Chapter 21 The Cardiovascular System: Blood Vessels and Hemodynamics

1. Chapter 21The Cardiovascular System: Blood Vessels and Hemodynamics • Structure and function of blood vessels • Forces involved in circulating blood • Major types of circulation to be studied in lab

2. Basic circulatory route Veins Heart Arteries Venules Capillaries Arterioles Tissues

3. Structure of Vessels • Comparison of Arteries and Veins • Blood flows away from heart in ________ arteries • Blood flows toward heart in ______ veins • Arteries are thicker than veins • Veins have regularly spaced valves • Which vessels have the highest pressure? • Which vessels carry about 64% of the blood?

4. Distribution of Blood

5. Vessel Structure -----------------Tunica Interna Endothelium, Basement Membrane & Elastic Fibers ---------------Tunica Media Smooth Muscle & Elastic Fibers ------------Tunica Externa Collagen & Elastic Fibers

6. Types of Arteries • Elastic Arteries • Less muscle and more elastic tissue • Larger arteries such as aorta • Why do the larger arteries have more elastic tissue? What purpose do they serve?

7. Types of Arteries • Muscular Arteries • Less elastic tissue and more muscle • Medium size to smaller arteries • Capable of greater vasoconstriction and vasodilation to adjust rate of flow

8. Smaller Vessels -Smallest arteries • Arterioles -Deliver blood to capillaries -Smallest ones lose tunica externa -Called resistance blood vessels because their vasoconstriction increases resistance, and their vasodilation (relaxation) decreases resistance to blood flow

9. Capillaries • Microscopic vessels – form microcirculation • Tubes of endothelium and basement membrane • Connect arterioles to venules • Function in exchange of substances with tissues • Interconnect like a net to form capillary beds

10. Types of Capillaries • -Adjacent endothelial cells form tight fit • Continuous -Least permeable -In muscle, brain, connective tissue and lungs • Fenestrated - Pores (holes) in endothelial cells - Quite permeable - In kidneys, intestines and endocrine (hormone) glands

11. Types of Capillaries • Sinusoids -Largest capillaries -Large fenestrations and large gaps between endothelial cells - Scant basement membranes - Most permeable - In liver, some endocrine glands and bone marrow

12. Types of Capillaries • Continuous Capillary • Fenestrated Capillary • Sinusoid

13. Venules • Small veins that collect blood from capillaries • Tunica media contains only a few smooth muscle cells & scattered fibroblasts • Rather porous endothelium

14. MicrocirculationArterioles, Capillaries and Venules ---------------Arteriole -------------------------Metarteriole ----------Capillary --------------Thoroughfare channel ---Venule

15. Anastomoses • Union of two or more arteries supplying the same body region • blockage of only one pathway has no effect • circle of willis underneath brain • coronary circulation of heart • Collateral Circulation: -Alternate route of blood flow through an anastomosis. - can occur in veins and venules as well

16. Physiology of Circulation-Blood Pressure • Blood pressure (BP) is the force the blood exerts against vessel walls • Difference in blood pressure (pressure gradient) along vessels causes blood to flow • Blood flows from higher to lower pressure • Pressure is highest in the aorta and lowest in the vena cavae

17. Blood Flow • Amount of blood flowing through vessels per unit of time (mL per minute)

18. Resistance (R) to blood flow • Produced as the blood encounters friction and turbulence against the vessel and heart walls • Increased resistance decreases blood flow • For blood to flow, BP must overcome R • Greatest R is in arterioles-called peripheral resistance (PR)

19. Blood Pressure Formula • Blood pressure = Flow X Resistance • Flow causes BP, Flow causes BP • R causes BP, R causes BP

20. Factors in Flow and Resistance • Factors in Flow • Cardiac Output (CO) = Amount of blood ejected by left ventricle in one minute • Blood volume = Total amount of blood in body • More than 10% drop causes drop in BP

21. Factors in Resistance • Diameter of vessels, especially arterioles vasoconstriction Has BP increased or decreased? • Viscosity of blood • Length of vessels

22. Measurements of Arterial blood pressure • Systolic pressure(SP) and diastolic pressure (DP) • Systolic pressure(SP) • Pressure in arteries when left ventricle is contracting • High number on blood pressure reading • Diastolic pressure(DP) • Pressure in arteries when left ventricle is relaxing • Low number on blood pressure reading

23. Measuring Arterial BP • BP measured in millimeters of mercury (mm Hg) • Use a manometer • Usually taken in upper arm • High number is systolic pressure • Low number is diastolic pressure • Typical reading is 120 mmHg/80 mmHg • 140/90 or above considered high

24. Sphygmomanometer

25. Other Pressures • Pulse pressure (PP) • Difference in Systolic and diastolic pressures or PP=SP-DP • High during exercise, anxiety, influence of certain drugs and with hardening of arteries • Mean Arterial Blood Pressure (MABP or MAP) • Single measure of arterial BP • Formula: MAP = Diastolic Pressure + Pulse Pressure/3

26. Pressure Gradients Different Vessels • Arterial Pressure Gradient = • Difference in arterial pressure from Aorta to capillaries • Averages about 60 mmHg • Capillary Pressure Gradient • Difference in pressure from arteriole to venule side of capillary bed • Averages about 20 mmHg • Venous Pressure Gradient • Difference in pressure from venules to Vena cavae • Averages about 16 mmHg

27. Blood Pressures in Various Vessels

28. Capillary Exchange • Passage of water and solutes between capillary plasma and interstitial fluid • Three Methods 1.Diffusion is movement of solute from ____ to ____ concentration high low 2.Transcytosis is movement of large molecules across capillary cells by ____________________________ formation of pinocytotic vesicles

29. Capillary Exchange 3.Bulk Flow – Filtration and Reabsorption - Movement of fluid and solute from capillaries into interstitial fluid is _______ filtration - Movement of fluid and solute from interstitial fluid into capillaries is __________ reabsorption • Two opposing pressures at work - Blood Hydrostatic Pressure (BHP) is the blood pressure that pushes fluid out of blood - Blood Colloidal Osmotic Pressure (BCOP) is a “suction” pressure that pulls fluid into blood

30. Capillary Exchange • Mechanism of Filtration and Reabsorption - On arteriole side of capillary, BHP BCOP – push pull   -On venule side of capillary, BCOP BHP – pull push   - Higher BHP on arteriole side pushes water and solute from capillary into interstitial fluid - filtration - Higher BCOP on venule side pulls water and solute from interstitial fluid into capillary - reabsorption

31. Drawing of Filtration and Reabsorption

32. Venous pressureand venous return • Venous pressure is very low and can not account for return of blood to heart • Factors that aid in venous return - Contraction of skeletal muscles squeeze veins and push blood toward heart - Breathing squeeze pulmonary vessels - Venous valves prevent backflow of blood once it is squeezed past them

33. Illustration of Venous Return

34. Velocity of Blood Flow • Blood flows fastest in _______ arteries • Blood flows slowest in _________ capillaries ----Cross-sectional Area ----Velocity Arteries & Arterioles Capillaries Venules & Veins

35. Blood Pressure Regulation • Local regulation within tissues • Central (neural) regulation by brain

36. Local Regulation to assure proper tissue perfusion • Autoregulation of Blood Flow -Tissues regulate blood flow to meet their needs • Local Vasodilators -↑CO2 or ↓O2 -↑acid -↑NO -inflammatory chemicals such as histamine -↑body temperature

37. Central Control of Blood Pressure & Flow • Role of Cardiovascular Centers - cardioaccelerator, cardioinhibitory & vasomotor centers of the medulla oblongata - Help regulate heart rate & stroke volume - Specific neurons regulate vessel diameter - Regulate by input from sensory receptors and output to heart

38. Input to the Cardiovascular Center • Higher brain centers such as cerebral cortex, limbic system & hypothalamus - anticipation of competition - increase in body temperature • Proprioceptors - input during physical activity • Baroreceptors - changes in pressure within blood vessels • Chemoreceptors - monitor concentration of chemicals in the blood

39. Output from the Cardiovascular Center • Heart -Parasympathetic (vagus nerve) -decreased heart rate -Sympathetic (cardiac accelerator nerves) - increased contractility & rate • Blood vessels -Sympathetic vasomotor nerves • Decreased stimulation produces dilation & decreased BP • Increased stimulation produces constriction & increased BP • Continual stimulation keeps arterioles in tonic contraction called vasomotor tone

40. Input and Output

41. Neural Regulation of Blood Pressure – Aortic/Carotid Reflexes • Baroreceptor reflexes - Carotid sinus reflex • Receptors in carotid artery wall • Sensory input to cardiovascular center in medulla • Maintains normal BP in the brain - Aortic reflex • Receptors in wall of ascending aorta • Sensory input to cardiovascular center in medulla • Maintains general systemic BP

42. Chemoreceptor Reflexes • Carotid bodies and aortic bodies • Detect changes in blood levels of O2, CO2, and H+ (hypoxia, hypercapnia or acidosis ) • Causes stimulation of cardiovascular center • Increases sympathetic stimulation to heart & vessels • Cardiac output and increase in blood pressure • Also change breathing rates

43. Diagram of Baroreceptor Reflexes ↓Stimulation of baroreceptors Sympathetic Cardiovascular Center Parasympathetic Cardiac Output and Vasoconstriction Homeostasis Disturbed, BP too low Return to Homeostasis ↓BP BP ↓Cardiac Output and Vasodilation ↓Cardiac Output and Vasodilation Homeostasis Disturbed, BP too high Stimulation of baroreceptors Parasympathetic Cardiovascular Center ↓Sympathetic

44. Innervation of the Heart • Speed up the heart with sympathetic stimulation • Slow it down with parasympathetic stimulation (X) • Sensory information from baroreceptors (IX)

45. Hormonal Regulation of Blood Pressure • Renin-angiotensin-aldosterone system • Decrease in BP or decreased blood flow to kidney • Release of renin results in formation angiotensin II • Systemic vasoconstriction • Causes release of aldosterone (H2O & Na+ reabsorption) • Epinephrine & norepinephrine • Increases heart rate & force of contraction • Causes vasoconstriction in skin & abdominal organs • Vasodilation in cardiac & skeletal muscle • Antidiuretic hormone (ADH) causes vasoconstriction and water retention

46. Clinical Terms • Hypertension: Blood pressure above 140/90 • Aneurysm: Localized abnormal dilatation of a blood Vessel. • Venous Claudication: Lameness due to inadequate venous drainage.

47. Deep Venous Thrombosis: A blood clot in a deep vein. • Phlebitis: Inflammation of a vein. • Phlebotomist: A person who draws blood. • Venipuncture: Puncture of a vein to obtain blood.