BIO 004 · Human Anatomy
The Heart
Block 3 · Module 2: The Heart, Structures, Valves, and the Pathway of Blood
A reference for the heart video and lab. This page covers the heart wall and pericardium, the four chambers and four valves, cardiac muscle tissue, the pathway of blood through the heart, and the great vessels. The focus is on structure.
How to use this sheet Toggle the toolbar above. Notes prints the full reference for review. Study prints as a fill-in-the-blank worksheet. Print it, then write each definition while you watch the video or read your book. Quiz me is on-screen typing practice: type the term, click Reveal to check yourself. The comparison grids respond to Study and Quiz too, with a Reveal button on each row.
The Foundations video gives you a complete foundational understanding of this topic, enough on its own for a foundational course. Learn it first, then move on to the Deep dive, which adds the majors-level material: the valves, cardiac muscle tissue, and the coronary circulation.
- Name the layers of the heart wall and the pericardium.
- Identify the four chambers and the four valves, and what each one separates.
- Describe cardiac muscle tissue and the intercalated disc.
- Trace the pathway of blood through the heart in order.
Your pre-work
Work through these the evening before class. None of it is turned in. It is how you learn the material and build your spaced recall.
This is more than a checklist. Ticking these boxes is the start, not the finish. Committing this material to memory and being able to apply it takes considerable time and repeated effort. You are not done when the boxes are checked. Put in the real hours, and keep coming back for frequent recall and review until the material is genuinely yours.
The heart in the mediastinum
Add a labeled view of the heart between the lungs, showing the apex, base, and pericardium.
A frontal section of the heart
Add a labeled frontal section showing the four chambers, the valves, and the great vessels.
The pathway of blood
Add a labeled diagram tracing blood through the chambers and valves with directional arrows.
The Heart, an Overview
The heart is a hollow, muscular pump about the size of a closed fist. It sits in the mediastinum and drives blood through two circuits, one to the lungs and one to the body.
- Hearta hollow, muscular organ that pumps blood through the blood vessels
- Locationin the mediastinum, between the two lungs, resting on the diaphragm and tilted to the left
- Apexthe blunt, rounded inferior tip, pointing down and to the left
- Basethe broad superior surface, where the great vessels enter and leave
- Pulmonary circuitthe loop the right side of the heart drives, carrying blood to the lungs and back
- Systemic circuitthe loop the left side of the heart drives, carrying blood to the body and back
The Heart Wall and Pericardium
The heart is wrapped in a double sac, the pericardium, and its own wall is built in three layers.
- Pericardiumthe double-walled sac that encloses the heart
- Fibrous pericardiumthe tough outer layer of dense connective tissue that protects the heart and anchors it in the mediastinum
- Serous pericardiumthe inner double membrane: a parietal layer lining the fibrous pericardium and a visceral layer on the heart surface
- Pericardial cavitythe space between the two serous layers, holding a film of serous fluid that reduces friction as the heart beats
The heart wall itself has three layers. Compare them from outside in.
| Layer | Position | Description |
|---|---|---|
| Epicardium | the outer layer | the visceral layer of the serous pericardium, a thin serous membrane on the heart surface |
| Myocardium | the thick middle layer | cardiac muscle tissue, the bulk of the heart and the layer that contracts |
| Endocardium | the inner layer | a smooth endothelium lining the chambers and covering the valves, continuous with the lining of the great vessels |
The Chambers
The heart has four chambers: two thin-walled atria that receive blood and two thick-walled ventricles that pump it out. Compare what each chamber receives and where it sends blood.
| Chamber | Receives blood from | Pumps blood to |
|---|---|---|
| Right atrium | the body, through the superior and inferior venae cavae, and the heart wall through the coronary sinus | the right ventricle |
| Right ventricle | the right atrium | the lungs, through the pulmonary trunk |
| Left atrium | the lungs, through the four pulmonary veins | the left ventricle |
| Left ventricle | the left atrium | the body, through the aorta; its wall is the thickest of the four chambers |
- Interatrial septumthe wall between the two atria
- Interventricular septumthe thick wall between the two ventricles
- Auriclea small wrinkled pouch on each atrium that slightly increases its capacity
The Heart Valves
Four valves keep blood moving in one direction. Each opens to let blood pass and closes to stop it flowing back. Compare them by type and location.
| Valve | Type | Location | Prevents backflow into |
|---|---|---|---|
| Tricuspid valve | atrioventricular, three cusps | between the right atrium and the right ventricle | the right atrium |
| Mitral valve | atrioventricular, two cusps; also called the bicuspid valve | between the left atrium and the left ventricle | the left atrium |
| Pulmonary valve | semilunar, three cusps | between the right ventricle and the pulmonary trunk | the right ventricle |
| Aortic valve | semilunar, three cusps | between the left ventricle and the aorta | the left ventricle |
- Chordae tendineaestrong fibrous cords that tie the cusps of an atrioventricular valve to the ventricle wall
- Papillary musclescone-shaped muscle projections of the ventricle wall that anchor the chordae tendineae and hold the valves shut against pressure
Cardiac Muscle Tissue
The myocardium is built of cardiac muscle, a tissue found nowhere else in the body. Its structure lets the whole heart contract as one coordinated unit.
- Cardiac musclethe involuntary, striated muscle tissue that forms the myocardium
- Cardiomyocytea cardiac muscle cell, short and branching, usually with a single central nucleus
- Striationscardiac muscle is striped, like skeletal muscle, because it too is built of ordered sarcomeres
- Intercalated discsthe specialized junctions where neighboring cardiomyocytes meet end to end
- Desmosomesanchoring junctions within the intercalated discs that keep the cells from pulling apart
- Gap junctionschannels within the intercalated discs that let the contraction signal pass directly from cell to cell
- Abundant mitochondriacardiac muscle is packed with mitochondria to fuel its constant, lifelong work
The Pathway of Blood
Follow one drop of blood through the heart, in order. It makes a full loop: into the right side, out to the lungs, back into the left side, and out to the body.
- Right atriumoxygen-poor blood returns from the body through the superior and inferior venae cavae
- Tricuspid valveblood passes from the right atrium down into the right ventricle
- Right ventriclecontracts and pumps the blood upward and out
- Pulmonary valveblood passes into the pulmonary trunk, which branches to the lungs
- Lungsblood picks up oxygen and releases carbon dioxide, then returns through the pulmonary veins
- Left atriumreceives the now oxygen-rich blood from the pulmonary veins
- Mitral valveblood passes from the left atrium down into the left ventricle
- Left ventriclethe thickest chamber contracts and pumps the blood out with force
- Aortic valveblood passes into the aorta and out to the body, completing the loop
The Great Vessels and Coronary Circulation
The great vessels are the large pipes attached to the base of the heart. The heart wall has its own blood supply, the coronary circulation.
The great vessels
- Superior vena cavareturns oxygen-poor blood from the head, neck, and upper limbs to the right atrium
- Inferior vena cavareturns oxygen-poor blood from the trunk and lower limbs to the right atrium
- Pulmonary trunkcarries blood from the right ventricle and branches into the right and left pulmonary arteries
- Pulmonary veinsfour veins that return oxygen-rich blood from the lungs to the left atrium
- Aortathe largest artery, carrying oxygen-rich blood from the left ventricle to the body
Coronary circulation
- Coronary arteriesthe right and left coronary arteries, which branch from the base of the aorta to supply the heart wall itself
- Cardiac veinsthe veins that drain used blood from the heart wall
- Coronary sinusthe large vein on the posterior heart that collects blood from the cardiac veins and empties it into the right atrium
See also: Blood for what the heart pumps, and The Cardiac Conduction System, the next page in this block.
Study questions
Work on answering these in writing, in your own words. They are the questions to bring to class, and good practice for the reasoning the exams ask for.
- Trace a drop of blood through the four chambers and four valves of the heart in order.
- Compare the two atrioventricular valves and the two semilunar valves by location and what each prevents.
- Name the layers of the heart wall and the membrane that surrounds the heart.
- Explain how the great vessels connect the heart to the pulmonary and systemic circuits.
Step 2 . Retrieval check
Now explain it back, in your own words.
In 60 words or more, pull together what the video just taught you. Include the key concepts. This is the point where the learning actually sticks. After you submit, your spaced-recall cards for this topic unlock.