Chapter 17 - Gas Exchange, Transport, and Respiratory Regulation

Since O₂ is not very soluble in plasma, what does it bind to?

Hb (hemoglobin)

What are the levels of respiration?

Systemic (internal) and pulmonary (external)

How does oxygen transport in pulmonary capillaries?

O₂ goes from the alveoli → passes capillary wall → reaches RBC → O₂ binds to Hb to be transported → becomes oxygenated → unbinds once it reaches systemic

How does oxygen transport in systemic capillaries?

O₂ into systemic → Hb and O₂ unbind and Hb stays in RBC → O₂ travels across capillary wall to reach the tissue cell

What factors increase the affinity of Hb for oxygen?

Decreased temperature, decreased hydrogen, increased pH

What factors decrease the affinity of Hb for oxygen?

Increased temperature, increased hydrogen, decreased pH

What are the 3 main ways of CO₂ transport?

Dissolved in plasma, carbamino effect, and dissolved as bicarbonate

What percent of CO₂ is dissolved in plasma?

10%

How is CO₂ transported using the carbamino effect?

CO₂ diffuses into RBC → binds with Hb to form HbCO₂ (carbaminohemoglobin)

What percent of CO₂ transports by the carbamino effect?

20%

How is CO2 transported by being dissolved as bicarbonate?

CO₂ binds with water → forms H₂CO₃ (carbonic acid) → disengages → H + HCO₃ (bicarbonate) → H binds to Hb → HCO₃ goes into plasma and Cl will shift into the RBC (chloride shift)

What percent of CO₂ is transported by being dissolved as bicarbonate?

70%

In systemic capillaries, CO₂ goes from where to where?

Goes from tissue cells into RBC

In pulmonary capillaries, CO₂ goes from where to where?

Goes from RBC to the alveoli

What is ventilation-perfusion matching?

Local control mechanisms that try to keep ventilation (alveolar air) and perfusion (blood flow) matched

What happens when there is a low ventilation-perfusion ratio?

There is an airway obstruction which decreases ventilation and causes increased perfusion

How to fix a low ventilation-perfusion ratio?

Increase ventilation = increased P_CO2 = bronchodilation

Decrease perfusion = decreased P_O2 = brochoconstriction

What happens when there is a high ventilation-perfusion ratio?

There is a blood vessel obstruction which decreases perfusion and causes increased ventilation

How to fix a high ventilation-perfusion ratio?

Decrease ventilation = decrease PCO2 = bronchoconstriction

Increase perfusion = increase PO2 = vasodilation

What controls voluntary breathing?

Motor neurons directed by the cerebral cortex, allowing conscious control of respiratory muscles

Can voluntary control override automatic breathing permanently?

No because rising CO₂ levels force automatic breathing to resume

What generates automatic breathing?

The brainstem, which sets the basic rhythm and depth of ventilation

What are the three respiratory neuron groups in the medulla?

VRG (ventral respiratory group), DRG (dorsal respiratory group), and CPG (central pattern generator)

What does the VRG do?

Contains inspiratory and expiratory neurons & controls depth of breathing

What does the DRG do?

Contains inspiratory neurons that help drive basic inspiration

What is the function of the CPG?

Sets the basic rate and depth of ventilation

What is the role of the PRG in the pons?

Modifies rhythm by signaling the VRG and DRG

What do chemoreceptors monitor to regulate breathing?

pH of CSF and CO₂ levels (most important)

Where are central chemoreceptors located and what do they detect?

In the medulla and detect H⁺ in CSF.

What is the response of central chemoreceptors to increased CO₂/H⁺?

Increase ventilation and it is responsible for 70–80% of the response

Where are peripheral chemoreceptors located?

Carotid bodies and aortic bodies

What triggers peripheral chemoreceptors?

Increased PCO₂, increased H⁺ (↓ pH), or PO₂ < 60 mmHg

What is the response of peripheral chemoreceptors?

Increase respiratory rate and depth which have a faster response than central

Where are respiratory mechanoreceptors located?

On the thoracic wall

What do stretch receptors do during inhalation?

Rib cage stretches → inhibit inspiratory neurons → prevents overinflation

What happens during exhalation with mechanoreceptors?

Rib cage recoils → inhibit expiratory neurons & stimulate inspiratory neurons → prevents lung collapse

What variable is ventilation primarily regulated to keep constant?

CO₂, because CO₂ strongly affects pH

What happens to CO₂, H⁺, and O₂ during hypoventilation?

Increased CO₂ (hypercapnia), increased H⁺, decreased O₂

What acid–base disorder results from hypoventilation?

Respiratory acidosis (pH ≤ 7.35)

In hypoventilation, which direction does the CO₂ + H₂O ↔ H₂CO₃ ↔ H⁺ + HCO₃⁻ reaction shift?

Shifts to the right, increasing H⁺

How does the body correct respiratory acidosis?

Increase ventilation

What happens to CO₂, H⁺, and O₂ during hyperventilation?

Decreased CO₂ (hypocapnia), decreased H⁺, increased O₂

What acid–base disorder results from hyperventilation?

Respiratory alkalosis (pH ≥ 7.45)

In hyperventilation, which direction does the CO₂ + H₂O ↔ H₂CO₃ ↔ H⁺ + HCO₃⁻ reaction shift?

Shifts to the left, decreasing H⁺

How does the body correct respiratory alkalosis?

Decrease ventilation

What causes respiratory acidosis?

Hypoventilation → increases CO₂ → decreases pH

What causes respiratory alkalosis?

Hyperventilation → decreases CO₂ → increases pH

What compensatory response occurs in metabolic acidosis?

Hyperventilation to blow off CO₂

What compensatory response occurs in metabolic alkalosis?

Hypoventilation to retain CO₂

Why don’t O₂ levels change ventilation as rapidly as CO₂?

Because hemoglobin stores O₂, creating a reserve

At what PO₂ level does ventilation significantly increase?

When PO₂ drops below 60 mmHg

Which receptors detect low blood O₂?

Peripheral chemoreceptors

What is the ventilatory response to low PO₂?

Increased respiratory rate and depth

How does low O₂ affect sensitivity to CO₂?

Low O₂ makes carotid bodies more sensitive to CO₂.