Path Ch 14. Tutoring notes
Fluid volume can influence hematocrit and hemoglobin concentration and this can give a false
positive for anemia.
MCV- average volume of RBCs in femtoliters (fL)
MCH- average content of hemoglobin per red cell in picograms
MCHC- average concentration of hemoglobin in a given volume of packed red cells, grams per
deciliter.
Red cell distribution width- coefficient of variation of red cell volume.
Iron in Hb (hemoglobin) is recaptured if it red cells leak into tissues, but the body loses iron if
there is a bleed into the gut or out of the body, and this can hamper the production of new red
cells.
If there is an excessive immobilization of red cell production by way of bone marrow then there
will be a progression from normocytic/normochromic to macrocytic/normochromic cells.
Hemolytic anemias:
Extravascular hemolysis- phagocytes in the bone marrow, liver, and spleen destroy red cells
under normal and abnormal conditions. This can lead to organomegaly like splenomegaly.
Extravascular hemolysis can be caused by the lack of RBC deformability and this condition
manifests as- anemia, splenomegaly, and jaundice.
Haptoglobin an alpha 2 globulin binds free Hb and prevents it from being excreted in urine.
Intravascular hemolysis manifests as anemia, hemoglobinemia, hemoglobinuria,
hemosiderinuria, and jaundice.
When there isn’t enough haptoglobin to bind all the Hb from the bleed then the Hb will be
oxidized to methemoglobin (brown in color).
The key is that in intravas. hemolys. there isn’t splenomegaly.
Hb-haptoglobin complex is broken down by phagocytes and the heme is converted to bilirubin
which causes jaundice.
Jaundice rarely occurs if liver is functioning properly, bilirubin is secreted in feces as urobilin.
Key features of hemolysis:
-hypoxia 2ndary to anemia-leading to increased erythropoietin and erythropoiesis.
Reticulocytosis. Hemosiderosis. Cholelithiasis.
Hereditary spherocytosis:
Inherited disorder that causes the formation of spheroid red cells due to cytoskeletal defects.
Key cytoskeletal proteins:
Spectrin-alpha and beta helices-heads bind to heads to form tetramers. Tails bind to actin
oligomers. Each actin can bind multiple tetramers.
Ankyrin and band 4.2 bind spectrin to band 3 which is a transmembrane ion transporter.
Protein 4.1 binds spectrin tails to glycophorin A (transmembrane protein).
Spectrin, ankyrin, band 4.2, and band 3 are most susceptible to mutation which leads to spherical
red cells.
Splenectomy is very beneficial in this instance because the spleen is the main reason for
premature destruction of the spherical red cells. Anemia can be corrected through this procedure.
Morphology of HS is small dark staining cells lacking the usual central pallor. Reticulocytosis,
marrow hyperplasia, hemosiderosis, and mild jaundice. Splenomegaly.
HS cells have an increased MCHC because they lose K+ and H2O.
Howell Jolly bodies are small dark nuclear remnants in HS cells.
Aplastic crises which is usually caused by an acute parvovirus infection leads to destruction of
red cell progenitors and hence with HS can lead to severe anemia and must be treated with a
transfusion.
G6PD deficiency can lead to hemolytic disease because- G6PD oxidizes G6P and then reduces
NADP to NADPH which then reduces glutathione. Glutathione in reduced forms can protect red
cells from oxidant damage.
G6PD deficiency is X-linked hence males are more susceptible.
Oxidative stress is most likely to present during an infection which leads to leukocyte ROS
production.
G6PD Mediterranean has the shortest half-life.
Fava beans generate oxidants when consumed and is detrimental to G6PD deficient individuals.
*Heinz bodies occur in G6PD deficient red cells which are exposed to high levels of oxidants.
These dark inclusions form through sulfhydryl cross linking on globin chains. Heinz bodies can
lead to hemolysis. The inclusion containing cells that don’t lyse immediately pass through the
splenic cords and the Heinz bodies are plucked out and spherocytic or half-bitten cells appear.
Since damage only occurs during oxidant stress and not continuously splenomegaly and
cholelithiasis are absent.
HbA-a2b2 (normal adult Hb)
HbA2-a2delta2 (minor component)
HbF-a2gamma2 (fetal)
HbC-like HbS but lysine for glutamate.
HbS-sickle cell anemia-6th codon point mutation of b-globin which leads to valine for glutamate
replacement.
Heterozygosity for HbS is largely asymptomatic and protective against malaria.
HbS molecules undergo polymerization under deoxygenated conditions.
HbS patho. manifestations include chronic hemolysis, microvascular occlusions, and tissue
damage.
In heterozygotes with HbA (60%) and HbS (40%) the cells wont sickle unless there is profound
hypoxia.
HbF prevents sickling even more than HbA does. Infants won’t manifest sickling until 5 to 6
months.
HbC and HbS (50%) cells are dehydrated and HbS polymerizes. HbSC is less severe than HbS
homozygotes.
A decrease in pH can lead to a sickling episode.
The spleen and bone marrow has a slow transit time so this allows for sickling to occur and
affect these locations. Slow transit times correlate to sickling ability.
Eventually sickled cells become irreversibly sickled and this correlates with the severity of
hemolysis be it extravascular or intravascular.
Sickle cells tend to have higher than normal adhesion molecules and are sticky.
Inflammation is a key factor to microvascular occlusion (w/ oxygen tension and sickling). Hb
released from sickled red cells binds NO and leads to vasoconstriction.
Full blown sickle cell anemia causes marrow hyperplasia and medullary bone resorption and
secondary bone formation (prominent cheekbones and skull changes that resemble a crew-cut in
x-ray). It also causes autosplenectomy due to splenic infarction and subsequent fibrosis.
Acute chest syndrome- vaso-occlusion of lung vasculature leading to worsening pulmonary and
systemic hypoxemia and sickling.
Sequestration crises- spleen in children entraps massive amounts of sickle cells which causes
splenomegaly, hypovolemia, and even shock.
Treat with hydroxyurea.
Thalassemia is an inherited disorder of decreased adult Hb synthesis.
Alpha chains are encoded by two identical genes on chromosome 16 and beta chains are encoded
by a single gene on chromosome 11.
Beta 0 and beta + are the two variants of beta thal. defects. 0= absent production and
+=diminished but not completely in production
Splicing mutations are the most common cause of beta + thal.
Promoter region mutations=beta +
Chain terminator mutations=beta 0
In beta thal. microcytic and hypochromic anemia can ensue, but more importantly alpha chains
polymerize and destroy red cell membranes.
Severe beta thal. effects red cell precursors also and leads to ineffective erythropoiesis.
Extramedullary hematopoiesis also occurs. Cachexia-muscle wasting. Bone abnormalities also
occur.
B-thal major- homozygous B-thal minor- heterozygous B-thal intermedia- milder/unusual
homozyg-/heterozygous groups.
Like sickle cell there is a crew-cut x-ray seen. Extramedullary hematopoiesis and splenomegaly.
Blood transfusions for beta thalassemia patients can alleviate anemia and its complications but it
can lead to iron overload and iron deposition in many organs.
Alpha thalassemia- gamma tetramers= known as Hb Barts. Beta tetramers= HbH
Alpha units are less soluble than gamma and beta thus hemolysis and ineffective erythropoiesis
is less severe in alpha thalassemia.
Alpha thal. occurs mainly due to deletions.
Alpha thal.=4 genes:
1 gene missing is a silent carrier state.
2 genes missing is alpha thal. trait. (a/a,-/-)=Asian and (a/-.a/-)=African; Asians have it more
common than Africans. This alpha trait is like beta thal. minor and not as severe.
3 genes missing lead to HbH in which beta tetramers form. HbH has a high tissue affinity which
is not useful for tissue oxygen delivery. This resemble beta thal. intermedia.
4 genes missing is Hydrops Fetalis- this is the most severe and early development survival is due
to zeta pairing with gamma. But then during third trimester anoxia can lead to death. Lifelong
blood transfusions or a bone marrow transplant can save the patient’s life.
Paroxysmal Nocturnal Hemoglobinuria- PIGA mutation, GPI-linked proteins are deficient.
Effects hematopoietic stems cells. Hemolysis occurs through complementation. PNH CD 59 is
most important and deficiency in this GPI cause cell lysis. Thrombosis is the leading cause of
death because of platelet defects causing prothrombotic states and NO sequestration by free Hb
from the hemolysis.
For immunohemolytic anemia do a direct Coombs or indirect Coombs antiglobulin test.
Warm antibody type- most common form of immunohemolytic anemia. IgG related. Idiopathic
or drug induced. Extravascular hemolysis. Active at 37 Celsius.
Cold agglutinin type- at less than 37 Celsius. Associated with infections. IgM mainly.
Cold hemolysin type- paroxysmal cold hemoglobinuria. IgGs. Virus related.
B12 and folate are needed for thymidine synthesis.
Megaloblastic anemia-macrocytes and oval. Other cells also effected (neutrophils,
megakaryocytes, granulocytes) all enlarged. Nuclear to cytoplasmic asynchrony due to decrease
DNA synthesis. Ineffective hematopoiesis.
B12 (Cobalamin) deficiency-autoimmune gastritis. Pernicious anemia. Intrinsic factor
deficiency. Intrin. factor is released by parietal cells of the stomach’s fundic mucosa. Pepsin
(from chief cells) removes B12 from food protein. B12 binds to salivary proteins called
cobalophilins or R-binders. In the duodenum it is released by pancreatic protease and it
associates intrinsic factor. It is absorbed in the ileum and associated with transcobalamin II. B12
is only required by two reactions in the body-1) methycobalamin for homocysteine to
methionine. Folate deficiency is the proximate cause of anemia in B12 deficiency since anemia
improves with administration of folic acid. 2) isomerization of methylmalonyl coenzyme A to
succinyl CoA. Acute gastritis mainly caused by autoreactive T-cell responses and secondarily by
autoantibodies. Ig type I prevents B12 and intrinsic factor binding, type II prevents B12-intrinsic
factor complex binding to receptors in ileum, and type III is subunits of gastric proton pump.
Path: The atrophy of fundic glands lead to intestinalization and goblet cells formation as a
replacement. Atrophic glossitis. CNS lesions mainly in dorsal and lateral spinal cord where there
is demyelination. Increased homocysteine causes atherosclerosis and thrombosis.
Parenteral B12 can fix anemia, prevent vascular disease, peripheral neurologic problems, but
can’t fix gastric atrophy and carcinoma risk.
Folate or pteroylmonoglutamic acid is needed for purine synthesis, homocysteine to methionine
conversion, and dTMP synthesis. Heating food destroys folic acid. Unlike B12, folate body
reserves are low. Folate is absorbed in the jejunum as monoglutamates which is modified to 5methyltetrahydrofolate.
Folate deficiency causes increased homocysteine, but methylmalonyl acid won’t increase, and
neurologic problems won’t happen. Folate can treat peripheral problems of B12 deficiency but
not neuro. problems because methymalonate will still be high.
Iron- free form is toxic, transferrin transports it and it is stored as ferritin and hemosiderin. Iron
absorption occurs at proximal duodenum. Heme (animal products) and nonheme (plant products)
iron. Nonheme iron is converted from Fe3+ to Fe2+ and transported across by DMT1 and then
ferroportin releases it into blood while Fe2+ is converted to Fe3+ via hephaestin or
ceruloplasmin. Hepcidin binds to ferriportin and causes it to be endocytosed and degraded this
prevents iron absorption into blood. Iron remains in the enterocyte via DMT1 facilitated
movement into the cells but the cells are sloughed off with iron and all.
Primary hemochromatosis- mutation in hepcidin or its genes
Secondary hemochromatosis- beta thalassemia can lead to hepcidin decrease and this along with
blood transfusions can cause iron overload.
Nonheme (inorganic) iron absorption is improved by ascorbic acid, citric acid, amino acids, and
sugars. Absorption is decreased by tannates (tea), carbonates, oxalates, and phosphates.
In the western world chronic blood loss is the main cause of iron deficiency.
Iron deficiency cells are hypochromic and microcytic.
Iron deficiency in the CNS causes pica in which they consume non food products or food
ingredients.
Plummer Vinson syndrome- esophageal webs, microcytic hypochromic anemia, and atrophic
glossitis.
Anemia of chronic disease- caused by inflammation (IL-6), the macrophages take in iron
probably to inhibit infective agent growth, high hepcidin lowers serum iron through ferriportin,
and there is low iron-binding capacity. Red cell destruction. This isn’t a lack of body iron but a
lack of iron in serum.
Aplastic anemia- Main cause is idiopathic (65%) and other causes include drug/chemical such as
chemotherapeutics, benzene, chloramphenicol, and gold salts, irradiation, infections,
telomere/telomerase defects. In addition, damage caused by the previously mentioned factors to
the progenitors can lead to T-cell mediated progenitor death if death didn’t occur with the insult
itself.
Aplastic anemia-dry tap bone marrow biopsy. Pancytopenia. Splenomegaly is missing.
Pure red cell aplasia- Parvovirus B19 mainly causes this effect to erythrocyte progenitors. This is
not a problem unless the patients are immune suppressed or have a hemolytic anemia.
Myelophthisic anemias- carcinomas or other infiltrative processes can displace marrow and
replace it with space occupying lesions. Immature red cell and leukocyte formation. Teardropshaped red cells that deform during their movement through fibrotic marrow.
Polycythemia- High RBC levels. Relative- decreased fluid in plasma thus an increased RBC
concentration. Absolute- polycythemia vera (mutation leading to growth of red cell progenitors)not linked with erythropoietin increase. Other absolutes which lead to a real red cell increase are
based on erythropoietin increase