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Bio unit 4 lesson 2.odt

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BLG 144
Richard Stew

y _ d o _ Circulation Review Unit #4 Lesson 2-3 Questions y o 1. Describe the differences between arteries and veins. u - arteries carry blood away from the heart towards the rest of the body _ - veins carry blood toward the heart f a - most arteries carry oxygenated blood i - most veins carry deoxygenated blood - pulmonary artery carries deoxygenated blood from the heart to the lungs n - pulmonary vein carries blood from the heart back to the lungs t - artery has elastic walls _ - vein has thinner wall with a larger circumference and lacks elasticity i f _ 2. Describe capillaries. y Capillaries are the smallest blood vessels, typically less than 1 mm long. They reach o every corner of the body. Capillaries have a diameter that is so small that red blood cells travel in single file through them. The thin walls allow exchange of materials u between blood and cells. Even though capillaries are the smallest blood vessels, _ they have the largest total surface area. s t a 3. What function do capillaries serve? n In a closed circulatory system, blood always remains inside the capillaries. It never d flows out to bathe the body's cells directly. Since the capillaries have very thin _ walls, all exchange takes place inside the capillaries. Capillaries regulate the f movement of fluids and other materials into and out of the blood stream. Blood o releases oxygen and nutrients, and picks up carbon dioxide and wastes. r _ 4. What causes a pulse? a A pulse is caused by a heart beat. The classic “lub-dup” sound is caused by the _ opening and closing of valves as they open to allow blood to be pushed out and l close to prevent blood from being sucked back into the heart. The “lub” sound is o the sound of the atrioventricular valves closing and the “dup” sound is the sound of n the valves between the ventricles and arteries snapping shut following the g contraction of ventricles. _ t i 5. What is the function of the pulmonary and aortic m semilunar valves? e The valves prevent blood from flowing back towards the heart because the left and right ventricle relax after contracting and forcing the blood out the heart through # the pulmonary vein and the aorta. i x z 6. In what kind of vessel is blood pressure highest? z The aorta (arteries) has the highest blood pressure because the blood needs to be 1 carried to the rest of the body so cells can use the oxygen in the blood for cellular d respiration. This process must be done very fast since our body has trillions of cells, and therefore, there is a need for a stronger force to move the blood through the X s aorta rapidly. Arteries have elastic walls which expand as a wave of blood passes z through and then snap back, keeping the blood flowing in the right direction and t d d w proving an exertion of force to keep the blood moving at a rapid pace. Thus, the blood pressure is highest in the aorta. 7. If blood pressure is low in the veins, explain how blood is returned to the heart? Since veins lack elasticity, they also lack the ability to contract so that blood flows through them at a fast rate. As a result, blood flows much slower in the veins when compared to arteries. In regions above the heart, gravity aids in moving blood back down faster through the veins to the heart. However, in regions below the heart, the blood must be pushed against the force of gravity, causing it to travel very slowly. To make up for the veins lack of ability to contract like the arteries, the blood is pushed forward when skeletal muscles contract because this exerts pressure on the veins lying in between the muscles. The pressure from the muscles aid in moving the blood forward. Veins are also equipped with one way valves which help to keep the blood moving toward the hard without fear of it being pushed backward due to a lower pressure. 8. It is not unheard of for soldiers to faint after standing at attention for a long period. Explain. In long standing cases, the leg muscles do not contract to compress the veins containing deoxygenated blood, and this delays the upward movement of the blood. This leads to pooling of blood in the leg's veins as the blood fails to ascend upward against gravity. As a result, the heart and brain do not receive enough blood and blood pressure drops. As a defense it shuts down to protect itself from damage, which leads to fainting. 9. Define vasoconstriction and vasodilation. Since arteries and arterioles have elastic walls, their diameter can be changed
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