Human Respiratory System Table
Interactive Timeline of Breathing. Trace the path of air from Nose to Lungs.
Nostrils/Nasal Cavity
Upper Respiratory TractNose can detect 1 trillion smells.
Pharynx (Throat)
Upper Respiratory TractAbout 5 inches long.
Larynx (Voice Box)
Upper Respiratory TractAdam's apple is larger in males.
Trachea (Windpipe)
Lower Respiratory TractCilia beat upwards to move mucus.
Bronchi (Left & Right)
Lower Respiratory TractRight bronchus is wider/shorter.
Bronchioles
Lower Respiratory TractDiameter less than 1mm.
Alveoli (Air Sacs)
Lower Respiratory TractTotal Surface Area ≈ Tennis Court
Lungs
Respiratory OrganLeft lung is slightly smaller.
Diaphragm
Respiratory MusclePrimary muscle of respiration.
Rib Cage
Respiratory Skeleton12 pairs of ribs.
The Human Respiratory System: A Complete Guide
The human respiratory system is a complex biological network responsible for the intake of Oxygen (O₂) and the expulsion of Carbon Dioxide (CO₂). Beyond just breathing, it plays a vital role in phonation (speech), olfaction (smell), and maintaining the body's acid-base balance (pH regulation).
1Anatomy of the Respiratory Tract
Upper Respiratory Tract
- Nose & Nasal CavityThe primary entry point. Lined with mucous membranes and cilia (tiny hairs) that warm, moisten, and filter dust particles from the incoming air.
- Pharynx (Throat)A muscular funnel that serves as a common pathway for both air (respiratory) and food (digestive). It divides into the nasopharynx, oropharynx, and laryngopharynx.
- Larynx (Voice Box)Connects the pharynx to the trachea. It contains the vocal cords which vibrate to produce sound. The Epiglottis acts as a lid to prevent food from entering the airway.
Lower Respiratory Tract
- Trachea (Windpipe)A 4-inch tube kept open by C-shaped cartilage rings. It conducts air down to the lungs and is lined with ciliated epithelium to sweep mucus upward.
- Bronchi & BronchiolesThe trachea splits into two primary bronchi (left/right). These branch repeatedly into smaller tubes called bronchioles, forming the "Bronchial Tree."
- AlveoliThe functional units of lungs. Approx 480 million microscopic air sacs where gas exchange occurs. They provide a massive surface area (approx 70m²) for efficiency.
2Physiology: How We Breathe
Breathing, or Pulmonary Ventilation, is driven by pressure differences created by muscle movements. Air always flows from high pressure to low pressure.
Inhalation
- DiaphragmContracts and moves DOWN (flattens).
- Rib CageIntercostal muscles contract, pulling ribs UP & OUT.
- Volume/PressureChest volume Increases → Pressure Decreases.
- ResultAir rushes INTO the lungs to equalize pressure.
Exhalation
- DiaphragmRelaxes and moves UP (dome shape).
- Rib CageRelaxes, ribs move DOWN & IN.
- Volume/PressureChest volume Decreases → Pressure Increases.
- ResultAir is pushed OUT of the lungs.
3Lung Volumes & Capacities
| Term | Approx Value | Definition |
|---|---|---|
| Tidal Volume (TV) | 500 ml | Volume of air inhaled or exhaled during normal breathing. |
| Expiratory Reserve Volume (ERV) | 1000 - 1100 ml | Additional air that can be forcibly exhaled after a normal exhalation. |
| Inspiratory Reserve Volume (IRV) | 2500 - 3000 ml | Additional air that can be forcibly inhaled after a normal inhalation. |
| Residual Volume (RV) | 1100 - 1200 ml | Volume of air remaining in lungs after forcible expiration (keeps lungs inflated). |
| Vital Capacity (VC) | 4600 ml | Maximum air a person can breathe in after a forced expiration (VC = ERV + TV + IRV). |
4Common Respiratory Disorders
Asthma
Inflammation and narrowing of bronchi/bronchioles causing difficulty in breathing, wheezing, and coughing. Often triggered by allergens.
Pneumonia
Infection that inflames the air sacs (alveoli) in one or both lungs. The alveoli may fill with fluid or pus (purulent material).
Emphysema
Chronic condition where alveolar walls are damaged, reducing surface area for gas exchange. Main cause is cigarette smoking.
Frequently Asked Questions
What is the main organ of the Respiratory System?
The Lungs are the main spongy organs located in the chest cavity. They facilitate the exchange of oxygen and carbon dioxide with the blood.
What is the function of the Diaphragm?
The Diaphragm is a dome-shaped muscle below the lungs. When it contracts (flattens), it increases chest volume, lowering pressure and pulling air IN (Inhalation).
Where does Gas Exchange occur?
Gas exchange happens in the Alveoli (tiny air sacs) at the end of bronchioles. Oxygen moves into the blood, and Carbon Dioxide moves out into the alveoli.
Why does the Trachea have cartilage rings?
The Trachea (windpipe) has C-shaped cartilaginous rings to keep the airway open and prevent it from collapsing when air pressure drops during inhalation.
What is the difference between Pharynx and Larynx?
The Pharynx (Throat) is a common passage for food and air. The Larynx (Voice Box) contains vocal cords for sound and sits atop the trachea.
What is the Epiglottis?
The Epiglottis is a leaf-like cartilaginous flap that closes the entrance to the windpipe (glottis) during swallowing to prevent food/water from entering the lungs.
How many lobes do the lungs have?
The Right Lung has 3 lobes (larger), while the Left Lung has 2 lobes (smaller) to accommodate the heart.
What is "Internal Respiration"?
Internal sensation refers to the exchange of gases between the blood capillaries and the body's tissues cells, utilizing oxygen for energy production.
What cleans the air we breathe?
Hairs and mucus in the nasal cavity trap dust and pathogens. Cilia in the trachea also sweep mucus and trapped particles upward away from the lungs.
What is Tidal Volume?
Tidal Volume is the amount of air inhaled or exhaled during a normal breath (approx 500ml in adults).