Biology AS (1)

ocr as human biology molecules,blood and gas exchange. 


Blood tests

  • Cells in the blood can provide info about health, and help to diagnose a number of conditions. 
  • Blood samples is taken that is large enough for several differnt tests can be carried out 
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Taking a blood sample.

  • Most blood samples are taken from a vein, commonly from around the elbow.

1. Tie a band (tourniquet) around the arm to make the vein stand out. This makes it easier to target the needle. 

2.You clean the area around the vein with an alcohol-based solution. 

3. You then push a sterlie needle into the vein, which is attached to a sterlie syringe.

4.As you pull the plunger back, blood is sucked into the syringe.

5. When enough blood has been removed,you remove the needle and place  cotton wall on the wound.

6. You press this for about 2 minuites untill the bleeding stops, then apply the dressing.

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making and staining a blood film.

Some of the blood taken by a sample, involves looking at it under a microscope, after the cells are stained.

In a pathology lad blood films are made by a machine

They are labelled with a barcode so the info can be stored on a computer. 

1.Place a very small drop of blood near the end of a clear microscope slide

2. Place the end of another slide (the 'spreader') on the sample slide. 

3. Hold the spreader at an angle of about 30 degree and push it along the slide, spreading the drop of blood as a smear.

4. Lable the slides with the patient's details. 

5. Allow the slide to dry in the air, so the cells stick to the slide. 

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6. Fix the slide using alcohol.

9.Stain the slide usinbg Romanowsky stain, such as Wright's or Leishman's stain. 

10.The stain is poure over the slide and left for about 2 minutes before being washed off with water. 

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A differential stain, such as Leishman's stain, makes some structures appear darker  or different in color from other structures.

In a normal blood sample the nuclei:

  • Leucocytes's will be stained purple 
  • Neutrophils, Lymphocytes and Monocytes to be identified by their nucleus shape. 
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Megaloblastic anemia

When a blood smear is made by a patient suffering from this, the red blood cells are larger and have an abnormal shape. 

The cause is usually a deficiency of Vitimin B12

It is reffered to as 'pernicious'

Increasing levels of iron will have no effect. 

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1. suggest why? 

  a) the equipment used to make a smear is sterile 

  b) the skin is cleared with an alcohol-based solution before taking the sample 

  c) blood is taken from the vein rather than a artery (hint: think about the structure and functions of veins and arteries.) 

2. when making a blood film suggest why 

a)the blood film must be very thin. 

b) the stain is used

c)The slide must be very clean and grease-free. 

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1, a)so that no pathogens/bacteria are introduced into the body 

b)To make sure there are no bacteria/pathagens on the skin, as these could enter the wound and cause an infection 

c)Veins are wider and nearer to the surface and have thinner walls, so it is easier to insert a needle. Also the blood in a vein is under less pressure, so there will be less bleeding afterwards. 

2. a)So that the cells can be distinguished from each other when viewed under a microscope.

b)To enable the blood cells, and the structures within then to show up more easily. 

c) So that the blood cells will stick to the slide. 

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3 starrs shitttt

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