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Respiratory System

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Nose (nasal cavity)

	Held open by skull bones and cartilage     GA
	Divided into left and right nasal cavities by the nasal septum     GA  GA External nares - anterior openings of right and left nasal cavities Also called anterior nares, or nostrils Singular of nares is "naris" Internal nares - posterior openings of right and left nasal cavities Also called posterior nares
	Lateral walls have three bony shelves (superior, middle, and inferior nasal conchae) that curl downward and inward     GA  Conchae = "snails"  (also called turbinates = "cone-shaped")      Conchae divide each nasal cavity into superior, middle, and inferior meati (tube-like passageways)     GA Septum and conchae cause the air to become turbulent, which causes particles to drop out of inspired air rather than being carried further into the tract
	Lining Respiratory mucosa - pseudostratified ciliated columnar Olfactory organ Roof of L & R nasal cavities Vibrissae = nose hairs

Paranasal sinuses

	Hollow spaces in skull connected to nasal cavity via membranous canals
	Lined with nasal mucosa
	Main purpose is to lighten the skull
	Passages are required to allow air pressure inside to equilibrate with atmospheric air pressure Also puts sinuses at risk for infection If passages swell during infection or allergy (sinusitis), may trap air/mucus inside and create pain

Pharynx (throat)     GA

	Air passage held open by bone and muscle Also a food passage Involved in phonation
	Lined with respiratory mucosa Tonsils provide some immune protection
	Three divisions of pharynx Nasopharynx (posterior to nasal cavities) Oropharynx (posterior to oral cavity) Laryngopharynx (posterior to opening of larynx)

Larynx (voice box)

	Held open by 9 pieces of cartilage that form a box with no bottom and hinged lid (epiglottis)     GA
	Front cartilages form a neck protrusion called the Adam's apple    GA   GA   GA

Passageway for air     GA The passage itself is called the glottis The epiglottis (lit. "on/over the glottis") is a the hinged lid that is pushed down to cover the glottis when you swallow

Vocal cords (vocal folds)     GA  GA  GA Lateral folds of elastic fibrous tissue that project toward middle of glottis (true vocal folds) Muscles in/around larynx can pull vocal cords to middle of glottis, shutting down air flow (or reducing air flow, depending on amount of muscle tension) False vocal folds = fold of mucosa just superior to the true vocal folds Ventricle = space between true and false vocal folds Protection Backs up protective function of epiglottis Keeps large particles/fluids from passing through the glottis Coughing     ANIM Vocal folds shut off glottis completely Thorax and abdomen compress, pressurizing air below the larynx Vocal folds open suddenly, allowing a blast of air from below to clear out the foreign material If the object is lodged in place, it may cause suffocation (see section in book on Heimlich maneuver) Voice production     FIG     FIG If cords almost cover glottis, passing air causes them to vibrate  ANIM Low-frequency vibrations cause low pitch sounds Pitch can be lowered by relaxing or lengthening vocal cords     GA High-frequency vibrations cause high pitch sounds Pitch can be raised by tightening or shortening vocal cords Size of larynx determines base length of cords Affected by sex hormones (male larger than female); age (adult larger than child) Voice is critical for communication needed for human survival behaviors Also makes radio programming possible

Trachea (windpipe)

	Low-pressure air passage to/from thoracic cavity
	Held open by C-shaped cartilage rings    PP      GA
	Lined with mucosa     GA Ciliary escalator (protective function) Cilia lining lower respiratory tract and larynx move dirty mucus upward and into esophagus for swallowing, keeping the lower tract free of debris

Bronchial tree     GA

	Literally, "branched tree"  (bronchus = "branch") (pl. bronchi) Primary bronchi branch to each lung      GA Secondary (lobar) bronchi diverge from primary bronchi and go to each lobe of a lung Tertiary (segmental) bronchi diverge from secondary bronchi and go to each segment of a lobe of a lung Successive levels of branching continue, eventually forming small bronchioles Terminal bronchioles (alveolar ducts) are the last non-gas-exchange portions of the bronchial tree Respiratory bronchioles are supplied by pulmonary capillaries (lead into multiple alveoli)     GA  GA
	Walls of bronchi and larger bronchioles supported by cartilage rings; smaller bronchioles have sufficient thickness to stay open without cartilage
	Low-pressure airway Bronchi and bronchioles have smooth muscle in walls to regulate air flow pp Some gas exchange (in respiratory bronchioles only) In-out change of direction of air flow gets less and less further down into brochial tree, so that by the respiratory bronchioles, there is virtually no tide of in-out flow of air (instead, relatively constant ventilation)

Alveoli (sing. alveolus)

	Microscopic air pouches at ends of bronchial tree     GA 300 million total (giving approx. area of 85 m2 = tennis court) Blind sacs arranged in a cluster (alveolar sac) Interalveolar openings maintain cross-ventilation
	Thin wall coated with watery film Allows easy diffusion of oxygen (inward) and carbon dioxide (outward) Respiratory membrane has three layers Alveolar wall (simple squamous epithelium) Interstitial connective tissue Endothelium of pulmonary capillary Water tends to "ball up" and cause alveolar walls to stick to one another Collapsed alveoli are very difficult to reinflate Prevented by surfactant made by Type II alveolar cells Surfactant reduces surface tension (attraction between water molecules) and thus reduces likelihood of collapse with normal breathing    pp Premature infants often lack surfactant, so they may suffer from respiratory distress syndrome (RDS) as they struggle to re-inflate collapsed lungs with each breath (may be fatal if not treated with mechanical respirator and/or application of surfactant)
	Contain macrophages that aid in tidying up the place (immunity)

Lungs (left and right; paired organs)

	Location: thoracic cavity (left and right pleural cavities)     GA  GA  GA
	Size: grow to fill available space     GA  GA Left lung is smaller than right lung (because of location of heart)     GA
	Apex is pointed top; base is broad bottom of each lung
	Divisions Lobes (2 on left; 3 on right)      GA   GA Segments - divisions of a lobe
	Coverings - pleurae Visceral pleura (on lung) Parietal pleura (lines thoracic cavity) Pleural space between layers contains pleural fluid     GA  GA Pleural fluid lubricates and keeps lungs "stuck to" inside of thoracic wall (thus holding lungs open) Pneumothorax occurs when air gets into pleural space, thus breaking the pleural fluid's hold (by increasing intrapleural pressure) and causing lung to collapse

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Ventilation

	Primary principle of ventilation Air moves down a pressure gradient (high pressure to low pressure)    pp
	Boyle's Law: air pressure is inversely proportional to air volume     ANIM That is, if volume goes up then pressure goes down and if volume goes down then pressure goes up     ANIM
	The respiratory cycle     ANIM   pp Inspiration Expand thorax/lungs, increasing the volume Decreases alveolar pressure (PA) below atmospheric pressure (PB), causing air to move from atmosphere into lung Inspiration: PA < PB Mostly the diaphragm that does this     GA  GA In deep breathing (as in exercising or as in sighing during A&P class [of course I hear you!]), external intercostal ("between the rib") muscles raise ribs up and out (further expanding thorax / lungs)      GA  GA  GA Compliance Ease of stretch Allows tissues of lungs/thorax to expand easily during inspiration Expiration Relax thorax/lungs, decreasing the volume Increases alveolar pressure (PA) above atmospheric pressure (PB), causing air to move from lung to atmosphere Expiration: PA > PB Mostly the elastic recoil of the diaphragm that does this In deep breathing, internal intercostals pull ribs downward and inward (further reducing volume of thorax / lungs)     GA

Pulmonary volumes and capacities

Acronym

Volume or capacity

Equivalent

Description

Interpretation

TV

Tidal volume (500 ml)

Volume moved during a normal quiet respiratory cycle

Low TV may indicate a restrictive disorder; TV is high during exercise

IRV

Inspiratory reserve volume (3000 ml)

Extra volume that can be inspired (forcefully) beyond the tidal volume

IRV decreases with increased tissue demand for oxygen, as in exercise

ERV

Expiratory reserve volume (1100 ml)

Extra volume (beyond tidal volume) moved during a forced expiration

ERV is highly variable among normal persons; it decreases during exercise as the tidal volume approaches the vital capacity

RV

Residual volume (1200 ml)

RV = TLC - VC

Volume of air that always remains in the respiratory tract, even after forced expiration.

RV greater than one third of total lung capacity may indicate an obstructive disorder.

Dead space (160 ml)

Physiological dead space: anatomical dead space volume plus volume of air in respiratory areas of tract that can't exchange gases with pulmonary blood

Anatomical dead space usually equals physiological dead space. If physiological dead space is higher, then lungs may not be adequately perfused with blood. Or, inspired air is more than needed for adequate gas exchange.

IC

Inspiratory capacity (3500 ml)

IC = IRV + TV

The total capacity for inspiration, including both tidal volume and inspiratory reserve.

Low IC may indicate a restrictive disorder

FRC

Functional residual capacity (2300 ml)

FRC = ERV + RV

Volume of air remaining in tract after a normal expiration

Overfilling of lungs, as in obstructive disorders, may cause a high FRC

VC

Vital capacity (4600 ml)

VC = IRV + TV + ERV

Total volume moved by forced expiration, starting from the inspiratory maximum

Low VC (with high flow rate) may indicate respiratory distress; High VC (with low flow rate) may indicate reduced gas exchange area in lungs

TLC

Total lung capacity (5800 ml)

Combined total of all four basic lung volumes: tidal volume, inspiratory reserve, expiratory reserve, residual volume

High TLC is associated with obstructive disorders; low TLC is associated with restrictive conditions

Total minute volume (6000 ml/minute)

TV x respiratory rate

Volume of air moved per minute during normal, quiet breathing

Low minute volume may indicate edema of the functional pulmonary tissues

FEV_x

Forced expiratory volume (FEV₁ = 83% of VC)

% VC expelled forcefully by end of interval x (sec)

Volume (or % VC) expired forcefully during a given interval, beginning at the point of maximum inspiration

Low FEV₁ associated with obstructive conditions

Gas Exchange

	Simple diffusion of gases dissolved in water Across thin membrane (alveolar wall, basement membrane, capillary wall)
	Gas fractions are expressed as "partial pressures" rather percent by volume Dalton's Law of Partial Pressures The total pressure exerted by a mixture of gases (such as air) results from the combined effect of each of the pressures of the individual gases in the mixture Thus, the partial pressure of a gas reflects the proportion of that particular gas in the whole mixture Partial pressure is expressed as Px where x is the formula for the gas (examples: PO2 or PCO2)
	Pulmonary gas exchange - in lungs Oxygen (O2) moves into blood  blood PO2 < alveolar PO2 Carbon dioxide (CO2) moves out of blood  blood Pco2 > alveolar Pco2 Ventilation/perfusion matching Perfusion (blood flow) is matched to ventilation (air flow) in each group of alveoli
	Systemic gas exchange - in all other tissues     ANIM Oxygen (O2) moves out of  blood blood PO2 > interstitial fluid (IF) PO2 Carbon dioxide (CO2) moves into blood blood Pco2 < interstitial fluid (IF) Pco2

Transport of gases

Oxygen transport Small amount (1-2%) of O2 is simply dissolved in plasma Most O2 is attached to hemoglobin (Hb), forming oxyhemoglobin (HbO2) O2 is attached to the iron (Fe) containing heme groups in the Hb molecule Hb loading and unloading of O2 is responsive to local conditions Oxyhemoglobin (HbO2) dissociation curve     FIG  FIG O2 is loaded onto Hb when local O2 levels are high --as in the alveolar capillaries O2 is unloaded from Hb when local O2 levels are low --as in the systemic capillaries More O2 can be unloaded at active tissues than resting tissues Conditions that increase O2 unloading from Hb happen to increase as the tissue becomes more active, thus causing additional unloading of O2 in more active tissues Conditions that cause further unloading of O2      ACT Higher temperature Higher CO2 concentration Lower pH Such conditions cause a "right shift" of the HbO2 dissociation curve     pp Bohr effect: when right shift is caused by increased Pco2 /decreased pH

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