Learning Objectives

• Identify the structures and functions of the respiratory system
• Know a few conditions/diseases of the respiratory system
• Know how the respiratory system develops

Introduction

The respiratory system provides the means for gas exchange required in living cells. Examples: Carbon Dioxide and Oxygen. When you inhale you are bringing oxygen to the lungs. When you exhale you are getting rid of carbon dioxide. When you hold your breath, does your body start saying breath I need oxygen or does it say help the carbon dioxide levels that are out of whack? If you said carbon dioxide levels you are correct. Let's take a look now at what the respiratory system consists:

There are 2 tracts of the respiratory system:

• Upper respiratory system
• Lower respiratory system

It also can be divided into a conducting portion and respiratory function.

• Conducting portion
  • Nose, Nasal cavity, pharynx, larynx, trachea and the smaller progressively airways (primary bronchi to terminal bronchioles)
  
  
• Respiratory portion is composed of small airways called respiratory branchioles, alveolar ducts and alveoli (air sacs)

RESPIRATORY SYSTEM FUNCTIONS
-Pulmonary Ventilation
Inhalation: bringing gas into the lungs
Exhalation: letting gas flow out of the lungs
- Gas exchange
Oxygen is drawn in by inhalation and is transported to the body cells from the lungs by blood circulation. The body uses the oxygen to generate carbon dioxide as a waste product which is then transported to the lungs and is then exhaled.
- Gas Conditioning:
Gases entering the body are "modified" before reaching the gas exchange surfaces. These gases are warmed to body temperature, filtered of any harmful particles and humidified by contact of the respiratory epithelium and the sticky mucus covering in the winding pathways in the nasal cavity and the paranasal sinuses.
- Sound Production:
Air is moved through the larynx to produce sound.
- Olfaction:
During inhalation through the nasal cavity, receptors called olfactory epithelium cover the superior region of the nasal cavity giving you a sense of smell.
- Defense:
The entrance of the respiratory system is lined with coarse hairs to protect large particles, microorganisms and insects from entering our lungs. Also goblet cells are worked into the hairs of the upper respiratory system to fight off harmful bacteria. In addition to these defenses our lungs contain mucus which is used to keep our epithelium from drying out and to create a lining which will secrete lysozymes to fight off bacteria in our respiratory system.


UPPER RESPIRATORY TRACT
- Consist of the nose, nasal cavity, paranasal sinuses, and the pharynx (throat)
- The Nose:
this is the main conducting airway which is supported with many bones and cartilage.
- The Nasal Cavity:
contains "internal nares" which connect the nasal cavity to the paranasal sinus. This cavity is lined with pseudostratified ciliated columnar epithelium and coarse hairs near the vestibule (cavity near the nostrils) called vibrissae which protect the lungs from large particles and bacteria as mentioned before. The superior, middle and inferior nasal conchae subdivide the nasal cavity into three separate air pathways called the nasal meatus which is responsible for the main functions of gas conditioning.
- The Paranasal Sinuses:
the paranasal sinuses contain sinuses from all the surrounding bones and are named accordingly: the frontal, ethmoidal, sphenoidal, and maxillary sinuses. All the sinuses communicate with the nasal cavity and their functions are to cleanse air, serve as chambers for sound resonance, and lighten the weight of the skull. They are all line with the same pseudostratified ciliated columnar epithelium lining as the nasal cavity.
- The Pharynx:
commonly called the throat, it is used for inhalation/exhalation and swallowing food. Posterior to the nasal and oral cavities and extends inferior towards the lower respiratory tract. It contains skeletal muscles and flexible walls also coated with mucus for protection. It is split into three regions: the nasopharynx, oropharynx, and laryngopharynx.
-nasopharynx the most superior region of the pharynx and is directly posterior to the nasal cavity and superior to the soft palate which forms a seal from the oral cavity. Most of the time only air passes through the nasopharynx, but occasionally when the seal on the soft palate doesn't form well we get food or vomit from our nose. On the lateral walls of the nasopharynx a pair of auditory tubes connect the nasopharynx to the middle ear. This is to relieve pressure from the ear drum through the nasopharynx.
-oropharynx immediately posterior to the oral cavity. The boundaries include the soft palate inferiorly and the hyoid bone inferiorly. This area is a common respiratory and digestive pathway so in order to withstand the stress and abrasiveness of food the oropharynx is lined with a tougher epithelium called the non-keratinized stratified squamous epithelium lines. Anterior and posterior palatoglossal arches form the entrance of the oropharynx from the oral cavity supported by muscles called fauces. The defense barrier .in this area are the tonsils of the palatine and tongue.
-laryngopharynx this area is the inferior narrowed region of the pharynx. The area covered by this region is from the inferior part of the hyoid bone to the superior part of the esophagus. This region is also lined with non-keratinized stratified squamous epithelium for protection.




LOWER RESPIRATORY TRACT
This area is made up of conducting airways which include the larynx, trachea, bronchi, bronchioles, respiratory bronchioles, alveolar ducts, and the alveoli.
- Larynx:
This area is also known as the "voice box" and is a short, cylindrical airway. It's location is inferior to the laryngopharynx, anterior to the esophagus, and superior to the trachea. The Larynx is lined with two types of epithelium, on the superior aspect it is lined with NKSSE and on the inferior aspect it is line with PCCE. The function of the larynx is to prevent swallowed material from entering the LRT and also produce sound. Since the larynx has such an important job of keeping out unwanted material of the LRT it is equipped with 9 different cartilage which are attached by ligaments and muscles. The largest cartilage is the thyroid cartilage which forms only the lateral and anterior walls of the larynx. Dense connective tissue called thyroid membrane attaches the superior border of the thyroid cartilage to the hyoid bone. The v-shaped anterior projection of thyroid cartilage, which is known as the "Adam's Apple" in males, is called the laryngeal prominence.
The ring shaped cartilage that forms the inferior base of the larynx and connects to the trachea is called the cricoid cartilage. Composed of hyline cartilage it has a narrow anterior connection but a wide posterior connection to support the the posterior larynx. Dense connective tissue that connect attach the cricoid cartilage to the inferior edge of the thyroid cartilage is called the cricothyroid ligament.
The Epiglottis is a spoon, leaf-shaped flap of elastic cartilage that is used as a cover for the larynx opening to prevent unwanted material from entering, it then returns to it's elevated position. From it's attachment on the thyroid cartilage the epiglottis projects superiorly into the pharynx.
The rest of the cartilage are three sets of paired cartilage. The first one is the paired arytenoid cartilages which are a pyramidal shape and are located on the superoposterior border of the cricoid cartilage. The second pair is the paired corniculate cartilage which is located on the superior surface of the arytenoid cartilage. The third pair is the paired cuneiform cartilage which is attached to connective tissue called aryepiglottic fold which extend to the lateral sides of the arytenoid cartilage and the epiglottis. It's job is to support some of the laryngeal soft tissue.


The larynx is not only responsible for support to keep unwanted materials out. It is also responsible for sound production. Two pairs of ligaments are responsible for sound production. The inferior pair of ligaments is called the vocal ligaments. They are covered with a mucous membrane. Together with the mucosa and the ligaments form the vocal folds, also know as the "true vocal cords". The superior pair of ligaments are called the vestibular ligaments. They too are covered with mucous membrane. With the ligaments and mucosa together they are called the vestibular folds or "false vocal cords". These cords attach to the corniculate cartilage and serves mainly as protection to the "true vocal cords". When the intrinsic muscles of the larynx force the arytenoid cartilage to pivot the vocal cords open. The opening between the vocal cords is called the rima glottidis. When air is forced through the glottis the fold begin to vibrate producing sound. By manipulating the length, tension, and position of the vocal folds you can determine the quality of the sound. Some factors include: the length of the vocal folds produce a lower pitches in voice, higher tension produces higher pitch, and more force on the air passing through the folds produces a louder voice.
-Trachea:
This organ is a flexible yet rigid tubular shaft which is also known as the "windpipe". It's position is anterior to the esophagus, inferior to the larynx, and superior to the primary bronchi of the lungs. It's is about 14 cm long and 2.5 cm wide. The lateral and anterior walls are covered by about 15 to 20 tracheal cartilage, these rings offer support to insure that the trachea stays open at all times. This cartilage is attached by anular ligaments to trachealis muscle. The mucosa lining is made up of PCCE with many goblet cells for defense with mucin secreting glands called lamina propria. At the base of the trachea the organ separates into two branches called the left and right primary bronchus. It continues to separate into smaller and smaller branches until it reaches the terminal bronchioles.
-Bronchial Tree: This air conducting organ branches off of the trachea, splitting into two branches and quickly making a complex tree of narrow branches. There are four levels of bronchi: The primary, secondary, tertiary, and smaller bronchi. The primary bronchi branches from the trachea into a one left and one right branch for each lung. The secondary bronchi splits into two left branches and three right branches (one branch for each lobe). The tertiary bronchi splits into 8 to 10 in the left lobe and 10 branches in the right lobe. The smaller bronchi split into an assortment of branches that narrow out until they become as thin as 1mm or less. The primary, secondary, tertiary, and the start of the smaller branches are all covered with PCCE and supported by cartilage. When the bronchi branches start to become as small as 1 mm they become bronchioles and start to take on new characteristics. The smaller branches have a new covering called simple cuboidal epithelium instead of the PCCE covering and they are replaced with thick smooth muscle to help with airway constriction and dilation instead of cartilage. When the bronchioles branches reach their end they become terminal bronchioles.
-Respiratory Bronchioles, Alveolar Ducts, and Alveoli:
This portion of the bronchi is called the respiratory portion. The epithelium in this section is much thinner then in the conducting portion. This section is branches from the terminal bronchioles to form the respiratory bronchioles. These branches divide to form smaller respiratory bronchioles, the smallest branches become alveolar ducts which are lined with simple squamous epithelium. At the distal end of this alveolar ducts terminate into alveolar sacs that are dilated. Along the previous branches (respiratory bronchioles and alveolar ducts) are out pocket sacs called alveoli (different from alveolar sacs). The thin wall covered with these alveolus sacs used to promote diffusion of gases between alveolus and blood in the pulmonary capillaries. There are about 300 to 400 million alveoli in the lungs. There are two types of cells in the alveolar walls. The first being alveolar type I cells (aka squamous alveolar cells) which promote rapid gas diffusion across the alveolar wall and are the more prominent cell. The second type of cell is the alveolar type II cell (aka septal cells), which secretes pulmonary surfactant which reduces the tension on the wall to prevent collapsing of the alveoli.


The lungs are lined with a serous membrane called pleura which is comprised primarily of melsothelium. The lung itself is covered by the visceral pleura while the internal thoracic walls, the mediastinum, and the superior portion of the esophagus is lined with parietal pleura. The pleural cavity -the space between the parietal and visceral pleura - is filled with a serous fluid to help lubricate and reduce friction as the lungs expand and contract.
The rounded area of the lung thatcontactsthe thoracic wall is called the costal surface (named because the the ribs are also called costals). The left lung contains an indentation on the medial side called the cardiac impression. This impression accommodates the location of the heart. The anterior portion of the cardiac impression is called the cardiac notch. Since each lung has more then one lobe it is divided by fissures. The right lung has three lobes: superior, middle and inferior lobes (also called upper, middle and lower in some cases). The lobes are separated by the horizontal fissure (separating the superior and middle lobes) and the oblique fissure (separating the middle and inferior lobes). The left lung has only two lobes: the superior and inferior lobes (or again, upper and lower) which are separated by an oblique fissure.
The left and right lung each have their own bronchopulmonary segments which is supplied by its own tertiary bronchus and branches of pulmonary arteries and veins. These bronchopulmonary segments are used to supply blood to the lungs. The nice thing about each lung having its own bronchopulmonary segment is that if one lung is diseased the affected lung can be taken out while the other functions perfectly.
-Blood Supply to and from the Lungs
Both pulmonary and systemic circulation supply the lungs with blood. Pulmonary circulation conducts blood to and from gas exchange surfaces by getting rid of CO2 and replenishing the blood with fresh O2. What happens is the blood comes from the right ventrical through the pulmonary trunk to the pulmonary arteries then head to the lung where it branches to pulmonary capillaries and gets rid of the CO2 and picks up the fresh O2 before heading back to the left atrium. In systemic circulation the tiny bronchial arteries and veins in the lung exchange directly with air inhaled and either drain back to the bodies veins or the arteries give oxygen to the bronchial tree.
Thoracic Wall Changes During Respiration and the Muscles Involved
For inspiration you use a few muscles: the scalenes which increase the thoracic cavity by elevating the first and second ribs during forced inhalation. The external intercostal muscles which connect between the superior rib inferomedially to the adjecent inferior rib making the ribs elevate upon contraction of this muscle. For experation there are different muscles involved: the internal intercostal muscles which lie deep to the external intercostal muscles and upon contraction forces the lungs to expire waste material out of the lungs. The transverse thoracis extends from the inner surface of the thoracic cage to ribs 2 to 6 helping depress them. Some assisting muscle include the serratus posterior superior which elevate ribs 2 to 5 for inspiration and also the serratus posterior inferior which depress ribs 8 to 12 for experation.

• If multiple adjacent ribs are broken in multiple places, resulting in a segment that is separate from the rest of the rib cage,part of the chest wall moves independently in a condition known as flail chest, or paradoxical motion, as seen in this video and drawing.A segment of the chest wall that is flail is unable to contribute to lung expansion. Because of the decreased ventilation, and because the underlying lung will have contusions, this can be a life-threatening condition.

-NERVES WITHIN THE RESPIRATORY SYSTEM
With the respiratory system there are two types of nerve innervations going on. In the first one, sympathetic innervation the sympathetic nerve open up and dilate the bronchioles. In the second innervation, parasympathetic nerves (CN X), the main function is to decrease the airway diameter of the bronchioles. These two nerves come together to form the pulmonary plexus which is responsible for the actions of the smooth muscles in breathing which stretch the lung. Within the brain the medulla oblongata control the depth of our breathing and contains a center for breathing known as the respiratory center. This center has two areas, the first being the dorsal respiratory group which controls the motor neurons which are responsible for inspiration. The second area is the ventral respiratory group which is the area that controls forced expiration. This area is inactive in normal breathing; it becomes active when the body needs to force out lots of air such as in exercise. Within the pons are two areas responsible for the rate of inspiration and experation. That area is the apneustic center and the pneumotaxic center. The apneustic center stimulates inspiration while th epneumotaxic center inhibits inspiration in order for the VRG to work.


THE DEVELOPING RESPIRATORY SYSTEM
The respiratory system begins to develop as early as the fourth week of pregnancy, although it is not called the respiratory system, instead it is known as the respiratory diverticulum. In the end of the forth week we see the budding of the left and right primary bronchial buds. In the fifth week of development we see the budding up secondary bronchial buds in each lung. In the sixth week of development we see the development of the tertiary brochi. In weeks 6 to16 we see the branching of bronchi into smaller bronchi and bronchioles. During weeks 16 to 28 we see the terminal ends of bronchioles branches forming. In weeks 28 to birth we see the development of primitive alveoli or terminal alveoli, also we see the covering of a mucous sac called pulmonary surfactant which keeps the alveoli cells open. After birth and continuing until we become eight years old we build more and more alveoli cells until we reach 300 to 400 million cells.

• Adult Respiratory Distress Syndrom - a type of lung failure that occurs in very ill or severely injured people. It is not a specifis disease and may be life-threatening. Tissue in the lungs swells up and fluid builds up in tiny air sacs that move oxygen into the bloodstream, which leads to low blood oxygen levels. Symptoms of ARDS may include rapid pulse, fast and labored breathing, chills, shortness of breath, fever, and headaches.
• Anaphylaxis - severe allergic reaction, which may be life-threatening. Reactions include hives, low blood pressure, facial swellind and difficulty breathing. Symptoms of anaphylaxis may be very mild or extremely severe, even resulting in death. Symtoms include lightheadedness, respiratory distress, nausea, vomiting, convulsions, and tightening of the chest.
• Aspiration Pneumonia - lung infection that results when food or liquid is accidentally inhaled. This is called aspiration. Symptoms include problems swallowing, fever, chest pain, rapid heart rate and shortness of breath. Asthma - narrowing and inflammation of the bronchial tubes. Asthma may be caused by a number of things such as exposure to allergens, certain medications, cold weather or even exercise may trigger an asthma attack. Symptoms include wheezing, difficulty breathing, chest pain and tightening of the chest.
• Bronchitis - inflammation of air passages of the lungs which makes breathing difficult and painful. The inflammation may be caused by inhalation of respiratory irritants, smoking, and bacterial infections. There are many symptoms of bronchitis which depend on the type of bronchitis the person has. The symptoms for Acute Bronchitis are sore throat, runny nose, fever, wheezing and back pain. Symptoms for Chronic Bronchitis are swelling of the feet, difficulty breating, bluish lips and skin and cough.
• Croup - infection or inflammation of voice box and windpipe. The inflammation makes tissue in the respiratory tract swell, making breathing difficult. There are many causes of croup such as measles virus, rhinovirus and influenza virus. Symptoms may include fever, hoarseness, poor appetite and loud, unusual coughing.
• Emphysema - chronic obstructive disease of lungs in which alveoli lose their elasticity and air becomes trapped. It is caused by inhaling toxins or other irritants. Symptoms of emphysema include wheezing, shortness of breath, coughing, fatigue, rapid breathing, heart failure and swelling in legs.
• Laryngitis - the mucous membrane of the larynx swells and becomes inflammed. If often leads to hoarseness and even loss of voice completely. It can be caused by upper respiratory tract infections, voice overuse, or airborne irritants. Symptoms of laryngitis may include changes in volume or pitch in voice, hoarseness and sore throat.
• Whooping Cough - bacteral infection of respiratory tract. Bacteria infects respiratory tract lining, causing inflammation and increases mucous secretion. Symptoms include sneezing, red and watery eyes, runny nose, fever, dry cough with forceful inhale (whoops).

Case Study

Normal city dwellers lung. Note black specks throughout Smokers lung with lung cancer, the cancer is the white on top; indicative of carbon deposits from pollution. of the lung which is what killed this person, the black is mostly tar deposits.





ASTHMA
This is a chronic condition where the airways experience episodes of bronchoconstriction, coughing, wheezing, SOB, and excess pulmonary mucous. This is due to a constriction of the bronchioles which can be a result of sensitivity to agents in the air such as pollen, smoke, mold, dust mites, or other particularly harmful pollutants. When the sensitive person is re-exposed to this the bronchi and bronchioles become coated with thick mucous. Eventually the airways become permanently coated with this mucosa leading to narrowing and SOB which if severe enough attacks and left untreated hospitalization or death can occur. Although environment is a strong factor in the onset of this disease there is also a genetic tie as well.
Treatments today include a "rescue inhaler" during an attack (usually with a steroid such as cortisone), or if the attack is bad enough and the inhaler doesn't work a "nebulizer" treatment can be administered which uses a liquid called Albuteral Sulfate. Although you don't have to wait for an attack to get treatment. These days you can take preventative medication to reduce your risk of asthma attacks such as a purple disk called Advair or if your asthma is triggered by pollens your can take some allergy medications such as Zyrtec or Singular.
This first video below will give you more incite to what asthma is all about while the second video will show you what an asthma related wheeze sounds like.

Respiratory Disease Lung diseases are conditions that occur within the lungs. Respiratory or lung diseases include asthma, pneumonia, tuberculosis, lung cancer, and many others. According to the American Lung Association:

• every year nearly 335,000 Americans die of lung disease.
  
  
• lung disease is the number three killer in America, responsible for one in seven deaths.
  
  
• lung disease and other breathing problems are the number one killer of babies younger than one year old.
  
  
• more than 30 million Americans are living with chronic obstructive pulmonary disease such as asthma, emphysema and chronic bronchitis.

ung disease can affect people of all ages, both genders, and all incomes, but affects a disproportionate share of minority populations -- particularly African-Americans.
Lung Diseases
This is a chest x-ray of a person with bronchial cancer. This is a front view. The lungs are the two dark areas. The heart and other structures are white areas visible in the middle of the chest. The light areas that appear as subtle branches extending from the center into the lungs are cancerous.

What Is Lung Cancer?

There are two major types of lung cancer:

• Non-small cell lung cancer - consists of 3 types:
  • Squamous cell carcinoma
  • Ademocarcinoma and
  • Large cell carcinoma
• Small cell lung cancer also called oat cell cancer. It usually spreads to different parts of the body more quickly than non-small cell and accounts for about 20% of all lung cancer

Causes Of Lung Cancer

Smoking is the number one cause of lung cancer. The more you smoke and the longer you smoke, the greater your risk. If you stop smoking however, the risk of lung cancer decreases. Year on year, abnormal cells are replaced by normal cells. After ten years, the risk drops to a level that is one-third to one-half of the risk for people who continue to smoke. There are also many more benefits.

• Quitting smoking greatly reduces the risk of developing other smoking-related diseases, such as heart disease, stroke, emphysema and chronic bronchitis.

Lung cancer normally takes many years to develop. Incidence tends to peaks between the ages of 55 and 65 years. The changes in the lung however can begin almost as soon as a person is exposed to carcinogenic chemicals. Soon after exposure begins, a few abnormal cells may appear in the lining of the bronchi (the main breathing tubes). Gradually as you continue your exposure to these substances, more abnormal cells appear. Some will become cancerous and tumour forming.



Mesothelioma Pictures & Lung Cancer Pictures

General description of an impact asbestos has on your lungs	Chart representing the corelation between the occupation and the risk of asbestosis	Diffuse malignant mesothelioma--epithelial type
Diffuse malignant mesothelioma--epithelial type	Diffuse malignant mesothelioma--sarcomatous type	Immunohistochemical results in malignant mesothelioma:
	Diffuse malignant mesothelioma--sarcomatous type

FUN FACTS ABOUT THE RESPIRATORY SYSTEM:


Why Do I Yawn?
When you are sleepy or drowsy the lungs do not take enough oxygen from the air. This causes a shortage of oxygen in our bodies. The brain senses this shortage of oxygen and sends a message that causes you to take a deep long breath---a YAWN.
Why Do I Sneeze?
Sneezing is like a cough in the upper breathing passages. It is the body's way of removing an irritant from the sensitive mucous membranes of the nose. Many things can irritate the mucous membranes. Dust, pollen, pepper or even a cold blast of air are just some of the many things that may cause you to sneeze.
What Causes Hiccups?
Hiccups are the sudden movements of the diaphragm. It is involuntary --- you have no control over hiccups, as you well know. There are many causes of hiccups. The diaphragm may get irritated, you may have eaten to fast, or maybe some substance in the blood could even have brought on the hiccups.

In the News

The Gates Foundation gets involved in anti-smoking campaigns.

Glossary

NKSSE- Non-keratinized Stratified Squamous Epithelium
PCCE- Pseudostratified Ciliated Columnar Epithelium
LRT- Lower Respiratory Tract

Connections to other body systems

Review Questions

1. Why do the bronchi not collapse during inspiration?
*a. Cartilaginous bands
b. Fibrous bands
c. Muscular bands
d. none of the above

2. Which part of the respiratory system is known as the " voice box".
*a. Larynx
b. Pharynx
c. Bronchioles
d. Bronchi

3. During inhalation the diaphragm moves
*a. inferiorly
b. superiorly
c. anteriorly
d. posteriorly

4. This part of the lungs is the actually site for gas exchange
a. Bronchiole
b. Bronchus
c. Carina
*d. Alveoli

5. Why does the left lung have only two primary bronchii branches?
a. It's lazy
b. The right lung is an over achiever
c. The heart occupies space, making the left lung slightly smaller
d. The right lung is used more

6. What is the cause of hick-ups?
a. A spasm in the diaphragm
b. Something you ate
c. None of these
d. Both of these