Cardiovascular System: Structure & Function

Overview

• Topic: Functions and structure of the cardiovascular (circulatory) system.
• Components: heart, blood vessels, blood; cardiopulmonary includes respiratory structures.
• Focus: heart anatomy, blood vessels, circulation types, cardiac cycle, conduction system, blood composition.

Heart Anatomy and Function

• Location: upper left chest, behind rib cage; ~size of clenched fist, ~10 ounces.
• Function: pumps blood through ~60,000 miles of vessels; ~100,000 beats per day.
• Layers of heart wall:
  • Epicardium: outer protective layer; contains coronary blood vessels.
  • Myocardium: muscular middle layer that contracts to pump blood.
  • Endocardium: thin inner layer lining chambers.
• Internal chambers:
  • Right atrium, right ventricle.
  • Left atrium, left ventricle.
• Valves (one-way):
  • Right AV (tricuspid) valve.
  • Pulmonary (pulmonary semilunar) valve.
  • Left AV (mitral/bicuspid) valve.
  • Aortic valve.
• Valve regurgitation: leaking valves allow backward flow, increasing cardiac workload.

Veins, Arteries, and Capillaries

• General rule:
  • Veins carry blood toward the heart.
  • Arteries carry blood away from the heart.
• Major veins to heart:
  • Superior vena cava: from upper body.
  • Inferior vena cava: from lower body.
  • Right and left pulmonary veins: carry oxygenated blood from lungs to heart.
  • Other major veins: jugular, subclavian, hepatic portal, renal, common iliac.
• Major arteries from heart:
  • Aorta: largest artery; distributes oxygenated blood bodywide.
  • Right and left pulmonary arteries: carry deoxygenated blood to lungs.
  • Coronary arteries: left and right supply myocardium.
  • Other major arteries: carotid, subclavian, common iliac, femoral, renal.
• Vessel hierarchy:
  • Arteries → arterioles → capillaries → venules → veins.
• Capillary beds: microscopic networks between arterioles and venules for nutrient and waste exchange.

Blood Circulation Pathways

• Two circulations:
  • Pulmonary circulation: heart ↔ lungs; deoxygenated blood to lungs, oxygenated blood back to heart.
  • Systemic circulation: heart ↔ rest of body; delivers oxygen/nutrients to tissues.
• Pathway through heart (oxygen-poor → oxygen-rich → body):
  • Superior/Inferior vena cava → right atrium → right AV valve → right ventricle.
  • Pulmonary semilunar valve → pulmonary arteries → lungs (oxygenation).
  • Pulmonary veins → left atrium → left AV valve → left ventricle.
  • Aortic valve → aorta → systemic circulation.
• Gas exchange location: capillaries in tissues swap CO2 for O2.

Cardiac Cycle and Electrical Conduction

• Cardiac cycle phases:
  • Systole: ventricles contract; pumps blood out; corresponds to systolic (top) blood pressure.
  • Diastole: ventricles relax and refill; corresponds to diastolic (bottom) blood pressure.
• Conduction system components:
  • SA node (sinoatrial): natural pacemaker; initiates atrial contraction.
  • AV node (atrioventricular): receives signal from SA node.
  • Bundle of His → bundle branches → Purkinje fibers: conduct impulse to ventricles causing contraction.
• Electrical activity visible on electrocardiogram (EKG).

Blood Composition and Functions

• Whole blood composition:
  • ~55% plasma (liquid) and ~45% formed elements (cells).
  • Average blood volume: men ~12 pints; women ~9 pints.
• Plasma: transports cells, nutrients, wastes, antibodies, clotting proteins, hormones.
• Formed elements:
  • Red blood cells (RBCs): contain hemoglobin; transport O2 to tissues and CO2 to lungs; produced in bone marrow.
  • White blood cells (WBCs): protect against infection.
  • Platelets: cell fragments that form clots to stop bleeding.
• Blood functions:
  • Transport O2 and nutrients to tissues.
  • Carry immune cells and antibodies.
  • Remove wastes to kidneys and liver.
  • Form clots to prevent excess bleeding.

Key Terms and Definitions

Review Question (Example)

• Question: Which vessel(s) contain oxygenated blood?
  • Options: inferior vena cava; pulmonary arteries; pulmonary veins; aorta; both pulmonary veins and aorta.
• Answer: Both pulmonary veins and aorta.
  • Pulmonary veins carry oxygenated blood from lungs to heart.
  • Aorta carries oxygenated blood from left ventricle to body.
  • Inferior vena cava and pulmonary arteries carry deoxygenated blood.

Action Items / Next Steps

• Review chamber and valve sequence of blood flow through the heart.
• Memorize conduction system order: SA node → AV node → His → branches → Purkinje fibers.
• Practice identifying major arteries and veins and their roles in pulmonary/systemic circulation.