The dog’s blood and lymph circulation
The dog’s blood and lymph circulation
In a dog that has developed normally, the heart’s axis is placed obliquely in relation to the body’s axis. The heart is more to the left side of the body than to the right (with 4/7 being on the left) and is flattened crosswise, which means that the right side of the heart is positioned cranially (toward the head) and the left side caudally (towards the tail). Thus, the base of the heart, where the blood vessels are located, is located cranially and dorsally, while the apex is positioned caudally and ventrally. The heart is located between the third and sixth ribs and its weight varies greatly depending on the breed.
-The heart is divided into four main parts: the right atrium receives deoxygenated blood and sends it to the right ventricle, which pumps it to the lungs; the left atrium receives the oxygenated blood from the lungs and sends it to the left ventricle, which in turn pumps it out to the various parts of the body.
Study of the circulatory system includes the blood vessels (veins and arteries) and the heart in both anatomical and physiological contexts. Adult and fetal circulation differ and so will be studied separately. Lymphatic circulation is the “drainage system” for the entire circulatory system.
The blood vessels begin forming when the embryo can no longer be adequately nourished by simple diffusion between cells. The development of internal organs requires that nutrients be carried directly to the cells involved. In contrast, the heart has a much more complicated origin. It is formed from the embryo’s outer cells and remains outside the embryo at first. Later, it is incorporated into the embryo and reaches its final position in the thoracic region. At first, the heart is rectangular (an evolutionary vestigial form). Later, it curves in, rotates and acquires its familiar form.
Fetal lungs are not functional, as oxygen is received from the umbilical veins coming from the mother, while carbon dioxide is eliminated through the umbilical arteries. Thus, a major part of the circulation is “shunted” through the foramen ovale, an opening between the two sides of the heart and through the ductus arteriosus, a canal linking the aorta (the main artery leaving the left side of the heart) to the pulmonary trunk (which exits from the right side of the heart). The chambers of the heart are not separate until the end of gestation and the first hours after birth. In contrast, the ductus arteriosus does not close until after birth, once the lungs have started functioning.
This developmental phenomenon can lead to anomalies such as a defect in the septum of the heart, persistence of the ductus arteriosus, or an improperly-placed heart.
