Cardiovascular System: Heart Anatomy, Function, and Electrical Activity

Heart

A two-sided pump with four chambers that circulates blood through pulmonary and systemic circuits

Right Atrium

Receives deoxygenated blood from the systemic circuit

Right Ventricle

Pumps deoxygenated blood into the pulmonary circuit

Left Atrium

Receives oxygenated blood from the pulmonary circuit

Left Ventricle

Pumps oxygenated blood into the systemic circuit

Mediastinum

Space in the thorax between the lungs where the heart is located

Pericardium

Sac surrounding the heart that protects and stabilizes it

Fibrous Pericardium

Tough outer layer of the pericardium

Serous Pericardium

Double-layered membrane (parietal + visceral layers)

Pericardial Cavity

Space between serous layers containing lubricating fluid

epicardium

Outer layer; also the visceral layer of the serous pericardium

Myocardium

Middle layer made of cardiac muscle responsible for contraction

Endocardium

Inner lining of the heart chambers and valves

Cardiac Muscle

Striated, involuntary muscle found only in the heart

Intercalated Discs

Structures connecting cardiac cells that allow synchronized contraction

Desmosomes

Hold cardiac cells together

Gap Junctions

Allow electrical signals to pass between cells

Functional Syncytium

Cardiac cells acting as one coordinated unit

Coronary Circulation

Blood supply to the heart muscle itself

Coronary Arteries

Arise from the aorta and supply oxygenated blood to myocardium

Coronary Veins

Drain deoxygenated blood from the heart

Coronary Sinus

Large vein that collects blood from coronary veins

Atrioventricular (AV) Valves

Allow blood flow from atria to ventricles only

Tricuspid Valve

Right AV valve (3 cusps)

Mitral (Bicuspid) Valve

Left AV valve (2 cusps)

Semilunar Valves

Control blood flow out of ventricles

Pulmonary Valve

Between right ventricle and pulmonary trunk

Aortic Valve

Between left ventricle and aorta

Chordae Tendineae

Tendinous cords that prevent valve inversion

Papillary Muscles

Tighten chordae tendineae during contraction

Cardiac Cycle

One complete heartbeat (systole + diastole)

Systole

Contraction phase when blood is pumped out

Diastole

Relaxation phase when chambers fill with blood

Atrial Systole

Atria contract to fill ventricles

Ventricular Systole

Ventricles contract to eject blood

Isovolumetric Contraction

Ventricles contract with no volume change (valves closed)

Ventricular Ejection

Blood is pumped out of ventricles

Isovolumetric Relaxation

Ventricles relax with all valves closed

Autorhythmicity

Heart's ability to beat without external stimulation

Sinoatrial (SA) Node

Natural pacemaker (60-100 bpm)

Internodal Pathways

Spread impulse through atria

Atrioventricular (AV) Node

Delays and relays impulse to ventricles

AV Bundle (Bundle of His)

Conducts signal to ventricles

Bundle Branches

Carry signal down interventricular septum

Purkinje Fibers

Distribute impulse through ventricles

Parasympathetic Stimulation

Decreases heart rate (via vagus nerve)

Sympathetic Stimulation

Increases heart rate (via norepinephrine)

Pacemaker Potential

Gradual depolarization in pacemaker cells

Cardiac Output (CO)

Volume of blood pumped per minute

Heart Rate (HR)

Beats per minute

Stroke Volume (SV)

Blood pumped per beat

Cardiac Output Formula

CO = HR × SV

Blood Pressure

Force of blood against vessel walls

Systolic Pressure

Pressure during ventricular contraction

Diastolic Pressure

Pressure during relaxation

Pulse Pressure

Difference between systolic and diastolic pressure

Mean Arterial Pressure (MAP)

Average arterial pressure

Peripheral Resistance

Resistance to blood flow in vessels

Vessel Diameter

Most important factor (smaller = more resistance)

Vessel Length

Longer vessels increase resistance

Viscosity

Thickness of blood (higher = more resistance)

Turbulence

Irregular flow that increases resistance

Blood Flow

Volume of blood moving through vessels over time

Pressure Gradient

Difference in pressure that drives flow

Relationship

Flow ∝ pressure and inversely ∝ resistance

Capillary Exchange

Movement of substances between blood and tissues

Diffusion

Movement from high to low concentration

Filtration

Movement out of capillaries due to pressure

Reabsorption

Movement back into capillaries

Capillary Hydrostatic Pressure (CHP)

Pushes fluid out

Blood Colloid Osmotic Pressure (BCOP)

Pulls fluid in

Net Filtration Pressure (NFP)

NFP = CHP − BCOP

Edema

Excess fluid accumulation in tissues

Autoregulation

Local control of blood flow

Central Regulation

Neural and hormonal control

Baroreceptors

Detect changes in blood pressure

Chemoreceptors

Detect CO₂, O₂, and pH levels

Epinephrine/Norepinephrine

Increase heart rate and blood pressure

Antidiuretic Hormone (ADH)

Increases blood volume

Angiotensin II

Raises blood pressure

Aldosterone

Increases sodium and water retention

Atrial Natriuretic Peptide (ANP)

Lowers blood pressure