Weeks 4 and 5Disturbances of Blood Flow

Dr.İ.Taci Cangül

Bursa-2008

Disturbances of Blood Flow

• Hyperemia and congestion• Hemorrhage• Ischemia • Thrombosis • Postmortem clots • Disseminated intravascular coagulation • Embolism • Infarction • Edema • Shock

Hyperemia and Congestion

Increased volume of blood in an affected tissue or part

• Hyperemia (active hyperemia): Arterial and arteriolar dilatation produces an increased flow of blood into capillary beds

• Congestion (passive congestion or venous congestion): Impaired venous drainage

Active Hyperemia

Too much arterial blood is brought to an organ or tissue by dilated arterioles and capillaries– Sympathetic neurogenic mechanisms or– The release of vasoactive substances

– Inflammatory reaction– Heat applied locally to a part– Increased physiological activity

Can the increased blood flow (active hyperemia) in acute inflammation be a defense mechanism of the body?

Passive Congestion

• Blood leaving an organ or part is impeded (impaired venous drainage)

• Grossly, the involved tissues appear bluish-red because of the poorly oxygenated venous blood

• Microscopically, congestion is similar to hyperemia (capillaries and veins are dilated and filled with blood)

Types of Passive Congestion

• Localized passive congestion

• Generalized passive congestion– Chronic generalized passive congestion of the

lungs: Reduced left ventricular output (left-sided heart failure).

– Chronic passive congestion of the liver: Right-sided heart failure (rarely from obstruction of the posterior vena cava).

Hemorrhage

The presence of erythrocytes outside the blood vessels– The vessel may be physically damaged so

that erythrocytes flow out through a break in the wall (hemorrhage by rhexis) or

– The erythrocytes may pass through an intact vascular wall by a process called diapedesis (hemorrhage by diapedesis)

Naming Hemorrhage-1

• Petechiae• Ecchymoses• Purpura• Agonal hemorrhages• Linear hemorrhages• Paint-brush hemorrhages• Hemothorax• Hemopericardium

Naming Hemorrhage-2

• Epistaxis

• Hemoptysis

• Enterorrhagia

• Metorrhagia

• Hematuria

The Significance of Hemorrhage Depends on:

(1) The volume of blood loss

(2) The rate of blood loss, and

(3) The site of hemorrhage

Ischemia

Local anemia or a deficiency of arterial blood to a portion of an organ or part. The chief causes of ischemia are:

(1) External pressure upon an artery

(2) Narrowing of the lumen of an artery

(3) A thrombus or embolus

Effects of Ischemia

• The organ involved

• The size of the vessel

• The degree of occlusion

• The degree of collateral circulation

• End artery (as in kidneys): Acute necrosis

• Gradual obstruction: Atrophy

Thrombosis

• Formation of a clot from elements of the circulating blood within the vascular system during life

• May decrease or obstruct vascular flow causing ischemic/hypoxic injury to cells, tissues and organs

• May become dislodged or fragmented to create emboli (an embolus is an intravascular mass carried in the bloodstream to some site remote from its origin)

Factors Effective in Thrombosis

(1) Injury to vascular endothelium

(2) Alterations in normal blood flow

(3) Alterations in the blood (hypercoagulability)

Arterial vs Venous Thrombus

• Grossly: Thrombi are friable, a mixture of red and gray in irregular layers, dull, and attached to the endothelium

• Arterial thrombus: Dry, friable gray masses composed of almost regularly arranged layers of platelets and fibrin, irregularly mixed with small amounts of darker red coagulated blood

(White or conglutination thrombus)• Venous thrombus: Red, gelatinous

(Stasis or red coagulation thrombus)

Nomenclature of Thrombi-I

• Mural thrombi - are attached to the wall of the heart or blood vessel

• Occluding thrombi - are attached to the entire circumference of the vessel

• Valvular thrombi - are attached to the heart valves

• Canalized thrombi - occur when new blood channels form in an organized thrombus

Nomenclature of Thrombi-II

• Saddle thrombi - straddle the bifurcation of blood vessels

• Septic thrombi - are those which contain bacteria

• Aseptic thrombi - are those that do not contain bacteria, etc.

The Thrombus may …

(1) increase in size and, by its enlargement, eventually cause obstruction of some critical vessel

(2) give rise to emboli

(3) be removed by fibrinolytic action or

(4) become organized

Disseminated Intravascular Coagulation (DIC)

• Widespread microthrombi formation in capillaries, arterioles and venules

• Composed largely of fibrin and aggregated platelets

• A complication of a diverse group of clinical diseases in which there is activation of the intrinsic pathway of blood clotting

Embolism

• Process of a foreign body moving through the circulatory system and becoming lodged in a vessel causing obstruction

• An embolus (plural, emboli) is a detached intravascular solid, liquid or gaseous mass that is carried by the blood to a site distant from its point of origin

Infarction

• A localized area of ischemic necrosis in an organ or tissue resulting from occlusion of either its arterial supply or venous drainage

• Usually caused by thrombosis and/or embolism of the arterial blood supply

• More rarely, external compression of vessels by expanding tumors, etc.

Edema

• Abnormal accumulation of fluid (water) in the intercellular tissue spaces or body cavities

• Localized (e.g. obstruction of venous outflow from the leg)

• Generalized in distribution (e.g. in chronic congestive heart failure)

Nomenclature

• Anasarca: Generalized edema in which fluid in subcutaneous tissues is especially prominent

• Ascites: Collection of edematous fluid in the peritoneal cavity

• Hydrothorax: Collection of edematous fluid in the thoracic cavity

• Hydropericardium or Pericardial Effusion: Collection of edematous fluid in the pericardial sac

Transudate-Exudate

• Inflammatory edema is referred to as an exudate and it is associated with an inflammatory reaction

• Non-inflammatory edema is referred to as a transudate

Edema is caused by …

(1) Decreased plasma osmotic pressure

(2) Increased hydrostatic pressure

(3) Increased permeability of vascular endothelium

(4) Lymphatic obstruction

Decreased Plasma Osmotic Pressure

• Deficiency of blood proteins (hypoproteinemia)

• Decreased formation or excessive loss

• Albumin

• More fluid is pushed into the intercellular spaces. Also, the force available to pull fluid into the bloodstream at the venous end of the capillary is reduced

Decreased Plasma Osmotic Pressure-I

• Malnutrition (starvation, emaciation)

• Severe or advanced liver diseases (cirrhosis, etc.)

• The loss of plasma proteins (intestine and kidneys)

Decreased Plasma Osmotic Pressure-II

• In the intestine, blood protein loss is usually the result of hemorrhage over a long period of time (stomach worms in sheep and cattle, slowly bleeding stomach ulcers in pigs and dogs, etc.)

• In the kidneys, renal amyloidosis is the only frequently encountered condition in animals in which large volumes of blood protein are lost through the urine

Increased Hydrostatic Pressure

• Venous stasis

• Subsequent to venous stasis, the capillaries become more permeable to large molecules (albumin and globulin), since they are deprived of their normal supply of oxygen and other nutrients

Increased Permeability of Capillary Endothelium

Occurs subsequent to venous stasis (resulting in increased hydrostatic pressure), as well as from direct damage, as in inflammation. Increased vascular permeability is the most important mechanism in the formation of inflammatory edema (exudate)

Lymphatic Obstruction

Occurs when any lesion impedes normal lymphatic drainage by pressure or obstruction. Under normal conditions, the lymphatics constantly drain small amounts of fluid from the intercellular spaces. Thus, in the absence of lymphatic drainage from a area, fluid accumulates

Shock

• Peripheral circulatory failure with pooling of the blood in the terminal circulatory beds (small capillaries)

• The fundamental disturbance is that blood volume is too small to fill the vascular system, resulting in a fall of blood pressure and cell damage due to anoxia

• Hypovolemic, septic, cardiogenic and neurogenic

Clinical Signs of Shock

• Inconsistent and vary with the precipitating cause

• Animals are usually inactive and unresponsive to external stimuli

• Muscle weakness is prominent and there is pallor and coolness of the skin

• Body temperature is subnormal and the heart rate is increased in most types of shock (but it may be slow and irregular). Depression of renal function and urine production often occur

Shock

• Hypovolemic shock: Due to loss of blood volume (hemorrhage, trauma, loss of fluids in burns, etc.)

• Septic shock: Septicemia or an overwhelming infection with gram-negative (endotoxic shock) or gram-positive (exotoxic shock) organisms. Peripheral dilatation of the capillary beds which subsequently lead to shock

Shock

• Cardiogenic (Cardiac) shock: “Pump failure." Subsequent to the sudden decrease in cardiac output

• Neurogenic shock: A shock state mediated by the nervous system which induces peripheral dilatation (dilatation of the capillary bed). It occurs in animals with severe fright, pain and trauma (without hemorrhage)