Resp - Physio (Hemoglobin & Oxygen)

Question 1

What are the components of Hemoglobin?

Answer 1

Hemoglobin (Hb) is composed of 4 polypeptide subunits (2 alpa and 2 beta)

Question 2

How many forms of (normal adult) Hemoglobin are there, what are they, and what distinguishes/defines each?

Answer 2

Exists in 2 forms: (1) T (taut) form has low affinity for O2 (2) R (relaxed) form has high affinity for O2.

Question 3

What kind of cooperativity and allostery does Hb exhibit?

Answer 3

Hb exhibits positive cooperativity and negative allostery.

Question 4

What 5 conditions favor taut over relaxed form of Hb? What effects does this have?

Answer 4

Increased (1) Cl- (2) H+ (3) CO2 (4) 2,3-BPG and (5) temperature favor taut form over relaxed form (shifts dissociation curve to right, leading to increased O2 unloading)

Question 5

Where are the taut versus relaxed forms of Hb found in the body?

Answer 5

Taut in Tissues, Relaxed in Respiratory Tract

Question 6

How does Fetal Hb differ from adult Hb in terms of structure?

Answer 6

Fetal Hb (2 alpha and 2 gamma subunits); (adult) Hemoglobin (Hb) is composed of 4 polypeptide subunits (2 alpa and 2 beta)

Question 7

How does Fetal Hb differ from adult Hb in terms of affinity?

Answer 7

Fetal Hb (2 alpha and 2 gamma subunits) has lower affinity for 2,3-BPG than adult Hb and thus has higher affinity for O2

Question 8

In general, what is the effect of hemoglobin modifications?

Answer 8

Lead to tissue hypoxia from decreased saturation and decreased O2 content

Question 9

What is Methemoglobinemia? What distinguishes it from normal hemoglobin in terms of function?

Answer 9

Oxidized form of Hb (ferric, Fe3+) that does not bind O2 as readily, but has increased affinity for cyanide

Question 10

What is the normal state of iron in Hb?

Answer 10

Iron in Hb is normally in a reduced state (ferrous, Fe2+); Think: “just the 2 of US: ferroUS is Fe2+”

Question 11

What are 2 ways that Methemoglobinemia may present?

Answer 11

Methemoglobinemia may present with cyanosis and chocolate-colored blood

Question 12

How is cyanide poisoning treated, and why?

Answer 12

To treat cyanide poisoning, use nitrites to oxidize Hb to methemoglobin, which binds cyanide. Use thiosulfate to bind this cyanide, forming thiocyanate, which is renally excreted.

Question 13

How can Methemoglobinemia be treated?

Answer 13

Methemoglobinemia can be treated with methylene blue.

Question 14

How do nitrites cause poisoning?

Answer 14

Nitrites cause poisoning by oxidizing Fe2+ to Fe3+

Question 15

What is Carboxyhemoglobin? What distinguishes it from normal hemoglobin in terms of function?

Answer 15

Form of Hb bound to CO in place of O2. Causes decreased oxygen-binding capacity with a left shift in the oxygen-hemoglobin dissociation curve. Decreased O2 unloading in tissues.

Question 16

What change does Carboxyhemoglobin cause to the oxygen-hemoglobin dissociation curve? What change does it have in the tissues?

Answer 16

Causes decreased oxygen-binding capacity with a left shift in the oxygen-hemoglobin dissociation curve. Decreased O2 unloading in tissues.

Question 17

What is the shape of the oxygen-hemoglobin dissociation curve, and why?

Answer 17

Sigmoidal shape due to positive cooperativity (i.e., tetrameric Hb molecule can bind O2 molecules and has higher affinity for each subsequent O2 molecule bound).

Question 18

How does the oxygen-myoglobin dissociation curve differ from the oxygen-hemoglobin one?

Answer 18

Myoglobin is monomeric and thus does not show positive cooperativity; curve lacks sigmoidal appearance

Question 19

What occurs with a shift to the right on the oxygen-hemoglobin dissociation curve?

Answer 19

When curve shifts to the right, decrease affinity of Hb for O2 (facilitates unloading of O2 to tissue).

Question 20

What factors cause shifts of the oxygen-hemoglobin dissociation curve, and what conditions cause which shifts?

Answer 20

Think: “BAT ACE: BPG (2,3-BPG), Altitude, Temperature, Acid, CO2, Exercise; An increase in all factors (including H+) causes a shift of the curve to the right; A decrease in all factors causes a shift of the curve to the left

Question 21

What shift on the oxygen-hemoglobin dissociation curve does Fetal Hb cause, and why?

Answer 21

Fetal Hb has a higher affinity for O2 than adult Hb, so its dissociation curve is shifted left.

Question 22

Graph the oxygen-hemoglobin dissociation curve, including myoglobin and normal blood curves. On the normal blood curve, label oxygenated blood leaving the lungs versus blood returning from tissues.

Answer 22

See p. 598 in First Aid 2014 for first graph

Question 23

Graph normal blood versus 50% CO Hb in terms of pCO2 in mmHg (x axis) and O2 bound to Hb in mL O2/100 mL (y axis).

Answer 23

See p. 598 in First Aid 2014 for second graph

Question 24

Define O2 content.

Answer 24

O2 content = (O2 binding capacity x % saturation) + dissolved O2

Question 25

How much O2 can 1 g of Hb normally bind?

Answer 25

Normally 1 g Hb can bind 1.34 mL O2

Question 26

What is the normal Hb amount in blood?

Answer 26

Normal Hb amount in blood is 15 g/dL

Question 27

Under what condition does cyanosis result?

Answer 27

Cyanosis results when deoxygenated Hb > 5 g/dL

Question 28

What is the typical value for O2 binding capacity?

Answer 28

O2 binding capacity ~ 20.1 mL O2/dL

Question 29

Which of the following factors decrease as Hb falls: O2 content of arterial blood, O2 saturation, arterial PO2.

Answer 29

O2 content of arterial blood decreases as Hb falls, but O2 saturation and arterial PO2 do not

Question 30

What is the equation for O2 delivery to tissues?

Answer 30

O2 delivery to tissues = cardiac output x O2 content of blood

Question 31

What changes (if any) to the following measurements occur with CO poisoning: (1) Hb level (2) % O2 sat of Hb (3) Dissolved O2 (PaO2) (4) Total O2 content?

Answer 31

(1) Normal (2) Decreased (CO competes with O2) (3) Normal (4) Decreased

Question 32

What changes (if any) to the following measurements occur with Anemia: (1) Hb level (2) % O2 sat of Hb (3) Dissolved O2 (PaO2) (4) Total O2 content?

Answer 32

(1) Decreased (2) Normal (3) Normal (4) Decreased

Question 33

What changes (if any) to the following measurements occur with Polycythemia: (1) Hb level (2) % O2 sat of Hb (3) Dissolved O2 (PaO2) (4) Total O2 content?

Answer 33

(1) Increased (2) Normal (3) Normal (4) Increased