Respiratory System Overview

Overview

This lecture explains the structure and function of the human respiratory system, how it coordinates with other body systems, and highlights its clinical significance and adaptations in other animals.

Human Respiratory System Overview

• The respiratory system enables gas exchange (O₂ in, CO₂ out), essential for cellular respiration and ATP production.
• Cellular respiration is the process where cells use oxygen and produce carbon dioxide as waste.
• The respiratory system works closely with the circulatory system to deliver oxygen and remove carbon dioxide.

Respiratory Tract Pathway

• Air enters through the nasal cavity, where it is warmed, humidified, and filtered by mucus and hairs.
• Air passes through the pharynx (shared with food), larynx (voice box), and trachea (supported by cartilage rings).
• The trachea branches into primary bronchi, then into secondary and tertiary bronchi, then bronchioles.
• The bronchial tree resembles an upside-down tree, getting narrower toward the lungs.

Lungs Structure and Gas Exchange

• Humans have two lungs: three lobes on the right, two on the left (with a cardiac notch for the heart).
• Bronchioles lead to alveolar ducts surrounded by alveolar sacs, which contain alveoli.
• Alveoli are thin-walled sacs, providing a large surface area for gas exchange with capillaries.

Coordination with Other Body Systems

• The skeletal system (ribs) protects the lungs.
• The muscular system aids breathing: intercostal muscles, diaphragm, and abdominal muscles help expand/contract the thoracic cavity.
• The nervous system regulates involuntary breathing, responding to blood pH changes.

Blood pH and Breathing Regulation

• Increased CO₂ raises H⁺ concentration, lowering blood pH (making it more acidic).
• The brain detects increased acidity and signals muscles to increase breathing rate and depth.
• This regulation maintains blood pH around 7.4, an example of homeostasis.

Variations in Other Species

• Earthworms exchange gases through their skin.
• Fish use gills; insects use a tracheal system with external spiracles and internal tubes.

Clinical Significance and Surfactant

• Understanding the respiratory system aids treatment of illnesses like asthma, emphysema, and in premature infants.
• Alveoli require surfactant (made by type 2 alveolar cells) to lower surface tension and prevent collapse.
• Lack of surfactant in premature babies can cause respiratory distress syndrome (RDS); artificial surfactant can treat this condition.

Key Terms & Definitions

• Alveoli — tiny air sacs in the lungs where gas exchange occurs.
• Surfactant — a substance that reduces surface tension in alveoli, preventing collapse.
• Intercostal muscles — muscles between ribs involved in breathing.
• Diaphragm — major muscle below lungs crucial for respiration.
• Homeostasis — maintaining stable internal conditions (like blood pH).
• pH — a scale measuring hydrogen ion concentration; lower pH = more acidic.
• Respiratory distress syndrome (RDS) — condition in infants due to insufficient surfactant causing alveoli collapse.

Action Items / Next Steps

• Review the pathway of air through the respiratory tract.
• Study the function of alveoli and surfactant.
• Explore further reading on CO₂’s effect on blood pH and gas exchange in non-human animals.