cardiovascular System

• Components:
  • Heart
  • Blood vessels
  • Blood
• Function:
  • Transport of substances, including:
  • Oxygen and nutrients to cells.
  • Wastes from cells to liver and kidneys.
  • Hormones, immune cells, and clotting proteins to specific target cells.

Heart

• Chambers:
  • Atria: Upper chambers that receive blood.
  • Interatrial septum: Wall separating the atria.
  • Ventricles: Lower chambers that pump blood.
  • Interventricular septum: Wall separating the ventricles.
• Valves: Ensure unidirectional blood flow.
  • Atrioventricular (AV) valves:
  • Tricuspid valve: Between right atrium and right ventricle.
  • Bicuspid (mitral) valve: Between left atrium and left ventricle.
  • Semilunar (SL) valves:
  • Pulmonary valve: Between right ventricle and pulmonary trunk.
  • Aortic valve: Between left ventricle and aorta.
• Base and apex:
  • Base: Top of the heart where major vessels attach.
  • Apex: Bottom of the heart.

Blood Vessels

• Closed system:
  • Comprises a network of pathways through which blood circulates.
• Vasculature:
  • Arteries: Large, branching vessels carrying blood away from the heart.
  • Arterioles: Smaller branches of arteries with high resistance that control blood flow.
  • Capillaries: Microscopic blood vessels where exchange of gases, nutrients, and wastes occurs.
  • Venules: Small vessels that collect blood from capillaries.
  • Veins: Larger vessels that return blood to the heart.
• Flow sequence:
  • From heart → arteries → arterioles → capillaries → venules → veins.

Blood

• Erythrocytes (Red Blood Cells, RBCs):
  • Function: Transport oxygen from lungs to body tissues and carbon dioxide from tissues to lungs.
• Leukocytes (White Blood Cells, WBCs):
  • Function: Key role in the immune response and fighting infections.
• Platelets:
  • Function: Essential for blood clotting and wound healing.
• Plasma:
  • Fluid component of blood, consisting of water, salts, and organic molecules.

13.2 The Path of Blood Flow Through the Heart and Vasculature

• Series flow through the cardiovascular system:
  • Blood travels through distinct routes: pulmonary and systemic circuits.
• Parallel flow within the systemic or pulmonary circuit:
  • Blood flow can be adjusted independently to multiple organ systems.

Series Flow Through the Cardiovascular System

• Pulmonary circuit:
  • Blood vessels from the heart through the lungs and back to the heart.
• Systemic circuit:
  • Blood vessels from the heart through systemic tissues and back to the heart. Includes:
  • Coronary circulation: Supplies blood to the heart muscle.

Path of Blood Flow

• Systemic Circuit:
  • Sequence: Left ventricle → aorta → tissues → vena cavae → right atrium.
• Pulmonary Circuit:
  • Sequence: Right ventricle → pulmonary artery → alveoli → pulmonary veins → left atrium.

Oxygen Exchanges

• Exchange process in capillaries:
  • In pulmonary capillaries:
  • Blood entering lungs is deoxygenated.
  • O2 diffuses from alveoli to blood.
  • Blood leaving lungs is oxygenated.
  • In systemic capillaries:
  • Blood entering tissues is oxygenated.
  • O2 diffuses from blood to tissues.
  • Blood leaving tissues is deoxygenated.

Parallel Blood Flow Within Cardiovascular System

• Path of blood flow:
  • Sequence: Aorta → arteries → arterioles → capillaries.
  • Capillaries further branch into venules and veins.
• Independent regulation of blood flow:
  • Enables the body to prioritize blood supply to different organs.
• Portal circulation:
  • Two capillary beds are involved:
  • Hypothalamus and anterior pituitary.
  • Intestines and liver.
  • Nephrons in kidneys.

Coronary Circulation

• Route:
  • Blood flows via coronary arteries → arterioles → capillaries → venules → veins.
  • Coronary arteries (left and right): Arise from the aorta.
• Conditions:
  • Myocardial ischemia: Reduced blood flow to heart muscle.
  • Myocardial infarction: Heart attack; occurs when blood flow is blocked.

13.3 Anatomy of the Heart

• Location:
  • Situated within the thoracic cavity, rests on the diaphragm.
• Size and weight:
  • Approximately the size of a fist; weighs between 250-350 grams.

Pericardium

• Structures:
  • Consists of epicardium and parietal pericardium.
  • Pericardial cavity: Contains pericardial fluid that reduces friction during heartbeats.
• Function:
  • Protects the heart, prevents over-expansion.
  • Pericarditis: Inflammation of the pericardium.

Myocardium and the Heart Wall

• Three layers of the heart wall:
  • Epicardium: Outer layer, external membrane.
  • Myocardium: Middle layer composed of cardiac muscle.
  • Endothelium: Inner layer formed of endothelial cells.
• Distinctions:
  • Left ventricle has thicker walls than the right ventricle to pump blood with greater force.

Valves and Unidirectional Blood Flow

• Pressure dynamics:
  • Changes during the heartbeat cycle create pressure gradients that dictate blood flow direction.
• Normal flow direction:
  • Blood flows from the atria to the ventricles, and from the ventricles to the arteries.
• Function of valves:
  • Prevent backward flow of blood; open and close based on pressure gradients.

Atrioventricular (AV) Valves

• Location: Between atria and ventricles.
• Types:
  • Right AV valve: Tricuspid valve.
  • Left AV valve: Bicuspid valve (also called mitral valve).
• Chordae tendineae and papillary muscles:
  • Control the opening and closing of AV valves by preventing their eversion during ventricular contraction.

Semilunar (SL) Valves

• Location: Between ventricles and corresponding great arteries.
• Types:
  • Pulmonary valve: Located between right ventricle and pulmonary trunk.
  • Aortic valve: Located between left ventricle and aorta.
• Function:
  • When ventricles contract, blood presses against semilunar valves, forcing them open to allow ejection into the aorta and pulmonary artery.
  • Conversely, when ventricles relax, blood in the aorta and pulmonary artery presses down against the valve cusps, forcing them to close.