Blood and blood cells

Question 1

List the main functions of the blood

Answer 1

1. Connective tissue
2. Transport (connects every part of body)
3. Heat distribution
4. Immunity
5. Haemostasis
6. MAINTAIN HOMEOSTASIS (constant internal environment)
7. Blood volume (5l male; 3.5l female)

Question 2

Explain the importance, basic structure and role of haemoglobin

Answer 2

Structure;

1. 4 subunits: each a polypeptide with a haem group
2. Haem contains Ferrous iron (Fe2+)
3. Each Fe2+ binds one O2 molecule
4. Oxidized form (methaemoglobin – Fe3+) cannot carry O2
5. Different form in foetus with higher O2 affinity
6. 100ml blood: 15.8g (male) 13.7g (female)

Oxygen binding;

1. Haemoglobin low affinity for oxygen due to conformational shape of globin molecules
2. Oxygen binding beaks conformation and opens up structure
3. Second oxygen molecule binds more easily and so on
4. This is cooperative binding
5. Allows more oxygen to be carried

Question 3

Recall the essential features of an erythrocyte and list its major functions

Answer 3

1. Red cells
2. Respiratory transport O2 (haemoglobin) oxyhaemoglobin and CO2 (carbonic anhydrase) biocrbonte
3. Biconcave disc (maximizes surface area/ diffusion, flexible so squeeze through capillaries)
4. No nuclei or organelles
5. Molecules on surface confer blood group

Life cycle;

1. Produced in bone marrow from precursors which produce haemoglobin then lose organelles
2. Immature erythrocytes contain ribosomes: reticulocytes.
3. High circulating reticulocytes diagnostic (e.g. anaemia, chemotherapy)
4. Removed through reticulo-endothelial system (phagocytic macrophages in spleen)
5. Lifespan = 120 days (short, no nuclei; 1% or 250 billion cells per day)
6. Dependent on dietary iron (meat, egg yolk, nuts), iron deficiency causes anaemia

Question 4

Define anaemia and list the major causes and subclasses, classify according to red blood cell volume

Answer 4

“Low blood haemoglobin concentration”

1. Microcytic (small MCV):
   
   • Failure of haemoglobin synthesis
   • Fe deficiency:
     
     • menstruation (daily loss 1mg M; 2mg F)
     • GIT lesions or cancers
     • parasitic infection
2. Normocytic (normal MCV)
   
   • Acute blood loss
3. Macrocytic (large MCV)
   
   • DNA synthesis and cell division fail and reduced division of progenitor cells so fewer but larger erythrocytes.
   • Folic acid (required for thymine synthesis) deficiency : pregnancy
   • Vit B12 (needed for folic acids actions) deficiency: autoimmune disease, destroys B12 uptake in gut: pernicious anaemia; vegetarians, vegans

Question 5

Leukocytes

Answer 5

1. White blood cells
2. Use circulation for transport
3. Travel near capillary wall and invade tissue space to fight infection
4. Classified by structure and dye binding

Types;

1. Polymorphonuclear granulocytes:
   
   • Multilobed nuclei, many granules
     
     • neutrophils (phagocytic, abundant)
     • eosinophils (allergy)
     • basophils (produce histamine)
2. Lymphocytes (antibody producing)
3. Monocytes (phagocytic)

more info on polymorphonuclear grnulocytes

1. Segmented nucleus
2. Full of cytoplasmic granules
3. First on scene
4. Adhere to blood vessels in infected area and migrate to tissue
5. Engulf, kill and digest microorganisms
6. Release inflammatory mediators: toxic oxygen products, digestive enzymes, vasodilators, chemotaxins

Leukocytosis = raised e.g. infection, cancer

Leukopenia – low e.g. chemotherapy, HIV

Question 6

B-lymphocytes (B cells)

Answer 6

1. Mature in bone marrow
2. Humoral (antibody-mediated) immunity
3. Foreign antigen → immunoglobulin (antibody) production
4. Immunoglobulins: IgM; IgG; IgA; IgD; IgE
5. Antibody-antigen reactions: assist phagocytosis by precipitation; agglutination (clumping) or coating in antibody (opsonisation) or prevent attachment of mico-organism to tissues (neutralisation)
6. Primary immune response: first exposure, antibodies appear after latent period, peak then fall
7. Secondary response: greater, quicker, longer response due to memory cells (long lived B-lymphocytes)
8. Passive immunity = transfer of antibodies e.g through the placenta

Question 7

T-lymphocytes (T cells)

Answer 7

1. Thymus dependent (derived in bone marrow, migrate to thymus, acquire surface antigenic molecules and become immunologically competent)
2. Cellular immunity (i.e. not antibodies)
3. Circulate → foreign antigen → blast transformation → progeny with receptors for antigen
4. Activated T-lymphocytes → chemotaxins (attract macrophages); lymphotoxin (kills cells); interferon (kills viruses)

Question 8

Monocytes

Answer 8

1. Large, single horse-shoe nucleus
2. Appear after granulocytes
3. In tissue become macrophages (“big eaters”)
4. Engulf micro-organisms, tissue debris and dead polymorphs
5. Secrete inflammatory mediators and stimulate angiogenesis (vessel growth = repair)

Question 9

Normal leukocyte count

Answer 9

1. Neutrophils; 2.5 - 7.5 (40 - 75%)
2. Eosinophils; 0.04 - 0.4 (1 - 6%)
3. Basophils; 0.01 - 0.1 (<1%)
4. Monocytes; 0.2 - 0.8 (2 - 10%)
5. Lymphocytes 1.5 - 4.0 (20 - 45%)

Question 10

Platelets and Haemostasis

Answer 10

• Derive from megakaryocytes
• 2 - 3 µm diameter (small)
• Normal platelet count 25 x 104/ml
• Life span 8 - 10 days
• Granules
• Many organelles, no nucleus

Haemostasis

1. Express surface receptors for platelet activators (e.g. collagen in vessels or thrombin from coagulation cascade)
2. Adhesion to exposed collagen in wound or atherosclerosis
3. Release of granules promotes platelet aggregation
4. Platelets produce thromboxane A2 from cycloxygenase enzyme
5. Aspirin inhibits cycloxygenase and is anti-platelet
6. Involved in clot or thrombus formation
7. The vascular endothelium produces e.g. prostacyclin and nitric oxide which inhibit platelet activation

Question 11

Plasma

Answer 11

1. Fluid component of blood
2. Carrier
   
   • “Organic and inorganic substances dissolved in water”
3. Plasma proteins
   
   • Exert osmotic pressure to maintain blood volume
   • Albumins
   • Globulins
   • Fibrinogen – clotting, platelet aggregation
4. • Serum: plasma with proteins removed due to clotting