PBL Week 9 Flashcards
What are the different functions of blood?
The purpose of blood is to transport various elements around the body. This includes gases (O2 and CO2), proteins, sugars, hormones, immune cells, platelets and waste products, which are taken to the kidneys and liver for processing. Blood also regulates our body temperature.
What are the definitions of the terms ‘formed elements’, ‘packed cell volume’, ‘plasma’ and ‘serum’?
Formed elements are all of the cells and cell fragments suspended in the blood plasma; it consists of white blood cells, red blood cells and platelets.
Packed cell volume (haematocrit) is the proportion of the blood that is made up of cells.
Plasma is the yellowish liquid in blood that holds the cells of the blood in suspension.
Serum is the fluid content of the blood and contains everything except red blood cells, white blood cells and platelets.
What are the key functions of different plasma proteins?
99% of plasma proteins are either albumin, globulins or fibrinogen. Albumin is important in maintaining oncotic pressure within the blood, as well as carrying non-soluble molecules (such as lipids and steroid hormones). Globulins transport ions and hormones, as well as assisting the immune system (immunoglobins/Ig). Fibrinogen is converted into Fibrin, which is essential for blood clotting. The remaining 1% of plasma proteins are regulatory proteins (e.g enzymes and hormones).
What is the shape and function of a red blood cell?
Red blood cells, or erythrocytes, have one function; they carry oxygen from the lungs to the tissues of the body and carbon dioxide from the tissues to the lungs. They have a biconcave shape; this is to maximise the surface area of the membrane for oxygen to diffuse through. They are also very small and flexible, allowing them to squeeze through the thin capillaries in our body. Inside the cells, there are no organelles; this is to maximise the amount of haemoglobin inside the cell’s cytoplasm.
Haemoglobin in a globular protein made up of 4 subunits, each of which is attached to a haem group, which contains a ferrous (Fe2+) iron molecule. This is what CO2 and O2 binds to, as well as CO.
What is the role of the acid-base balance and why is it important?
The acid-base balance is the body’s balance between acidity and alkalinity. The blood is slightly basic, with a PH of 7.4. Changes in PH can have drastic consequences including the denaturation of enzymes and the breakdown of protein structure. Therefore, the body has to maintain this PH. In the blood, this is regulated by the lungs, the kidneys and buffer systems.
The lungs work by releasing CO2, a slightly acidic waste product from respiration. This is to avoid CO2 build up, lowering the PH. Whenever the brain detects the PH lowering, it signals the lungs to breathe harder and faster. The kidneys work by excreting any excess acids or bases. They have some control over how much they excrete, but this change is far slower than the lungs. Finally, buffer systems is the presence of a weak acid (carbonic acid) and a weak base (bicarbonate ions). They work chemically to reduce the effect of acids and alkalis on our PH by adjusting the proportion of acids and bases when needed.
How are the shape of red blood cells maintained and what is hereditary spherocytosis?
The membrane and the concave shape of an erythrocyte is maintained by a complex mix of membrane proteins found within red blood cells. In hereditary spherocytosis, there is a deficiency in the surface area of the membrane, leading to sphere shaped red blood cells. This is caused by defects in the membrane proteins, in particular ankyrin, as well as spectrin and protein 4.2. This leads to a reduced density in the membrane skeleton and a destabilisation of the lipid bilayer. These dysfunctional spherocytes cannot enter capillaries as easily, are prone to rupture and are destroyed by the spleen, leading to anaemia.
What are the haematological indices in blood?
The haematological indices are the data obtained from a blood test. The biochemistry of the blood is measured, which involves taking levels of salts and waste products. For example, testing for the levels of creatinine in the blood is a measure for how well the kidneys are working. Inflammatory markers, such as c reactive protein (CRP), are also measured. High levels can indicate infection, trauma, cancers or autoimmune conditions.
The final measure of the blood is the full blood count. This includes:
The total white blood cell count - high indicates infection, low due to chemotherapy or bone marrow issue.
Differential white blood cell count - high neutrophils for bacterial infection and low for chemotherapy, high/low lymphocytes depending on infection (mostly high for viral).
Platelet count - low platelets could inidcate blood cancer, cancer treatment, bone marrow failure or an infection. High levels could indicate the removal of the spleen, some blood cancers and an iron deficiency.
Haemoglobin count - Low means the patient is anaemic, which can be caused by iron deficiency, low B12 or bowel cancers.
Mean corpuscular volume - measure of the size of red blood cells. Low caused by iron deficiency, high caused by B12 or folate deficiency, alcohol excess or hyperthyroidism.
Haematocrit - measure of proportion of blood made of cells. Higher if dehydrated and lower if patient is given IV fluids or has anaemia.
What is the “behind the scenes” of NHS blood transfusions?
All donated blood is assigned a product code and put through a filtration device to make sure it’s safe. A centrifuge is then used to seperate red blood cells from the plasma. An alternative to this is using an optopress. A leukocart additive solution is then added to extend the life of the red blood cells, as the plasma has been removed. The pack is then labeled and stored a 4 degrees in a fridge, as well as tested to make sure it’s safe for patients. Red blood cells are used for significant blood loss, plasma is used for replacing clotting factors and increasing blood volume after trauma and platelets are used for immunocompromised patients.
What are the different factors needed to take into account when giving a blood transfusion?
The most important factor is blood type. There are 2 factors to a blood type: antigen and rhesus factor. Red blood cells can have A, B, AB or none (O) antigens on the outside of the cells. Whatever antigen is present, the opposite antibody will be found in the plasma. So A blood type has A antigens on the blood cell and B antibodies in the blood. AB blood has both antigens and neither antibody, while O blood has neither antigen but both antibodies. This means that the body will attack certain red blood cells. For example, if someone with blood type A was given B blood, the B antibodies in their plasma would attack the B blood cells.
Rhesus factor is also important - the protein can be present (+) or not (-). Positive blood groups can accept both positive and negative blood types, while negative blood groups can only accept negative blood types. Therefore, AB+ is the universal acceptor and O- is the universal donor.
Other factors needed to be taken into account is how much blood is lost (less than 30% means it isn’t even needed) and religious reasons (some groups, like Jehovah’s Witnesses, don’t allow blood transfusions in their religion).
What are the scandals that undermined confidence in transfusion medicine?
The biggest scandal is the contaminated blood scandal, where blood infected with Hepatitis C and HIV were unknowingly given to patients in the 1970s and 80s. This lead to a confirmed 1,246 deaths as a result of the scandal, although many estimate that this number is much higher. Furthermore, the NHS or government have never taken any responsibility for this error and haven’t given any sort of compensation to the victims. This lead to a big distrust in transfusions among the public, as people were concerned in contracting these diseases.
