Vascular and Lymphatic System Pathology

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Vascular and Lymphatic System Pathology
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Blood Flow

• 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

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Structure of blood vessels

• Tunica intima
• Endothelium and connective tissue
• Tunica media
• Smooth muscle and elastic tissue
• Tunica externa or tunica adventitia
• Connective and elastic tissue

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Arteries

• 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.

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Capillaries

• 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

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Veins

• 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

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Control of systemic circulation

• Nervous control innervated by sympathetic
  nervous system ONLY
• Cardiac control center (primarily in medulla
  oblongata)
• Heart has both Sympathetic and Parasympathetic
  innervations.

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

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Compliance

• 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 vessels response to changes in
  pressure.

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Blood pressure

• 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.

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Blood pressure

• BP Cardiac Output Total Peripheral Resistance

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Lymphatic 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

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Lymph nodes

• Lie along lymphatic vessels
• Contain lymphocytes that filter lymph and
  eliminate microbes/damaged cells/ toxins
• Biological filtration

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Diseases of Arteries and Veins

• 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

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Arterial thrombus

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

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Venous thrombus

• Forms differently due to decreased blood flow
• Mixed region at site of attachment
• More blood clotting forms a downstream red cap

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Factors that predispose to thrombosis

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

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Factors that predispose to thrombosis

• 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

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

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Other Causes

• Aging
• Immobilization
• Injury to vessel endothelium
• Increased clotting response
• Effects
• Decreased venous emptying
• Increased venous pressures
• Edema
• Pain

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Sequelae of Thrombosis

• 1 Resolution
• Anticoagulation system
• Fibrolytic system
• Moderate exercise increases thrombus resolution

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• 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

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Recanalization
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• 3 Propagation
• Thrombus extends further down the vessel,
  usually a vein.
• Initial thrombus acts as a site for further
  platelet adherence.

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Propagation
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• 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

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

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Treatment

• Anticoagulants
• Fibrinolytics t-Pas
• Prophylactic aspirin therapy

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Arterial Occlusions

• 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

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Atherosclerosis

• 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 gt
  60 of blood supply is blocked

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• Progressive over years
• Starts with some injury to endothelium
• Smoking, hypertension, hyperlipidemia, diabetes,
  autoimmune disease, and infection
• 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

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• 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

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Clinical manifestations

• 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

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Treatment

• Exercise
• Smoking cessation
• Control of hypertension and/ or diabetes
• Reduce LDL cholesterol by diet or medication or
  both

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Other arterial problems

• 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

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• 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

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Systemic Hypertension

• 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

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• Causes one in eight deaths worldwide
• Third leading cause of death in the world
• Affects 50 million Americans

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Primary 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

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Other risk factors

• Smoking
• Nicotine is a vasoconstrictor
• Greater than 3 alcoholic drinks/ day
• 2-4 drinks / week lowers blood pressure

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Suspected causes

• Interaction of genetics and environment
• Overactivity of sympathetic nervous system
• Overactivity of renin / angiotensin/ aldosterone
  system
• Salt and water retention by kidneys
• And others

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Secondary hypertension

• 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)

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Complicated hypertension

• 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).

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Clinical manifestations

• None in early stages other than elevated BP
• Some individuals never have symptoms others
  become very ill and die

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Treatment

• 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

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Venous Disorders

• 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

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Treatment

• 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.