Understanding Circulation: Blood Flow Dynamics in Systemic and Pulmonary Systems

1. Under Pressure

2. Circulation • Both systemic and pulmonary circulation utilize blood vessels to transport blood • Arteries • Capillaries • Veins • The connection between 2 blood vessels is called an anastomosis

4. Arteries • Smooth muscle under autonomic control • Lined with epithelium • Easy flow • Clot prevention • Chemical secretion • Vasoconstriction • Vasodilation

5. Arterial Flow • From the heart, blood enters the • Pulmonary artery (lungs) • Aorta (body) • Arteries branch into arterioles • Arterioles branch into capillaries

6. Capillaries • Extension of arterial lining – simple squamous • Location of material exchange with interstitial fluid • Semipermeable: space between cells • Flow controlled by smooth muscle at anastomosis

7. Chemical Exchange • Diffusion • Higher concentration of O2, nutrients in blood  exit capillaries • Higher concentration of CO2, waste in i.f.  enter capillaries

8. Chemical Exchange • Filtration • Chemicals forced out by hydrostatic pressure • Created by ventricular systole • Pressure is higher at artery end of capillary

9. Chemical Exchange • Osmosis • Draw water in to counteract the outward hydrostatic force • Still, more fluid exits than enters • Lymphatic system!

11. Venous Flow • Venules extend from capillaries • Venules merge into veins • Veins merge into vena cavae (systemic) or pulmonary vein • Empty directly into heart to start the process over

12. Veins • 3 layers, as with arteries, but middle, muscular layer is much less developed

13. Veins • Some have semilunar valves • Pushed closed in the event of backflow • Sympathetic stimulation of veins can control volume of blood entering hear • Ex: drop in arterial pressure and hemorrhaging  vasoconstriction  more blood to heart

14. Blood Pressure • BP = the force blood exerts on the inner walls of the blood vessels

15. Blood Pressure • Varies throughout the CV system • Traditional measured level is in arteries supplied by aortic branches • Systolic = due to ventricular contraction • Diastolic = lowest pressure prior to contraction

18. Pulse • Artery walls are elastic • The measurable pulse is the expanding and recoiling of artery walls in response to the pressure change • Used to calculate HR • High BP  strong, full pulse • Low BP  weak, easily compressed

19. Contributors to BP

20. Contributors to BP • Blood Volume • Heart Action: Cardiac Output • Stroke volume x heart rate • Peripheral Resistance • Friction between blood and walls • Viscosity: ease of flow • Drop in cell number or plasma proteins decreases blood pressure (anemia)

21. Control of BP • Frank-Starling law • Ensures cardiac output is roughly equal to venous return • Utilizes input from baroreceptors • Renin-angiotensin system • Hormone system that regulates blood pressure and fluid retention

22. RAS • When blood volume is low: • Kidneys secrete renin • Liver produces angiotensin I • Converted to angiotensin II • Constricts blood vessles • Adrenal cortex releases aldosterone kidneys retain more water • Blood Pressure increases

24. Factors Affecting BP • CO2, O2, H+ • Affect smooth muscle thus affecting peripheral resistance • Chemicals • Nitric oxide, bradykinin: vasodilators • Angiotensin: vasocontrictors

25. Varying BP • Since BP varies by location – particularly with distance from the heart – the venous end of capillaries have very little pressure So how does the blood get back to the heart?

26. Venous Circulation • Skeletal muscle contraction: massaging action • Breathing movements • Diaphragm contracts  rib cage expands  pressure on abdominal cavity  blood squeezed out of abdominal veins into thoracic ones • Vasoconstriction

28. Coronary Circulation • The heart has its own path of blood flow to supply its own muscles • Coronary arteries branch off of aorta • Pressure here is lowest during contraction b/c they are compressed • Branch into capillaries to supply myocardium • Converge into cardiac veins • Veins empty directly into right atrium

30. Coronary Artery Disease • Any blockage in coronary arteries leads to tissue death • Cardiac muscle cells do not divide • Stem cell differentiation only (injury trigger) • Empty spots refilled by adipose & connective tissue • Result is thickening walls which can increase BP

31. Aterio vs. Atherosclerosis • Both types of coronary artery disease • Arteriosclerosis: walls of arteries harden and thicken • Atherosclerosis: plaque build up; a type of arteriosclerosis

32. Hypertension • Persistently elevated arterial pressure • Diet • In some people, high sodium intake causes vasoconstriction • Stress • Obesity • Increases peripheral resistance

33. Other CV problems • Marfan’s • Connective tissue defect • Enlarged, weakened aorta • Familial Hypercholesterolemia • Lack LDL receptors on liver cells • Cholesterol not filtered out of blood and body is not stopped from making it

34. Other CV problems • Familial Hypertrophic Cardiomyopathy • Myosin defect • Sudden death in young athletes