Week 1/2 - A - Physiology 1 - Expiration/Inspiration, Ventilation, Alveoli, Boyles Law, LaPlace, Pneumothorax

Question 1

Which type of respiration refers to the intracellular mechanisms which consumes O2 and produces CO2? Which type of respiration refers to the sequence of events that lead to the exchange of O2 and CO2 between the external environment and the cells of the body ?

Answer 1

Internal respiration refers to the intracellular mechanisms which consume O2 and produce CO2 Extracellular respiration refers to the sequence of events leading to the exchange of O2 and CO2 between the external environment and cells of the body

Question 2

Define internal and external respiration?

Answer 2

Internal respiration refers to the intracellular mechanisms which consume O2 and produce CO2 External respiration refers to the sequence of events that exchange O2 and CO2 between the external environment and the cells of the body

Question 3

External respiration is comprised of 4 main steps What are these steps? (don’t need to describe them exactly, can do that next card)

Answer 3

Ventilation Gas exchange - between alveoli and blood Gas transport - in circulating blood Gas exchange - between circulating blood and the body cells

Question 4

Describe the 4 steps of external respiration?

Answer 4

Ventilation - mechanical process of moving air in and out of the lungs

Gas exchange - exchange of O2 & CO2 between the air in the alveoli and the blood in the pulmonary capillaries

Gas transport - binding and transport of O2 and CO2 in the blood

Gas exchange - exchange of O2 &CO2 between the blood in the systemic capillaries and the body cells

Question 5

VENTILATION - mechanical process of moving air in and out of the lungs Air flows down a pressure gradient from a region of high pressure to a region of low pressure How is the difference in intra-alveolar pressure and atmospheric pressure achieved to allow air to flow down the pressure gradient? and in accordance to which law?

Answer 5

Before inspiration, the intra-alveolar pressure is equivalent to the atmospheric pressure During inspiration, the thorax and lungs expand as a result of contraction of the inspiratory muscles. This lowers the intra-alveolar pressure in accordance to Boyle’s law allowing air to flow from atmosphere to alveoli.

Question 6

During inspiration, the thorax and lungs expand as a result of contraction of the inspiratory muscles. This lowers the intra-alveolar pressure in accordance to Boyle’s law allowing air to flow from atmosphere to alveoli. Define Boyle’s Law?

Answer 6

At any constant temperature, the pressure exerted by a gas varies inversely with the volume of the gas Therefore at any constant temperature, as the volume of gas increases (ie the thorax and lungs expanding during inspiration), the pressure exerted by the gas decrease (allowing air to flow down a gradient)

Question 7

What are the pleura attached to?

Answer 7

The visceral pleura lines the surface of the lung The parietal pleura lines the inner surface of the chest wall

Question 8

During inspiration the thorax and lungs expand as a result of contraction of inspiratory muscles There is no physical connection between the chest wall and the lungs. Therefore we need to think how do the lungs expand when the chest expands. Name the two forces holding the thoracic wall and the lungs in close opposition?

Answer 8

The two forces holding the thoracic wall and the lungs in close opposition are: Intrapleural fluid cohesiveness Negative intrapleural pressure (subatmospheric intrapleural pressure)

Question 9

Describe the intrapleural fluid cohesiveness and how this affects lung expansion

Answer 9

The intrapleural fluid cohesiveness - the water molecules in the intrapleural fluid are attracted to each other and resist being pulled apart. Therefore the pleural membranes tend to stick together - when the chest wall expands, the lungs expands.

Question 10

Describe the negative intrapleural pressure and how this affects lung expansion Pip - pressure intrapleural Pa - pressure atmosphere Pia - pressure intralaveola

Answer 10

Negative intrapleural pressure - the Pip (subatmospheric intrapleural pressure) is lower than Pa - creating a transmural pressure gradient across both the lung wall and the chest wall. Therefore during inspiration the lungs are forced outwards (as Pia > Pip) and the chest wall is forced to squeeze inwards (as Pa > Pip)

Question 11

* We have disccused how during inspiration, the negative intrapleural pressure allows the lungs to expand and squeezes the chest wall as well as intrapleural fluid cohesiveness keeping the chest wall/lungs in close opposition * Then when inspiration increases, due to Boyle’s law, the pressure in the lungs decreases below the atmosphere allowing for the entry of O2 Now, is inspiration and active or passive process?

Answer 11

Inspiration is an active process depending on muscle contraction

Question 12

What does contraction of the diaphragm cause to the dimensions of the thoracic cavity? (vertical) What does contraction of the external intercostal muscles cause to the dimensions of the thoracic cavity? (side to side and front to back)

Answer 12

Contraction of diaphragm causes the muscle to lower therefore increasing the vertical dimension of TC

Contraction of the external intercostals causes elevation of the ribs which increases the side to side dimension of the TC. Elevation of the ribs causes the sternum to move up and outward, which increases front to back dimension of the TC.

Question 13

Is normal expiration active or passive? Describe how the chest wall and stretched lungs recoil to their preinspiratory size and how the alveolar pressure once again becomes equivalent to the atmospheric pressure?

Answer 13

Normal expiration is passive due to the relaxation of the inspiratory muscles The chest walls and stretched lungs recoil due to the elastic connective tissue in the lungs The recoil of the lungs increases the intra-alveolar pressure due to Boyle’s law (smaller volume, bigger pressure). Air now leaves the lung down its pressure gradient until it becomes equal to the atmospheric pressure

Question 14

What is a pneumothorax?

Answer 14

Pneumothorax is air in the pleural space

Question 15

How does a pneumothorax abolish the transmural pressure gradient? What may this lead to?

Answer 15

Be it a spontanoeus pneumothorax (hole in the lung) or traumatic (puncture wound in chest wall), air will enter the pleural space (from atmosphere or lungs) This can abolish the transmural pressure gradient and prevent the lung expanding therefore leading to lung collapse

Question 16

What is the difference between a primary and secondary pneumothorax?

Answer 16

A primary spontaneous pneumothorax is one that occurs without an apparent cause and in the absence of significant lung disease. A secondary spontaneous pneumothorax occurs in the presence of existing lung disease or smoker > 50 years old.

Question 17

Treatment of the pneumothorax depends on the type and the side What is the treatment of a tension pneumothorax? (emergency) What size does the treatment of a spontaneous pneumothorax depend on? (Primary or secondary)

Answer 17

Tension pneumothorax- immediate needle decompression 2nd intercostal space midlclavicular line (do this before requesting xray if suspected) - insert a chest tube afterwards Spontaneous pneumothorax - if SOB or rim of air >2cm on CXR then aspiration decompression/chest drain

Question 18

Where is the large bore cannula inserted for percutaneous aspiration of a pneumothorax?

Answer 18

The needle can be instered into the 2nd intercostal space mid-clavicular line or The 4th-6th intercostal space mid-axillary line

Question 19

Treatment differs for primary and secondary spontaneous penumothorax Primary, what is the treatment if - * No SOB, no rim between lung margin and chest wall >2cm on CXR? * SOB but no rim >2cm on CXR? * Rim >2cm but no SOB on CXR?

Answer 19

Primary spontaneous pneumothorax No SOB and no rim >2cm on CXR between lung and chest wall –> observation and oxygen SOB or rim >2cm on CXR - percutaneous aspiration via 2nd intercostal space midclavicular line and oxygen (16G cannula)

Question 20

Secondary, What treatment is given if - * No SOB, no rim between lung margin and chest wall >1cm on CXR? * No SOB but rim 1-2cm on CX? * SOB or Rim >2cm on CXR?

Answer 20

Secondary spontaneous pneumothorax No SOB, no rim between lung margin and chest wall >1cm on CXR - observe and oxygen No SOB but rim 1-2cm on CXR - oxygen and percutaneous aspiration, 2n intertcostal space midclaicular line SOB or Rim >2cm on CXR - Chest drain inserted into the safe triangle

Question 21

If aspiration fails in either primary or spontaneous pneumothorax, what treatment is recommened?

Answer 21

Primary pneumohtroax- if SOB or >2cm rim on CXR - aspiration Secondary pneumothorax - if no SOB however moderate rim (1-2cm) on CXR - aspiraition If aspiration fails then chest drain into the safe triangle is recommened

Question 22

What forces promote lungs to recoil during expiration?

Answer 22

The elastic connective tissue in the lungs But more importantly, the alveolar surface tension

Question 23

What is the alveolar surface tension? What happens if the alveolar surface tension is too strong?

Answer 23

The alveolar surface tension is the attraction between water molecules at the liquid air interface which resists the stretching of the lungs. If the alveoli were lined with water alone the tension would be too strong and the alveoli would collapse. Therefore surfactant exisits.

Question 24

Surfactant reduces the alveolar surface tension What is pulmonary surfactant, what produces it and how does it do this?

Answer 24

Pulmonary surfactant is a mixture of lipids and proteins secreted by type II alveolar cells (type II pneumocytes) which lowers the alveolar surface tension by interspersing between water molecules therefore reducing the attraction between the water molecules

Question 25

What is the surfactant effect on surface tension in differently sized alveoli?

Answer 25

surfactant lowers surface tension more in smaller alveoli than in larger alveoli so that pressure in smaller alveoli roughly equals pressure in larger alveoli. Surfactant has decreased the likelihood of the alveoli to collapse

Question 26

What does the law of LaPlace state in relation to the alveoli and radius?

Answer 26

If we take the alveoli to be spherical, then the inward collapsing pressure on the alveoli is inversely proportional to the radius of the alveoli (ie the smaller the alveoli, the greater the likelihood to collapse) Law of LaPlace * P = 2T / r * P = inward collapsing pressure * T = alveolar surface tension * r = radius

Question 27

Another factor which helps keep the alveoli open is: The Alveolar Interdependence How does alveolar interdependence work?

Answer 27

When an alveolus in a group of interconnected alveoli starts to collapse, the surrounding alveoli are stretched by the collapsing alveolus. As the neighboring alveoli recoil in resistance to being stretched, they pull outward on the collapsing alveolus pulling it open.

Question 28

Name 3 forces that act to keep the alveoli open Name 2 forces that act to promote alveolar collapse

Answer 28

Open * Transmural pressure gradient * Surfactant * Alveolar interdependence Collapse * Elasticity of stretched connective tissue * Alveolar surface tension - attraction between water molecules at liquid air interface