As Human Biology F221
OCR BIOLOGY UNIT F221
Blood tests
1. Put a band (tourniquet) around the arm to make the vein stand out
2. Clean the area around the vein with an alcohol based solution
3. Push a sterile needle, attached to a sterile syringe into the vein
4. Pull back the plunger of the syringe to suck the blood into the syringe
5. When the necessary volume of blood has been extracted, remove the syringe and needle, loosen the tourniquet and press a small ball of cotton wool over the wound, then apply a suitable dressing (plaster).
Making a blood film
1. Place a small drop of blood near the edge of a clean microscope slide
2. Place the end of another slide (the spreader) on the sample slide
3. Hold the spreader at an angle of approx 30oC and push it along the slide, spreading the drop of blood into a smear.
4. Label the slide with the patient’s details and allow it to air dry, so the cells stick to the slide
5. Fix the slide using alcohol, this preserves the cells
6. Stain the slide using a Romanowsky stain, e.g. Wright’s or Leishman’s. The stain is poured over the slide, left for approx 2 minutes and the excess is washed off with water.
Differential stain
E.g. Leishman’s, makes some structures appear darker or a different colour. In a blood film the nucleus of leucocytes will be stained purple, this allows neutrophils, lymphocytes and monocytes to be identified from each other by the shape of their nuclei.
Haemocytometer
A special counting chamber designed for counting blood cells. It has a central platform with grooves either side of it. There is a tiny grid etched onto the platform, this looks a bit like graph paper. In the centre of the grid there are some triple lined squares, these measure exactly 0.2 x 0.2 mm. When you put the cover slip on top the platform is exactly 0.1mm below the cover slip. This means that when you look at one of the triple lined squares under the microscope
Blood tests
1. Put a band (tourniquet) around the arm to make the vein stand out
2. Clean the area around the vein with an alcohol based solution
3. Push a sterile needle, attached to a sterile syringe into the vein
4. Pull back the plunger of the syringe to suck the blood into the syringe
5. When the necessary volume of blood has been extracted, remove the syringe and needle, loosen the tourniquet and press a small ball of cotton wool over the wound, then apply a suitable dressing (plaster).
Making a blood film
1. Place a small drop of blood near the edge of a clean microscope slide
2. Place the end of another slide (the spreader) on the sample slide
3. Hold the spreader at an angle of approx 30oC and push it along the slide, spreading the drop of blood into a smear.
4. Label the slide with the patient’s details and allow it to air dry, so the cells stick to the slide
5. Fix the slide using alcohol, this preserves the cells
6. Stain the slide using a Romanowsky stain, e.g. Wright’s or Leishman’s. The stain is poured over the slide, left for approx 2 minutes and the excess is washed off with water.
Differential stain
E.g. Leishman’s, makes some structures appear darker or a different colour. In a blood film the nucleus of leucocytes will be stained purple, this allows neutrophils, lymphocytes and monocytes to be identified from each other by the shape of their nuclei.
Haemocytometer
A special counting chamber designed for counting blood cells. It has a central platform with grooves either side of it. There is a tiny grid etched onto the platform, this looks a bit like graph paper. In the centre of the grid there are some triple lined squares, these measure exactly 0.2 x 0.2 mm. When you put the cover slip on top the platform is exactly 0.1mm below the cover slip. This means that when you look at one of the triple lined squares under the microscope