Anatomy of the Respiratory System Pulmonary Ventilation Gas Exchange and Transport Respiratory Disorders

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Nose Pharynx Larynx Trachea Bronchi Lungs

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Airflow in lungs bronchi bronchioles alveoli

Conducting division = Passages for airflow Nostrils to bronchioles

Respiratory division = Gas exchange regions Alveoli

Upper respiratory tract = Parts in the head and neck Nose through larynx

Lower respiratory tract = Parts in the thorax Trachea through lungs

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Functions warms, cleanses, humidifies inhaled air detects odors resonating chamber that amplifies the voice

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Superior, middle and inferior nasal conchae 3 folds of tissue on lateral wall of nasal fossa mucous membranes supported by thin scroll-like

turbinate bones Meatuses

narrow air passage beneath each conchae narrowness and turbulence ensures air contacts

mucous membranes

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Olfactory mucosa lines roof of nasal fossa

Respiratory mucosa lines rest of nasal cavity with ciliated pseudostratified

epithelium Defensive role of mucosa

mucus (from goblet cells) traps inhaled particles bacteria destroyed by lysozyme

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Function of cilia of respiratory epithelium sweep debris-laden mucus into pharynx to be swallowed

Erectile tissue of inferior concha venous plexus that rhythmically engorges with blood and

shifts flow of air from one side of fossa to the other once or twice an hour to prevent drying

Spontaneous epistaxis (nosebleed) most common site is inferior concha

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Nasopharynx pseudostratified epithelium posterior to choanae, dorsal to soft

palate receives auditory tubes and contains

pharyngeal tonsil 90 downward turn traps large particles

(>10m)

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Oropharynx stratifeid squamous epithelium space between soft palate and root of

tongue, inferiorly as far as hyoid bone, contains palatine and lingual tonsils

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Laryngopharynx stratified squamous hyoid bone to level of cricoid cartilage

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Glottis – vocal cords and opening between Epiglottis

flap of tissue that guards glottis directs food and drink to esophagus

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Epiglottic cartilage - most superior Thyroid cartilage – largest; laryngeal

prominence Cricoid cartilage - connects larynx to

trachea Arytenoid cartilages (2) - posterior to

thyroid cartilage

Corniculate cartilages (2) - attached to arytenoid cartilages like a pair of little horns

Cuneiform cartilages (2) - support soft tissue between arytenoids and epiglottis

Rigid tube ~4.5 in. long and ~2.5 in. diameter.

Anterior to esophagus Supported by 16 to 20 C-

shaped cartilaginous rings opening in rings faces

posteriorly towards esophagus trachealis spans opening in

rings, adjusts airflow by expanding or contracting

Larynx and trachea lined with ciliated pseudostratified epithelium which functions as mucociliary escalator

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Right lung has 3 lobes Superior Middle (smallest) Inferior

Left Lung has 2 lobes Room for the heart

Carina

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Primary bronchi (C-shaped rings) from trachea; after 2-3 cm enter

hilum of lungs right bronchus slightly wider and

more vertical (aspiration)

Secondary (lobar) bronchi (overlapping plates) one for each lobe of lung

Tertiary (segmental) bronchi (overlapping plates) 10 right, 8 left

Bronchioles (lack cartilage) layer of smooth muscle pulmonary lobule is the

portion ventilated by one bronchiole

divides into 50 - 80 terminal bronchioles

Each divides into 2-10 alveolar ducts; end in alveolar sacs

Alveoli main site for gas exchange

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Similar to the pericardium except around the lungs Visceral (on lungs) and parietal (lines rib cage) pleurae Pleural cavity - space between pleurae, lubricated with

fluid Functions

reduce friction compartmentalization

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Breathing (pulmonary ventilation) – one cycle of inspiration and expiration quiet respiration – at rest forced respiration – during exercise

Flow of air in and out of lung requires a pressure difference between air pressure within lungs and outside body

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Diaphragm (dome shaped) contraction flattens

diaphragm Scalenes

hold first pair of ribs stationary

External and internal intercostals stiffen thoracic cage;

increases diameter

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Pectoralis minor, sternocleidomastoid and erector spinae muscles used in forced inspiration

Abdominals and latissimus dorsi forced expiration (to sing, cough, sneeze)

Breathing depends on repetitive stimuli from brain

Neurons in medulla oblongata and pons control unconscious breathing

Voluntary control provided by motor cortex

Inspiratory neurons: fire during inspiration

Expiratory neurons: fire during forced expiration

Fibers of phrenic nerve go to diaphragm; intercostal nerves to intercostal muscles

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Respiratory nuclei in medulla The Dorsal Respiratory Group

(formerly called the inspiratory center)

The Ventral Respiratory Group (formerly called the expiratory center )

Pons The Pontine Respiratory Center

(formerly the pneumotaxic and apneustic centers)

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From limbic system and hypothalamus respiratory effects of pain and emotion

From airways and lungs irritant receptors in respiratory mucosa

stimulate vagal afferents to medulla, results in bronchoconstriction or coughing

stretch receptors in airways - inflation reflex excessive inflation triggers reflex stops inspiration

From chemoreceptors monitor blood pH, CO2 and O2 levels

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Peripheral chemoreceptors found in major blood vessels

aortic bodies signals medulla by vagus

nerves carotid bodies

signals medulla by glossopharyngeal nerves

Central chemoreceptors in medulla

primarily monitor pH of CSF

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Atmospheric pressure drives respiration 1 atmosphere (atm) = 760 mmHg

Intrapulmonary pressure and lung volume pressure is inversely proportional to volume

for a given amount of gas, as volume , pressure and as volume , pressure

Pressure gradients difference between atmospheric and intrapulmonary

pressure created by changes in volume thoracic cavity

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Atmospheric pressure drives respiration 1 atmosphere (atm) =

760 mmHg intrapulmonary

pressure lungs expand with

visceral pleura 500 ml of air flows with

a quiet breath

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During quiet breathing, expiration achieved by elasticity of lungs and thoracic cage

As volume of thoracic cavity , intrapulmonary pressure and air is expelled

After inspiration, phrenic nerves continue to stimulate diaphragm to produce a braking action to elastic recoil

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Internal intercostal muscles depress the ribs Contract abdominal muscles

intra-abdominal pressure forces diaphragm upward pressure on thoracic cavity

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Presence of air in pleural cavity Collapse of lung (or part of lung) is called atelectasis

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Atelectasis is the decrease or loss of air in all or part of the lung

Tumors obstructing a bronchus Foreign body (an inhaled marble?) Serious pneumonia Lack of surfactant Smoke inhalation Post-operative complication

Pulmonary compliance distensibility of lungs

Bronchiolar diameter primary control over resistance to airflow bronchoconstriction

triggered by airborne irritants, cold air, parasympathetic stimulation, histamine

bronchodilation sympathetic nerves, epinephrine

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Compliance is reduced by smoking and by fibrotic conditions such as sarcoidosis or lupus

Asthma

Thin film of water needed for gas exchange creates surface tension that acts to collapse alveoli and distal

bronchioles Pulmonary surfactant decreases surface tension Premature infants that lack surfactant suffer from

respiratory distress syndrome

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Spirometer - measures ventilation Respiratory volumes

tidal volume: volume of air in one quiet breath inspiratory reserve volume

air in excess of tidal inspiration that can be inhaled with maximum effort

expiratory reserve volume air in excess of tidal expiration that can be exhaled with

maximum effort residual volume (keeps alveoli inflated)

air remaining in lungs after maximum expiration

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Respiratory volumes tidal volume: inspiratory reserve volume expiratory reserve volume residual volume

Vital capacity total amount of air that can be

exhaled with effort after maximum inspiration

assesses strength of thoracic muscles and pulmonary function

Age - lung compliance, respiratory muscles weaken Exercise - maintains strength of respiratory muscles Body size - proportional, big body/large lungs Restrictive disorders

compliance and vital capacity Obstructive disorders

interfere with airflow, expiration requires more effort or less complete

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Mixture of gases; each contributes its partial pressure At sea level 1 atm. of pressure = 760 mmHg Air is about 79% nitrogen = 597 mmHg Air is only about 21% oxygen = 159 mmHg Air has almost no carbon dioxide = 0.3 mmHg

In Denver (or Reno) atmospheric pressure = 625 (to 645) mmHg Air is about 79% nitrogen = 494 (510) mmHg Air is only about 21% oxygen = 131 (135) mmHg Air has almost no carbon dioxide = 0.3 mmHg

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Important for gas exchange between air in lungs and blood in capillaries

Gases diffuse down their concentration gradients

Amount of gas that dissolves in water is determined by its solubility in water and its partial pressure in air

Time required for gases to equilibrate = 0.25 sec

RBC transit time at rest = 0.75 sec to pass through alveolar capillary

RBC transit time with vigorous exercise = 0.3 sec

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What percentage of O2 loading at 0.75 sec transit time is now possible?

Membrane thickness - only 0.5 m thick

Membrane surface area - 100 ml blood in alveolar capillaries, spread over 70 m2

Ventilation-perfusion coupling areas of good ventilation need

good perfusion (vasodilation)

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Concentration in arterial blood 20 ml/dl

98.5% bound to hemoglobin 1.5% dissolved

Binding to hemoglobin each heme group of 4 globin chains

may bind O2

oxyhemoglobin (HbO2 ) deoxyhemoglobin (HHb)

As bicarbonate (and carbonic acid) - 90% CO2 + H2O H2CO3 HCO3

- + H+

As carbaminohemoglobin (HbCO2)- 5% binds to amino groups of Hb (and plasma proteins)

As dissolved gas - 5%

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CO2 loading carbonic anhydrase in RBC catalyzes

CO2 + H2O H2CO3 HCO3- + H+

chloride shift keeps reaction proceeding exchanges HCO3

- for Cl-

(H+ binds to hemoglobin)

O2 unloading H+ binding to HbO2 its affinity for O2

Hb arrives 97% saturated Hb leaves 75% saturated venous reserve

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Reactions in the alveolus are the reverse of systemic gas exchange

Active tissues need oxygen! ambient PO

2: active tissue has PO

2 ; O2 is released

temperature: active tissue has temp; O2 is released

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Active tissues need oxygen! Bohr effect: active tissue has CO2, which lowers pH (muscle

burn); O2 is released

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Haldane effect HbO2 does not bind CO2 as well as deoxyhemoglobin low level of HbO2 (as in active tissue) enables blood to

transport more CO2

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Rate and depth of breathing adjusted to maintain levels of:

pH

PCO2

PO2

Let’s look at their effects on respiration:

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pH of CSF (most powerful respiratory stimulus) Respiratory acidosis (pH < 7.35) caused by failure of

pulmonary ventilation hypercapnia: PCO

2 > 43 mmHg

CO2 easily crosses blood-brain barrier in CSF the CO2 reacts with water and releases H+

central chemoreceptors strongly stimulate inspiratory center “blowing off ” CO2 pushes reaction to the left

CO2 (expired) + H2O H2CO3 HCO3- + H+

The induction of hyperventilation reduces H+ (reduces acid)

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Respiratory alkalosis (pH > 7.45) caused by hyperventilation hypocapnia: PCO

2 < 37 mmHg

The induction of hypoventilation ( CO2), pushes reaction to the right CO2 + H2O H2CO3 HCO3

- + H+

H+ (increases acid), lowers pH to normal pH imbalances can have metabolic causes

eg - uncontrolled diabetes mellitus can cause acidosis fat oxidation causes ketoacidosis, may be compensated for

by Kussmaul respiration (deep rapid breathing)

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Hypoxia is a deficiency in the amount of oxygen reaching the tissues

Dyspnea is difficult or labored breathing, “air hunger” Cyanosis is a blueish color of the skin and mucous membranes Causes of hypoxia

hypoxemic hypoxia - usually due to inadequate pulmonary gas exchange high altitudes, drowning, aspiration, respiratory arrest, degenerative lung

diseases, CO poisoning ischemic hypoxia - inadequate circulation anemic hypoxia - anemia histotoxic hypoxia - metabolic poison (cyanide)

Primary effect of hypoxia tissue necrosis, organs with high metabolic demands affected first

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Oxygen toxicity: pure O2 breathed at 2.5 atm or greater generates free radicals and H2O2 which destroys enzymes damages

CNS – seizures, coma death Eyes – blindness Lungs – painful breathing

Hyperbaric oxygen (high % O2 under increased atmospheric pressures) formerly used to treat premature infants

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Asthma (if it is poorly controlled) allergen triggers

histamine release intense

bronchoconstriction (blocks air flow)

COPD is most often associated with smoking chronic bronchitis leads to emphysema

Chronic bronchitis cilia immobilized and in number goblet cells enlarge and produce excess mucus sputum formed (mucus and cellular debris)

ideal growth media for bacteria leads to chronic infection and bronchial inflammation

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Emphysema alveolar walls break down

much less respiratory membrane for gas exchange lungs fibrotic and less elastic air passages collapse

obstruct outflow of air air trapped in lungs

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pulmonary compliance and vital capacity Hypoxemia, hypercapnia, respiratory acidosis

hypoxemia stimulates erythropoietin release and leads to polycythemia

Cor pulmonale hypertrophy and potential failure of right heart due to

obstruction of pulmonary circulation

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Lung cancer accounts for more deaths than any other form of cancer most important cause is smoking (15 carcinogens)

90% originate in primary bronchi Tumor invades bronchial wall, compresses airway; may

cause atelectasis Often first sign is coughing up blood Metastasis is rapid; usually occurs by time of diagnosis

common sites: pericardium, heart, bones, liver, lymph nodes and brain

Prognosis poor after diagnosis only 7% of patients survive 5 years

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