RESPIRATORY SYSTEM

• The respiratory system helps meet the metabolic needs of the body by bringing oxygen into the bloodstream where it can be transported to all body cells.

• It also removes carbon dioxide from the blood, sending it outside the body.

I. Organs of the Respiratory System

A. Upper Respiratory Tract1. The nose:

The only externally visible part of the respiratory system.It is an initial receiving chamber for inhaled air.

The nose1. Provides an airway for

respiration2. Moistens and warms

entering air3. Filters and cleans inspired air4. Serves as a resonating

chamber for speech5. Houses the olfactory

receptors

The external nose:• The root: the area between the eyebrows

• The bridge: the area below the root

• The dorsum nasi…the anterior margin that ends in the tip of the nose (the apex)

• Philtrum: the “dent” inferior to the apex

The internal nose

• The nasal cavity is divided into to nares by a medial septum.

• The region superior to the nares is called the nasal vestibule

The vestibule contains coarse hairs that filter air and is lined with mucous membranes that warm (due to numerous blood vessels) and moisten inhaled air.

The cells of the mucous membranes have cilia which move the mucous towards the pharynx where trapped particles such as bacteria, dust, etc are generally swallowed.

2. The PharynxA chamber extending from the back of the nasal cavity to the larynx.Its walls are skeletal muscle lined with mucous membraneIt is also referred to as the throat.It is a common passageway for air and food.

• It is divided into 3 sections:1. Nasopharynx: this portion is

only for air and contains the soft palate and the uvula which work to close off the nasopharynx preventing food from entering the nasal cavity. The adenoids are high on the posterior wall and trap and destroys pathogens that enter with the air.

2. The Oropharynx: this is a pathway for both food and air. Two (of the three) types of tonsils are embedded in the oropharynx mucosa. Tonsils protect against inhaled or ingested pathogens.

3. The Larynogopharynx: also has food and air traveling through it. During swallowing, the passage of air ceases.

• We breathe through our mouth when airflow through the pharynx is restricted for any reason.

• Breathing through your mouth results in the air not being properly moistened, warmed or filtered before reaching the lungs.

3. The Larynx

• It is also called the voice box.

• It runs from the laryngopharynx into the trachea.

• The walls are cartilaginous and lined with ciliated mucous membranes.

• It has 3 functions:–Provide an open airway–Act as a switching mechanism to route food and air appropriately

–Voice production

• The opening to the larynx is called the glottis.

• The epiglottis is cartilage that is suspended over the opening. It presses down during swallowing, closing off the glottis preventing food or liquid from entering the lower respiratory tract.

Speech• Speech occurs due to the intermittent release of air combined with the opening and closing of the glottis.

• Pitch changes as the length and tension of the vocal cords changes.

• For deep tones, the glottis is wide open…for high-pitched sounds, the glottis is only a narrow slit.

• Boys’ voices deepen when the larynx enlarges during puberty causing the vocal cords to become longer and thicker causing them to vibrate slower resulting in deeper tones

• Loudness is determined by the force with which air is forced over the vocal cords…greater force causes stronger vibrations resulting in louder sounds.

• The vocal cords don’t move at all when we whisper but they vibrate with vigor when we yell.

• The muscles of the chest, abdomen and back provide the “power source” for the air moving over the vocal cords.

B. Lower respiratory tract

1. The tracheaAKA: the windpipeA tubular passageway for air located anterior to the esophagus.

It extends downward from the larynx into the thoracic cavity dividing into right and left bronchi.

Its walls are supported by rings of cartilage, smooth muscle and elastic fibers making it flexible and mobile.

The elastic nature of the trachea allows it to stretch and move during inspiration and expiration, and the cartilage rings prevent it from collapsing due to the pressure changes that occur during breathing and closing off the air passageway.

The cartilage rings are made of hyaline cartilage and are C-shaped which leaves the posterior portion open. This allows the esophagus to expand as swallowed food moves through it.

The walls contain ciliated mucous membranes that move the mucous towards the pharynx to be expelled or swallowed.

Contraction of the trachealis muscle decreases the diameter of the trachea adding much force to expired air which aids in expelling mucous during coughing.

The exhaled air can reach speeds of 100 mph!

2. Bronchi

The distal end of the trachea splits into the right and left bronchi.

Once inside the lungs, each bronchi further subdivides into:

• lobar bronchi (3 on the right, 2 on the left

and

• Segmental bronchi which continue to subdivide into smaller and smaller bronchi

• Passages smaller than 1mm in diameter are called bronchioles

• Terminal bronchioles are the tiniest at less than 0.5 mm in diameter

• The walls of the primary bronchi are supported by cartilage and smooth muscle and are lined with ciliated mucous membranes much like the trachea.

• As the bronchi branch into the lungs and the tubes become smaller, many changes occur

The amount of cartilage decreases in size and amount until it disappears altogether.

Elastic fibers remain throughout.

The amount of smooth muscle increases

The mucosal membrane thins and cilia becomes less abundant

3. Alveoli• Alveoli are microscopic pouches located at the terminal end of the bronchioles.

• They provide the only site of gas exchange between the external environment and the bloodstream

• The alveolar structure can be equated to a bunch of grapes with the alveolar sac being the bunch of grapes and the alveoli being the individual grapes

• There are upwards of 300 million gas-filled alveoli in the lungs

• The average adult has ~300 to 500 million alveoli in their lungs resulting in a surface area 80 times greater than that of the entire outside of the body!

• The walls of the alveoli are predominantly a single layer of squamous epithelial cells surrounded by pulmonary capillaries.

• This allows for gas exchange by diffusion

• Alveolar macrophages “crawl” freely throughout the internal surfaces of the alveoli removing the numerous infectious microorganisms that are carried into the alveoli.

• Aged and dead macrophages are moved to the pharynx where they are cleared and swallowed.

• We swallow over 2 million alveolar macrophages every hour!

Yum

Alveolar cells are lined with a lipid molecule called surfactant and a fluid that moistens the surface facilitating diffusion of gases.

The fluid creates a high surface tension which would cause the alveoli to collapse

• The surfactant counteracts this surface tension allowing the alveoli to reopen after each breath.

• The huge muscular effort that would be necessary to reopen the alveoli would result in suffocation without the presence of surfactant.

Because surfactant is not produced before the seventh month of gestation, this can cause problems for infants born prematurely. Often this is what is being referred to when doctors state that the lungs are not developed enough for infant viability

4. The lungs

The lungs are organs of the respiratory tract that function as the site of gas exchange between the atmosphere and the bloodstream

The lungs are soft, spongy, cone-shaped organs that extend from just above the clavicles to the diaphragm with the ribs bordering their anterior and posterior surfaces.

Each lung is surrounded by two layers of membranes called pleurae which are separated by the pleural cavity

The pleural cavity is filled with a fluid that lubricates the pleural membranes . This fluid reduces the friction that would be produced when the lungs contract and expand during breathing.

If this fluid were reduced or absent, the membranes would scrape together resulting in considerable pain (pleurisy is a condition in which the pleurae become inflamed and rough)

The pleurae also help to divide the thoracic cavity into three chambers which helps prevent the mobile thoracic organs from interfering with one another as well as limiting the spread of local infection

Each lung is divided into smaller compartments called lobes.

The right lung has 3 lobes, the left lung has 2 lobes.

The lobes are further divided into lobules which contain the bronchioles and alveoli

II. The Mechanics of BreathingA. Inspiration (inhalation)

Occurs due to the change in air pressure in the alveoli…when the alveolar air pressure is less than that of the external environment

1. Respiratory muscles contract

2. the diaphragm presses downward

3. intercostal muscles contract and raise the ribs

4. the sternum is elevated5. the thoracic cavity expands

6. the pleurae move out, increasing the volume decreasing the pressure

7. a pressure gradient is created causing air to rush into the alveoli to restore equilibrium

B. Expiration (exhalation)

• A passive process which does not require muscular contractions to occur.

1. Diaphragm and external intercostal muscles relax

2. Thoracic cavity decreases in size

3. Pleural cavity pressure increases

4. Alveolar pressure becomes greater than atmospheric pressure

5. Air flows out of the lungs.

• A penetrating injury or wound to the chest that causes a pressure leak or increased pressure on the thoracic cavity by a tumor can cause the lung (or a portion of it) to collapse, obstructing air flow.

III. The Control of Breathing

A. The respiratory center located in the medulla oblongata and the pons is the main source of control.

B. Changes in blood chemistry (levels of O2, H+ ions and CO2) can also control breathing

C. Stretch receptors in the lungs trigger expiration when the bronchi and/or bronchioles become overstretched

D. Mental health influences breathing rates and rhythm

• Breathing can be controlled voluntarily…up to a certain point. When self-imposed conditions arise that are life threatening, consciousness ceases and breathing resumes.

• When CO2 levels reach a certain point, the respiratory center automatically sends impulses to respiratory muscles to resume breathing.

Oh yeahit’s

the end!