Respiratory Physiology Lecture 5 Part 24: Transport of Oxygen in the Blood

Question 1

What 2 forms can oxygen be carried in blood?

Answer 1

• Dissolved (2 %) (in plasma)
• Combined with hemoglobin (98 %) (RBC)

Question 2

Oxygen solubility in blood

Answer 2

O2 solubility is LOW:

• 3mL O2/ L blood [DISSOLVED O2]
• 197mL O2/ L blood [O2 bound to Hemoglobin]

Question 3

What Law does dissolved oxygen follow?

Answer 3

Dissolved O2 follow Henry’s law → O2content ∝(proportional to) PO2 and solubility

Question 4

O2 content in blood that is carried to peripheral tissue

Answer 4

Cardiac output is 5 L blood/min, thus total O2 content in blood that is carried to peripheral tissue is 1000 mL O2/min

200 mL (3 mL + 197 mL) x 5 L = 1000 mL

Question 5

How does RBC transport Oxygen?

Answer 5

Most O2 (98 % = 197 mL/L) carried attached to hemoglobin in red blood cells (RBC, erythrocytes)

Question 6

Hemoglobion

Answer 6

Hb

protein composed of 4 amino acid subunits called Globins (2 alpha and 2 beta) and 4 Heme groups

Question 7

HEME structure

Answer 7

• Each HEME group has a porphyrin ring structure that contains an iron atom in the ferrous (Fe2+) form, to which O2 binds
• Each Hb molecule can bind up to 4 O2 molecules (One per subunit)

Question 8

What 2 forms can Hb exist in?

Answer 8

• deoxyhemoglobin
• oxyhemoglobin

Question 9

What influences which form Hb takes on?

Answer 9

Influenced by arterial partial pressure of oxygen

Question 10

How can O₂ + Hb ↔ HbO₂ reaction be explained?

Answer 10

this reaction can be described by the oxygen dissociation curve

Question 11

oxygen dissociation curve

Answer 11

• Relationship between Hb and arterial partial pressure of oxygen
• Level of O2 varies between 40-100 at rest so amount unloaded into tissue is pretty minimal

Question 12

P_O2 at 40 mmHg

Answer 12

Found in peripheral tissue → systematic venous → Found in peripheral tissue

Question 13

P_O2 at 100 mmHg

Answer 13

Systemic arterial → Value if PO2 in capilleries of lungs when it diffuses to capillaries from aveoli

Question 14

O₂ Capacity

Answer 14

max amount of O2 that can be combined with Hb

• 1g Hb combines with 1.39mL O2
• In normal conditions, 15g Hb/100 mL blood → O2 capacity is 20.8 mL O2/100 mL blood
• If amount of Hb changes so will the oxygen capacity; if Hb increases there will be increased oxygen capacity and vicversa

Question 15

Hb Saturation

Answer 15

percentage of the available Hb binding sites that have O2 attached

• Hb saturation of arterial blood with 100 mmHg PO2 is 97.5
• Hb saturation of mixed venous blood with 40 mmHg PO2 is 75 %