Red Blood Cells, Anemia and Polycythemia

Prof. dr. Zoran ValićDepartment of PhysiologyUniversity of Split School of Medicine

Red Blood Cells (Erythrocytes)

functions:1) transport of hemoglobin (O2)

in some animals it circulates as free protein in humans within RBC – loss by filtration 3%

2) large quantity of carbonic anhydrase (CO2 and H2O)

3) an excelent acid-base buffer (proteins)

biconcave discs (φ=7,8 μm; V=90-95 μm3) shape can change remarkably (squeeze through

capillaries, excess of membrane) M = 5,2x1012

F = 4,7x1012

chemoglobin in RBC < 340 g/L Ht = 40-45% chemohlobin in blood = 160-140 g/L

1) yolk sac (few early weeks)2) liver; spleen and lymph nodes(middle

trimester of gestation)3) bone marrow beyond the age of 20 most RBC are

produced in membranous bones (vertebrae, sternum, ribs and ilia)

growth inducers – proteins which control growth and reproduction of stem cells

interleukin-3 – promotes growth and reproduction of virtually all stem cells

differentiation inducers (low oxygen, infectious diseases)

1%bone marrow

tissue oxygenation – most essential regulator (viscosity)

hemorrhage, x-ray therapy, high altitudes, cardiac failure, lung diseases

erythropoietin (glycoprotein; 34000) 90% is formed in kidneys (unknown, liver) fibroblast-like interstitial cells surrounding the

tubules? renal tissue hypoxia (and some other) HIF-

1 erythropoietin quick secretion (min – 24 h), RBC in 5 days production of proerythroblasts, speeding up

erythropoietic cells are among the most rapidly growing and reproducing cells

person’s nutritional status vitamin B12 and folic acid (thymidine) macrocytes – flimsy membrane and irregular,

large shape – shorten life span (1/2-1/3 normal) B12 – pernicious anemia (atrophic gastric

mucosa; parietal cells – intrinsic factor) folic (pteroylglutaminic) acid – widely

spread but destroyed during cooking – sprue

Formation of Hemoglobin

begins in proerythroblasts and continues even into the reticulocyte stage

succinyl-CoA from Krebs metabolic cycle alpha, beta, gamma and delta chains most common – hemoglobin A (2 alpha, 2

beta chains) each hemoglobin molecule transports 4

molecules of oxygen

sickle cell anemia –the amino acid valine is substituted for glutamic acid at one point in each of the two beta chains

15 μm elongated crystals in low oxygen environment

loosely and reversibly combining with O2

“coordination bond”, molecular oxygen

Iron Metabolism

hemoglobin, myoglobin, cytochrome-oksidase, peroxidase and catalase

total iron in the body – 4-5g (65% in hemoglobin, 4% in myoglobin, 15-30% in reticuloendothelial system and liver parenchymal cells)

transferrin molecule binds strongly with receptors in the cell membrane s of erythroblasts in bone marrow – endocytosis

inadequate quantities of transferrin – failure to transport iron to the erythroblasts – hypochromic anemia

Absorption of Iron

liver secretes moderate amounts of apotransferrin into the bile – transferrin (with the iron, pinocytosis into enterocyts, plasma transferrin)

absorption is slow and limited; total body iron is regulated mainly by altering the rate of absorption

Life Span of RBC

average circulating time 120 days cytoplasmic enzymes:

1) maintaining pliability of the cell membrane2) maintain membrane transport of ions3) keep the iron in ferrous, rather than ferric form4) prevent oxidation of the RBC proteins

many RBC self-destruct in the spleen (when squeezing through the red pulp)

hemoglobin is phagocytized by macrophages (Kupffer cells of the liver) iron and bilirubin (from porphyrin portion)

Anemias (deficiency of hemoglobin)

1) microcytic hypochromic anemia – blood loss anemia (acute and chronic)

2) aplastic anemia – bone marrow aplasia (high-dose radiation, chemotherapy, drugs, toxic chemicals – insecticides or benzene)

3) megaloblastic anemia (lack of B12 (pernicious) or folic acid)

4) hemolytic anemia (abnormalities (hereditary) of RBC)

1) hereditary spherocytosis (small and spherical RBC)

2) sickle cell anemia (hemoglobin S, crisis)3) erythroblastosis fetalis

Effects of Anemia on Circulation

viscosity of blood depends largely on RBC fall in blood viscosity decrease in total

resistance (added tissue hypoxia – vasodilation) increase in CO (3-4x) increased pumping workload on the heart

problems during exercise – acute cardiac failure

Polycythemia

secondary polycythemia – due to hypoxia (at high altitude, cardiac failure) – 6-7 x 1012 (30%)

polycythemia vera (erythremia) – 7-8 x 1012 (Ht = 60-70%) – genetic aberration in the hemocytoblastic cells

increased viscosity – CO almost normal (decreased venous return, but increased blood volume), ruddy complexion with a bluish (cyanotic) tint to the skin)

Blood Types; Transfusion; Tissue and Organ

Transplatation

Antigenicity

first attempts were unsuccessful transfusion reaction and death blood posses antigenic and immune

properties at least 30 commonly occurring, and

hundreds of other antigens most of antigens are week, used to establish

parentage systems: O-A-B and Rh

OAB system is discovered by Austrian scientist Karl Landsteiner 1900. (three types, awarded Nobel prize 1930; simultaneously with Czech serologist Jan Janský)

also with Alexander S Wiener identified Rh factor 1937.

O-A-B Blood Types

antigens A i B (also called agglutinogens – cause blood cell agglutination) occur on the surface of the RBC

because of the way of inheritance people may have neither of them on their cells, they may have one or they may have both simultaneously

when neither A or B agglutinogen is present – blood (person) is blood type O

only agglutinogen A – blood is type A only agglutinogen B – blood is type B when both agglutinogens are present –

blood is type AB

antigen H – essential precursor of OAB blood antigens

located on chromosome 19, posses 3 exons which are coding enzyme fucosyltransferase

enzyme creates H antigen on RBC carbohydrate chain: β-D-galactose, β -D-N-

acetilglucosamine, β -D-galactose i α-L-fucose (connection with protein or ceramid)

OAB locus is on chromosome 9, has 7 exons

exon 7 is the biggest and contains the greatest portion of coding sequence

OAB locus has 3 allele types: O, A, B

allele A codes glycosyltransferase which bindes N-acetylgalactosamine on D-galactose end of H antigen

allele B codes glycosyltransferase which bindes α -D-galactose on D-galactose end of H antigen

allele 0 has deletion in exon 6 – loss of enzimatic activity – only H antigen is present

Relative Frequencies of the Different Blood Types:

0 47%A 41%B 9%AB 3%

there are 6 different allele types among white population: (A1, A2, B1, O1, O1v i O2), in Asian population B type is more frequent

Agglutinins

antibodies directed at agglutinogens immediately after birth – not present they are formed 2-8 month after the birth maximum titer is reached 8-10 years of age gamma-globulins (IgM i IgG) why are they produced? environmental antigens (bacteria, viruses,

plants, foods)

for anti-A agglutinins – influenza for anti-B agglutinins – gram-negative

bacteria (E. coli)

“light in the dark” theory – viruses during replication process incorporate parts of host membrane

Agglutination Process

agglutinins have 2 (IgG) or 10 (IgM) binding sites for agglutinogens

attaching to two or more RBC – bounding together (clump of cells) – agglutination

plugging of small blood vessels throughout the circulation – physical distortion of the cells or phagocytosis – hemolysis of the RBC

Acute Hemolysis

on rare occasion hemolysis occurs immediately in

circulating blood activation of the complement system –

release of proteolytic enzymes (the lytic complex) – rupture of the cell membranes (existence of high titer of IgM antibodies – hemolysins)

Blood Typing

blood typing and blood matching RBC are separated from the plasma and

diluted with saline; mixing with anti-A and anti-B agglutinins

Rh Blood Types

spontaneous agglutinins almost never occur (difference)

person must first be massively exposed (transfusion)

six common types of Rh antigens (C, D, E, c, “d”, e; one of each pair in every person)

most prevalent is type D antigen (Rh +) about 85 percent of white people are Rh +

in reality two genes: RHCE i RHD proteins which carry Rh antigens are

transmembranic proteins (ion channel?) RHD gene codes RhD protein with D

antigen (on chromosome 1p) RHCE gene codes RhCE protein with C, E,

c, e antigens there is no d antigen, “d” means lack of D

antigen

Rh Immune Response maximum concentration of anti-Rh

agglutinins develop about 2 to 4 months after transfusion

delayed, mild transfusion reaction erythroblastosis fetalis (mother Rh -, father

Rh +, child inherits Rh from father; mother develops agglutinins for Rh which diffuse through the placenta into the fetus and cause red blood cell agglutination)

firstborn usually doesn’t develop, second born in 3%, third born in 10%

agglutination of the fetus's blood – hemolysis – release of hemoglobin (jaundice)

newborn baby is usually anemic, liver and spleen become greatly enlarged, early forms of RBC are passed from the baby's bone marrow into the circulatory system, permanent mental impairment or damage to motor areas of the brain because of precipitation of bilirubin in the neuronal cells – kernicterus

treatment – replacing the neonate's blood with Rh-negative blood (400 ml during 1,5 hours)

RBC are replaced by infant's own at the time anti-Rh agglutinins that had come from the mother are destroyed

Prevention of Erythroblastosis Fetalis

development of Rh immunoglobulin globin, an anti-D antibody

administered to the expectant mother starting at 28 to 30 weeks of gestation or after delivery

Transfusion Reactions

usually agglutination of the RBC from the donor, rarely agglutination of cells in recipient (dilution of plasma)

hemolysis (immediate – hemolysins, later – phagocytosis)

jaundice (more than 400 milliliters of blood is hemolyzed in less than a day)

acute kidney failure 1) release of toxic substances – renal

vasoconstriction2) loss of circulating RBC – circulatory

shock3) hemoglobin precipitates and blocks

many of the kidney tubules 4) patient dies within a week to 12 days

Transplantation of Tissues and Organs

beside RBC antigens each tissue posses additional set of antigens which are responsible for immunological reactions

resisting invasion by foreign bacteria or red cells

Type of Transplant

autograft – tissue or whole organ from one part of the same animal to another part

isograft – from one identical twin to another

allograft – from one human being to another or from any animal to another animal of the same species

xenograft – from a lower animal to a human being or from an animal of one species to one of another species

xenografts – immune reactions almost always occur, causing death of the cells in the graft within 1 day to 5 weeks after transplantation

skin, kidney (5 to 15 years), heart, liver, glandular tissue, bone marrow, and lung

most important antigens for causing graft rejection are a complex called the HLA antigens (6 of these antigens are present on the tissue cell membranes of each person, but there are about 150 different HLA antigens to choose from – more than a trillion possible combinations; on the white blood cells, as well as on the tissue cells – tissue typing)

Prevention of Graft Rejection suppressing the immune system T cells are mainly the portion of the

immune system important for killing grafted cells

1) glucocorticoid hormones and similar drugs2) drugs that have a toxic effect on the lymphoid

system – azathioprine3) cyclosporine – specific inhibitory effect on the

formation of helper T cells infectious disease, incidence of cancer!