Lab 7: Respiratory Air Flow and Volume

Background

• the primary function of the respiratory system is to release carbon dioxide from the body and to acquire oxygen for use by the body

• our bodies accomplish this through respiration

• respiration can be thought of as 4 steps: pulmonary ventilation, external respiration, transport of respiratory gases, and internal respiration

• pulmonary ventilation is the movement of air into (inspiration) and out of (expiration the lungs so that the gases in the lung are constantly refreshed with infusions of new air and effusions of old air (the respiratory system does this)

• during external respiration carbon dioxide diffuses to the lungs from the blood, and oxygen diffuses to the blood from the lungs (this also occurs in the respiratory system)

• the transport of respiratory gases is accomplished using the blood of the cardiovascular system

• carbon dioxide is transported from the cells of body tissues to the lungs, and oxygen is transported from the lungs to the cells of the body tissues

• internal respiration occurs as oxygen diffuses from the cells of the body to the blood

• carbon dioxide is produced and oxygen is used, by cells, for energy production during cellular respiration

Background 2

• the upper respiratory system (figure 1) consists of the structures from the nose to the larynx and the lower respiratory system consists of the larynx and the structures inferior to it

• the nose warms and moistens entering air, provides a resonating chamber for vocalizations, cleans and filters entering air, and houses the olfactory receptors

• the differences in nasal cartilages accounts for the differences in nose shapes people have (the bones that form parts of the nose are pretty consistent in regards to the external appearance they facilitate)

• a small portion of the superior nasal cavity is lined with olfactory mucosa epithelium containing the receptors for smell

• the rest of the nasal cavity is lined with respiratory mucosa composed of pseudostratified ciliated columnar epithelium with goblet cells and seromucous nasal glands

• these seromucous nasal glands are composed of cells that secrete mucus (traps bacteria, dust, and debris) and cells that secrete a watery (to humidify incoming air), enzyme rich (contains lysozyme which is antibacterial) fluid

Background 3

• the respiratory mucosa epithelial cells secrete antibiotic defensins to assist in killing microbial invaders

• the cilia of the nasal cavity sweep the contaminated mucus toward the throat to be swallowed and digested

• cold air slows the cilia and thus allows some of the mucus to dribble out the nostrils

• a sneeze reflex is triggered when irritants (dust, pollen, etc.) contact the rich supply of sensory nerve endings in the nasal cavity

• a sneeze forces these irritants out to protect the body from them

Background 4

• many thin walled veins and plexuses of capillaries lie just beneath the nasal epithelium and warm the air as it is inspired

• cold inspired air reflexively stimulates these plexuses to engorge with blood allowing for greater heat transfer

• the superficial location of these vessels does not expose them and make them easy to damage leading to nose bleeds

• the nasal conchae increase surface area and help create turbulence which deflects non-gaseous particles onto the mucus coatings

• inspired air is warmed, and in the process, cools the conchae so that on expiration the cooled conchae causes moisture to precipitate out and heat to be exchanged into the conchae to warm them

• in this way, the heat and moisture gradient is constantly flipping each time we breath out, and when we breath in

Background 5

• paranasal sinuses are located in the frontal, sphenoid, maxillary, and ethmoid bones

• these sinuses lighten the skull but are prone to inflammation, especially due to infections or allergies

• when the sinuses are inflamed (sinusitis), additional mucus (and inflammatory products) are produced and can block the openings between the sinuses and the nasal cavity

• when this happens, the air in the sinus is absorbed and a partial vacuum is created which causes the pain associated with a sinus a headache

• inflammation of the nasal mucosa, such as due to viral or bacterial infection, or allergic reactions, causes excessive mucus production leading to congestion and post nasal drip

Background 6

• when swallowing food, the muscular soft palate and uvula move superiorly to block off the nasopharynx, and the epiglottis flaps over the larynx, to keep food out of the nasal cavity and lungs

• in the nasopharynx, cilia propel mucus toward the stomach

• the pharyngeal tonsil (adenoid) of the nasopharynx contains lymphatic tissue that traps and destroys pathogens

• infected and swollen tonsils can be very painful

• when the pharyngeal tonsils are swollen they can block air passage and force the patient to breath through the mouth which greatly decreases the warming, filtering, and humidifying effect on the air compared to air brought in through the nose

• the pharyngotympanic tubes connect the middle ear to the nasopharynx so that air in the middle ear can math pressure with atmospheric air which is important for sound conduction and proper hearing

• the oropharynx and laryngopharynx receive both food and air and thus have a more protective stratified squamous epithelium

Background 7

• the respiratory system can be thought of as having a respiratory zone and a conducting zone

• the respiratory zone is the site of external respiration (where gas is exchanged) and is made up of microscopic alveoli (the main site of exchange), alveolar ducts, and respiratory bronchioles (figure 2)

• the conducting zone consists of all the tubes transporting air from the nose to the respiratory bronchioles

• during passage through the conducting zone, air is humidified, warmed, and filtered/cleansed

• the larynx houses the vocal folds (commonly called vocal cords) for voice production

• the laryngeal prominence of the thyroid cartilage can be seen external to the body as the Adam’s apply and is more prominent in males than females because the thyroid cartilage is stimulated by androgens during male puberty and grow larger

• also, estrogens stimulate fat deposition in the necks of females that obscure their smaller laryngeal prominence

Background 8

• the arytenoid cartilages anchor the vocal folds

• when we are conscious, anything other than air entering the larynx will generate a cough reflex to expel it

• for this reason, liquids should never be given orally to a patient who is unconscious

• the vocal folds and the openings between them (air passes through and produces sound when the vocal folds are positioned strategically) are collectively termed the glottis

Figure 1. Illustration of human oral cavity

what is 1?

sphenoid sinus

what is 2?

adenoid tonsil

what is 3?

pharyngeal opening of the Eustachian tube

what is 4?

soft palate

what is 5?

uvula

what is 6?

palatine tonsil

what is 7?

oropharynx

what is 8?

hypopharynx (laryngopharynx)

what is 9?

esophagus

what is 10?

frontal sinus

what is 11?

superior nasal concha

what is 12?

middle nasal concha

what is 13?

nasopharynx

what is 14?

inferior nasal concha

what is 15?

horizontal plate of palatine bone

what is 16?

epiglottis

what is 17?

hyoid bone

what is 18?

thyroid cartilage

what is 19?

laryngeal cartilages

what is 20?

cricoid cartilage

what is 21?

trachea

Background 9

• below the vocal folds, into the larynx and trachea, the epithelium changes back to pseudostratified ciliated columnar epithelium but the cilia here sweep mucus up toward the pharynx so that it can be swallowed

• the glottis opens and closes during intermittent expiration to produce speech

• the laryngeal muscles move the cartilages of the larynx (mostly the arytenoid) to change the the pitch and produce vocalization

• tense vocal folds will vibrate more to produce a higher pitch

• during male puberty, when the thyroid cartilage is enlarging, the rest of the larynx, including the vocal folds (they become longer and thicker), also enlarge to produce a deeper voice

• loudness is also determined by the force with which the air is expires across the vocal folds (more force equates to louder sound)

• the pharynx, nasal, oral, and sinus cavities resonate these sounds to enhance and amplify them

• enunciation to produce recognizable sounds as words is completed by muscles in the lips, soft palate, tongue, and pharynx that fine tune the sound as the waves escape us

• laryngitis is an inflammation of the vocal folds causing them to swell and vibrate incorrectly

• this results in a hoarse tone, and is most commonly caused by viral infection

• under certain conditions, the vocal folds can completely close over the glottis to stop air passage, such as when straining to defecate

• in this case, the abdominal muscles contract, and the glottis closes, to increase the intra-abdominal pressure to help empty the rectum (this is known as the Valsalva maneuver)

• the Valsalva maneuver also increases pressure in the thorax which decreases venous return to the heart by squeezing on the major blood vessels and presses on the vagus nerve to increase vagal tone, both of which slow the heart rate (table 1)

Figure 2. Breakdown of the respiratory system

Table 1. Effects if sinus arrhythmia

Breathing Mechanics and the Bronchial Tree

• the volume of the thorax is changed to produce the forces the allow for pulmonary ventilation (figure 3)

• volume changes cause pressure changes which in turn causes gases to flow down pressure gradients

• at a constant temperature, the pressure of a gas varies inversely with its volume (Boyle’s law)

• gases always fill the volume of the container they are in

• a given mass of gas in a large volume will spread out creating a small pressure while the same mass of gas in a small volume will be confined and create a larger pressure

• in order to exhale air, we squeeze of the thorax and decrease the volume by relaxing (expiration is largely passive in normal breathing due to recoil of the pulmonary structures) the diaphragm (relaxed domes up into the thorax) and external intercostal muscles (relaxed allows ribs and sternum to depress and ratchet down) to increase pressure in the thorax until the intra-thorax pressure exceeds atmospheric pressure which then forces air out of our lungs

Figure 3. Changes in thoracic volume and sequence of events during inspiration and expiration