8/4- Red Cell Physiology Flashcards

1
Q

What are the main functions of RBCs?

A

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

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2
Q

The total body hematocrit is higher or lower than hematocrit observed in blood drawn from a large vein?

A

The total body hematocrit is somewhat lower than the hematocrit observed in blood drawn from a large vein

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3
Q

Is human blood a Newtonian or Non-Newtonian fluid? How so?

A

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
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4
Q

What is shown on the left? right?

Which is more mature?

A

Left: reticulocyte

  • Excess surface area with gathers into a hilum
  • Left over area contains mitochondria, ribosomes, etc.

Right: discocyte (more mature)

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5
Q

Geometry of RBC? Dimensions?

A

7-8 um diameter

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6
Q

What are Howell Jolly bodies?

A

Left over bits of DNA of RBCs removed by the spleen?

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7
Q

What is seen in pts who have had their spleens removed/impaired?

A
  • 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.
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8
Q

Components of the RBC?

A
  • Membrane
  • Hemoglobin (globin, Porphyrin–HEME)
  • Enzymes
  • 2,3 DPG
  • Cations (K mostly)
  • Water
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9
Q

Structure of the RBC membrane?

A
  • 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
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10
Q

How many RBCs in a vein are echinocytic?

What favors this state?

A

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
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11
Q

What is this?

A

Echinocyte (Burr cell)

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12
Q

What is this? When is it seen?

A

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.
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13
Q

What is this? When is it seen?

A

Spherocyte

  • Osmotic swelling —one side of the biconcave disk pops out and with further swelling both sides are out—a spherocyte.
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14
Q

What are these? When are they seen?

A

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 LCATlescithin 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.

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15
Q

What are these? When are they seen?

A

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)
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16
Q

Characteristics of echinocytes/Burr cells vs. acanthocytes?

A

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.

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17
Q

The RBC cytoskeleton is comprised of what main types of interactions?

What property is each responsible for?

A

Vertical interactions: preventing lipid bilayer form becoming unstable soap bubble

Horizontal interactions: elastic behavior; integrity

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18
Q

Structure of alpha and beta spectrin?

A
  • 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)

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19
Q

Rh protein is part of what?

A

Two principle vertical structures

20
Q

Structure of hemoglobin?

A
  • 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
21
Q

What are hemoglobinopathies?

A

Mutations that affect the structure of beta or alpha chains

22
Q

What are thalassemias?

A

Mutations that affect the balance of production of alpha and beta chains such that not enough alpha or bet chains exist

23
Q

What are the three periods of development in terms of RBC/hemoglobin production?

What hemoglobin types are seen in them?

A
  • Embryonic yolk sac
  • Fetal
  • Adult
24
Q

When does gamma predominate?

When does it switch/to what?

A

Gamma predominates in utero

  • Switch to adult beta in the 3rd TM
25
Q

When do beta chain problems arise? Ex?

A
  • Sickle cell disease or beta thalassemia
  • Manifested 6 mo or later after birth
26
Q

When do alpha chain problems arise?

A

Alpha chain problems are recognized at birth (or even in utero if more severe)

27
Q

What are the components of the principal adult hemoglobins?

A
  • 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
28
Q

Oxyhemoglobin is relaxed (R) or taut (T) conformation?

A

Oxyhemoglobin is relaxed (R) conformation

29
Q

Deoxyhemoglobin is relaxed (R) or taut (T) conformation?

A

Deoxyhemoglobin is taut (T) conformation

30
Q

Hemoglobin oxygen saturation relationship?

A
  • S shaped curve
  • Lower % saturation at low tissue PO2
  • DPG stabilizes the taut formation, favoring deoxygenation
31
Q

O2 saturation cruve

A
32
Q

What are standard conditions for blood?

A

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%

33
Q

Effect of temperature on oxygen binding?

A

Increased temperature causes decreased oxygen affinity (binding is exothermic)

34
Q

What is the acid Bohr effect?

A

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%
35
Q

Does a curves shift left or right correspond to lower oxygen affinity?

A

Right shift = lower oxygen affinity

36
Q

What things affect Hb O2 affinity? How?

A
  • Note that in hypothermia oxygen isn’t released so well from hemoglobin
  • Anemia results in increased 2,3 BPG and decreased affinity
37
Q

What are some homotropic ligands?

A

CO and NO

38
Q

Where does CO come from in the body?

A

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

39
Q

What is HbA1C?

A

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
40
Q

What is Met Hb?

A

Fe++ -> Fe+++ (2-> 3)

  • Usually about 1% of Hb
41
Q

What is the structure of Hb F?

A

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
42
Q

What is the human heme biosynthetic pathway?

A

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

43
Q

Porphyrin metabolism steps/regulation?

A

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
44
Q

Mutations in ALAS2 are associated with what?

A

X-linked sideroblastic anemia

45
Q

What is Acute Intermittent Porphyria (AIP)?

A

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)

46
Q

What is Porphyria Cutanea Tarda?

A

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

47
Q

Regulation of Hb Synthesis?

A

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