the ventilatory system - updated 2016

IBSports, exercise and health science

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2.1.1 List the principal structures of the ventilatory system

Topic 2Exercise Physiology

The principle structures of the respiratory system are: Nose/Mouth Pharynx Larynx: voice box Trachea Bronchi Bronchioles Lungs Alveoli

1. Structure & function of the ventilatory system

2. Structure & function of the cardiovascular system


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http://www.umm.edu/respiratory/images/respiratory_anatomy.jpg


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Smooth muscle tissue is found on the walls of some of our internal hollow organs It produces smooth, rhythmical actions. We can not consciously control the action of smooth muscle. It is subsequently termed involuntary.

e.g. movement of blood and air in the lungsDET PDHPE Distance Education Programme




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The trachea is a thin walled tube about the diameter of an average garden hose. It is composed of very thin, tough connective tissue and is strengthened at intervals by incomplete rings of cartilage.

The trachea muscle runs down the posterior wall of the trachea. This is an example of smooth muscle.Solomon & Davis




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2.1.2 Outline the functions of the conducting airways


The nostrils are fringed with coarse hair, which strains large particles out of the airstream and may also serve to protect the nasal cavity from invasion by insects. The interior of the nasal cavity contains projections of considerable surface area. These projections, nasal conchae, make the airstream turbulent and subsequently warm and hydrate it. Thanks to the structure of the nose, air entering the trachea is virtually 100% humidified.

Solomon & Davis




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www.nlm.nih.gov



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Air passes through the 3 portions of the pharynx, which provides a low resistance path for airflow, to the trachea via the larynx. In addition to it’s function as the voice box the larynx protects the trachea from invasion by foods and fluids. The cartilaginous trachea, branches into the two main bronchi.

The lining of the tracheobronchial system is designed to protect the lungs from dehydration and invasion by foreign particles, including micro-organisms.Solomon & Davis




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The lungs themselves develop at the end of the bronchi. They are elastic spongy organs.

Gas exchange is carried out by a complex of structures at the end of each terminal bronchioles.

They are simple thin walled structures which also have numerous thin-walled outpocketings called alveoli, which are specialised for the function of gaseous exchange.

Solomon & Davis1. Structure & function of the ventilatory system



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2.1.3 Define respiratory termsTopic 2Exercise Physiology

Pulmonary ventilation: is commonly referred to as breathing. It is the process of air flowing into the lungs during inspiration (inhalation) and out of the lungs during expiration (exhalation). Air flows because of pressure differences between the atmosphere and gases inside the lungs.

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Air, like other gases, flows from a region with higher pressure to a region with lower pressure. Muscular breathing movements and recoil of elastic tissues create the changes in pressure that result in ventilation. Pulmonary ventilation involves three different pressures:

• Atmospheric pressure • Intraalveolar (intrapulmonary) pressure • Intrapleural pressure

Atmospheric pressure is the pressure of the air outside the body. Intraalveolar pressure is the pressure inside the alveoli of the lungs. Intrapleural pressure is the pressure within the pleural cavity. These three pressures are responsible for pulmonary ventilation.

http://training.seer.cancer.gov/module_anatomy/unit9_2_resp_vent_mechanics.html1. Structure & function of the ventilatory system



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It is important to understand the various volumes and capacities of the lungs in order to appreciate the effects of exercise on the respiratory system.

Total lung capacity can be calculated by adding vital capacity to residual volume of the lungs. During normal, quiet respiration, about 500mL of air is inspired. The same amount of air

moves out with expiration. This volume of air is called the tidal volume. When we forcibly take a deep breath, we can take in up to 3100mL above the tidal volume.

This additional air is the inspiratory reserve volume. Browne et. al 2001




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We can also forcibly exhale. This is termed the expiratory reserve volume.

Even after the expiratory reserve volume is expelled, some air is still trapped in the lungs because of pressure. This is called the residual volume.

Browne et al 2001

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2.1.4 Explain the mechanics of ventilation in the human lungs


To understand how a person breathes, you need to know that a substance called pleural fluid lies between the lungs and the chest wall.

Have you ever put two pieces of wet glass together (e.g. microscope slides) and found that you could not easily pull them apart. This phenomenon results from a combination of forces – surface tension, molecular cohesion and atmospheric pressure.

Solomon & Davis




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Think of the walls of the chest and the lungs as the two wet slides and the pleural fluid as the film of water. When the chest expands during breathing, the film of pleural fluid causes the membranous walls of the lungs to be pulled outward along with the chest walls. This means the space within the lungs increases. The air molecules in the lungs now move momentarily farther apart, so that the pressure in of the air in the lungs falls below the pressure of the atmosphere outside the body.

Consequently, air from outside rushes down the trachea and into the lungs until the two pressures are equal again. This is the process of inspiration.

Solomon & Davis




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Observation of the skeleton reveals that each rib pivots about a vertebral joint. If it is lifted upward it also swings outward, with the thoracic cavity being enlarged anteriorly and superiorly. This is the task in quiet breathing of the external intercostal muscles.

At the same time the ribs are lifted, the diaphragm (the muscular floor of the thoracic cavity) contracts downward enlarging the thoracic cavity inferiorly. This process enlarges the cavity twofold.

Solomon & Davis




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Expiration is almost entirely a passive process that depends on the elasticity of the lungs and chest structures, as well as fluid film surface tensions within the lungs. When inspiratory muscles are relaxed, air simply leaves the lung, much as it would leave an untied balloon.

Solomon & Davis




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This above description is for quiet breathing. When one speaks or runs, the abdominal muscles press upon the abdominal contents, squeezing them upwards against the diaphragm. The internal intercostal muscles oppose the external intercostals and pull the ribcage downward, helping to decrease the thoracic cavity volume and forcibly empty the lungs. The diaphragm may also function in forcible expiration.

In laboured inspiration (e.g. accompanying exercise) many of the muscles of the upper trunk are also recruited. They are only indirectly attached to the ribs and are inefficient as respiratory muscles. E.g. Pectoralis major and minor, Trapezius, Rhomboideus.

Solomon & Davis




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http://www.lib.mcg.edu/edu/eshuphysio/program/section4/4ch1/4ch1img/page17.jpg




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2.1.5 Describe the significance of carbon dioxide in the control of pulmonary ventilation


The entire respiratory system would be useless unless the alveolar air were regularly changed. Since humans do not possess a one-way system for air circulation through the lungs, inhaled an exhaled air must be mixed to some degree. This does not normally produce any difficulty, since the respiratory system possesses a two to threefold margin of safety and is ordinarily far more effective than it needs to be in regard to oxygen absorption.

Solomon & Davis




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This is less true, however for carbon dioxide removal, which is an equally important task of the respiratory system. Fortunately, carbon dioxide diffuses through the alveolar walls far more readily than oxygen, but dissolved carbonic acid does not readily breakdown to form carbon dioxide. Were it not for the enzyme carbonic anhydrase, which speeds the dissociation of carbonic acid as well as it’s formation, the elimination of this gas would be hopelessly inadequate.

As it is, carbon dioxide excretion is far more easily hindered than is oxygen absorption. Thus breathing is governed not by oxygen, but the carbon dioxide content of the blood.

Solomon & Davis




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Whilst respiration appears at first a voluntary activity, if that were true it would not continue when were asleep or inattentive. It is subject to great conscious influence, but despite the fact it is carried out by such voluntary muscles as the intercostals and the diaphragm, breathing is basically an automatic and involuntary activity.

Solomon & Davis




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Exercise physiology

2.1.6 Outline the role of hemoglobin in oxygen transportation




http://www.nlm.nih.gov/medlineplus/ency/images/ency/fullsize/19510.jpg


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2.1.6 Outline the role of hemoglobin in oxygen transportation


Hemoglobin is the iron containing oxygen transport protein in the red blood cells. It transports oxygen from the lungs to the rest of the body, such as the muscles, where it releases it’s load of oxygen.The name hemoglobin is the concatenation of heme and globin, reflecting the fact that each subunit of hemoglobin is a globular protein with an embedded heme (or haem) group; each heme group contains an iron atom, and this is responsible for the binding of oxygen. In humans, each heme group is able to bind one oxygen molecule with one hemoglobin molecule can therefore bind four oxygen molecules.

http://en.wikipedia.org/wiki/Hemoglobin




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2.1.7 Explain the process of gaseous exchange at the alveoli


Gas exchanges between the air in the alveoli and the blood capillaries occur across the respiratory membrane in a process known as pulmonary diffusion. The most critical factor for gas exchange

between alveoli and the blood is the pressure gradient between the gases in the two areas.

According to Dalton’s law of partial pressures, the pressure of a mixture of gases equals the sum of the individual pressures (partial pressures) of each gas in the mixture.

Browne et.al




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If we take a normal breath of air, which contains nitrogen, oxygen and carbon dioxide, the total pressure of the air is equal to the sum of the partial pressures of the individual gases in the blood and the alveoli create a pressure gradient, so one into the other (from high partial pressure to low partial pressure)

The partial pressure of oxygen arriving at the alveoli is high, and the partial pressure of it in the capillaries is low. Therefore oxygen diffuses from the alveoli into the blood. The opposite is true for carbon dioxide.

Browne et.al




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Exercise physiology





Be prepared for discussions

• Affect of exercise on hemoglobin at altitude

• What are some of the effects/results of breathing air at altitude? Below sea level?

• What is the theory behind hyperventilation for improved breath holding ability?