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what is the respiratory tract
pathway through which gases enter and exit the lungs
what does the respiratory tract consist of
mouth/ nose → pharnyx → larnyx → trachea → bronchi → alverolar sacs
mouth/ nasal cavity
opening of the respiratory tract
pharynx
shared between digestive and respiratory system
located behind mouth
larynx
vocal cords
underneath pharnyx
what is the trachea surrounded by
surrounded by rings of cartilage that make it rigid and prevent its collapse.
rigidity is termed airway patency
trachea vs esophagus difference
trachea can not collapse
esophagus collapses when not in use
apnea
cessation of breathing
lack of open airway
when does apnea usually happen
generally occurs when the upper airway muscles surrounding the trachea are relaxed during sleep.
These muscles, when active, help to “pull on” the trachea keeping it open (patent) and preventing collapse.
apnea is often causesd by
obesity
obstructive sleep apnea
When the upper airway muscles relax, the excess weight in the throat and neck push on the trachea and cause it to collapse
90% of sleep apnea cases
central sleep apnea
abnormalities in the respiratory control centres in the brain
other 10% of sleep apnea cases
glottis
The opening of the trachea
epiglottis
flap of tissue acts as a barrier to prevent ingested food and drink from entering the trachea rather than the glottis
how is glottis controlled
controlled by a laryngeal branch of the vagus nerve. The epiglottis covers the glottis during the swallowing reflex.
branching of trachea
form two primary bronchi
they branch into secondary bronchi, tertiary
bronchi and so on - normally there are between twenty to twenty-five orders of bronchi branching
All of these orders of bronchi end in
what are called terminal bronchi
which have little offshoots called respiratory bronchioles that end in
alveolar sacs.
humans breathe as a reponse to what
contraction of the diaphragm (the major respiratory muscle).
contracting of the diaphram
diaphragm contracts and moves downward (towards the abdomen).
this causes the chest and the lungs to expand essentially “sucking” air into the lungs through the mouth and nostrils.
how is the diaphram controlled
controlled by the phrenic nerve
fires during inspritation
location of phrenic nerve
the phrenic nerve leaves the spinal cord in the region of the neck. It then travels downward through the body cavity to innervate the diaphragm which sits at the border of the chest and abdomen.
A beneficial consequence of this is that a relatively high spinal injury will not prevent breathing as long as the injury is below the location that the phrenic nerve comes off the spinal cord
Inspiration
brings oxygen into lungs
Expiration
expels oxygen from lungs
How does gas exchange occur in the lungs?
Blood picks up oxygen from lung gas and releases CO₂ into the lung gas, which is expelled during exhalation.
How does gas exchange occur in tissues?
Blood delivers oxygen to metabolically active tissues and picks up CO₂, a metabolic waste product.
So, how do we transport O2 from the lungs to the tissues and how do we transport CO2 from the tissues to the lungs?
Haemoglobin
Where is haemoglobin found?
Haemoglobin is packaged within red blood cells (RBCs)
What is the structure of haemoglobin?
Haemoglobin consists of 4 globin subunits: 2 alpha and 2 beta subunits.
What is the role of the heme group in haemoglobin?
Each subunit contains a heme group with an iron (Fe) molecule at its center, where oxygen binds.
hemoglobin role in binding co
Carbon monoxide (CO) binds to haemoglobin at the same site that oxygen binds.
oxygen vs co binding hemoglobin
oxygen binds relatively “loosely”.
Oxygen goes on and comes off of haemoglobin relatively easily
Carbon monoxide binds to haemoglobin and it doesn’t come off (at least not for several days and only then if you are still alive). This is why CO is so dangerous
Carbon Monoxide Poisoning
CO binds to haemoglobin at the same site that oxygen does but it doesn’t come off. If CO is bound to haemoglobin, then oxygen cannot bind and we cannot get oxygen from the lungs to the tissues.
What are pulmonary function tests used for?
Pulmonary function tests measure lung volumes and help diagnose lung disorders.
What are the two main types of lung diseases?
restrictive or obstructive.
restrictive pulmonary disease
interferes with lung expansion,
affects inspiration,
may be caused by damage to the chest wall, the lungs or the pleura.
harder to exhale
Examples of restrictive pulmonary diseases
include pulmonary edema, - expansion of the alveoli is inhibited by fluid in the lungs.
Pulmonary fibrosis and asbestosis are also restrictive diseases.
obstructive [ulmonary disease
hinder expiration.
Since air does not leave the lungs efficiently, the lungs over-inflate.
harder to inhale
examples of obstructive disorders.
Diseases that damage the alveoli, such as asthma or emphysema
How is asthma classified?
Asthma is a heterogeneous disease,
classified as
allergic vs. non-allergic
adult-onset vs. child-onset.
based on the type of immune cells that mediate or trigger various pathologies
What are the three major pathologies of asthma?
Inflammation and swelling of the airways
Excessive mucus production
Reduction in airway diameter (caused by other 2)
major symptoms of asthma
wheezing, shortness of breth, cough, chest tightness, airflow obstruction
COPD
Chronic obstructive pulmonary diseases (COPD)
What two diseases make up COPD?
Chronic bronchitis and emphysema.
What is chronic bronchitis?
Bronchitis is a disease in which there is inflammation and narrowing of
the airways. This increases the resistance to airflow and makes it harder to breathe out (exhale).
Emphysema
a disease in which there is breakdown of the alveolar walls. This reduces the elastic recoil of the lungs when they return to a deflated state from an inflated state. This also reduces airflow
during exhalation.
how is copd defined
defined by airflow obstruction, chronic respiratory symptoms and a risk factor
such as smoking or exposure to pollution
how is copd diagnosed
Clinically, COPD is the diagnosis as it is hard to distinguish between the effects of chronic bronchitis
and emphysema. Emphysema can only be confirmed upon autopsy
What is the most common respiratory condition?
COPD is the most common respiratory affliction.
Pulmonary Fibrosis
a Restrictive Lung Disease
Pulmonary fibrosis is a condition in which the lung tissue becomes damaged and scarred.
This makes it stiffer and harder to expand.
This makes it harder to inhale and get air into the lungs.
Idiopathic pulmonary fibrosis (IPF)
is a form of interstitial (extracellular) fibrosis that develops in the absence of a clear precipitating factor. It is not curable.
The deposition of fibrous material within the alveoli increases the diffusion barrier for oxygen to move from the lung gas into the blood and for CO2 to move from the blood into the lung gas.
What type of virus is COVID-19? and what system does it infect
COVID-19 is a SARS-like coronavirus that infects the respiratory system.
What are the primary cells infected by COVID-19?
Pneumocytes (alveolar wall cells)
Bronchial epithelial cells (airway walls)
Capillary endothelial cells (pulmonary capillaries)
How does COVID-19 enter host cells?
The virus uses its spike protein to bind to the ACE2 receptor, allowing entry into cells.
What happens when COVID-19 infects bronchial epithelial cells?
It triggers inflammation, leading to tracheal narrowing and bronchitis, causing obstructive lung disease.
harder to exhale
What happens when COVID-19 infects alveolar cells?
The immune response causes fibrosis (scar tissue formation), leading to restrictive lung disease.
intubate
insert a tube into the trachea to allow for artificial ventilation
decision to intubate is based on a
number of factors
Refractory hypoxemia
Hypercapnia
Hemodynamic instability
Refractory hypoxemia
low level of blood oxygenation despite the inspired oxygen level being sufficient to, lead to a normal level of oxygenation.
Hypercapnia
in this case refers to an increase in the partial pressure of carbon dioxide
(PCO2) in the arterial blood. Since CO2 in an aqueous solution is an acid,
increased CO2 levels lead to a decrease in pH in the blood (acisiosis)
Hemodynamic instability
refers to unstable or low blood pressure.
Why was prone positioning used for ventilated COVID-19 patients?
Lying on the front (prone) improved lung aeration in arease that were not ventilated, allowing for better gas exchange compared to lying on the back (supine).
What is long COVID?
The persistence of symptoms after clearing the infection, possibly due to immune dysfunction or autoimmune responses.
What are potential causes of long COVID?
Immune system dysfunction
Inappropriate autoimmune responses
In some cases, prolonged virus presence in the body
What is the general definition of sleep?
Sleep is a cyclically occurring state of decreased motor activity and perception, occurring in various stages where neurons range from very quiescent to extremely active.
What are some possible purposes of sleep?
Brain maturation during development
Strengthening synaptic connections
Enhancing the immune system
How can sleep stages be identified?
Sleep stages can be determined using EEG activity (electroencephalography).
What are the two main types of sleep?
Slow-Wave Sleep (SWS) – four stages of progressively deeper sleep
Rapid Eye Movement (REM) Sleep – associated with dreaming and brain activity
How does the sleep cycle change over the course of the night?
As sleep progresses, we spend more time in REM sleep and less time in SWS, particularly in stages 1 and 2.
What are the characteristics of slow-wave sleep (SWS)?
Low-frequency EEG waves
Decreased muscle tone
Mostly decreased brain activity
Increased parasympathetic activity
Some logical dreams and possible snoring
What are the characteristics of REM sleep?
High brain activity
Muscle atonia (paralysis)
Most dreams occur here
Rapid eye movements
What is narcolepsy?
A neurological disorder where REM sleep intrudes into wakefulness.
What are the four key symptoms of narcolepsy?
Excessive daytime sleepiness
Cataplexy – sudden muscle weakness triggered by strong emotions
Sleep paralysis – temporary inability to move when falling asleep or waking up
Hypnagogic hallucinations – vivid, dream-like images at sleep onset
Obstructive Sleep Apnea Case Study - Key physiological responses include:
Reduced rib cage movement due to airway obstruction.
Declining blood oxygen levels as breathing stops.
Temporary airway opening, allowing deep breaths and oxygen recovery.
Heart rate and blood pressure spikes, stressing the cardiovascular system and increasing the risk of heart attacks and strokes.
EEG (brain activity), rib cage movement, and blood oxygen levels can help diagnose sleep apnea episodes.
Partial Paralysis of the Diaphragm Case Study - key findings
While awake, she breathes relatively normally (using her other msucels intercostal and abdominal muscles), maintaining normal blood oxygen levels.
During slow-wave sleep, breathing effort decreases slightly, but oxygen levels remain stable.
In REM sleep, postural muscle paralysis (a normal REM phenomenon) affects the intercostal muscles, drastically reducing rib cage movement. Since her diaphragm is impaired, she relies only on abdominal muscles, leading to decreased airflow and lower blood oxygen levels.
Higher brain centres
are not critical for breathing although they can/do have influence over breathing
during wakefulness that isn’t really noticed until sleep occurs.
corticospinal tract
the connection between the cerebral
cortex and the brainstem is called the corticospinal tract. The lack of voluntary control of breathing
during sleep can lead to some sleep-related breathing disorders.
Ondine's Curse
refers to a failure of automatic breathing when asleep. When awake we have some conscious influence over our breathing even though breathing is mostly an automatic process controlled by the brainstem
Ondine’s Curse Case Study
key finidnsg s
Blood-gas levels indicate respiratory failure (low oxygen, high carbon dioxide, acidic pH).
Chest X-ray shows cardiomegaly, high blood pressure, and fluid in the lungs.
ECG suggests coronary ischemia, a potential heart attack risk.
She enters a coma, requires mechanical ventilation, and is later discharged. However, she is readmitted months later with the same symptoms. Tests confirm Ondine’s Curse, a disorder where automatic breathing fails during sleep.
Her treatment requires nighttime mechanical ventilation to ensure breathing while asleep.
What enzyme catalyzes the CO₂ hydration-dehydration reaction?
Carbonic anhydrase (CA).
What is the chemical reaction for CO₂ hydration in an aqueous solution?
CO₂ + H₂O ⇌ H₂CO₃ ⇌ HCO₃⁻ + H⁺
How does CO₂ function as an acid in an aqueous solution?
CO₂ dissolves in water to form carbonic acid (H₂CO₃), which dissociates into HCO₃⁻ and H⁺, increasing acidity (lowering pH).
What happens when CO₂ is added to a system?
The reaction shifts toward producing HCO₃⁻ and H⁺, leading to a decrease in pH.
What happens when CO₂ is removed from a system?
The reaction shifts toward producing more CO₂ by combining HCO₃⁻ and H⁺, increasing pH.
Why does an increase in CO₂ lead to a decrease in pH?
Higher CO₂ levels increase H⁺ concentration, which lowers pH.
What physiological processes involve the CO₂ hydration-dehydration reaction?
CO₂ sensing in the brain, gas transport in red blood cells, HCl secretion in the stomach, and acid-base balance in the kidneys.
What role does HCO₃⁻ (bicarbonate) play at physiological pH levels?
It acts as a buffer, helping to regulate pH.
