Transport, exchange & defense · Topic 11 of 18

The Heart: Structure, Blood Flow & Conduction

Heart Structure & Blood Flow

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Anatomy & Physiology · the heart

Heart Structure & Blood Flow

Four chambers and four one-way valves: blood goes right atrium → right ventricle → lungs → left atrium → left ventricle → aorta.

01 · Right sideRA → tricuspid → RV → pulmonary valve

02 · Left sideLA → mitral → LV → aortic valve → aorta

03 · Four valvesAV: tricuspid, mitral · SL: pulmonary, aortic

What it is

Right heart: O₂-poor blood → lungs; left heart: O₂-rich blood → body must know

Parts & jobs

4 chambers: 2 atria receive blood, 2 ventricles pump it out must know

AV valves (tricuspid, mitral) + semilunar valves (pulmonary, aortic) must know

Heart: in the mediastinum between the lungs; fist-sized; apex at the bottom

Pericardium = the sac around the heart; its fluid cuts friction

Wall layers out → in: epicardium, myocardium (muscle), endocardium

Septum = the wall dividing the right and left heart

Chordae tendineae anchor the AV valves so they don't flip into the atria

Path of blood through the heart

Venae cavae → RA → tricuspid → RV → pulmonary valve → lungs

Pulmonary veins → LA → mitral → LV → aortic valve → aorta

The rules

Left ventricle = thickest wall (pumps blood to the whole body)

Right or left side of the heart?

Commonly confused

	Right side	Left side
Blood	Oxygen-poor	Oxygen-rich
Atrium receives from	Superior and inferior venae cavae	Pulmonary veins
AV valve	Tricuspid (3 flaps)	Mitral / bicuspid (2 flaps)
Ventricle pumps to	Pulmonary arteries → lungs	Aorta → body
Ventricle wall	Thinner	Thickest in the heart

Mix-ups to avoid

Both ventricles pump equal volumes; the left just pumps at higher pressure

Tricuspid = right (3 flaps); mitral or bicuspid = left (2 flaps)

More detail

Show 4 more facts

Semilunar valves have no cords: their cusps fill and seal shut

Fossa ovalis = remnant of the fetal opening between the atria

Endocardium lining is continuous with the blood-vessel lining

Auricle = ear-shaped pouch on each atrium

Pearl

Try before you buy: the tricuspid valve (right side) comes before the bicuspid valve (left side).

Sources · OpenStax Anatomy & Physiology 2e §19.1 Heart Anatomy · Union Test Prep — HESI A&P study guide p. 5 (cardiovascular system) · Union Test Prep — HESI A&P study guide p. 3 (cardiac muscle and the myocardium) · TSTC Library — HESI A2 guide (A&P: describe the functions of the circulatory system) · Built from the verified NurseSavvy HESI A2 fact map (facts reviewed 2026-10-16). HESI is a trademark of Elsevier; NurseSavvy is not affiliated with Elsevier.

Conduction & the Cardiac Cycle

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Anatomy & Physiology · the heart

Conduction & the Cardiac Cycle

The SA node fires, the AV node pauses, and the bundle of His and Purkinje fibers trigger ventricular systole; in diastole the chambers refill.

01 · PacemakerSA node (right atrium) = the pacemaker

02 · PathwaySA → AV → His → bundle branches → Purkinje

03 · CycleSystole = contract · diastole = relax + fill

What it is

Systole = contraction (pumping); diastole = relaxation (filling) must know

Heart muscle makes its own impulses (autorhythmicity)

Cardiac cycle = one heartbeat: atria contract, ventricles contract, all relax

Parts & jobs

SA node (right atrium) = the pacemaker that starts each beat must know

Step by step

SA node → AV node → bundle of His → bundle branches → Purkinje fibers

The cardiac cycle

Step by step

Atrial systole: the atria top off the ventricles

Ventricular systole: AV valves shut, semilunar valves open, blood ejected

Diastole: semilunar valves shut, AV valves open, ventricles refill

The rules

AV node delays the signal so the atria empty before the ventricles contract must know

Purkinje fibers spread the signal; ventricles squeeze from the apex up

Lub (S1) = AV valves close; dub (S2) = semilunar valves close

Sympathetic speeds the heart; vagus (parasympathetic) slows it

Ventricular systole or diastole?

Commonly confused

	Systole	Diastole
Ventricle muscle	Contracts	Relaxes
AV valves (tricuspid, mitral)	Closed	Open
Semilunar valves	Open	Closed
Blood	Pumped into the pulmonary trunk and aorta	Flows from the atria into the ventricles
Sound at its start	Lub (S1)	Dub (S2)

Mix-ups to avoid

Chordae tendineae are NOT conduction tissue — they anchor valves

Heart sounds = valves closing, not opening

More detail

Show 4 more facts

Backup pacemaker: the AV node, at about 40–60 bpm

ECG: P = atria fire; QRS = ventricles fire; T = ventricles recover

Most filling (70–80%) is passive; atrial contraction adds 20–30%

Cardiac output = heart rate × stroke volume (80 × 70 mL = 5.6 L/min)

Pearl

The SA node starts the beat, the AV node pauses it, and the Purkinje fibers spread it through the ventricles.

Sources · OpenStax Anatomy & Physiology 2e §19.2 Cardiac Muscle and Electrical Activity · OpenStax Anatomy & Physiology 2e §19.3 Cardiac Cycle · OpenStax Anatomy & Physiology 2e §19.4 Cardiac Physiology · Union Test Prep — HESI A&P study guide p. 5 (electrical conduction of the heart) · TSTC Library — HESI A2 guide (A&P: describe the functions of the circulatory system) · Built from the verified NurseSavvy HESI A2 fact map (facts reviewed 2026-10-16). HESI is a trademark of Elsevier; NurseSavvy is not affiliated with Elsevier.

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