1. 1 Topics to be addressed: Blood Anatomy of Blood Vessels Anatomy of the Heart The Conduction System The Cardiac Cycle Cardiodynamics Blood Flow and its Regulation Adaptation and Disorders of the Cardiovascular System Overview of the Cardiovascular System

2. The Cardiovascular System: Regulating Blood Flow Organs must receive a steady supply of oxygen and nutrients in order to survive. Maintaining a steady flow of blood to the organs is the job of the cardiovascular system. Both the heart and the blood vessels are capable of change in order to adjust the flow of blood. There are only 5 liters of blood in the body, and it is constantly being redistributed between different organ systems 2

3. 3 Flow is a Function of Pressure and Resistance Blood Flow to tissues = Difference in blood pressure between heart and capillaries Peripheral Resistance Blood flows from a region of high pressure to one of lower pressure; the greater the pressure difference driving the movement, the greater the flow The heart generates pressure to overcome resistance; the greater the peripheral resistance, the lower the flow

4. 4 What produces the pressure in the cardiovascular system? Blood flows from area of high pressure to area of low pressure

5. 5 What is meant by the term “Blood Pressure” The pressure exerted by blood onto the vessel wall Arterial Blood pressure (BP) : usually refers specifically to arterial pressure Capillary hydrostatic pressure : Pressure within the capillary beds Venous pressure : Pressure in the venous system

6. 6 Vessel pressure declines along the circuit TERMS TO KNOW Systolic Pressure : the peak arterial pressure during ventricular systole Diastolic Pressure : the minimum arterial pressure during diastole 120 leaving left ventricle <10 returning to right atrium

7. 7 Systolic and Diastolic Pressure in Elastic Arteries During systole, the heart forces blood into the vessels and exerts great pressure on the vessel walls. During diastole, the heart is not pushing blood, but the recoil of the walls of the elastic arteries continues to push blood and exert pressure.

8. 8 Elastic Arteries Have Different Pressures at Systole and Diastole TERMS TO KNOW Pulse pressure : the difference between systolic pressure and diastolic pressure Blood Pressure is Recorded in two ways: 1. Systolic/Diastolic Pressure Typically 120/80 Hypertension : Abnormally high blood pressure (greater than 140/90) Hypotension : Abnormally low blood pressure (less than 90/60) 2. Mean arterial pressure (MAP) = diastolic pressure + 1/3 pulse pressure; Typically 93

9. 9 Pulse Points Arteries large enough to have pulse pressure Arteries close enough to skin surface to palpate Pulse Pressure Creates a Throbbing Sensation in the Artery

10. 10 Flow is a Function of Pressure and Resistance Where does RESISTANCE come from? 3 Sources : 1.Vascular Resistance Due to friction between blood and the vessel wall Dependent on vessel length (constant) and diameter (adjustable) 2.Viscosity Resistance caused by molecules and suspended materials in a liquid (cells, proteins, etc.) : blood is about 4 times more viscous than water 3.Turbulence Swirling action within vessel that disturbs smooth flow

11. Patterns of Blood Flow Regulating Perfusion of Tissues 11

12. The main regulator of peripheral resistance is vessel diameter 12 Arterioles, the smallest diameter arteries, are the main site of regulation of peripheral resistance Changing vessel diameter on the arterial side of the circuit changes blood flow into organs

13. Factors that affect pressure and resistance can work locally (within a tissue) or systemically (in blood, affecting all tissues) 13

14. Summary : The two main forces at work in regulation of blood flow 14

15. 15 Changing vessel diameter on the venous side of the circuit influences preload Recall that veins are the capacitance vessels There is more blood volume on the venous side of circulation Venous constriction redistributes blood flow and enhances cardiac output

16. 16 Exchange of materials at capillaries is vital to homeostasis Capillaries and their beds are OPTIMIZED for exchange Capillary Dynamics A continuous capillary, the most common capillary in the body, has a wall one squamous cell thick. Exchange occurs across this wall.

17. 17 Capillary beds are optimized for exchange of materials : the power in numbers Although one capillary has the smallest diameter of any vessel, there are so many of them that the TOTAL cross- sectional area is higher at the capillary level than at any other point of the circulation.

18. 18 The high cross-sectional area of the capillary circulation creates a drop in pressure at that point of the circulation, and a decrease in flow velocity. **These two features – low pressure and slow flow - optimize exchange in the capillary beds. Capillary beds are optimized for exchange of materials : the power in numbers

19. 19 Exchange of materials at capillaries is vital to homeostasis Once blood gets to the capillary, how does exchange of materials with tissues occur? 3 forces at work moving materials across capillary walls: Diffusion Filtration Reabsorption Capillary Dynamics

20. 20 Diffusion: The movement of ions or molecules along a concentration gradient from high concentration to low concentration Diffusion Routes for important substances: Passive movement, so ongoing Lipids and lipid-soluble materials such as O 2 and CO 2 diffuse through endothelial plasma membranes Some ions (Na +, K +, Ca 2+, Cl - ) diffuse through ion channels in plasma membranes Water, ions, and small molecules such as glucose diffuse between adjacent endothelial cells or through fenestrated capillaries Large, water-soluble compounds like plasma proteins and blood cells are too big to pass through continuous or fenestrated capillaries and can only get across the big, leaky sinusoidal capillaries. Forces in Capillary Exchange : Diffusion

21. 21 Variable Forces in Capillary Exchange : Filtration and Reabsorption Filtration: Water and small solutes squeezed out of the capillary into the interstitial fluid Driven by blood pressure (capillary hydrostatic pressure) Reabsorption: Water drawn back into the capillary from the interstitial fluid Pulled by osmotic pressure exerted by large plasma proteins trapped in blood

22. 22 How does the Filtration Force change across a capillary bed? Capillary Hydrostatic Pressure (CHP) at arterial end 35 mmHg Capillary Hydrostatic Pressure at venous end is 21 mmHg Filtration pressure declines as blood moves across capillary bed Forces in Capillary Exchange

23. 23 Forces in Capillary Exchange How does the Reabsorptive Force change across a capillary bed? Plasma proteins are trapped in blood, so exert a constant force along the bed This force is called the colloid osmotic pressure (COP)

24. 24 Net Filtration Pressure (NFP) is the difference between net hydrostatic pressure and net osmotic pressure (how much is pushed out minus how much is drawn back in) Forces in Capillary Exchange

25. Net Filtration Pressure changes along the length of the capillary –At arterial end of capillary, fluid moves out of capillary, into interstitial fluid –At venous end of capillary, fluid moves into capillary, out of interstitial fluid –These movements are not equal RESULT: Normally capillaries filter more than they reabsorb up to 3 liters of fluid per day leave the blood and collect in the tissues without being reabsorbed; how is this fluid recovered? Forces in Capillary Exchange Picture from different textbook, so different NFP numbers, but the pattern is the same

26. 26 Recovery of interstitial fluid Lymphatic vessels return interstitial fluid to the bloodstream –A separate set of vessels; do not carry blood –One way drainage system, not a “lymphatic circuit” Interstitial fluid collected into lymphatic vessels is called lymph

27. 27 Recovery of interstitial fluid Lymphatic fluid is drained through a series of lymphatic vessels and returned to the blood stream close to the heart. Lymph nodes interspersed along the lymphatic channels serves as filters to remove pathogens before the lymph is returned to the bloodstream

28. 28 Elephantiasis is caused by a parasitic infection which invades and blocks lymphatic vessels Failure of the lymphatic system to return interstitial fluid results in edema

29. 29 Disorders Often Affect Capillary Dynamics 1. Hemorrhage decrease in BP reduces CHP and NFP net increase in reabsorption of interstitial fluid (recall of fluids) 2.Cardiac failure decrease in stroke volume backs blood up into venous circulation, increasing CHP and NFP, leading to edema 3. Dehydration Increases blood osmotic pressure, decreasing NFP Accelerates reabsorption Pitting edema

30. 30 Cardiovascular Regulation Goal is to maintain Tissue Perfusion (Blood flow through the tissues) Deliver O 2 and nutrients to tissues and organs Remove CO 2 and wastes from tissues Flow is affected by Cardiac output Peripheral resistance Blood pressure Cardiovascular regulation changes blood flow to a specific area Different organs have different metabolic needs at different times

31. 31 Cardiovascular Regulation 3 Factors Influence Cardiac Output and Blood Pressure –Autoregulation Causes immediate, localized homeostatic adjustments –Neural mechanisms Respond quickly to changes at specific sites –Endocrine mechanisms Slowest, direct long-term changes

32. 32 Cardiovascular Regulation : Autoregulation Local Regulation of Blood Flow within Tissues : Adjusted by changing peripheral resistance while cardiac output stays the same; the main effect is to change the diameter of the blood vessel wall Local vasodilators increase local blood flow some are local chemical changes in busy tissues some are chemicals released by inflammation (histamine) elevated local temperature is an additional factor Local vasoconstrictors decrease local blood flow some are local chemical changes in quiet tissues some are chemicals released by damaged tissues

33. 33 Cardiovascular Regulation : Fast Alterations

34. 34 Cardiovascular Regulation : Neural Reflexes respond to changes in flow and the chemicals in the blood The Cardiovascular Center in the brainstem monitors the state of the bloodstream (sensory input) and adjusts the performance of organs (motor). Baroreceptor reflexes respond to changes in blood pressure Chemoreceptor reflexes respond to changes in chemical composition, particularly pH and dissolved gases

35. 35 Cardiovascular Regulation : The Baroreceptor Reflex is a Neural Mechanism Input: sensory feedback from aortic arch and carotid body Integration: cardiovascular center of medulla decides what adjustments need to be made Output: 1.alterations in balance of sympathetic and parasympathetic output to heart to adjust cardiac output 2.Alteration in sympathetic output to blood vessels

36. 36 Cardiovascular Regulation : Baroreceptor Reflex Cardiovascular center

37. 37 Longer Term Cardiovascular Regulation : Hormones affecting kidney have profound effects on cardiovascular function

38. 38