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Biology LibreTexts

Part 2: Circulatory System

  • Page ID
    20797
  • Note the following features:

    Arteries, which carry high-pressure blood away from the heart, are generally thicker walled than veins, which carry lower-pressure blood back to the heart. Mammalian hearts have four chambers. Each side of the heart has an atrium that receives blood from elsewhere in the body and a ventricle that pumps the blood out of the heart. The right atrium receives blood from the systemic circulation and passes it to the right ventricle, which pumps the blood to the pulmonary circuit. After the blood passes through the lungs it goes to the left atrium and then into the left ventricle, which pumps the blood into the systemic circuit. The first part of the systemic arterial circuit is the aorta, which soon branches out to supply various regions of the body.

    Fetal circulation is different from adult circulation. In the fetus, blood doesn’t get oxygenated in the lungs; it gets oxygenated at the placenta. The umbilical arteries carry blood from the fetus to the placenta. The umbilical vein carries blood from the placenta back to the fetus. (In the placenta substances are exchanged between fetal and maternal blood, but the blood itself does not mix.) Therefore, the most highly oxygenated blood in the fetus is in the umbilical vein. Blood from the umbilical vein gets mixed with the rest of the systemic circulation and returns to the right atrium. The blood entering the right atrium is the most oxygenated blood in the fetal heart, but it’s the least oxygenated blood in the adult heart. The fetus has two key tricks to adapt to this fact: First, some of the blood that leaves the right ventricle bypasses the lungs. In an adult, this blood needs to go to the lungs to get oxygenated, but the fetus has a ductus arteriosus that shortcircuits this blood flow, allowing some blood to go directly into the aorta and then into the systemic circulation. Second, in the fetal heart, there is an opening between the right atrium and the left atrium. This opening is called the foramen ovale. The foramen ovale is helpful in the fetus because it lets the oxygenated blood from the placenta get circulated faster. The foramen ovale normally closes up at birth, keeping blood flow of the two sides of the heart completely separate. In some people, the foramen ovale does not close up. This condition, called patent foramen ovale, can result in serious health problems.

    Dissection of the Thoracic Cavity

    Arteries

    Note: The diagram below only focuses on arteries and you do not need to know all of them.

    1. Find the diaphragm again. Remember that the diaphragm separates the abdominal cavity from the thoracic cavity and it aids in breathing.  Above the diaphragm, center of chest, is the heart.
    2. Remove the pericardium, which is a thin membrane that surrounds the heart.
    3. The structures visible on the heart are the two atria (12,13), the ventricle (14), which has two chambers not easily visible from the outside. Pig Circulatory System.PNG
    4. The most obvious vessel on the front of the heart is the pulmonary trunk (1).  It curves upward and joins the aorta (2) - a vessel which arches from the heart and curves around to go to the lower part of the body -where it is called the abdominal (dorsal) aorta (9). The aorta supplies the body with blood.
    5. Find the vessel anterior to the heart in the base of the neck. This is the common carotid (4).
    6. The common carotid will branch into the left (7) and right carotid arteries (8).  The carotid arteries supply blood to the head and neck.
    7. Observe the coronary vessels (6) on the outside of the heart - these vessels supply blood to the muscle of the heart.

    Veins

    1. Lift the heart to look on its dorsal side (toward the back), you should be able to see the anterior and posterior vena cavae, which bring blood back to heart from the body. In addition, you should also be able to find the left and right jugular veins that drain blood from the head and run parallel to the carotids. Note: Veins are injected with blue latex.

    Review

    Identify the structure:

    1. Membrane over the heart.
    2. Blood supply to head
    3. Lower heart chambers
    4. Blood supply to lower body
    5. Muscle to aid breathing
    6. Returns blood to heart
    7. Large artery that arches over top of heart
    8. Arteries on heart surface.