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Medical Studies 1 > 5.1 Structure and Function of the Respiratory System > Flashcards

5.1 Structure and Function of the Respiratory System Flashcards

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USMLE® Step 1 flashcards
1
Q

What is the largest surface area in the body that is exposed to the outer environment?

A

The alveoli

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2
Q

Alveoli diameter in micrometers

A

75-300

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3
Q

Describe six types of cells present in the alveoli-capillary unit

A
  • Type 1/Type 2 pneumocytes
  • Pericytes
  • Capillary endothelium
  • Fibroblasts
  • Immune cells (APCs, macrophages and T cells)
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4
Q

What percentage of the alveoli surface area is made of type 1 vs type 2 pneumocytes?

A
  • Type 1: 95%
  • Type 2: 5%
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5
Q

What type of cell occupies most of the alveolar surface (in terms of cell number)?

A
  • Type 2 pneumocytes (60%)
  • Since type 1 are so flat, they make up more area despite smaller numbers
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6
Q

How is it that type 2 pneumocytes are a “reservoir” of cells?

A

Type 1 pneumocytes can be generated out of type 2 pneumocytes, enabling them to be replenished

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7
Q

Which cells recycle surfactant from the alveolar surface? What proportion of recycling occurs in each?

A

Type 2 pneumocytes: 90%
Macrophages: 10%

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8
Q

List five functions of pulmonary surfactant

A
  • Reduction in surface tension
  • Increase in compliance
  • Stabilisation of alveolar structure
  • Prevents movement of fluid into alveoli
  • Activates the immune system
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9
Q

Recall the Law of Laplace

A

P = 2T/r (P: Pressure, T: Tension, r: radius)

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10
Q

As an alveoli decreases in size, the surfactant ____ their surface tension

A

Decreases

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11
Q

Describe the three classes of substances that make up pulmonary surfactant, and the percentage made up by each

A
  • Phospholipids (80%)
  • Neutral lipids (10%)
  • Surfactant proteins (10%)
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12
Q

At what day of embyronic development does the respiratory system begin to develop?

A

28 days

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13
Q

Which germ layer does the pulmonary epithelium arise from?

A

Endoderm

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14
Q

Which germ layer do the muscles and connective tissue of the respiratory system arise from?

A

Mesoderm

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15
Q

At what week of embryonic development are cilia present?

A

Wk 10

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16
Q

At what week of embryonic development are mucosal glands present?

A

Wk 12

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17
Q

At what week of embryonic development is there enough surfactant to support lung function?

A

~Wk 35

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18
Q

Other than gas exchange, cell production, and surfactant production, what is the other role of pneumocytes?

A

Controlling fluid exchange into and out of alveoli (want to prevent oedema)

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19
Q

How do the pneumocytes regulate fluid levels in the alveoli of an uninjured lung? (in terms of the bloodstream, not the lymphatics)

A

Actively transporting sodium, and chloride ions into bloodstream, creating an osmotic gradient that causes water to follow through aquaporins

20
Q

Where do alveolar macrophages reside in the respiratory system?

A

In the mucous layer

21
Q

Briefly describe the process of alveolar fibrosis following an insult to the epithelial lining

A
  • 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
22
Q

Cigarette smoke leads to overactivation of the immune system. Describe to mechanisms by which this causes harm

A
  1. Alveolar wall destruction (emphysema) from overactivated proteases
  2. Mucus hypersecretion leads to decreased efficiency of gas exchange (caused by inflammatory response)
23
Q

Is the pulmonary circulation a low-pressure system or a high-pressure system? How does this influence the thickness of pulmonary artery walls?

A
  • Low pressure.
  • Therefore, pulmonary arteries have relatively thin walls
24
Q

Do arteries and veins travel together in pulmonary circulation? If not, where?

A
  • No
  • Arteries travel with air ways
  • Veins travel in septa between pulmonary lobuli
25
Q

How does the pulmonary circulation respond differently than the systemic circulation when it comes to hypoxia?

A
  • 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
26
Q

Where do the bronchial arteries stem from?

A

The aorta

27
Q

Where do bronchial veins stem from?

A

The azygous vein, which drains into the SVC

28
Q

Why is it that the airways are so good at swelling up?

A

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

29
Q

Why might you see enlarged lymph nodes in someone with heart failure?

A
  • Heart failure
  • Pulmonary oedema
  • Fluid removal via capillaries and lymph nodes
  • Lymphatic circulation swells
30
Q

Which lymph nodes do the lymphatic vessels of the lungs drain into (directly)?

A

Bronchopulmonary

31
Q

Describe lymph drainage of the lower lung

A
  1. Bronchopulmonary
  2. Tracheobronchial
  3. Bronchomediastinal

(all of the above are nodes)

32
Q

Describe the lymph drainage of the upper lung

A
  • Ipsilateral lymph nodes
  • paratracheal lumph nodes
  • left and right bronchomediastinal trunks
  • Thoracic duct + RLD
33
Q

What are the two classifications of lymph vessels in the lung?

A
  • Pleural (visceral pleura)
  • Interlobular
34
Q

Fundamentally, what is a cough?

A
  • Forced expiration against a closed glottis
  • Upon opening, there’s an explosive release of air, which is the cough
35
Q

Describe some common causes of cough

A
  • Upper respiratory tract infections
  • Chronic cough (>8 weeks) as in COPD
  • Whooping cough; due to bacterial infection
  • Reflux can activate sensory fibres and cough
36
Q

Where are the sensory fibres responsible for the coughing reflex located (in terms of respiratory pathways)? Which nerve do they belong to?

A
  • Pharynx
  • Trachea
  • Main bronchi

All belong to the vagus nerve (which is mostly sensory)

37
Q

What two types of receptors are present on the sensory fibres that cause the cough reflex?

A
  • Nociceptors (pain)
  • Mechanoreceptors
38
Q

What are the two types of mechanoreceptors that trigger the cough reflex? How do they differ?

A

Rapidly adapting receptors (RARs): send out action potentials upon receiving stimulus
Slowly adapting receptors (SARs): send out action potentials until stimulus is removed

39
Q

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

A
  • ATP

It acts as a neurotransmitter, triggering sodium influx and AP being carried to the CNS

40
Q

Where do the sensory fibres of the respiratory tract end in the CNS?

A

In the brainstem, predominantly at the level of the nucleus of the solitary tract (nTs)

41
Q

Describe the motor reflex of coughing, starting from the nucleus of the solitary tract

A
  • Signal is carried to central pattern generator
  • Impulse sent via motor neurons to respiratory muscles
  • COUGH
42
Q

Which muscles are involved in coughing? From what level of the spinal cord/what nerves are they innervated?

A
  • Diaphragm (C3-C5)
  • Intercostal muscles (T1-T11)
  • Intrinsic laryngeal muscles (Vagus)
  • Superior laryngeal muscles (Nucleus ambiguous)
  • Abdominal muscles (T6-T12)
43
Q

What is the role of higher brain centres in coughing?

A
  • Voluntary cough
  • Generating the urge to cough (for whatever reason)
44
Q

How can coughing cause an immune response?

A

When activated, sensory neurons release local factors that can lead to oedema and inflammation

45
Q

Sputum production during illness mech

A
  • Inflammation of airways
  • Goblet cell hypersecretion
  • Sputum production
46
Q

Where do the bronchial arteries arise from?

A

The thoracic aorta

47
Q

Where do the bronchial veins arise from?

A

The azygous vein

Medical Studies 1 (90 decks)

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