9. The valves of the heart. The histology and development of the heart.

9. The valves of the heart. The histology and development of the heart.

Anatomy: The valves of the heart.

Valves of Heart
all of valves of heart originate from anulus fibrosus
2 valves on arterial end and 2 valves at AV Jxn

View of valves @ level of anulus fibrosus

Semilunar valves

• made of 3 semilunar cusps
• NOTE – Pumonary valve has an R, L, and ant cusp & Aortic valve has a R,L, and post cusp —> So it is always P & A – Pulmonary has Ant, and Aortic has Post
  
• Each cusps has a pars flaccida, and a pars tecta
• The side of each cusp, thin CT area = lunule
• peak of every cusp, fibrous = nodule
• When valve closes, the lunules and nodules meet in the center.

Pulmonary Valve:

• @ border b/w conus arteriosus of R ventricle & pul trunk
• has an ant, R, L cusps
• opened in ventricular systole & shuts after aortic valve closes
• SP = behind med end of L 3rd costal cartilage & sternum connects there
• Auscultation Point = heard best @ L 2nd IC space, just lat to sternum
• each cusp is concave from superior view, project into pul trunk, but flatten against wall when blood is flowing through
• cusps open up when they close, and catch backflow and prevent blood from going back into R ventricle
• just above each cusp of valve, pul trunk bulges out, forming the pulmonary sinuses – these prevent cusps from sticking to the walls of the pulmonary trunk.
  

Aortic Valve:

• b/w L ventricle and asc aorta
• has R,L, post cusps
• each cusp is concave from superior view, project into ascending aorta, but flatten against wall when blood is flowing through
• cusps open up when they close, and catch backflow and prevent blood from going back into L ventricle
• just above each cusp of valve, asc aorta bulges out, forming the aortic sinuses – these prevent cusps from sticking to the walls of the pulmonary trunk.
• R&L coronary a originate from the aortic sinuses above R&L cusps
• Post cusp’s sinus does not have an a. originate from it
• blood pumped into coronary a in diastole
• SP = behind L 1/2 sternum @  3rd IC space
• Auscultation Point = heard best @ R 2nd IC space, just lat to sternum
• closed during ventricular systole
• 2nd Heart sound

Parts of Semilunar/Cuspid Heart valves, showing lunules, nodules, etc

Cuspid Valves
3 main structures:

1. Cusps w/ core of CT
2. papillary m (emerging from myocardium) –  cone shaped m that attach to cordae tendinae, valves open when these contract
   
3. chordae tendinae – threads of dense reg CT connecting papillary m w/ cusps of valve

Location and Parts of cuspid valves

Tricuspid Valve = R AV valve

• B/w R atria & R ventricle
• SP = opposite 4th IC space, covered by endocardium
• Has Ant, Post, Septal cusps = Ant works the most!
• closed during ventricular systole ( contraction)
• Auscultation Point = heard best @ R lower sternum body

Bicuspid valve = mitral = L AV valve:

• b/w L atria and ventricle
• SP = behind L 1/ sternum @ 4th costal cart
• has Ant cusp & smaller post cusp
• closed @ onset of ventricular systole
• Ausculation point = heard best @ L 5th IC space @ midclavicular line

Mechanism of contration:

1. Papillary m contract during ventricular systole, wall of ventricle, contracts and shorten, cusps stay closed
2. If no contraction occurs, chords will relax, cusps flip open to atria
3. If pap m. shorten too much, chordae pull down cusps, and they will open during diastole
4. NOTE – b/c action of valve opening is active, when musc not contracted, valve closes passively, and shape of each cusp stops backflow back into atria

Histology: Histology of the heart.

Embryology: development of the heart.

Anim 1 = Early Heart and Primitive Heart Tube Folding

Anim 2 = Overview of Heart Tube Folding and Early Heartbeat

Anim 3 = Interatrial Septum Development

Anim 4 = Division of the Atrioventricular Canal

The primordium of the heart forms in the cardiogenic plate located at the cranial end of the embryo. Angiogenic cell clusters which lie in a horse-shoe shape configuration in the plate coalesce to form two endocardial tubes. These tubes are then forced into the thoracic region due to cephalic and lateral foldings where they fuse together forming a single endocardial tube.

The tube can be subdivided into primordial heart chambers starting caudally at the inflow end: the sinus venosus, primitive atria, ventricle, and bulbus cordis.

The heart tube begins to grow rapidly forcing it to bend upon itself. The result is the bulboventricular loop. Septa begin to grow in the atria, ventricle and bulbus cordis to form right and left atria, right and left ventricles and two great vessels- the pulmonary artery and the aorta. By the end of the eighth week partitioning is completed and the fetal heart has formed.

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