Circulatory System

Hematopoietic System Introduction

Blood supplies cells with water, electrolytes, nutrients, and hormones and removes waste products. The cellular elements supply oxygen ( RBCs), protect against foreign organisms and antigens ( WBCs), and initiate coagulation ( platelets). Because of the diversity of the hematopoietic system, its diseases are best discussed from a functional perspective. Function may be classified as either normal responses to abnormal situations (eg, leukocytosis and left shift in response to inflammation) or primary abnormalities of the hematopoietic system (eg, pancytopenia from marrow failure). Furthermore, abnormalities may be quantitative (ie, too many or too few cells) or qualitative (ie, abnormalities in function). (Also All.see The Biology of the Immune System.)
Anemia

Anemia is an absolute decrease in RBC numbers, hemoglobin concentration, or PCV. Signs include pale mucous membranes, increased heart rate, and hypotension. Diagnosis can be made by CBC, but may be refined by additional tests. Treatment can be symptomatic, but often requires addressing the underlying cause.
Blood Groups and Blood Transfusions

Blood groups are determined by genetically controlled, polymorphic, antigenic components of the RBC membrane. The allelic products of a particular genetic locus are classified as a blood group system. Some of these systems are highly complex, with many alleles defined at a locus; others consist of a single defined antigen. Blood group systems, in general, are independent of each other, and their inheritance conforms to Mendelian dominance. For polymorphic blood group systems, an animal inherits one allele from each parent and thus expresses no more than two blood group antigens of a system. An exception is in cattle, in which multiple alleles are inherited.
Blood Parasites

Anaplasmosis is a tickborne disease of ruminants caused by intracellular bacteria that infect red blood cells, causing fever and anemia. Diagnosis relies upon Giemsa-stained blood smears and serologic tests such as ELISA. Key treatments include tetracyclines and imidocarb; in some countries, less pathogenic species are used as live vaccines for the control of bovine anaplasmosis.
Lymphoma in Dogs

Dogs with lymphoma (a cancer of malignant lymphocytes) most commonly develop nonpainful, generalized lymphadenopathy. Clinical signs such as lethargy, weight loss, and constitutional decline can occur with more advanced disease. Lymphoma can be diagnosed by means of either fine-needle aspiration with cytologic evaluation or lymph node biopsy with histologic evaluation. Molecular diagnostic techniques, including flow cytometry and PCR for antigen receptor rearrangement (PARR) assay, can also be helpful. Treatment is systemic with chemotherapy.
- Lymphoma in Dogs
Erythrocytosis (Polycythemia)

Erythrocytosis is a relative or absolute increase in the number of circulating RBCs, resulting in the PCV, hematocrit, RBC count, and hemoglobin concentration increasing above reference intervals.
- Erythrocytosis (Polycythemia) in Animals
- Erythrocytosis in Horses
Hemostatic Disorders

Effective hemostasis depends on an adequate number of functional platelets, an adequate concentration and activity of plasma coagulation and fibrinolytic proteins, and a normally responsive blood vasculature. The diagnosis, treatment, and monitoring of hypo- and hypercoagulable animals is difficult with regard to both progression of disease and monitoring blood component and/or anticoagulation therapy. Citrated plasma samples are often used in veterinary medicine to determine fibrinogen concentration, activated partial thromboplastin time (APTT), prothrombin time (PT), and d-dimer or fibrinogen degradation product (FDP) concentration.
Leukocyte Disorders

Leukocytes, or WBCs, in the blood of healthy mammals include segmented neutrophils, band neutrophils, lymphocytes, monocytes, eosinophils, and basophils. Abnormal leukocytes include neutrophils less mature than bands (eg, metamyelocytes, myelocytes, progranulocytes), blast cells of any hematopoietic lineage, mast cells, and other neoplastic cells. WBCs vary in their site of production, their duration of circulation, and the stimuli that affect their release into and migration out of the vascular system. Differences in leukocyte physiology account for species differences in normal blood cell concentrations and their responses to disease.
Lymphadenitis and Lymphangitis of Large Animals

Caseous lymphadenitis is a chronic, infectious disease that manifests clinically as abscesses of peripheral (external) and/or internal lymph nodes and organs. The characteristic purulent material is very thick and nonodorous. The peripheral form presents as abscesses of single or multiple palpable lymph nodes. The internal form typically manifests as chronic weight loss and ill thrift. Culture of active lesions for Corynebacterium pseudotuberculosis is diagnostically definitive. Affected animals are often culled. If treatment is pursued, it consists of consistent, sustained antimicrobial administration to decrease the numbers of active draining lesions, as well as isolation from other herdmates until lesions are dry and/or resolved.
- Caseous Lymphadenitis of Sheep and Goats
- Lymphangitis of Horses and Cattle
Cardiovascular System Introduction

The cardiovascular system comprises the heart, veins, arteries, and capillary beds. The atrioventricular (mitral and tricuspid) and semilunar (aortic and pulmonic) valves keep blood flowing in one direction through the heart, and valves in large veins keep blood flowing back toward the heart. The rate and force of contraction of the heart and the degree of constriction or dilatation of blood vessels are determined by the autonomic nervous system (sympathetic and parasympathetic) and hormones produced either by the heart and blood vessels (ie, paracrine or autocrine) or at a distance from the heart and blood vessels (ie, endocrine).
Congenital and Inherited Anomalies of the Cardiovascular System

Congenital anomalies of the cardiovascular system are defects that are present at birth and can occur as a result of genetic, environmental, infectious, toxicologic, pharmaceutical, nutritional, or other factors or a combination of factors. For several defects, an inherited basis is suspected based on breed predilections and breeding studies. Congenital heart defects are significant not only for the effects they produce but also for their potential to be transmitted to offspring through breeding and thus affect an entire breeding population. In addition to congenital heart defects, many other cardiovascular disorders have been shown, or are suspected, to have a genetic basis. Diseases such as hypertrophic cardiomyopathy, dilated cardiomyopathy, and degenerative valvular disease of small breeds of dogs may have a significant heritable component.
Diagnosis of Heart Disease

Heart disease is defined as any functional, structural, or electrical abnormality of the heart. It encompasses a wide range of abnormalities, including congenital anomalies, as well as anatomical and physiologic disorders of varying causes. Heart disease can be classified by various characteristics, including presence at birth (eg, congenital or acquired), cause (eg, infectious, degenerative, genetic, or heritable), duration (eg, chronic or acute), clinical status (eg, left heart failure, right heart failure, or biventricular failure), anatomic malformation (eg, ventricular septal defect), or electrical disturbance (eg, atrial fibrillation, ventricular premature complexes).
- Diagnosis of Heart Disease in Animals
Heart Disease: Conduction Abnormalities in Dogs and Cats
- Heart Disease: Conduction Abnormalities in Dogs and Cats
Heart Failure in Dogs and Cats
- Heart Failure in Dogs and Cats
Cardiomyopathy in Dogs and Cats

Cardiomyopathy is defined as a primary disease of the myocardium. Most of the cardiomyopathies of animals are idiopathic diseases that are not the result of any systemic or other primary cardiac disease. The cause has been identified in some cases as a genetic mutation and in others as an inherited trait. In animals (primarily dogs and cats), cardiomyopathies are classified as dilated cardiomyopathy, hypertrophic cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy, and restrictive cardiomyopathy. In cats, if a specific cardiomyopathy cannot be identified, the disease is classified as cardiomyopathy, nonspecific phenotype. Cases in which a disease process has been identified as the cause of myocardial dysfunction are more correctly identified as secondary myocardial diseases or with a descriptive term preceding the term "cardiomyopathy" (eg, taurine-responsive dilated cardiomyopathy or hyperthyroid heart disease).
Various Heart Diseases in Dogs and Cats

Myxomatous degeneration is a process by which the fibrous layer of an atrioventricular (AV) valve breaks down to cause valve prolapse (hooding) and the spongiform layer proliferates to cause nodular thickening of the cardiac valve leaflets, most severely at their tips. Myxomatous degeneration commonly affects the mitral and tricuspid valves in older dogs. Chordae tendineae are also affected by the degenerative process, making them prone to rupture. The exact cause of myxomatous degeneration is unknown; in Cavalier King Charles Spaniels and Dachshunds, however, it is an inherited trait. Myxomatous degenerative valve disease is the most common cardiac disease in dogs, accounting for ~75% of cardiovascular disease in this species; ~60% of affected dogs have only the mitral valve affected, 30% have lesions in both the tricuspid and mitral valves, and
Various Cardiovascular Diseases in Dogs and Cats

Overt intravascular thrombus formation is rare with heart failure in most species other than domestic cats and humans. Cats frequently form a thrombus in a severely enlarged left atrium, most commonly in the left auricle. This thrombus then commonly breaks loose and flows into the systemic circulation. Although thrombus formation in cats occurs most commonly when the left atrium is large because of cardiomyopathy, it can also occur without left atrial enlargement, sometimes even in an otherwise healthy cat. In a cat with severe left atrial enlargement, the primary reason for development of the thrombus is assumed to be blood flow stasis. Red cells aggregate when blood flow decreases below a critical velocity. When the left atrium enlarges, blood flow velocity decreases (assuming no mitral regurgitation). The area of lowest velocity is the left auricle. In some cats, red cell aggregation can be visualized as so-called spontaneous contrast, or "smoke," within the left atrium. In some cats, both a thrombus and spontaneous contrast can be noted. In a cat with a thromboembolism, the left atrial thrombus has already detached and is gone by the time an echocardiogram is done.
- Arterial Thromboembolism in Dogs and Cats
- Systemic and Pulmonary Hypertension in Dogs and Cats
Heartworm Disease

Heartworm disease (dirofilariasis), produced by Dirofilaria immitis, primarily affects the pulmonary arteries, producing inflammation, vascular dysfunction, and pulmonary hypertension. Secondarily, this results in right-side cardiac pressure overload and progressive pulmonary insufficiency. Tertiary problems include aberrant heartworm migration, caval syndrome, coagulopathies (DIC), and heart failure. Most infected dogs are subclinically affected, but the most common clinical signs are weight loss, exercise intolerance, cough, and labored breathing. Prevention, with macrocyclic lactones, is crucial. Clearing a heartworm infection typically requires melarsomine, an organic arsenic compound, administered IM in three injections. Chronic use of certain macrocyclic lactones with doxycycline has also been effective when melarsomine cannot be used or is unavailable.
- Heartworm Disease in Dogs, Cats, and Ferrets
Bovine High-mountain Disease

Bovine high-mountain disease is a condition that occurs in cattle pastured at high altitude. Low oxygen saturation in the air leads to pulmonary hypertension, with subsequent edema in ventral tissues of the chest and abdomen. Treatment typically requires movement to lower elevation, and prevention through selective breeding for resistant stock is often preferred.
- Bovine High-mountain Disease
Thrombosis, Embolism, and Aneurysm

Thrombosis (clot formation within a blood vessel), embolism (process by which unattached material (emboli) such as a blood clot, fat or cholesterol deposit, gas, tissue, or foreign material travels within the bloodstream and occludes flow within a vessel), and aneurysm (dilation or outpouching of a blood vessel wall) are pathologic abnormalities that can occur within the vasculature. Clinical signs, diagnostic testing, and therapy vary based on the classification, location, severity, chronicity, and associated or concurrent comorbidities. Typically, mainstays of treatment include addressing the underlying disease process and antithrombotic drugs.
- Thrombosis, Embolism, and Aneurysm in Animals

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