Heart Valves and Circulation
Valve Description
Valves open and close in response to pressure changes as the heart contracts and relaxes. They ensure one-way flow of blood and prevent backflow (regurgitation).
Types of Valves
| Category | Valves |
|---|---|
| Atrioventricular (AV) Valves | Tricuspid valve (right), Bicuspid/Mitral valve (left) |
| Semilunar (SL) Valves | Pulmonary valve (right), Aortic valve (left) |
Atrioventricular (AV) Valves
Anchored by the fibrous skeleton and located between an atrium and a ventricle. Each consists of cusps, chordae tendineae, and papillary muscles.
How AV Valves Work:
- Ventricular diastole (relaxation): Papillary muscles are relaxed, chordae tendineae are slack. Blood flows from the contracting atria (higher pressure) to the relaxed ventricles (lower pressure).
- Ventricular systole (contraction): Ventricular pressure rises. Blood pushes the AV valves upward until their edges meet and close. Papillary muscles contract, pulling the chordae tendineae to prevent valve prolapse.
| Valve | Location | Function |
|---|---|---|
| Tricuspid valve | Between RA and RV | Prevents backflow into the RA |
| Mitral (Bicuspid) valve | Between LA and LV | Prevents backflow into the LA |
Semilunar (SL) Valves
Anchored by the fibrous skeleton and located between a ventricle and the pulmonary artery or aorta. Each consists of three crescent moon-shaped cusps.
How SL Valves Work:
- Ventricular diastole: Blood starts to flow back toward the heart, filling the cusps and closing the SL valves.
- Ventricular systole: Pressure increases, forcing the SL valves open.
| Valve | Location | Function |
|---|---|---|
| Aortic valve | Between LV and aorta | Prevents backflow into the LV |
| Pulmonic valve | Between RV and pulmonary artery | Prevents backflow into the RV |
Circulation of Blood
The heart pumps blood through two closed circuits: systemic and pulmonary.
Systemic Circulation (Left Side)
Receives oxygenated blood from the lungs and pumps it to the body.
Route: Heart → Aorta → Arteries → Arterioles → Capillaries → Venules → Veins → Superior/Inferior Vena Cava → Heart
- Oxygenated blood is carried away from the heart; deoxygenated blood returns
- High pressure system
Pulmonary Circulation (Right Side)
Receives deoxygenated blood from the body and pumps it to the lungs.
Route: Heart → Pulmonary Trunk → Pulmonary Arteries → Lungs → Pulmonary Capillaries → Pulmonary Veins → Heart
- Deoxygenated blood is carried to the lungs; oxygenated blood returns
- Low pressure system
Major Arterial Routes (Away from Heart)
| Artery | Region Supplied |
|---|---|
| Aortic arch | Elastic artery that distributes blood to the upper body |
| Carotid arteries (right and left) | Oxygenated blood to the brain |
| Subclavian arteries | Oxygenated blood to the upper limbs |
| Brachial arteries | Medial side of biceps brachii |
| Radial arteries | Posterior compartment of forearm |
| Ulnar arteries | Anterior compartment of forearm |
| Iliac arteries | Oxygenated blood to the lower limbs |
| Femoral arteries | Inferior to inguinal ligament |
| Popliteal arteries | Posterior to knee |
| Dorsalis pedis | Top of foot |
Major Venous Routes (Return to Heart)
| Vein | Region Drained |
|---|---|
| Inferior vena cava | Largest vein (~3.5 cm diameter); returns blood from lower body to RA |
| Superior vena cava | (~7.5 cm long, 2 cm diameter); returns blood from upper body to RA |
| Jugular veins | Drain deoxygenated blood from brain, face, and neck |
| Cephalic veins | Superficial vein of the upper limb |
| Basilic veins | Superficial vein of the upper limb |
Coronary Circulation
The myocardium has its own network of blood vessels — the coronary arteries and coronary veins.
Coronary Arteries
| Artery | Branch | Location | Region Supplied |
|---|---|---|---|
| Left coronary artery | Anterior interventricular (LAD) | Anterior interventricular sulcus | Walls of both ventricles |
| Circumflex branch | Coronary sulcus | Walls of LV and LA | |
| Right coronary artery | Posterior interventricular | Posterior interventricular sulcus | Walls of both ventricles |
| Marginal branch | Coronary sulcus (right margin) | Right ventricle |
Coronary Veins
| Vein | Location | Region Drained |
|---|---|---|
| Great cardiac vein | Anterior interventricular sulcus | Both ventricles and LA; area supplied by left coronary artery |
| Middle cardiac vein | Posterior interventricular sulcus | Both ventricles; area supplied by posterior interventricular branch |
| Small cardiac vein | Coronary sulcus | RA and RV; area supplied by right coronary artery and marginal branch |
| Anterior cardiac veins | Right margin of heart | RV |
All coronary veins drain into the coronary sinus, which then empties into the right atrium.