The Heart Anatomy, Conduction, and Physiology

Flashcards covering heart anatomy, circulation circuits, cardiac membranes and layers, internal structures, electrical conduction, ECG traces, cardiac cycle phases, and autonomic physiology.

Where is the heart located in the body, and what structure covers it?

The heart is found in the thoracic cavity between the lungs in a space called the mediastinum. It is covered by the pericardium and sits in the pericardial cavity.

What are the anatomical locations of the heart's base and apex?

The base is the most superior surface where major blood vessels emerge at the level of the 3rd rib. The apex is the inferior tip lying just to the left of the sternum.

What are auricles and what is their primary function?

Auricles are external muscular pouches attached to the atria that increase the total volume of the atria.

What distinct circulatory circuits do the right and left ventricles supply?

The right ventricle pumps deoxygenated blood into the pulmonary circulation to each lung, while the left ventricle pumps oxygenated blood into the systemic circulation to virtually all body tissues.

Which regions of the body do the superior and inferior venae cavae drain blood from?

The superior vena cava drains blood from regions superior to the diaphragm, whereas the inferior vena cava drains blood from regions inferior to the diaphragm.

What are the structural layers of the pericardium?

The pericardium consists of a tough outer fibrous pericardium and an inner serous pericardium, which itself has an outer parietal layer fused to the fibrous pericardium and an inner visceral layer (epicardium) fused to the heart wall.

What are the three layers of the heart wall from outermost to innermost?

The three layers are the epicardium (outermost, visceral layer of serous pericardium), myocardium (thickest middle layer made of cardiac muscle cells), and endocardium (innermost thin layer made of endothelium).

Why is the myocardium surrounding the left ventricle thicker than that of the right ventricle?

The left ventricle's myocardium is thicker to generate larger pressure to overcome the greater resistance in the systemic circuit compared to the pulmonary circuit.

What is the fossa ovalis and what fetal structure is it a remnant of?

The fossa ovalis is an oval depression in the interatrial septum that is a remnant of the fetal foramen ovale, an opening that allowed blood to pass directly from the right to the left atrium.

What are the names of the right and left atrioventricular (AV) valves, and how many papillary muscles attach to each?

The right AV valve is the tricuspid valve, attached via chordae tendineae to 3 papillary muscles (anterior, posterior, and septal). The left AV valve is the mitral (bicuspid) valve, attached to 2 papillary muscles (anterior and posterior).

Where do the coronary arteries originate, and where do coronary veins drain before entering the right atrium?

Right and left coronary arteries branch off the aorta immediately after it leaves the left ventricle. Coronary veins drain into the coronary sinus, which empties directly into the right atrium.

What is the function of the sinoatrial (SA) node and what rhythm does it establish?

The SA node acts as the pacemaker of the heart by initiating action potentials in the upper posterior wall of the right atrium, setting the normal sinus rhythm.

Why is there a conduction delay at the atrioventricular (AV) node?

The smaller cell diameter and slower conduction between nodal cells delay the electrical impulse, allowing the atria to completely empty blood into the ventricles before ventricular contraction begins.

What is the complete pathway of an electrical impulse through the cardiac conduction system?

Sinoatrial (SA) node $\rightarrow$ Atrioventricular (AV) node $\rightarrow$ Atrioventricular (AV) bundle (Bundle of His) $\rightarrow$ Right and left bundle branches $\rightarrow$ Purkinje fibers.

What is the total elapsed time from SA node impulse generation to ventricular contraction?

The total elapsed time is $225\,\text{ms}$.

How many electrodes and leads are used in a standard electrocardiogram (ECG)?

A standard ECG uses $10$ electrodes placed on the skin to record $12$ electrical leads.

In this ECG trace, what cardiac electrical events do the P wave, QRS complex, and T wave represent?

The P wave represents atrial depolarization, the QRS complex represents ventricular depolarization (masking atrial repolarization), and the T wave represents ventricular repolarization.

What physical events produce the S1 and S2 heart sounds ('lub-dub')?

S1 ('lub') is caused by the closing of the atrioventricular valves during ventricular systole. S2 ('dub') is caused by the closing of the semilunar valves during ventricular diastole.

What resting heart rates define bradycardia and tachycardia in adults?

Bradycardia is defined as a resting heart rate below $60\,\text{bpm}$, whereas tachycardia is defined as a resting heart rate above $100\,\text{bpm}$.

Which medullary cardiovascular centers control heart rate and via which nervous pathways?

The cardioacceleratory region increases heart rate via the sympathetic nervous system (releasing norepinephrine). The cardioinhibitory region decreases heart rate via the parasympathetic nervous system via the vagus nerve (releasing acetylcholine).

How do blood concentration levels of $Ca^{2+}$ and $K^+$ affect heart rate and contractility?

High $Ca^{2+}$ levels increase heart rate and contractility, while low $Ca^{2+}$ decreases them. Conversely, high $K^+$ levels decrease heart rate and contractility, while low $K^+$ increases them.