Lecture 5: Erythrocytes

Function & Normal/Abnormal Destruction

What are the three main functions of erythrocytes?

• transport of oxygen

• transport of carbon dioxide

• buffering of hydrogen ions

What increases oxygen carrying capacity of blood?

hemoglobin

What levels would you check to evaluate blood oxygen content?

• hemoglobin content

• pO2

• hemoglobin oxygen affinity (P50)

What type of graph would you examine to determine how well oxygen is being transported throughout the body?

sigmoid oxygen dissociation curve

What is the point where hemoglobin is 50% saturated with oxygen?

P50

On an oxyhemoglobin dissociation curve, what does a right shift imply?

lower O2 affinity, higher P50

On an oxyhemoglobin dissociation curve, what does a left shift imply?

higher O2 affinity, lower P50

With a lower P50 and higher O2 affinity, what decreases?

• 2,3-DPG

• temp

• CO2

• H+

What is produced in a side pathway of glycolysis and decreases Hb oxygen affinity inside RBCs?

2,3-DPG

Why does 2,3-DPG concentration decrease when oxygen affinity increases?

usually binds to deoxyhemoglobin and lowers oxygen affinity, but when oxygen binds hemoglobin, the conformation change causes 2,3-DPG to not be accomadated

Why is fetal blood having a higher affinity of Hb for O2 (lower P50) beneficial?

because the fetus lives in a low O2 environment

What percent of CO2 is actually disolved?

5%

Why is the predominant way the body stores CO2?

bicarbonate

Why do erythrocytes contain the enzyme carbonic anhydrase?

to catalyze the reaction between carbon dioxide and water into carbonic acid, which will dissociated in to bicarbonate and protons (H+)

What is the importance of carbamino groups in CO2 transport?

carbaminohemoglobin (CO2 + hemoglobin with attached amine) has an increased CO2 carrying capacity to transport it to tissues and lungs

What does hemoglobin buffer in the blood?

proteins and organic acids produced by metabolism

True or false: DeoxyHb is a weaker acid than OxyHb.

true

What happens to Hb when CO2 and H+ concentrations increase in tissues?

release of O2 from OxyHb is promotes and the DeoxyHb that is formed binds the increased amounts of H+ and CO2

What is the result of increased O2 concentrations in the lungs?

formation of OxyHb and the release of CO2 and H+ → H+ released combines with bicarb (HCO3-) forming carbonic acid (H2CO3) which reversibly forms CO2 and water

What contributes to the membrane fluidity of erythrocytes?

phospholipids

What is intercalated with the fatty acid chains pointed to the center of the phospholipid bilayer making up erythrocyte membranes?

unesterified cholesterol

What are the integral erythrocyte membrane proteins?

• transmembrane glycoproteins (CHO outward)

• receptors and transport proteins (Band 3 anion transporter)

• erythrocyte antigens

What are the erythrocyte skeletal membrane proteins?

• cytoskeleton lattice-like arrangement on inner surface of membrane

• determine membrane shape, deformability, and durability

What type of antigens are blood group antigens?

alloantigens (isoantigens) = self-antigens

What are most blood group antigens produced by?

erythroid cells

How soon are antibodies expected to appear in plasma after a mismatched blood transfusion?

3-5 days

What is the major blood group antigen of dogs?

DEA 1

What is the major blood group antigen of cats?

AB group, Mik antigen

What is the major blood group antigens of horses?

A and Q factors

Natural antibodies are present and clinically important in dogs, but not cats.

false: present by not clinically important in dogs, but are important in cats

What type of antibodies do B positive cats usually have?

high amounts strong-acting anti-A antibodies in plasma

What type of antibodies do A positive cats usually have?

variable amounts of weak-acting anti-B antibodies in plasma

True or false: mammalian erythrocytes have no ribosomes, mitochondria, or ER, so they cannot perform the Krebs cycle, protein synthesis, or lipid synthesis.

true

What pathways do mammalian erythrocytes use for metabolism?

• 90-95% glycolysis (Embden-Meyerhof pathway)

• 5-10% pentose phosphate pathwya

• DPG pathway (no net ATP generated)

Anaerobic glycolysis generates ______ per _______ metabolized.

2 ATP per glucose

What is responsible for maintenance of RBC shape and deformability?

Mg++-ATPase

What are the energy requirements of erythrocytes?

• maintain Na+ and K+

• maintenance of high concentrations of 2,3-DPG in dogs, horses, and pigs

• pentose phosphate pathway protection against oxidant injury using NADPH

What enzyme deficiencies cause dogs to have insufficient ATP and severe anemias?

phosphofructokinase and pyruvate kinase (PFK and PK)

How might erythrocytes suffer an oxidative injury?

exposure to low levels of oxidants (oxygen and nitrogen free radicals) from environment or normal metabolic processes

What enzymes protect against oxidants?

glutathione and antioxidant enzymes

How does NADPH from the pentose phosphate pathway protect from oxidative injury?

provides electrons for reduction of oxidants

What is the function of reduced glutathione (GSH)?

electron donor for reductive enzyme reactions

What is generated by the pentose phosphate pathway to protect against oxidants?

NADPH

What happens when hemoglobin suffer an oxidative injury?

methemoglobin forms which cannot carry oxygen and heinz bodies are formed

What happens to erythrocyte membranes after oxidative injuries?

eccentrocytes (erythrocytes with hemoglobin shifted to one side), hemolysis, increased phagocytosis

What is the difference between oxygenation vs oxidation?

oxygenation: adding oxygen

oxidation: losing electrons

What change occurs in Hb when oxygenated vs oxidated?

oxygenated = deoxyhemoglobin → oxyhemoglobin

oxidated = hemoglobin → methemoglobin + superoxide

When is it easiest to recognize the brownish color of methemoglobin?

when blood is oxygenated

What can reduced methemoglobin into functional hemoglobin in erythrocytes?

cytochrom b5 reductase (Cb5R) enzymes, using NADH as the electron donor

What deficiency does this dog have?

blue tongue = not enough oxygen to tissues = too much methemoglobin = methemoglobin reductase deficiency

What can be seen in this RBCs with oxidized denatured hemoglobin?

heinz bodies

What is characteristic of horses with glutathione reductase (GR) and G6PD hereditary enzyme deficiencies?

erythrocyte membrane damage and anemia

True or false: normally, RBC loss from blood is not random.

true

What is erythrocyte life span related too?

body weight (longer in bigger animals)

What is the average erythrocyte life span in domestic mammals?

2-5 months

What occurs in cumulative oxidant injury of erythrocytes?

• eryptosis (cell death like apoptosis)

• membrane damage with altered phospholipids and carbohydrates

• band 3 clustering forms a senescent antigen

What is this an example of?

eryptosis

What recognizes damaged erythrocyte membranes to initiate erythrophagocytosis?

macrophage receptors

How does an antibody promote phagocytosis of an erythrocyte?

binds to senescent antigen (altered band 3) and promotes phagocytosis through Fc and C3b receptors

What is produced when a macrophage phagocytizes an erythrocyte?

bilirubin and non-hemoglobin heme

How does bilirubin make it to the liver?

exits macrophage and binds to albumin in plasma