this chapter deals with all the major pathologies oriented around the heart. the first section is a reminder of the physiology of the heart, dividing the organ into several different aspects anatomically and physiologically: heart muscle, valves, conduction system, blood flow. to begin with cardiac muscle: as we learned in organ systems last year, cardiac muscle cells, myocytes, are structurally similar to both skeletal muscle (striations) and smooth muscle (cell size). connecting the myocytes are intercalated discs, which join the cells mechanically via adhesion molecules and electrically through gap junctions. ventricular myocytes are arranged circumferentially around the ventricles in a spiral pattern, while the smaller-celled atrial myocytes are more haphazardly arranged. atrial myocytes also contain "specific atrial granules" which contain atrial natriuretic peptide, the role of which will be discussed later on.
heart valves are specialized tissue flaps that coordinate the outflow and inflow of blood between and out of chambers. there are 4 valves: mitral and tricuspid valves control blood between the atria and ventricles of each side and the semilunar valves control the outflow of blood from the ventricles to the lungs or to the aorta. all of these valves have the same general components: a spongy loose connective tissue core, elastic layer, dense collagenous layer, endothelium. in addition, interstitial cells are scattered throughout, which produce and repair extracellular matrix, vital in the valves' ability to withstand rapidly changing mechanical conditions.
the next major aspect of heart function is the conduction system, which coordinates rhythmic contraction of the myocytes. the SA node is at the junction of the right atrial appendage and the superior vena cava and is considered to be the pacemaker because of its faster rate of spontaneous depolarization. in contrast, the AV node is situated at the right atrium, along the atrial septum, and considered the gatekeeper because it delays conduction between the atria and ventricles, ensuring that the atria contract first. the other major component of the conduction system is the bundle of His, which runs from the right atrium down to the ventricular septum and then branches further into the ventricles.
myocytes rely almost exclusively on oxidative phosphorylation for energy production, making the blood flow to the heart crucial in maintaining proper physiology. this is accomplished via the coronary arteries, which arise distal to the aortic valve, run along the surface of the heart (called epicardial arteries) and then penetrate the heart muscle itself (called intramural arteries). the main epicardial arteries are the left anterior descending artery, the left circumflex artery, and the right coronary arteries. blockage of any of these arteries by a variety of factors can prove to be fatal to heart function.
these 4 different aspects of the heart can be damaged by specific pathological stressors, and can also be the victim of age related pathological changes. epicardial fat increases with age, especially over the right anterior surface and atrial septum. atrial size increases and ventricular size decreases. valves are prone to dysfunction due to calcification and fibrosis. the myocardium itself changes, with fewer monocytes, more collagen, and possible amyloid deposition. "brown atrophy" is a particular type of pathological change associated with age that is the result of excess lipofuscin deposits in a small, atrophied heart.
questions
heart intro...
1. how much blood does the heart pump on a daily basis?
2. what is the approximate weight of the heart?
myocardium...
3. what is the heart muscle cell called?
4. describe the orientation / arrangement of ventricular myocytes.
5. describe the difference between atrial and ventricular myocytes.
6. what are the cytoplasmic granules in atrial myocytes and what do they do?
7. what are intercalated discs?
valves...
8. what are the general tissue components to all 4 heart valves?
9. describe the role of interstitial cells in valve physiology.
10. what is an example of a disturbance in semilunar valve functioning?
11. what are some factors that can disturb mitral and tricuspid valve functioning?
12. what are the three common pathologies that occur with heart valves?
conduction system...
13. what are the key components of the conduction system of the heart?
14. where is the SA node located?
15. where is the AV node located?
16. where is the bundle of His located?
17. which component of the conduction system is considered the pacemaker and why?
18. which component of the conduction system is considered the gatekeeper and why?
blood flow...
19. how do cardiac myocytes meet their energy needs?
20. describe the course of the coronary arteries along the heart.
21. what are the three major epicardial branches of the coronary artery?
22. when does most blood flow to myocardium occur during the contraction cycle?
age related changes...
23. age's effect on epicardial fat...
24. age's effect on left ventricle...
25. age's effects on valves...
26. age's effects on myocardium...
27. what is "brown atrophy"?
answers
1. over 6000 liters.
2. 250-300g females, 300-350g males.
3. the myocyte.
4. ventricular myocytes are circumferentially arranged in a spiral orientation.
5. atrial myocytes are smaller and arranged more haphazardly.
6. electron dense granules: specific atrial granules which store atrial natriuretic peptide.
7. the junctions between myocytes which link the cells mechanically and electrically (via gap junctions).
8. dense collagenous core near the outflow surface, layer of elastin near the inflow surface, central spongy core of loose connective tissue and an endothelial covering.
9. interstitial cells are spread throughout the valve tissues, where they produce and repair extracellular matrix- allowing valves to adapt and respond to changing conditions.
10. aortic root dilation interfering with coordinated cuspal closure (CCC)
11. in addition to the factors that interfere with semilunar valve closure (the leaflets themselves and the tissues they are attached to), these valves are also dependent on the tendons they are attached to as well as the papillary muscles.
12. damage to collagen tissue, nodular calcification, and fibrotic thickening. (thick chalky fibers)
13. the SA node, AV node, and bundle of His.
14. junction of the right atrial appendage and the superior vena cava.
15. right atrium, along the atrial septum.
16. from the right atrium down to the ventricular septum, and from their branches out into the ventricles further.
17. the SA node because it spontaneously depolarizes at the fastest rate, 60-100bpm.
18. the AV node, because it delays conduction between the atrium and ventricles to ensure that atrial contraction precedes ventricular contraction.
19. almost exclusively from oxidative phosphorylation
20. the coronary arteries arise immediately distal to the aortic valve and run along the surface of the heart (epicardial), then penetrate the heart muscle (intramural).
21. left anterior descending, left circumflex, and right coronary
22. during diastole, when myocardium is not compressed by contraction.
23. increased, especially over anterior surface of right ventricle and atrial septum.
24. decreased chamber size, exacerbated by hypertension or sigmoid septum; resulting in a functional outflow obstruction.
25. calcification, fibrosis, or small filiform processes.
26. fewer myocytes, more collagen and possible amyloid deposition.
27. extensive lipofuscin deposits in a small, atrophied heart.
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