Cardiovascular_PP__2023_

Cardiovascular System

1. Introduction

• The cardiovascular system consists of the heart and vascular structures, including arteries, capillaries, and veins.

• It plays a vital role in:

  • Supplying oxygen and nutrients to tissues.

  • Removing waste products from tissues.

• Blood flow consists of two primary circuits:

  • Pulmonary Circuit:

    • Transports deoxygenated blood to the lungs for oxygenation.

  • Systemic Circuit:

    • Distributes oxygenated blood to body cells.

2. Heart Anatomy

A. Structure of the Heart

• The heart is a hollow, cone-shaped muscular pump located in the thoracic cavity

• Size: Average adult heart is 14 cm long and 9 cm wide.

• Location: Lies in the mediastinum beneath the sternum; apex reaches the fifth intercostal space.

B. Coverings of the Heart

1. Pericardium:

   • Encloses the heart and consists of two layers:

     • Fibrous Pericardium: Outer tough layer.

     • Visceral Pericardium (Epicardium): Delicate inner layer surrounding the heart.

   • Parietal Pericardium: Lines the fibrous pericardium at the base of the heart.

   • The pericardial cavity between these layers is filled with serous fluid.

C. Wall of the Heart

1. Composed of three layers:

   • Epicardium: Outermost layer, containing connective tissue and epithelium; includes blood vessels.

   • Myocardium: Thickest layer composed of cardiac muscle, responsible for contractions.

   • Endocardium: Smooth inner layer continuous with the endothelium of large vessels; contains Purkinje fibers.

D. Heart Chambers and Valves

1. The heart contains four chambers:

   • Atria: Two upper chambers that receive blood, characterized by thin walls and auricles.

   • Ventricles: Two lower chambers that pump blood to the body, with thicker muscular walls.

2. Valves:

   • Atrioventricular (A-V) Valves: Prevent backflow of blood; include:

     • Right A-V valve (Tricuspid)

     • Left A-V valve (Bicuspid or Mitral)

   • Pulmonary and Aortic Valves: Prevent backflow from arteries into the ventricles.

E. Heart Function

1. Blood flow sequence:

   • Deoxygenated blood returns to the right atrium via the vena cavae.

   • Right atrium > Tricuspid valve > Right ventricle > Pulmonary valve > Pulmonary trunk > Lungs.

   • Oxygenated blood returns to the left atrium > Left atrium > Bicuspid valve > Left ventricle > Aortic valve > Aorta > Body.

3. Blood Supply to the Heart

• Coronary arteries (first branches of the aorta) supply oxygenated blood to the heart muscle.

• Smaller branches form anastomoses to ensure a continuous blood supply.

• Cardiac veins drain deoxygenated blood from the heart tissue into the coronary sinus, which empties into the right atrium.

4. Cardiac Cycle and Heart Actions

A. Cardiac Cycle

• Consists of:

  1. Atrial Systole: Contraction of atria.

  2. Ventricular Systole: Contraction of ventricles.

  3. Diastole: Brief relaxation phase.

• Changes in pressure govern blood flow and valve function.

B. Heart Sounds

• Heart sounds result from vibrations as blood moves through the heart, producing:

  • "Lubb" sound: Occurs when A-V valves close during ventricular contraction.

  • "Dupp" sound: Occurs when aortic and pulmonary valves close during ventricular relaxation.

5. Electrocardiogram (ECG)

• Records electrical changes during the cardiac cycle:

  1. P wave: Atrial depolarization.

  2. QRS complex: Ventricular depolarization.

  3. T wave: Ventricular repolarization.

6. Regulation of the Cardiac Cycle

1. Heart rate adjusts based on physiological needs, influenced by:

   • S-A Node: Pacemaker of the heart, controls heartbeat.

   • Central Nervous System (CNS): Sympathetic (increases HR) and parasympathetic (decreases HR) innervation.

7. Blood Vessels

A. Structure and Function

• Blood vessels form a closed circuit carrying blood throughout the body.

• Types of blood vessels:

  • Arteries: Carry blood away from the heart under high pressure.

  • Capillaries: Site of exchange between blood and tissues.

  • Veins: Return blood to the heart; lower pressure than arteries.

8. Circulation Pathways

A. Pulmonary Circuit

• Vessels carry blood from the right ventricle to the lungs for gas exchange, returning oxygenated blood to the left atrium.

B. Systemic Circuit

• Transports oxygenated blood from the left ventricle via the aorta to all body tissues, returning deoxygenated blood to the right atrium.

9. Arteries and Their Branches

• The aorta is the largest artery with major branches supplying various body regions:

1. Coronary Arteries: Supply the heart.

2. Brachiocephalic, Common Carotid, Subclavian Arteries: Supply the head, neck, and arms.

3. Abdominal Aorta: Gives rise to various branches for organs and limbs.

10. Venous System

A. Characteristics

• Veins carry deoxygenated blood, with larger veins paralleling arteries; smaller veins have irregular paths.

B. Higher Level Structure

• Venous drainage from upper body into the superior vena cava and from the lower body into the inferior vena cava.

11. Hepatic Portal System

• Blood from gastrointestinal organs first drains into the liver for processing through the hepatic portal vein before returning to the systemic circulation.