The pig has a circulatory system that is quite similar to the human circulatory system. In pigs, the circulatory system is composed of the heart, blood, and the blood vessels. As the name suggests, this system is responsible for circulating blood and nutrients throughout the body.
The heart of a pig is four-chambered. The top two chambers are known as atria (singular atrium), while the bottom two chambers are called ventricles. The inner surface of the heart is lined by a type of smooth tissue, known as endocardium.
The heart acts like 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 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 is the body fluid composed of 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 disease-causing agents like bacteria and viruses. The red blood cells or erythrocytes contain a protein known as hemoglobin, that transports oxygen to various parts of the body. Blood also contains platelets, which are responsible for blood clotting.
The blood vessels, known as 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 receive water, oxygen, and nutrients from blood, and 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.
The entire circulatory mechanism in pigs can be classified into two parts - pulmonary and systemic circulation. Pulmonary circulation refers to the 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 the 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. It is then transported to the lungs through the pulmonary arteries for oxygenation.
The oxygen-rich blood from the lungs is carried to the heart by the pulmonary veins. 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. It is then carried by the numerous arteries to the different parts of the body.
Pig Fetal Circulation
The circulation of blood in pig fetus is somewhat different. The pig 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 the 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 blood in the right atrium enters the right ventricle, and then the pulmonary trunk. From here, the blood goes into the aorta through the shunt 'ductus arteriosus' and is then circulated throughout the 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 circulation, and hamper the vital functions of the body. The lungs also play an important role in circulation, as they oxygenate blood. So, any disease of the lungs may result in the shortage of oxygen in the cells and tissues, which can disrupt their normal functioning.