Blood

Structure and Function

Blood consists of plasma > contains dissolved solutes.
Made in bone marrow.
Leucocytes are white blood cells.

Erythrocytes > 7um > Biconcave disk, small and flexible shape, no nucleus > haemoglobin.
Platelets > Small cytoplasm and membrane > no nucleus.
Leucocytes:
Neutrophils > 9um > Small granules of cytoplasm, lobed nucleus > Engulf microbes by phagocytosis.
Lymphoctyes > 5.5um > large nucleus, little cytoplasm, B and T > B produce antibodies, T destroy infected cells.
Monocytes > 13 - 20um > Large cells, bean shaped nucleus > Macrophages after 3 days in blood.
Macrophages > 15 - 20um > Large phagocytic cells in blood, also fixed.

Taking a Sample

• Taken from vein in arm or hand.
• Apply tourniquet > vein stands out.
• Alcohol swab cleans area.
• Sterile neelde sucks blood into syringe.
• Cotton wool applied.
• Gentle pressure stops bleeding.
• plaster applied.

Blood Smear

• Blood smear/thin film is made > spread blood across slide using second slide.
• Labelled > allowed to dry.
• Foxed using alcohol.
• Differential stain added > Left for 2 minutes (heat?)
• Washed off using water.

Haemocytometer

• Slide etched with grid > total volume 0.1mm^3.
• Blood diluted to 1 in 200 dilution with blood pipette.
• Cells counted in 5 of the 0.004mm^3 squares.
• White cells > dilution factor is 1 in 20.
• Dilutin fluid > red cells burst > white cells counted.
• Larger squares used > volume of 0.1mm^3.