Respiratory System

Why do we need a respiratory system?

• Gas exchange in cells

Respiratory systems in diverse animals

1. Aquatic Invertebrates have gills
2. Insects have hollow tubes called tracheae
3. Fish have complex gills
4. Frogs breathe through their skin and lungs
5. Birds have a one-way respiratory system
6. Mammals have lungs with many branches

Structure of the mammalian respiratory system

1. Oral cavity & Nose: Filter, warm and humidify air
2. Trachea: Conduct air to lungs & trap particles
   • Ciliated epithelium
3. Bronchi & bronchioles branch ~ 23 times
4. Alveoli: tiny sacs for gas exchange
5. Pulmonary circulation
   • Pulmonary artery: brings oxygen-poor blood from the heart
   • Pulmonary capillaries: pick up oxygen, release CO2
   • Pulmonary vein: takes oxygen-rich blood back to the heart

How breathing (ventilation) works

1. Inhaling
   • Diaphragm contracts (lowers)
   • Rib cage raised
   • Chest cavity expands
   • This creates negative pressure inside lungs (suction!)
2. Exhaling
   • Diaphragm relaxes
   • Rib cage lowered
   • Chest cavity compresses
   • This creates higher pressure in lungs (forces air out)
3. Forced respiration (e.g. exercise)
   • Rib muscles assist in inhaling, exhaling
4. Control of breathing
   • Breathing is controlled by the brain stem (medulla)
   • Respiratory center there tells muscles to contract (inhale) every so often
   • Can speed up breathing if:
     • Oxygen is low
     • CO2 is high
     • Blood pH is low

    

Gas exchange and transport

1. Oxygen transport
   • Red blood cells!
   • Hemoglobin: a protein with iron in it
2. CO2 transport
   • In plasma: CO2
   • In red blood cells

Respiratory disorders

1. Emphysema: breakdown of alveoli
2. Smoking
3. Carbon monoxide poisoning
4. Anemia