Respiratory System Pt 3

pt 1 & 2 together

Where are the respiratory centers located?

The brainstem:

• Medulla oblongata

• Pons

They automatically control breathing.

What is the function of the Ventral Respiratory Group (VRG)?

• Located in the medulla oblongata

• Sets the basic rhythm of breathing

• Acts as the breathing "pacemaker"

What is the function of the Dorsal Respiratory Group (DRG)?

• Located in the medulla oblongata

• Modifies the VRG

• Adjusts the rate and depth of breathing

• Receives information from chemoreceptors and stretch receptors

What is the function of the Pontine Respiratory Group (PRG)?

• Located in the pons

• Limits the duration of inspiration

• Makes breathing smooth and regular

Which respiratory center sets the basic breathing rhythm?

Ventral Respiratory Group (VRG)

Which respiratory center adjusts the breathing rate and depth?

Dorsal Respiratory Group (DRG)

Which respiratory center limits inspiration?

Pontine Respiratory Group (PRG)

What is partial pressure?

The amount of pressure contributed by one gas in a mixture of gases.

Atmospheric pressure at sea level equals:

760 mm Hg

What percentage of atmospheric air is oxygen?

21%

What is the partial pressure of oxygen (PO₂) in atmospheric air?

160 mm Hg

Calculation:

0.21 × 760 = 160 mm Hg

Gases always diffuse from _________ partial pressure to _________ partial pressure.

high > low

What do central chemoreceptors mainly monitor?

pH of the cerebrospinal fluid (CSF)

They respond indirectly to high CO₂.

Where are central chemoreceptors located?

Ventral medulla oblongata

Why do central chemoreceptors respond to CO₂ instead of directly to H⁺?

H⁺ does not cross the blood-brain barrier well.

CO₂ does cross.

Inside the brain:

CO₂ + H₂O → H₂CO₃ → H⁺ + HCO₃⁻

The newly formed H⁺ stimulates the receptors.

What is the primary stimulus that controls normal breathing?

High CO₂ (PCO₂)

Not low oxygen.

Where are peripheral chemoreceptors located?

• Carotid bodies

• Aortic bodies

What do peripheral chemoreceptors detect?

pH of the cerebrospinal fluid (CSF)

They respond indirectly to high CO₂.

What happens when peripheral chemoreceptors detect low oxygen?

• Breathing rate increases

• Tidal volume increases

• Alveolar ventilation increases

Peripheral chemoreceptors usually respond only after oxygen falls to approximately:

50% of normal

Central chemoreceptors vs Peripheral chemoreceptors

Central

• Medulla

• Detect CO₂ (through H⁺ in CSF)

Peripheral

• Carotid & Aortic bodies

• Detect low O₂

What is the purpose of the Hering–Breuer (Inflation) Reflex?

Prevents overinflation of the lungs.

Which receptors start the Hering–Breuer reflex?

Stretch receptors in the lungs.

Which nerve carries impulses during the Hering–Breuer reflex?

Vagus nerve

What happens after stretch receptors are activated?

Breathing stops before lungs overinflate.

List the major factors that affect breathing.

• PO₂

• PCO₂

• H⁺ concentration (pH)

• Lung stretch

• Emotions

• Physical activity

What are the TWO main controllers of breathing?

1. PCO₂

2. H⁺ concentration

What happens if blood PCO₂ increases?

Breathing increases.

What happens if blood pH decreases (more acidic)?

Breathing increases.

What happens if blood PO₂ decreases significantly?

Peripheral chemoreceptors increase breathing.

Why does breathing increase during exercise?

• Cerebral cortex stimulates respiratory centers.

• Proprioceptors (joint reflex) stimulate respiratory centers.

Do blood oxygen and carbon dioxide levels change significantly during normal exercise?

No.

They stay nearly normal.

If someone becomes short of breath during exercise, it is usually because which system cannot keep up?

The cardiovascular system.

It cannot move enough blood between the lungs and body tissues.

the respiratory centers.

VRG

↓

Sets rhythm

DRG

↓

Adjusts rhythm

PRG

↓

Limits inspiration

the chemoreceptors

Central

↓

High CO₂ (through H⁺ in CSF)

Peripheral

↓

Low O₂

the Hering–Breuer Reflex

Lungs stretch

↓

Stretch receptors

↓

Vagus nerve

↓

Medulla

↓

Stops inspiration

↓

Prevents overinflation

Respiratory changes with aging.

• Fewer cilia

• Less active cilia

• Thicker mucus

• Slower cough and gag reflexes

• Less efficient macrophages

What happens to bronchioles with aging?

Connective tissue replaces muscle.

↓

Less bronchodilation.

What happens to alveoli with aging?

Alveoli merge.

↓

Surface area decreases.

↓

Gas exchange decreases.

Why is breathing harder in older adults?

• Stiffer costal cartilage

• Thoracic cavity changes

• Less elastic lungs

What is the primary function of the alveoli?

Site of gas exchange between the air and pulmonary capillary blood.

What are alveolar pores?

Small openings that allow air to move from one alveolus to another, providing alternate air pathways.

What cells clean the alveoli?

Alveolar macrophages

They remove:

• Dust

• Bacteria

• Dead cells

• Other debris

Type I alveolar cells

• Simple squamous epithelial cells

• Form most of the alveolar wall

• Major component of the respiratory membrane

• Primary function: Gas exchange

Type II alveolar cells

Produce pulmonary surfactant

Surfactant:

• Reduces surface tension

• Prevents alveolar collapse

• Makes breathing easier

Type I vs. Type II cells.

Type I = Gas exchange

Type II = Surfactant

What structures make up the respiratory membrane?

• Alveolar wall (Type I cells)

• Fused basement membranes

• Capillary wall

Why is the respiratory membrane so thin?

Allows rapid diffusion of oxygen and carbon dioxide.

Gases diffuse from:

High partial pressure

↓

Low partial pressure

Oxygen diffuses:

High partial pressure

↓

Low partial pressure

Carbon dioxide diffuses:

Blood

↓

Alveoli

↓

Exhaled

What increases diffusion?

• Greater surface area

• Shorter diffusion distance

• Greater gas solubility

• Larger partial pressure gradient

What decreases diffusion?

• Smaller surface area

• Damage to respiratory membrane

• Thicker membrane

Partial pressure in alveoli:

PO₂ = 104 mm Hg

PCO₂ = 40 mm Hg

Partial pressure entering pulmonary capillaries:

PO₂ = 40 mm Hg

PCO₂ = 45 mm Hg

At high altitude, oxygen concentration is:

Still 21%

BUT

Atmospheric pressure is lower.

↓

PO₂ decreases.

Body adaptations to high altitude.

• Increased breathing

• Increased heart rate

• Increased RBC production

• Increased hemoglobin production

What is HAPE?

High-Altitude Pulmonary Edema

Caused by pulmonary vasoconstriction leading to increased capillary pressure and fluid leakage.

Pneumonia

Alveoli fill with:

• Fluid

• White blood cells

↓

Less gas exchange

Tuberculosis

Forms connective tissue tubercles.

↓

Respiratory membrane thickens.

↓

Surface area decreases.

Atelectasis

Collapse of lung tissue.

↓

Less gas exchange.

ARDS

Acute Respiratory Distress Syndrome

• Severe atelectasis

• Alveoli collapse

• Oxygen delivery greatly reduced

How is oxygen transported?

98–99%

↓

Bound to hemoglobin

1–2%

↓

Dissolved in plasma

What is oxyhemoglobin?

Hemoglobin with oxygen bound to its iron (Fe).

Each hemoglobin can bind 4 oxygen molecules.

Where does oxygen bind on hemoglobin?

Iron (Fe)

What increases oxygen release from hemoglobin?

• ↓ PO₂

• ↑ PCO₂

• ↑ Acidity (↓ pH)

• ↑ Temperature

About what percentage of oxygen remains bound to hemoglobin in venous blood?

About 75%

As carbon dioxide increases...

More oxygen is released.

As pH decreases...

More oxygen is released.

As temperature increases...

More oxygen is released.