Lecture 4: Respiratory System

Biomedicine

Biomedicine

Human Sciences - The study of biological and physiological processes in humans, particularly in relation to health and disease.

Respiratory System

The organ system responsible for gas exchange, including structures such as the nose, trachea, bronchi, and lungs.

Gas Exchange

The process of oxygen (O2) entering the blood and carbon dioxide (CO2) being expelled, essential for cellular respiration.

Mucociliary Escalator

A defense mechanism in the respiratory tract that uses cilia and mucus to trap and remove inhaled particles and pathogens.

Alveoli

small air sacs in the lungs where gas exchange occurs. They have a large surface area, thin walls, are surrounded by capillaries, and are moist, all of which maximize oxygen and carbon dioxide transfer efficiency.

External Respiration

The exchange of gases between the lungs and the blood, primarily occurring in the alveoli.

Internal Respiration

The exchange of gases between the blood and body cells, crucial for cellular metabolism.

Cellular Respiration

The metabolic process by which cells convert glucose and oxygen into energy (ATP), producing carbon dioxide as a byproduct.

Pulmonary Surfactant

a mixture of lipids and proteins that reduces surface tension in the alveoli, preventing their collapse and making it easier to re-inflate them during breathing. It is not produced until 24-28 weeks of gestation.

COPD (Chronic Obstructive Pulmonary Disease)

a progressive lung condition that causes irreversible airflow limitation due to damage to the airways and lung tissue, often caused by smoking or exposure to irritants. It includes emphysema and chronic bronchitis. Symptoms include chronic cough, sputum, wheezing, shortness of breath, and frequent infections. Complications may include respiratory failure, hypoxia, and pulmonary hypertension. Treatment focuses on smoking cessation, bronchodilators, corticosteroids, and oxygen therapy.

Asthma

a chronic airway disease causing reversible narrowing of the bronchi and bronchioles due to inflammation, mucus buildup, and muscle tightening, making exhaling difficult. Common in children and the elderly, it presents with breathlessness, chest tightness, wheezing, and nocturnal coughing. Diagnosis involves symptoms and spirometry, with treatment using bronchodilators and corticosteroids.

Pneumonia

a bacterial lung infection that affects the alveoli and bronchioles, causing inflammation and fluid buildup. Symptoms include cough with pus or blood, fever, breathlessness, and fatigue. It is most common in infants, the elderly, and those with weakened immune systems. Signs include rapid breathing and crackling sounds in the lungs.

Rhinitis

inflammation of the nasal lining, causing swelling, increased mucus, and symptoms like a runny or stuffy nose, sneezing, and reduced smell. It can result from infections, allergies (e.g., pollen), or non-allergic triggers like pollution or stress. Treatment includes antihistamines, decongestants, and steroid sprays.

Bronchitis

inflammation of the bronchial tubes, which can be acute or chronic. It is often caused by viral or bacterial infections or exposure to environmental irritants. The condition leads to excessive mucus, coughing, breathing difficulties, and symptoms like fever, sore throat, shortness of breath, and fatigue. Severe cases may involve rapid breathing, crackling sounds, or bluish skin. Treatment typically includes antibiotics for bacterial infections.

Ventilation

the process of moving oxygen and carbon dioxide to and from the lungs, typically involving 12-15 breaths per minute with inhalation lasting about two seconds and exhalation around three seconds. It includes abdominal (diaphragmatic) breathing and upper rib breathing.

Cilia

Microscopic hair-like structures in the respiratory tract that help move mucus and trapped particles out of the lungs.

Eustachian Tubes

Tubes that connect the nasopharynx to the middle ear, helping to equalize pressure in the ear.

Alveolar Macrophages

Immune cells located in the alveoli that engulf and destroy pathogens and debris, playing a key role in lung immunity.

Blood pH Regulation

The process of maintaining stable blood pH levels, influenced by carbon dioxide levels and bicarbonate buffering.

Sputum

Mucus that is coughed up from the respiratory tract, which can provide diagnostic information about respiratory conditions.

respiratory system functions

gas exchange, where oxygen (O2) is absorbed for cell respiration and carbon dioxide (CO2) is expelled as a waste product; warming, cooling, and moistening the air we breathe; removing inhaled particles through the nose, mucociliary escalator, and alveolar macrophages in the alveoli; and enabling voice production and the sense of smell.

Respiratory System Structures

Air flows through the nose, paranasal sinuses, pharynx (throat), larynx (voice box), trachea (windpipe), bronchi (left and right), bronchioles, and alveoli (air sacs)

Mucous Membrane

lines the respiratory tract, providing a barrier and facilitating the trapping of pathogens and debris. contains cilia and mucus-secreting cells.

mucociliary escalator

mechanism that helps clear mucus and debris from the airways. Mucus traps particles and microbes, while cilia move it out of the lungs to protect against infection.

Nose and Nasal Cavity

first part of the respiratory system, conditioning the air. It contains hairs to trap particles, nasal concha to increase surface area, and olfactory receptors for smell. The internal lining includes mucous membranes and capillaries.

Nasal Cavity Functions

filters air using hairs, cilia, and mucus to trap particles. Nasal concha spin the air to enhance filtration. It also warms and humidifies the air, with strong blood flow in the mucosa. The nose has a sneezing reflex for irritation and contains olfactory receptors for smell.

Paranasal Sinuses

air-filled cavities in facial and cranial bones, lined with mucous membranes connected to the nasal cavity. They include the frontal, ethmoid, sphenoid, and maxillary sinuses. Their functions include aiding in speech resonance, lightening the cranial mass, draining tears, and humidifying the air.

Pharynx

a 13cm muscular tube connecting the nose and throat, composed of the nasopharynx, oropharynx, and laryngopharynx. It contains the eustachian tubes that link the nasopharynx to the middle ear.

pharynx functions

air and food passage, warming and humidifying, taste, hearing, pressure equalisation in the middle ear, immune protection (tonsils), and speech resonance.

Larynx

also known as voice box, connects the laryngopharynx to the trachea. It contains nine cartilage pieces and vocal cords, which are controlled by laryngeal muscles. Relaxed muscles create low tone, while contracted muscles produce high tone through rapid vibrations.

larynx functions

produces sound through the vocal cords and helps with speech. It also prevents food from entering the lungs by closing the trachea during swallowing. Additionally, it serves as an air passage and helps warm and humidify the air.

Trachea

also known as windpipe, is roughly 12cm long and is made of incomplete C-shaped rings of hyaline cartilage. supported by incomplete cartilage rings connected by smooth muscle called trachealis. The sympathetic response causes tracheal dilation, while the parasympathetic response leads to tracheal constriction.

trachea functions

ensures unobstructed air flow and helps trap and remove inhaled particles through the mucociliary escalator. It also plays a role in the cough reflex and in warming, humidifying, and filtering the air.

Coughing Reflex

A protective mechanism that expels air rapidly from the lungs to clear the airways of irritants, mucus, or foreign particles. It is triggered by stimulation of nerve signals.

Bronchi

the two tubes that branch from the trachea to deliver air to the lungs. They are kept open by cartilage and lined with cilia. The right bronchus is wider and more vertical than the left, and the carina is a sensitive area that triggers the cough reflex.

Bronchioles

small airways that branch from the bronchi and lead to the alveoli for gas exchange. They have smooth muscle instead of cartilage and control air entry through the sympathetic and parasympathetic nervous systems.

Alveolar Gas Exchange

oxygen diffuses from the air into the blood, oxygenating it, while carbon dioxide moves from the blood into the alveoli to be exhaled. This gas exchange occurs through diffusion between the alveoli and surrounding capillaries.

Type I alveolar cells

simple epithelial cells, covering 90% of the alveolar surface and are very thin to support gas exchange.

Type II alveolar cells

secrete fluid containing pulmonary surfactant, which reduces surface tension to prevent alveolar collapse and enables gas diffusion.

Lung Anatomy

two cone-shaped organs, separated by the heart, with surfaces including the apex (above the clavicle), base (over the diaphragm), costal (rib) surface, and medial surface. The right lung has three lobes, while the left lung has two lobes due to the heart. Blood supply comes from the left and right pulmonary arteries.

Pleura and Pleural Cavity

serous membranes surrounding the lungs, consisting of a visceral and parietal layer with a pleural cavity in between. The cavity contains 5-10 ml of serous fluid, preventing friction and aiding lung expansion. A pneumothorax occurs when air enters the pleural cavity due to damage to the pleura.

Intercostal muscles

located between the ribs, with internal and external types. When contracted, they pull the ribs upward, expanding the rib cage to assist in inhalation.

Diaphragm

domed muscle attached to the lower ribs, sternum, and lumbar spine, separating the thoracic and abdominal cavities. Its contraction moves it downward, drawing air into the lungs.

Secondary/Accessory muscles

assist in breathing, especially during breathlessness. They are located around the neck and chest, and include muscles like the trapezius, sternocleidomastoid, and scalenes. These muscles can become fatigued when overused, such as in conditions like asthma.

Inhalation

an active process that requires muscle contraction. Negative pressure in the thoracic cavity causes air to enter the lungs down a pressure gradient.

Exhalation

a passive process where muscles relax, and air is expelled through the lungs' elastic recoil. It becomes active during forceful breathing or if lung elasticity is reduced.

Lung Volumes

Ir can hold about six liters of air, but only a small amount is used during normal breathing. Tidal volume is the amount of air inhaled during normal breathing, typically about 500ml. It tends to be larger in men, taller individuals, non-smokers, athletes, and those living at higher altitudes.

Gases

Inspired air is mostly nitrogen and oxygen. Oxygen binds readily to hemoglobin in red blood cells for transport, while nitrogen remains unchanged and is not utilized by the body.

Gases in Blood: Oxygen

it’s primarily transported by hemoglobin (98.5%), with a small amount (1.5%) dissolved in plasma. Hemoglobin changes color based on oxygen levels, forming oxyhemoglobin when oxygen-rich and deoxyhemoglobin when oxygen is absent. Oxygen is vital for energy production in cells.

Gases in Blood: Carbon Dioxide

It moves from cells into the blood and is mainly transported as bicarbonate (70%), with smaller amounts bound to hemoglobin (23%) and dissolved in plasma (7%). It reacts with water to form carbonic acid, which breaks into bicarbonate and hydrogen ions, helping maintain stable blood pH.

Blood pH

measures how acidic or alkaline the blood is and must stay within a narrow range. A low pH indicates higher acidity, which can result from increased carbon dioxide, lactic acid from exercise, or ketoacids from fasting.

Blood pH regulation

The body regulates blood pH by using buffer systems to neutralize acidity, exhaling carbon dioxide to reduce acid levels, and adjusting hydrogen ion and bicarbonate levels through the kidneys. This process ensures that blood pH remains within a narrow range, crucial for proper physiological function.

Cell Respiration

this is how cells make energy (ATP), mainly from glucose. There is aerobic and anaerobic respiration. Oxygen supply depends on breathing and blood circulation.

Aerobic respiration

the process of producing cellular energy in the presence of oxygen, resulting in the complete oxidation of glucose to carbon dioxide and water. Generates 38 ATP.

Anaerobic respiration

is the process of producing energy without oxygen, resulting in the partial oxidation of glucose and the production of byproducts like lactic acid or ethanol. It generates 2 ATP and is used by muscles during intense exercise.

Ventilation Control

it’s controlled by the brainstem, which responds to signals from the body. It uses receptors to measure CO2, oxygen, and acidity levels in the blood and airways. If CO2 levels are too high, it triggers faster breathing to remove the excess.

Smoking

harms the lungs by introducing cancer-causing substances and damaging the cilia, which normally clear out particles. This leads to mucus buildup, causing a cough and increasing the risk of infections, bronchitis, and emphysema. It also causes genetic mutations, with 15 cigarettes leading to one mutation.

Cyanosis

condition where there is inadequate oxygenated blood in an area, often caused by peripheral arterial disease (blockage), lung disease (poor gas exchange), or heart failure (inability to deliver oxygenated blood).

respiratory investigations: common signs and symptoms

include congestion, runny nose, sneezing, coughing, sputum, wheezing, chest pain, and breathlessness. Other signs include difficulty breathing (dyspnoea), breathlessness when lying down (orthopnoea), over-breathing (hyperventilation), and cyanosis (bluish skin due to low oxygen). These symptoms can indicate various lung or airway issues.

Mucoid

this sputum is clear, grey or white and the possible causes are asthma or bronchitis

Purulent

this sputum is thick, yellow or green, indicating bacterial infection.

Serous

This sputum is clear, frothy and pink and a possibly cause is Pulmonary oedema.

Blood

This sputum is caused from lung cancer, TB, pulmonary embolism and clotting disorders

Investigations

Medical ones for respiratory conditions include blood tests (for white blood cell count and inflammatory markers), biochemistry tests, sputum analysis, and imaging (such as chest X-rays, MRI, and CT scans). Physical examinations involve percussion (tapping on the chest) and auscultation (listening to lung sounds), as well as respiratory function tests to assess lung capacity and gas exchange.

Respiratory Examination

These consist of finger clubbing, x-ray, percussion, auscultation, chest deformity

Common cold

a viral infection of the upper respiratory tract, often affecting those with lower immunity. Symptoms include a runny nose, sneezing, sore throat, and mild fever, lasting 2-7 days. Treatment focuses on relieving symptoms with painkillers and decongestants.

Influenza (Flu)

acute respiratory illness caused by flu viruses, with symptoms like fever, muscle pain, sore throat, and fatigue. It spreads quickly, often mutates, and can lead to complications like secondary infections or chronic fatigue. Treatment includes antiviral drugs and flu vaccines for vulnerable groups.

Sinusitis

Inflammation of the lining of one or more sinuses, often following a respiratory infection or tooth infection. It can be acute or chronic and may occur with immune compromise. Symptoms include sinus pain, congestion, headaches, fever, nasal drip, and a reduced sense of smell. Treatment is Painkillers and decongestants

Nasal Polyps

soft, non-cancerous growths in the nasal lining caused by chronic inflammation from infections or allergies. Symptoms include a runny or stuffy nose, difficulty breathing, reduced sense of smell, sinus infections, and snoring. Treatment options include nasal steroids, antihistamines, antifungals, or surgery.

Tonsillitis

the inflammation of the tonsils, often caused by viral or bacterial infections. It commonly affects children and young adults and presents with a sore throat, fever, coughing, and red, swollen tonsils. Complications may include ear infections or abscesses. Treatment includes painkillers, antibiotics, or surgery in severe cases.

Quinsy (peritonsillar abscess)

an abscess around the tonsils caused by tonsillitis, common in adolescents and young adults. Symptoms include severe throat pain, difficulty swallowing, earache, fever, and swollen lymph nodes. Treatment involves antibiotics, draining the abscess, or surgery.

Pharyngitis

inflammation of the pharynx's mucous membrane, often linked to colds or tonsillitis and accompanied by swollen lymph nodes. Treatment includes painkillers for viral cases and antibiotics for bacterial infections.

Laryngitis

inflammation of the larynx, which can be acute (caused by infections) or chronic (from overuse, irritants, or acid reflux). Symptoms include hoarseness, weak voice, sore or dry throat, dry cough, and breathing difficulties in children. Treatment includes avoiding irritants, maintaining hygiene, and using antibiotics when necessary.

Extrinsic (or atopic) asthma

Affecting children typically, immunologically mediated with an increase in IgE antibodies. Brought on by exposure to allergens e.g., pollen, dust, animal dander.

Intrinsic asthma

A bronchial reaction that is not due to antigen-antibody stimulation. Adult onset typically. Common triggers include anxiety, chemicals, exercise, cold air, drugs (NSAIDs, beta blockers), stress, dust, etc.

Asthma Attack

a potentially life-threatening event marked by difficulty speaking, rapid breathing, and severe breathlessness. The patient should sit upright, stay calm, and use a blue inhaler every 30–60 seconds (up to 10 puffs). Call an ambulance if symptoms persist or worsen.

Leukotrienes

key chemical inflammatory mediators in asthma. They are bronchoconstrictors.

Pulmonary Fibrosis

a condition where scar tissue replaces the lining of the lungs, making it harder to breathe. It can be caused by smoking, certain diseases, or unknown factors. Symptoms include shortness of breath, chronic cough, fatigue, and weight loss. There is no effective treatment currently.

Obstructive Sleep Apnoea

a condition where the upper airway repeatedly collapses during sleep, causing interrupted breathing. It is more common in obese individuals, men, middle-aged people, smokers, and those who use alcohol or sedatives. Symptoms include loud snoring, daytime sleepiness, morning headaches, and nocturnal choking. Treatment includes CPAP therapy and lifestyle changes.

Pneumothorax

the accumulation of air in the pleural cavity, causing part or all of the lung to collapse. It can be caused by trauma (e.g., rib fracture) or spontaneously due to conditions like tuberculosis or emphysema. Symptoms include shortness of breath, sharp chest pain, and cyanosis. Treatment often involves a chest drain to remove the air and repair the pleura.

Pleurisy

inflammation of the pleura, often caused by infection or tumors. It leads to sharp chest pain worsened by breathing, coughing, or movement, along with shortness of breath and a dry cough. A friction rub may be heard on auscultation.

Pulmonary Embolism

a blockage in the pulmonary arteries, often caused by a blood clot traveling from a deep vein (DVT). Symptoms include shortness of breath, chest pain, coughing (sometimes with blood), and calf pain. It is a medical emergency that can lead to heart failure or cardiac arrest. Treatment includes anticoagulants and oxygen.

Cystic Fibrosis

a genetic disease affecting chloride channels, leading to thick mucus that clogs the lungs and digestive organs. It causes persistent cough, lung infections, malnutrition, and pancreatic enzyme insufficiency. Treatment includes antibiotics, physiotherapy, and medications to clear mucus.