Respiratory System

• Components of Respiration

  1. Breathing :

  • Inhalation - taking in oxygen (O2) from the external environment
  • Exhalation - expelling carbon dioxide (CO2)
• 2. External Respiration

  • Exchange of gases between alveoli and the blood
  • O2 diffuses INTO the organism (blood)
  • CO2 diffuses OUT of the organism (lungs)
  • The lung surface is LARGE and moist
• 3. Internal Respiration

  • Exchange of gases between the blood in capillaries and individual cells
  • O2 diffuses INTO the cells
  • CO2 diffuses OUT of the cells

  Internal respiration takes place in the tissues. 

  External respiration occurs in the lungs.
• 4. Cellular Respiration

  • The breakdown of sugar molecules into usable energy molecules
  • Occurs in the mitochondria
  • Requires the presence of O2
  • Results in the production of CO2
• 1. Nasal and Oral Cavities

  • Air entering through the nose is warmed, moistened and filtered
  • Warm air is used more efficiently
  • Moist air prevents drying out of lungs
  • Mucus traps small particles
  • Nose hairs filter out large particles
  • Cilia sweep mucus and trapped particles to the opening of the nose or down the esophagus
  • Air entering through the oral cavity misses some of these important steps
• Pharynx

  • Area at the back of the mouth that acts as a common path for both food and air
  • Branches into two pipes:
  • Esophagus: leads to stomach
  • Trachea: leads to lungs
  • A flap-like structure, the epiglottis, covers the opening of the trachea when eating
• What happens when things “ go down the wrong tube”?

  Air in the esophagus? → escapes as a burp

  Food in the trachea? → coughing ejects food matter
• 3. Larynx

  • Also known as the voice box
  • Made up of several pieces of cartilage
  • Sounds are produced by vibrations of the vocal cords and vibrations in the air as it passes through the larynx and out the mouth
• Trachea

  • Tube connecting the pharynx and the lungs
  • Surrounded by rings of cartilage for support
  • Lined with mucus to trap particles and moisten air
  • Cilia sweep mucus and trapped particles up and out of the trachea
  • Branches into two pipes called bronchi (plural)
  • Left Bronchus - leads to left lung
  • Right Bronchus - leads to right lung
• 5. Bronchi and Bronchioles

  • Bronchi branch into smaller and smaller tubes, within the lungs called bronchioles
  • Bronchi and the larger of bronchioles are lined with cilia and mucus for further filtering of air
  • Mucus is directed upwards by cilia (tiny hair like fibers) to the epiglottis where the mucus is swallowed and digested
• Alveoli

  • The smallest bronchioles end in a cluster of tiny hollow air sacs - alveoli - where gas exchange takes place
  • The human lungs contain approximately 300 million alveoli!
  • Increases surface area of lungs therefore increase rate of gas exchange
  • Each alveolus is surrounded by a network of capillaries
  • The walls of the alveoli and capillaries are each only one cell thick
• Characteristics of all Gas Exchange Surfaces

  • High Surface Area – if you were to expand the alveoli they would cover an entire tennis court
  • Short Diffusion Distance – the alveoli are only 1 cell thick
  • High Concentration Gradient – there is always new oxygen arriving in the lungs and the concentration of oxygen is higher in the lungs than in the blood 
• Reminder: Gas Exchange 

  • External Respiration: the exchange of gases across the respiratory surface between the alveoli and the blood Internal Respiration: the exchange of gases between the blood and the individual cells in the tissue
• • Breathing is based on the principle of negative pressure - air always moves from a high pressure area to a low pressure area
• Inhalation

  • Diaphragm contracts and moves down
  • Intercostal muscles (muscles between ribs) contract and expands ribcage
  • There is a decrease in pressure inside the chest cavity
  • RESULT: volume of chest cavity increases, air rushes in
  • Air flows from high pressure area (outside) to low pressure area (inside lungs)
• Exhalation

  • Diaphragm relaxes and returns to curved position
  • Intercostal muscles relax and contract rib cage
  • There is an increase in pressure in the chest cavity
  • RESULT: volume of chest cavity decreases, air rushes out  
  • air will from from high pressure within lungs to low pressure outside
• Control of Breathing

  • Breathing is involuntary activity, controlled by the medulla oblongata in the brain
• Control of Breathing

  • Chemoreceptors in the medulla oblongata detect CO2 levels in the blood:
  • When you don’t breathe, build up of CO2 in the blood
  • CO2 and water form carbonic acid in the blood, which lowers the pH
  • Chemoreceptors sense low pH and relay message to stimulate the diaphragm and intercostal muscles
  • When CO2 levels decrease, and blood pH is returned to normal, the chemoreceptors are inactivated
• Pathway of Oxygen

  Reminder - Hemoglobin is a protein found in red blood cells that contains 4 atoms of iron. Each atom binds to an O2 molecule.

  • O2 reaches the lungs and diffuses from alveoli to the capillaries
• Gas Exchange in the Alveoli 

  • Deoxygenated blood arrives at the lungs from the heart
  • This blood flows through the capillary network around the alveoli
  • Gas exchange occurs because:
  • In the blood, CO2 levels are high, and O2 levels are low
  • In the alveoli, CO2 levels are low, and O2 levels are high
  • Gas molecules move by diffusion 
  • Oxygenated blood returns to the heart, to be pumped to the rest of the body
• Gas Transportation in the Blood - Oxygen

  • Oxygen is transported by hemoglobin - a protein found in red blood cells
  • Each hemoglobin protein has four iron atoms in its structure, each of which can form a loose bond with oxygen
  • When hemoglobin is bound to O2 → “oxyhemoglobin”
  • Near cells, where the concentration of O2 is low, O2 is released from hemoglobin, and moves by  diffusion into the cells
• Gas Transportation in the Blood - Carbon Dioxide

  • Most CO2 in the blood is in the form of carbonic acid (H2CO3) or bicarbonate ions (HCO3)
  • Some carbon dioxide can be carried by hemoglobin
  • Deoxygenated blood travels back to heart where it is pumped to the lungs 
  • In the lungs CO2 is released and diffuses from the capillaries tothe alveoli
  • CO2 is expelled (exhalation)
• Lung Volumes 

  • Tidal volume: the amount of air that passes in and out of the lungs with each breath
  • Total lung capacity: the maximum volume of air that can be held in the lungs
  • After the normal tidal volume is exhaled, more air can be forcefully exhaled = expiratory reserve volume
  • During a deep breath, an extra volume of air can be inhaled = inspiratory reserve volume
• Vital Capacity

  • The maximum amount of air that can be moved into and out of the respiratory system is called the vital capacity; this value is always 1-1.5L LESS than the total lung capacity… WHY?

  → because if the lungs became completely deflated, they would collapse

  The 1-1.5L of air that always remains in the lungs is called the residual volume
• Lung Disorders

  Are conditions that interfere with the primary function of the respiratory system by either: 

  1. Restricting flow of air into and out of the lungs
  2. Damaging the alveoli impairing gas exchange
• Chronic Obstructive Pulmonary Disease (COPD)

  • Long term respiratory disease (bronchitis and emphysema)
  • 80-90% of cases caused by cigarette smoke
  • Alveoli permanently damaged -- lose elasticity and shape
  • Reduced surface area of respiratory membranes 
  • ↓ oxygen in blood, ↑ carbon dioxide in tissues
  • leads to increase in breathing and heart rate to compensate
  • Lifestyle change can help - often early death from pneumonia, heart failure or respiratory failure
• Cystic Fibrosis

  • Genetic - excess mucus production that is thick and sticky, clogging the airways
• Respiratory Infections

  The flu:  

  • Caused by a virus
  • Highly contagious
  • Causes fever, coughing, sore throat, runny nose, muscle aches
  • Spread through moisture in air (respiratory system is vulnerable because of constant exposure to external environment)