Cardiovascular System of the Horse
Function
Blood Vessels
Arteries
Arteries - Arterioles - Capillaries - Venules - Veins
Veins
Capillaries
- thick muscular walls of smooth muscle tissue
- contract and helps pump blood around the body
- carry blood away from the heart
- higher blood pressure than veins
- thinner layer of smooth muscle and vessel walls
- less pressure inside vessels
- contain valves
- valves help push blood against gravity and back to the heart
- carry blood towards the heart
- very narrow and thin walled vessels
- site of gaseous exchange in body tissue and lungs
Pathway of Blood
Deoxygenated Blood:
- superior/inferior vena cava
- right atrium
- tricuspid valve
- right ventricle
- semi-lunar valve
- pulmonary artery
- lungs
Valves
Oxygenated Blood:
- pulmonary vein
- left atrium
- bicuspid valve
- left ventricle
- semi-lunar valve
- aorta
- body
Cardiac Cycle: Miocardium
- signal from contraction of the heart starts in the Sinoatrial Node
- signal is transmitted via gap junction to the Atrial Myocardium
- atria contract and blood is forced into the ventricles
- Sinoatrial Node also sends signals to the Atrioventricular Node
- Atrioventricular Node is triggered by signals from Sinoatrial Node
- signals are sent down the septum via the Bundle Of His
- Bundle Of His triggers Purkinje Fibres in the wall of the ventricles
- ventricles contract and blood is forced into the arteries
- pump blood around the body
- oxygenated blood - respiration in cells creastes energy - ATP = muscle contractions
- gets rid of waste products e.g. carbon dioxide
- transports nutrients from digested food around the body
- transports white blood cells and antibodies to site of infection
- held in place by tendinous cords attached to the walls of the heart
- only open in one direction to prevent backflow
- backflow happens when too much pressure in the left and right atrium builds up
- blood enters the ventricle, increasing the pressure inside the ventricle
- tendinous cords will prevent the valves from opening into the atrium
Cardiovascular Disorders
Ventricular Septal Defect
EIPH
Atrial Fibrillation
Tricuspid Dysplasia
Cause
Treatment
What?
- disorder in the natural electrical stimulation of the heartbeat
- leads to irregular heartbeat which can become chaotic and the atria may flutter rather than beating normally
- theres no rythem to the heartbeat.
- abnormalities or damages to the heart
- commonly caused by enlargement of the heart
- E.g. Hypertension, Coronary Stenosis, Double pointed valves, congenital heart disease, Pneumonia
- anti - arrhythmic drugs
- electrical stimulation
- electric cardioversion
- drugs - quinidine sulphate
- transvenous electrical cardiovension
Cause
Treatment
What?
- opening in the intreventricular septum causing shunt between ventricles
- large defects often result in significant left to right shunt
- causing shortness of breath when feeding and poor growth during infancy
- genetic defect
- environmental conditions
- infection
- poisoning
- medication takes by the dam
- poor maternal nutrition
- plugging / patching holes between ventricles
- medication- blood thinner to prevent clotting
- removal of excess red blood cell if present
Cause
Treatment
What?
Symptoms
Treatment
What?
- exercise enduced disorder
- presence of blood in airways causing irritation and inflammation of the lung - caused by strenuous exercise
- causes bleeding through the horses nose
- to much workload on the heart increasing blood pressure, causing blood vessels to burst.
- blood enters the lungs due to fractured capillaries
- most likely cause = multi - fractorial condition involving airways, vascular, inflammatory, blood, cardiac, remodelling components
- no treatment or prevention methods
- reduced by salix - this reduces the chance a horse has of developing the disease.
- salix works as a diuretic - increases urine producion and decreases blood volume and weight
- reduces stress on pulmonary capillaries, reducing severity of the bleeding
- abnormal development or malfuntion of the tricuspid valve
- allowing regurgitation of the blood back into the right atrium
- severity determins the degree of right heart enlargement and risk of right side CHF
- systolic murmur may be heard
- shortness of breath
- coughing
- fatigue
- accumulation of fluid in lungs, limbs or abdomen
- no treatment currently
- therapy isnt usually instituted untul signs of right sided heart enlargement are present
- medical therapy is aimed at improving quality of life, delaying congestive heart failure and controlling fluid accumulation once heart failure has developed
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