The Cardiovascular System

1. The Cardiovascular System Cardiovascular Control During Exercise Chapter 11 and 12

2. Heart Structure and Blood Flow • The atria receive blood into the heart; the ventricles eject blood from the heart. Atria Ventricles

3. The Myocardium • Because the left ventricle must produce more power than other chambers, its myocardium is thicker due to hypertrophy.

4. Cardiac Conduction • Cardiac tissue is capable of autoconduction. • It initiates its own pulse without neural control.

5. Cardiac Conduction • The sinoatrial (SA) node is the heart’s pacemaker, establishing the pulse and coordinating activity throughout the heart.

6. Extrinsic Control of Heart Activity • Heart rate and contraction strength can be altered by the autonomic nervous system or the endocrine system.

7. Electrocardiography (ECG) • The ECG is a recording of the heart’s electrical functioning. • An exercise ECG may reveal underlying cardiac disorders. r p t q s

8. Cardiac Function • The cardiac cycle: • Relaxation = diastole. • Contraction = systole. • ECG waves: P, QRS, T. • Stroke volume.

9. Cardiac Function • Ejection fraction from left ventricle (60% at rest). • Cardiac output (4.8-6.4 L. min-1)

10. Vascular System: • Arteries. • Arterioles. • Capillaries. • Venules. • Veins.

11. Venous Return • Blood returns to the heart through the veins, assisted by: • Breathing. • Muscle pump. • Valves. • Valsalva Manuever

12. Distribution of Blood • Activity dictates distribution. • Vasoconstriction. • Vasodilation.

13. Blood Pressure (NHLBI, 2003)

14. Blood • Blood and lymph are the substances that transport materials to and from body tissues. • Fluid from plasma enters tissues, becoming interstitial fluid.

15. Blood • Most interstitial fluid returns to the capillaries, but some enters the lymphatic system as lymph, eventually returning to the blood.

16. Blood • Blood is about 55% to 60% plasma and 40-45% formed elements including RBCs, WBCs, etc. • Hematocrit – ration of blood cells to total blood volume.

17. Blood • Oxygen is primarily transported bound to the hemoglobin in red blood cells. • As blood viscosity increases, so does resistance to flow.

18. Total Peripheral Resistance • TPR = length x viscosity ______________ (Radius)4

19. Response to Exercise • As exercise intensity increases, HR increases.

20. Exercise • The heart ejects blood more often, thus speeding up circulation.

21. Response to Exercise • Stroke volume also increases, so the amount of blood ejected with each contraction increases. • Increases in HR and SV increase cardiac output.

22. Response to Exercise • More blood is forced out of the heart during exercise then when at rest, and circulation speeds up.

23. Response to Exercise • This insures that adequate supplies of the needed materials - oxygen and nutrients - reach the tissues and that waste products, which build up much more rapidly during exercise, are quickly cleared away.

24. Major Changes in Blood During Exercise • The a-vO2 difference increases. • Increased extraction of oxygen from the blood for use by the active muscles.

25. Major Changes in Blood During Exercise • Plasma volume decreases during exercise. • Water is forced into tissues by increased blood pressure. • Water also evaporates.

26. Major Changes in Blood During Exercise • Hemoconcentration occurs as plasma fluid (water) is lost. • Although the actual number of red blood cells might not increase, the relative number of red blood cells per unit of blood increases, which increases O2 carrying capacity.

27. Major Changes in Blood During Exercise • pH levels drops from resting values of 7.4 to 7.0 or lower. • Muscle pH decreases even further. • The decrease in pH results primarily from increased blood lactate accumulation with increasing exercise intensity.