Chapter 21 – The Respiratory System

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