Blood Vessels and Circulation PDF

Blood Vessels and Circulation Chapter 21 Fundamentals of Anatomy and Physiology Martini/Nath/Bartholomew  The anatomy of the blood vessels Learning objectives ❖ Identify the three layers that constitute the walls of most blood vessels. ❖ Compare the different types of blood vessels i...

Blood Vessels and Circulation Chapter 21 Fundamentals of Anatomy and Physiology Martini/Nath/Bartholomew  The anatomy of the blood vessels Learning objectives ❖ Identify the three layers that constitute the walls of most blood vessels. ❖ Compare the different types of blood vessels in terms of their structure, functions and location. ❖ Briefly describe the distribution of blood amongst the different types of blood vessels. © 2015 Pearson Education, Inc 2  Classes of Blood Vessels Five general classes of Return blood vessels Carry blood blood to away from heart heart Collect blood Are smallest from capillaries branches of Are smallest blood arteries vessels Location of chemical and gaseous exchange between blood and interstitial fluid © 2015 Pearson Education, Inc 3  Blood Vessels The Tunica Intima (tunica interna) the inner layer includes: The endothelial lining Connective tissue layer with variable numbers of elastic fibers Internal elastic membrane (In arteries, is a layer of elastic fibers in outer margin of tunica intima) © 2015 Pearson Education, Inc 4  Blood Vessels The Tunica Media (Middle Layer): Contains concentric sheets of smooth muscle in loose connective tissue External elastic membrane (arteries) of the tunica media Separates tunica media from tunica externa Thickest layer in a small artery Smooth muscle contraction = decrease on vessel diameter Smooth muscle relaxation = increase on vessel diameter © 2015 Pearson Education, Inc 5  Blood Vessels The Tunica Externa (tunica adventitia) the outer layer: Connective tissue sheath Anchors vessel to adjacent tissues. In arteries Contains collagen fibers with scattered elastic fibers In veins Generally thicker than tunica media Contains elastic fibers and smooth muscle cells Vasa vasorum (“vessels of vessels”) Small arteries and veins In walls of large arteries and veins Supply cells of tunica media and tunica externa © 2015 Pearson Education, Inc 6  Blood Vessels Differences between Arteries and Veins Arteries have thicker walls and higher blood pressure Tunica media of artery contains more smooth muscle and elastic fibers than does that of a vein Collapsed artery has small, round lumen (internal space) Vein has a large, flat lumen Endothelial lining of artery cannot contract → when the artery constricts, its endothelium becomes folded Endothelial lining of vein contracts → lining of the vein lacks folds Arteries more elastic Veins have valves © 2015 Pearson Education, Inc 7  Task!! Tabulate the differences between arteries and veins ARTERIES VEINS Vessel walls Vessel lumen Vessel lining General appearance in sectional view Presence of valves Tunica intima Tunica media Tunica externa 8 © 2015 Pearson Education, Inc Figure 21-1 Comparisons of a Typical Artery and a Typical Vein (Part 1 of 2). Tunica externa Tunica media Tunica intima Smooth muscle Lumen of vein Internal elastic membrane External elastic Lumen membrane of artery Endothelium Elastic fiber ARTERY Artery and vein LM × 60 9 Figure 21-1 Comparisons of a Typical Artery and a Typical Vein (Part 2 of 2). Tunica externa Tunica media Tunica intima Lumen of vein Smooth muscle Lumen of artery Endothelium Artery and vein LM × 60 VEIN 10  Structure and Function of Arteries Arteries Elasticity allows arteries to absorb pressure waves that come with each heartbeat Permits vessel diameter to change passively in response to blood pressure changes Contractility Arteries change diameter actively Controlled by sympathetic division of autonomic nervous system (ANS) Vasoconstriction- contraction of arterial smooth muscle by the ANS Vasodilation- The relaxation of arterial smooth muscle © 2015 Pearson Education, Inc 11  Structure and Function of Arteries Elastic Arteries (conducting arteries) Large vessels (e.g., pulmonary trunk and aorta) Tunica media has many elastic fibers and few smooth muscle cells=more resilience Elastic arteries help to make blood flow continuous © 2015 Pearson Education, Inc 12  Structure and Function of Arteries Muscular Arteries (distribution arteries) Are medium sized (most arteries) Distribute blood to skeletal muscles and internal organs Tunica media has many smooth muscle cells Superficial muscular arteries = pressure points © 2015 Pearson Education, Inc 13  Structure and Function of Arteries Arterioles Are small Have little or no tunica externa Have thin or incomplete tunica media Artery Diameter Small muscular arteries and arterioles Change with sympathetic or endocrine stimulation Constricted arteries oppose blood flow Resistance (R) Resistance vessels - arterioles © 2015 Pearson Education, Inc 14  Structure and Function of Capillaries Capillaries Are smallest vessels with thin walls Microscopic capillary networks permeate all active tissues Capillary function Location of all exchange functions of cardiovascular system Materials diffuse between blood and interstitial fluid © 2015 Pearson Education, Inc 15  Structure and Function of Capillaries Capillary Structure Endothelial tube, inside thin basement membrane No tunica media, no tunica externa Diameter is similar to red blood cell © 2015 Pearson Education, Inc 16  Continuous Capillaries Fenestrated Capillaries Have pores or “windows” in endothelial lining Location Structure Have complete endothelial lining Are found in all tissues Choroid plexus, Endocrine organs except epithelia and (hypothalamus, pineal), Kidneys (filtration sites), cartilage Intestinal tract Permit diffusion of water, Permit rapid exchange of water and larger Function small solutes, and lipid- solutes between plasma and interstitial fluid soluble materials Block blood cells and plasma proteins Sinusoids (Sinusoidal Capillaries) Have gaps between adjacent endothelial cells (liver, spleen, bone marrow, endocrine organs) Permit free exchange of water and large plasma proteins between blood and interstitial fluid 17 Figure 21-3 Capillary Structure. Basement membrane Endothelial cell Nucleus Endosomes Endosomes Fenestrations, or pores Boundary Boundary between between endothelial Gap between Basement endothelial Basement cells adjacent cells membrane cells membrane a Continuous capillary b Fenestrated capillary c Sinusoid 18  Structure and Function of Capillaries Capillary Beds (Capillary Plexus) Connect one arteriole and one venule Precapillary Sphincter Guards entrance to each capillary Opens and closes, causing capillary blood to flow in pulses Thoroughfare Channels Direct capillary connections between arterioles and venules Controlled by smooth muscle segments (metarterioles) © 2015 Pearson Education, Inc 19 Figure 21-4a The Organization of a Capillary Bed. Vein Collateral Smooth arteries muscle cells Venule Arteriole Thoroughfare Metarterioles channel Capillaries Section of precapillary sphincter Small venule Precapillary sphincters KEY Arteriovenous Consistent blood flow anastomosis Variable blood flow a A typical capillary bed. Solid arrows indicate consistent blood flow; dashed arrows indicate variable or pulsating blood flow. 20  Structure and Function of Veins Veins Collect blood from capillaries in tissues and organs Return blood to heart Are larger in diameter than arteries Have thinner walls than arteries Have lower blood pressure © 2015 Pearson Education, Inc 21  Structure and Function of Veins Venules Very small veins Collect blood from capillaries Some venules lack a tunica media Medium-sized veins Thin tunica media and few smooth muscle cells Tunica externa with longitudinal bundles of elastic fibers Large Veins Have all three tunica layers Thick tunica externa Thin tunica media © 2015 Pearson Education, Inc 22  Structure and Function of Veins Venous Valves Folds of tunica intima Prevent blood from flowing backward Compression pushes blood toward heart © 2015 Pearson Education, Inc 23 Figure 21-5 The Function of Valves in the Venous System. Valve closed Valve opens superior to contracting muscle Valve closed Valve closes inferior to contracting muscle 24 Figure 21-2 Histological Structure of Blood Vessels. Veins Arteries Large Vein Elastic Artery Tunica externa Internal elastic membrane Tunica Tunica media Endothelium intima Endothelium Tunica media Tunica intima Tunica externa Medium-sized Vein Muscular Artery Tunica externa Tunica externa Tunica media Tunica media Endothelium Endothelium Tunica intima Tunica intima Venule Arteriole Smooth muscle cells (tunica media) Tunica externa Endothelium Endothelium Basement membrane Fenestrated Capillary Capillaries Continuous Capillary Pores Endothelial Endothelial cells cells Basement membrane Basement membrane 25 Figure 21-6 The Distribution of Blood in the Cardiovascular System. Large veins 18% Large venous networks (liver, bone marrow, skin) 21% Venules and medium-sized veins 25% 26 The role of the blood vessels and blood circulation in maintaining adequate tissue perfusion Learning objectives ❖ Explain the role of pressure and resistance in ensuring blood flow through the circulatory system. ❖ Describe how pressure and resistance is created and regulated. © 2015 Pearson Education, Inc 27  Pressure and Resistance Total Capillary Blood Flow Equals cardiac output (CO) Amount of blood (mL) pumped by the left ventricle in one min. Indication of blood flow through the peripheral tissues If CO ↑, blood flow through capillary beds ↑ If CO ↓, blood flow through capillary beds ↓ CO=HR x SV (mL/min)= (beats/min) x (mL/beat) © 2015 Pearson Education, Inc 28  Pressure and Resistance Total Capillary Blood Flow Is determined by: Pressure (P) and resistance (R) in the cardiovascular system To keep blood moving, the heart must generate enough pressure to overcome the resistance in the pulmonary and systemic circuits © 2015 Pearson Education, Inc 29  Pressure and Resistance Generally flow is directly proportional to the pressure ↑ pressure = ↑ flow And inversely proportional to resistance ↑ resistance = ↓ flow However the absolute pressure is less important than the pressure gradient, therefore flow (F) is proportional to the pressure gradient (∆P) divided by resistance (R) Equation: F α ∆P/R © 2015 Pearson Education, Inc 30  Pressure and Resistance The Pressure Gradient ( P) The difference in pressure from one end of a vessel to the other The difference between: E.g. Largest Pressure at the heart (base of aorta) pressure gradient And pressure at peripheral capillary beds © 2015 Pearson Education, Inc 31  Pressure and Resistance F α P/R ↑ pressure, ↑ flow ↑ resistance, ↓ flow © 2015 Pearson Education, Inc 32  Pressure and Resistance Measuring Pressure 1. Blood pressure (BP) Arterial pressure (mm Hg) 2. Capillary hydrostatic pressure (CHP) Pressure within the capillary beds 3. Venous pressure Pressure in the venous system © 2015 Pearson Education, Inc 33  Pressure and Resistance Circulatory Pressure ∆P across the systemic circuit (about 100 mm Hg) Circulatory pressure must overcome total peripheral resistance (resistance of entire cardiovascular system) © 2015 Pearson Education, Inc 34  Pressure and Resistance Total Peripheral Resistance Vascular resistance Forces that oppose blood flow in blood vessels Blood viscosity Resistance to flow caused by interactions among molecules and suspended materials in liquid Turbulence Eddies and swirls due to irregular surfaces, high flow rates © 2015 Pearson Education, Inc 35  Pressure and Resistance Vascular Resistance Due to friction between blood and vessel walls Depends on vessel length and vessel diameter Length: Longer the vessel the greater the friction Diameter: Vessel diameter varies by vasodilation and vasoconstriction Resistance increases exponentially as vessel diameter decreases © 2015 Pearson Education, Inc 36 Figure 21-7 Factors Affecting Friction and Vascular Resistance. Factors Affecting Vascular Resistance Friction and Vessel Length Resistance to flow = 1 Internal surface Flow = 1 area = 1 Resistance to flow = 2 Internal surface area = 2 Flow = 12 Friction and Vessel Diameter Greatest resistance near surfaces, slowest flow Least resistance at center greatest flow Vessel Length versus Vessel Diameter Diameter = 2 cm Resistance to flow = 1 Diameter = 1 cm Resistance to flow = 16 Turbulence Plaque deposit Turbulence 37  Pressure and Resistance Viscosity Resistance caused by molecules and suspended materials in a liquid Whole blood viscosity is about four to five times that of water ↑ viscosity = ↑ resistance © 2015 Pearson Education, Inc 38  Pressure and Resistance Turbulence Swirling action that disturbs smooth flow of liquid Occurs in heart chambers and great vessels Atherosclerotic plaques cause abnormal turbulence © 2015 Pearson Education, Inc 39 Table 21-1 Key Terms and Relationships Pertaining to Blood Circulation. © 2015 Pearson Education, Inc  Summary ↑ vessel length, ↑ friction = ↑ resistance ↑ friction at the zone closest to vessel wall = ↑ resistance ↓ diameter of blood vessel = ↑ resistance ↑ blood viscosity = ↑ resistance ↑ turbulence = ↑ resistance © 2015 Pearson Education, Inc 41  Pressure and Resistance An Overview of Cardiovascular Pressures Vessel diameters Total cross-sectional areas Pressures Velocity of blood flow © 2015 Pearson Education, Inc 42 Figure 21-8a Relationships among Vessel Diameter, Cross-Sectional Area, Blood Pressure, and Blood Velocity within the Systemic Circuit. 3 2 Vessel diameter 1 (cm) 0 Elastic Muscular Arterioles Capillaries Venules Veins Venae arteries arteries cavae Aorta a Vessel diameter 43 Figure 21-8b Relationships among Vessel Diameter, Cross-Sectional Area, Blood Pressure, and Blood Velocity within the Systemic Circuit. 5000 4000 Cross- 3000 sectional area 2000 (cm2) 1000 0 Elastic Muscular ArteriolesCapillaries Venules Veins Venae arteries arteries cavae Aorta b Total cross-sectional area of vessels 44 Figure 21-8c Relationships among Vessel Diameter, Cross-Sectional Area, Blood Pressure, and Blood Velocity within the Systemic Circuit. 120 100 80 Average blood 60 pressure (mm Hg) 40 20 0 Elastic Muscular Arterioles Capillaries Venules Veins Venae arteries arteries cavae Aorta c Average blood pressure 45 Figure 21-8d Relationships among Vessel Diameter, Cross-Sectional Area, Blood Pressure, and Blood Velocity within the Systemic Circuit. 35 28 Velocity of blood 21 flow (cm/sec) 14 7 0 Elastic Muscular Arterioles Capillaries Venules Veins Venae arteries arteries cavae Aorta d Velocity of blood flow 46  The role of the blood vessels and blood circulation in maintaining adequate tissue perfusion Learning objectives ❖ Differentiate between mean arterial pressure, pulse pressure, capillary pressure and venous pressure and explain how each of these pressures is sustained. ❖ Describe the process of capillary exchange. © 2015 Pearson Education, Inc 47  Pressure and Resistance Arterial Blood Pressure Systolic pressure Peak blood pressure during ventricular systole Diastolic pressure Minimum blood pressure during ventricular diastole 160/100 160 = systolic pressure 100 = diastolic pressure © 2015 Pearson Education, Inc 48  Pressure and Resistance Arterial Blood Pressure Pulse: rhythmic fluctuation in pressure that accompanies each heartbeat Pulse pressure Difference between systolic pressure and diastolic pressure Mean arterial pressure (MAP) MAP = diastolic pressure + pulse pressure/3 © 2015 Pearson Education, Inc 49  Pressure and Resistance Abnormal Blood Pressure Normal = 120/80 Hypertension Abnormally high blood pressure Greater than 140/90 Hypotension Abnormally low blood pressure © 2015 Pearson Education, Inc 50  Pressure and Resistance Elastic rebound As systolic pressure ↑, arterial walls stretch When diastole begins, blood pressure falls and arteries recoil to their original dimensions © 2015 Pearson Education, Inc 51  Pressure and Resistance Pressures in Small Arteries and Arterioles Pressure and distance MAP and pulse pressure decrease with distance from heart Blood pressure decreases as it overcomes friction © 2015 Pearson Education, Inc 52  Pressure and Resistance Venous Pressure and Venous Return Low pressure in venous system Venous pressure determines venous return - the amount of blood arriving at right atrium each minute Venous return directly impacts cardiac output © 2015 Pearson Education, Inc 53  Pressure and Resistance Venous Pressure and Venous Return Two factors assist low venous pressures in propelling blood towards the heart: Muscular compression (“muscular pump”) of peripheral veins Compression of skeletal muscles pushes blood toward heart (one-way valves) © 2015 Pearson Education, Inc 54  Pressure and Resistance Venous Pressure and Venous Return Two factors assist low venous pressures in propelling blood towards the heart: The respiratory pump Thoracic cavity action Inhaling decreases thoracic pressure Pulls blood into inferior vena cava and right atrium Exhaling raises thoracic pressure Pushes the venous blood into the right atrium © 2015 Pearson Education, Inc 55  Pressure and Resistance Capillary Pressures and Capillary Exchange Vital to homeostasis Moves materials across capillary walls by: Diffusion, Filtration and Reabsorption © 2015 Pearson Education, Inc 56  Pressure and Resistance Diffusion Movement of ions or molecules from high concentration to lower concentration along the concentration gradient Diffusion Routes 1. Water, ions, and small molecules such as glucose diffuse between adjacent endothelial cells or through fenestrated capillaries 2. Some ions (Na+, K+, Ca2+, Cl−) diffuse through channels in plasma membranes 3. Large, water-soluble compounds pass through fenestrated capillaries 4. Lipids and lipid-soluble materials such as O2 and CO2 diffuse through endothelial plasma membranes 5. Plasma proteins cross endothelial lining in sinusoids © 2015 Pearson Education, Inc 57  Pressure and Resistance Filtration Removal of solutes as a solution flows across a porous membrane Driven by hydrostatic pressure (HP) HP= force exerted against a liquid (fluid pressure) Pushes water from an area of higher pressure to an area of lower pressure Water and small solutes forced through capillary wall Leaves larger solutes in bloodstream © 2015 Pearson Education, Inc 58 Figure 21-10 Capillary Filtration. Capillary hydrostatic pressure (CHP) Amino acid Blood protein Glucose Ions Interstitial fluid Small solutes Hydrogen bond Water molecule Endothelial Endothelial cell 1 cell 2 59  Pressure and Resistance Reabsorption Occurs as the result of osmosis water molecules diffuse across a membrane towards the solution containing a higher solute concentration Osmotic pressure (OP) pressure that must be applied to prevent osmosis © 2015 Pearson Education, Inc 60  Pressure and Resistance Reabsorption Blood colloid osmotic pressure (BCOP) Caused by suspended blood proteins that are too large to cross capillary walls Equals pressure required to prevent osmosis Also called “oncotic pressure” © 2015 Pearson Education, Inc 61  Pressure and Resistance Interplay between Filtration and Reabsorption 1. Ensures that plasma and interstitial fluid are in constant communication and mutual exchange 2. Accelerates distribution of nutrients, hormones, and dissolved gases throughout tissues 3. Assists in the transport of insoluble lipids and tissue proteins that cannot enter bloodstream by crossing capillary walls 4. Has a flushing action that carries bacterial toxins and other chemical stimuli to lymphatic tissues and organs responsible for providing immunity to disease © 2015 Pearson Education, Inc 62  Pressure and Resistance Interplay between Filtration and Reabsorption Net hydrostatic pressure (NHP) Forces water out of solution Net osmotic pressure (NCOP) Forces water into solution Both control filtration and reabsorption through capillaries © 2015 Pearson Education, Inc 63  Pressure and Resistance Factors that Contribute to the Net Hydrostatic Pressure (NHP) Capillary hydrostatic pressure (CHP) Interstitial fluid hydrostatic pressure (IHP) Net capillary hydrostatic pressure tends to push water and solutes out of capillaries and into interstitial fluid NHP = CHP – IHP Under normal circumstances IHP = 0 Therefore: NHP = CHP © 2015 Pearson Education, Inc 64  Pressure and Resistance Factors that Contribute to the Net Capillary Colloid Osmotic Pressure (NCOP) Is the difference between: Blood colloid osmotic pressure (BCOP) Interstitial fluid colloid osmotic pressure (ICOP) Pulls water and solutes into a capillary from interstitial fluid NCOP = BCOP- ICOP Under normal circumstances ICOP = 0 Therefore: NCOP = BCOP © 2015 Pearson Education, Inc 65  Pressure and Resistance Interplay between Filtration and Reabsorption Important to remember Net hydrostatic pressure (NHP) = CHP Forces water out of solution Net osmotic pressure (NCOP) = BCOP Forces water into solution Both control filtration and reabsorption through capillaries © 2015 Pearson Education, Inc 66  Pressure and Resistance Net Filtration Pressure (NFP) The difference between: Net hydrostatic pressure Net osmotic pressure NFP = (CHP – IHP) – (BCOP – ICOP) NFP = CHP - BCOP © 2015 Pearson Education, Inc 67  Pressure and Resistance Capillary Exchange 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 Capillaries filter more than they reabsorb Excess fluid enters lymphatic vessels © 2015 Pearson Education, Inc 68 Figure 21-11 Forces Acting across Capillary Walls. NFP = CHP - BCOP Return to circulation 3.6 L/day flows into lymphatic vessels Arteriole KEY Venule CHP (Capillary hydrostatic pressure) Filtration Reabsorption BOP (Blood No net fluid movement 20.4 L/day osmotic pressure) 24 L/day 35 25 25 25 18 25 mm mm mm mm mm mm NFP (Net filtration Hg Hg Hg Hg Hg Hg pressure) NFP = +10 mm Hg NFP = 0 NFP = −7 mm Hg CHP > BCOP CHP = BCOP BCOP > CHP Fluid forced No net Fluid moves out of capillary movement into capillary of fluid 69  Reference Martini (FH), Nath (JL) and Bartholomew (EF) (2015). Fundamentals of Anatomy and Physiology. 10th Edition. 70