The Respiratory System
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Respiration
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• This exchange takes place within the lungs at air-filled pockets called alveoli
– The cardiovascular system provides the link between the interstitial fluids and the exchange surfaces of
the lungs
Functions
– The respiratory system has 5 basic functions:
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The Respiratory System
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• Can be divided into the upper conducting portion and lower respiratory portion
• Respiratory mucosa lines the upper portion
– The surfaces of the respiratory system can be severely damaged by contaminated air
Respiratory System: Functional Anatomy
– Major organs
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The Nose
– Air enters through the external nares (____________) travels through the nasal vestibule and enters the
nasal cavity
• The nasal cavity is protected by coarse hairs
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• The nasal cavity opens into the nasopharynx at the internal nares
– The respiratory surfaces of the nasal cavity are also protected by mucosa produced in the paranasal
sinuses
Pharynx (______________________)
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– 3 subdivisions:
1. _____________________________
– Goes from the internal nares to the level of the hyoid bone
– Contains the pharyngeal tonsil and openings to the auditory tubes
2. _____________________________
– Goes from the soft palate to the base of the tongue
– Contains the palatine tonsils
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3. _____________________________
– Goes from the level of the hyoid bone to the esophagus
Larynx (______________________)
– Air enters the larynx through the glottis
– Consists of 9 cartilages (the 3 largest are the epiglottis, thyroid cartilage, and cricoid cartilage)
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– Ridge on the surface forms the “Adam’s apple”
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Vocal Cords and Sound Production
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• Extend across the larynx reducing the size of the glottis
• Help prevent foreign objects from entering the glottis and protect the true vocal cords
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• Contains elastic ligaments that extend between the thyroid and arytenoid cartilages
• Small muscles change their position and the tension exerted on them
• Food or liquids that touch these cords triggers the coughing reflex
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• Air passing through the glottis vibrates the vocal cords, producing sound waves
• Pitch depends on diameter, length, and tension of the cords
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Trachea (______________________)
– Extends from the larynx into the mediastinum
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• The ends are connected by an elastic ligament and the trachealis muscle (a band of smooth
muscle)
Bronchi
– The trachea branches into the ______________________________________ which supply the right and
left lung respectively
– The primary bronchi branch into smaller and smaller airways that make up the __________________
– As the primary bronchi enter the lung they give rise to the ______________________
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• 1mm thick, cartilage free branches are the bronchioles
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» Extreme constriction (_______________) occurs during asthma and allergies
Lungs – Alveolar Ducts & Alveoli
– Bronchioles branch further into the finest air passageways (_________________________)
• Each terminal bronchiole supplies air to one lobule of the lung
– Within a lobule the terminal bronchioles branch into respiratory bronchioles
(____________________________________________________________________)
» Respiratory bronchioles open into passageways called alveolar ducts ending in
alveolar sacs (which contain individual alveoli)
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Roaming alveolar macrophages (dust cells) patrol alveolar epithelium
phagocytizing dust and debris
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Lungs
– Gas exchange occurs across the respiratory membrane of the alveoli which has 3 layers:
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– The right lung has 3 lobes (______________________________________) and the left lung has 2 lobes
(_________________________________)
– The medial surface of the right lung forms a vertical line and the medial surface of the left lung is
indented at the cardiac notch
– Each lung occupies a pleural cavity lined with a membrane called the pleura
• The pleura has 2 layers: ________________________________________________________
Mechanics of Breathing
– Pulmonary ventilation (________________) consists of two processes:
• External respiration: __________________________________________________________
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– 3 steps:
1. Pulmonary ventilation (_______________)
2. Gas diffusion (_____________________________________________)
3. Transport of oxygen and carbon dioxide
• Internal respiration: ___________________________________________________________
– If oxygen concentrations decline, _____________ (low tissue oxygen levels) and _____________
(complete lack of oxygen) can occur
Pulmonary Ventilation
– Pulmonary ventilation is the exchange of air between the atmosphere and the lungs
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– Breathing functions to maintain adequate alveolar ventilation (the movement of air into and out of the
alveoli)
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Pulmonary Ventilation
– Air flows from areas of high pressure to low pressure (______________________________________)
– In lungs, the pressure on a gas can be changed by increasing or decreasing the container’s volume
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• Changes in the volume of the thoracic cavity result from movements of the diaphragm & rib cage
Pulmonary Ventilation
– Compliance in lungs is the indication of their resilience and ability to expand
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– The amount of air moved into or out of the lungs during a single respiratory cycle is the tidal volume
– The amount of air in the lungs can be expressed as various volumes and capacities:
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______________________________________ is the amount of air that could be voluntarily
expelled at the end of a normal respiratory cycle
______________________________________ is the amount of air that can be taken in over and
above the resting tidal volume
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Gas Exchange
– This process depends on:
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– The atmosphere we breathe in is a mixture of gases (nitrogen, oxygen, water vapor, and carbon dioxide).
Atmospheric pressure at sea level is 760 mmHg
• Each of the gases in air contributes to the total atmospheric pressure based on its proportion.
The pressure contributed by a single gas is the partial pressure (P) of that gas
– Example: Air is 20.9% oxygen, therefore PO2 is 20.9% of 760 mmHg = 159 mmHg
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Transport of Respiratory Gases
– RBCs take up oxygen and carbon dioxide molecules from plasma and either bind them (______________)
or use them to manufacture soluble compounds (______________________)
• This is reversible: if plasma concentrations are high the excess molecules are removed by RBCs, if
they are too low then RBCs release their stored reserves
– Oxygen transport
• Oxygen is bound to hemoglobin (Hb) in the RBCs
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– Carbon dioxide transport
• After entering the bloodstream carbon dioxide may: ____________________________________
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Control of Respiration
– Cells continuously absorb oxygen and generate carbon dioxide. Under normal conditions, these rates are
matched by the delivery and removal rates at the capillaries and the oxygen absorption and carbon
dioxide excretion at the lungs
• If these rates become unbalanced the respiratory and cardiovascular systems have to make
adjustments:
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» The brains involuntary respiratory centers (medulla oblongata and pons) regulate
the respiratory muscles and control the respiratory rate and the depth of
breathing
» The voluntary control of respiration takes place in the cerebral cortex with the
control of respiratory muscles
Respiratory Rhythmicity Centers
– Medullary respiratory centers
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– Contains an inspiratory center that functions in all breathing
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– Contains an expiratory center and only functions in forced breathing
– Their output is adjusted by the 2 pairs of nuclei making up the respiratory centers of the pons
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Respiratory Reflexes
– Normal breathing is automatic but is modified by sensory information from:
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– Respond to changes in lung volume or arterial blood pressure
» _____________________ prevents lung overexpansion by stopping inhalation
and triggering exhalation and ____________________ stops the expiratory
center and triggers the inspiratory center
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» When blood pressure falls, respiratory rate increases; when blood pressure
increases, respiratory rates fall
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– Respond to chemical changes (pH, PCO2, and PO2) in the blood and CSF