Circulatory System of a Pig

The circulatory system of a pig is quite similar to that of humans. In pigs, the circulatory system mainly consists of the heart, blood and blood vessels and is responsible for circulation of blood and nutrients throughout the body.

Heart
Like human beings, the heart of a pig is four chambered. The top two chambers are known as atria (singular atrium) right and left atria, while the bottom two chambers are called ventricles, left and right ventricles. The inner surface of the heart is lined by a smooth tissue known as endocardium. The heart operates as a pumping organ. The number of times the heart beats in a minute is called heart rate or pulse rate. In an adult pig, the heart rate is usually 70 beats, while in case of young piglets, it can be about 200 beats per minute. In pigs, the heart rate can be felt at the base of the ear or under the tail.

Blood
Blood is mainly composed of two parts, plasma and blood cells. Blood cells are of two types, white and red blood cells. The white blood cells are an important part of the body's defense or immune system as they fight against disease causing agents like bacteria and viruses. The red blood cells or erythrocytes contain a protein known as hemoglobin, that transports oxygen to the various parts of the body. Blood also contains platelets, which are mainly responsible for blood clotting.

Blood Vessels
The blood vessels called arteries and veins circulate blood throughout the body. Arteries are responsible for carrying blood from the heart to the entire body, while veins return blood to the heart. The large arteries branch off into smaller arteries and arterioles, which further branch off into some tiny microscopic capillaries. The capillaries can interchange fluids through their walls and thereby help the cells to receive water, oxygen and nutrients from blood and also to get rid of waste products like carbon dioxide. The fine capillaries then combine and widen to become venules, and then veins, which carry blood to the heart.

Circulatory Mechanism
The circulatory system includes both pulmonary and systemic circulation. Pulmonary circulation refers to circulation of blood between the heart and the lungs, while systemic circulation is the circulation of blood between the heart and the rest of the body, excepting the lungs. The deoxygenated or oxygen deprived blood is collected from the body by a series of veins that terminate into two main large main veins, anterior and posterior vena cava. The deoxygenated blood first reaches the right atrium of the heart, from where it is transported to the right ventricle. Then this blood is transported to the lungs through the pulmonary arteries for the purpose of oxygenation. Following this, the oxygen rich blood is carried by the pulmonary veins to the heart. The blood enters the left atrium first, from where it is pumped into the left ventricle. Finally, the oxygenated blood is pumped out of the heart into the aorta or the main artery. From there it is carried by the numerous arteries to the different regions of the entire body.

Pig Fetal Circulation
The circulation of blood in fetal pigs is somewhat different. The fetus receives oxygen rich blood from the placenta through the umbilical vein. The umbilical vein reaches the liver, from where the blood enters the posterior vena cava through the passage ductus venosus. Posterior vena cava carries blood to the heart. In fetal stage, the pulmonary circuit (which pumps blood from the heart to the lungs) is non-functional. So, almost half of the blood that enters the right atrium, directly reaches the left atrium through a small opening called foramen ovale. Then it enters the left ventricle, from where it flows into the aorta to be circulated throughout the body. The remaining amount of the blood in the right atrium enters the right ventricle and then moves out to the pulmonary trunk. From here, the blood goes into the aorta through the shunt ductus arteriosus and is then circulated to the entire body.

For proper circulation of blood within the body, the health of the heart and the blood vessels is very crucial. Any damage to these organs can impair the process of circulation and hamper the vital functions of the body. Besides heart and blood vessels, lungs also play an important role as it oxygenates blood. So, any disease of the lungs may result in shortage of oxygen in the cells and tissues and disrupt their normal functioning.