The Cardiovascular System

1. The Cardiovascular System

2. Functions • Provides oxygen and nutrients to tissues • Removes wastes • FYI • Pumps 7,000 liter per day • Beats 2.5 Billion times in your lifetime

3. Structure • Hollow, cone-shaped • Lies within thoracic cavity • Rests on diaphragm • Average Size • 14cm long and 9cm wide

4. Coverings of the Heart • Enclosed by layered pericardium • Visceral – inner layer • Parietal – outer layer • Pericardial Cavity • Space between the parietal and visceral layers of the pericardium

6. FYI • Pericarditis • Inflammation of pericardium • Adhesions cause layers of pericardium to attach to each other • Very painful • Interferes with heart movements

7. Walls of the Heart • Epicardium • Outer layer • Visceral pericardium • Protects heart • reduces friction • Myocardium • Middle layer • Pumps blood out of heart chambers • Endocardium • Inner layer

8. Heart Chambers and Valves • Two atria • Upper chambers • Receive blood returning to heart • Two ventricles • Lower chambers • Receive blood from atria • Contract to force blood out of heart

9. Right Chambers and Valves • Right atrium • receives blood from inferior vena cava, superior vena cava and coronary sinus • Tricuspid valve • Separates right atrium from right ventricle • Prevents back flow when ventricle contracts • Chordae Tendineae • Right Ventricle • Pumps blood to lungs • Thin walls • Pulmonary Valve • Sends blood through pulmonary arteries to lungs

10. Left Chambers and Valves • Left Atrium • Receives blood from lungs • Arrives through pulmonary veins • Mitral Valve • Biscuspid valve • Left Ventricle • Aorta • Aortic valve

11. Skeleton of Heart • Fibrous rings enclose base of pulmonary artery and aorta • Attachments for heart valves and muscle fibers • Prevent chambers from dilating during contraction • Blood Supply • Coronary arteries • First two branches of aorta • Supply blood to myocardium • Returns through cardiac veins and coronary sinus

12. Diseases • Mitral Valve Prolapse • Blood gets back into atrium during ventricular contraction • Chest pain, palpitations, fatigue and anxiety • Often caused by Streptococcus bacteria • Angina Pectoris • Narrowing of coronary arteries • Deprives heart cells of oxygen • Heavy pressure, tightening or squeezing of chest • Myocardial Infarction • Heart attack • Blood clot obstructs artery and kills part of heart

13. Heart Actions • Cardiac Cycle • Atria contract (systole) while ventricles relax (diastole) • Ventricles contract while atria relax • Both relax for brief interval

14. Cardicac Cycle – A Closer Look

15. Heart Sounds • Due to vibrations the valve movements produce • Lubb-Dubb • Lubb • Ventricular contractions • A-V valves closing • Dubb • Ventricular Relaxation • Pulmonary and Aortic valves closing

16. Heart Murmurs • Edges of valves erode away and don’t close completely • Blood leaks back through the valve • Can be caused by endocarditis (inflammation of endocardium) • Repaired through open heart surgery

17. Cardiac Muscle Fibers • Functional Syncytium • Mass of merging cells that function as a unit • We have atrial syncytium and ventricular syncytium • If any part of the syncytium is stimulated, the whole structure contracts as a unit

18. Cardiac Conduction System • Initiates and conducts impulses throughout the myocardium • Begins in Sinoatrial Node (S-A Node) • Located under right atrium • Fibers continuous with atrial syncytium • Cells reach threshold on their own • Membranes contract • Rhythmic • 70-80 times/minute • Pacemaker

19. Cardiac Conduction System • Impulse travels from S-A Node to atrial syncytium • Right and left atria contract • Impulse goes to Atrioventricular Node (A-V Node) by way of junctional fibers • Impulse enters A-V bundle • This bundle gives way to Purkinje Fibers • Gives way to twisting contraction of ventricles

20. Cardiac Conduction System

21. Electrocardiogram (ECG) • Records electrical changes in myocardium during a cardiac cycle • Body fluids conduct electrical currents • P wave • Atrial depolarization • QRS Complex • Ventricular depolarization • T wave • Ventricular repolarization

22. Regulation of Cardiac Cycle • Parasympathetic Fibers • Braking Action • Nerve impulse reach fiber endings and secrete acteylcholine • Decreases S-A and A-V node activity • Increase in impulses – decreased heartrate • Decrease in impulses – increased heartrate • Sympathetic Fibers • Secrete norepinephrine • Increases rate and force of myocardial contractions

23. Regulation of Cardiac Cycle • Cardiac Center • Located in Medulla Oblongata • Keeps balance between sympathetic and parasympathetic impulses • Baroreceptors control blood pressure – rising pressure lowers heart rate – lowers blood pressure • Fainting – decreases heart rate • Anxiety – increases heart rate • Temperature – increase in temp increases heart rate • Potassium – too much decreases rate and force of contractions • Calcium – too much increases heart actions

24. Blood Vessels • Closed circuit of tubes that carry blood from heart to cells and back • Include arteries, arterioles, capillaries, venules and veins • Human body has 62,000 miles • Can circle globe 2 ½ times

25. Arteries and Arterioles • Arteries • Strong, elastic vessels • Adapted to carry blood at high pressure • Branch and subdivide into arterioles • Made of 3 layers • Tunica interna • Tunica media • Tunica externa • Vasoconstriction – arteries contract – get smaller • Vasodilation – arteries relax – get larger • These two functions influence blood flow and blood pressure

26. Capillaries • Connect arterioles and venules • Wall is single layer of cells that forms a semipermeable membrane • Gas, nutrient and waste exchange occurs here • Openings in walls vary from tissue to tissue • Smaller in muscles • Larger in endocrine glands, kidneys and small intestines • Density varies with cellular needs • Muscle and nerves have high need for nutrients – so they have many capillaries • Cartilage, epidermis and cornea – no need – no capillaries

27. Capillaries • Precapillary Sphincters • Regulate blood flow • During exercise muscle cells have most need so they get the most blood- digestive system capillaries close because they aren’t really working at that time

28. Exchanges in Capillaries • Capillary blood and tissue fluid exchange gases, nutrients, and metabolic by-products • Diffusion provides the most important means of transport • Filtration, which is due to hydrostatic pressure of blood, causes a net outward movement of fluid at the arteriorlar end of a capillary • Osmosis due to colloid osmotic pressure causes a net inward movement of fluid at the venular end

29. Veins and Venules • Venules • Microscopic vessels that continue from capillary and merge to form veins • Veins • Carry blood back to heart • Made of three layers but middle layer is weak • Don’t have to be as strong because blood pressure is lower • Have valves to keep blood moving in right direction • Serve as reservoirs • Up to 25% of blood here

30. Arterial Blood Pressure • Blood pressure is the force blood exerts against the insides of blood vessels • Rises and falls with phases of cardiac cycle • Systolic pressure • Ventricle contracts • Top number – should be <120 • Diastolic pressure • Ventricle relaxes • Bottom number – should be <80

31. Factors influencing blood pressure • Heart Action • Stroke volume – amount discharged with each contraction – 70ml for average male at rest • Cardiac Output – volume discharged per minute • If these number go up – so does blood pressure • Blood Volume • Approximately 5 liters (8% of body weight) • More blood – higher blood pressure

32. Factors influencing blood pressure • Peripheral Resistance • Friction between blood and walls of blood vessels • More friction – higher blood pressure • Plaque build-up in arteries • Blood Viscosity • Thicker blood – higher blood pressure

33. Control of Blood Pressure • Controlled by the mechanisms that regulate cardiac output and peripheral resistance • More blood enters heart stronger contraction greater stroke volume and greater cardiac output

34. Venous Blood Flow • Little pressure left after blood moves through arteries, arterioles and capillaries • Depends on • Skeletal muscle contractions – when muscles contract blood in veins gets pushed from one valve reservoir to the next • Respiratory movements – when rib cage expands applies pressure on abdominal veins and blood gets pushed from abdominal veins into thoracic veins • Venoconstriction – if blood is lost veins contract, empty reservoirs and push blood back to heart.

35. Paths of Circulation • Pulmonary Circuit • Consists of vessels that carry blood from the right ventricle to the lungs and back to the left atrium • Systemic Circuit • Consists of vessels that lead from the heart to the body cells (including the heart itself) and back to the heart • Includes the aorta and its branches