Equine Circulatory System PDF

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Equine circulatory system...

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Circulatory System: cardiovascular system o The heart and the system of vessels that distribute blood to cells, tissues, and organs of the body. o Horses have an efficient closed circulatory system  Blood is pumped by the heart through the arteries, veins, and capillaries  Capillaries surround organs, ensuring nourishment of all cells and removal of waste products o Functions  Transport of nutrients, oxygen, and hormones to body cells  Removal of metabolic wastes (co2s and N)  Protection of the body by white blood cells, antibodies, and complement proteins that circulate in the blood  Clotting mechanisms protect the body from blood loss after injuries  Regulation of body temperature, pH, and water content of cells o Components  Pump-heart  Left heart- collects o2 rich blood from the lungs and dispenses it to the body  Right heart- collects blood returning from the body and delivers it to the lungs  ********Be able to describe flow of blood from a single point!!  EXAMPLE: Vena cava's to right atrium (RA), right atrium through tricuspid valve to right ventricle, right ventricle through the pulmonary valve to pulmonary arteries (PA), pulmonary arteries to lungs, from lungs via pulmonary veins (PV), PV to the left atrium (LA), LA through the mitral valve to left ventricle (LV), and left ventricle through aortic valve into aorta to the circulatory system and back to vena cava's…  Distribution- arteries  Exchange areas- capillary beds  Collection and return system- veins o The horse has disproportionate skeletal muscle mass, heart size, and pumping capacity and lung capacity. o How big is the avg. horse's heart?  9g/kg…..conversion 2.2 g/lb  1200lb/2.2g/lb= 545kg (9g/kg)= 4.9kg or 10.8lbs  Avg heart avg: 4g/kg  160lb human: 72kg (4g/kg)= 0.28kg or =0.63lb o The energetic capability of horse muscle far surpass the capacity of the respiratory and cardiovascular system to deliver O2 o In the horse, skeletal muscle comprises over 50% of body mass  Avg human muscle mass: Male=42% and female=36% o The lungs cannot grow with exercise but the heart, skeletal muscle, and blood components can, and do! o Blood volume and red blood cell concentration also factor into circulatory function, fitness, and athleticism o How much blood does the average horse have?

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 6-10% of its body weight  Blood weighs slightly more than water: 8.8lb/gal (1.05/l)  1200lb horse: 72-120lbs of blood or 8-13.6 gallons  Can lose up to 35% at any given time o Positively correlated to exercise performance  Heart and spleen volume are important contributors  At rest 35% of the horse's blood volume is red blood cells  Up to 50% of the total red blood cells stored in the spleen  Exercise induced splenic contraction can increase red blood cell count on demand to 65% of blood volume  The horse has a proportionally larger spleen per unit of body mass as compared to other mammals o Dependent on 3 major factors:  Heart rate (HR)  Heart beats per minute  AKA pulse rate  Avg resting heart rate:  30-40bpm  Max cardiac output  200-240bpm  The horses unique capacity for a 10 fold increase in HR is a contributing factor to its athletic superiority among animals  Cardiac output (CO)  The volume of blood pumped per minute  Two phases  Contraction/ejection phase  Systole  Relaxation/ filling phase  Diastole  The output of the heart is a product of the volume of systole and heart rate known as stroke volume  The volume of blood pumped per minute  CO=HR*SV  Avg resting horse CO:  35bpm* 1000mL/beat= 35L/m or 9gallons  Peak exercise  110bpm*1700mL= 187L/m (50 gallons)  Performance limiting factor  Also correlated with [hemoglobin] and muscle mass  Stroke volume (SV)  The volume of blood pumped from one ventricle with each beat  Determined by heart mass and contractility  2-2.5mL/kg at rest to 3-4mL/kg at exertion  Avg equine SV:  1000mL/beat at rest  1700mL conditioned at peak exercise  Other determining factors: heart and spleen mass Cardiac

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Function The heart is a major determinant in VO2 max, a measure of aerobic capacity VO2 max is the maximal rate of o2 consumption Vo2 max is det. By cardiac output (SV*HR), lung capacity and the ability of muscle cells to extract oxygen from the blood  During exercise the oxygen req. by muscles can increase to 35 times the resting rate  Oxygen req. differ for horses of different muscle types

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