PBL 4- Lungs and Pneumothorax

Question 1

Describe the structure and function of the trachea

Answer 1

• 5 inch long tube made of 10-12 C shaped hyaline cartilage rings which keeps the airways open
• lined with pseudostratified cliliated columnar epithelium which produces mucous that traps foreign materials and prevents it from reaching the lungs.

Question 2

Describe the structure and function of the lungs

Answer 2

Base- inferior surface that sits on top of the diaphragm
Apex- extends above rib 1
Lobes- (right has 3 and let has 2)
- R lung: superior, middle and inferior
- L lung: superior and inferior
lobes are separated by fissures (oblique and horizontal)
Surfaces:
- Costal surface: lies adjacent to ribs
- Mediastinal surface: lies against the mediastinum and contains the hilum through which structures enter and exit
- Diaphragmatic surface- rests on the dome of the diaphragm
Borders:
- anterior border: has cardiac notch on left lung
- inferior border: separates base of lung to costal and mediastinal surfaces
- posterior border: formed by the costal and mediastinal surfaces meeting posteriorly.
Root and hilum:
- the lung root is a group of structures (lymphatic vessels, pulmonary artery) that suspends the lung from the mediastinum. these structures enter or exit the lung through the hilum.
Also has bronchial tree

Question 3

Describe the structure and function of the bronchial tree.

Answer 3

• Begins with the trachea which divides into a left and right (primary bronchi)
• primary bronchi pass through the lungs and divide into secondary lobar bronchi (2 in L lungs and 3 in R lungs)
• each lobar bronchi further divides into tertiary segmental bronchi > conducting bronchiole
• they divide into terminal bronchioles
• each terminal bronchioles give rise to respiratory bronchioles
• RB leads into alveolar ducts
• > alveolar sacs
• > alveoli (provide large S.A for gas exchange)

Question 4

Describe Type 1 alveoli cell type.

Answer 4

• 97% alveolar cells
• squamos epithelial cells
• involved in gas exchange

Question 5

Describe Type 2 alevoli cell type

Answer 5

• 3% alveolar cells
• cuboidal epithelial cells
• produces surfactant
• reduces surface tension

Question 6

Describe the structure and function of the pleura

Answer 6

There are 2 pleurae in the body- one covering each lung. they consist of a serous membrane (layer of simple squamous cells)
Each pleura is divided into 2 parts:
- Outer visceral pleura (covers the lungs)
- Inner parietal pleura (covers the internal surface of the thoracic cavity)

Parietal Pleura:

• thicker than the visceral pleura
• can be subdivided into parts of the body that it is in contact with (mediastinal pleura, costal pleura, cervical pleura, diaphragmatic pleura)

Pleural Cavity:
- potential space between the two pleurae
Functions:
- lubricates the surfaces of the pleurae, allowing them to slide over each other
- produces surface tension, pulling the parietal and visceral pleura together

Pleural Recesses:

• anteriorly and posterioroinferiorly the pleural cavity is not filled by the lungs
• gives rise to pleural recesses- in which two layers of the parietal pleurae touch each other
• Costodiaphragmatic
• Costomediastinal

Question 7

What is the rate of diffusion increased by?

Answer 7

• large S.A for gas exchange
• large partial pressure gradients
• gases with advantageous diffusion properties
• specialised mechanisms for transporting O2 and CO2 between lungs and tissues

Question 8

What is the function of the respiratory membrane and what is it composed of?

Answer 8

Function: provides a large S.A for the gaseous exchange of O2 and CO2. 
Composed of Alveolar Wall and Capillary wall. 
Alveolar wall:
- Type 1 and Type 2 alveoli
- Alveoli macrophages 
- Alveoli basement membrane 
Capillary Wall: 
- Capillary basement membrane 
- Capillary endothelium

Question 9

What is partial pressure?

Answer 9

Partial pressure is the pressure exerted by a single gas in a mixture of gases.
Measured in millimetres of mercury (mm Hg)

Question 10

What is Dalton’s law?

Answer 10

How gases move across a permeable membrane in relation to pressure differences in their surroundings.
Atmospheric pressure = 760 mm Hg

Question 11

What is Henry’s law?

Answer 11

How the solubility and partial pressure of a gas relates to its diffusion properties.

Question 12

Why is there more CO2 present in the blood than O2 even at the same partial pressure.

Answer 12

Henry’s law helps us understand this:

CO2 is more soluble in blood than O2

Question 13

Describe external respiration.

Answer 13

It is Pulmonary Circulation
In the pulmonary capillaries:
PO2 moves from alveolar air(100) to venous blood(40)
PCO2 moves from venous blood(46) to alveolar air(40)
- allows removal of CO2 from body and delivery of O2 into capillaries

Question 14

What gradient do gases move?

Answer 14

Gases move down their pressure gradients

Question 15

What is the difference between CO2 and O2 pressure gradient?

Answer 15

O2 pressure gradient is bigger than CO2

i.e. in alveolar air there is 100 for O2 and 40 for CO2

Question 16

Describe Internal respiration

Answer 16

It is Systematic circulation
In the systematic capillaries:
PO2 moves from arterial capillaries(100) to tissues(40)
PCO2 moves from tissues(46) to arterial capillaries(40)
- allows delivery of O2 to all tissues of the body

Question 17

Explain oxygen transport in blood.

Answer 17

Transported in 2 ways:

• dissolved (1.5%)
• Bound to haemoglobin (98.5%)

Hb is a major transporter of O2, found in red blood cells and is a tetramer with 4 subunits, composed of:

• Heme (iron compound)- 4 hemes
• Globin- polypeptide chain of 2x α chains 2x β chains

Question 18

Explain Carbon Dioxide transport in blood.

Answer 18

Transported in 3 ways:

• 70% converted to bicarbonate
• 23% bound to Hb
• 7% dissolved

Question 19

List the factors that can affect O2 binding to Hb.

Answer 19

O2 binding to Hb is reversible. these factors affect Hb’s affinity for O2:

• temperature
• partial pressure of O2
• partial pressure of CO2
• pH
• DPG

Question 20

What are the inspiratory and expiratory muscles involved in breathing.

Answer 20

Inspiratory:

• Diaphragm
• External intercostal muscles

Expiratory:

• Abdominal muscles
• Internal intercostal muscles

Question 21

Explain the difference between inspiration and expiration.

Answer 21

Inspiration:
- active
Expiration:
- passive 
- elastic recoil of the lungs and thoracic wall

Question 22

Define pneumothorax.

Answer 22

abnormal collection of air in the pleural space between the chest wall and the lungs.

Question 23

Describe the types of pneumothorax.

Answer 23

1) Primary spontaneous: in absence of any lung diseases. Could be due to blebs or risk factors (male sex, smoking or family history of pneumothorax)
2) Secondary spontaneous: occurs in the setting of a variety of lung diseases. Most common is due to COPD
3) Traumatic: may occur due to blunt trauma or a penetrating injury to the chest wall
4) Tension pneumothorax: due to mechanical ventilation where ventilator can create an imbalance of air pressure within the chest
5) Catamenial pneumothorax: extremely rare, in conjuction with menstrual periods and could be due to endometriosis of the pleura.

Question 24

Explain the treatments available for pneumothorax.

Answer 24

The goal is to relieve the pressure on the lungs- allowing it to re-expand and then treating any underlying cause.

• Needle aspiration
• Chest tube insertion
• non-surgical repair (bronchoscope)
• surgery