IBHS 527 lecture 2

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VASUpharm14
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IBHS 527 lecture 2
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2011-01-16 19:05:26
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Vessels, endothelial cells
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  1. 2 functions of the circulatory system
    • 1. distribution of oxygen, nutrients
    • 2. removal of metabolic wastes like carbon dioxide and urea
  2. 2 circuits of the circulatory system
    • 1. pulmonary
    • 2. systemic
  3. pathway of the circulatory system
    (1) right heart --> (2) pulmonary arteries --> (3) pulmonary veins --> (4) left heart --> (5) aorta --> (6) arteries ("away" from heart) --> (7) arterioles --> (8) capillaries --> (9) venules --> (10) veins ("back" to heart) --> (11) vena cava
  4. 5 main types of blood vessels
    • 1. arteries
    • 2. arterioles
    • 3. capillaries
    • 4. venules
    • 5. veins
  5. context: 5 main types of blood vessels
    arteries
    • carry blood away from heart
    • transport blood under high pressure
  6. context: 5 main types of blood vessels
    arterioles
    smallest arterial branches, strong muscular walls
  7. context: 5 main types of blood vessels
    capillaries
    where diffusion occurs between blood and interstitial fluid - exchange of fluid, gas, nutrients, etc.
  8. context: 5 main types of blood vessels
    venules
    small veins that carry blood from capillaries
  9. context: 5 main types of blood vessels
    veins
    larger vessels, blood transport back to heart, blood reservoir (where most blood is located)
  10. 3 layers of both arteries and veins
    • 1. tunica intima (innermost layer): endothelium, internal elastic membrane (arteries only)
    • 2. tunica media (middle layer): smooth muscle tissue, external elastic membrane (arteries only)
    • 3. tunica externa (outmost layer): connective tissue sheath
  11. Arteries vs Veins
    • arteries:
    • 1. thicker walls
    • 2. thicker tunica media (more contractile and elastic components - to handle the change in blood pressure by stretching and recoiling to resist breaking)
    • 3. endothelial lining has pleated appearance
    • veins:
    • 1. thinner walls
    • 2. tunica externa is thicker than tunica media
    • 3. no elastic membranes
    • 4. contains smooth muscle cells (SMC) in tunica externa
  12. 2 changes in arterial diameter
    • controlled by autonomic nervous system
    • 1. vasoconstriction: contraction of smooth muscle cells
    • 2. vasodilation: relaxation of smooth muscle cells
  13. vasodilation and vasoconstriction affect 3 things
    • 1. afterload on heart (how hard the heart has to work to pump into the vessel)
    • 2. peripheral blood pressure
    • 3. capillary blood flow
  14. context: arteries
    3 types of arteries
    • 1. elastic
    • 2. muscular
    • 3. arterioles
  15. context: 3 types of arteries
    elastic arteries
    • tunica media contains elastic fibers, few SMCs
    • helps stabilize changes in pressure during systole and diastole
    • ex: aorta, pulmonary arteries
  16. context: 3 types of arteries
    muscular arteries (most)
    • thick tunica media contains more smooth muscle cells (SMCs)
    • ex: external carotid arteries, brachial arteries, femoral arteries
  17. context: 3 types of arteries
    arterioles
    • aka resistance vessels (can INC. or DEC. resistance by dilation, constriction)
    • smallest in size of arteries
    • poorly defined tunica externa
    • can dilate or constrict in response to sympathetic nervous system, endocrine system, local factors
  18. context: 5 main blood types of vessels
    capillaries characteristics
    • thin walls
    • slow blood flow
    • consists of endothelial tube within a basal lamina
    • no tunica media or externa (only one layer)
    • diamater is close to RBC
  19. 2 types of capillaries
    • 1. continuous
    • 2. fenestrated
    • *depending on size of molecules to get through
  20. context: 2 types of capillaries
    continuous capillaries
    • complete endothelium
    • permit diffusion of H2O, small molecules, lipid-soluble materials
    • movement across membrane via pinocytosis
  21. context: 2 types of capillaries
    fenestrated capillaries
    • endothelium contains pores
    • pores permit rapid exchange of H2O and larger solutes (even small peptides)
    • found in GI tract (absorption), kidneys, hypothalamus, pituitary
  22. context: continuous capillaries
    specialized continuous capillaries
    • located in central nervous system ex. blood brain barrier (BBB)
    • tight junctions allow passage of water, glucose, amino acids, inorganic ions, lipid soluble molecules
    • very restricted permeability via active and passive transport
  23. 2 types of membrane transport
    • 1. facilitated diffusion (passive)
    • 2. active transport
    • *both use carrier proteins to regulate/allow only specific molecules to come through
  24. context: fenestrated capillaries
    sinusoids
    • resemble fenestrated capillaries (irregularly shaped, flattened)
    • difference: contains gaps between endothelial cells, thin or absent basal lamina
    • permits free exchange of H2O and large solutes (even proteins)
    • significant in liver where plasma proteins enter blood and for liver, spleen, bone marrow where phagocytic cells monitor the passing blood
  25. 3 characteristics of capillary beds
    • 1. precapillary sphincter:
    • -band of smooth muscle
    • -guards entrance to capillary
    • 2. direct connections between arterioles and venules:
    • -Metarteriole: smooeth muscle that can change in diamter
    • -thoroughfare channel: resembles a capillary
    • 3. collaterals (vessels):
    • -capillaries can receive blood from more than 1 artery (back-up plan). arterial anastomosis
  26. microcirculation
    • regulation of diameter of metarterioles and precapillary sphincters
    • -local regulation of [oxygen] in tissues and the rate of tissue metabolism
  27. vasomotion
    • continuous cycling of contraction and relaxation of smooth muscles that regulate blood flow through capillaries
    • -help meet demands of tissue
  28. diffusion through capillaries
    • players:
    • capillaries are the only vessels that allow exchange (of gas and nutrients)
    • relies on 3 things:
    • 1. wall thickness
    • 2. flow velocity
    • 3. diameter
  29. context: veins
    3 types of veins
    • 1. venules
    • 2. medium-sized veins
    • 3. large veins
  30. context: 3 types of veins
    venules
    • smallest venous vessels, collect blood from capillaries
    • some lack tunica media
  31. context: 3 types of veins
    medium-sized veins
    • similar in size to muscular arteries
    • thin tunica media
    • thick tunica externa containing collagen and elastic fibers
  32. context: 3 types of veins
    large veins
    • contains all 3 layers
    • thin tunica media, thick tunica externa
    • ex: vena cava
  33. distribution of blood
    • majority of blood at rest is at the systemic venous system with 64%
    • systemic venous system > systemic arterial system > pulmonary circuit > systemic capillaries = heart
    • *veins expand easily at low pressures (capacitance vessels)
    • -the majority of the blood volume is in veins and the largest cross-sectional area are in capillaries because of the gas and nutrients exchange occurring here
  34. distensibility
    • for a given rise in blood pressure, amount of stretch in vessel
    • -expandibility
  35. venous reserve
    amount of blood that can be shifted into general circulation (~20)
  36. why are venous blood reserves relevant?
    • hemorrhage
    • -systemic veins constrict (venoconstriction) to help increase blood volume in circulation
    • -constriction of veins in liver, skin, lungs which shunts blood to delicate organs (brain) and active skeletal muscles
  37. context: blood pressures in the circulatory system
    systemic circuit
    • 1. arterial system = high pressure
    • 2. venous system = low pressure (expands easily)
  38. relatives pressures due to gravity: INC. pressure at the feet which makes it harder for blood to return to the heart. 2 ways to overcome or help blood go back to the heart.
    • 1. venous valves: 1 way valves that prevent backflow into capillaries and that affects the venous return (rate of blood flow to heart)
    • 2. muscle or venous pump: muscles help squeeze the blood up
    • *if standing perfectly still- DEC. in venous return because not flexing muscles
  39. varicose veins
    • excess stretching of veins due to INC. pressure over weeks, months, or years - long periods of time
    • veins distend, but valves do not
    • blood pools in veins, distends them more
  40. symptoms of varicose veins
    • aching or heavy felling in legs
    • throbbing
    • muscle cramping
    • itching around veins
    • skin ulcers around veins
  41. risk factors for varicose veins
    • age
    • sex - more toward females
    • genetics
    • obesity
    • standing for long periods of time
  42. treatments for varicose veins
    • 1. self-help:
    • -exercise
    • -weight loss
    • -elevated legs
    • 2. surgery or outpatient procedures:
    • -sclerotherapy
    • -vein stripping/removal
  43. prevention of varicose veins
    • exercise
    • weight control
    • avoid wearing heels
    • avoid tight clothes
    • elevate legs
    • don't cross legs
  44. aneurysms
    • abnormal bulge in the weakened wall of a blood vessel
    • location:
    • -brain = stroke
    • -aorta = death
    • tend to form gradually
    • often go undetected until they leak or rupture
    • risk of rupture depends on size
  45. context: aneurysms
    2 types of aortic aneurysms
    • *most common aneurysm
    • 2 types:
    • 1. thoracic aortic aneurysm (TAA) - ~25%
    • 2. abdominal aortic aneurysm (AAA) - ~75% MOST
  46. 3 causes of aneurysms
    • 1. high blood pressure (BP)
    • 2. atherosclerosis
    • 3. Marfan syndrom - connective tissue disorder
  47. risk factors of aneursyms
    • advanced age
    • male sex 5-10X greater risk
    • tobacco use
    • family history
    • race (whites at greater risk)
  48. 2 treatments of aneurysms
    • 1. drugs: ß-blockers, vasodilators
    • 2. surgery: removal of aneurysm, insertion of stent
  49. causes of Peripheral Arterial Disease (PAD)
    • atherosclerosis (main cause)
    • blood clots, injury to limbs, altered anatomy of ligaments or muscles, infection
  50. risk factors of Peripheral Arterial Disease (PAD)
    smoking, diabetes, obesity, high BP, high cholesterol, increased aged, family history
  51. symptoms of Peripheral Arterial Disease (PAD)
    • leg pain while walking
    • leg numbness or weakness
    • changes in toenails or color of legs
    • coldness and/or hair loss on legs
  52. complications of Peripheral Arterial Disease (PAD)
    increased risk for coronary artery disease, heart attack, stroke, and transient ischemic attacks (TIA) - mini stroke
  53. 5 drug treatments of Peripheral Arterial Disease (PAD)
    • 1. statins (cholesterol lowering drugs):
    • -simvastatin, lovastatin, atorvastatin (LIPITOR)
    • 2. ß-blockers or ACE inhibitors:
    • -Atenolol, carvedilol (COREG), metoprolol (TOPROL XL) or enalapril, lisinopril
    • 3. medication to control blood sugar
    • 4. clot prevention:
    • -daily aspirin or clopidogrel (PLAVIX)
    • 5. symptom relief medication
    • *Lifestyle modifications:
    • -quit smoking, exercise, healthy diet, careful foot care
  54. 4 roles of endothelial cells
    • 1. line blood vessels
    • 2. vasoregulation:
    • -vasodilators secreted: NO (nitric oxide - also anti-thrombotic), PGI2
    • -vasocontrictors secreted: endothelin
    • -balance is key!!
    • 3. coagulation:
    • -normal conditions: endothelium is smooth surface, anti-thrombotic (inhibits platelet adhesion and clotting by secretion of NO, PGI2, and tPA)
    • -physical or chemical perturbation: endothelium becomes pro-thrombotic (platelet-activating factor (PAF; promotes platelet activation and adhesion); switch is initiated by induction of tissue factor
    • 4. interaction with blood cells:
    • -in response to tissue injury or infection (inflammation)
    • -leukocytes (via cellular adhesion molecules or CAMs) and platelets can adhere to endothelium; release of cytokines
    • -permeability of vessel increases

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