Blood Vessels and Circulation

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dallas.dawn
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209523
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Blood Vessels and Circulation
Updated:
2013-03-25 23:12:55
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chapter 21
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  1. Arteries
    carry blood away from the heart
  2. smallest artery?
    Arteries will get smaller in size and the smallest arteries are called arterioles
  3. arterioles then go to capillaries 
    capillaries

    Diffusion of oxygen/carbon dioxide occurs between body tissue and capillaries
  4. Venules? 

    venules form what?
    • Blood enters into venules from capillaries
    • Venules will form veins that return blood to the heart
  5. Structure of vessel walls 
    Tunica intima
    • Inner layer of the blood vessel
    • In arteries, the tunica intima contains a thick layer of elastic fibers called elastic membrane 
  6. Structure of Vessel wall 
    Tunica media 
    Middle layer of a blood vessel

    • Contains smooth muscle 
    • Tunica media is thickest in arteries

    Separated from the surrounding tunica externa by a band of elastic fibers called external elastic membrane
  7. structure of vessel wall.. 
    Tunica externa
    • Outer layer of a blood vessel
    • Is made up of connective tissue
    • In veins, the tunica externa is thicker than the tunica media
  8. Arteries vs. veins 

    Vessel walls 
    • arteries have thicker walls 
    • Tunica media thickest layer in arteries
    • Tunica media and externa same thickness in most veins
  9. arteries vs. veins 
    vessel lumen 
    The lumen (opening) of the artery is smaller because the artery walls constrict the lumen

    Arteries will also keep their circular lumen appearance
  10. arteries vs. veins 

    veins and valves
    Veins contain valves which are internal structures that prevent backflow of the blood
  11. arteries 
    The thick muscular walls of an artery makes them elastic and give them the ability to contract

    From the heart blood travels through: elastic arteries  muscular arteries  arterioles  capillaries
  12. vasocontriction 
    When the artery contracts and constricts the lumen
  13. vasodilation 
    When the smooth muscle of the artery relaxes and the diameter of the lumen increases
  14. Types of Arteries
    Elastic Arteries
    • 1.) Also known as conducting arteries because they carry large volumes of blood away from the heart
    • 2.) Largest arteries
    • 3.)Tunica media contains a lot of elastic fibers so they are able to expand and recoil back (think about a rubber band)
  15. types of arteries 
    Muscular Arteries
    • 1.) Are medium-sized arteries
    • 2) Known as distribution arteries because they distribute blood to the body’s skeletal muscles and organs
    • 3) Most of the arteries in the body are muscular arteries
    • 4) Not as much elastic fibers in the tunica media
  16. Types of arteries 
    Arterioles
    • 1. ) Smallest arteries
    • 2) Does not have a ___tunica externa 
    • 3) Arterioles are primary arteries that respond to sympathetic or endocrine stimulation causing the arterioles to vasoconstrict or vasodilate
  17. Capillaries
    1.)These microscopic vessels that are within most tissues do most of the work of the cardiovascular system

    Capillaries are the only blood vessel whose walls permit exchange between the blood and the surrounding body tissues

    Walls of the capillary are very thin
  18. Continuous Capillary
    • 1.)The lining of the capillary is complete and intact
    • 2.)Main type of capillary
    • 3.)Permit water, small solutes, and lipid-soluble materials to diffuse through the vessel
    • 4)Continuous capillaries make up the blood brain barrier in the nervous system
  19. Fenestrated Capillaries
    • Contain pores in the outside lining of the capillaries
    • Allow rapid exchange of water and solutes
  20. capillary beds(capillary plexus)
    Capillaries don’t function as an individual unit, they function as an interconnected network called a capillary bed

    A single arteriole gives rise to dozens of capillaries

    More than one artery may supply blood to a capillary bed
  21. Entrance of each capillary is controlled by a precapillary sphincter
    Contraction of the smooth muscle cells of the sphincter narrows the capillary entrance which reduces/stops the flow of blood

    When one precapillary spincter constricts, blood is diverted into other branches of the network

    When a sphincter relaxes, the entrance dilates and blood flows into that capillary
  22. capillary beds..
    arterial anastomosis
    When multiple arteries fuse together to supply a capillary bed it is called an arterial anastomosis

    An anastomosis is the joining of blood vessels
  23. Angiogenesis
    formation of new blood vessels 

    Primarily occurs during development

    Can occur during pathological conditions – cancerous cells stimulate the body to undergo angiogenesis so the tumor will have its own blood supply
  24. Veins 
    • Veins collect blood from tissues and organs and return it to the heart
    • Walls of veins can be thinner because the blood pressure in the veins is lower than in arteries
  25. venules 
    • Smallest venous vessels
    • Collect blood from capillary beds
  26. Medium-sized veins
    • Comparable in size to muscular arteries
    • Thin tunica media
    • Thickest layer is the tunica externa
  27. large veins 
    • Include the superior and inferior vena cava
    • Have all 3 layers, tunica externa still the thickest
  28. Because the blood pressure is so low in veins, it cannot overcome the force of gravity and needs ___valves _ to prevent the blood from backflowing
    Valves are folds of the tunica intima that project from the vessel wall and point in the direction of blood flow

    Only permit blood to flow in 1 direction – toward the heart

    Contraction of surrounding skeletal muscle is the primary way that veins return their blood to the heart

    If the veins cannot function properly, blood will pool in your veins

    This can lead to either varicose veins if it is occurs in the superficial veins, or even hemorrhoids
  29. capillary blood flow
    Essential to maintain adequate blood flow through the capillaries in to the peripheral tissues and organs

    Capillary blood flow is determined by the interplay between pressure and resistance
  30. capillary blood flow 
    pressure 
    blood pressure 
    Directly measures the arterial pressure
  31. capillary blood flow 
    pressure 
    Capillary Hydrostatic Pressure
    The pressure within the capillaries
  32. capillary blood flow 
    pressure 
    venous pressure
    pressure within the veins
  33. Capillary blood flow 

    Resistance – the total peripheral resistance of the cardiovascular system reflects a combination of factors



    Vascular resistance
    Is the forces that oppose blood flow in the blood vessels

    Primarily dependent on the friction between the blood and the vessel walls

    The amount of friction depends on the vessel length and vessel diameter

    Increasing length = more friction/resistance

    Decreasing diameter = _______more friction/ resistance 

    ***FASTEST =short and wide diameter****
  34. Cap blood flow
    resistance factors:
    Blood viscosity
    Viscosity is the resistance to flow caused by interactions among molecules and materials in a liquid
  35. cap blood flow 
    resistance factors 
    turbulence
    High flow rates, irregular surfaces, and sudden changes in vessel diameter upset the smooth flow of blood

    Most often occurs when atherosclerotic plaques build up in the walls of vessels
  36. Arterial Blood Pressure
    Arterial pressure must always be high to maintain blood flow to the capillaries

    Arterial pressure rises during ventricular systole and falls during ventricular diastole

    BP measurement – systolic/diastolic – 120/75
  37. Hypertension
    Hypertension – abnormally high blood pressure (above 140/90)

    What is considered a normal BP? 120/80

    121/81  139/89 – pre-hypertension
  38. hypotension
    abnormally low blood pressure

    Below 120/80
  39. Venous Pressure

    While low, venous pressure determines venous return

    Because it is so low, and since gravity works against you, need help to return blood to the heart:

    Muscular compression
    Contractions of skeletal muscles compress nearby veins
  40. respiratory pump
    When you force air out of your lungs it pushes venous blood into the ___________right atrium______ from your superior vena cava
  41. Capillary Pressure and Capillary Exchange
    • Capillary exchange is very important in homeostasis
    • Relies on diffusion, filtration, and reabsorption
  42. Diffusion 
    Water, ions, glucose, amino acids, urea can enter or leave bloodstream by diffusion

    Many ions (sodium, potassium, calcium, chloride) diffuse through channels in the membrane

    • Large water-soluble compounds can only enter/leave blood through fenestrated capillaries
    • Lipids can cross capillary walls by diffusion 

    Plasma proteins normally unable to cross except in the liver
  43. Filtration 
    • Filtration is the removal of solutes as a solution flows across a porous membrane
    • Solutes to large to pass through pores are filtered out of a solution

    • Driving force is hydrostatic pressure
    • Hydrostatic pressure forces water out of a solution

    Filtration primarily takes place at arterial end of capillary
  44. Reabsorption 
    Reabsorption occurs as the result of osmosis

    Osmosis pressure draws water into a solution

    The presence of suspended proteins that cannot cross capillary walls creates an osmotic pressure called blood colloid osmotic pressure (BCOP)

    Osmotic water movement continues until either the solute concentrations are equalized or an opposing hydrostatic pressure prevents the movement
  45. Interplay between filtration and reabsorption
    At the arterial end of the capillary, capillary hydrostatic pressure is greater than BCOP  fluid moves _out of the capillary (filtration)

    Near the venule, the capillary hydrostatic pressure is lower than BCOP  water moves into the capillary (reabsorption)
  46. Interplay between filtration and reabsorption
    Net filtration pressure
    Net filtration pressure is the difference between the net hydrostatic pressure and the net osmotic pressure

    A positive value (occurs at the arterial end) means fluid will move out of the capillary

    A negative value (occurs at the venule end) means fluid will move into the capillary
  47. Cardiovascular Regulatory Mechanisms
    • Homeostatic mechanisms regulate cardiovascular activity to ensure that blood flows through tissues, which is called tissue perfusion
    • 3 main mechanisms that ensure tissue perfusion: autoregulation, nervous system, endocrine system
  48. Autoregulation
    Factors that promote dilation of precapillary sphincters (vasodilators)
    • Decreased tissue oxygen or increased CO2 levels
    • Lactic acid
    • Nitric oxide
    • Histamine
  49. Autoregulation 

    Factors that stimulate precapillary sphincters to constrict (vasoconstrictors)
    Prostaglandins and thromboxaes released by platelets and WBCs
  50. Neural Mechanisms
    Centers in the medulla oblongata that help maintain tissue perfusion: cardiac center and vasomotor center
  51. Neural Mechanisms
    Centers
    Cardiac center
    cardioacceleratory
    Has a cardioacceleratory center which increases cardiac output (sympathetic nervous system )
  52. Neural Mechanisms 
    Centers 
    Cardiac center
    cardioinhibitory
    Has a cardioinhibitory center which decreases cardiac output
  53. Neural mechanisms
    centers
    Vasomotor center
    • Center that controls vasoconstricton
    • Center that controls vasodilation
  54. NM
    Reflex Control of Cardiovascular function

    Baroreceptor reflexes
    • Monitor stretch (blood pressure) in vessels
    • Located in carotid sinus and aortic sinus
  55. When blood pressure increases the baroreceptors alters activity in the cardiac and vasomotor centers and produces
    A decrease in cardiac output via parasympathetic stimulation

    Widespread vasodilation
  56. Baroreceptor reflexes 
    When blood pressure decreases:
    • Increase in cardiac output via sympathetic stimulation
    • Widespread vasoconstriction
  57. NM
    Reflex Control of Cardiovascular function

    Chemoreceptor reflexes
    Respond to changes in carbon dioxide, oxygen, or pH levels in the blood and CSF

    • Located in carotid bodies and aortic bodies
    • When detect a rise in CO2 or fall in pH or O2 levels:

    Increase in cardiac output, peripheral vasoconstriction, and rise in BP
  58. What is the specific cardiac center that increases cardiac output?
    cardioacceleratory center
  59. Endocrine regulation
    Vasopressin increases blood volume and BP

    Erythropoietin (EPO) can induce vasoconstriction which can increase BP

    Natriuretic peptides produced by the cardiac muscle cells of the right atrium reduce blood volume and BP

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