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Cardiovascular System

A closed system of the heart and blood vessels that transports blood throughout the body, delivering oxygen/nutrients and removing wastes.

Heart Size

Approximately the size of a closed fist, weighs 250-350g in adults.

Heart Location

Mediastinum of thoracic cavity, between lungs, posterior to sternum, anterior to vertebral column, rests on diaphragm.

Heart Orientation

Apex points left/inferior (5th intercostal space), base is superior/posterior (2nd rib level).

Fibrous Pericardium

Tough, dense connective tissue outer layer; prevents overdistension, anchors heart.

Parietal Pericardium

Inner layer of fibrous pericardium; lines pericardial cavity.

Visceral Pericardium (Epicardium)

Innermost layer; adheres to heart surface, contains fat deposits.

Pericardial Cavity

Potential space containing 15-50ml serous fluid for lubrication.

Epicardium

Visceral pericardium + areolar tissue/fat; outermost heart layer.

Myocardium

Middle layer of cardiac muscle; thickest in left ventricle (10-15mm).

Endocardium

Endothelial lining + subendothelial connective tissue; continuous with vessel linings.

Right Atrium

Receives deoxygenated blood from SVC, IVC, coronary sinus; contains pectinate muscles.

Left Atrium

Receives oxygenated blood from 4 pulmonary veins; smooth-walled.

Right Ventricle

Pumps to pulmonary trunk; thin wall (3-5mm), crescent-shaped cavity.

Left Ventricle

Pumps to aorta; thick wall (10-15mm), conical cavity.

Interatrial Septum

Wall between atria; contains fossa ovalis (remnant of foramen ovale).

Interventricular Septum

Muscular (inferior) + membranous (superior) portions; separates ventricles.

Tricuspid Valve

Right AV valve with 3 cusps; anchored by chordae tendineae to papillary muscles.

Mitral Valve

Left AV valve (bicuspid); 2 cusps, stronger than tricuspid.

Pulmonary Valve

Semilunar valve at pulmonary trunk origin; 3 cusps, no chordae.

Aortic Valve

Semilunar valve at aortic orifice; 3 cusps (right, left, posterior).

Chordae Tendineae

Fibrous strings connecting AV valve cusps to papillary muscles.

Papillary Muscles

Projections of myocardium that prevent valve prolapse.

Pulmonary Circuit

Right heart → lungs → left heart; low-pressure (15-30mmHg).

Systemic Circuit

Left heart → body → right heart; high-pressure (100-140mmHg).

Coronary Arteries

First aortic branches; right coronary supplies RA/RV; left coronary divides into LAD/circumflex.

Cardiac Veins

Great cardiac vein → coronary sinus → RA; small/middle cardiac veins drain directly.

SA Node

Pacemaker; 60-100bpm; located at SVC/RA junction.

AV Node

Delays impulse (0.1s); located in interatrial septum.

Bundle of His

Only electrical connection between atria/ventricles; divides into bundle branches.

Purkinje Fibers

Terminal conduction fibers; rapid ventricular depolarization.

Cardiac Cycle

0.8s total: atrial systole (0.1s), ventricular systole (0.3s), relaxation (0.4s).

Systole

Contraction phase; ventricles eject blood (120mmHg).

Diastole

Relaxation phase; chambers fill (80mmHg).

Lub Sound

AV valves closing (S1); loud/long at ventricular systole onset.

Dup Sound

Semilunar valves closing (S2); short/sharp at diastole onset.

Cardiac Output

4-8L/min; CO = HR × SV.

Stroke Volume

70ml/beat; determined by preload, contractility, afterload.

Starling's Law

Increased venous return → greater stretch → stronger contraction.

Preload

Degree of myocardial stretch before contraction (end-diastolic volume).

Afterload

Pressure ventricles must overcome to eject blood (aortic pressure).

Tunica Intima

Innermost vessel layer: endothelium + basement membrane + internal elastic lamina.

Tunica Media

Middle layer: smooth muscle + elastic fibers; thick in arteries.

Tunica Externa

Outer layer: collagen/elastic fibers; contains vasa vasorum in large vessels.

Elastic Arteries

Large arteries (aorta) with abundant elastin; pressure reservoirs.

Muscular Arteries

Distributing arteries (brachial); thick tunica media for vasoconstriction.

Arterioles

Resistance vessels; regulate blood flow via smooth muscle sphincters.

Capillaries

Single endothelial cell layer; sites of exchange (continuous, fenestrated, sinusoidal).

Venules

Small veins collecting from capillaries; porous for WBC migration.

Veins

Thin walls, large lumens, valves; contain 60% blood volume.

Vascular Sinuses

Flattened veins (coronary sinus, dural sinuses) with thin walls.

Aorta

Ascending → arch → descending (thoracic/abdominal); largest artery.

Brachiocephalic Trunk

First aortic arch branch; divides into right subclavian + right common carotid.

Common Carotid Arteries

Branch to internal (brain) + external (head) carotids at C4.

Subclavian Arteries

Become axillary → brachial → radial/ulnar arteries.

Celiac Trunk

First abdominal branch: left gastric, splenic, common hepatic arteries.

Superior Mesenteric Artery

Supplies small intestine + proximal colon.

Renal Arteries

Lateral branches at L1; supply kidneys.

Common Iliac Arteries

Terminal aortic branches; divide into internal/external iliacs.

Superior Vena Cava

Returns blood from head/arms/chest to RA; formed by brachiocephalic veins.

Inferior Vena Cava

Returns blood from lower body to RA; formed by common iliac veins at L5.

Hepatic Portal System

Capillary beds of GI tract → hepatic portal vein → liver sinusoids → hepatic veins → IVC.

Blood Pressure

Force per unit area on vessel walls (mmHg); systolic/diastolic.

Pulse Pressure

Systolic - diastolic (normal: 40mmHg).

Mean Arterial Pressure

Diastolic + 1/3 pulse pressure (normal: 70-110mmHg).

Hypertension

Sustained BP ≥140/90mmHg; primary or secondary causes.

Hypotension

BP <90/60mmHg; may cause syncope/shock.

Capillary Exchange

Diffusion (O2/CO2), transcytosis (proteins), bulk flow (fluid).

Hydrostatic Pressure

"Pushing" force from blood pressure; highest at arterial end (35mmHg).

Colloid Osmotic Pressure

"Pulling" force from proteins (25mmHg); constant along capillary.

Net Filtration Pressure

(HPc - HPif) - (OPc - OPif); positive = filtration, negative = reabsorption.

Lymphatic Drainage

Returns filtered fluid to veins via thoracic duct (left) + right lymphatic duct.