60 Questions
What is the primary substance within an erythrocyte?
Hemoglobin
What is the estimated number of erythrocytes in the human body?
Over 20 trillion
Why is most oxygen transported on hemoglobin rather than dissolved in plasma?
Hemoglobin has a higher oxygen carrying capacity
Where does carbon dioxide diffuse into from the blood in the pulmonary capillaries?
The alveoli
How is carbon dioxide transported from systemic cells to the lungs?
Through the systemic circulation to the right side of the heart, then to the pulmonary circulation
What is the approximate amount of carbon dioxide produced by cells per minute?
200 mL/min
What is the approximate oxygen saturation of hemoglobin in the blood as it leaves the lungs?
65%
What is the maximum number of oxygen molecules that can bind to a single hemoglobin molecule?
4
What is the meaning of a hemoglobin being 25% saturated with oxygen?
One-quarter of the available iron binding sites are occupied by oxygen.
During resting conditions, what percentage of the oxygen transported by hemoglobin is released as it passes through systemic capillaries?
60%
What happens to the hemoglobin saturation in the blood leaving systemic capillaries during vigorous exercise?
It decreases to 35%
Which of the following is NOT a substance that hemoglobin transports relative to respiration activities?
Nitrogen bound to the globin
What is the percentage of oxygen reserve bound to hemoglobin after passing through systemic capillaries?
30%
How does the binding or release of one substance by hemoglobin influence its ability to bind or release the other two substances?
It causes a conformational change in the hemoglobin molecule that temporarily alters its shape.
What is the most important variable that determines the percent oxygen saturation of hemoglobin?
The partial pressure of oxygen (PO2) in the blood
If systemic cell Po2 decreases to 20 mm Hg during vigorous exercise, what happens to the hemoglobin saturation?
It decreases to 40%
What purpose does the oxygen reserve serve in the body?
To provide additional oxygen to systemic cells under increased metabolic demands
What is the meaning of hemoglobin being 100% saturated with oxygen?
All of the available iron binding sites on the hemoglobin molecules are occupied by oxygen.
What is the approximate hemoglobin saturation at an altitude of 17,000 feet?
75%
At what altitude does altitude sickness typically occur for most individuals?
8,200 feet
What are some milder symptoms of altitude sickness?
Headache
How do changes in altitude initially affect hemoglobin saturation?
Small changes
What is the approximate alveolar PO2 at an altitude of 9000 feet?
65 mm Hg
At what altitude do adverse physiologic effects from a decrease in alveolar PO2, known as altitude sickness, start occurring?
6,600 feet
What happens when CO2 and H+ are released from hemoglobin during pulmonary gas exchange?
It facilitates oxygen binding to hemoglobin
What is the effect of CO2 and H+ binding to hemoglobin during tissue gas exchange?
It causes hemoglobin to release oxygen
What is the effect of an increase in body temperature on hemoglobin during tissue gas exchange?
It causes hemoglobin to release more oxygen
Which of the following statements about the role of hemoglobin in gas exchange is correct?
Hemoglobin transports oxygen and facilitates the transport of CO2
What is the name given to the effect where the binding of CO2 and H+ to hemoglobin decreases its affinity for oxygen?
Bohr effect
Which of the following statements about the transport of gases by hemoglobin is incorrect?
The binding of oxygen to hemoglobin causes a conformational change that facilitates CO2 release
What is the primary factor determining the ability of blood to transport oxygen?
Solubility coefficient of oxygen in blood plasma
What is hemoglobin referred to when it is bound to oxygen?
Oxyhemoglobin
Where does oxygen mainly attach within the blood for transport?
Hemoglobin within erythrocytes
What is the term used for deoxygenated hemoglobin?
Deoxyhemoglobin
Which term describes hemoglobin with carbon monoxide bound to it?
Carboxyhemoglobin
What percentage of the total oxygen in the blood is typically dissolved in the plasma?
~2%
At an altitude of approximately 9000 feet, the hemoglobin saturation would be:
91%
What is the approximate hemoglobin saturation at an altitude of 17,000 feet?
75%
At what altitude do adverse physiologic effects from a decrease in alveolar Po2, known as altitude sickness, start occurring for some individuals?
6600 feet
Which of the following is NOT mentioned as a milder symptom of altitude sickness?
Pulmonary edema
What happens to hemoglobin saturation as altitude increases from sea level?
It decreases gradually
What is the relationship between the binding of CO2 and H+ to hemoglobin and its affinity for oxygen during tissue gas exchange?
The binding of CO2 and H+ decreases hemoglobin's affinity for oxygen
What effect does the release of CO2 and H+ from hemoglobin have during pulmonary gas exchange?
It increases the affinity of hemoglobin for oxygen
During tissue gas exchange, the binding of CO2 and H+ to hemoglobin causes:
A decrease in hemoglobin's affinity for oxygen
What is the effect of an increase in body temperature on hemoglobin during tissue gas exchange?
It decreases hemoglobin's affinity for oxygen
Which of the following statements is correct regarding the transport of gases by hemoglobin?
Hemoglobin transports both oxygen and carbon dioxide
What is the name given to the effect where the binding of CO2 and H+ to hemoglobin decreases its affinity for oxygen?
Bohr effect
What is the primary substance within an erythrocyte?
Hemoglobin
What is the primary role of carbonic anhydrase within erythrocytes in the transport of CO2?
It facilitates the conversion of CO2 to H2CO3, keeping the PCO2 relatively low and allowing continuous diffusion of CO2 from systemic cells into erythrocytes.
What happens to the CO2 that diffuses into erythrocytes from systemic cells?
It is converted to H2CO3 by carbonic anhydrase, which dissociates into H+ and HCO3-.
What is the role of the chloride shift in the transport of CO2?
It allows for the exchange of Cl- and HCO3- between erythrocytes and plasma, helping to buffer H+ and maintain pH.
What happens to the H2CO3 formed within erythrocytes during CO2 transport?
It dissociates into CO2 and H2O, with the CO2 being expelled in the lungs.
What is the primary function of hemoglobin in the transport of respiratory gases?
To bind and transport O2 from the lungs to systemic cells, and release it as needed.
What happens to the CO2 that diffuses from the plasma into the alveoli during pulmonary gas exchange?
It is expelled from the body during expiration.
What is the primary function of 2,3-BPG (2,3-biphosphoglycerate) in erythrocytes?
It decreases hemoglobin's affinity for oxygen.
Which of the following factors does NOT influence the oxygen-hemoglobin saturation curve?
Altitude
What is the effect of an increase in temperature on hemoglobin's affinity for oxygen?
It decreases hemoglobin's affinity for oxygen.
Which of the following hormones is NOT mentioned as stimulating the production of 2,3-BPG in erythrocytes?
Insulin
What is the effect of a decrease in pH (increase in H+ concentration) on hemoglobin's affinity for oxygen?
It decreases hemoglobin's affinity for oxygen.
Which of the following statements about the binding of CO2 and H+ to hemoglobin is correct?
Binding of CO2 and H+ decreases hemoglobin's affinity for oxygen.
Study Notes
Erythrocytes and Hemoglobin
- Erythrocytes are biconcave, flexible cells with no nucleus or mitochondria and few organelles.
- They retain their plasma membrane, and their primary substance is hemoglobin.
- An erythrocyte can be described as a "bag of hemoglobin."
- There are approximately 20 trillion erythrocytes in the human body, each containing about 280 million hemoglobin molecules.
Oxygen Transport
- Oxygen is transported within blood from the alveoli to systemic cells in body tissues.
- The ability of blood to transport oxygen is dependent upon two factors:
- Solubility coefficient of oxygen in blood plasma (only 2% of oxygen is dissolved in plasma)
- Presence of hemoglobin (Hb)
- Hemoglobin binds to oxygen, forming oxyhemoglobin (HbO2), which allows for 98% of oxygen to be transported within erythrocytes.
Carbon Dioxide Transport
- Carbon dioxide is transported from systemic cells to the lungs through deoxygenated blood.
- Carbon dioxide diffuses from systemic cells into the blood, then into pulmonary capillaries, and finally into the alveoli.
- The majority of carbon dioxide is transported in the form of bicarbonate ions (HCO3-) within erythrocytes.
Hemoglobin as a Transport Molecule
- Hemoglobin transports three substances relative to respiration activities:
- Oxygen attached to iron
- Carbon dioxide bound to the globin
- Hydrogen ions bound to the globin
- The binding or release of one substance causes a conformational change in hemoglobin, influencing the ability to bind or release the other two substances.
Oxygen-Hemoglobin Saturation Curve
- The oxygen-hemoglobin saturation curve shows how PO2 influences the percent saturation of hemoglobin during tissue gas exchange.
- Variables that influence the oxygen-hemoglobin saturation curve include:
- Temperature (increased temperature decreases hemoglobin saturation)
- pH (increased H+ concentration decreases hemoglobin saturation)
- 2,3-BPG (increased concentration decreases hemoglobin saturation)
- Altitude (increased altitude decreases hemoglobin saturation)
Tissue Gas Exchange
- Oxygen is released from hemoglobin during tissue gas exchange due to the conformational change caused by the binding of CO2 and H+.
- This release of oxygen is known as the Bohr effect.
- The oxygen-hemoglobin saturation curve helps to understand how PO2 influences the percent saturation of hemoglobin during tissue gas exchange.
Learn about the structure and function of erythrocytes - the red blood cells responsible for carrying oxygen in the body. Understand the unique characteristics of erythrocytes, including their lack of nucleus, mitochondria, and organelles, and their high hemoglobin content.
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