Posted by ESB on August 21, 2011 at 23:41:08:
In Reply to: Heart posted by isz on August 19, 2011 at 22:05:02:
: Heart
: 1. What is the apex and base of the heart? How are they oriented in the body?
The base of the heart primarily consists of the left atrium facing posteriorly. The great veins enter the atria here, and fix the base posteriorly to the pericardial thoracic wall. The left atrium is separated from the posterior thoracic wall by (left to right) the descending aorta, thoracic duct, and esophagus. The heart projects anteriorly and inferiorly from the base to form the somewhat pointed apex consisting of the left ventricle. The lateral border of the apex is the mediastinal edge of the left lung and the inferior surface contacts the diaphragm superior to the left lobe of the liver and the stomach fundus.
: 2. Define the pericardium - fibrous coat and serous pericardium.
The outermost layer of the pericardium is a fibrous outer covering adhered to the parietal layer of the serous pericardium. This parietal lamina reflects around the areas where the great vessels enter the heart, where it joins with the visceral layer of the serous pericardium. Between the parietal and serous pericardium lies the pericardial cavity. This pericardial cavity, similar to the pleural cavity, contains only a thin layer of fluid when in a normal state. This fluid lubricates the facing layers of the visceral and parietal lamina.
: 3. What "anchors" the heart in the thorax?
The heart is anchored to the posterior wall of the thorax by the adventitia of the great vessels posteriorly, to the sternum by the sternopericardial ligaments anteriorly, to the diaphragm by the central tendon inferiorly, and to the pretracheal fascia descending from the neck superiorly.
: 4. What is venous mesocardium?
The reflection of the parietal pericardium down and around the SVC, IVC and pulmonary veins.
: 5. What is arterial mesocardium?
The reflection of the parietal pericardium down and around the aorta and pulmonary trunk.
: 6. What is the transverse sinus?
A tunnel of pericardial cavity formed between the venous and arterial mesocardia.
: 7. What is the oblique sinus?
A blind cave of pericardial cavity running inferior-superior between the pulmonary veins, caused by the reflections of parietal layer forming the venous mesocardium.
: 8. What is epicardium? Myocardium? Endocardium?
The epicardium is the visceral lamina of the serous pericardium, loosely bound to the myocardium. The myocardium is composed of the muscular layer surrounding the atria and ventricles, lined by the endothelial endocardium that is continuous with the endothelium lining the vessels entering and leaving the heart.
: 9. What is the blood supply to the heart?
The right and left coronary arteries arise from the right and left aortic sinuses. The right coronary artery runs down the coronary sulcus while it supplies the right atrium and right ventricle, then turns posterior (where it gives off the marginal artery branch) around the bottom of the heart staying in the coronary sulcus and becoming the posterior interventricular branch supplying the interventricular septum and diaphragmatic surfaces of the ventricles. It also gives off smaller branches to the SA and AV nodes. The left coronary artery comes off the left aortic sinus and almost immediately branches into the anterior interventricular artery and the circumflex branch. The anterior interventricular artery runs down the anterior interventricular sulcus while supplying both ventricles and the interventricular septum. The circumflex branch of the left coronary artery runs between the left auricle and left ventricle, then circles toward the posterior of the heart. If it reaches the posterior interventricular sulcus, it's renames the posterior interventricular artery.
: 10. In the right atrium, define the: crista terminalis, sulcus terminalis, pectinate muscles, coronary sinus, fossa ovalis.
The crista terminalis is a muscular ridge on the interior aspect of the atrium running just anterior to the entrances of the SVC and IVC. The walls of the atrium posterior to this line are smooth and derived from the right horn of the sinus venosus in the embryonic heart. The walls of the atrium anterior to this line are roughened by pectinate muscles fanning out from the crista terminale. This area derived from the primitive atrium of the embryonic heart. The coronary sinus opens medial to the IVC, and the depression just superior to the IVC is the fossa ovalis - a remnant of the foramen ovalis during heart development.
: 11. In the right ventricule, define the : trabeculae carnae, papillary muscles, chordae tendinae, moderator band, conus arteriosus/infundibulum.
The right ventricle is C shaped, with an anterior and posterior limb. The conus arteriosus is on the superior portion of the anterior limb, where blood is pumped out into the pulmonary arteries. The walls of the posterior inflow limb are roughened by ridges of trabeculae carnae that give rise to papillary muscles, whose apices form tendons called chordae tendinae that run to the cusps of the AV valve. In one of these ridges (the septomarginal trabeculae) runs the AV bundle.
: 12. Contrast the right atrium with the left atrium in terms of structure.
Like the right atrium, the left atrium has roughened outflow and smooth inflow walls, but there's no defining line like the crista terminalis in the right atrium. The anterior portion of the left atrium (with pectinate muscles) forms the left auricle - a structure not present in the right. Four pulmonary veins enter instead of two vena cava.
: 13. Contrast the right ventricle with the left ventricle in terms of structure.
The right ventricle has thinner walls and clearer inflow and outflow tracts and coarser trabeculae carnae than the left ventricle.
: 14. What is the interventricular septum?
The anterior right wall of the left ventricle that separates it from the right ventricle. Inferiorly it is thick and muscular; the superior part is more membranous. It's one of the most common places for congenital heart defects.
: 15. Discuss the structure and function of the atrioventricular valves.
The atrioventricular valves have two (mitral) or three (tricuspid) cusps attached to chordae tendinae that originate in papillary muscles. They are secured to fibrous rings and project into the ventricles when opened. Papillary muscles contract during ventricular contraction, applying tension to the cusps so they are not everted into the atrium when ventricles contract.
: 16. Discuss the structure and function of the semilunar valves.
The semilunar valves contain three cusps formed like pockets everted into either the aorta or pulmonary trunk. After blood is ejected from the ventricles, the cusps fill and the distension forces the cusps together so that blood can't backflow into the ventricle.
: 17. Define the skeleton of the heart.
The cardiac muscle fibers are bound by investing fascia that forms a connective tissue skeleton to which the muscle fibers bind. This connective tissue also forms 4 stiff rings to which the heart valves are attached. The muscles of the heart are arranged in several superficial and deep looping bands; the looping bands forming the ventricles are also surrounded by flattened reinforcing sheets of muscle fibers.
: 18. Define the SA node, AV node, AV bundle, moderator band, and Purkinje fibers.
The SA node is a small crescent-shaped node extending all the way through the myocardium immediately anterior to the entrance of the SVC in the right atrium. It's independent of the central and peripheral nervous system and does not require outside innervation to continue its function of being the pacemaker of the heart, spreading impulses to the AV node. The oval AV node is located in the interatrial septum near the tricuspid valve; it sends fibers out in two bundle branches (the right one runs in the septomarginal trabecula/moderator band) across the ventricles, where the fibers in the bundle branches spread out over the ventricular walls as Purkinje fibers.
: 19. Discuss the cornary arteries of the heart.
(see answer to Q#9)
: 20. Discuss the coronary veins of the heart.
The great cardiac vein runs up the anterior interventricular sulcus (along the anterior interventricular artery), turns left at the coronary sulcus (along the circumflex branch), and then reaches the coronary sinus, where it ends in the posterior wall of the right atrium. The oblique vein of the left atrium also drains into the coronary sinus. The middle cardiac vein runs in the posterior interventricular sulcus and the small cardiac vein runs in the coronary sulcus. Both of these drain into the coronary sinus. The posterior veins of the left ventricle drain the diaphragmatic heart surface into the coronary sinus.
: 21. What is the cardiac cycle - systole/diastole?
In diastole, the semilunar valves are closed and blood is pouring into the atria and ventricles through the open AV valves. The ventricles begin to contract, forcing the AV valves closed (S1 and the beginning of systole). Concurrent with the rising ventricular pressure, the semilunar valves open and blood is forced out the great arteries. When the ventricles stop contracting, the blood pressure in the great arteries forces the semilunar valves closed (S2 and beginning of diastole). The AV valves open again and the cycle is repeated.
: 22. Why is there no correlation to the thoracic projections of the valves of the heart with the sites of auscultation?
The only valve that's heard best over its own projection is the right AV valve over the sternum near the 5th rib. The sounds from the other three are carried along with the blood to points of optimal intensity (at least according to Hollinshead). The pulmonary valve is best head at the second intercostal space along the sternal border, the aortic valve is heard best at the junction of the third rib with the sternum, and the mitral valve is best heard over the apex just medial to the sternum somewhere around the 4th intercostal space.
: 23. What is the ductus venosus?
An embryonic structure that shuttled blood from the left umbilical and vitteline veins to the right umbilical vein. The inferior vena cava eventually develops from the terminal segment of the right umbilical vein, and after birth, the shunt (the ductus venosus) closes down to form the ligamentum venosum.
: 24. What is the foramen ovale?
An opening between the right and left atrium formed by the incomplete fusion of the septum secundom with the endocardial cushion before birth. The hole closes gradually after birth to form the fossa ovalis. It's purpose in utero was was to allow cross-circulation between the pulmonary and systemic circulatory system