Systemic blood flow is a circuit : Systemic blood flow is a circuit



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Systemic blood flow is a circuit :

  • Systemic blood flow is a circuit :

  • Heart →Arteries→ Arterioles→ Capillaries→ Venules→ Veins→ Heart

  • Artery – any vessels that carries blood away from the heart.

  • Vein – any vessels that carries blood toward the heart





Tunica intima

  • Tunica intima

    • Endothelium and connective tissue
  • Tunica media

    • Smooth muscle and elastic tissue
  • Tunica externa or tunica adventitia

    • Connective and elastic tissue






Large arteries are elastic (conducting) arteries – pressure reservoirs

  • Large arteries are elastic (conducting) arteries – pressure reservoirs

  • Medium arteries are muscular (distributing) arteries – more smooth muscle

  • Contraction or relaxation of muscle changes the size of the lumen, and so controls the blood pressure in the vessel.





Only a single layer of endothelium and a basement membrane

  • Only a single layer of endothelium and a basement membrane

  • Connect arterioles and venules

  • Functional part of system

  • True capillaries begin at a precapillary sphincter which controls blood flow through the capillary





Relatively thin; less elastic

  • Relatively thin; less elastic

  • Larger in diameter than arteries

  • Have valves to prevent backflow of blood

  • Flow to heart is assisted by contraction of skeletal muscles









Nervous control – innervated by sympathetic nervous system ONLY

  • Nervous control – innervated by sympathetic nervous system ONLY

  • Cardiac control center (primarily in medulla oblongata)

  • Heart has both Sympathetic and Parasympathetic innervations.



Baroreceptors and chemoreceptors:

  • Baroreceptors and chemoreceptors:

    • Monitor pressure
    • Monitor blood levels of O2, CO2 and H+
    • Send information to cardiovascular center, which responds


The increase in volume a vessel can accommodate for a given increase in pressure.

  • The increase in volume a vessel can accommodate for a given increase in pressure.

    • Depends on the ratio of elastic fibers to muscle fibers in the vessel wall.
      • Elastic arteries more compliant than muscular arteries
      • Veins more compliant than either artery (blood reservoirs)
  • Decreased compliance suggests an increased stiffness of vessel wall.

  • Determines the vessel’s response to changes in pressure.



Mean arterial pressure is the average in pressure in the arteries throughout the cardiac cycle.

  • Mean arterial pressure is the average in pressure in the arteries throughout the cardiac cycle.

  • Depends on the compliance of the arteries and the amount of blood in the arterial system.



A vascular system that runs “parallel” to the blood vascular system

  • A vascular system that runs “parallel” to the blood vascular system

  • Flow does not circulate – begins in tissue

  • Returns to venous system at subclavian veins

  • Fluid in vessels is lymph – mostly water and proteins

  • Interstitial fluid→ lymphatic capillaries→ lymphatic vessels→ lymphatic trunks→ lymphatic ducts







Lie along lymphatic vessels

  • Lie along lymphatic vessels

  • Contain lymphocytes that filter lymph and eliminate microbes/damaged cells/ toxins

  • Biological filtration





Thrombus- “clotting” in an unbroken vessel

  • Thrombus- “clotting” in an unbroken vessel

    • Maintains a point of attachment
    • Organized differently than a clot
    • usually due to damage to endothelium and exposure of collagen in the basement membrane


Forms where blood is moving rapidly – see alternating lines of platelets and red cells trapped in fibrin

  • Forms where blood is moving rapidly – see alternating lines of platelets and red cells trapped in fibrin

  • Lines of Zahn



Forms differently due to decreased blood flow

  • Forms differently due to decreased blood flow

  • Mixed region at site of attachment

  • More blood clotting forms a downstream red cap



Endothelial damage

  • Endothelial damage

    • Bacterial damage
    • Damage to the myocardium
    • Wear and tear – hemodynamic stress
      • Hypertension increases this
      • Arteriosclerosis
    • Inflammation
    • Tumors and irritation by their products


Flow abnormalities

  • Flow abnormalities

    • Increases platelet contact with endothelium
    • Reduction in flow:
      • Arterial:
        • Cardiac damage and decreased pumping action
        • Increased blood viscosity
      • Venous:
        • Physical inactivity
        • Varicose veins


Turbulence:

    • Turbulence:
      • Damaged heart valves
      • Congenital heart defects
      • Compression of the vessel
      • Weakened arterial wall - aneurysm


Aging

  • Aging

  • Immobilization

  • Injury to vessel endothelium

  • Increased clotting response

  • Effects:

  • Decreased venous emptying

  • Increased venous pressures

  • Edema

  • Pain



1 Resolution –

  • 1 Resolution –

  • Anticoagulation system

  • Fibrolytic system

  • Moderate exercise increases thrombus resolution



2 Organization

  • 2 Organization

  • The thrombus is digested by phagocytes and replaced by connective tissue – incorporating the thrombus into the vessel wall.

  • May recanalize – small channels open up and restore blood flow





3 Propagation –

  • 3 Propagation –

  • Thrombus extends further down the vessel, usually a vein.

  • Initial thrombus acts as a site for further platelet adherence.





4 Infarction –

  • 4 Infarction –

  • an infarct is an area of necrosis caused by ischemia and hypoxia.

  • More common in arteries than veins due to blood flow patterns

  • Collateral circulation and anastomosis prevent infarction





Embolism – obstruction of vessel by matter circulating in blood stream

    • Embolism – obstruction of vessel by matter circulating in blood stream
    • Matter could be fat, air, infant’s cells, in addition to pieces of clot – thromboemboli
    • Thromboemoboli from the venous system tend to end up in the:
    • lungs and liver




Anticoagulants

  • Anticoagulants

  • Fibrinolytics – t-Pas

  • Prophylactic aspirin therapy





Arteriosclerosis – abnormal thickening and hardening of the arterial walls

  • Arteriosclerosis – abnormal thickening and hardening of the arterial walls

    • Smooth muscle cells and collagen fibers migrate into the tunica intima, causing stiffening and thickening, narrowing the lumen
    • Can exacerbate high blood pressure, and cause weakening and outpouching of vessel walls




A form of arteriosclerosis where soft deposits of intra-arterial fat and fibrin harden over time – atheroma

  • A form of arteriosclerosis where soft deposits of intra-arterial fat and fibrin harden over time – atheroma

  • May see build up in skin – Xanthoma or arcus in cornea.

  • In general, patients suffer few symptoms unless > 60 % of blood supply is blocked



Progressive over years

  • Progressive over years

    • Starts with some injury to endothelium
    • Inflammation, release of enzymes by macrophages causes oxidation of LDL, which is then consumed by macrophages – foam cells – accumulate to form fatty streaks
    • Fatty streaks of lipid material appear first as yellow streaks and spots
    • Smooth muscle cells proliferate, and migrate over the streak forming a fibrous plaque


Fibrous plaque results in necrosis of underlying tissue and narrowing of lumen

  • Fibrous plaque results in necrosis of underlying tissue and narrowing of lumen

  • Inflammation can result in ulceration and rupture of the plaque, resulting in platelet adherence to the lesion = complicated lesion

  • Can result in rapid thrombus formation with complete vessel occlusion → tissue ischemia and infarction







Signs and symptoms of inadequate perfusion – TIAs, often associated with exercise or stress

  • Signs and symptoms of inadequate perfusion – TIAs, often associated with exercise or stress

  • When lesion becomes complicated, can result in tissue infarction

    • Coronary artery disease – myocardial ischemia
    • In brain – major cause of stroke


Exercise

  • Exercise

  • Smoking cessation

  • Control of hypertension and/ or diabetes

  • Reduce LDL cholesterol by diet or medication or both



Aneurism – dilation in the arterial wall

  • Aneurism – dilation in the arterial wall

  • Most arise in aorta or major branches as a result of atherosclerotic wall damage

  • Males over 50 at greatest risk for aortic aneurysms

  • Disturbs blood flow, predisposing to thrombus formation - can release thromoemboli



Asymptomatic until rupture

  • Asymptomatic until rupture

    • Embolism
    • Death
  • Treatment by surgical repair

  • Aortic Dissection –bleeding into vessel wall, separating vessel layers

    • Men in 40-60 y.o. age group with hypertension
    • Younger persons with connective tissue disease or congenital defects
    • Presents with pain – life threatening


A consistent increase in arterial blood pressure caused by increased Cardiac output or increased peripheral resistance or both

  • A consistent increase in arterial blood pressure caused by increased Cardiac output or increased peripheral resistance or both

  • Leads to damage of vessel walls

  • If arteries constrict over a long time with increased pressure in vessel, the wall becomes thicker to withstand the stress.

  • Results in narrowing of arterial lumen

  • Leads to inflammatory response



Causes one in eight deaths worldwide

  • Causes one in eight deaths worldwide

  • Third leading cause of death in the world

  • Affects 50 million Americans



Also called essential or idiopathic hypertension

  • Also called essential or idiopathic hypertension

  • 92- 95 % of all cases

  • No specific cause identified

  • Can happen with retention of sodium and water → increased blood volume.

  • Also low dietary potassium, calcium and magnesium intakes



Smoking

  • Smoking

    • Nicotine is a vasoconstrictor
  • Greater than 3 alcoholic drinks/ day

    • 2-4 drinks / week lowers blood pressure


Interaction of genetics and environment

  • Interaction of genetics and environment

  • Overactivity of sympathetic nervous system

  • Overactivity of renin / angiotensin/ aldosterone system

  • Salt and water retention by kidneys

  • And others



Caused by a systemic disease process that raises peripheral resistance or cardiac output = 5 - 10 % of cases.

  • Caused by a systemic disease process that raises peripheral resistance or cardiac output = 5 - 10 % of cases.

  • Renal vascular disease

  • Adrenocortical tumors

  • Adrenomedullary tumors

  • Drugs ( oral contraceptives, corticosteroids, antihistamines)



Sustained primary hypertension that damages the structure and function of the vessels themselves.

  • Sustained primary hypertension that damages the structure and function of the vessels themselves.

  • Commonly affects heart, aorta, kidneys, eyes, brain, and lower extremities (target-organ damage).



None in early stages other than elevated BP

  • None in early stages other than elevated BP

  • Some individuals never have symptoms; others become very ill and die



Modification of life style

  • Modification of life style

  • Drugs

    • Diuretics, beta-blockers, angiotensin converting enzyme inhibitor
  • Compliance is often difficult – patients stop taking medication when they feel better – can get rebound effects



Varicose veins – dilations, can lead to valvular insufficiency

  • Varicose veins – dilations, can lead to valvular insufficiency

  • Can occur in superficial veins (saphenous) or deep veins

  • Causes of secondary varicose veins:

    • Deep vein thrombosis
    • Congenital defects and pressure on abdominal veins


Prevention – little can be done after valves become incompetent

  • Prevention – little can be done after valves become incompetent

  • Avoid stressors, such as standing for long periods

  • Elastic support stockings

  • Sclerotherapy – injections of drugs to induce fibrosis of vessel

  • Surgical removal - but only when deep vein are open.



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