RBCs and Hemoglobin binding Flashcards
Erythrocytes
red blood cells
Packed Cell volume (PCV)
amount of RBCs as measured from centrifuged blood in a microhematocrit tube= height of the red blood cells column
Hematocrit
a percentage of red blood cells in blood volume
Species variance of hemocrit
- Different species have different hemocrit or PCV values
- Used to estimate the % of blood that is erythrocytes and therefore how much oxygen would be able to be carried
What causes normal variation in RBC number?
- Species
- Breed (thoroughbreds > draft horses)
- Age (adult vs. neonates (more))
- Excitement
- Exercise
- Pregnancy, lactation, stage of estrous cycle
- Altitude (high altitude = decreased arterial oxygen tension)
What causes abnormal variation in RBC number?
1.Poor Nutritional status can result in anemia (too little RBCs)
- RBCs have 120 days lifespan so need nutrition to rebuild and maintain equilibrium
- Blood volume- dehydration (appear too much)
- Less volume will make hematocrit seem higher - Erythrocytosis (too much)
- Too many RBCs in circulation
Function of erythrocytes
- Deliver oxygen to tissues which is conducted by hemoglobin (95% of solid material)
- Carbonic anhydrase- converts CO2 to carbonic acid
What Molecules are associated with erythrocyte membranes?
- Membrane lipids
- Surface glycoproteins (determine blood groups)
- Cytoskeleton (spectrin which binds to actin and helps maintain shape)
What is the Metabolism of erythrocytes?
Relies on glycolysis because no mitochondria
Erythrocyte nucleus
- No nucleus in mammals
- exception is amphibians, reptiles and birds
Electrolytes used by erythrocytes
- Na, K
- Maintenance of osmotic equilibrium by Na/K ATPase pump
Blood types
- Different between species and are not universally compatible
- Mismatched transfusions can lead to severe reactions, including delayed hemolytic reactions, inflammation, and death
- Blood typing or cross matching is essential before transfusion
Number of Blood types in species
- Dogs- 8 groups
- Cats- 3 groups
- Horses- more than 30 groups
- Cattle- 11 groups
- Sheep- 7 groups
Canine blood types
- DEA 1
- DEA 7
Feline blood types
- A
- B
- mic
Equine blood types
- A
- C
- Q
Bovine blood types
- B
- J
Ovine blood types
- B
- R
Shape of RBCs
Normal: biconcave disc shape with a shallow center
- Maximizes surface area to volume ratio which optimizes gas exchange
- Also allows RBCs to fold up, bend as they move through the vasculature (narrow blood vessels)
Poikilocyte
abnormally shaped blood cell
Functions of Erythrocytes
- Transport O2- needs hemoglobin
- Transport CO2- in blood (carbonic anhydrase) and hemoglobin needed
- Buffer- hemoglobin
Oxygen Transport
Diffusion based on concentration gradients for oxygen
- Partial pressure relates to the concentration of gases
Most O transported in blood by hemoglobin (98.5%)
- Hemoglobin keeps the oxygen concentration low in the RBCs ensuring oxygen is constantly picked up by hemoglobin (high to low concentration)
Hemoglobin and its structure
67 k/Da
Made of 4 polypeptide chains (2 alpha, and 2 beta globins)
Each globin has a heme group bound to iron Fe 2+ (ferrous) which acts as the oxygen binding site
Myoglobin
hemoglobin in the muscle, contains only one polypeptide chain and one heme
Different Binding states of oxygen and hemoglobin
Deoxygenated state
- Heme will be non-planar
- Appears darker red (~blue)
Oxygenated state
- Heme will be planar
- Appears bright red
Cooperative binding of oxygen to hemoglobin
- Unique feature enhancing hemoglobin’s oxygen carrying capacity
- When one O2 molecule binds to a subunit, it induces changes in neighbouring subunits, increasing their affinity for O2
Hemoglobin & heme binding
- Hemoglobin has 4 globins, each with a Fe2+ therefore 4 hemes
- Each heme binds one O2, so one hemoglobin can bind 4 O2 molecules
- Cooperative binding occurs at these sites
Planarity of heme when O2 binds
- O2 binding to heme causes the histidine to be pulled towards the heme altering the structure so that the globin subunit appears planar
- Changes colour to red
Hemoglobin structure in dissociation curve
- Displays cooperative binding of hemoglobin
- Sigmoidal curve (would be linear without cooperative binding)
- As more oxygen is bound, need less concentration to bind
How much oxygen carried by hemoglobin?
- 1g hemoglobin can carry 1.34ml O2
- Normally 150g hemoglobin/L or 15g/100ml hemoglobin in blood
- Multiply together: Therefore when hemoglobin is completely saturated, 20% of blood carries oxygen.
Fully saturated hemoglobin
- Means that when all the heme sites in one hemoglobin are carrying O2 they are carrying 20%
- In reality, a hemoglobin does not need to be fully saturated so may not be carrying 20% of oxygen because the 20% is the best case scenario
Hemoglobin binding in arterial blood and venous blood at normal and exercise
At 100% saturation, 20% of the blood volume contains O2
Arterial blood (lung to tissue):
- 100 PO2 (mm Hg), 20% saturation
Venous blood (when in tissues delivering oxygen):
- 40 PO2 (mm Hg), 14% saturation
Venous blood during exercise:
- 20 PO2 (mm Hg), 4% saturation
Bohr effect and hemoglobin saturation
Hemoglobin shifts oxygen delivery depending on condition. Can deliver more oxygen to tissue when demand is high
- Normal: hemoglobin= ~65%
- Shift to right (oxygen demand high)= 55%
- Shift to left (oxygen demand is less; oxygen bound tighter)= 75%
What factors cause a shift to the right in dissociation curve (bohr effect)?
- Increased hydrogen ions (exercise/lactic acid)
- Increased CO2 (exercise results in increased metabolism and CO2 release)
- Increased temperature (by-product of metabolism)
- Increased BPG (by-product of glycolysis; increased metabolism)
Hemoglobin toxicities
- Carbon monoxide poisoning
- Methemoglobinemia
Carbon monoxide poisoning
- CO binds to heme 220x better than O2. At just 0.1% CO, 50% of hemoglobin becomes saturated
Causes:
- Shifts O2 hemoglobin dissociation curve to the left
- Inhibits O2 delivery to tissues
Hemoglobin will appear more cherry red
Methemoglobinemia
- Iron in hemoglobin is oxidized from ferrous (Fe2+) to ferric (Fe3+) state
- Hemoglobin in this state cannot bind O2
- Will make the hemoglobin more red-brown in colour
What causes methemoglobinemia?
- Nitrites, some antibiotics and chlorates
- Over the counter acetaminophen
- Topical anesthetics
Main values of CBC chem
- Hemoglobin
- PCV
- RBC
- MCV
- MCH
- MCHC
RBC number on blood test
- The number of red blood cells per L of blood
- Measured by light scattering instrument
MCV (Mean cell volume) on blood test
- The average size of RBCs
- Measured by light scattering instrument
Light scattering instrument and calculating hemocrit
Used to calculate RBC and MCV
RBCs diluted in isotonic solution
Electric current between the two electrodes and vacuum causes the RBCs to move through the aperture
Device counts how many RBCs pass through and their size
- Multiply RBC number and MCV to get the hematocrit
Hematocrit
The ratio of the volume of RBCs to the total volume of blood
Hemoglobin
- Concentration of hemoglobin in blood
- Measured by diluting the RBCs in buffer with lysing agents that cause RBCs to release hemoglobin. Can be calculated by absorption of light.
MCHC (Mean corpuscular hemoglobin concentration
- The measurement of the amount of hemoglobin a RBC has relative to its size
- Calculated from hemoglobin concentration and hematocrit
Equation for MCHC
MCHC= hemoglobin concentration in blood/ hematocrit
If hemoglobin is 150g/L in blood and the hematocrit is 46%, what is the MCHC?
MCHC= (150g/L) / (0.46 L/L) = 326 g/L
Means there is 326 grams of hemoglobin per litre of blood
Normochromic
Normal hemoglobin concentration in cells
Hypochromic
- Low hemoglobin in cells
- Iron deficiency or immature RBCs
Hyperchromic
- High hemoglobin
- Usually an artifact
MCH (Mean corpuscular hemoglobin)
The average weight of hemoglobin in an individual RBC. The average concentration of hemoglobin per red blood cell
Equation for MCH
MCH= hemoglobin concentration in blood/ red blood cell concentration
If hemoglobin is 150g/L in blood and the concentration of erythrocytes is 7x10^12/L, what is the MCH?
MCH = (150g/L)/ (7x10^12/L) = 21.4 x 10^-12 grams OR 21.4 picograms
There is 21.4 picograms of hemoglobin per RBC
