Name: _______________________________________________ Period: _____ Date: ____________ Lab – Anatomy of the Mink Part Two: Cardiovascular and Respiratory Systems Introduction The respiratory system functions as a gas exchange mechanism between the external medium (air) and the blood. The respiratory system is comprised of the nose and nasal passages, pharynx, larynx, trachea, lungs, and diaphragm. Air enters the body through the nose or mouth, is directed into the trachea (windpipe) when the epiglottis (small muscular flap) is open, and is distributed in the lobes of the lungs. The trachea has cartilage rings around it to prevent the windpipe from collapsing, therefore allowing for a smooth flow of air. The diaphragm is an upside down U-shaped muscle that controls the process of breathing. When contracted, the diaphragm pulls the lungs down which increases the volume of the lungs. This increase in volume decreases the pressure inside, causing the air pressure in the atmosphere to be greater. The air moves from high pressure (outside of the lungs) to low pressure (inside the lungs)—a process we simply call ―breathing in‖. When the diaphragm muscle is relaxed, the volume of the lungs decreases causing the pressure to increase. This causes the air inside the lungs to be pushed from high pressure (inside the lungs) to low pressure (outside the lungs)—a process we simply call ―breathing out‖. Once air has reached the lungs, oxygen diffuses across the membranes of the alveoli into the blood, which carries it to the tissues with the help of hemoglobin (a protein in the red blood cells). Oxygen is used by the mitochondria of the cells during cellular respiration (metabolism of glucose). Carbon dioxide is produced as a waste product of this same cellular metabolism. The carbon dioxide that is picked up by the blood from the tissues is released to the medium (air) by diffusion through the alveoli membranes as well. Increased surface area allows the lungs to be very efficient in their gas exchange. The cardiovascular (circulatory) system functions as a transportation system of materials between the lungs, heart, and body tissues. It is comprised of a closed system of vessels containing a liquid, blood, which is pumped by the muscular heart. The blood transports nutrients, wastes, hormones, gases, and cells (white blood cells, red blood cells, and platelets) within the body. Arteries are the vessels that carry oxygenated blood away from the heart, thin capillaries allow for gas exchange between the body/lung tissues and the red blood cells, and veins carry deoxygenated blood back to the heart. These blood vessels are more easily seen if injected with colored latex; red latex is used to inject the arteries and blue latex is used for the veins. The cells of the blood transport gases (red blood cells), repair wounds (platelets), and fight infection (white blood cells). The heart is the muscle that pumps the fluid blood, moving it in a circular manner carrying nutrients and oxygen to the tissues and carrying away carbon dioxide and waste products. The chambers of the right side of the heart (right atrium and right ventricle) are reserved for deoxygenated (oxygen-poor) blood while the chambers of the left side of the heart (left atrium and left ventricle) have oxygenated (oxygen-rich) blood pass through. In addition to transporting nutrients, gases, and wastes, the blood also transports heat. Blood is warmed by the heat generated during muscle contraction and cooled in the skin that is in contact with the air. Advance Preparation Please answer the following questions in complete sentences, after reading through the entire lab… 1. Is the blood that enters the right atrium oxygen-rich or oxygen-poor? In the superior vena cava? 2. Blood that enters the inferior vena cava comes from what part of the mink? 3. What vessels carry blood to the heart? Are these usually oxygen-rich or oxygen-poor? What is the one exception to this rule? 4. What artery/arteries will you seeing lying on top of the heart? 5. What is the purpose of having cartilage rings in the trachea and bronchi? 6. Why is red latex used to inject the arteries? Blue for the veins? Procedure Structures of Interest Circulatory Heart Aorta Inferior vena cava Superior vena cava Coronary arteries Pulmonary arteries/veins Respiratory Mouth/nares Epiglottis Larynx Trachea Bronchi Lungs (5 lobes) Diaphragm 1. Take your scissors or scalpel and cut a line from the abdomen all the way up to the chin of the mink, staying just to the left or right of the sternum (breastbone) and trachea. Keep the tips of the scissors pointed upward to keep them from jabbing down into the organs underneath. Be very careful that you do not puncture the trachea (windpipe), which lies just deep to the throat. Fully expose the thoracic (chest) cavity. You will need to cut through and detach the diaphragm, a muscle that separates the two cavities. 2. You will be looking in the thoracic cavity for the remainder of this lab. When looking for the heart one first notices the thymus gland. This triangular gland lies over the heart and is part of the immune system, not the circulatory system. It is important in the maturing of T-cells (―T‖ because of thymus.) It is relatively large and usually a light tan color. Push the thymus to the side. 3. When looking at the heart (see diagram below) you may see a number of different blood vessels on the heart muscle itself. These are the coronary arteries. If the coronary arteries were to become blocked by fatty deposits (as is the case in atherosclerosis) blood flow to the heart muscle cells would be restricted. If there is not enough blood flow, a heart attack will result. Right View of Heart Left View of Heart 4. Locate the dark, muscular flaps called auricles (―little ears‖) that are at the top of the heart. These chambers help the atria store blood before delivering it to the ventricles. 7. Let’s trace the path of the blood through the heart and lungs. Oxygen-poor blood enters the right side of the heart through the inferior and superior vena cava. Carefully turn the heart to your right and pick away some of the membranous tissue. You should see the large blue superior vena cava entering the right atrium from the top of the heart (returning all the blood from the upper body to the heart). From the bottom of the heart you may also be able to see the blue inferior vena cava (returning all the blood from the lower body to the heart). This may be difficult to see while the heart is in situ, but be careful not to damage the lung tissue or bronchi! 8. The blood will then travel to the right ventricle where it will be pumped from the body to the lungs. The blood leaves the right ventricle through the pulmonary arteries, which carry the blood to the lungs. One pulmonary artery carries blood to each lung, where the blood will pick up oxygen and release carbon dioxide to be exhaled. The now oxygen-rich blood will return to the heart through pulmonary veins. These pulmonary veins will now deliver the blood to the left atrium. The blood will then pass down to the left ventricle where it will be squeezed under a very high pressure out of the heart. It will be very difficult to identify the pulmonary vessels, but you should understand this pathway and what type of blood they carry. 9. The oxygen-rich blood leaves the left ventricle through the largest artery of the body, the aorta. You should find the large, red aorta emerging from the top of your mink’s heart. It is often a thick, muscular tube that goes behind the heart, where it will further divide into smaller and smaller arteries, delivering blood to all of the other tissues of the body other than the lungs. Push the mink’s left lung to your left and following the aorta along the dorsal thoracic wall. The aorta goes through the diaphragm into the abdominal cavity. 10. Remove the cardiovascular system intact as follows: heart, aorta (at least 1 inch long), superior vena cava (at least 1 inch long), and the inferior vena cava (at least 1 inch long). You may want to take the cardiovascular system out with the respiratory system so read on! 12. You will now need to do a little digging (a.k.a. removing muscle and fat tissues). Clean out the area surrounding your mink’s neck until you actually see the larynx. Carefully look directly below the larynx (on top of the trachea) for a small mass of brown tissue called the thyroid gland. This is not part of the respiratory system. Instead, it is part of the endocrine system because it releases hormones that control the rate of metabolism directly into the blood. 13. Continue cleaning posteriorly, following the cartilaginous tube that extends from the larynx. This will take time! Be patient, but thorough. It is best to use a probe to do this, however feel free to use scissors to cut out some of the tissues if your mink is quite large and has a lot of tissue here. The cartilaginous tube that you are uncovering is the trachea, or ―windpipe‖. The trachea has many C-shaped cartilage rings within its walls. These rings keep the trachea open so that air can easily pass to the lungs. 14. The open part of the C faces to the dorsal side of the trachea where the esophagus fits. This allows the esophagus to easily fit in the space. Push the trachea to the side slightly and you should be able to see the thin, flat esophagus directly behind it. Use your probe to sweep away any connective tissue holding these two tubes together; the esophagus will be removed with the digestive system. 15. Note the lungs in the thoracic cavity, which are surrounded by ribs. Note that the left lung has three lobes (apical, cardiac, and diaphragmatic lobes) and the right lung has four lobes (apical, cardiac, diaphragmatic, and intermediate lobes). The fourth lobe of the right lung lies posterior to the heart. 16. At the very posterior end of the trachea when it reaches the lungs, the trachea divides into two tubes, with one going to each lung. These two tubes are called bronchi. See whether you can follow the trachea down far enough to see where it branches in your mink. The bronchi have the same structure as the trachea, including cartilage rings. Within each lung the bronchi further subdivide into smaller and smaller tubes, called bronchioles. The bronchioles have no cartilage rings. The pharynx, larynx, trachea, and bronchi allow for no gas exchange. They only serve to bring air into the microscopic alveoli, the tiny air sacs of the lungs, where gases can be exchanged. 17. Take your scissors and cut at the very top of the trachea such that you cut across the tube as close to the pharynx as possible. If you want extra credit, keep the tongue attached to the trachea. Carefully remove the larynx, trachea, lungs, and circulatory system listed above all as a single unit. You can also receive extra credit if you can blow up the lungs by inserting a straw into the trachea (this means you can’t have damaged any of your bronchi/bronchioles!) and/or leave the tongue attached to the trachea. 18. With the time that remains, review previous systems, structures and functions in your mink. Place the respiratory tree back into your mink, wrap in a moist paper towel and bag, and return to the instructed area. Clean up your table thoroughly. Interior of the Heart 19. Use the scalpel to carefully cut longitudinally through the heart so that you can see the thickness of the atria and ventricles. Which is thicker…atria or ventricles? Why do you think this is so? Do you notice a difference in thickness between the left and right sides of the heart? Why do you think this is so? 20. Blood does not mix from the right and left sides of the heart. A thick muscular wall between them called the septum separates the two ventricles. This will be difficult to locate since you just cut through the heart – you probably also cut through it!
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