Functions of Cardiovascular system
 system circulates blood throughout body
• transports energy substrates (glucose, FA, ect.),
electrolytes and hormones to tissues
• removes waste products
lactate, CO2 & H2O
thermoregulation
Heart
 heart rate mass:
• average
• untrained horse
• trained
1.0%
0.94%
1.1%
 greyhound
• heart size of a clenched fist
• located in the chest
• weighs about 1% of its BW
Heart
 located in thoracic cavity
 approx. 9-10 lbs (1% of BW)
 split 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
 systole - contraction
 diastole - relaxation
 aorta has elastic walls
 pulse
• expand during systole
• recoil during diastole
 arteries/arterioles have muscular walls allowing for
vasoconstriction and vasodilation
• blood pressure increases when the walls of the arteries
constrict
Capillaries
 Constructed of permeable walls
 sight of gas, nutrient and waste product exchange
• pulmonary capillaries discard CO2 and extract O2 from
the alveoli of the lungs
 capillaries are very small in diameter
• RBC flow through single file (blood is sluggish if the
PCV is high)
 conditioning (training) can increase capillary density 50%
• provides more efficient O2 delivery
Venous System
 venules and veins have lower blood pressure than arteries
 horse legs have valves to provide unidirectional blood flow
in veins
 venous flow depends on muscle contractions
• activity provides better venous blood movement
• inactive - blood pools in extremities
“stocking-up”
• accumulation of fluid in legs
Blood
 10% of horse BW of about 40 liters at rest
• pulmonary circulation
20%
• heart, arteries and arterioles 15%
• venules and veins
60%
 blood is comprised of plasma and cells
• plasma:
55% of the total blood volume
91% water and 9% solids (proteins)
• albumin, globulin and fibrinogen
Blood Cell Composition
 red blood cells (RBC) - erythrocytes - contain hemoglobin
• manufactured from bone marrow
• life span of 100-120 days
 white blood cells (WBC) - leukocytes - fight infection
• manufactured in the spleen
• renewed every 10 days
• 5 types
neutrophils (50-60%), eosinophils (2-5%), basophils (<1%),
monocytes (5-6%), lymphocytes (30-40%)
 platelets - thrombocytes - clot blood
• life span of 5-9 days
Blood Analysis
 blood scan: 5 minutes
• for major changes from normal (PCV, total protein,
hemoglobin and estimate white blood cell count)
 full blood count: 30 minutes
• main count of WBC’s to detect infection, stress,
allergies, ect.
 blood profile: 24 hours
• detailed RBC count, individual WBC counts, enzymes,
electrolytes, ect.
 Plasma - fluid spun from unclotted blood
 serum - blood is allowed to clot and fluid is spun from the
clot (contains no fibrinogen)
Spleen
 About 1% of BW
 splenic contraction
• 1/3 to 1/2 RBC stored in spleen at rest
• hematocrit or packed cell volume (PCV)
rest 35-45%
maximum 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
 Heart rate - bpm
• resting HR 25-45 bpm
• maximal HR 240 bpm
 desirable cardiovascular features
• large, muscular heart
• low resting HR
• high maximal HR
 HR: 20-110
• not very predictable
 intensity of work
• 120 (low),160 (moderate), 200 (intense)
 steady state 2-3 minutes
• regulated by sympathetic nervous activity and/or
hormones
 steady state constant during sub-maximal work
 continual increase in HR with intense exercise (warm-up)
 monitor HR - indication of any problems
 Fatigue
• 170 bpm
24 min
• 205 bpm
4 min
 cardiovascular drift