The Respiratory System

• The respiratory system facilitates gas exchange, providing oxygen for cellular respiration and removing carbon dioxide.
• The respiratory system works with the circulatory system to supply oxygen to the body and remove carbon dioxide.
• Cellular respiration occurs within cells to produce ATP.

Pathway of Air

• Air enters through the nasal cavity, where it is warmed, humidified, and filtered by mucus and hairs (including cilia).

• The pharynx serves as a junction for both food and air.

• The larynx, also known as the voice box.

• The trachea is a cylinder tube supported by cartilage rings to keep it open.

• Food travels down the esophagus, not the trachea, because of the epiglottis.

• The trachea branches into two primary bronchi, one for each lung.

• Lungs are divided into lobes, with three on the right and two on the left.

• The left lung is smaller with a cardiac notch to accommodate the heart.

• Primary bronchi divide into secondary bronchi.

• Secondary bronchi divide into tertiary bronchi.

• Bronchioles are smaller tubes branching from the tertiary bronchi.

• Respiratory bronchioles branch into alveolar ducts.

• Alveolar ducts are surrounded by grape-like clusters of alveolar sacs.

• Gas exchange occurs in the tiny sacs within the alveolar sacs known as alveoli.

Respiratory System Recap

• The pathway of airflow: Nasal cavity → Pharynx → Larynx → Trachea → Primary bronchi → Secondary bronchi → Tertiary Bronchi → Bronchioles

Gas Exchange in Alveoli

• Alveoli are thin-walled cells with a large surface area in direct contact with capillaries, facilitating gas exchange.
• Red blood cells in the capillaries pick up oxygen and release carbon dioxide.

Systems Working Together

• Circulatory system transports oxygen and carbon dioxide.
• Skeletal System: Ribs protect the lungs.
• Muscular system, including intercostal muscles, diaphragm, and abdominal muscles, expand and contract the thoracic cavity.

Regulation of Breathing

• Breathing is controlled by the nervous system, primarily involuntarily, by monitoring blood pH.
• pH Scale: Based on hydrogen ion concentration (H+), where acidic substances have higher H+ concentration (lower pH) and bases have lower H+ concentration (higher pH).
• Increased carbon dioxide levels in the blood increase H+ concentration, lowering the blood pH (making it more acidic).
• This change is detected by the brain, which then adjusts the rate and depth of breathing to restore normal blood pH (~7.4), maintaining homeostasis.

Gas Exchange in Other Organisms

• Earthworms: Gas exchange through their skin.
• Fish: Gas exchange through gills.
• Insects: Tracheal system with spiracles for gas exchange.

Respiratory Distress Syndrome (RDS)

• Premature babies may lack sufficient surfactant, leading to Respiratory Distress Syndrome (RDS).
• Surfactant: A substance, including phospholipids and proteins, produced by type II alveolar cells that reduces the surface tension of water in the alveoli, preventing collapse.
• Artificial surfactants treat premature infants with RDS, significantly improving their outcomes.