Chapter 21 – The Respiratory System
Nose
• External nose is composed of 2 nasal bones (root/bridge) and hyaline cartilage
• Internal nasal cavity is divided into left and right sides by nasal septum – Superiorly – perpendicular
plate of the ethmoid bone; inferiorly – vomer
Nose cont
• Lined with mucous membrane– Olfactory – chemoreceptors for sense of smell – Respiratory • Pseudostratified columnar epithelium
– Ciliated to trap debris • Mucous glands/goblet cells • Serous glands – lysozyme
Respiratory epithelium
Nose cont
• Lateral walls have projections – conchae – Superior and middle
conchae are part of the ethmoid bone; inferior conchae are paired bones
– Increases air turbulence • Large particles get trapped
in mucus – Warms and moistens air
• Better gas diffusion
Paranasal sinuses
• Frontal, maxillary, ethmoid, and sphenoid bones • Warms and moistens air • Lightens skull bones • Resonance chambers
Pharynx
• Connects nasal cavity with inferior respiratory structures
• Common to both digestive and respiratory systems
• From superior → inferior – Nasopharynx– Oropharynx– Laryngopharynx
Pharynx cont
• Nasopharynx – Passageway for air only (not
shared with digestive system)
– Contains singular pharyngeal tonsil (“adenoid”)• Lymphoid material • Swelling can cause restriction
of air flow – Contains opening to
auditory/pharyngotympanic tube
Pharynx cont • Oropharynx
– For both air and food/fluid– Contains paired palantine and
paired lingual tonsils – Tissue changes to stratified
squamous • Offers more protection
• Laryngopharynx – For both air and food/fluid – Splits into anterior larynx
(respiratory system) and posterior esophagus (digestive system)
Larynx • Supported by cartilage – Epiglottis
• Moves inferiorly during swallowing to cover opening of larynx – food or fluid enters esophagus
– Thyroid cartilage• “Adam’s apple”
– Cricoid cartilage – complete ring
– Arytenoid cartilage – attaches to vocal cords
– Corniculate – “little horns”
Larynx cont • Voicebox
– True vocal cords – inferior – False vocal cords/vestibular cords – superior
• Aid in closing of the glottis – opening between true vocal cords
Trachea • “windpipe”• Ciliated pseudostratified • Supported by C-rings of
cartilage – Incomplete posteriorly;
allows esophagus to expand anteriorly when swallowing
• Carina – projection of cartilage just before split into primary bronchi – Initates coughing when
touched
Bronchi • Trachea branches into left
and right primary bronchi – Each enters a lung at hilum
(depression)– Right primary is wider, shorter,
and more vertical • Food can get lodged there more
easily
• Each primary bronchus branches into secondary/lobar bronchi– 3 on right; 2 on left
Bronchi cont
• Bronchi branch repeatedly – Transition of cartilage
rings to cartilage plates – Lead to smaller
bronchioles – Terminal bronchi →
terminal bronchioles → respiratory bronchioles • Respiratory bronchioles
have scattered alveoli • Alveolar sacs resemble
clusters of grapes
Alveoli • Type I cells
– Simple squamous epithelium • Site of gas exchange • Surrounded by capillary beds
• Type II cells– Cuboidal cells
• Secrete surfactant – Keep alveoli from collapsing
• Alveolar pores connect adjacent alveoli so gas pressure is equalized
• Macrophages on interior of alveoli
Zones
• Conducting zone– Nasal cavity to terminal bronchioles – Passageway for gases only
• Respiratory zone– Respiratory bronchioles to alveoli – Actual site of gas exchange
Lungs • Apex – most superior portion;
base – most inferior (lies on top of diaphragm)
• Medial surface has a depression – hilum – Entrance of primary bronchi,
passage for blood vessels • Left lung
– 2 lobes (superior and inferior) separated by oblique fissure
– Cardiac notch • Depression to accommodate heart
• Right lung – 3 lobes (superior, middle, and
inferior)– Oblique and
horizontal/transverse fissures
Lung blood supply • Pulmonary circulation– Pulmonary arteries – oxygen-poor blood to
alveolar capillaries – Pulmonary veins – oxygen-rich blood back to heart
• Systemic circulation – Bronchial arteries – branch from aorta to supply
lung tissue (except alveoli)– Oxygen-poor blood from lung tissue enters small
bronchial veins
Pleural layers
• Parietal – more superficial – Lines thoracic wall and
superior portion of diaphragm
• Visceral – deep– Right on top of lung surface;
dips into fissures • In between layers is
pleural cavity – Pleural fluid for lubrication
Respiratory system function • Supplies blood with oxygen and removes waste carbon dioxide • 4 stages
– Pulmonary ventilation• “breathing”
– External respiration• Gas exchange at capillaries covering alveoli • Oxygen loading; carbon dioxide unloading
– Transport of respiratory gases• By cardiovascular system
– Internal respiration • Gas exchange at systemic capillaries • Oxygen unloading; carbon dioxide loading
Mechanics of Breathing
• Pressure relationship – Atmospheric pressure – 760mm Hg– Intrapulmonary pressure – inside alveoli – Intrapleural pressure – inside pleural cavity – Differences between intrapulmonary and intrapleural
pressures keep airways open • Elasticity of lungs – recoil into small shape; surface
tension of surfactant keeps alveoli small – Opposition to this is the expansion of the thoracic cavity,
which increases volume
Pulmonary ventilation
• Boyle’s law– At constant
temperature, gas pressure is inversely proportional to volume
• Change in lung volume will affect lung pressure – Pressure changes leads
to gas movement (high pressure area to low pressure area
Pulmonary ventilation cont• Inspiration
– Diaphragm contracts from upward dome to flattened shape• Increases height of lungs
– Contraction of intercostal muscles causes ribcage to swing outward • Increases depth of lungs
– Lung volume increases, which decreases pressure in lungs• Pressure is now less than
atmospheric pressure – Gas rushes into lungs
• Expiration– Relaxation of diaphragm and
intercostals allows lungs to recoil and assume smaller volume • Increase in pressure causes gas to
rush out
Respiratory volumes
Gas exchange
• Basic gas properties – Dalton’s law of partial pressure • In a mixture of gases, each gas exerts pressure based on
its relative %– Partial pressure
– Henry’s law• When gas comes in contact with a liquid, the gas will
dissolve into the liquid • If partial pressure of the gas is greater in liquid, gas will
resume gaseous form and exit from liquid
Gas exchange cont • Carbon dioxide is most soluble in water; oxygen 1/20 of carbon
dioxide • External respiration
– Pressure of oxygen in alveolar capillaries is low compared to in alveoli – CO2 + H2O ↔ H2CO3 (carbonic acid) ↔ HCO3
-(bicarbonate ion) + H+ (hydrogen ion)• Carbon dioxide is in 3 forms in blood
– Bicarbonate ions– Carbaminohemoglobin– Dissolved in plasma
– Partial pressure of carbon dioxide is higher in alveolar capillaries compared to alveoli
• Internal respiration – Opposite movement of external respiration
Control of respiration • Brainstem – Detects rising CO2 levels in blood –causes drop in pH (too
acidic)– Medulla oblongata
• Controls rate/rhythm of breathing by contraction of diaphragm and external intercostals
– Pons• Smooth out signal sent by medulla
• Chemoreceptors– In aortic arch and carotid bodies (branch of internal and
external) – Detect both rising CO2 levels and dropping O2 levels
• Sends appropriate signal to brainstem to increase rate of respiration