19.1 ana

By the end of this section, you will be able to:

Describe the location and position of the heart within the body cavity.
Describe the internal and external anatomy of the heart.
Identify the tissue layers of the heart.
Relate the structure of the heart to its function as a pump.
Compare systemic circulation to pulmonary circulation.
Identify the veins and arteries of the coronary circulation system.
Trace the pathway of oxygenated and deoxygenated blood through the chambers of the heart.

The vital importance of the heart is apparent when considering its extensive activity:

Assuming an average contraction rate of 75 contractions per minute:
- A human heart contracts approximately 108,000 times in one day.
- Over one year, the heart contracts more than 39 million times.
- In a lifespan of around 75 years, it would contract nearly 3 billion times.

Each major pumping chamber of the heart ejects approximately:

70 mL of blood per contraction in a resting adult.
- This equates to:
- 5.25 liters of blood per minute.
- Approximately 14,000 liters of blood per day.
- An astounding 10,000,000 liters or 2.6 million gallons of blood in one year.

The heart circulates blood through roughly 60,000 miles of vessels, underlining the necessity of understanding its anatomy and physiology.

The human heart is located within the thoracic cavity, medially, between the lungs in an area known as the mediastinum.
It is protected by a tough membrane known as the pericardium (or pericardial sac) and located in a space referred to as the pericardial cavity.
Orientation:
- The dorsal surface of the heart rests against the vertebral bodies.
- The anterior surface sits deep to the sternum and costal cartilages.
Major Vessels:
- Base of the heart (located at the level of the third costal cartilage): This is where the great veins, the superior and inferior venae cavae, and the major arteries, the aorta and pulmonary trunk, are attached.
- Apex of the heart (located just to the left of the sternum between the junction of the fourth and fifth ribs).
Orientation:
- Right side of the heart is tilted anteriorly; left side is tilted posteriorly.
- The slight deviation of the apex leads to a corresponding depression in the medial surface of the superior lobe of the left lung, known as the cardiac notch.

The consideration of the heart’s location is vital during the application of cardiopulmonary resuscitation (CPR):
- CPR can restart blood flow if the heart stops; compressions are applied to the sternum between T4 and T9 to manually push blood into the pulmonary and systemic circuits.
- Current CPR standards include:
- Chest compressions at least 5 cm deep.
- At a rate of 100 compressions per minute (notably to the beat of “Staying Alive” by the Bee Gees).
High-quality chest compressions are emphasized over artificial respiration during initial stages. CPR should continue until either:
- The patient regains spontaneous heart function.
- An experienced healthcare professional declares the patient dead.
Risks of CPR include broken ribs or sternum, as well as possible harm to the liver if hands are placed too low on the sternum.
Proper training is crucial, and CPR courses are widely available.

The heart resembles a pinecone; broad at the base and tapering to an apex.
Typical dimensions are approximately:
- 12 cm (5 in) in length,
- 8 cm (3.5 in) wide,
- 6 cm (2.5 in) thick.
Weight:
- Female heart: 250–300 grams (9 to 11 ounces)
- Male heart: 300–350 grams (11 to 12 ounces)
- Athlete's hearts can be larger due to hypertrophy, influencing blood pumping efficiency.

The human heart consists of four chambers:

Atria (Upper Chambers):
- Right Atrium and Left Atrium – receive blood and push it into the ventricles.
Ventricles (Lower Chambers):
- Right Ventricle and Left Ventricle – act as major pumps for blood circulation.

Pulmonary Circuit:
- Transports deoxygenated blood from the right ventricle into the pulmonary trunk, which bifurcates into the left and right pulmonary arteries leading to the lungs for gas exchange.
- Blood is returned from the lungs as oxygenated blood via the pulmonary veins to the left atrium, then into the left ventricle and into the aorta circulating through the systemic circuit.
Systemic Circuit:
- Distributes oxygenated blood to tissues, returning deoxygenated blood to the right atrium via the superior and inferior vena cavae.

Diagram illustrating blood flow through the heart's pulmonary and systemic circuits.

Pericardium: A double-layer surrounds the heart:
- Fibrous Pericardium: Tough outer layer.
- Serous Pericardium: Delicate inner layer comprising:
- Parietal pericardium (outer)
- Visceral pericardium (Epicardium) (inner, fused to the heart).
Heart Wall consists of:
- Epicardium (outermost layer, also part of pericardial sac).
- Myocardium (thickest layer made of cardiac muscle, crucial for contraction).
- Endocardium (lines chambers and covers the heart valves).
- The myocardium has a unique muscle pattern facilitating effective blood pumping.

A condition where excess fluid accumulation in the pericardial space prevents the heart from relaxing fully, leading to reduced blood ejection.
Can result from trauma, cancer, or surgery.
Treatment often requires drainage of excess fluid through inserted tubes to restore normal function.

Including:

Patent foramen ovale: An unclosed remnant of fetal opening causing abnormal blood flow between atria.
Coarctation of the aorta: Narrowing affecting blood flow; may require surgical intervention.
Tetralogy of Fallot: A condition presenting with a ventricular septal defect, affecting oxygenation; requires surgical repair.

The heart has its own dedicated blood supply in the form of coronary arteries.
Major coronary arteries branch from the aorta:
- Left Coronary Artery (supplies left side of the heart).
- Right Coronary Artery (supplies right side).
Coronary circulation is cyclical; perfusion peaks during heart relaxation.

Heart attack caused by restricted blood flow to heart muscle due to atherosclerosis.
Symptoms might include chest pain (angina pectoris), often differing by gender.
Confirmation via ECG changes, lab tests for troponin levels, and imaging techniques.
Treatment encompasses oxygen, aspirin, thrombolytics, and surgical options depending on severity.

Leading cause of mortality worldwide, characterized by plaque buildup in coronary arteries.
Symptoms may manifest as angina pectoris; untreated can lead to myocardial infarction.
Diagnosis by angiography showing occlusions, followed by management strategies including lifestyle modifications and potential surgeries like angioplasty or bypass surgery.