Date post: | 18-Dec-2015 |
Category: |
Documents |
View: | 276 times |
Download: | 0 times |
2
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
4
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
7
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.
9
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
11
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
15
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.
16
• Baroreceptors and chemoreceptors:– Monitor pressure
– Monitor blood levels of O2, CO2 and H+
– Send information to cardiovascular center, which responds
17
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 vessel’s response to changes in pressure.
18
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.
19
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
22
Lymph nodes• Lie along lymphatic vessels
• Contain lymphocytes that filter lymph and eliminate microbes/damaged cells/ toxins
• Biological filtration
24
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
25
Arterial thrombus
• Forms where blood is moving rapidly – see alternating lines of platelets and red cells trapped in fibrin
• Lines of Zahn
26
Venous thrombus
• Forms differently due to decreased blood flow
• Mixed region at site of attachment
• More blood clotting forms a downstream red cap
27
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
28
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
29
– Turbulence:
• Damaged heart valves
• Congenital heart defects
• Compression of the vessel
• Weakened arterial wall - aneurysm
30
Other Causes • Aging
• Immobilization
• Injury to vessel endothelium
• Increased clotting response
Effects:
• Decreased venous emptying
• Increased venous pressures
• Edema
• Pain
31
Sequelae of Thrombosis1 Resolution –
Anticoagulation system
Fibrolytic system
Moderate exercise increases thrombus resolution
32
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
34
3 Propagation –
Thrombus extends further down the vessel, usually a vein.
Initial thrombus acts as a site for further platelet adherence.
36
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
38
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
42
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
44
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 > 60 % of blood supply is blocked
45
• 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
46
• 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
49
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
50
Treatment
• Exercise
• Smoking cessation
• Control of hypertension and/ or diabetes
• Reduce LDL cholesterol by diet or medication or both
51
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
52
• 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
53
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
54
• Causes one in eight deaths worldwide
• Third leading cause of death in the world
• Affects 50 million Americans
55
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
56
Other risk factors• Smoking
– Nicotine is a vasoconstrictor
• Greater than 3 alcoholic drinks/ day
– 2-4 drinks / week lowers blood pressure
57
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
58
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)
59
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).
60
Clinical manifestations
• None in early stages other than elevated BP
• Some individuals never have symptoms; others become very ill and die
61
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
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
62