Human Respiratory System

The Respiratory System

Functions to supply the body w/ O2 and remove CO2

“Respiration” is actually 4 distinct processes:

Ventilation – Movement of air into & out of the

lungs

External Respiration – Gas exchange btwn blood and air-

filled chambers of the lungs

Transport of Gases – Accomplished by CV

Internal Respiration – Gas exchange btwn systemic blood and the

tissue cells

The Respiratory System

The respiratory system works with the cardiovascular system

to exchange gases between the air and

blood (external respiration) and

between blood and tissue fluids (internal

respiration).

Inspiration and expiration move air

in and out of the lungs during breathing.

Cellular respiration is the final

destination where ATP is produced in

cells.

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings

Overview of Respiratory Exchange

Figure 18-1: Overview of oxygen and exchange and Transport CO2

Dalton’s Law of Partial Pressures

States the total pressure exerted by a mixture of gases is the sum of the pressures exerted individually by each gas in the mixture.•PTotal = P1 + P2 + P3 + P4 + … Pn

We can restate this law as the total pressure exerted by a mixture of gases is the sum of the partial pressures exerted by each gas.

Also, the partial pressure exerted by a gas is directly proportional to its % in the mixture.

Gas Movement

► Factors that can influence the diffusion of CO2 and O2 across the respiratory membrane include:

1) Partial pressure gradients & solubilities

2) Matching of alveolar ventilation w/ pulmonary perfusion

3) Thickness and surface area of the respiratory membrane

PP and Solubilities

►Po2 of venous blood is 40mmHg. Po2 of alveolar air is 104mmHg. What does this mean?

►Pco2 of venous blood is 45mmHg. Pco2 of alveolar air is 40mmHg. What does this mean?

►Although the P is much greater for O2, since the solubility of CO2 is so much larger equal amts of gas will be exchanged.

►What about exchange between the blood and the tissues?

Respiratory Membrane

► In healthy lungs, the respiratory membrane is 0.5-1.0 um thick and gas exchange is efficient.

► In pneumonia, the thickness of the RM How will this affect the efficiency of gas

exchange?►The surface area of healthy lungs is

enormous. In emphysema, walls of adjacent alveoli

break thru and the size of the alveolar chambers ►How will this affect lung surface area and gas

exchange?

O2 Transport

Molecular oxygen in the blood is either dissolved in the

plasma (1.5%) or bound to hemoglobin w/i the RBCs (98.5%).

Each Hb can bind 4 molecules of O2 and this binding is quite

reversible.

Hb containing bound O2 is oxyhemoglobin

and Hb w/o O2 is deoxyhemoglobin.

Carbon monoxide has an extremely high affinity for hemoglobin’s oxygen binding site • Why is this bad?

O2 Transport

► Loading and unloading of O2 is given by a simple reversible equation:

HHb+O2 HbO2 + H+

►O2 binding is “cooperative” The binding of the 1st O2 molecule causes the

Hb to change shape which makes it easier for the 2nd O2 to bind. Binding of the 2nd O2 makes it easier for the 3rd and binding of the 3rd makes it easier for the 4th.

O2 Transport

As O2 loading proceeds, the

affinity of Hb for O2

When Hb has 4 bound O2

molecules it is saturated. When

it has 1,2, or 3 it’s unsaturated

When the saturation of Hb is

plotted against the Po2, we get

the oxygen-hemoglobin dissociation

curve.

► Hb-O2 dissociation curve is sigmoidal. Why?

► Hb is almost completely saturated at a Po2 of 70mmHg.

► At pulmonary Po2 of 104mmHg, Hb is completely saturated.

► Even at the tissue Po2 of 40mmHg, Hb is still 75% saturated – meaning that it still has 3 molecules of O2 bound to it. Thus large amts of O2

are still available in venous blood (the so-called venous reserve)

As the tissue Po2 decreases, what happens to the amt of O2 available in the venous reserve?

Factors affecting O2 binding

►As cellular metabolism proceeds, CO2, acids, and heat are all generated.

►As Pco2, [H+]Plasma, and temperature , the affinity Hb has for O2 will .

►All these factors shift the Hb-O2 dissociation curve to the right.

►What does all this mean and why does it make sense?

►The Bohr Effect

►Carbon dioxide is transported in the blood in three forms Dissolved in plasma – 7 to 10% Chemically bound to hemoglobin –

20% is carried in RBCs Bicarbonate ion in plasma – 70% is

transported as bicarbonate (HCO3–)

Carbon Dioxide Transport

CO2 Transport

►7% is simply dissolved in plasma.

►23% is bound to certain amino acids in the polypeptide portion of Hb (carbaminohemoglobin)

►70% is transported as HCO3-, the

bicarbonate ion.

►CO2 made in tissue cells will dissolve into the RBC where it combines with water to yield carbonic acid. Carbonic acid then dissociates to yield bicarbonate and a hydrogen ion.

CO2 Transport

CO2 + H2O H2CO3 HCO3- + H+

►This rxn occurs in the RBCs because the RBCs contain the enzyme (carbonic anhydrase) that catalyzes both steps.

►Once generated, the HCO3- exits the

RBC. ►To maintain charge balance, a Cl-

enters the RBC when the HCO3-

leaves. This is known as the chloride shift.

►Carbon dioxide diffuses into RBCs and combines with water to form carbonic acid (H2CO3), which quickly dissociates into hydrogen ions and bicarbonate ions

► In RBCs, carbonic anhydrase reversibly catalyzes the conversion of carbon dioxide and water to carbonic acid

Transport and Exchange of Carbon Dioxide

CO2 + H2O H2CO3 H+ + HCO3–

Carbon

dioxide

Water

Carbonic acid

Hydrogen ion

Bicarbonate ion

Transport and Exchange of Carbon Dioxide

Figure 22.22a

►At the lungs, these processes are reversed Bicarbonate ions move into the RBCs

and bind with hydrogen ions to form carbonic acid

Carbonic acid is then split by carbonic anhydrase to release carbon dioxide and water

Carbon dioxide then diffuses from the blood into the alveoli

Transport and Exchange of Carbon Dioxide

Transport and Exchange of Carbon Dioxide

Figure 22.22b