Cardiovascular Systerm

• Cardiovascular system


  Consists of heart, blood vessels, and blood. Transports oxygen, hormones, nutrients to cells. Removes CO2 and waste from the body. Regulates body temperature via vasodilation and vasoconstriction.
• Heart chambers


  • Right and left atrium; right and left ventricle
  • Atria act as low-pressure collecting chambers
  • Ventricles act as high-power pumps
  • Interatrial septum separates right and left atria
  • Interventricular septum separates right and left ventricles
  • Prevents oxygen-rich and oxygen-poor blood from mixing
• Blood flow through the heart

  1. Right atrium: Deoxygenated blood enters from inferior and superior vena cava

  2. Tricuspid valve: Opens due to pressure; right ventricle fills passively. Atrial contraction completes filling

  3. Right ventricle: Contracts, tricuspid valve closes, pulmonary valve opens. Blood enters pulmonary artery

  4. Lungs: Blood oxygenated in capillaries

  5. Left atrium: Oxygenated blood returns via pulmonary veins

  6. Mitral valve: Opens due to pressure; left ventricle fills passively. Atrial contraction completes filling

  7. Left ventricle: Contracts, mitral valve closes, aortic valve opens. Blood enters aorta

  8. Aorta: Oxygenated blood distributed to body
• Walls of the heart


  • Enclosed in fluid-filled pericardium
  • Epicardium: Outer layer, inner layer of pericardial sac
  • Myocardium: Middle layer, 2/3 of heart muscle
  • Endocardium: Innermost layer, lines chambers and valves
• Cardiac cycle


  • Two phases: Diastole (relaxation): chambers fill with blood. Systole (contraction): chambers pump blood out
  • Cycle duration: Approx. 0.8 seconds
  • Time split: 2/3 in diastole, 1/3 in systole
• Internal control of heart rate

  1. Pacemaker sinoatrial (SA) node: located in right atrium

  2. Sets default rate: 60-100 bpm
• External control of heart rate

  1. Cardiac centre in medulla oblongata receives input from autonomic nervous system

  2. Adjusts heart rate, contraction strength, stroke volume

  3. Baroreceptors: monitor blood pressure

  4. Parasympathetic nervous system: dominant at rest, slows heart rate

  5. Sympathetic nervous system: active during stress/exercise, increases rate
• Control of stroke volume


  • Preload: stretch of ventricle muscles during diastole
  • Contractility: heart muscle's ability to contract. Influenced by preload
  • Afterload: pressure to overcome aorta resistance
• The conduction system


  1. SA Node: Initiates impulse

  2. AV Node: Delays impulse 1/10 second

  3. Bundle of His, Left/Right bundle branches: Carry impulse to ventricles

  4. Purkinje Fibres: Trigger ventricular contraction
• Electrocardiogram (ECG)


  • Records electrical activity
  • P wave: SA node firing, atrial contraction
  • QRS Complex: impulses to Purkinje fibres, ventricular contraction
  • T wave: ventricular relaxation, chamber filling
• Blood vessels


  • Types: arteries, capillaries, veins
  • Subdivisions: arterioles, venules
• Layers in blood vessel walls

  • Tunica intima: smooth, frictionless surface
  • Tunica media: smooth muscle, controls vasodilation/vasoconstriction. Influences blood pressure
  • Tunica externa: fibrous tissue, adds support
• Differences: arteries vs. veins


  Arteries: Thick, strong walls. Carry blood away from the heart. Withstand high pressure.

  Veins: Thinner, less elastic walls. Carry blood toward the heart. House 2/3 of body's blood. One-way valves assist in venous return. Skeletal muscles and respiratory system assist in pumping blood back.
• Capillaries


  • Smallest blood vessels, 0.0025-0.25 cm. Red blood cells pass in single file.

  Function: Site for O2 and CO2 gas exchange. Pores in kidneys, liver, etc., allow passage of hormones, white blood cells.

  Blood flow control: Precapillary sphincter controls blood flow. Reacts to local chemical conditions like pH, O2, CO2, temperature.

  During exercise: Blood flow to muscles increases from 15% to 85%.

  Capillary beds: Interconnected network. Merge with venules, then larger veins, leading back to the heart.
• Pulmonary circulation


  Entry: deoxygenated blood enters right atrium via inferior/superior venae cavae.

  Right atrium to right ventricle: through tricuspid valve.

  Pulmonary valve: right ventricle contracts, blood goes to pulmonary artery.

  Pulmonary artery: splits into smaller arteries to lungs.

  Arterioles and capillaries: merge in lungs.

  Oxygenation: blood oxygenated in lungs, moves to venules.

  To heart: via four pulmonary veins to left atrium.
• Systemic circulatory system


  Closed-loop network: arteries, arterioles, capillaries, venules, veins.

  Functions: Transports oxygen, hormones, water, and nutrients to tissues; returns waste and CO2 to the heart.

  Start of systemic circulation: Left ventricle pumps blood to aorta. Ascending aorta rises and arches left, becoming descending aorta in thorax and abdomen.

  Major arterial branches: Right and left coronary arteries from ascending aorta -> heart. Brachiocephalic, left common carotid, left subclavian from aortic arch -> head, neck, arms. Descending aorta branches -> organs like liver, spleen, kidneys.

  Microcirculation and return: Arteries -> arterioles -> capillaries for exchange. Blood drains into venules, merges into veins.

  End of systemic circulation: Lower veins -> inferior vena cava. Upper veins -> superior vena cava. Both drain into right atrium.
• Cardiac circulation


  Oxygen supply to the heart: Heart's oxygen not supplied by blood in its chambers. Right and left coronary arteries supply oxygen-rich blood.

  Origin and timing: Coronary arteries arise from base of aorta. Fill when ventricles are relaxed; closed during ventricular contraction.

  Drainage: Blood from coronary arteries -> cardiac veins. Drains into coronary sinus on posterior wall of right atrium.