Cremo 3: Hemoglobin and blood gas transport

Question 1

O2 sensing mechanism of Hb

Answer 1

O2 binds to Fe2+ and affects the degree to which Fe2+ is in the plane of the ring. The movement drags the His side chain with it and Hb can sense this shift.

Question 2

How do RBCs take care of Hb?

Answer 2

1. protects it from proteases

2. protects it from oxidizing environment of plasma

Question 3

How does Hb take care of heme?

Answer 3

Hb has hydrophobic binding sites that keep heme soluble.

Question 4

How does Hb-protoporphyrin-IX take care of Fe2+?

Answer 4

Protects fe2+ from oxidation to fe3+

Question 5

How does Fe2+ take care of O2?

Answer 5

Provides for reversible binding of O2 and transport

Question 6

2 functional reasons for Hb

Answer 6

1. prevents Fe2+ from irreversible oxidation to Fe3+

2. allows for reversible binding of O2 to Fe2+

Question 7

As you add O2 to Hb, it becomes easier to bind the O2. Why is this so?

Answer 7

Some salt links have already been broken!

Question 8

How do you find SaO2?

Answer 8

(HbO2/Hb+HbO2) * 100

Question 9

What does a lower P50 indicate?

Answer 9

Tighter binding affinity of O2 for Hb

Question 10

Normal P50 for HbA

Answer 10

27mmHg

Question 11

From lungs to tissues, about what percent of O2 binding sites have dumped their O2?

Answer 11

18%

Question 12

If there is hypoxia, RBCs can dump up to (blank)% of their oxygen to the tissues that need it most.

Answer 12

63%

Question 13

Things that can shift the Hb-O2 dissociation curve to the right?

Answer 13

pH, CO2, temperature, BPG

Question 14

Things that cause weaker binding of O2 to Hb (right shift)

Answer 14

Hot, sweating, gasping

1. increased temp
2. increased [H+], lower pH
3. increased PaCO2

Question 15

How does increased H+ weaken O2 binding?

Answer 15

H+ stabilizes the salt bridges that need to be broken for O2 to bind!

Question 16

H+ and O2 do not like to bind at the same time. So what does decreased pH (more H+) cause?

Answer 16

Decreasing pH forces Hb to dump some O2 to tissues. This is helpful under acidic conditions, because tissues need more oxygen!

Question 17

How does CO2 weaken O2 binding to Hb?

Answer 17

Favors formation of carbamate, which stabilizes salt bridges that must be broken for O2 to bind.

Question 18

So, what are the two things that do not like to bind with O2?

Answer 18

H+ and CO2

Question 19

(Bohr/Haldane) says that CO2/H+ weakens O2 binding to Hb. (Bohr/Haldane) says O2 weakens CO2/H+ binding to Hb.

Answer 19

Bohr; Haldane

Question 20

How does BPG weaken O2 binding to Hb?

Answer 20

Binds in the central hole in Hb. O2 and BPG do not like to bind to Hb at the same time. So, this causes chronic hypoxia.

Question 21

What three things increase at high altitude?

Answer 21

1. number of RBCs
2. [Hb]
3. [BPG]

Question 22

What are the three pathways that describe carbohydrate metabolism in the RBC?

Answer 22

1. Glycolysis
2. 2,3-BPG metabolism
3. Pentose phosphate shunt

Question 23

Fetal hemoglobin has a (blank) affinity for oxygen, and causes a (blank) shift in the O2 curve.

Answer 23

Higher; left

Question 24

Main compound that we talked about that can compete with O2 at heme binding site?

Answer 24

CO – CO binds 200 times more tightly to heme than O2.

Question 25

CO decreases maximal O2 binding capacity, so at high [CO] patient can be hypoxic while maintaining a normal (blank)

Answer 25

PaO2

Question 26

An altered state of hemoglobin in which the ferrous (2+) form of heme is oxidized to the ferric form (3+) thus making the heme moiety unable to bind oxygen

Answer 26

Methemoglobin

Question 27

What does a pulse ox measure?

Answer 27

SaO2

Question 28

What is the equation for total O2 content? What variable in the eq is reported by PaO2 and which is not?

Answer 28

CaO2 = Hb · 1.34 · SaO2/100 Total O2 content = CaO2 = O2(dissolved) + O2(bound to Hb) O2 dissolved is reported by PaO2, but O2(bound to Hb) is not!

Question 29

Is there more O2 bound to Hb or freely dissolved?

Answer 29

Much more bound to Hb. Ex: 20ml bound, 0.48ml free

Question 30

So what is the main difference between PaO2 and CaO2?

Answer 30

PaO2 represents only dissolved O2 content, and does not account for O2 bound to Hb. CaO2 includes all O2 present!

Question 31

What is a normal CaO2?

Answer 31

20!

Question 32

Which value is most useful? PaO2 or CaO2?

Answer 32

CaO2! A patient can have a normal PaO2 and be starved of O2!

Question 33

Impaired O2 delivery to the tissues

Answer 33

Hypoxia

Question 34

Low CaO2 (oxygen content) caused by reduction in PaO2, SaO2, or [Hb]

Answer 34

Hypoxemia

Question 35

3 causes of hypoxia

Answer 35

1. Hypoxemia: reduced PaO2, SaO2, or [Hb] 2. Reduced O2 delivery to the tissues 3. Decreased tissue O2 uptake

Question 36

PCO2 equation

Answer 36

PaCO2 = VCO2 * 0.863 / VE – VD

Question 37

Henderson-Hasselbalch equation

Answer 37

pH = 6.1 + log [HCO3-]/0.03*PaCO2

Question 38

Alveolar gas equation

Answer 38

PAO2 = PIO2 – 1.2(PaCO2)

Question 39

A-a difference equation

Answer 39

P(A-a)O2 = PAO2 – PaO2

Question 40

Oxygen content equation (CaO2)

Answer 40

CaO2 = Hb · 1.34 · SaO2