Structure and Functions of the Respiratory System

Structure and Functions of the Respiratory System

Key Knowledge

• The respiratory system's structure and function, including:
  • Lungs: structure and function
  • Mechanics of breathing
  • Gaseous exchange: alveoli/capillary and capillary/muscle interface
• Interaction of cardiovascular and respiratory systems:
  • Oxygen transport around the body: at rest, during physical activity, sport and exercise

Key Skills

• Use anatomical terminology: identify structures and functions of cardiovascular and respiratory systems
• Investigate and describe the process of gaseous exchange
• Use primary data: measure and analyze changes to cardiovascular and respiratory systems at rest vs. exercise intensities

Key Terms

• Respiratory system
• Mechanics of breathing
• Gas exchange
• Expiration
• Alveoli/capillary interface
• Respiratory responses to physical activity
• Interaction of the cardiovascular and respiratory systems during physical activity
• Tidal volume
• Increased oxygen uptake
• Inspiration
• Capillary/muscle interface
• Respiratory rate
• Increased carbon dioxide removal
• Ventilation
• Pulmonary diffusion

Functions of the Respiratory System

• Brings air from the atmosphere into the lungs
• Transfers oxygen into the blood
• Removes carbon-dioxide from the blood
• Expels heat and water vapor in the air breathed out
• Allows vocal cords to create speech as air is breather out

Structure of the Respiratory System

• Lungs: major organs of the respiratory system.
• Located in the chest cavity behind the ribs
• Consists of three main parts:
  • The conducting system
  • The pleura
  • The diaphragm

The Conducting System

The conducting system comprises the following:

• Nasal cavity
• Pharynx
• Larynx
• Trachea
• Bronchus / Bronchi
• Bronchioles
• Alveoli
• Lungs
• Pleura
• Diaphragm

Nasal Cavity

• Initial pathway for air from outside the body.
• Air is warmed and moistened.
• Septa covered with cilia: filter foreign particles.

Pharynx

• Section of the throat where the backs of the mouth and nose combine.
• Food is channeled into the esophagus; air moves into the larynx.
• Air is further warmed.

Larynx

• More evident in males ('Adam’s apple').
• Contains the vocal cords that create the voice as air passes through them.

Trachea

• Referred to as the windpipe.
• Constructed of rings of hyaline cartilage enclosed by other cartilage and tissue.
• Sits mostly behind the sternum to provide a protected medium for air passage into the lungs.

Bronchi / Bronchus

• The trachea divides into two bronchi.
• Each bronchus has the same characteristics as the trachea.
• Each bronchus feeds one of the lungs.

Bronchioles

• Each bronchus subdivides into a series of further sub-dividing bronchioles.
• The system of gradually diminishing air passages is similar to an inverted tree.

Alveoli

• Microscopic cup-shaped sacs at the ends of the smallest bronchiole.
• Each alveolus is only one cell thick
• Surrounded by a rich network of capillaries that continually exchange oxygen for carbon dioxide and water

The Pleura

• The pleura covers each lung.
• The gap between the membrane and each lung is filled with a fluid
• Allows the lung to expand and contract with minimal friction between the lung and its surrounding body tissue.
• The pleura is attached to the inside of the chest cavity and to the top of the diaphragm.

The Diaphragm

• Involuntary or smooth muscle contracts and relaxes to aid breathing.
• Diaphragm moves up and down: the chest cavity decreases and increases in size causing breathing.
• A blow to the midriff area during sport may hit the diaphragm, causing it to spasm.
• The individual is 'winded' and may have difficulty breathing

The Respiratory System: Mechanics of Breathing and Gaseous Exchange

Ventilation (V)

• Is the amount of air breathed in (inspiration) and out (expiration) during 1 minute.
• V = TV \times RR
  • TV = Tidal Volume
  • RR = Respiratory Rate
• At rest example:
  • TV = 0.5L
  • RR = 12 breaths per minute
  • V = 0.5 \times 12 = 6 L /min

Mechanics of Breathing - Inspiration

• The diaphragm muscle contracts & flattens.
• Lungs expand.
• The chest cavity is enlarged & pressure reduced.
• Air is drawn in.

Mechanics of Breathing - Expiration

• Diaphragm relaxes & forms a dome shape.
• Lungs deflate.
• The chest cavity is reduced.
• Air is forced out.

Lung Volume

• Tidal volume: Amount of air inspired and expired with each breath
• Total lung capacity: Amount of air that can be held in your lungs after you breathe in maximally (so maximal inspiration)
• Vital capacity: Maximum amount of air that can be expired (breathed out) after maximal inspiration
• Residual volume: Amount of air left in the lungs at the end of maximal expiration
• Inspiratory reserve capacity: Maximal amount of air that can be inspired after a normal inspiration
• Expiratory reserve capacity: Maximal amount of air that can be expired after a normal expiration

Maximum Oxygen Uptake - VO_2 MAX

• Is the maximum amount of oxygen per minute that can be taken in, transported to, and used by the working muscles to produce ATP.
• This reading reflects aerobic power
• VO_2max is different for males and females due to lung capacity differences:
  • Males generally have a greater VO_2 max than females due to larger heart and lung capacity.
• VO_2 max tests in a laboratory are the best way to measure the efficiency of the cardiovascular, respiratory and muscular systems under exercise conditions.

Gaseous Exchange

• The respiratory and the cardiovascular system work together to transfer and transport gas molecules, in particular oxygen and carbon dioxide, around the body.
• In order to do this, gases are exchanged through the process of diffusion.

Gaseous Exchange - Diffusion

• Diffusion involves the movement of a molecule from a higher concentration to a lower concentration
• The sites of exchange important for the delivery of oxygen for energy production and the removal of waste occur at the
  • alveoli/capillary interface in the lungs and
  • the capillary/muscle interface at the cell site.

Exchange of Gases in the Lungs

• Pulmonary diffusion is the process to describe the exchange of gases in the lungs.
• Inspiration involves air entering the lungs and traveling into the alveoli.
• Capillaries surround the alveoli.
• Both structures allow the oxygen just breathed in to move from the higher concentration in the alveoli to the lower concentration of the surrounding capillaries in the blood.
• During expiration, the carbon dioxide in the capillaries is under higher concentration than the air in the alveoli.
• The carbon dioxide diffuses into the alveoli and is expelled on outward breaths.

Exchange of Gases at the Muscle (Cell) Site

• At the muscle (cell) site, the concentration of the gases inside and outside the capillaries is the reverse of those within the lungs.
• Oxygen-rich blood is transported to the muscles in response to the increased demand for energy production.
• The low levels of oxygen within the muscles attract the higher concentration oxygen from within the capillaries in the blood
• The by products of muscles using oxygen is carbon dioxide produced.
• Therefore the muscles have a higher concentration of carbon dioxide which gets diffused to the lower concentration in the capillaries.

Responses of the Respiratory System to Physical Activity

• As an individual begins to exercise, a number of changes occur within the respiratory system to meet the requirements of the body.
• As with the cardiovascular system, these changes revolve around the greater demand for oxygen to be delivered to the working muscles to create energy, and the associated removal of waste products

Responses of the Respiratory System to Physical Activity

• Increased breathing rate
• Increased tidal volume
• Increased ventilation
• Increased diffusion
• Increased oxygen uptake (VO_2)
• Increased efforts from ribcage muscles and diaphragm

Increased Respiratory Rate

• At rest, adult respiration rate is 12–15 breaths per minute.
• Under high intensity exercise, RR can reach 35–45+ breaths per minute due to the increased demand for oxygen and the need for removal of carbon dioxide.

Increased Tidal Volume

• Depth of breathing (tidal volume) at rest is approximately 0.5 liters per breath.
• This can increase to 4–5 liters per breath at maximal workloads in order to supply more oxygen to the blood to deliver to working muscles.

Increased Ventilation

• Due to the increases in respiratory rate (RR) and tidal volume (TV), ventilation (V) will also increase.
• At rest, ventilation is approximately 6.0 L/min.
• During maximal exercise, this value can increase dramatically. Eg has high as 180 L/min

Increased Diffusion

• During physical activity, the diffusion capacity at the alveoli/capillary and muscle/capillary interface is increased to allow greater amounts of oxygen and carbon dioxide to be exchanged at these sites.

Increased Oxygen Uptake (VO_2)

• Oxygen uptake increases due to the greater demand for oxygen by the muscles.
• This increase is linear, but will not increase further once maximum levels of oxygen uptake are achieved (i.e.VO_2 max).
• At rest, the average amount of oxygen that an individual can take into the body is about 0.35 L /min.
• During submaximal exercise, this can increase to around 2.0–3.5L /min.
• Under maximal exercise, depending on the individual’s aerobic fitness levels, this can reach 4–6 L /min.

Increased Efforts from Ribcage Muscles and Diaphragm

• During physical activity, the external and internal intercostal muscles as well as the diaphragm will all work harder to enable increased expansion and contraction of the thoracic cavity.
• This increased movement of the cavity will accommodate the increased air volumes that are being demanded by the working muscles in order to gain their extra oxygen.

Summary of Interactions of the Cardio-Vascular and Respiratory Systems During Physical Activity

• Ventilation (Inspiration)
  • Nasal Cavity -> Pharynx -> Larynx -> Trachea -> Bronchus -> Bronchioles -> Alveoli
• Ventilation (Expiration)
  • Alveoli -> Bronchioles -> Bronchus -> Trachea -> Larynx -> Pharynx -> Nasal Cavity
• Diffusion of Oxygen at the Alveoli/Capillary Interface
  • Alveoli -> Capillaries O2 -> Pulmonary Vein -> Left Atrium -> Left Ventricle -> Aorta -> Arteries -> Capillary O2 -> Diffusion: Muscle and Capillaries
• Diffusion of Carbon Dioxide at the Capillary/Alveoli Interface
  • Capillary CO2 -> Pulmonary Artery -> Right Ventricle -> Right Atrium -> Vena Cava -> Vein -> Capillary CO2