System Physiology Ch 15

Oxygen–Hemoglobin (O₂–Hb) Saturation Curve

• Shows how much O₂ hemoglobin carries at different PO₂ levels

• Higher PO₂ → more O₂ bound to Hb

• Curve is S-shaped (sigmoid) → helps loading & unloading O₂ efficiently

• “Right = Release, Left = Lock”

Left Shift (holds O₂ tightly)

• ↑ pH (alkaline)

• ↓ temperature

Right Shift (releases O₂)

• ↓ pH (acidic)

• ↑ temperature

• ↑ CO₂

Bohr Effect

• CO₂ ↑ → pH ↓ → Hb releases more O₂

• Happens in active tissues (like muscles during exercise)

A runner’s muscles produce lots of CO₂ → blood becomes acidic → Hb releases more O₂

better oxygen delivery to muscles

CO₂ Transport in Blood

• 65% → as bicarbonate (HCO₃⁻)

• 25% → bound to Hb (carbaminohemoglobin)

• 10% → dissolved in plasma

Patient with lung disease can’t remove CO₂ → CO₂ builds up

respiratory acidosis

Medulla (MAIN control)

• DRG (Dorsal) → inspiration

• VRG (Ventral) → breathing rhythm

Pons (fine-tuning)

• Smooths breathing transitions

Overdose patient → medulla suppressed

breathing stops (respiratory arrest) Drugs like opioids (morphine, fentanyl, heroin) suppress breathing → can cause death

Chemoreceptors (Breathing Sensors): What do they detect?

• ↑ CO₂ (MOST IMPORTANT)

• ↓ pH

• ↓ O₂ (less sensitive)

• CO₂ controls breathing”

• ↑ CO₂ → brain increases breathing rate

• ↓ CO₂ → breathing slows

Hypercapnia (high CO₂)

rapid breathing

Hypocapnia (low CO₂)

slow breathing

Hypoventilation

Slow/shallow breathing

CO₂ ↑ → respiratory acidosis

Causes:

• Asthma

• Drug overdose

Hyperventilation

• Fast breathing

• CO₂ ↓ → respiratory alkalosis

• Causes:

  • Panic attacks

  • Anxiety

Breathing During Exercise

• Breathing ↑ to match CO₂ production

• Not true hyperventilation (because CO₂ is balanced)

• In exercise → ↑ temperature + ↑ CO₂
  → O₂ unloads more easily (right shift)

During intense exercise:

• Muscles heat up + produce CO₂

• Hb releases more O₂ → improves performance

Goal of respiration control = maintain:

• O₂ delivery

• CO₂ removal

• Blood pH (VERY important)

• “O₂ in, CO₂ out, pH stable”