Name: ______Hour: ______
Observing Blood Under a Microscope
Anatomy & Physiology/Cardiovascular Unit
Pre-Lab Warm-Up
The circulatory system carries blood throughout the body, delivering materials to cells and picking up cell wastes. The blood is moved by the rhythmic contractions of the heart. The liquid portion of the blood is called plasma. In addition, blood also contains red blood cells, several types of white blood cells and cell fragments called platelets. Red blood cells carry oxygen. White blood cells provide protection against disease. Platelets are involved in the clotting process. Blood is unique among all the tissues of the body because it is a liquid.
Blood leaves the heart through blood vessels called arteries. Arteries branch into smaller blood vessels called arterioles as they move throughout the body. The smallest blood vessels are called capillaries, which weave together to form capillary beds. Capillaries have thin walls. Through these walls, materials can diffuse into and out of the blood to service the body cells. Blood leaving the capillaries flows back to the heart through small vessels called venules, which thicken as they merge into larger vessels called veins.
Except for some microscopic capillaries, the walls of blood vessels have three coats, or tunics. The tunica intima, which lines the lumen or interior of the vessels, is a thin layer of endothelium (squamous epithelial cells). Its cells form a slick surface that decreases friction as blood flows through the vessel. The tunic media is the bulky middle coat. It is mostly smooth muscle and elastic tissue. The smooth muscle, which is controlled by the nervous system, is active in changing the diameter of the vessels. As the vessels constrict or dilate, blood pressure increases or decreases, respectively. The tunica externa is the outermost tunic. It is composed largely of fibrous connective tissue. Its function is basically to support and protect the vessels.
The walls of arteries are usually much thicker than the walls of the veins. Their tunica media, in particular, tends to be much heavier. This structural difference is related to difference in function of these two types of vessels. Arteries, which are closer to the pumping action of the heart, must be able to expand as blood is forced into them and then recoil passively as the blood flows out. Their walls must be strong and stretchy enough to take these continuous changes in pressure.
Veins, on the other hand, are far from the heart in the circulatory pathway, and the pressure in them tends to be low all the time. Thus, veins have thinner walls. However, since the blood pressure in veins is usually too low to force the blood back to the heart and blood returning to the heart often flows against gravity, veins are modified to ensure that the amount of blood returning to the heart equals the amount being pumped out of the heart at any time. The lumens of veins tend to be much larger than those of corresponding arteries, and the larger veins have valves that prevent backflow of blood.
Pre-Lab Questions
1.
Label the following idealized diagram using the following terms: artery, vein, arteriole, venule, capillary:
2.
Label the following more realistic diagram using the same terms as Question 1:
3.
Label the following electron microscope image using the following terms: erythrocyte (red blood cell), leukocyte (white blood cell) and thrombocyte (platelet):
4. Complete the following table with information about the layers or “tunics” of the blood vessels:
Tunica Intima / Tunica Media / Tunica ExternaWhich layer is it?
What is it made of?
What is its function?
5. What are two differences between arteries and veins?
6. Explain how these differences are related to the specific function of each blood vessel.
Observing Blood Under a Microscope Lab
Purpose: Observe blood cells under a microscope using a sample of simulated blood.
Procedure:
Materials: Microscope, Prepared blood smear slide, Prepared slide of artery and vein
1. Obtain a prepared blood smear slide. If you are using simulated blood, rather than a prepared slide, follow your teacher’s instructions on how to prepare the slide.
2. Place the slide under a microscope and focus the sample on low power. Switch to high power, refocus and observe.
The blood smear has been stain with Wright’s stain making the red blood cells appear pink. The white blood cells can be identified by their dark blue nuclei and the platelets appear as solid blue specks.
3. Draw a diagram of the blood cells as they appear under the microscope in the space provided below. Label each type of cell you observe in your drawing.
4. Obtain a prepared slide of a vein and artery.
5. Place the slide under a microscope and focus the sample on low power. Switch the high power, refocus and observe.
6. Draw a diagram of both the vein and the artery in the appropriate box below. Label the layers of tissue that make up the vein and artery in your drawing.
Vein Artery
Post Lab Follow-Up Questions
1. Describe the size, appearance and relative number of red blood cells in the blood smear.
2. Describe the size, appearance, and relative abundance of white blood cells in the blood smear.
3. Describe the size, appearance and relative abundance of platelets in the blood smear.
4. If a blood smear shows a higher than normal number of white blood cells, what might this indicate to a doctor?
5. Compare the size and appearance of the tunics of the vein and the artery.
6. Compare the size and appearance of the lumen of the vein and the artery.
7. What would be the result of decreasing the thickness of the artery’s tunics?
8. What would be the result of decreasing the thickness of the vein’s lumen?
Extension Activity
If available, examine prepared slides of sickle cell anemia and/or leukemia.
Label each diagram with the type of sample being observed. Pay special attention to the shapes of the cells and the ratio of different types of cells. Note any differences between these slides and normal blood slides.
What differences did you observe in these cells as compared to the first cells you observed? ______
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