Gas Transport & Erythrocyte Physiology Flashcards
What are the fxns of erythrocytes?
- deliver oxygen and nutrients
- remove wastes
- maintain homeostasis (acid/base buffering)
- circulation
What is the hematocrit (ratio of RBC) in an adult male?
-45 percent
What is the hematocrit (ratio of RBC) in an adult female?
-40 percent
What is the hematocrit (ratio of RBC) in a 2-month-old infant?
-35 percent
What is the hematocrit (ratio of RBC) in a newborn?
-55 percent
Delineate the cell stages of erythropoiesis.
Hematopoietic Stem Cell
Reticulocyte
Erythrocyte
What is the main influence on erythrocyte maturation?
oxygen demand
What hormone is the main regulator of erythrocyte production?
erythropoietin (EPO)
Where is erythropoietin (EPO) synthesized?
kidney
What situations prompt the synthesis of erythropoietin (EPO)?
- anemia
- low Hb
- low blood volume (particularly RBF)
- central hypoxia
What transcription factor is responsible for regulating synthesis of erythropoietin (EPO)?
hypoxia inducible factor (HIF)
How long is the life cycle of an erythrocyte?
120 days
Where does an erythrocyte go to “die” (aka rupture)?
red pulp of the spleen
How does the Hb from a ruptured RBC get “taken up”?
Hb is ingested immediately by macrophages
What happens to the heme from a ruptured RBC?
it gets converted and is excreted in the feces
- biliverdin, bilirubin, urobilinogen, stercobilin
- stercobilin makes feces brown
What happens to peptides released from ruptured erythrocytes in the spleen?
peptides get broken down into amino acids and are re-used in protein synthesis
What happens to the iron released from ruptured erythrocytes in the spleen?
-iron is bound to transferrin and taken to the liver
- stored as ferritin
- shipped to marrow for RBC production
What are the ways oxygen is transported in the blood?
- dissolved
- bound to Hb (majority)
What are the ways that carbon dioxide is transported in the blood?
- dissolved
- carbamino compounds
- bound to an amine group other than heme
- bicarbonate (majority)
What is a Haldane shift?
-the presence of oxygen reduces the affinity of the other amine groups for carbon dioxide
What enzyme converts carbon dioxide to bicarbonate plus a hydrogen ion?
carbonic anhydrase
What ion helps export dissolved carbon dioxide from the blood?
chloride
Chloride Shift, aka Hamburger Shift
What is the approximate volume of oxygen carried in the blood versus carbon dioxide?
20 mL oxygen per 100 mL blood
50 mL carbon dioxide per 100 mL blood
What is the major form of oxygen in the blood?
bound to Hb
What is the major form of carbon dioxide in the blood?
bicarbonate
What is a normal amount of dissolved oxygen in the blood versus carbon dioxide?
0.3 mL oxygen per 100 mL blood
3 mL carbon dioxide per 100 mL blood
What is a normal amt of Hb in the blood?
15 g per 100 mL blood
How much oxygen can bind to 1 g of Hb?
1.34 mL
What is a normal oxygen concentration in blood?
15 x 1.34 = 20.1
20.1 mL oxygen per 100 mL blood
What does a L shift in the oxygen-dissociation curve represent?
-increased affinity of Hb for oxygen
What are two conditions associated with a L shift of the oxygen-dissociation curve?
polycythemia
methemoglobinemia
What does a R shift in the oxygen-dissociation curve represent?
-decreased affinity of Hb for oxygen
What medical condition is associated with a R shift of the oxygen-dissociation curve?
anemia
What parameters are increased in a R shift of the oxygen-dissociation curve?
- carbon dioxide
- more acidic muslce
- BPG
- exercise
- local temperature, metabolism
Why are B12 (cobalamin) and B9 (folate) important for RBC production?
B12 and B9 are req’d for DNA synthesis
Why is iron important for RBC production?
iron is req’d for Hb to bind oxygen
True or False: erythrocytes have mitochondria
False
Why do erythrocytes need ATP?
- ATP is used to maintain iron in the ferrous (Fe2+) state
- w/o ATP, cells are exposed to oxidative damage
How does iron-deficient anemia impact the oxygen-carrying capacity of blood?
-less Hb = less oxygen content
- 15 g x 1.34 = 20.1 mL oxygen per 100 mL blood
- 8 g x 1.34 = 10.72 mL oxygen per 100 mL blood
What does percent saturation indicate when referring to Hb and oxygen?
- what percentage of the Hb’s are bound to an oxygen
- thus, oxygen content of the blood can decrease d/t less Hb, while percent saturation doesn’t change!
What is hemochromatosis?
iron overload
What are some causes of hemochromatosis?
- neonatal (unknown cause develops in utero)
- primary (genetic)
-secondary (multiple blood transfusions, increased iron intake, ineffective erythropoiesis)
What are some characteristics of primary polycythemia (genetic)?
- low EPO
- extra RBC’s
- increased blood volume
- increased viscosity
- normal-ish cardiac output
What are some characteristics of secondary polycythemia?
- causes: hypoxia, neoplasms, cancer, kidney disease
- increased EPO
- extra RBC’s
- abnormal cardiac output
What are some characteristics of physiologic polycythemia?
- high altitude adaptation
- extra RBC’s
- normal cardiac output
What are the characteristics of methemoglobinemia?
- increased met-Hb
- iron is in the ferric (Fe3+) form
- decreased oxygen availability to tissues
- chocolate-colored blood
- blue skin
What is the equation to calculate arteriovenous (a-v) oxygen difference?
PaO2 going into a tissue
minus
PvO2 coming out of a tissue
What is the arteriovenous oxygen difference used for?
-indicates oxygen consumption in a certain tissue
What situations could have an increased arteriovenous oxygen difference?
- exercise
- certain tissue types such as the kidney
What does the respiratory quotient describe?
the relationship b/w amt of oxygen consumed and carbon dioxide produced
What factor changes the respiratory quotient?
the type of fuel being used by the body
- glucose = 1.0
- mixed fuels = 0.8
What situations would cause the respiratory quotient to increase?
exercise
