13. Hemoglobin and Oxygen Transport
What are the three forms that CO2 is carried in the blood
1. Dissolved in plasma (more soluble than O2) 2. Carbaminohemoglobin - CO2 bound to amino acid in hemoglobin 3. Bicarbonate ions (major method of transport)
What are the different factors that affect Hb-oxygen affinity
1. PCO2 2. pH 3. 2,3 DPG 4. Exercise 5. Temperature
How many molecules of oxygen can each hemoglobin carry
4
What makes up hemoglobin
4 polypeptide globins (2 alpha and 2 beta)
What is the typical pH range
7.35-7.45
How prevalent is sickle cell anemia
8-11% of african americans
How much of the oxygen carried in the arterial blood is bound to hemoglobin
97%
At a PO2 of 100mmHg, what is Hb saturation At a PO2 of 40 mmHg, what is Hb saturation What does this represent
97% 75% This represents a 22% unloading of O2 between the arterials and veins
What is % oxyhemoglobin saturation
A quantitative assessment of how well the lungs have oxygenated the blood
What is the oxygen dissociation curve
A sigmoidal (s-shaped) curve that demonstrates the relationship between PO2, Hb saturation, and oxygen content in the blood
Respiratory acidosis or alkalosis occurs with what?
Abnormal CO2 plasma concentration
Metabolic acidosis or alkalosis occurs with what?
Abnormal bicarbonate plasma concentration
What happens to affinity at higher pCO2
Affinity decreases at a higher PCO2
What is the bohr effect
Affinity decreases at a lower pH and increases at a higher pH
What happens to oxygen affinity at high temperatures Why? Shift?
Affinity decreases at high temperatures and increases at low temperatures More O2 unloaded to mm during exercise Shift right
What is the major buffer in the blood
Bicarbonate
What buffers nonvolatile acids (lactic, fatty, ketone acids)
Bicarbonate, and can not be regulated by breathing but rather the kidneys
What buffers carbonic acid
Breathing
Why is affinity lower at a higher PCO2
CO2 binds Hb to displace O2
What is metabolic acidosis
Caused by excessive consumption of acids in diet (high protein/high fat), excessive production of non-volatile acids (lactic acid or ketone bodies) or loss of bicarbonate (diarrhea)
What is repiratory alkalosis
Caused by hyperventalation; "blow off" CO2, H+ decreases, pH increases
What is respiratory acidosis
Caused by hypoventilation; rise of CO2 which increases H+ and lowers pH
What is metabolic alkalosis
Caused by loss of acids (excessive vomiting) or over consumption of bicarbonates
What is sickle cell
Deoxygenated hemoglobin S polymerizes into long fibers, creating a sickle-shaped RBC This hinders flexibility and the ability to pass through small vessels
What is oxyhemoglobin called when reduced
Deoxyhemoglobin
Where is the remaining three percent of oxygen that is not bound to hemoglobin found
Dissolved in plasma
Does fetal hemoglobin or regular hemoglobin have a higher affinity for O2
Fetal so that oxygen can be transferred to the fetus
Where do RBCs get energy? What occurs during this process
From anaerobic metabolism of glucose (has no nucleus or mitochondira) During the process, 2,3 diphophoglyceric acid (2,3-DPG) is made
What is methemoglobin
Further oxidized iron (ferric state Fe3+) and can't bind to oxygen
What is carbaminohemoglobin
Hb bound to CO2
How do HbF, HbS, and HbA compare
HbF is functional vs. HbS, but HbF has a higher affinity for O2 than HbA
What is carboxyhemoglobin
Hemoglobin is bound with carbon monoxide Hemoglobin binds CO 200 times stronger than with O2
What is the affinity for oxygen of myoglobin
Higher affinity to oxygen; oxygen is only released when PO2 is very low
How does increased CO2 influence oxygen loading/unloading
Increased CO2 Increase in H+ Lowers pH Increases O2 unloading at tissues
What leads to decreased pH of blood and what does this do to oxygen unloading
Increased metabolism leads to increased H+ Lower pH Increases O2 unloading at the tissues
What does 2,3 DPG do to oxygen loading/unloading? Shift?
Increases oxygen unloading Shifts the oxyhemoglobin dissociation curve to the right
What is is oxyhemoglobin
Iron is in oxidized form (ferrous state Fe2+) and can bind with O2
What is the function of oxygen that remains in the veins
It serves as an oxygen reserve
At the steep part of the oxygen dissociation curve, small changes in PO2 produce what
Large changes in % saturation
Does a high PO2 favor loading or unloading
Loading
What regulates acid base balance
Lungs and kidneys
What is erythropoietin
Made in the kidneys stimulates hemoglobin/RBC production in red bone marrow when O2 lvels are low
Where is thalassemia found
Mainly in people of mediterranean heritage
How do you measure % oxyhemoglobin saturation
Measured with a pulse oximeter or blood-gas machine as SpO2 (peripheral capillary oxygen saturation)
What are the different forms of hemoglobin
Oxyhemoglobin Carbaminohemoglobin Methmeoglobin Carboxyhemoglobin
What does total O2 content of blood depend on
PO2 and hemoglobin concentration
What is the direction of oxygen loading/unloading dependent on
PO2 of the environment and affinity of hemoglobin for O2
What does SpO2 measure? What is normal in arterial blood
Percentage of oxyhemoglobin to total hemoglobin 97%
What causes thalassemia
Production of either alpha or beta chains is defective Increases synthesis of gamma chains Many mutations are possible giving a wide range of symptoms
What is muscle myoglobin
Red pigment found in skeletal and cardiac mm
How do kidneys help bicarbonate regulate pH
Releasing H+ in the urine and by producing more bicarbonate
What are the two types of acidosis
Respiratory Metabolic
What causes formation of methemoglobin
Some drugs
What is the function of muscle myoglobin
Stores oxygen and serves as go-between in transferring oxygen from blood to mitochondria
Decrease of pH shifts the oxygen dissociation curve which way?
To the right
What is the treatment for sickle cell, and how does it work
Treated with hydroxyurea Stimulates production of fetal hemoglobin (HbF)
What makes each form of hemoglobin different than one another
Unique colour and absorption spectrum
Is bicarbonate an acid or base
Weak base
What is acidosis
When blood pH falls below 7.35
What is alkalosis
When blood pH rises above 7.45
What is oxygen loading
When hemoglobin binds to oxygen in the lungs (external respiration)
What is oxygen unloading
When oxyhemoglobin drops off oxygen to the tissues (internal respiration)
Is muscle myoglobin similar to hemoglobin
Yes, but with 1 heme so it can only carry 1 oxygem molecule
What is normal blood pH maintained when
bicarbonate and CO2 are at a ratio of 20:1
What kind of hemoglobin cannot bind to 2,3 DPG
fetal hemoglobin (hemoglobin F)
Sickle cell blood flow to organs?
restricted and RBCs hemolyse