Cardiovascular System: Complete Notes | Heart, Blood Vessels & Circulation
CARDIOVASCULAR SYSTEM
1. ANATOMY OF THE HEART
Location & Basic Structure
Location: Muscular organ in the thoracic cavity, slightly left of midline
Function: Pumps blood throughout the body via the circulatory system
A. Heart Chambers (4 chambers)
The heart is divided into right and left sides, each containing an upper chamber (atrium) and lower chamber (ventricle):
❖ Key Point: The right side handles deoxygenated blood; the left side handles oxygenated blood.
B. Heart Valves (4 valves)
Valves ensure unidirectional (one-way) blood flow through the heart:
❖ Key Point: AV Valve = Tricuspid Valve + Mitral Valve || Semilunar Valve = Pulmonary Valve + Aortic Valve
C. Heart Covering & Layers
☞ Pericardium: Protective sac that surrounds and supports the heart
❖ Three Layers of Heart Wall:
2. BLOOD CIRCULATION PATHWAY
Complete Circuit : (ADULT)
Superior/Inferior Vena Cava (S= Upper Blood Circulation, L= Lower Blood Circulation) →
Right Atrium →
(Tricuspid Valve) →
Right Ventricle →
(Pulmonary Valve) →
Lungs (gas exchange occurs) →
Pulmonary Veins (4 veins) →
Left Atrium →
(Mitral/Bicuspid Valve) →
Left Ventricle →
(Aortic Valve) →
Aorta → Body tissues
❖ Note: There are 4 pulmonary veins that carry oxygenated blood from lungs to left atrium. Also umbilical veins carries oxygenated blood.
Complete Circuit : (FETAL)
Superior/Inferior Vena Cava →
Right Atrium (Foramen Ovale) →
Left Atrium (Bicuspid Valve) →
Left Ventricle (Aortic Valve) →
Aorta → Body tissues
3. CARDIAC PHYSIOLOGY
A. Stroke Volume (SV)
Definition: Amount of blood ejected from each ventricle per heartbeat
Formula: Stroke Volume = End Diastolic Volume (EDV) - End Systolic Volume (ESV)
Normal Values:
Stroke Volume: ~70 ml
End Diastolic Volume (EDV): 110-120 ml (blood in ventricle at end of diastole/relaxation)
End Systolic Volume (ESV): 40-50 ml (blood remaining in ventricle after contraction)
Example Calculation:
If EDV = 120 ml and ESV = 60 ml
Stroke Volume = 120 - 60 = 60 ml
B. Heart Rate (HR)
Definition: Number of heartbeats per minute
Normal Range: 60-90 beats/minute
Factors Affecting Heart Rate:
Increases HR (Tachycardia):
Inspiration
Excitement, anger
Painful stimuli
Hypoxia (low oxygen)
Exercise
Fever
Decreases HR (Bradycardia):
Expiration
Fear
Increased intracranial pressure
C. Cardiac Output (CO)
Definition: Amount of blood ejected from each ventricle per minute
Formula: Cardiac Output = Stroke Volume × Heart Rate
Normal Value: ~5000 ml/min (5 liters/min)
Example Calculation:
If HR = 80 beats/min and SV = 70 ml
Cardiac Output = 70 × 80 = 5600 ml/min
Factors Regulating Cardiac Output:
Directly Proportional (↑ = ↑ CO):
Venous return (VR)
Force of contraction
Heart rate
Inversely Proportional (↑ = ↓ CO):
Total Peripheral Resistance (TPR)
Atrial pressure (afterload)
D. Factors Influencing Cardiac Output
Physiological Factors:
Age: CO higher in adults than children (more blood volume)
Gender: Males (5.6 L/min) > Females (4.9 L/min)
Surface Area: More surface area = higher CO
Posture: Increased when lying/sitting; decreased when standing
Exercise: Significantly increases CO
Emotion: Increases during emotional expressions
Pregnancy: Increases CO
Pathological Factors:
Increased CO:
Hyperthyroidism
Anemia
Fever
Decreased CO:
Hypothyroidism
Hemorrhage
Congestive Cardiac Failure (CCF)
Shock
E. Venous Return
Definition: Rate of blood flow returning to the heart
Important: Under normal conditions, venous return must equal cardiac output
Factors Affecting Venous Return:
Musculo-venous Pump: Walking, running, swimming → increases venous return (muscles squeeze veins)
Respiratory Pump:
Inspiration → decreased venous pressure → increased venous return
Forceful expiration (Valsalva maneuver) → decreased venous return
Blood Volume: Increased blood volume → increased venous return
Pressure Gradient: Increased gradient → increased venous return
4. CARDIAC CYCLE
Definition: Cyclic repetition of changes in the heart from beat to beat
Duration (at 72 beats/minute):
Systole (contraction): 0.3 seconds
Diastole (relaxation): 0.5 seconds
Complete Cardiac Cycle: 0.8 seconds
Heart Sounds
5. BLOOD PRESSURE
Factors Affecting Blood Pressure
Blood pressure depends on osmolarity of blood, influenced by:
Genetic Factors: ~40%
Other Factors (~60%):
High salt intake (sodium-rich diet)
Lack of physical activity
Overweight/Obesity
Osmolarity Influenced By:
80% = Table salt (sodium)
20% = Protein
❖ Note: Red meat = Protein + Cholesterol → Hypertension + Atherosclerosis
❖ Daily protein intake: 0.8 gm/kg/day (e.g., 70 kg person = 56 gm/day)
Types of Blood Pressure
Example Calculation (BP = 120/80 mmHg):
Pulse Pressure = 120 - 80 = 40 mmHg
Mean Pressure = 80 + (40/3) = 80 + 13 = 93 mmHg
6. CARDIAC CONDUCTION SYSTEM
Definition: Specialized cardiac muscle cells that generate and conduct electrical impulses
Pathway of Electrical Impulse:
SA Node (Sinoatrial Node) - "Pacemaker of the heart" - initiates electrical impulse
AV Node (Atrioventricular Node)
Bundle of His
Bundle Branches
Purkinje Fibers
❖ Key Point: The SA Node is called the pacemaker because it naturally generates electrical impulses that set the heart rate.
Electrocardiogram (ECG/EKG)
Definition: Medical test recording electrical activity of the heart over time
Purpose: Detects arrhythmias, heart attacks, and other cardiac conditions
12-Lead ECG Components:
Standard Limb Leads (3 leads):
Lead I: Right arm to left arm
Lead II: Right arm to left leg
Lead III: Left arm to left leg
Augmented Limb Leads (3 leads):
aVR: Right arm
aVL: Left arm
aVF: Left leg
Precordial/Chest Leads (6 leads):
V1 to V6: Placed on specific chest positions
These 12 leads provide comprehensive views of heart's electrical function from multiple angles.
7. COMMON CARDIOVASCULAR TERMINOLOGY
HEART RATE ABNORMALITIES :
Tachycardia
Definition: Increased heart rate (above normal range)
Normal range: 60-90 beats/minute
Tachycardia: Heart rate >100 beats/minute
Bradycardia
Definition: Decreased heart rate (below normal range)
Bradycardia: Heart rate <60 beats/minute
Supraventricular Tachycardia (SVT)
Definition: Rapid heart rhythm originating from the atria or AV node
Characteristics:
Sudden onset
Heart rate typically >150 beats/minute
Originates above the ventricles (hence "supraventricular")
Ventricular Tachycardia (VT)
Definition: Rapid heart rhythm originating from the ventricles
Characteristics:
Potentially life-threatening condition
May lead to cardiac arrest
Requires immediate medical attention
Can progress to ventricular fibrillation
Arrhythmia
Definition: Irregular heart rate or rhythm
Characteristics:
Heart beats too fast, too slow, or irregularly
Can affect heart's ability to pump blood effectively
Atrial Fibrillation/Flutter
Definition: Irregular or rapid atrial rhythm
Atrial Fibrillation (AFib): Irregular, chaotic atrial rhythm
Atrial Flutter: Rapid but more organized atrial rhythm
Complications: May cause stroke due to blood clot formation
Risk: Increases risk of stroke by 5 times
CARDIAC PROCEDURES :
CABG (Coronary Artery Bypass Grafting)
Definition: Surgical procedure to improve blood flow to the heart
Purpose: Treats coronary artery disease
Procedure: Uses blood vessels from other parts of body to bypass blocked coronary arteries
Indication: Severe coronary artery blockage
CONGENITAL HEART DEFECTS (CHD) :
Atrial Septal Defect (ASD)
Definition: Hole in the wall (septum) between the two atria
Effect:
Allows mixing of oxygenated and deoxygenated blood
Blood shunts from left atrium to right atrium
Increases blood flow to lungs
Symptoms: May be asymptomatic or cause fatigue, shortness of breath
Treatment: May require surgical repair or catheter-based closure
Ventricular Septal Defect (VSD)
Definition: Hole in the wall (septum) between the two ventricles
Significance: Most common congenital heart defect
Effect:
Allows mixing of oxygenated and deoxygenated blood
Blood shunts from left ventricle to right ventricle
Increases pulmonary blood flow
Symptoms: Varies from asymptomatic to heart failure
Treatment: Small VSDs may close spontaneously; large ones require surgical repair
Patent Ductus Arteriosus (PDA)
Definition: Persistence of fetal ductus arteriosus after birth
Normal Physiology:
In fetus, ductus arteriosus connects pulmonary artery to aorta
Should close within first few days after birth
PDA Problem: Ductus arteriosus remains open after birth
Effect:
Causes abnormal blood flow between aorta and pulmonary artery
Blood from aorta flows back into pulmonary artery
Increases pulmonary blood flow and workload on left heart
Symptoms: Heart murmur, rapid breathing, poor feeding
Treatment: Medication (in premature infants) or surgical closure
Pulmonary Stenosis
Definition: Narrowing of the pulmonary valve or pulmonary artery
Effect: Restricts blood flow from right ventricle to lungs
Consequences:
Right ventricle must work harder
May cause right ventricular hypertrophy
Reduced oxygenation of blood
Symptoms: Fatigue, shortness of breath, chest pain
Treatment: Balloon valvuloplasty or surgical repair
Tetralogy of Fallot (TOF)
Definition: Combination of FOUR congenital heart defects
The Four Defects:
VSD (Ventricular Septal Defect) - Hole between ventricles
Pulmonary Stenosis - Narrowing of pulmonary valve/artery
Right Ventricular Hypertrophy - Thickened right ventricular wall
Overriding Aorta - Aorta positioned over the VSD (instead of solely over left ventricle)
Effect:
Deoxygenated blood bypasses lungs and enters systemic circulation
Causes cyanosis (blue discoloration of skin)
Baby appears "blue"
Symptoms:
Cyanosis (bluish skin)
Difficulty breathing
Poor weight gain
"Tet spells" - sudden episodes of severe cyanosis
Treatment: Requires surgical repair in infancy
Key Point: Remember "TOF = 4 defects"
SUMMARY TABLE: CONGENITAL HEART DEFECTS :
KEY POINTS TO REMEMBER :
VSD is the most common congenital heart defect
TOF consists of exactly 4 defects (hence "Tetralogy")
SVT originates above the ventricles (supraventricular)
VT is life-threatening and may lead to cardiac arrest
Atrial Fibrillation significantly increases stroke risk
PDA is a persistence of a normal fetal structure
CABG is used for severe coronary artery disease
CLINICAL SIGNIFICANCE :
Cyanotic vs Acyanotic Defects :
Acyanotic Defects (Left-to-Right Shunt):
ASD
VSD
PDA
Blood goes from oxygenated side to deoxygenated side
No cyanosis initially
Cyanotic Defects (Right-to-Left Shunt):
TOF
Deoxygenated blood enters systemic circulation
Causes cyanosis (blue baby syndrome)
ONE-LINERS FOR QUICK REVISION:
SA node is the natural pacemaker of the heart.
Normal cardiac output is 4-8 L/min.
Preload refers to ventricular stretch at end diastole.
Afterload is the resistance the heart must pump against.
Left-sided heart failure causes pulmonary congestion.
Right-sided heart failure causes systemic congestion (edema, JVD).
Angina is chest pain due to myocardial ischemia.
Stable angina occurs with exertion, relieved by rest/nitroglycerin.
Unstable angina is unpredictable and a medical emergency.
Myocardial infarction (MI) causes irreversible myocardial necrosis.
Troponin is the most specific cardiac marker for MI.
MONA (Morphine, Oxygen, Nitrates, Aspirin) is emergency MI treatment.
Hypertension is defined as BP ≥ 140/90 mmHg.
Beta-blockers reduce heart rate and myocardial oxygen demand.
ACE inhibitors prevent ventricular remodeling post-MI.
Diuretics reduce preload by removing excess fluid.
Digoxin increases contractility but lowers heart rate.
Bradycardia is HR < 60 bpm; tachycardia is HR > 100 bpm.
Atrial fibrillation shows irregularly irregular rhythm with no P waves.
Ventricular fibrillation is a shockable rhythm immediate defibrillation!
CABG is performed to bypass blocked coronary arteries.
Cardiac tamponade presents with muffled heart sounds, JVD, hypotension.
Pericarditis causes chest pain that is relieved by leaning forward.
Endocarditis risk is high in patients with prosthetic valves.
Deep vein thrombosis (DVT) risk increases with immobility.
Pulmonary embolism is a life-threatening complication of DVT.
Aneurysm rupture presents with sudden severe pain and hypotension.
Nitroglycerin causes vasodilation and relieves chest pain.
ECG ST elevation indicates myocardial infarction.
Pacemaker maintains adequate HR in bradyarrhythmias.
Mean Arterial Pressure (MAP) should be ≥ 60 mmHg for organ perfusion.
S3 heart sound is common in heart failure (ventricular gallop).
S4 heart sound occurs with stiff ventricles, like in hypertension.
Mitral valve lies between the left atrium and left ventricle.
Tricuspid valve lies between the right atrium and right ventricle.
Aortic valve is semilunar and opens during systole.
Pulmonic valve directs blood from RV to pulmonary artery.
Cardiac catheterization requires checking for allergy to iodine.
Post-cardiac cath priority: check distal pulses and bleeding at site.
PTCA (angioplasty) is used to reopen narrowed coronary arteries.
CHF symptoms: dyspnea, fatigue, edema, crackles, orthopnea.
BNP (B-type natriuretic peptide) is elevated in heart failure.
Orthostatic hypotension: drop in BP ≥ 20 mmHg systolic or ≥ 10 mmHg diastolic on standing.
Raynaud's disease causes vasospasm of fingers in cold/stress.
Buerger's disease (thromboangiitis obliterans) affects young male smokers.
Aortic dissection: tearing chest/back pain, unequal BP in arms.
Shock= inadequate tissue perfusion and oxygenation.
Cardiogenic shock results from impaired pumping (e.g., MI).
Neurogenic shock is due to spinal cord injury-bradycardia is hallmark.
Septic shock = hypotension + infection + elevated lactate.
Cardiac enzymes: Troponin I (↑ within 3-6 hrs), CK-MB, Myoglobin.
Pericardial friction rub = classic finding in pericarditis.
HTN crisis: BP > 180/120 mmHg; treat with IV antihypertensives.
Elevated ST segment = MI; depressed ST segment = ischemia.
Defibrillation is used for pulseless VT and VF.
Cardioversion is synchronized and used in atrial fibrillation or SVT.
QT prolongation increases risk of torsades de pointes.
Vasopressors (e.g., norepinephrine) are used in hypotensive shock.
Calcium channel blockers (e.g., amlodipine) cause vasodilation.
Hyperkalemia ECG: peaked T waves, widened QRS.
Hypokalemia ECG: flattened T wave, presence of U wave.
Infective endocarditis: Osler nodes, Janeway lesions, Roth spots.
Heparin monitored with aPTT; Warfarin with INR.
Coronary arteries fill during diastole.
Dopamine is a vasopressor used to increase BP and kidney perfusion.
Pulsus paradoxus (↓ SBP >10 mmHg on inspiration) → cardiac tamponade.
Elevated JVD = sign of right heart failure or fluid overload.
Pitting edema suggests fluid retention or heart failure.
Postural drainage contraindicated in unstable cardiac patients.
Allen's test done before drawing ABG or inserting radial line.
MAP formula: MAP = (SBP + 2xDBP) ÷ 3.
Coronary artery disease (CAD) is the most common cause of angina & MI.
Silent MI is common in diabetics due to neuropathy.
Nitroglycerin causes headache and hypotension common side effects.
Hold digoxin if HR < 60 bpm in adults or < 100 bpm in infants.
Digoxin toxicity signs: nausea, visual halos, bradycardia.
Thiazide diuretics can cause hypokalemia and hyperglycemia.
Loop diuretics (e.g., furosemide) cause ototoxicity if given too fast.
Spironolactone is potassium-sparing - risk of hyperkalemia.
Statins lower LDL; watch for rhabdomyolysis (muscle pain).
Clopidogrel is an antiplatelet monitor for bleeding.
Aspirin inhibits platelet aggregation give in MI.
Aortic stenosis: systolic murmur, syncope, angina, dyspnea.
Mitral regurgitation: pansystolic murmur best at apex.
Aortic regurgitation: bounding pulse (water hammer pulse).
Coarctation of aorta: upper limb HTN, lower limb hypotension.
Tetralogy of Fallot: VSD, Pulmonary stenosis, Overriding aorta, RV hypertrophy.
Transposition of great arteries requires prostaglandin E1 to keep ductus open.
Patent ductus arteriosus (PDA) causes machinery murmur.
Heart transplant patients are immunosuppressed for life.
Cardiac rehab includes exercise, diet, smoking cessation, stress reduction.
Heparin antidote is protamine sulfate; warfarin antidote is vitamin K.
Pericardiocentesis relieves tamponade done with emergency setup.
CHF diet: low sodium, fluid restriction, monitor daily weight.
Unexplained syncope may indicate arrhythmia or structural heart disease.
Aneurysms are diagnosed by ultrasound or CT angiography.
AAA (abdominal aortic aneurysm) may show pulsatile abdominal mass.
BP goal in diabetes: < 130/80 mmHg.
Coronary artery bypass graft (CABG) uses saphenous vein or internal mammary artery.
Cardiac rehabilitation reduces future cardiovascular events by 20-30%.
HEMATOLOGIC SYSTEM
1. BLOOD - BASIC INFORMATION
Definition: Specialized body fluid delivering nutrients and oxygen to cells and removing waste products
Amount: Blood makes up 7-8% of total body weight
Functions of Blood:
Transporting O₂ and nutrients to lungs and tissues
Removal of waste (CO₂, urea, lactic acid) from tissues
Immunological functions (circulation of WBC; antibody detection of foreign materials)
Coagulation (blood clotting)
Messenger functions (hormone transport)
Regulation of core body temperature
2. BLOOD COMPOSITION
A. Blood Cells (40-45% of blood; 3% of body weight)
1. Erythrocytes (Red Blood Cells - RBC)
Size:
Diameter: 6.2-8.2 micrometers (μm), average 7-8 μm
Thickness: 2-2.5 μm
Life Span: 120 days
Components:
Hemoglobin: 95%
Cell membrane
Cytoplasm
Important Note: RBCs have NO nucleus - they are essentially "special bags" of hemoglobin
Function: Carry oxygen throughout body via hemoglobin
2. Leucocytes (White Blood Cells - WBC)
Also Called: "True cells" (because they have nuclei)
Life Span: 12-20 days
Two Main Types:
a) Granulocytes (have granules in cytoplasm; multi-lobed nucleus):
Neutrophils
Eosinophils
Basophils
b) Agranulocytes (no granules; oval-shaped nucleus):
Lymphocytes
Monocytes
Function: Immune defense, fighting infections
3. Thrombocytes (Platelets)
Description: Non-nucleated, small disc-like cell fragments
Size: 2-4 micrometers (μm)
Life Span: 8-10 days
Function: Assist in blood coagulation (clotting)
B. Plasma (55% of blood; 5% of body weight)
Definition: Liquid part of blood
Components:
Water: 91%
Protein: 8%
Salts: 0.8% (Sodium, Chloride, Potassium, Magnesium, Copper, Iodine, etc.)
Others: 0.2% (Glucose, Fats, Uric Acid, Amino Acids, Vitamins, Hormones, etc.)
3. BLOOD GROUPS
Definition: Blood group determined by genes inherited from parents
Total Blood Groups: 8 types
4 main types: A, B, AB, O
Each can be RhD positive or RhD negative
Antibodies and Antigens
Antigens: Protein molecules on surface of red blood cells
Antibodies: Proteins in plasma; part of body's natural defenses
The ABO System :
Key Points to Remember:
Blood Group O: Has NO antigens but has BOTH antibodies
Blood Group AB: Has BOTH antigens but NO antibodies
Blood group O is the most common blood group
For transfusion compatibility, consider both antigens and antibodies
QUICK REFERENCE SUMMARY
Important Numbers to Remeantibodie :
FORMULAS TO MEMORIZE
Stroke Volume = EDV - ESV
Cardiac Output = Stroke Volume × Heart Rate
Pulse Pressure = Systolic BP - Diastolic BP
Mean Arterial Pressure = Diastolic BP + (1/3 × Pulse Pressure)
Daily Protein Intake = 0.8 gm/kg/day
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