THE RESPIRATORY SYSTEMMODULE 14

FUNCTIONS OF THE RESPIRATORY SYSTEM

1. Olfaction

2. Voice

3. Ventilation

4. Respiration

ANATOMY OF THE RESPIRATORY SYSTEM

• Includes the nasal cavity, the paranasal sinuses, the pharynx, the larynx, the trachea, the bronchi, and the lungs.

• The respiratory system is divided into two parts:

Upper respiratory tract- The part of the respiratory system containing the nasal cavity, paranasal sinuses, and pharynx.

Lower respiratory tract- The part of the respiratory system containing the larynx, trachea, bronchi, and lungs.

PARANASAL SINUSES

• The paranasal sinuses are air-filled extensions of the respiratory part of the nasal cavity.

• There are four paired sinuses, named according to the bone in which they are located; maxillary, frontal, sphenoid and ethmoid.

THE NASAL CAVITY

• The nasal cavity has two functions.

• First, it provides for olfaction: In order to smell something, airborne chemicals must reach the olfactory epithelium in the upper part of the nasal cavity.

• Second, it acts as an air conditioner: it changes the inhaled air in a way that makes it more favorable to the body.

• When you breathe in through the nasal cavity, the air is warmed by the blood in the vessels, moistened by the mucus, and cleansed of particles because particles stick to the mucous membrane.

THE PHARYNX

• When air passes through your nasal cavity, it enters your pharynx.

• The pharynx is divided into three parts.

• The superior part of the pharynx is called the nasopharynx. • It ends at the uvula, a small process that hangs off of the soft

palate.

• The uvula aids the soft palate in closing off the nasal cavity during glutition.

• The openings for the two eustachian (auditory) tubes are found in the nasopharynx.

THE PHARYNX

• Inferior to the nasopharynx is the oropharynx.

• It extends from the uvula to the epiglottis.

• Both food and air pass through the oropharynx.

• Two pairs of tonsils are located in this region.

•Posterior to the larynx is the laryngopharynx.

• When the epiglottis is open, air travels through the laryngopharynx to the larynx.

• When the epiglottis is closed, food passes from the laryngopharynx into the esophagus.

THE PHARYNX

THE LARYNX

• When air moves through the larynx, it produces the voicefunction of the respiratory system.

• The larynx, also called the voice box, contains the vocal cords.

• The vocal cords give you the ability to make intricate sounds so that you can speak or sing.

THE TRACHEA

• Once air travels through the larynx, it enters the trachea, which is also called the windpipe.

• It consists of about 20 pieces of cartilage that are shaped like the letter C.

• Dense regular connective tissue and smooth muscle hold these pieces of cartilage together.

• The trachea splits into two bronchi, which each carry air to and from a lung.

Ventilation- The process of getting air into the lungs and back out.

RESPIRATION

• The alveoli are involved with another vital function of the respiratory system: respiration.

• This process involves three specific steps:

1. External respiration- The process of oxygen (O2) and carbon dioxide (CO2) exchange between the alveoliand the blood.• The O2 diffuses into the blood, and from there it can be

sent to the cells.• The CO2 is released from the blood into the alveoli by

diffusion and is exhaled back into the atmosphere.

RESPIRATION

2. Gas transport in the blood• Oxygenated blood leaves the lungs and goes to the heart and then

to the body tissues, where it can supply the cells with O2.

• At the same time, blood picks up CO2 from the cells. The CO2 is then transported back to the lungs so it can be eliminated from the body.

3. Internal respiration- The process of O2 and CO2 exchange between the cells and the blood.• Internal respiration occurs everywhere in the body and doesn’t

directly involve respiratory structures.

• External respiration happens in the lungs, and internal respiration happens in the body.

VOCAL CORDS

• There are two types of vocal cords in the larynx: true vocal cords (also called vocal folds) and false vocal cords (also called vestibular folds).

• Both are mucosa-covered ligaments and are found in the upper portion of the larynx.

• The false vocal cords are superior to (above) the true vocal cords.

• Both help close the larynx during deglutition. The true vocal cords form a tight seal across the airway each time you swallow.

• The true vocal cords actually produce sound.

THE LARYNX

VOICE

• Volume: you control the volume of your voice by controlling how forcefully air passes through the larynx. The more air you use, the louder your voice is.

• Pitch: you vary the pitch of your voice by varying the thickness and tension of your vocal cords. The thinner the vocal cords and the higher the tension, the higher the pitch.

• Resonance: There are air chambers in the body (the chest cavity, the pharynx, and the paranasal sinuses) and air vibrates within those chambers. The larger the cavities, the more the resonance.

• Articulation: The ability to make the intricate sounds of speech. You use your tongue, lips, pharynx, larynx, palate and teeth.

THE MUSCLES OF VENTILATION

• The muscles of ventilation are divided into three groups:

1. Muscles of principal inspiration:• The diaphragm• External intercostals

2. Muscles of forced inspiration:• Sternocleidomastoid• Scalene• Pectoralis minor

3. Muscles of forced expiration• Abdominal• Internal intercostals

BOYLE’S LAW

• Boyle’s law states that at constant temperatures, the pressure of a gas increases with decreasing volume and decreases with increasing volume.

• When your thoracic cavity gets smaller, there is less volume available to the air inside your lungs. This increases air pressure in the lungs.

• The pressure inside the lungs is now higher than the pressure outside the lungs (atmospheric pressure), so air will flow out of the lungs.

• When the thoracic cavity gets larger, the volume increases, which decreases the pressure in the lungs below atmospheric pressure. Air will now rush into the lungs.

FACTORS THAT AID VENTILATION

•Although the actions of muscles are the driving force behind inspiration and expiration, there are other factors that aid in these processes:

• Two processes aid in expiration:1. Elastic fibers2. Surface tension of alveolar fluid

• Two processes aid in inspiration:1. Negative pressure within the pleural cavity2. Surfactant

LUNG ELASTICITY

• There are elastic fibers in the lungs.

• The lungs are a bit like balloons. Their elastic nature allows them to stretch.

• When nothing is forcing them to stretch, they will recoil back to a smaller size.

• The elasticity of the lungs aids in expiration.

EMPHYSEMA

• Emphysema is a common lung disease that can be caused by smoking or being exposed to excess air pollution.

• In this disease, the walls of the tiny alveoli degenerate, and many tiny alveoli join together to make one large alveolus.

• This decreases the surface area of the lungs, causing less oxygen to be exchanged with the blood.

• As the walls of the alveoli degenerate, the elastic tissue degenerates and is replaced with scar tissue, causing the lungs to lose their elasticity.

• People with emphysema have no trouble inhaling, but have trouble exhaling.

ALVEOLAR FLUID

• The wall of an alveolus is lined with simple squamous epithelium which is moistened with alveolar fluid that covers the entire inner surface of the alveolus.

• The principal component is water, which is strongly attracted to other water molecules. This cohesion creates surface tension.

• When an alveolus inflates with air, the watery alveolar fluid has to “stretch out” to cover the increasing surface area.

• The alveolar fluid aids in expiration because the surface tension of the water molecules pull to get the alveolus closed.

THE PLEURAL CAVITY

• The pleural cavities around each lung have no air in them, only pleural fluid.

• The pleural cavities are under negative pressure, creating a vacuum seal.

• Since the pleural cavity is at a pressure lower than atmospheric pressure, it puts suction on the lung, holding it open. This helps inspiration.

• If the vacuum seal of the pleural cavity is lost, air will rush into the pleural cavity and the lung will collapse. This is called a pneumothorax.

SURFACTANT

• A molecule secreted by specialized cells in the lungs to reduce the surface tension of the alveolar fluid to allow for proper breathing.

• Surfactant is a detergent made of molecules with a hydrophilic (water-soluble) end and a hydrophobic (oil-soluble) end. It reduces cohesion of water molecules.

• As a result, the alveoli are far easier to inflate than they would otherwise be, therefore surfactant in the alveolar fluid aids inspiration.

• Infant respiratory distress syndrome was a common problem in premature babies, which were unable to make surfactant and therefore had a difficult time inhaling.

COMPLIANCE

• A newborn’s lungs are hardest to fill on their first breath. That’s because compliance of the lungs is low.

Compliance- The ease with which the lungs inflate.

• Each subsequent breath increases the lung’s compliance so that within two hours after birth, the baby’s lungs have about the same compliance as an adult’s lungs.

AIRWAY RESISTANCE

• When air travels through a tube, the walls of the tube resist the flow. That’s called airway resistance.

• The lower the airway resistance, the easier it is to get air into and out of the lungs.

• Most of the airway resistance occurs in the bronchioles, which are about one millimeter wide or less.

• Asthma is a disease that increases airway resistance by resulting in a narrowing of the bronchi and especially the bronchioles. It can be treated with bronchial dilators.

EXTERNAL RESPIRATION

• External respiration refers to the diffusion of oxygen from the alveoli into the blood and the diffusion of carbon dioxide from the blood into the alveoli.

• Your blood is virtually 100% oxygenated when it leaves the lungs, regardless of whether you are in good physical shape or poor physical shape.

• As long as you have no serious abnormalities, the oxygen level of your blood is virtually independent of your physical condition.

• There are six reasons for this fact and they all center around the process of external respiration.

EXTERNAL RESPIRATION

ANATOMICAL FEATURES THAT MAKE EXTERNAL RESPIRATION EFFICIENT

1. The respiratory membrane is very thin.• Molecules will diffuse across a thin membrane more easily than a

thick membrane.

2. The surface area of the alveoli is large.• The larger the surface area, the more gas exchange.

3. The capillaries of the lung are narrow.• Oxygen molecules immediately find red blood cells because they

flow single file.

4. Red blood cells are biconcave discs.• This increases the surface area of the cell, making oxygen

absorption more efficient.

PHYSIOLOGICAL FEATURES THAT MAKE EXTERNAL RESPIRATION EFFICIENT

1. Controlled relationship between ventilation and capillary blood flow in the lungs.• If your heart starts beating faster, reflexes coordinated in

the medulla oblongata cause you to start breathing faster.• If this relationship is interrupted, the consequences can

be deadly:• Aspiration

• Pneumonia

• Pulmonary embolism

2. The functional residual capacity of the lungs.

LUNG CAPACITIES AND VOLUMES

• Tidal volume- The volume of air inspired or expired during normal, quiet breathing (about half a liter).

• Functional residual capacity- The volume of air left in the lungs after a normal expiration (about 2 liters).• Even after you have exhaled, there is still enough functional

residual air in the alveoli to transfer plenty of oxygen to the blood.

• This ensures that all of the RBCs become fully oxygenated.

• Total lung capacity- The maximum volume of air contained in the lungs after a forceful inspiration (about 5 to 6 liters).

• Residual volume- The volume of air left in the lungs after a forceful expiration (about one liter).

~ 1 L

~ 2 L

~ 0.5 L ~ 5-6 L

GAS EXCHANGE DURING EXTERNAL AND INTERNAL RESPIRATION

• When it comes to gases, we use the term partial pressure instead of concentration.

• Dalton’s law states that the pressure exerted by a mixture of gases is equal to the sum of the partial pressure of each gas in the mixture.

• Substances diffuse from areas of high concentration to areas of low concentration.

• Therefore, oxygen enters the blood at the alveoli and exits at the tissues while carbon dioxide enters the blood at the tissues and exits at the alveoli.

In Air

P02 = 152 mmHgPCO2 = 0.3 mmHg

RESPIRATORY CONTROL

• Even though your diaphragm and the other muscles of ventilation are skeletal muscles, they are controlled automatically.

• You also have some conscious control over breathing, otherwise you couldn’t speak or hold your breath.

• Control of ventilation/respiration takes place mainly in the medullary respiratory center of the medulla oblongata.

• In addition, the Hering-Breuer reflex prevents you from inhaling too deeply and damaging your lungs. Receptors in the bronchioles send inhibitory signals to the medulla oblongata, stopping inspiration.

CHEMICAL CONTROL OF VENTILATION

• In addition to the respiratory control centers in the brain, the body has a chemical control system to regulate the depth and rate at which you breathe.

• Carbon dioxide levels, via their effect on pH, are the major controllers of ventilation.

• The more CO2 in the blood plasma, the LOWER the pH of the blood.

• If the pH is too low, the body increases the rate and depth of ventilation to remove CO2.

CELLULAR RESPIRATION

• The point of respiration is to provide oxygen to the tissues and to carry away carbon dioxide.

• Why do tissues need oxygen and why do they make carbon dioxide?

• Cells burn food for energy in a process called cellular respiration.

• The most efficient way for cells to produce energy is through aerobic respiration, which involves converting glucose into carbon dioxide and water.

• This process requires oxygen, which is why it is called aerobic respiration.

AEROBIC RESPIRATION

• The overall chemical reaction for aerobic respiration is as follows: