BIO 265 – Human A&P

1. BIO 265 – Human A&P Chapter 18 The Heart

2. The Heart • Size • Form • Location – mediastinum • Figure 18.1 and from other text

3. Heart Anatomy • Pericardium (pericardial sac) • Figures 18.1 and 18.2

4. Heart Anatomy • Heart Wall • Epicardium • Myocardium • Endocardium • Figure 18.2

5. Heart Structure and Function • What are the heart chambers? • Overview of heart function • Figure 18.5

6. Coronary Circulation • In order for the heart to function, it must have a constant supply of oxygen • The coronary arteries carry the blood to the heart • Figure 18.7

7. Heart Attack • What is a heart attack or myocardial infarction? • CD Animation

8. Heart Valves • What are the 4 valves in the heart? • Figure 18.8

9. Heart Valves • Heart valve function – Figures 18.9 and 18.10

10. Heart Valves • Heart sounds result from the closing of the heart valves • Heart murmurs occur when a valve does not open or close properly • CD Animation

11. Histology • What are the characteristics of cardiac muscle? • Branched fibers • Mitochondria • T-tubules • Intercalated disks with gap junctions • Figure 18.11

12. Conducting System • What are the components? • Figure 18.14

13. Conducting System • All cardiac muscle cells are autorhythmic • They can generate spontaneous AP • But the SA node is the pacemaker (it depolarizes faster than other areas of the heart) • Figure 18.13

14. Conducting System • Once the AP is generated it spreads through the atria to the AV node • What role does the AV node play? • Delays the AP for a split second • The AP then passes very quickly through the bundle branches • The effect is contraction at the apex first • Figure 18.14

15. Electrical Properties • Cardiac muscle has an RMP similar to skeletal muscle • Differences between cardiac and skeletal AP – Figure from other text

16. Cardiac Action Potentials • Phases of AP in contractile cells: • Depolarization • Na+ channels (fast channels) open • K+ channels are closed • Ca2+ channels (slow channels) begin to open • Early repolarization and plateau • Na+ channels close • Some K+ channels open • Ca2+ channels stay open • Figure from other text

17. Cardiac Action Potentials • Final repolarization • Ca2+ channels close • many K+ channels open • Figure from other text

18. Cardiac Action Potentials • How would the AP in cardiac muscle stimulate a contraction? • Notice that Ca2+ comes from the extracellular fluid as well as the SR • Cool CD Animations! (my CD)

19. Electrocardiogram • ECG wave patterns – Figures 18.16, 18.17, and 18.18

20. The Cardiac Cycle • The cardiac cycle refers to the repetitive pumping process that occurs in the heart • Systole – contraction of the heart • Diastole – relaxation of the heart • CD animation

21. The Cardiac Cycle • Steps: • Ventricular filling • Passive – during complete diastole • Active – during atrial systole • Ventricular Systole • Isovolumetric Contraction – closes AV valves and opens semilunar valves • Period of Ejection – blood leaves the ventricles • Ventricular Diastole • Isovolumetric relaxation – semilunar valves close • Figure 18.20

22. The Cardiac Cycle • Assuming an average 75 bpm: • Cardiac Cycle = 0.8 s • Atrial systole = 0.1 s • Ventricular systole = 0.3 s • Diastole = 0.4 s • Awesome CD animation (my CD)

23. Cardiac Output • Cardiac output (CO) = Heart rate (HR) x Stroke volume (SV) of one ventricle • Calculations (p.698) • Resting 75 bpm x 70 ml/beat = 5250 ml/min • Or in other words your entire volume of blood passes through each side of your heart each minute!!! • Exercise 20 liters/min to 35 liters/min

24. Regulation of the Heart • Regulation of cardiac output is critical for homeostasis • Starlings law of the heart: • The greater the venous return to the heart, • The greater the stretch of the heart wall, • This results in a more forceful contraction and therefore a greater stroke volume

25. Regulation of the Heart • Neural regulation: • The heart is innervated by both sympathetic and parasympathetic fibers • Parasympathetic – decrease heart rate by releasing acetylcholine • It opens ligand-gated K+ channels • Effect? • Figure 18.15

26. Regulation of the Heart • Sympathetic – increases heart rate and force of contraction (stroke volume) • Norepinephrine (a neurotransmitter) stimulates the opening of the slow Ca2+ channels • It works through a G-protein system that synthesizes cAMP • Figures 18.22 and 18.15

27. Regulation of the Heart • Hormonal Control • Epinephrine and norepinephrine – same effect as above • Problems in Regulation: • Tachycardia – over 100 bpm • Bradycardia – under 60 bpm (can be normal in athletes)

28. Regulation of the Heart • Congestive Heart Failure – cardiac output is too low to meet body tissue needs • Blood builds up in the veins (causing the “congestion”) • Causes: • Coronary Atherosclerosis – decreases the hearts pumping ability • Hypertension (high blood pressure) – ventricles can’t push the blood out into the arteries • Myocardial infarction

29. Heart and Homeostasis • How does the heart help maintain homeostasis? • Blood pressure example • Baroreceptors, the cardioregulatory center, and nerves • Figures from other text

30. The Fetal Heart • There are some interesting differences between the fetal and adult hearts • Why? • Foramen ovalis in the atrial septum • Ductus arteriosis between the pulmonary trunk and the aorta • Figures 18.4b and e