Equine Circulatory System
Vet, Horse First Aid

From: Horse Anatomy | Care

See also: Tack | Clipping | Rugs | Worming

Race Horse

Circulatory System
This is the system that transports blood throughout the horses body.  The horses circulatory system uses the heart, arteries, veins and capillaries to transport oxygenated blood, nutrients, lymph and hormones  to vital organs and tissues and remove waste products such as carbon dioxide away to the lungs.

The two main types of circulation are systemic circulation and pulmonary circulation

The circulatory system consists of  the heart, blood and blood vessels.

The  Heart
It is through the heart that oxygenated blood first arrives and it does this via the Pulmonary Vein which comes to it straight from the lungs.  The heart itself is split up into 4 chambers, the blood first enters the heart through the Pulmonary Vein into the Left Atrium which is the first chamber, there is a valve called the bicuspid valve which acts as a one way valve allowing the blood to then flow when ready into the Left Ventricle. From here the blood exit s the heart and travels to all the major organs  and tissues supplying them with oxygenated blood and collecting any waste products for removal. On returning to the heart the blood is now de oxygenated and it enters via the Aorta and  goes into the Right Atrium where there is a tricuspid valve regulating the flow of blood into the Right Ventricle. From the Right Ventricle the deoxygenated blood is taken to the lungs and tissues in the horses body.

The Heart Rate
The horses heart rate beats at around 36 to 42 Beats per minute at rest and with exercise can go up to 220 beats per minute.

The Blood Vessels
The blood vessels are the veins, arteries and capillaries and they are used to transport the blood around the body to and from the heart.

These carry oxygenated blood away from the heart to all around the body.  Some examples of  arteries are  the Aorta , Illiac Artery and  Hepatic Artery. Smaller Arteries are called Arterioles and these branch out to link with Capillaries where blood exchange occurs between Arteries and veins. The Pulmonary Artery is the exception to the rules as it  carries deoxygenated blood from the heart to the lungs.

These carry deoxygenated blood back to the heart. An example would be the Vena Cava which carries blood into the right Atrium of the heart. The smaller veins are known as venules and these branch out to link with Capillaries where blood exchange occurs between Arteries and veins.

These allow blood to flow from  the Arteries to Veins via the Arterioles and Venules

The Blood
Blood  is made up of red blood cells, white blood cells, platelets and plasma and is required for the following reasons:-

Red Blood Cells
These are made in the bone marrow and contain haemoglobin which are not only rich in iron but are also the means through which oxygen is transported  around the body, the oxygen molecules attach on to the haemoglobin and once delivered to a tissue or organ carbon dioxide molecules then attaches themselves to  the haemoglobin within the red blood cell and is taken away to the lungs  for removal..

White Blood Cells
These are also known as leucocytes and are known for fighting off infection. White blood cells can be put into two main groups known as granulocytes and agranulocytes. Granulocytes for example  are Basophils which fight allergic reactions, Neutrophils which  fight off bacterial and fungal infections and Eosinophils which fight off parasitic infections. Agranulocytes are Lymphocytes which produce antibodies,  monocytes and macrophage cells which help to  remove foreign bodies and fight off any infection

These are cells that are formed in the bone marrow and  circulate within the blood and help in the formation of blood clots and controlling the blood flow. When a cut occurs it is the  contact with air that triggers off a reaction with the platelets within the blood, the platelets  quickly divide and act in particular with the protein Fibrinogen  to form Fibrin.  It is the formation of  Fibrin  which acts on the cut  by  producing a weave of threads which cover the cut and  start to form a blood clot which will halt the flow of blood. Continued contact with the air helps the Fibrin to dry and become hard to form a scab.

This is the fluid that the blood cells are suspended in. The fluid also contains water, antibodies and dissolved minerals such as calcium.


Circulatory Disorders

The circulatory system is made up of the heart, blood and blood vessels. A disruption to any of these can cause  anything from a mild to a more serious problem, careful consultation with your vet is always advised as they will have up to date knowledge of  the best course of action.

These are some of the disorders that can affect  the circulatory system of the horse