Laboratory 16a Blood Vessels and Peripheral Circulation Objectives: Describe differences between arteries and veins, both at a gross anatomical level and at a histological level. Identify the major arteries and veins in the human body. 1. Blood Vessel Overview: Blood vessels are closed, tube- like structures that serve as the passageway for blood as it travels from the heart to the tissues and returns to the heart. Contraction of the heart ventricles propels blood out of the heart through the arteries. The arteries become smaller and smaller until they become thin- walled capillaries. The thin, often single- cell layer capillaries allow exchange of nutrients and wastes from the blood inside the capillary with the tissues. Blood leaving the capillaries then collects in the veins, which carry blood back to the heart. Arteries and veins have three layers of tissue. The tunica interna, or innermost layer, is a thin simple squamous cell layer than lines the blood vessels and is continuous with the endothelium of the heart. The large tunica media consists of smooth muscle that can control the diameter of the vessel. The outermost tunica externa is connective tissue that supports and anchors the vessels. Histologically, arteries have more pronounced tunica media than veins and more regular, rounded cross- sectional shapes. (Figure 1). Veins have thin layers of smooth muscle, frequently appear flattened or irregular, and sometimes venous valves can be seen in histological sections. Capillaries, by contrast, consist only of a tunica interna. Activity: Examine differences between arteries and veins on provided slides. 55
2. Systemic and Pulmonary Circuits: The cardiovascular system has both a systemic and pulmonary circuits. Pulmonary circulation is the movement of blood from the heart, to the lungs for oxygenation, and back to the heart again, as shown in figure 2. Oxygen- depleted blood from the body leaves the systemic circulation when it enters the right atrium through the superior vena cava and inferior vena cava. The blood is then pumped through the tricuspid valve into the right ventricle. From the right ventricle, blood is pumped through the pulmonary valve and into the pulmonary artery. The pulmonary artery splits into the right and left pulmonary arteries and travel to each lung. At the lungs, the blood Figure 2. Pulmonary Circuit of the Circulatory System. travels through capillary beds on the alveoli where external respiration occurs removing carbon dioxide and adding oxygen to the blood. Systemic circulation is the movement of blood from the heart, through the body to provide oxygen and nutrients, bringing deoxygenated blood back to the heart. Oxygen- rich blood from the lungs leaves the pulmonary circulation when it enters the left atrium through the pulmonary veins. The blood is then pumped through the mitral valve into the left ventricle. From the left ventricle, blood is pumped through the aortic valve and into the aorta, the body's largest artery. The aorta arches and branches into major arteries to the upper body before passing through the diaphragm, where it branches further into arteries which supply the lower parts of the body. The arteries branch into smaller arteries, arterioles, and finally capillaries. Waste and carbon dioxide diffuse out of the cell into the blood, while oxygen in the blood diffuses out of the blood and into the cell. The deoxygenated blood continues through the capillaries which merge into venules, then veins, and finally the venae cavae, which drain into the right atrium of the heart. From the right atrium, the blood will travel through the pulmonary circulation to be oxygenated before returning gain to the system circulation. Coronary circulation, blood supply to the heart muscle itself, is also part of the systemic circulation. 3. The Aorta: The aorta is the largest artery in the body, originating from the left ventricle of the heart and extending down to the abdomen, where it bifurcates into two smaller arteries (the common iliacs). The major segments of the aorta are: o Ascending aorta the section between the heart and the arch of aorta o Aortic arch the peak part that looks somewhat like an inverted "U" o Descending aorta the section from the arch of aorta to the point where it divides into the common iliac arteries Figure 3. The aorta. 56
Thoracic aorta the half of the descending aorta above the diaphragm Abdominal aorta the half of the descending aorta below the diaphragm These can be seen in Figure 3. The blood vessels of the system circulation branch off of the aorta. From the ascending aorta, the blood vessels that supply the heart, the right and left coronary arteries branch. From the aortic arch, branches the brachiocephalic (which then branches into the right common carotid and right subclavian), the left common carotid artery, and the left subclavian artery. From vessels that leave the thoracic aorta provide blood to the tissues surrounding the heart, the esophagus, and the diaphragm. Several vessels supplying the abdominal organs branch from the abdominal aorta including the celiac artery (whose branches include the gastric, hepatic and spleenic arteries. The paired renal arteries branch off near the level of L2. Near the level of the fourth lumbar vertebrae, the decending abdominal aorta branches into the right and left common iliac arteries. Activity: Identify the major branches of the aorta on heart and circulatory models. 4. Major Blood Vessels of the Head and Neck: The left and right common carotid arteries supply the head and neck. The left and right common carotid arteries follow the same course except that the right common carotid artery orginates from the brachiocephalic trunk and the left common carotid artery from the aortic arch. They divide in the neck to form the external carotid arteries which supply the face, neck andexterior of the head, and internal carotid arteries which supply the brain. Blood from the brain and neck flows back toward the heart via the internal jugular veins. The right and left external jugular veins drain from the facial muscles and superficial cranium. Both sets of jugular veins drain into the subclavian veins. 5. Major Blood Vessels of the Upper Limbs: 57
6: Major Blood Vessels of the Lower Limbs: 7. Veins of the Abdomen and Thorax: 58
Use the following diagram to identify major blood vessels (from the list provided by your instructor): Using models, identify the major arteries and veins of the human body. 59
Attributions: Figure 1. Tacoma Community College. (n.d.) [Arteries Histology]. Tacoma Community College. Figure 2. US Cancer Institute. (2006). [Pul]. Wikimedia Commons. Retrieved July 16, 2012 from http://en.wikipedia.org/wiki/file:illu_pulmonary_circuit.jpg. Figure 3. Edoarado. (2012) [Aorta artery and it's branches in anterior view]. Wikimedia Commons. Retrieved Dec 6, 2012 from http://commons.wikimedia.org/wiki/file:aorta_scheme_notags.svg. Figure 4. LadyofHats (2009). [Venous system]. Wikimedia Commons. Retrieved July 16, 2012 from http://commons.wikimedia.org/wiki/file:venous_system_en.svg. 60
Lab 16a Blood Vessels and Blood Pressure Name Section 1. Draw an example of an artery and a vein. 2. Identify the blood vessels: 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 61
3. Starting in the right hand, trace the pathway of an erythrocyte as it travels back to heart, becomes oxygenated, and carries oxygen to the left foot. Name specifically all blood vessels that are on your identification list that the erythrocyte travels through. Vessels not on the list can be included just using the terms: artery, arteriole, capillary, venule, or vein. 62