Biology106Updated Sep 26, 20266 pages

Comprehensive Heart Anatomy Notes (BSCI 21020)

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allison gibson@allison.gibson

The heart and circulatory system form the foundation of your body's transport network. This amazing system pumps blood through two main circuits, delivering oxygen and nutrients while removing waste from every cell in your body. Understanding how this system works helps you appreciate the incredible machine that keeps you alive every second of every day.

anatomy (BSCI 21020) heart notes – page 1

Heart Basics and Structure

Ever wondered what keeps your blood moving 24/7? Your heart is about the size of your fist, located between your lungs in an area called the mediastinum. It has a broad upper portion (the base) and tapers to a point at the bottom (the apex), which tilts slightly to the left.

The heart has three main layers that work together. The endocardium is the smooth inner lining that acts like a sealant. The middle layer, the myocardium, is the thickest and consists of cardiac muscle that does the actual pumping. The outer layer, the epicardium (also called visceral pericardium), is a protective membrane covering the heart.

Surrounding everything is the pericardium, which has two layers that form a cavity containing a small amount of fluid $5-30 mL$ . This fluid reduces friction as your heart beats, allowing it to work efficiently without wearing itself out.

Fun Fact: Your heart will beat roughly 2.5 billion times in an average lifetime! That's a lot of work for an organ about the size of your fist.

anatomy (BSCI 21020) heart notes – page 2

Heart Chambers and Valves

Your heart is essentially two pumps working side by side. It has four chambers: two atria at the top that receive blood, and two ventricles at the bottom that pump blood out. Remember that arteries always carry blood away from the heart while veins bring it back—regardless of whether the blood is oxygen-rich or oxygen-poor.

Four valves ensure blood flows in the correct direction through your heart. The atrioventricular (AV) valves sit between the atria and ventricles, preventing backflow when pressure rises. These valves are anchored to the ventricular walls by cord-like structures called chordae tendineae, which attach to papillary muscles to keep the valves from inverting.

The semilunar valves guard the entrances to the major arteries leaving the heart. The pulmonary semilunar valve sits at the entrance to the pulmonary artery, while the aortic semilunar valve guards the entrance to the aorta—the largest artery in your body. The aorta carries high-pressure, oxygen-rich blood from your left ventricle to the rest of your body.

Remember This: Think of valves as one-way doors that keep blood moving forward. Without them, your heart's pumping would be much less efficient, similar to trying to push water uphill with a leaky pipe.

anatomy (BSCI 21020) heart notes – page 3

Coronary Arteries and Cardiac Muscle

Your heart works non-stop, so it needs its own blood supply. The coronary arteries branch directly from the aorta and run along grooves (interventricular sulci) on your heart's surface. The left coronary artery supplies the front of your heart, while the right coronary artery supplies the back and right side.

Heart muscle is unique in your body. Cardiac muscle cells (cardiocytes) are striated like skeletal muscle but shorter and branched. They connect to each other through special junctions called intercalated discs that allow electrical signals to pass between cells. This creates a synchronized contraction—essential for effective pumping.

Your heart is an energy powerhouse. Cardiac cells contain numerous large mitochondria that support continuous aerobic respiration. They're rich in myoglobin (an oxygen-storing protein) and glycogen (stored glucose). Your heart primarily uses fatty acids for fuel but can also burn glucose and ketones when needed.

Critical Point: The heart's electrical system is completely independent of your brain. It's myogenic, meaning the heartbeat originates within the heart itself, and autorhythmic, creating a regular, spontaneous rhythm without any external nerve signals.

anatomy (BSCI 21020) heart notes – page 4

Cardiac Conduction and Rhythms

Your heart has its own electrical system that coordinates contractions. It all starts with the sinoatrial (SA) node, your heart's natural pacemaker located in the wall of the right atrium. This tiny bundle of specialized cells spontaneously generates electrical impulses that spread through the atria.

The signal then reaches the atrioventricular (AV) node, which acts like a gatekeeper. It briefly delays the signal before sending it through the AV bundle (also called the bundle of His) and into a network of Purkinje fibers that stimulate the ventricles to contract.

Your nervous system can adjust your heart rate as needed. Sympathetic nerves increase your heart rate during exercise or stress, while parasympathetic nerves decrease it when you're resting. These nerves don't initiate the heartbeat—they just modify the rate set by the SA node.

Warning Sign: An arrhythmia occurs when this electrical system malfunctions. If you frequently experience irregular heartbeats, especially with dizziness or shortness of breath, talk to a doctor. Ventricular fibrillation, where electrical signals become completely disorganized, is a life-threatening emergency.

anatomy (BSCI 21020) heart notes – page 5

Cardiac Cycle and Blood Pressure

The cardiac cycle is the sequence of events in one complete heartbeat. It involves alternating periods of contraction (systole) and relaxation (diastole) in all four chambers. Interestingly, your atria and ventricles work in opposite phases—when atria contract, ventricles relax, and vice versa.

Blood flows through your cardiovascular system because of pressure differences. Blood pressure represents the force exerted by blood against vessel walls, measured in millimeters of mercury (mmHg). Blood always flows from areas of higher pressure to lower pressure—this pressure gradient is what keeps everything moving.

The familiar "lub-dub" of your heartbeat comes from your heart valves closing. The first sound ("lub" or S1) occurs when the AV valves close as ventricles contract. The second sound ("dub" or S2) happens when the semilunar valves snap shut after blood has been ejected into the arteries.

Did You Know?: Your cardiac output—the amount of blood your heart pumps per minute—can increase from a resting 4-6 liters to an amazing 21-35 liters during intense exercise. That's like going from pumping a gallon of milk to nearly 9 gallons every minute!

anatomy (BSCI 21020) heart notes – page 6

Heart Rate and Disorders

Your heart rate varies by age, gender, and physical condition. Adult women typically have rates of 72-80 beats per minute (bpm), while men average 64-72 bpm. Infants have much higher rates around 120 bpm. A rate above 100 bpm is called tachycardia, while below 60 bpm is bradycardia (which can be normal in athletes).

Coronary artery disease (CAD) develops when coronary arteries become narrowed or blocked, usually due to a buildup of fatty deposits called plaques. This reduces blood flow to the heart muscle itself, potentially causing chest pain or a heart attack.

Heart failure doesn't mean your heart stops—it means it can't pump efficiently. If the left ventricle fails, blood backs up into the lungs causing pulmonary edema and breathing difficulties. Right ventricular failure causes blood to back up into the body, resulting in swelling in the liver and extremities.

Technology Connection: An electrocardiogram (ECG or EKG) records your heart's electrical activity through electrodes placed on your skin. The distinctive PQRST wave pattern shows different phases of the cardiac cycle. Doctors can spot many heart problems by analyzing variations in this pattern.

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Comprehensive Heart Anatomy Notes (BSCI 21020)

Heart Basics and Structure

Heart Chambers and Valves

Coronary Arteries and Cardiac Muscle

Cardiac Conduction and Rhythms

Cardiac Cycle and Blood Pressure

Heart Rate and Disorders

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