Blood components

How can we check blood?

• Most commonly by venepuncture

• Each vacutainer is colour coded to describe its contents

• Tubes are lined with additives often to prevent coagulation, however how this is done depends on what tests will be run later,

  • Heparin

  • Citrate

  • EDTA

• Sometimes a procogulant tube is used to obtain a clotted sample

What are plasma proteins?

• Normal level of plasma proteins is 60-80g/L

• Albumin maintains osmotic pressure and transports insoluble molecules

• Globulins (a,B,y) transport ions, hormones and lipids assist in immune function

• Fibrinogen - ‘molecular glue’ involved in blood coagulation

What are leukocytes?

• Also known as white blood cells

• 3 main types

  • Granulocytes

  • Lymphocytes

  • Monocytes and macrophages

What are neutrophils?

• Life span: 6h to a few days

• Most numerous leukocyte

• Defence against bacteria (mainly) and some fungi

• They are active phagocytes, engulfing bacteria and destroy them using enzymes stored within lysosomes

• Produce reactive oxygen species such as hydrogen peroxide to degrade the pathogen.

What are eosinophils?

• Life span: ~5 days

• Large coarse granules that stain red with acid dyes, filled with a unique variety of digestive enzymes

• Lead attack against parasitic worms that are too large to be phagocytosed

• When they encounter a worm many cells gather around it and released their cytoplasmic granules onto the parasite surface, digesting it.

• Differentiate from myeloid progenitor cell

What are basophils?

Life span: a few hours - a few days

Large coarse granules that stain purple/black with basic dyes pack the cytoplasm

Filled with histamine (an inflammatory mediator) that acts as a vasodilator

What are mast cells?

• Generated in the bone marrow and terminal differentiation & proliferation occurs in the target tissue.

• Important role in allergic reactions and inflammation, involving the release of histamine from their secretory granules

• Important in defence against parasites because they recruit other types of leukocytes

• Involved in angiogenesis

What are monocytes and macrophages?

• Life span: months

• Monocytes present in circulation for 1-3 days

• First line of defence against viruses

• Also phagocytose dead cells and bacteria

• Circulating monocytes are precursors of tissue macrophages (which are actively phagocytic)

• Important in the inflammatory response

What are lymphocytes?

• Large nucleus (dark), small amount of cytoplasm (blue).

• 6-14um diameter

• Most circulate in lymphoid tissues and lymph, only in blood for a few hours at a time.

• 3 types:

• B-Lymphocytes (B-cells)

• T-lymphocytes (T-cells)

• Natural Killer cells (NK cells)

What are B-lymphocytes?

• Main role to destroy bacteria and inactivating their toxins

• Differentiate into plasma cells that secrete antibodies when stimulated by antigen

• Antibodies are immunoglobulins that act against antigens by:

• Agglutination

• Opsonisation

What are T-lymphocytes?

• T-lymphocytes mature in the thymus

• Recognise specific foreign proteins

• Attack cells that have been infected by viruses and tumour cells.

• Responsible for the rejection of transplanted organs

• Stimulate B-cells to produce antibodies

What are natural killer cells?

• Attack a wide variety of infected body cells

• Also detect and control early signs of cancer

• Specialized NK cells found in the placenta, suggested to protect against infection during pregnancy.

• Recruit macrophages and other immune cells to enhance the immune response.

What are platelets?

• Also called thrombocytes

• Promote blood clotting when blood vessels are damaged

• Generated in bone marrow by budding off from megakaryocytes, each producing 5 - 10,000 platelets

• Lifespan = ~5-9 days

• Physical features:

• No nucleus

• 2-4mm diameter

• ~1 x 1011 platelets/day produced by a healthy individual

What are erythrocytes?

• red blood cells

• the most abundant cells in the blood

• physical properties

  • small

  • biconcave disc

  • lacking a nucleus and most organelles

  • lifespan of 120 days

• Function: transport O₂ and CO₂ facilitated by haemoglobin

• To maintain equilibrium

What is erythropoiesis?

• Process of generating mature erythrocytes (red blood cells)

• Regulated in a feedback process by the hormone erythroprotein (EPO)

• Cytokines, growth factors and hormones influence erythyroid proliferation, differentiation and maturation.

How is erythrocyte broken down?

• Proteases degrade hameoglobin in lysosomes of macrophages

• Globin is broken down into amino acids and re-used

• Haem is degraded into bilirubin, which is then metabolised and bile acids are used to make it soluble

• Fe²⁺ is recycled: it binds transferrin to be transported to the bone marrow for the new erythrocyte synthesis

• 10% of the old cells haemolytic in the circulation, engulfed by circulating monocytes.

What. is haematocrit?

• Useful to estimate proportion of erthrocytes in a blood sample to indicate O₂ carrying capability

• Haematocrit (Hct):

  • proportion of blood made up by cells (erythrocytes and leukocytes)

  • given as a ratio

  • also known as packed cell volume (PCV)

What happens when you need blood?

• saline, a salt solution, can be used to increase blood volume

• Fresh frozen plasma

• platelets

• packed red blood cells - whole blood from which most of the plasma and the leukocytes have been removed

• Replacement coagulation factors - for patients with genetic disorders

• Activated coagulation factors - for patients with genetic disorders

• activated coagulation factors

• fibrinolysis inhibitors