Blood Characteristics

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Blood Characteristics Plasma is the fluid portion of the blood (55 percent). Cells (45 percent) Erythrocytes are red blood cells. They are responsible for oxygen distribution.

3 Blood Characteristics Plasma is the fluid portion of the blood (55 percent). Cells (45 percent) Erythrocytes are red blood cells. They are responsible for oxygen distribution. Leukocytes are the white blood cells; they are responsible for cleaning the system of foreign invaders. Thrombocytes or platelets are responsible for blood clotting. Serum is the liquid that separates from the blood when a clot is formed.

8 Blood Terminology ABO blood groups based on having A, B, both, or no antigens on red blood cells Rh factor may be present on red blood cells; positive if present and negative if not Antigen a substance that can stimulate the body to make antibodies. Certain antigens (proteins) found in the plasma of the red blood cell s membrane account for blood type. Antibody a substance that reacts with an antigen Agglutination clumping of red blood cells; will result if blood types with different antigens are mixed

9 Blood Typing Blood type A has antigen A on the surface of the cell and will agglutinate with blood type B. Blood type B has antigen B on the surface of the cell and will agglutinate with blood type A. Blood type AB has antigens A and B on the surface of the cells and will not agglutinate with either type A or type B blood. Blood type O has neither antigen A nor B and will not agglutinate.

11 Blood Groups Type Antigen Antibody Can Give Blood To Can Get Blood From A A B A, AB O, A B B A B, AB O, B AB A and B Neither A nor B AB A, B, O, AB O Neither A nor B A and B A, B, O, AB O

14 Conditions Affecting Shape of Blood Droplet Size of the droplet Angle of impact Velocity at which the blood droplet left its origin Height Texture of the target surface On clean glass or plastic droplet will have smooth outside edges On a rough surface will produce scalloping on the edges

collected from the scene and determine the height from

17 Blood spatter evidence recovered. Determine the diameter of the blood spatter evidence collected from the scene and determine the height from which the blood drop fell. (This may reflect the height of the wound and help determine the site.)

19 BLOOD SPATTER LAB Relationship Between Blood Drop Shape and Impact Angle Materials Needed per Group Simulated Drip and Projected Blood 5 X 8 notecards 15 cm and 30 cm rulers Impact angle apparatus Tape

20 Assembling the Impact angle apparatus Tape one end of the clipboard to a table by making a hinge out of tape. The clipboard should be right at the edge of the table. Hold the protector to the edge of the clipboard so that the protractor is perpendicular to the table top and aligned so that the center of the protractor is at the edge of the hinged-end of the clipboard. See the figure in the next slide.

21 Impact Angle Apparatus Clipboar d Protractor Table 30 º 60 Tape

22 Select an Impact Angle to Study Your data table (on your worksheet) includes angles from 10 to 90. Once you have selected an impact angle, indicate the angle on the card and then attach the card to the board.

23 Clipboard Clip Notecard Clipboard

24 Directions continued. Set the angle of the board using the protractor so that the board will have the correct impact angle. You will need to work together as a team to achieve this. To obtain the desired impact angle, set the impact angle board to a protractor setting of 90 minus the desired impact angle. (For example, to obtain a 60 impact angle, set the board at a protractor setting of 30 ).

25 Directions continued. Using the Simulated Drip and Projected Blood, place the dropper at approximately 30 cm above the impact angle board. Allow two to three drops to fall sequentially onto the card. Move your hand so that the drops don t overlap. Using multiple drops will allow you to see the variation that single drops may display when striking the surface. Leave the card in position for 2-3 minutes before carefully removing it.

26 Directions continued.. Allow the drops to dry thoroughly on the cards and then store in a safe place. When we return, we will record your observations including a sketch in the data table provided. We will also include the diameter and length of the circle or ellipse created.

28 Calculations with Blood Spatters To find the point of hemorrhage (POH), you must first determine the two-dimensional point of convergence (POC). The POC is the intersection where lines drawn through the center of the individual drops meet (at the X-Y axis intersection). This is determined by drawing lines or placing strings through the long axis of individual spatters.

29 Point of Convergence (POC)

31 Can you complete this one?

32 Angle of Impact (AOI) The AOI for representative bloodstains helps to generate the 3 rd dimension (z-axis) in a crime scene. This shows how high up off the ground the impact occurred.

33 To Determine the Angle of Impact (AOI): i. Where opposite = width (W) and hypotenuse = length (L) i. Angle of impact = ArcSIN of W/L ratio a) First calculate ratio (W/L) b) You should remember that you can use SIN - 1 (2 nd key) to get degree of AOI.

Unit 5: Blood and Blood Stain Analysis

Unit 5: Blood and Blood Stain Analysis Name Period Blood Composition and Function By the end of this chapter you will be able to: Explain the composition of blood Describe the function of blood cells Determine the blood type of a blood sample