Complete Respiratory System - BIOL 221

Main function of the respiratory system

Gas exchange: bringing O₂ into blood and removing CO₂.

Waste product of aerobic respiration

Carbon dioxide (CO₂).

How the respiratory system maintains homeostasis

Brings in O₂, removes CO₂, and helps maintain normal blood pH.

Pathway of oxygen (O₂)

Atmosphere → Lungs → Blood → Cells.

Pathway of carbon dioxide (CO₂)

Cells → Blood → Lungs → Atmosphere.

Additional functions of the respiratory system

Sound production, smell detection, pathogen defense, pH regulation, and venous/lymph movement.

Pulmonary ventilation

Movement of air into and out of the lungs (breathing).

External respiration

Exchange of O₂ and CO₂ between alveoli and blood.

Gas transport

Movement of gases through the bloodstream.

Internal respiration

Exchange of O₂ and CO₂ between blood and body tissues.

Cellular respiration

Cells use oxygen to produce ATP and generate CO₂.

Conducting zone

Structures that move, warm, humidify, and filter air.

Structures in the conducting zone

Nose through terminal bronchioles.

Does gas exchange occur in the conducting zone?

No.

Respiratory zone

Structures where gas exchange occurs.

Structures in the respiratory zone

Respiratory bronchioles, alveolar ducts, and alveoli.

Factors making lungs efficient at gas exchange

Huge surface area, thin respiratory membrane, and rich blood supply.

Why huge surface area improves gas exchange

Millions of alveoli create an enormous exchange area.

Why a thin respiratory membrane improves gas exchange

Short diffusion distance allows faster gas transfer.

Why a rich blood supply is important for gas exchange

Dense capillaries and constant flow maintain strong diffusion gradients.

Airflow pathway

Nose/mouth → Pharynx → Larynx → Trachea → Bronchi → Bronchioles → Alveoli.

Nostrils (nares)

External openings allowing air into the respiratory system.

Function of nasal hairs

Trap large particles and debris.

Function of nasal cartilage

Provides flexibility to the nose.

Structure supporting the bridge of the nose

Bone.

How the nasal cavity conditions incoming air

Warms, humidifies, and filters the air.

Function of nasal conchae

Increase surface area and create turbulence.

Importance of turbulence in the nasal cavity

Allows mucosa more time to warm, humidify, and trap particles.

Function of the nasal septum

Divides the nasal cavity into right and left sides.

Cells that produce mucus

Goblet cells.

Functions of mucus

Traps dust and microbes, and moisturizes incoming air.

Function of cilia in the respiratory tract

Move mucus upward toward the pharynx.

Mucus escalator

Ciliary motion pushing trapped particles upward away from lungs.

Effect of smoking on cilia

Damages and paralyzes them.

Consequences of smoking-induced ciliary damage

Mucus buildup, chronic cough, and increased risk of infection.

Location of olfactory receptors

Superior region of the nasal cavity.

Function of olfactory receptors

Detect airborne chemicals (odors).

Why nasal congestion reduces smell

Blocks airflow carrying odor molecules to receptors.

Paranasal sinuses

Air-filled cavities in skull bones around the nasal cavity.

Functions of paranasal sinuses

Lighten skull, add voice resonance, and increase mucosal surface area.

Effects of sinus inflammation or mucus buildup

Causes pressure and headaches.

Why nose breathing is better than mouth breathing

The nose warms, humidifies, and filters air effectively.

Pharynx (throat)

Shared passageway for air to lungs and food/liquids to esophagus.

Three regions of the pharynx

Nasopharynx, oropharynx, and laryngopharynx.

Function of the tonsils

Contains lymphoid tissue to detect pathogens entering nose and mouth.

Types of tonsils

Pharyngeal (adenoid), palatine, and lingual tonsils.

Effects of swollen tonsils

Painful swallowing, obstructed airflow, increased mouth breathing, and snoring.

Functions of the larynx

Maintains open airway, produces sound, and prevents food entering trachea.

Steps during swallowing

Larynx moves upward, epiglottis folds downward, food enters esophagus.

What happens if food enters the larynx?

Coughing helps expel it.

Function of the trachea

Provides open airway between larynx and bronchi to conduct air.

Function of C-shaped cartilage rings

Keeps airway open while allowing esophagus to expand during swallowing.

Respiratory mucosa of the trachea

Goblet cells produce mucus; cilia move trapped particles toward pharynx.

What does the trachea branch into?

Right and left primary bronchi.

How do bronchi change as they branch?

They become smaller, more numerous, and have less cartilage support.

Branching pattern of the bronchi

Primary bronchi → Secondary bronchi → Tertiary bronchi.

Why are inhaled objects more likely to enter the right lung?

The right primary bronchus is wider and more vertical.

Bronchioles

Small airways that lack cartilage.

How do bronchioles control airflow?

Smooth muscle changes the airway diameter.

Bronchoconstriction

Smooth muscle contracts, narrowing airway and decreasing airflow.

Bronchodilation

Smooth muscle relaxes, widening airway and increasing airflow.

How does asthma affect the bronchioles?

Excessive bronchoconstriction makes breathing difficult.

Pulmonary alveoli

Tiny air sacs surrounded by capillaries where gas exchange occurs.

Why are alveoli effective for diffusion?

Thin walls, huge surface area, and dense capillary networks.

Gas movement at the alveoli

O₂ diffuses into blood; CO₂ diffuses into alveoli.

Type I alveolar cells

Thin squamous cells where gas exchange occurs.

Type II alveolar cells

Produce surfactant.

Alveolar macrophages

Mobile immune cells that remove dust and microbes from alveoli.

Why is surfactant important?

Reduces surface tension and keeps alveoli open.

What creates surface tension in the alveoli?

A thin layer of water lining the alveoli.

What happens without surfactant?

Surface tension can collapse alveoli during exhalation.

Neonatal respiratory distress syndrome

Premature infants lacking surfactant suffer alveolar collapse.

Structures contained in the lungs

Airways, alveoli, blood vessels, and connective tissue.

Lobes of the right lung

Superior, middle, and inferior.

Lobes of the left lung

Superior and inferior only.

Why is the left lung smaller than the right?

The heart occupies space on the left side of the thoracic cavity.

Visceral pleura

Covers the surface of the lungs.

Parietal pleura

Lines the thoracic wall.

Pleural fluid

Reduces friction and helps keep lungs expanded.

Why do the lungs stay inflated?

Pleural fluid and negative intrapleural pressure hold lungs against thoracic wall.

Pneumothorax

Air entering the pleural cavity, which can cause lung collapse.

How does air move during breathing?

Flows from higher pressure to lower pressure.

How does the body move air into and out of the lungs?

By altering lung volume to change internal pressure.

Atmospheric pressure

Pressure of the outside air.

Intra-alveolar pressure

Pressure inside the alveoli.

Intrapleural pressure

Pressure within the pleural cavity.

Inspiration (inhalation)

Process of drawing air into the lungs.

Step 1 of inspiration

Inspiratory muscles contract: diaphragm flattens downward and external intercostals lift ribs upward and outward.

Step 2 of inspiration

Thoracic cavity volume increases, causing the lungs to expand.

Step 3 of inspiration

Intra-alveolar pressure decreases below atmospheric pressure.

Step 4 of inspiration

Air flows into the lungs until pressures equalize.

Expiration (exhalation)

During quiet breathing, expiration is mostly passive.

What happens during quiet expiration?

Inspiratory muscles relax, thoracic cavity volume decreases, lungs recoil inward, and intra-alveolar pressure rises.

Why does air leave the lungs during expiration?

Pressure inside the lungs becomes greater than atmospheric pressure.

Forceful expiration

Internal intercostals and abdominal muscles actively push more air out.

Why do the lungs naturally recoil inward?

They contain elastic tissue.

Why is negative intrapleural pressure important?

It, along with pleural fluid, helps keep the lungs expanded.

How are the lungs attached to the thoracic wall?

Pleural fluid keeps the lungs "stuck" to the thoracic wall.

What happens if air enters the pleural cavity?

The lung can collapse.

Spirometry

Measures how much air moves during breathing.