4. Respiratory System Flashcards
Functions of the Respiratory System
- Gas exchange: Oxygen (O2) & Carbon dioxide (CO2).
O2 is required for cell respiration.
CO2 is a waste product of cell respiration.
By breathing, we are able to inhale O2 and exhale CO2. - Warming or Cooling and Moistening of air.
- Removal of inhaled particles (immunity):
Removal of larger substances in nose.
Smaller substances by mucociliaryescalator.
Alveolar macrophages in alveoli. - Voice production and olfaction (smell).
Types of Respiration
- External respiration
- Internal respiration
- Cellular respiration
External Respiration
- Exchange of gases between the blood & lungs (air).‘Pulmonary capillaries’ carry blood around alveoli.
- Air is inhaled and exhaled -this is called‘ventilation’.
Internal Respiration
Exchange of gsaes between blood & cells
Cellular Respiration
Metabolic process whereby energy (ATP) is obtained by metabolising carbohydrates, fats & proteins.
Respiratory Tract Mucous Membrane
- The respiratory tract is lined with a mucous membrane. This is a ciliated epithelial membrane that contains mucous-secreting goblet cells.
- Mucus traps inhaled particlesand acts as a surfactant (lowers the surface tension of a liquid, allowing easier spreading). It also has antimicrobial properties.
- Cilia move the trapped particles towards the oesophagus where they can then be swallowed, thus protecting the lungs from inhaled pathogens. This mechanism is called the mucociliary escalator.
Nose & Nasal Cavity
- The nasal cavity is the first contact organ in the respiratory system and ‘conditions’ air.
- It is an irregular cavity, divided by a septum (cartilage). Bordered posteriorly by skull bones.
- The nasal cavity contains hairs that trap larger particles.
- Internally has 3 nasal concha (‘turbinates’) –shelves that increase surface area and trap water during exhalation’.
- Contains olfactory receptors (interpret smell).
- Internal nose lined by mucous membrane and capillaries
Nasal Cavity Functions
- Filtering air:
• Hairs (larger particles) & cilia/mucous (trap smaller particles, protect epithelium, cilia beat towards mouth).
• Nasal concha (turbinates) spin air within the nasal cavity, which filters air and encourages particles to become trapped in the mucous. - Warming air -strong vascularity of mucosa .
- Humidification-air travels over moist mucosa.
- Sneezing reflex –if case of mucosal irritation.
- Olfactory function -olfactory receptors.
Paranasal Sinuses
- The paranasal sinuses are air filled cavities within certain facial and cranial bones.
- They are lined with mucous membranes that are continuous with the nasal mucosa lining. Secretions drain into nasal cavity.
- Includes: frontal, ethmoid, sphenoid, maxillary.
Paranasal Sinuses - Functions
The sinuses perform the following functions:
- Resonance in speech.
- Lighten cranial mass.
- Nasolacrimal ducts drain tears from the eyes.
- Moisten/humidify the air.
Pharynx
- The pharynx is a straight muscular tube that connects the nose & throat.
- The pharynx is roughly 13cm long and sits anterior to the cervical spine, terminating at the larynx.
- Consists of the nasopharynx, oropharynx & laryngopharynx.
- The pharynx contains the ‘eustachian tubes’, which connect the nasopharynx to the middle ear and allow equalisation of pressure in the middle ear.
- Contains adenoids (‘nasopharyngealtonsils’).
Pharynx - Functions
- Passagewayfor air & food.
- Warmingand humidifying.
- Taste.
- Hearing.
- Equalisation of pressure in middle ear (eustachian tubes).
- Immune protection: tonsils.
- Speech: resonating chamber.
Larynx
- The larynx is also known as the voice box (Adam’s apple) and connects the laryngopharynx with the trachea.
- Consists of 9 pieces of cartilage (including the thyroid cartilage & epiglottis) and vocal cords.
- The vocal cords are composed of mucous membrane foldings stretched horizontally.
- Laryngeal muscles attach to the vocal cords and when contracted stretch them:
- Relaxed muscles = loose cords = low tone
- Contract muscles = tight cords = high tone (vibrate rapidly).
Larynx - Functions
- Production of sound (vocal cords) & speech (tongue, lips & cheeks).
- Protection–the ‘epiglottis’ closes off the trachea during swallowing and hence prevents food entering the lungs.
- Air passageway.
- Warming & humidifying.
Trachea
- The trachea (or “windpipe”)is roughly 12 cm long and is made of incomplete C-shaped rings of hyaline cartilage.
- The incomplete rings of cartilage are connected by smooth muscle, which is called “trachealis”.
- Sympathetic (‘fight or flight’) response tracheal dilation.
- Parasympathetic (‘rest & digest’) response tracheal constriction.
Trachea - Functions
- Air flow: rings keep trachea open and unobstructed.
- Mucociliary escalator: trapping inhaled particles and removing them from the respiratory tract.
- Cough Reflex.
- Warming, humidifying, filtering (it is usually warm and humid by this point).
Bronchi
- The trachea divides into left and right bronchi at the vertebral level of T5.
- The bronchi deliver air into the lungs.
- Bronchi contain cartilage rings that maintain an open airway. Bronchi are lined with ciliated epithelium.
- The right bronchi is more vertical, shorter and wider. Hence an aspirated object is more likely to enter the right lung.
- Where the trachea divide into the two bronchi, an internal ridge called the carina is formed (this is the most sensitive structure in the system and triggers cough reflex).
Bronchioles
• The bronchioles are continuations of bronchi.
• Bronchioles have no cartilage in their structure and instead contain more smooth muscle.
• The bronchioles lead directly into the alveoli, where gas exchange occurs.
Control of air-entry via:
• Sympatheticnervous system (SNS: “fight or flight”) = Bronchodilation.
• Parasympathetic nervous system(PSNS: “rest & digest”) = Bronchoconstriction.
Alveoli
• Alveoli are small hollow cavities that make up most of the lung volume.
• The bronchioles terminate into alveolar sacs.
• Alveoli are the sites of gas exchange in the lungs.
• Alveolar gas exchange is maximised by the following:
A large surface area (approximately 80m2) created by 250 million alveoli in each lung.
Alveolar walls are very thin (single-layered).
Surrounded by many blood capillaries.
Alveolar surfaces are moist(gases exchange more easily when in water).
Alveolar Cells
Type I alveolar cells:
• These are simple epithelial cells, covering 90% of the alveolar surface and are very thin to support gas exchange.
Type II alveolar cells:
• Secrete ‘alveolar fluid’ that contains ‘pulmonary surfactant’.
• Pulmonary surfactant reduces alveoli surface tension, preventing alveolar collapse.
• The fluid allows gases to diffuse through it.
Alveolar Macrophages:
• These are strategically located white blood cells (leukocytes) that engulf and destroy microbes entering the alveoli.
Pulmonary Surfactant
• Surfactant is a mixture of lipids and proteins
that forms a surface film in alveoli.
• The protein part is hydrophilic and resides in the alveolar fluid, whilst the lipid component is hydrophobic and faces the air.
• Through this structure, surfactant reduces the surface tension within the alveoli, preventing them from
collapsing and reducing the pressure required to re-inflate them.
• Surfactant is not produced until 34 weeks gestation, so consider lung development in a premature baby.
• Two thirds of the work of breathing is to overcome surface tension.
Lung Anatomy
• 2 cone shaped lungs, separated by the heart. Surfaces: • Apex (extends above clavicle!) • Base (over diaphragm). • Costal (rib) surface. • Medial surface.
Lobes:
• Right lung: 3 lobes.
• Left lung: 2 lobes (due to the heart).
Blood supply:
• From the pulmonary artery (left & right).
Pleura & Pleural Cavity
- The pleura is a serous membrane that surrounds the lungs.
- The pleura contains a visceral and parietal layer, with a ‘pleural cavity’ in between.
- The visceral & parietal pleura form a double layer separated by 5-10ml of serous fluid that prevents friction.
- The pleura adhere to the lungs so that the lungs are sucked to the pleura(‘passive dilation’) -helps expansion of the lungs.
- A pneumothorax occurs when the pleura is damaged and air enters the pleural cavity.
Muscles of Ventilation: Primary
Intercostal muscles(internal & external):
• Attached between ribs at right angles.
•Contraction pulls ribs upwards(inspiration) expanding outward & increasing size of rib cage.
Diaphragm:
• Attached to the lower ribs, sternum & lumbar spine.
•A domed muscle that separates the thoracic & abdominal cavity.
• Contraction moves the diaphragm into the abdomen and draws air into the lungs.
Muscles of Ventilation: Secondar
- These muscles are often over-recruitedin patients suffering with breathlessness (e.g. asthmatics). They can become shortened and fatigued.
- Most accessory muscles are located around the neck and chest.
- Examples of secondary muscles of ventilation include trapezius, sternocleidomastoid and the scalenes.
Ventillation
Inspiration:
• Inspiration is an active process requiring muscles.
• Negative pressure in the thoracic cavity causes air to enter lungs down a pressure gradient.
Expiration:
• Expiration is typically a passive process -muscles relax.
• This occurs through the elastic recoil of the lungs.
• Should only be active during forceful breathing.
• If elasticity is lost, for example, in pulmonary fibrosis, expiration can become active with the recruitment of internal intercostal and abdominal muscles.
Lung Volumes
- The average pair of human lungs can hold about 6 litres of air.
- However, only a small amount of this capacity is used during normal breathing.
- The ‘tidal volume’ represents the normal volume of air that enters the lungs during inspiration when no extra effort is applied.
- A normal tidal volume is about 500ml.
- Men generally have larger lung volumes. As do taller individuals, non-smokers, athletes and those living at higher altitudes.
Gases
• Inspired air contains a large quantity of nitrogen & oxygen.
• As oxygen has a strong affinity (attraction) for haemoglobin, oxygen will readily enter the blood and bind with haemoblogin molecules.
• Haemoglobin is the key component of red blood cells and transports oxygen in the blood.
• Nitrogen doesn’t bind to haemoglobin. Furthermore, nitrogen is not used or created in the body, so any nitrogen that has dissolved in the blood will
remain at the same concentration.
Gases in Blood: Oxygen
- 98.5% of oxygen in the blood is transported by Haemoglobin (Hb) in red blood cells.
- 1.5% of oxygen is dissolved in plasma (oxygen dissolves poorly in water).
- Haemoglobin changes colour depending on how much oxygen is bound to the molecule.
- Oxyhaemoglobin is when plenty of oxygen is bound to Hb. Deoxyhaemoglobinis Hb that lacks oxygen.
- Oxygen is an essential gas in the body. Cells use oxygen to create the energy that is required for various processes.
Gasses in Blood: Carbon Dioxide
Carbon dioxide diffuses into the blood from respiring cells easily. It is transported in the following ways:
• And 70% found in plasma as HCO3- (bicarbonate).
• 23% carried in RBCs (bound to haemoglobin).
• 7% dissolved in plasma(the water component of blood).
Bicarbonate Buffer Reaction
- CO2 diffuses down its concentration gradient from tissues into the blood.
- Because of the high water content of blood, CO2 combines with water to produce carbonic acid (H2CO3).
- As carbonic acid is unstable, it decomposes immediately into bicarbonate and H+ .
- Hydrogen is exhaled and excreted into urine to reduce the acidity. In addition, the bicarbonate formed is alkaline, which ‘buffers’ the acidity of blood to keep pH stable.
Respiratory System: Blood pH
- pH is the measure of acidity, alkalinity and neutrality.
- Blood pH needs to be controlled within very narrow limits.
- Low pH = elevated H+ion concentration (more acidic).
- High pH = more alkaline.
What causes a low pH (acidity) in the blood?
• rising CO2: when CO2 dissolves in the blood, it causes an increase in H+ ions and thus an increase in acidity. This leads to ‘respiratory acidosis’.
• It is not just CO2that causes acidosis; exercise produces lactic acid and fasting produces ketoacids which enter the blood. This is called ‘metabolic acidosis’.
• Ventilation helps to lower the acidity of body fluids via exhalation of CO2.
Regulating Blood pH
Increase in acidity is managed in 3 ways:
1. Buffer systems
•Temporarily bind to H+ removing them from solution (i.e. proteins, bicarbonate).
2. Increased exhalation of CO2
3. Kidney excretion of H+
•Slow mechanism.
•Kidneys can also synthesise new bicarbonate and reabsorb bicarbonate, thus influencing pH.
Cell Respiration
• Cell respiration describes the process of energy production (ATP) within cells.
• Glucose is the primary organic molecule metabolised for ATP production. Fats and proteins are also used.
Energy is produced by either:
1. Aerobic respiration(with oxygen)
38 ATP (total yield) + water + CO2.
2. Anaerobic respiration (no oxygen)
2 ATP (total yield) + lactic acid.
Ventillation Control
The control of ventilation is primarily involuntary.
• The‘respiratory centre’ is located in the brainstem(medulla oblongata & pons). This receives inputs from different parts of the body.
• Central chemoreceptors found in the medulla oblongata measure CO2 and acidity (H+concentration).
•Peripheral chemoreceptors in the aorta & carotid artery measure CO2, O2 & acidity levels.
•Stretch receptors in the walls of the bronchi and bronchioles detect over-inflation.
•If receptors detect high arterial CO2, this triggers hyperventilation (to excrete/exhale excess CO2).
Smoking
•
Smoking cigarettes significant increases the risk of lung diseases.
•Cigarettes contain substances known as ‘carcinogens’. Carcinogens are substances that can cause cancer.
•Smoking also damages the delicate ‘cilia’(hair cells) that line the respiratory tract. Normally these cilia would sweep trapped particles out of the lungs.
•Following cilia damage, mucous and trapped particles build up in the lungs, causing a ‘smokers cough’, whilst also increasing the risk ofpulmonary infections, bronchitis and emphysema.
Research has shown that 15 cigarettes smoked = 1 genetic mutation
Respiratory Common Signs & Symptoms
Common Signs & Symptoms • Congestion • Runny nose • Sneezing • Cough • Sputum • Wheezing • Chest Pain • Breathlessness • ‘Dyspnoea’ (difficulty breathing) • ‘Orthopnoea’: breathless whenlying down. • Hyperventilation: over-breathing. • Cyanosis 1. A peripheral arterial disease (i.e. blockage). 2. Lung disease (poor gas exchange). 3. Heart failure (inability to deliver oxygenated blood)
Sputum Differential: Mucoid
Clear, grey/white
Causes: Asthma & bronchitis
Sputum Differential: Purulent
Thick, yellow/green (containing pus)
Infections (bronchitis, pneumonia
Sputum Differential: Serous
Clear, frothy, pink
Pulmonary oedema
Sputum Differential: Blood
Blood
Lung cancer, TB, pulmonary embolism, clotting disorders
Respiratory Investigations
Medical investigations: • Blood test (i.e. white blood cell count, inflammatory markers). • Biochemistry tests. • Sputum analysis & microbiology. • Imaging –chest x-ray, MRI, CT.
Physical examination:
• Percussion (‘tapping to the thoracic cage’) & auscultation.
• Respiratory function tests –measure inspiration/expiration of lungs & gaseous exchange in the lungs / circulation.
