Cardiovascular+Overview_Cardiac+Cycle

Overview of The Cardiovascular System & The Cardiac Cycle

• Study materials for BIOL 2930 taught by Prof. O’Connor.

Lecture Overview

• Key components and functions of the circulatory system.

• Structure of the heart, consisting of:

  • Atria

  • Ventricles

  • Valves

• Differentiation between systemic and pulmonary systems.

• Introduction to the cardiac cycle, including:

  • Ventricular systole

  • Isovolumetric contraction

  • Ejection

  • Ventricular diastole

  • Isovolumetric relaxation

  • Ventricular filling

  • Atrial contraction

Functions and Components of the Circulatory System

• Functions:

  1. Transportation

     • Movement of respiratory gases, nutrients, and wastes.

  2. Regulation

     • Maintenance of hormonal balance and temperature regulation.

  3. Protection

     • Role in clotting and immune response.

Major Components of the Circulatory System

1. Cardiovascular System

   • Heart: A four-chambered pump serving pulmonary and systemic circulations.

   • Blood Vessels: Arteries (carry blood away from the heart), arterioles, capillaries, venules, and veins (return blood to the heart).

   • Blood: Comprises cells and plasma.

2. Lymphatic System

   • Involves lymphatic vessels, lymphoid tissues, and organs (spleen, thymus, tonsils, lymph nodes).

   • Lymph: Fluid derived from blood that returns to circulation.

Structure of the Heart

• Four Chambers:

  • Right atrium: Receives deoxygenated blood from the body.

  • Left atrium: Receives oxygenated blood from the lungs.

  • Right ventricle: Pumps deoxygenated blood to the lungs.

  • Left ventricle: Pumps oxygenated blood to the body.

Separation of Chambers

• The right and left sides are separated by the septum, which prevents mixing of oxygen-rich and oxygen-poor blood.

• Fibrous Skeleton:

  • Separates atria from ventricles, allowing them to function as separate units (myocardium).

  • Forms annuli fibrosi rings supporting heart valves.

Circulatory Pathways

1. Pulmonary Circulation:

   • Blood flows from the heart to the lungs via pulmonary arteries and back to the heart via pulmonary veins.

2. Systemic Circulation:

   • Blood is pumped to body tissues via the aorta and returns through the superior and inferior venae cavae.

Blood Vessels

• Arteries: Carry blood away from the heart, generally oxygenated (except pulmonary artery).

• Veins: Carry blood towards the heart, generally deoxygenated (except pulmonary vein).

Atrioventricular and Semilunar Valves

1. Atrioventricular (AV) Valves:

   • Located between atria and ventricles, prevent backflow.

     • Tricuspid valve (right atrium and ventricle).

     • Bicuspid or mitral valve (left atrium and ventricle).

   • Supported by papillary muscles and chordae tendineae to prevent eversion.

2. Semilunar Valves:

   • Located between ventricles and arteries, prevent backflow.

     • Pulmonary valve (between right ventricle and pulmonary trunk).

     • Aortic valve (between left ventricle and aorta).

Pressure, Valves & Blood Flow

• Valves operate unidirectionally based on pressure differentials between vessels and heart compartments, created by cardiac muscle contractions.

  • Cardiac cycle begins with ventricular contraction, followed by atrial contraction.

The Cardiac Cycle

• Definition:

  • A repeating sequence of heart contraction (systole) and relaxation (diastole).

• End-Diastolic Volume: Total blood in ventricles at the end of diastole.

• End-Systolic Volume: The residual blood in left ventricle post-systole, typically 1/3 of end-diastolic volume.

• At 75 beats/min, the cardiac cycle duration is approximately 0.8 seconds.

Phases of the Cardiac Cycle

1. Isovolumetric Contraction (Systole):

   • Ventricles contract, intraventricular pressure rises, AV valves close (first heart sound: "lub").

2. Ejection (Systole):

   • Further rise in intraventricular pressure causes semilunar valves to open, ejecting blood into arteries.

3. Isovolumetric Relaxation (Diastole):

   • Ventricles relax, pressure falls, semilunar valves close (second heart sound: "dub").

4. Ventricular Filling:

   • Ventricular pressure decreases below atrial pressure, AV valves open, ventricles fill with blood.

5. Atrial Contraction:

   • Atria contract, forcing remaining blood into ventricles through open AV valves.

Abnormal Blood Flow & Sounds

• Septal Defects:

  • Holes in interventricular or interatrial septa may allow blood to cross sides. Example: Patent ductus arteriosus (failure of foramen ovale closure).

• Heart Murmurs:

  • Abnormal heart sounds resulting from irregular blood flow, often due to defective valves or conditions like rheumatic endocarditis.

  • Mitral Stenosis: Mitral valve calcification impacts flow between left atrium and ventricle, potential pulmonary hypertension.

  • Incompetent Valves: Malfunctioning valves may be due to damaged papillary muscles or conditions like mitral valve prolapse.

Cardiac Cycle Game

• Interactive tool to better understand the cardiac cycle mechanics.