ANATOMY AND FUNCTIONS OF HEART
INTRODUCTION:
The heart is a muscular organ that serves to collect deoxygenated blood from all parts of the body, carries it to the lungs to be oxygenated and release carbon dioxide. Then, it transports the oxygenated blood from the lungs and distributes it to all the body parts.
- The heart pumps around 7,200 litres of blood in a day throughout the body.
- The heart is situated at the centre of the chest and points slightly towards the left.
- On average, the heart beats about 100,000 times a day, i.e., around 3 billion beats in a lifetime.
- An adult heart beats about 60 to 80 times per minute, and newborn babies’ hearts beat faster than an adult (70 to 190 beats per minute).
Functions: Heart’s main function is to move blood throughout your body. It also controls the rhythm and speed of heart rate and maintains blood pressure.
ANATOMY:
The heart is a roughly cone-shaped hollow muscular organ. It is about 10 cm long, about the size of the owner’s fist, weighing about 225 g in women and 310 g in men.
POSITION:
The heart lies in the thoracic cavity in the mediastinum between the lungs. It lies obliquely, slightly more to the left than the right, presenting a base above and an apex below. The apex is about 9 cm to the left of the midline at the 5th intercostal space. The base extends to the level of the 2nd rib.
ORGANS ASSOCIATED WITH THE HEART:
- Inferiorly — apex rests on the central tendon of the diaphragm
- Superiorly — great blood vessels (aorta, superior vena cava, pulmonary artery and veins)
- Posteriorly — oesophagus, trachea, left and right bronchus, descending aorta, inferior vena cava, thoracic vertebrae
- Laterally — lungs (left lung overlaps left side of the heart)
- Anteriorly — sternum, ribs and intercostal muscles
PERICARDIUM:
The pericardium is the membrane that surrounds and protects the heart, confining it to its position in the mediastinum while allowing movement. It has two main parts:
- Fibrous pericardium: tough, inelastic connective tissue providing protection, anchoring, and preventing overstretching.
- Serous pericardium: thin double-layer membrane (parietal and visceral/epicardium) with pericardial fluid reducing friction.
PARTS OF THE HEART’S ANATOMY:
The heart has walls, chambers, valves, blood vessels, and an electrical conduction system.
1. LAYERS OF THE HEART WALLS:
- Epicardium: Outer layer, visceral layer of serous pericardium with mesothelium, fibroelastic tissue, adipose tissue, blood vessels, and lymphatics.
- Myocardium: Middle muscular layer responsible for pumping action, organized in bundles of cardiac muscle fibers.
- Endocardium: Inner layer, smooth endothelial lining of chambers and valves, continuous with blood vessels.
2. CHAMBERS OF THE HEART:
The heart has four chambers:
- Atria: Superior receiving chambers; have auricles to increase capacity.
- Ventricles: Inferior pumping chambers; separated by interventricular septum.
Right Atrium:
- Receives blood from superior vena cava, inferior vena cava, and coronary sinus.
- Contains pectinate muscles in anterior wall; interatrial septum with fossa ovalis.
- Blood passes to right ventricle through tricuspid (right AV) valve.
Right Ventricle:
- Forms most of the anterior surface; contains trabeculae carneae.
- Tricuspid valve cusps anchored by chordae tendineae to papillary muscles.
- Blood exits via pulmonary (SL) valve to pulmonary trunk and arteries.
Left Atrium
- Receives blood from four pulmonary veins.
- Blood passes to left ventricle through bicuspid/mitral (left AV) valve.
Left Ventricle
- Thickest chamber; contains trabeculae carneae and chordae tendineae connected to papillary muscles.
- Blood passes through aortic (SL) valve to ascending aorta; coronary arteries supply the heart.
- Ductus arteriosus in fetal life shunts blood to aorta; becomes ligamentum arteriosum after birth.
3. HEART VALVES:
- Atrioventricular (AV) valves: Tricuspid (right) and Mitral/Bicuspid (left)
- Semilunar (SL) valves: Pulmonary (right) and Aortic (left)
4. BLOOD VESSELS:
- Arteries carry oxygen-rich blood (except pulmonary arteries).
- Veins carry oxygen-poor blood.
- Capillaries exchange oxygen and carbon dioxide between blood and tissues.
- Coronary arteries supply heart muscle.
5. ELECTRICAL CONDUCTION SYSTEM:
- Sino-atrial (SA) node: initiates heartbeat.
- Atrio-ventricular (AV) node: transmits impulses from atria to ventricles.
- Bundle of His, left and right bundle branches, and Purkinje fibers control ventricular contraction.
Detailed Notes:
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