5.1 Structure and Function of the Respiratory System Flashcards
What is the largest surface area in the body that is exposed to the outer environment?
The alveoli
Alveoli diameter in micrometers
75-300
Describe six types of cells present in the alveoli-capillary unit
- Type 1/Type 2 pneumocytes
- Pericytes
- Capillary endothelium
- Fibroblasts
- Immune cells (APCs, macrophages and T cells)
What percentage of the alveoli surface area is made of type 1 vs type 2 pneumocytes?
- Type 1: 95%
- Type 2: 5%
What type of cell occupies most of the alveolar surface (in terms of cell number)?
- Type 2 pneumocytes (60%)
- Since type 1 are so flat, they make up more area despite smaller numbers
How is it that type 2 pneumocytes are a “reservoir” of cells?
Type 1 pneumocytes can be generated out of type 2 pneumocytes, enabling them to be replenished
Which cells recycle surfactant from the alveolar surface? What proportion of recycling occurs in each?
Type 2 pneumocytes: 90%
Macrophages: 10%
List five functions of pulmonary surfactant
- Reduction in surface tension
- Increase in compliance
- Stabilisation of alveolar structure
- Prevents movement of fluid into alveoli
- Activates the immune system
Recall the Law of Laplace
P = 2T/r (P: Pressure, T: Tension, r: radius)
As an alveoli decreases in size, the surfactant ____ their surface tension
Decreases
Describe the three classes of substances that make up pulmonary surfactant, and the percentage made up by each
- Phospholipids (80%)
- Neutral lipids (10%)
- Surfactant proteins (10%)
At what day of embyronic development does the respiratory system begin to develop?
28 days
Which germ layer does the pulmonary epithelium arise from?
Endoderm
Which germ layer do the muscles and connective tissue of the respiratory system arise from?
Mesoderm
At what week of embryonic development are cilia present?
Wk 10
At what week of embryonic development are mucosal glands present?
Wk 12
At what week of embryonic development is there enough surfactant to support lung function?
~Wk 35
Other than gas exchange, cell production, and surfactant production, what is the other role of pneumocytes?
Controlling fluid exchange into and out of alveoli (want to prevent oedema)
How do the pneumocytes regulate fluid levels in the alveoli of an uninjured lung? (in terms of the bloodstream, not the lymphatics)
Actively transporting sodium, and chloride ions into bloodstream, creating an osmotic gradient that causes water to follow through aquaporins
Where do alveolar macrophages reside in the respiratory system?
In the mucous layer
Briefly describe the process of alveolar fibrosis following an insult to the epithelial lining
- Insult to epithelial lining
- Detected by T2 pneumocytes
- Signal to fibroblasts, which migrate and proliferate at the site of the insult
- Over time, more fibroblasts migrate, and fibrous clot increases in size, thus decreasing the efficiency of the alveolus
Cigarette smoke leads to overactivation of the immune system. Describe to mechanisms by which this causes harm
- Alveolar wall destruction (emphysema) from overactivated proteases
- Mucus hypersecretion leads to decreased efficiency of gas exchange (caused by inflammatory response)
Is the pulmonary circulation a low-pressure system or a high-pressure system? How does this influence the thickness of pulmonary artery walls?
- Low pressure.
- Therefore, pulmonary arteries have relatively thin walls
Do arteries and veins travel together in pulmonary circulation? If not, where?
- No
- Arteries travel with air ways
- Veins travel in septa between pulmonary lobuli
How does the pulmonary circulation respond differently than the systemic circulation when it comes to hypoxia?
- In the systemic circulation, blood vessels will dilate in response to hypoxia
- In the pulmonary circulation, blood vessels will constrict in response to hypoxia, helping to match perfusion with ventilation
Where do the bronchial arteries stem from?
The aorta
Where do bronchial veins stem from?
The azygous vein, which drains into the SVC
Why is it that the airways are so good at swelling up?
The bronchial circulation provides many blood vessels in the submucosa of the medium sized airways (other vessels also supply the airways). Therefore, during the inflammatory response, a large reaction can occur
Why might you see enlarged lymph nodes in someone with heart failure?
- Heart failure
- Pulmonary oedema
- Fluid removal via capillaries and lymph nodes
- Lymphatic circulation swells
Which lymph nodes do the lymphatic vessels of the lungs drain into (directly)?
Bronchopulmonary
Describe lymph drainage of the lower lung
- Bronchopulmonary
- Tracheobronchial
- Bronchomediastinal
(all of the above are nodes)
Describe the lymph drainage of the upper lung
- Ipsilateral lymph nodes
- paratracheal lumph nodes
- left and right bronchomediastinal trunks
- Thoracic duct + RLD
What are the two classifications of lymph vessels in the lung?
- Pleural (visceral pleura)
- Interlobular
Fundamentally, what is a cough?
- Forced expiration against a closed glottis
- Upon opening, there’s an explosive release of air, which is the cough
Describe some common causes of cough
- Upper respiratory tract infections
- Chronic cough (>8 weeks) as in COPD
- Whooping cough; due to bacterial infection
- Reflux can activate sensory fibres and cough
Where are the sensory fibres responsible for the coughing reflex located (in terms of respiratory pathways)? Which nerve do they belong to?
- Pharynx
- Trachea
- Main bronchi
All belong to the vagus nerve (which is mostly sensory)
What two types of receptors are present on the sensory fibres that cause the cough reflex?
- Nociceptors (pain)
- Mechanoreceptors
What are the two types of mechanoreceptors that trigger the cough reflex? How do they differ?
Rapidly adapting receptors (RARs): send out action potentials upon receiving stimulus
Slowly adapting receptors (SARs): send out action potentials until stimulus is removed
Nerves in the respiratory epithelium are positioned to detect damage of respiratory lining. Give one example of substances they have receptors for, and explain how this substance triggers a response
- ATP
It acts as a neurotransmitter, triggering sodium influx and AP being carried to the CNS
Where do the sensory fibres of the respiratory tract end in the CNS?
In the brainstem, predominantly at the level of the nucleus of the solitary tract (nTs)
Describe the motor reflex of coughing, starting from the nucleus of the solitary tract
- Signal is carried to central pattern generator
- Impulse sent via motor neurons to respiratory muscles
- COUGH
Which muscles are involved in coughing? From what level of the spinal cord/what nerves are they innervated?
- Diaphragm (C3-C5)
- Intercostal muscles (T1-T11)
- Intrinsic laryngeal muscles (Vagus)
- Superior laryngeal muscles (Nucleus ambiguous)
- Abdominal muscles (T6-T12)
What is the role of higher brain centres in coughing?
- Voluntary cough
- Generating the urge to cough (for whatever reason)
How can coughing cause an immune response?
When activated, sensory neurons release local factors that can lead to oedema and inflammation
Sputum production during illness mech
- Inflammation of airways
- Goblet cell hypersecretion
- Sputum production
Where do the bronchial arteries arise from?
The thoracic aorta
Where do the bronchial veins arise from?
The azygous vein
