cardiovascular system

• Heart anatomy and the function of the 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
• The heart: location and size

  • Located in the thoracic cavity, under the sternum
  • Size of a clenched fist; weighs less than two cricket balls
  • Sits on diaphragm, flanked by lungs
  • Base near the 2nd rib; apex points to left hip at about the 5th rib
• The four chambers of the heart

  • 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


  1. Right atrium: Receives deoxygenated blood via vena cava

  2. Right ventricle: Pumps blood to lungs

  3. Left atrium: Receives oxygenated blood from lungs

  4. Left ventricle: Pumps blood to body through aorta

  5. Both ventricles contract almost simultaneously
• The heart valves


  Four valves control one-way blood flow
• Atrioventricular valves (AV valves)

  • Located between atria and ventricles
  • Open: blood flows from atria to ventricles
  • Closed: prevent backflow into atria
  • Right AV valve: tricuspid (three cusps)
  • Left AV valve: bicuspid/mitral (two cusps)
• Chordae tendinae & papillary muscles

  • Fibrous cords attached to valve cusps
  • Contract with ventricles to prevent valve inversion
• Semilunar valves


  • Control flow from ventricles to lungs/body
  • Pulmonary valve: right side, leads to lungs
  • Aortic valve: left side, leads to body
  • Three "half-moon" cusps, self-supporting when closed
• 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
  • Three layers: Epicardium (outer layer, inner layer of pericardial sac), Myocardium (middle layer, 2/3 of heart muscle), Endocardium (innermost layer, lines chambers and valves)
• The 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
• Cardiac output


  • Blood pumped per minute
  • Calculated: Heart rate × stroke volume
  • Avg. for 70 kg male: 72 bpm, 70 ml/beat → 5,040 ml/min
  • Influenced by body size, exercise, emotions, diet, activity
• Regulation of the heart

  Three mechanisms: one internal, two external
• Internal control of heart rate

  • Pacemaker sinoatrial (SA) node: located in right atrium
  • Sets default rate: 60-100 bpm
• External control of heart rate

  • Cardiac centre in medulla oblongata: Receives input from autonomic nervous system, Adjusts heart rate, contraction strength, stroke volume
  • Baroreceptors: monitor blood pressure
  • Parasympathetic nervous system: dominant at rest, slows heart rate
  • Sympathetic nervous system: active during stress/exercise, increases rate
• Endocrine system


  • Influenced by emotions, physical activity
  • Fight or flight: limbic system activates sympathetic branch
  • Parasympathetic releases acetylcholine; sympathetic releases noradrenaline
• Control of stroke volume

  • Three main factors: Preload, Contractility, Afterload
  • 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


  • Includes nodal tissue and conduction fibres
  • SA Node: Initiates impulse
  • AV Node: Delays impulse 1/10 second
  • Bundle of His, Left/Right bundle branches: Carry impulse to ventricles
  • 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
• Three 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
• Circulation: blood flow in the body

  Cardiopulmonary circulation consists of: Pulmonary circulation (heart to lungs), Systemic circulation (heart to body)
• Sequence in pulmonary circulation

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

  2. Right atrium to right ventricle: through tricuspid valve

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

  4. Pulmonary artery: splits into smaller arteries to lungs

  5. Arterioles and capillaries: merge in lungs

  6. Oxygenation: blood oxygenated in lungs, moves to venules

  7. To heart: via four pulmonary veins to left atrium

  8. Left atrium to left ventricle: through mitral valve

  9. To body: left ventricle contracts, oxygenated blood to aorta
• 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
  • 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