mlab 1415- hematology keri brophy-martinez chapter 6: hemoglobin

MLAB 1415- Hematology

Keri Brophy-Martinez

Chapter 6: Hemoglobin

Hemoglobin

What is it? Iron- bearing protein which is the main component of the RBC Gives the red cell its color

Synthesis Majority synthesized at the polychromatophilic normoblast stage

Regulation Stimulated by tissue hypoxia Hypoxia causes the kidneys to increase production of EPO, which

increases RBC and hemoglobin production Function

Carry oxygen from the lungs to the tissues Remove CO2

Buffering action, maintains blood pH as it changes from oxyhemoglobin (carrying O2) to deoxyhemoglobin ( without O2)

Hemoglobin Reference Ranges

Adults Male 14-17.4 g/dL Female12-16.0 g/dL

Children Birth 13.5-20.0 g/mL 6-12 years 11.5-15.5 g/mL

**Refer to inside cover of text for other age ranges

Structure

4 polypeptide Subunits Heme group

Porphyrin ring Ferrous iron

Globin chain 2 Alpha Chains 2 Beta chains

Hemoglobin Synthesis

Synthesis Occurs in the mitochondria of developing red cells

as they mature in the bone marrow Processes necessary for normal synthesis

Adequate iron supply & delivery Adequate synthesis of protoporphyrins Adequate globin synthesis

Heme Synthesis

Chain of Events Iron delivery & supply

Iron is delivered to the reticulocyte by transferrin

Synthesis of protoporphyrins

Occurs in the mitochondria of RBC precursors

Mediated by EPO and vitamin B6

Protoporphyrin + iron = heme

Globin Synthesis

Chain of Events The rate of globin synthesis is

proportional to the rate of porphyrin synthesis.

Proper globin synthesis depends on genes. The precise order of amino acids in the globin chains is critical to the structure and function of hemoglobin.

Chain designations are as follows

Alpha α, beta β, delta δ, epsilon ε, gamma γ, zetaζ

Normal hemoglobins

Hemoglobin Synthesis

Oxygen transport

The amount of O2 bound to hemoglobin and released to tissues depends on PO2 and PCO2, but also the affinity of hemoglobin for O2.

Oxyhemoglobin: hemoglobin with oxygen Deoxyhemoglobin: hemoglobin without

oxygen Oxygen affinity is the ease with which

hemoglobin binds and releases oxygen.

Oxygen Affinity

Determines the proportion of O2 released to the tissues or loaded onto the cell at a given oxygen pressure.

Increases in oxygen affinity means hemoglobin has an increased affinity for O2, so it binds more. However, it does not want to give it up.

Decreases in oxygen affinity, cause O2 to be released.

Bohr Effect

Alterations in blood pH, shifts oxygen dissociation curve

In acidic pH, the curve shifts to the right Results in an enhanced capacity to release

O2 where it is needed

Oxygen Dissociation Curve

Right-Shift Hgb has less attraction

for O2

Hgb willing to release O2 to tissue

Examples: anemia, acidosis

Even though there may be less RBC’s, they act more efficiently to deliver O2

to target

Oxygen Dissociation Curve

Left shift Hgb has more

attraction for O2

Hgb less willing to release O2 to tissue

Examples: presence of abnormal Hgb’s, alkalosis

Carbon Dioxide Transport

Three mechanisms of transport Dissolution in the plasma Formation of bicarbonic acid Binding to carbaminohemoglobin

Nonfunctional hemoglobins

What do they do? Hypoxia

Inadequate amount of O2 in the blood

Cyanosis Presence of > 5 g/dl deoxyhemoglobin in blood Patient appears blue

Nonfunctional hemoglobins

Carboxyhemoglobin Oxygen molecules bound to heme are replaced by carbon monoxide. Slightly increased levels of carboxyhemoglobin are present in heavy

smokers and as a result of environmental pollution. Can revert to oxyhemoglobin.

Methemoglobin Iron in the hemoglobin molecule is in the ferric (Fe3) state instead of the

ferrous (Fe2) state. Incapable of combining with oxygen. Can occur as a result of strong oxidative drugs or to an enzyme

deficiency (more discussion to follow). Can revert to oxyhemoglobin

Sulfhemoglobin Hemoglobin molecule contains sulfur. Caused by certain sulfur-containing drugs or chronic constipation. Cannot revert to oxyhemoglobin and may cause death.

References

McKenzie, S. B. (2010). Clinical Laboratory Hematology (2nd ed.). Upper Saddle River, NJ: Pearson Education, Inc..