Introduction to the Structure and Function of Blood

Question 1

What are red blood cells like?

Answer 1

Red blood cells (RBC)
Aka Erythrocytes
Biconcave discs
No nucleus and do not contain DNA, RNA or mitochondria
120 days lifespan
Major constituent is the protein haemoglobin
Hb binds oxygen

Question 2

What are white blood cells like?

Answer 2

White blood cells (WBC)
Aka Leukocytes
Colourless
The two most common types are:
Neutrophils
Lymphocytes
Neutrophil:
Polymorphonuclear- Irregular, multi-lobed nucleus
Granulocyte- prominent cytoplasmic granules

Question 3

What are three types of granulocytes?

Answer 3

Neutrophils- weakly staining granules, commonest white blood cell
Eosinophil- granules stain red with eosin
Basophil- granules stain blue/purple with basic dyes

Question 4

What are mononuclear cells?

Answer 4

Lack granules
Large, regular nuclei
Two types:
Monocyte- largest type of wbc
Lymphocytes

Question 5

What are platelets

Answer 5

Platelets (aka thrombocytes)
Cytoplasmic fragments 
No nucleus
Membrane bound
Contain granules

Question 6

Where do blood cells come from?

Answer 6

Mature blood cells are produced from stem cells in the bone marrow
Bone marrow contains many immature cells
Some blood disease can be treated with a bone marrow transplantation

Question 7

What is plasma?

Answer 7

Fluid containing:
Water
Salts
Proteins
Organic molecules e.g. metabolites, carbohydrates, lipids
Ionic constituents of plasma
Positive ions (cations)
Sodium Na+
Also potassium, calcium, magnesium and hydrogen ions
Negative ions (anions)
Chloride Cl-
Also bicarbonate, phosphate, sulphate & organic anions

Question 8

What is the difference between plasma and serum?

Answer 8

Plasma is the fluid component of whole blood
Serum is the fluid left after blood clotting
Some blood tests require unclotted blood (you can use anticoagulants e.g. EDTA)
Other tests work better with serum than plasma

Question 9

What are the functions of blood?

Answer 9

1. TRANSPORT
   Carry oxygen/nutrients to tissues
   Remove CO2/ other waste products from tissues
   Transport other substances (e.g. hormones) from sites of production –> sites of action
   
   2. DEFENCE
      Immunity- WBC and plasma proteins
      Clotting (aka haemostasis)- platelets and plasma proteins
   3. HOMEOSTASIS
      Keeping the internal environment of the body constant:
      Maintaining pH (7.4)
      Controlling distribution of water and solutes
      Distributing heat

Question 10

What role do erythrocytes play when it comes to transport?

Answer 10

Transport oxygen from lungs –> body tissues
Help in removal of CO2 from body tissues —> lungs
Most CO2 carried as bicarbonate in plasma
Red cell enzyme carbonic anhydrase helps CO2
To dissolve in plasma in the tissues and come out of solution in the lungs

Question 11

What is haemoglobin?

Answer 11

Haemoglobin is a protein tetramer made up of 4 polypeptide chains-
○ 2 alpha globin chains
○ 2 beta globin chains
Each globin chain carries a haem molecule
The haem holds a ferrous (Fe++) iron atom
Oxygen binds reversibly to the iron atom
Oxyhaemoglobin
○ Fully saturated with O2 = bright red
Deoxyhaemoglobin
○ Lost all O2 = dark red
Basis of pulse oximetry
Measures the colour of the haemoglobin
Determines if patient is hypoxic

Question 12

What do plasma proteins do?

Answer 12

Plasma proteins carry substances which are poorly soluble in water e.g.
○ lipids
○ lipid soluble hormones and vitamins
Plasma proteins also carry metal ions e.g. Ca++, Fe++, Cu++
Example:
Albumin acts as a general purpose carrier
But many substances have a specialised carrier e.g.
○ Thyroxine binding globulin (TBG)
○ Transferrin

Question 13

What are the different types of white blood cells?

Answer 13

Neutrophils
	○ Phagocytose and kill bacteria & fungi
	○ Main mediators of innate immunity
Lymphocytes
	○ Main mediators of adaptive (acquired) immunity
	○ Produce antibodies
	○ Kill virus infected cells
Eosinophils
	○ Kill parasites
	○ Involved in allergic responses
Basophils
	○ Kill parasites
	○ Involved in allergic responses
	○ Involved in inflammation
Monocytes (macrophages)
	○ Phagocytosis of dead cells and pathogens

Question 14

What are the platelets major roles?

Answer 14

Major role: Primary Haemostasis
	○ Recognise damage at blood vessel wall
	○ Form a platelet plug
	○ Prevent / stop bleeding
Platelet plug stops bleeding– but insecure & temporary.

Question 15

What does plasma have to do with homeostasis?

Answer 15

Plasma pH, ion concentrations and protein concentrations must be kept within safe limits
Otherwise bad things happen
Disturbed by disorders of:
Kidney
Liver
Lungs
Cardiovascular system
Endocrine organs

Question 16

Name a couple of common blood tests?

Answer 16

Haemoglobin concentration (Hb in g/l)
	® Overall concentration of haemoglobin in the blood
	® Used to diagnose anaemia
Mean (red) cell volume (MCV)
	® Size of the rbcs
Mean (red) cell haemoglobin content (MCHC)
	® How much Hb in each red cell
Haematocrit (Ht or Hc)
	® These help to diagnose the type of anaemia
Full blood count (FBC) also includes:
Total white blood cell count (WBC)-
Neutrophil count
Lymphocyte count