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Chapter 19 Phys - Red Blood Cells

What is hemoglobin (Hb)?
*Red pigmented, globular heme protein that carries iron
How many hemoglobin molecules are found in each red blood cell?
~ 250 million hemoglobin molecules per red blood cell
What is the structure of adult hemoglobin (HbA)?
*Contains 4 individual globin protein units
-2 alpha and 2 beta globins

*Each globin contains a heme (so 4 hemes in each Hb molecule)
What is the difference in structure between fetal hemoglobin (HbF) and adult hemogolbin (HbA)?
*Fetal hemoglobin contain GAMMA globins NOT BETA
-Contains 2 alpha and 2 gamma globins

*Contains different globins than HbA becuase HbF has to be able to bind oxygen tighten than HbA

*Fetal hemoglobin (HbF) becomes adult hemoglobin (HbA) at birth)
What is a heme?
*Each globin in hemoglobin contains one heme

*Heme is a porphyrin molecule that contains iron

*Each heme iron can bind one oxygen molecule (so each hemoglobin molecule can bind a maximum of 4 oxygen molecules

*Iron gives RBC its red color
How many oxygen molecules can each red blood cell carry?
~ 1 billion

*250 million hemoglobin molecules in each red blood cell

*Each hemoglobin molecule can bind 4 oxygen molecules
What is an oxyhemoglobin?
*Hemoglobin that is carrying oxygen

*Can carry up to 4 oxygen molecules

*Fully saturated when carrying 4 oxygen molecules
What is deoxyhemoglobin?
Hemoglobin with no oxygen bound to it
What is a pulse oximeter?
*Device that measures the percent of hemoglobin fully saturated with oxygen in arterial blood

*Normal is 95-99%
Do red blood cells have nuclei?

*Allows for greater volume for a greater number of hemoglobin molecules

*Nucleus is present during formation of the RBC, but condenses during later stages of development

*Lack of a nucleus means that the RBC cannot produce new proteins or divide (so RBC can't repair damage)
Do red blood cells have mitochondria?

*Produce ATP via anaerobic glycolysis only (2 net ATP per glucose molecule)
What is erythropoiesis?
Production of red blood cells
How red blood cells are produced per second?
~ 2.5 million RBCs produced per second
How long does it take a red blood cell to mature?
~ four days
What situations can cause red blood cell production to increase to more than 2.5 million per second?
*Any condition that lowers the oxygen carrying capabilities of blood, such as:

-Decreased or defective red blood cells
-Decreased or defective hemoglobin
-Low blood oxygen levels
What conditions and disease cause low blood oxygen levels?
*Lung disease (ex: emphysema)
*Cardiovascular disease (ex: heart failure)
*High altitude
*Strenuous exercise
How does the body increase the number of red blood cells being produced?
*When a condition that causes lower oxygen carrying capacity of blood occurs, erythropoietin (EPO) is released fro the kidneys

*This stimulates porerythroblast formation

***The red bone marrow is not DIRECTLY triggered
How many red blood cells are destroyed every second?
~ 2.5 million red blood cells destroyed every second

(This keeps the RBC count fairly constant)
What is the average lifespan of a red blood cell?
~ 120 days

*Can't repair damage because it can't produce new proteins (no nucleus, no genetic info)
What happens when worn red blood cells pass through the spleen and liver?
*They rupture and are phagocytized by macrophages

*They are broken down into heme and globin molecules
What happens to the globin portion of a phagocytized red blood cell?
*The globin is broken down to amino acids, which are recycled into new proteins
What happens to the heme portion of a phagocytized red blood cell?
*The heme is broken down into:
-Carbon Monoxide
What happens to the iron portion of the heme of a phagocytized red blood cell?
*The iron attaches to TRANSFERRIN (a plasma protein) and is transferred to one of the three following places:

1. Most (~60%) of the iron is taken to the LIVER where the the transferrin passes it off to APOFERRITIN (apoferritin + iron = FERRITIN). The iron is stored in liver as ferritin.

2. To the SPLEEN, stored as ferritin

3. To the BONE MARROW to make hemoglobin
What happens to the biliverdin portion of the heme of a phagocytized red blood cell?
*Biliverdin (GREEN) is converted into bilirubin (YELLOW)

*Bilirubin attaches to ALBUMIN (a plasma protein) (bilirubin + albumin = FREE BILIRUBIN)

*Free bilirubin is LIPID SOLUBLE (bilirubin cannot exit the body when lipid soluble only water soluble)

*Free bilirubin is transported to the liver and joined to GLUCURONIC ACID (free bilirubin + glucuronic acid = CONJUGATED BILIRUBIN

*Conjugated bilirubin is WATER SOLUBLE

*Conjugated bilirubin is used to produce bile, which is released into small bowel
-Most is excreted in feces (gives feces brown color)

-Some is absorbed into the blood and excreted by kidneys (gives urine yellow color)
What happens to the carbon monoxide portion of the heme of a phagocytized red blood cell?
*Combines with hemoglobin to form carboxyhemoglobin

*Normally is ~ 1%