Functions of Cardiovascular system Þsystem circulates blood throughout body transports energy substrates (glucose, FA, ect.), electrolytes and hormones to tissues removes waste products Ýlactate, CO 2 & H 2 O Ýthermoregulation

Heart Þheart rate mass: average1.0% untrained horse0.94% trained1.1% Þgreyhound heart size of a clenched fist located in the chest weighs about 1% of its BW

Heart Þlocated in thoracic cavity Þapprox lbs (1% of BW) Þsplit into left and right halves both contain an atria and a ventricle left side circulates blood to systemic system right side circulates blood to the pulmonary system Þsystole - contraction Þdiastole - relaxation

Þaorta has elastic walls Þpulse expand during systole recoil during diastole Þarteries/arterioles have muscular walls allowing for vasoconstriction and vasodilation blood pressure increases when the walls of the arteries constrict

Capillaries ÞConstructed of permeable walls Þsight of gas, nutrient and waste product exchange pulmonary capillaries discard CO 2 and extract O 2 from the alveoli of the lungs Þcapillaries are very small in diameter RBC flow through single file (blood is sluggish if the PCV is high) Þconditioning (training) can increase capillary density 50% provides more efficient O 2 delivery

Venous System Þvenules and veins have lower blood pressure than arteries Þhorse legs have valves to provide unidirectional blood flow in veins Þvenous flow depends on muscle contractions activity provides better venous blood movement inactive - blood pools in extremities Ý“stocking-up” accumulation of fluid in legs

Blood Þ10% of horse BW of about 40 liters at rest pulmonary circulation20% heart, arteries and arterioles15% venules and veins60% Þblood is comprised of plasma and cells plasma: Ý55% of the total blood volume Ý91% water and 9% solids (proteins) albumin, globulin and fibrinogen

Blood Cell Composition Þred blood cells (RBC) - erythrocytes - contain hemoglobin manufactured from bone marrow life span of days Þwhite blood cells (WBC) - leukocytes - fight infection manufactured in the spleen renewed every 10 days 5 types Ýneutrophils (50-60%), eosinophils (2-5%), basophils (<1%), monocytes (5-6%), lymphocytes (30-40%) Þplatelets - thrombocytes - clot blood life span of 5-9 days

Blood Analysis Þblood scan: 5 minutes for major changes from normal (PCV, total protein, hemoglobin and estimate white blood cell count) Þfull blood count: 30 minutes main count of WBC’s to detect infection, stress, allergies, ect. Þblood profile: 24 hours detailed RBC count, individual WBC counts, enzymes, electrolytes, ect. ÞPlasma - fluid spun from unclotted blood Þserum - blood is allowed to clot and fluid is spun from the clot (contains no fibrinogen)

Spleen ÞAbout 1% of BW Þsplenic contraction 1/3 to 1/2 RBC stored in spleen at rest hematocrit or packed cell volume (PCV) Ýrest 35-45% Ýmaximum 60-65% hemoglobin content of extra RBC in the blood acts as a pH buffer, enabling horses to tolerate extremely high blood lactate concentrations

Function During Exercise ÞHeart rate - bpm resting HR bpm maximal HR 240 bpm Þdesirable cardiovascular features large, muscular heart low resting HR high maximal HR

ÞHR: not very predictable Þintensity of work 120 (low),160 (moderate), 200 (intense) Þsteady state 2-3 minutes regulated by sympathetic nervous activity and/or hormones Þsteady state constant during sub-maximal work Þcontinual increase in HR with intense exercise (warm-up) Þmonitor HR - indication of any problems

ÞFatigue 170 bpm24 min 205 bpm 4 min Þcardiovascular drift