RESPIRATION DURING EXERCISEFunction of the Lung

Structure of the Respiratory SystemMechanics of BreathingPulmonary VentilationPulmonary Volumes and CapacitiesDiffusion of GasesBlood Flow to the LungVentilation – Perfusion Relationships

Respiration

The integrated system of organs involved in the intake and exchange of oxygen and carbon dioxide between the body and the environment and including the nasal passages, larynx, trachea, bronchial tubes, and lungs.

Pulmonary Respiration – During inspiration, the lungs and alveoli

expand and fill up with oxygen. Since the concentration of oxygen is higher in the alveoli, oxygen diffuses out into the capillaries. Conversely, the carbon-dioxide concentration is higher in the capillaries than in the alveoli and it diffuses into the alveoli. The carbon-dioxide exits the body through expiration. (Includes transport of gases by blood and exchange of gases by tissue)Cellular Respiration –

IS THE OXYGEN UTILIZATION AND PRODUCTION OF CARBON DIOXIDE BY THE TISSUE.

FUNCTION OF THE LUNGThe primary purpose of the respiratory system is to provide a means of gas exchange between the external environment and the body. That is, the respiratory system provides the individual with means of replacing O2 and CO2 from the blood. The exchange of O2 and CO2 between the lung and blood occurs as result of ventilation and diffusion.

Ventilation – mechanical process of moving air into and out of the lungsDiffusion – the random movement of molecules from an area of high concentration to an area of lower concentration.

Diffusion in the respiratory system occurs rapidly because there is a large surface area within the lungs and a very short diffusion distance between blood and gas in the lungs.

Normal Lung Function – When the O2 and CO2 tension in the blood leaving the lungs is almost in complete equilibrium with the O2 and CO2 tension found within the lungs.

STRUCTURE OF THE RESPIRATORY SYSTEMThe human respiratory system consists of a group of passages that filter air and transport it into the lungs where gas exchange occurs within microscopic air sacs called alveoli.

Organs –Nose and nasal cavities –Pharynx and larynx –Trachea and bronchial tree –Lungs

Alveoli - Site of gas exchange –Diaphragm –Major muscle of inspiration

– Lungs are enclosed by membranes called pleura –Visceral pleura = On outer surface of

lung –Parietal pleura =Lines the thoracic wall

–Intrapleural space =intrapleural pressure is lower than atmospheric

=Prevents collapse of alveoli

The Major Components of the Respiratory System( figure 10.1)

The Anatomical Position of the Lungs(figure 10.2)

*Note that both right and left lungs are enclosed by a set of membranes called PLEURA.

– Lungs are enclosed by membranes called pleura –Visceral pleura -On outer surface of lung –Parietal pleura Lines the thoracic wall

–Intrapleural space Intrapleural pressure is lower than atmospheric –Prevents collapse of alve

Pleura – The visceral pleura adheres to the outer surface of the lung, whereas the parietal pleura lines the thoracic walls and the diaphragm.

The Air Passages of the respiratory system are divided into two functional zones:

CONDUCTING ZONEConducts air to respiratory zone •Humidifies, warms, and filters air •Components:

–Trachea –Bronchial tree –Bronchioles

RESPIRATORY ZONEExchange of gases between air and blood •Components:

–Respiratory bronchioles –Alveolar sacs - Surfactant prevents alveolar collapse

MECAHNICS OF BREATHINGAs previously mentioned, movement of air from the environment to the lungs is called pulmonary ventilation and occurs via a process known as bulk flow.

Mechanics of BreathingBulk Flow – refers to the movement of molecules along a passageway due to a pressure difference between the two ends of the passageway.

Thus, inspiration occurs due to the pressure in the lungs (intrapulmonary) being reproduced below atmospheric pressure.Conversely, expiration occurs when the pressure within the lungs exceeds atmospheric pressure.

RESPIRATIONWhen breathing in, the muscles of the diaphragm contract. This pulls the diaphragm downwards, which increases the volume in the thorax. As the same time the external intercostal muscles contract. This pulls the rib cage upwards and outwards. Together, these movements increase the volume of the thorax. As the volume of the thorax increases, the pressure inside it falls below atmospheric pressure. Extra space has been made and something must come into fill it up. Air therefore rushes in along the trachea and bronchi to the lungs.

EXPIRATION

When breathing out the muscles of the diaphragm relax. The diaphragm springs back up into its diamond shape because it is made of elastic tissue. This decreases the volume of the thorax. The external inter costal muscles also relax. The rib cage drops down again into its normal position. This also decreases the volume of the thorax. As the volume of the thorax decreases, the pressure inside it increases. Air is squeezed out through the trachea into the nose and mouth, and on out of the body.

AIRWAY RESISTANCE Is the opposition to flow caused by the forces of friction. It is defined as the ratio of driving pressure to the rate of air flow.

Airflow depends on: –Pressure difference between two ends of airway –Resistance of airways

•Airway resistance depends on diameter –Chronic obstructive lung disease –Asthma and exercise-induced asthma

Pulmonary VentilationPulmonary ventilation refers to the

amount of gas moved into and out of the lungs. The amount of gas moved per minute is the product of tidal volume times breathing frequency.

• The amount of air moved in or out of the lungs per minute (V)

–Tidal volume (VT) • Amount of air moved per breath

–Breathing frequency (f) • Number of breaths per minute • V = VT x f

Alveolar ventilation (VA) Volume of air that reaches the respiratory zone

Dead-space ventilation (VD) Volume of air remaining in

conducting airways V = VA + VD

PULMONARY VOLUMES AND CAPACITIESVital capacity (VC)

–Maximum amount of gas that can be expired after a maximum inspiration

Residual volume (RV)–Volume of gas remaining in lungs after

maximum expiration Total lung capacity (TLC)

–Amount of gas in the lungs after a maximum inspiration.

Diffusion of Gas Partial Pressure of Gases

•Dalton’s law –The total pressure of a gas mixture is equal to the sum of the pressure that each gas would exert independently

•Calculation of partial pressure Fick’s law of diffusion

–The rate of gas transfer (V gas) is proportional to the tissue area, the diffusion coefficient of the gas, and the difference in the partial pressure of the gas on the two sides of the tissue, and inversely proportional to the thickness. V gas = A T x D x (P1 – P2)

gas = rate of diffusion A = tissue area T = tissue thickness D = diffusion coefficient of gas P1 – P2 = difference in partial pressure

Gas moves across the blood-gas interface in the lung due to simple diffusion.

The rate of diffusion is described by Fick’s law, which states: the volume of gas that moves across a tissue is proportional to the area for diffusion and the difference in partial pressure across the membrane, and is inversely proportional to membrane thickness.

BLOOD FLOW TO THE LUNGBlood Flow to the LungPulmonary circuit

–Same rate of flow as systemic circuit –Lower pressure

During exercise, more blood flow to apex

When standing, most of the blood flow is to the base of the lung

–Due to gravitational force

VENTILATION – PERFUSION RELATIONSHIPVentilation/perfusion ratio (V/Q) –Indicates matching of blood flow to

ventilation –Ideal: ~1.0

•Apex of lung –Underperfused (ratio <1.0)

•Base of lung –Overperfused (ratio >1.0)

•During exercise –Light exercise improves V/Q ratio –Heavy exercise results in V/Q

inequality

Efficient gas exchange between the blood and the lung requires proper matching of blood flow to ventilation (called ventilation-perfusion relationships).

The ideal ratio of ventilation to perfusion is 1.0 or slightly greater, since this ratio implies a perfect matching on blood flow to ventilation.