Respiratory System: Functional Anatomy

• Summaries of functional anatomy of the respiratory system

Structure and Function of the Respiratory System

• Basic structures are: the lungs, diaphragm, and alveoli
• The system delivers oxygen from the atmosphere to the lungs
• It provides the method of gaseous exchange within the lungs, where oxygen enters the blood, and carbon dioxide exits
• It creates speech as air passes over the vocal cords, facilitates sense of smell
• It expels heat and water vapor in the air breathed out

Structure of the Respiratory System

• Comprises of 3 main sections: air passages, lungs, and diaphragm

Air Passages

• Where the nasal cavity & mouth enters the respiratory system
• The pharynx is where the back of the mouth and nose meet
• The larynx produces sound when air passes over it
• The trachea assists with air delivery, also known as a windpipe
• The bronchi tubes provide air to the lungs
• Bronchioles subdivide from each bronchus, with smaller branches
• Alveoli: cup-shaped sacs found at the end of bronchioles, surrounded by capillaries, where 02 and CO2 exchange occurs
• Diffusion: movement of gas from an area of high concentration to low concentration

The Lungs

• Located within the thoracic cavity and protected by the sternum, ribs, and vertebral column
• Contain bronchi, bronchioles, and alveoli
• Gas exchange occurs at the site of the alveoli

Gas Exchange in the Body

• The exchange of oxygen and carbon dioxide occurs at two sites: the lungs (Alveoli/Capillary interface) and the muscles (Capillary/Muscle interface)
• Diffusion is the movement of substances from a high to low concentration through a semi-permeable membrane
• Oxygen exchange moves from the alveoli of the lungs into the capillaries, while carbon dioxide moves from the capillaries into the alveoli
• Oxygen has a high concentration in the alveoli and capillaries, while carbon dioxide has a high presence in muscles

Gas exchange at the alveoli/capillary interface

• A high concentration gradient is maintained by continuous inspiration of oxygen and expiration of the carbon dioxide and continuous flow of blood to and from the blood capillaries
• Alveoli features that allow efficient gas exchange to occur, include:
  • Large surface area to volume ratio
  • Surrounded by capillaries
  • Very thin walls - to promote diffusion of gases

Gas exchange at the capillary/muscle interface

• Gases diffuse to allow the transport of oxygen to allow the muscle tissue and to cause the removal of carbon dioxide as a byproduct

Oxygen Molecule Pathway

• An oxygen molecule in the body goes through these key structures:
  • Lungs, pulmonary artery, capillaries, pulmonary vein, aorta, vena cavae, arteries, veins, and all body tissues
• Oxygen enters the lungs then diffuses into the bloodstream, which leads to the heart to transport the oxygen throughout the body via arteries and capillaries
• It then reaches the body tissues where it's used for various metabolic processes
• The oxygen molecule is converted to carbon dioxide

Alveoli and Oxygen

• When inhaling, O₂ moves through the lungs and into the alveoli for diffusion into the blood
• Gas exchange takes place due to a concentration difference known as concentration gradient
  • The alveoli have a high concentration of O₂
  • The venous blood capillary has a low concentration of O2
  • The concentration differential causes O₂ to move into the blood capillary (from a high to low concentration area)

Diaphragm

• Involuntary smooth muscle that contracts and relaxes to aid breathing at all times
• Size of the chest cavity changes as the diaphragm moves up and down, to cause breathing

Ventilation

• Ventilation = Tidal Volume x Respiratory Rate
• Tidal Volume is the amount of air breathed in and out in 1 breath
• Respiratory Rate is the amount of breaths per minute
• Ventilation the amount of air that is inspired and expired during 1 minute

Breathing and the Brain

• The brain constantly monitors the levels of CO2 and O₂ in the blood
• Increased levels of CO2 trigger the need to breathe
• The brain senses the change in these levels after exercise and responds by increasing heart and respiratory rate

Mechanics of breathing

• There are 2 movements, inspiration and expiration which operate on the principal that gases move from an area of high pressure to low pressure

Inspiration

• The breathing process involves the following:
  • The volume of lungs increases
  • External intercostal muscles contract, and internal intercostal muscles relax to lift rib cage up. The diaphragm contracts to become flatter
  • Air enters the lungs moving from area of high pressure to low pressure

Expiration

• Breathing out involves the following:
  • The volume of lungs decreases
  • External intercostal muscles relax and internal intercostal muscles contract to lower rib cage. The diaphragm relaxes to become dome shaped
  • Air exits the lungs from an area of high pressure to low.