Semilunar valves

Examples of Semilunar valves in the following topics:

• Operation of Semilunar Valves

  • The semilunar valves allow blood to be pumped into the major arteries, but prevent backflow of blood from the arteries into the ventricles.
  • The semilunar valves act in concert with the atrioventricular valves to direct blood flow in the heart.
  • When the atrioventricular valves shut, the semilunar valves open, forcing blood into the aorta and pulmonary artery.
  • This anterior view of the heart indicates the semilunar valves, the aortic and pulmonary valves.
  • Describe the operation of the semilunar valves, the aortic and pulmonary valves

• Blood Flow in the Lungs

  • From the right ventricle of the heart, blood is pumped through the pulmonary semilunar valve into the left and right pulmonary arteries (one for each lung) and travels through the lungs.
  • This blood is then pumped through the bicuspid valve into the left ventricle.

• Structures of the Heart

  • The heart pumps blood through the body with the help of structures such as ventricles, atria, and valves.
  • After blood passes through the pulmonary arteries, the right semilunar valves close, preventing the blood from flowing backwards into the right ventricle.
  • The valve separating the chambers on the left side of the heart is called the biscuspid or mitral valve (left atrioventricular valve).The blood passes through the bicuspid valve to the left ventricle where it is pumped out through the aorta, the major artery of the body, taking oxygenated blood to the organs and muscles of the body.
  • Once blood is pumped out of the left ventricle and into the aorta, the aortic semilunar valve (or aortic valve) closes, preventing blood from flowing backward into the left ventricle.
  • One-way valves separate the four chambers.

• The Cardiac Cycle

  • The atria contract at the same time, forcing blood through the atrioventricular valves into the ventricles.
  • Closing of the atrioventricular valves produces a monosyllabic "lup" sound.
  • Following a brief delay, the ventricles contract at the same time forcing blood through the semilunar valves into the aorta and the pulmonary artery (which transports blood to the lungs).
  • Closing of the semilunar valves produces a monosyllabic "dup" sound.
  • The signal is initiated at the sinoatrial valve.

• Velocity of Blood Flow

  • At arterial bifurcations or divisions, reflected waves rebound to return to semilunar valves and the origin of the aorta.
  • These return waves create the dicrotic notch displayed in the aortic pressure curve during the cardiac cycle, as these reflected waves push on the aortic semilunar valve.
  • Valves in veins, breathing, and an induced pumping force from contraction of skeletal muscles also influences blood pressure.

• Ureters

  • After the urine enters the bladder from the ureters, small folds in the bladder mucosa act like valves preventing backward flow of the urine, which are called the ureteral valves.
  • The ureteral valves function similarly to the semilunar valves in the veins of the body, but are structurally different, consisting of transverse mucosal epithelial folds.

• Lymphatic Vessel Structure

  • One of the main structural features of lymph vessels is their valves, which are semilunar structures attached to opposite sides of the lymphatic endothelium.
  • Valves are found in larger lymph vessels and collecting vessels and are absent in the lymphatic capillaries.
  • As the pressure falls, the open valve then closes so that the lymph fluid cannot flow backwards.
  • A lymphagion is the term for the space between two semilunar valves in a lymphatic vessel, and represents a functional unit of the lymphatic system.
  • Blood vessels also have valves, but only in low pressure venous circulation, and they function similarly to lymphatic valves, though are comparatively more dependent on skeletal muscle contractions by comparison.

• Heart Murmurs

  • Heart murmurs are pathologic heart sounds indicative of valve and blood flow abnormalities.
  • Yet most heart problems do not produce any murmur and most valve problems also do not produce an audible murmur.
  • Anatomical sources of heart murmurs include stenosis of the bicuspid aortic valve which tends to appear between 40 and 70 years of age, and stenosis of the tricuspid aortic valve where symptoms more likely to appear after 80 years of age.
  • The first heart sound is caused by the atrioventricular valves--Mitral (M) and Tricuspid (T)--and the second heart sound is caused by the semilunar valves--Aortic (A) and Pulmonary/Pulmonic (P).
  • Heart murmurs are often the result of leaky valves.

• Heart Sounds

  • The two major heart sounds are 'lub' (from the closure of AV-valves) and 'dub' (from the closure of aortic and pulmonary valves).
  • The closing of the heart valves produces a sound.
  • It is caused by the closure of the semilunar (aortic and pulmonary) valves following ventricular systole.
  • S2 is split because aortic valve closure occurs before pulmonary valve closure.
  • Abnormal heart sounds may indicate problems with the health of the valves.

• Heart Valve Disorders

  • Valvular heart disease is any disease process involving one or more of the valves of the heart (the aortic and mitral valves on the left and the pulmonary and tricuspid valves on the right).
  • Valvular heart disease includes aortic and mitral valve disorders, and pulmonary and tricuspid valve disorders.
  • Pulmonary valve diseases are the least common heart valve disease in adults.
  • The most common types of pulmonary valve diseases are: pulmonary valve insufficiency, pulmonary valve incompetence, and pulmonary valve regurgitation.
  • Both tricuspid and pulmonary valve diseases are less common than aortic or mitral valve diseases due to the lower pressure those valves experience.