A&P 2: Respiratory Systems (Gas Exchange)

what is external respiration?

O2 moves from the alveoli into pulomnary capillaries

CO2 moves from pulmonary capillaries into alveoli

What is internal respiration?

O2 moves from systemic capillaries into body cells

CO2 moves from body cells into systemic capillaries

what is Dalton's Law?

the total pressure of a gas mixture equals the sum of the partial pressures of each gas

how does Dalton's law relate to O2 and CO2 in respiration?

the partial pressure of each gas is proportional to the amount of that gas in the mixture

more O2 in air = higher PCO2

more CO2 = higher PCO2

what is Henry's Law?

at constant temp, the amount of gas that dissoles in a liquid depends on..

1. the gas's partial pressure

2. the gas's solubility in that liquid

how does Henry's Law relate to O2 and CO2 in blood?

CO2 dissolves in blood more easily than O2, so a smaller pressure gradient is needed for CO2 movement. O2 requires a larger partial pressure to dissolve in blood.

what are the 3 factors influencing external respiration?

1. partial pressure gradients

2. thinness and surface area of respiratory membrane

3. ventilation-perfusion (V/Q) coupling

which factor has the greatest influence on gas movement during external respiration?

differences in partial pressures are the major driving force for gas diffusion

why does O2 rapidly diffuse into pulmonary capillaries?

because alveolar PO2 (about 104 mmHg) is much higher than pulmonary capillary PO2 (about 40 mmHg), which creates a large diffusion gradient

why does 3x increase in cardiac output during exercise still fully oxygenate blood?

the PO2 gradient is so high that blood becomes oxygenated very quickly, even though blood spends less time in pulmonary capillaries

why is the CO2 partial pressure gradient relatively low?

Co2 is mostly transported as bicarbonate (HCO3-), not dissolved gas

CO2 dissolves easily in blood (Henry's Law)

why is a low CO2 pressure gradient "no problem"?

CO2 is highly soluble, so even a small pressure gradient allows large amounts of CO2 to diffuse and be "blown off" during expiration

how does converting CO2 into bicarbonate affect PCO2?

converting gaseous CO2 into HCO3- lowers dissolved CO2 levels, helping maintain a diffusion gradient for continued CO2 transport

what is the bicarbonate "reserve"?

the large amount of CO2 transported in blood as bicarbonate mlcs (HCO3-) --> it helps buffer blood PH

which gas law explains why CO2 is effectively "blown off" during expiration?

Henry's law - CO2 is highly soluble, so even low pressure gradients allow substantial diffusion out of blood

why are thiness and large surface area important for external respiration?

they maximize diffusion efficiency across the respiratory membrane

what happens if respiratory membrane surface area decreases?

gas exchange efficiency decreases

which disease decreases respiratory membrane surface area?

emphysema

how does emphysema reduce gas exchange?

alveolar walls are destroyed, reducing surface area and elasticitiy

define ventilation-perfusion (V/Q) coupling

a homeostatic mechanism that matches airflow (ventilation) with blood flow (perfusion)

what happens in V/Q coupling when an alveolus is blocked? why send blood to an alveolus that isn't getting air?

ventilation decreases, so less air reaches the alveolus

alveolar PO2 decreases because fresh O2 is not entering

the pulmoary arteriole sense low O2, so it constricts (less blood)

this causes perfusion to decrease -> blood flow now matches the low ventilation

what happens in V/Q coupling when a pulmonary arteriole is blocked? why send air to an alveolus that isn't getting blood?

if a pulmonary arteriole is blocked...

1. perfusion decreases bc less blood reaches the alveolus

2. alveolar PCO2 decreases bc little/no blood is bringing CO2 to that alveolus

3. the bronchiole sense low CO2 -> constricts -> less air sent there

4. ventilation decreases -> airflow now matches the low blood flow

is chronic bronchitis mainly a ventilation or perfusion problem?

Ventilation problem — airflow is obstructed by inflammation, edema, mucus, and bronchospasm.

Why is chronic bronchitis called "blue bloater"?

Poor ventilation causes hypoxemia/cyanosis ("blue"), fluid retention/edema, productive cough, wheezing, and frequent infections.

Is emphysema mainly a ventilation or gas exchange problem?

Gas exchange problem — alveolar walls are destroyed, reducing respiratory membrane surface area and elasticity.

why is emphysema called "pink puffer"?

Patients compensate by breathing hard ("puffing") to maintain oxygenation. They often have severe dyspnea, air trapping, and hyperinflated lungs.

What causes V/Q mismatch in COPD?

Ventilation and perfusion become poorly matched due to airway obstruction, inflammation, air trapping, and/or destruction of alveoli.

what are the 3 forms of hemoglobin?

HHb = deoxyhemoblobin

HbO2 = oxyhemoglobin

HbCO2 = carbaminohemoglobin

What is bound to hemoglobin in HHb?

No oxygen is bound to iron (deoxygenated form). Heme is in the domed conformation.

What is bound to hemoglobin in HbO₂?

Oxygen is bound to iron.

Heme is in the planar/flat conformation.

What is bound to hemoglobin in HbCO₂?

Carbon dioxide is bound to the globin portion of hemoglobin (not iron).

What are the axes of the O₂-Hb dissociation curve?

X-axis = PO₂ (mmHg)

Y-axis = % O₂ saturation of hemoglobin

(LOOK BACK AT THIS GRAPH)

What does the O₂-Hb dissociation curve show?

It shows how hemoglobin affinity for oxygen changes as PO₂ changes.

What happens to Hb-O₂ affinity in the lungs?

In the lungs, oxygen binds easily to hemoglobin because PO₂ is high.

What happens to Hb-O₂ affinity in resting tissues?

In resting tissues, some oxygen leaves hemoglobin and enters the tissues because PO₂ is lower.

What happens to Hb-O₂ affinity in exercising tissues?

In exercising tissues, hemoglobin releases lots of oxygen because tissues need more O₂.

Why is lower Hb-O₂ affinity helpful during exercise?

It helps active muscles receive more oxygen for ATP production.

What is a right shift of the O₂-Hb dissociation curve?

A right shift means hemoglobin lets go of oxygen more easily.

What causes a right shift of the O₂-Hb dissociation curve?

High temperature and low pH.

Why is a right shift helpful during exercise?

It helps more oxygen unload into exercising muscles.

What is a left shift of the O₂-Hb dissociation curve?

A left shift means hemoglobin holds onto oxygen more tightly.

What are the 3 forms of CO₂ transport in blood?

10% dissolved in plasma, 20% bound to hemoglobin (HbCO₂), 70% transported as bicarbonate (HCO₃⁻)

What is the bicarbonate reserve?

Most CO₂ in blood is converted into bicarbonate (HCO₃⁻), which serves as a transport form and blood pH buffer.

Where is CO₂ converted into bicarbonate?

Inside red blood cells.

What enzyme converts CO₂ into bicarbonate?

Carbonic anhydrase.

What reaction converts CO₂ into bicarbonate?

CO₂ + H₂O ⇌ H₂CO₃ ⇌ HCO₃⁻ + H⁺

What is the chloride shift?

As bicarbonate leaves the red blood cell, chloride enters to maintain electrical balance.

What happens to the H⁺ produced during bicarbonate formation?

Hemoglobin binds the H⁺ as a temporary placeholder/buffer.

What happens to CO₂ at systemic tissues?

CO₂ enters blood and red blood cells, where much of it is converted into bicarbonate for transport.

What happens to bicarbonate at the lungs?

Bicarbonate re-enters red blood cells and is converted back into CO₂, which diffuses into alveoli and is exhaled.

What is the Haldane effect?

At the lungs, oxygen binding to hemoglobin helps displace/release CO₂ from blood.