8/4- Red Cell Physiology Flashcards
What are the main functions of RBCs?
Transport of Oxygen/CO2
- Also a scavenger of nitrix oxide (NO)! (for BP)
Hemostasis
- Increasing hemostatic effects of platelets (blood transfusions or EPO will shorten prolonged bleeding time of uremic pts)
(e. g. anemic pts with fewer RBCs have longer bleeding time b/c platelets are more central in the vessel)
Clearance of immune complexes
The total body hematocrit is higher or lower than hematocrit observed in blood drawn from a large vein?
The total body hematocrit is somewhat lower than the hematocrit observed in blood drawn from a large vein
Is human blood a Newtonian or Non-Newtonian fluid? How so?
Human blood is a Non-Newtonian fluid; its viscosity depends on shear rate
- In arterial flow, blood is thinner than blood flowing more slowly in a vein
- In areas of slow flow, RBCs tend to aggregate, increasing viscosity
What is shown on the left? right?
Which is more mature?
Left: reticulocyte
- Excess surface area with gathers into a hilum
- Left over area contains mitochondria, ribosomes, etc.
Right: discocyte (more mature)
Geometry of RBC? Dimensions?
7-8 um diameter
What are Howell Jolly bodies?
Left over bits of DNA of RBCs removed by the spleen?
What is seen in pts who have had their spleens removed/impaired?
- Increased number of acanthocytes and Howell Jolly bodies are seen
- Also there are intracellular vacuoles in normal red blood cells which have the appearance of pits or pocks when viewed under interferance (Nomarski) optics.
Components of the RBC?
- Membrane
- Hemoglobin (globin, Porphyrin–HEME)
- Enzymes
- 2,3 DPG
- Cations (K mostly)
- Water
Structure of the RBC membrane?
- Lipid bilayer (asymmetric)
Inner layer:
- Aminophospholipids PS and PE
Outer layer:
- Phosphatidyl choline
- Sphingomyelin
- Unesterified cholesterol (enriched)
Transmembrane:
- Band 3 (anion transporter)
- Glycophorin A, B
Cytoskeleton
- Spectrin (Stabilized by cytoskeleton comprised of spectrin alpha and beta (share homology with myosin))
- Actin
How many RBCs in a vein are echinocytic?
What favors this state?
About 1%
- Echinocytic state is favored by aging in a test tube, uremia, and exposure to glass surfaces if there isn’t much protein around. Certain agents can intercalate into the outer membrane leaflet and cause a similar change
What is this?
Echinocyte (Burr cell)
What is this? When is it seen?
Stromatocyte
- Common artefact
- Real in patients who have a lot of alcohol on board
- Certain drugs or agents which intercalate in the inner membrane leaflet.
- Osmotic swelling will produce the same effect—one side of the biconcave disk pops out and with further swelling both sides are out—a spherocyte.
What is this? When is it seen?
Spherocyte
- Osmotic swelling —one side of the biconcave disk pops out and with further swelling both sides are out—a spherocyte.
What are these? When are they seen?
Target cells (codocyte)- results from increased surface area to volume ratio of a RBC
- Can occur in liver disease with partitioning of lipids into the membrane—giving macrocytosis and targeting
- The enzyme disorder LCAT—lescithin cholesterol acyl transferase deficiency also does this; cholesterol and lecithin are increased in the membrane
- Hemoglobinopathies—C and E hemoglobins—activate membrane transport to dehydrate the red blood cell, the decrease in volume results in targets.
- Thalassemia and also iron deficiency will show targets—this slide is sickle beta thalassemia.
Hb S trait does not give you anything, but the thalassemia here does that.
What are these? When are they seen?
Acanthocytes (claw cells)
- Seen in post splenectomy states and in certain conditions such as a betalipoproteinemia
- Rare McCleod phenotype- an X linked disorder with these sorts of red blood cell and problems with transfusion because they don’t express Kell red blood cell antigens
- When cholesterol is increased in the plasma it can partition with the red cell to give shapes like this (some times only one big claw is present—a spur cell)
Characteristics of echinocytes/Burr cells vs. acanthocytes?
Echinocytes/Burr cells: lots of small spicules.
Acanthocytes: smaller number of spicules which are larger
Note the acanthocyte here and the Howell Jolly Body—their presence indicates the absence of splenic function.
The RBC cytoskeleton is comprised of what main types of interactions?
What property is each responsible for?
Vertical interactions: preventing lipid bilayer form becoming unstable soap bubble
Horizontal interactions: elastic behavior; integrity
Structure of alpha and beta spectrin?
- Alpha and beta chains self-associate to form dimers
- Two dimers can associate to form a tetramer
- At the non-self associated end of the dimer, there is an actin junctional complex
(Spectrin is an analog of myosin)
Rh protein is part of what?
Two principle vertical structures
Structure of hemoglobin?
- Alpha and beta globins are translated into protein on their respective ribosomes and heme is inserted
- Alpha and beta globins combine to form a very stable dimer
- Dimers attach to form a tetramer
- Alpha chain is negatively charged overall and the beta chain is positively charged
- Involves 8 alpha helices, heme pocket, and heme ring containing and iron molecule
What are hemoglobinopathies?
Mutations that affect the structure of beta or alpha chains
What are thalassemias?
Mutations that affect the balance of production of alpha and beta chains such that not enough alpha or bet chains exist
What are the three periods of development in terms of RBC/hemoglobin production?
What hemoglobin types are seen in them?
- Embryonic yolk sac
- Fetal
- Adult
When does gamma predominate?
When does it switch/to what?
Gamma predominates in utero
- Switch to adult beta in the 3rd TM
When do beta chain problems arise? Ex?
- Sickle cell disease or beta thalassemia
- Manifested 6 mo or later after birth
When do alpha chain problems arise?
Alpha chain problems are recognized at birth (or even in utero if more severe)
What are the components of the principal adult hemoglobins?
- All adult hemoglobins share a common alpha chain
- Can predict the A2 will go up in beta thalassemia (when beta globin is reduced/absent)
- Hb F is not uniformly expressed in RBCs; certain cells (a subpopulation) have a lot of F so they are called F cells
Oxyhemoglobin is relaxed (R) or taut (T) conformation?
Oxyhemoglobin is relaxed (R) conformation
Deoxyhemoglobin is relaxed (R) or taut (T) conformation?
Deoxyhemoglobin is taut (T) conformation
Hemoglobin oxygen saturation relationship?
- S shaped curve
- Lower % saturation at low tissue PO2
- DPG stabilizes the taut formation, favoring deoxygenation
O2 saturation cruve
What are standard conditions for blood?
Temp = 37’C
pH = 7.4
PCO2 = 40 mmHg
BPG = 5 mmol/L
Arterial:
PO2 (art) = 90-100 mmHg
Sat = 98-100%
Venous:
PO2 vein = 35-40 mmHg
Sat = 66-73%
Effect of temperature on oxygen binding?
Increased temperature causes decreased oxygen affinity (binding is exothermic)
What is the acid Bohr effect?
Stabilization of the deoxy form of Hb in the presence of H+ ions
- So in the tissues which are slightly acidotic, deoxygenation is favored
- Normal resting muscle pH is 7.03
- Exercise pH goes to 6.0 and increases extraction of O2 form 30 to 70%
Does a curves shift left or right correspond to lower oxygen affinity?
Right shift = lower oxygen affinity
What things affect Hb O2 affinity? How?
- Note that in hypothermia oxygen isn’t released so well from hemoglobin
- Anemia results in increased 2,3 BPG and decreased affinity
What are some homotropic ligands?
CO and NO
Where does CO come from in the body?
Produced by porphyrin metabolism
- 1-2 % of Hb is HbCO
- Binding of CO to two subunit increases the O2 affinity of the remaining 3 subunits
Darling-Roughton effect
- Shifts oxygen saturation curve to LEFT
- One/250 CO/O2 results in 50 % CO Hb
- CO binds more slowly, but dissociation is way slow
CO may be higher in people living in an urban environment and is also higher in smokers and a cause of erythrocytosis
What is HbA1C?
Hb + glucose
- Criteria for DM
- Need a normal RB life span for this to be informative
- Normal range: 4-5.6%
- At risk for DM: 5.7-6.4
- DM: 6.5
What is Met Hb?
Fe++ -> Fe+++ (2-> 3)
- Usually about 1% of Hb
What is the structure of Hb F?
a2y2 (alpha2, gamma2)
- Primary fetal Hb
- In adults produced by a subset of cells or “F-Cells”. F hemoglobin is heterogenously distributed.
- Doesn’t bind 2,3 BPG—high affinity Hb
- Can form mixed tetramers with Hb A (when beta is a S Hb, the gamma in the tetramer inhibits sickling)
- It is about 1% of normal adult Hb
What is the human heme biosynthetic pathway?
8 enzymatic steps:
- 4 in mitochondria
- 4 in cytosol
Heme is exported from mitochondria for incorporation into cellular hemoproteins and, particularly in liver, exerts feedback regulation
Porphyrin metabolism steps/regulation?
Starts with ALAS1 (liver) or ALAS2 (red cell precursors)
ALAS1 negative feed back by Heme
ALAS2 control by Iron Response Element
- Iron deficiency inhibits
- Iron presence increases activity
Mutations in ALAS2 are associated with what?
X-linked sideroblastic anemia
What is Acute Intermittent Porphyria (AIP)?
Mutations in Porphobilinogen deaminase
Presentation after puberty
- Abdominal pain, tachycardia, HTN
- Neuropathy, psychosis
- Hyponatremia and seizures
- Precipitated by drugs/starvation/ETOH
Increased porphyrins in blood and urine
- Watson Schwartz Reaction
Response to glucose infusions and Hematin
(King George)
What is Porphyria Cutanea Tarda?
Uroporphyrinogen decarboxylase (UROD)
- Hereditary
- Association with hemochromatosis
- Acquired: Hepatitis C, Iron overload, HIV, Halogenated hydrocarbons
Involves skin and liver
Most stiking feature is bullous dermatosis on light exposed areas
Regulation of Hb Synthesis?
Alpha and Beta chain production are similar
Globin production is inhibited when heme is absent
- HRI heme regulated eIF2alpha kinase
- This increases if Heme is absent
- Protein synthesis at the ribosome is halted ALA syntase is regulated by IRE Feline leukemia virus sub group C receptor (FLVCR)
- Heme exporter Alpha hemoglobin stabilizing protein, AHSP
