Non respiratory functions of the lungs

Question 1

Non respiratory functions of the

lungs

Answer 1

• Immune response

* Lymphatic function (fluid balance) • Metabolic function

Question 2

Immune response in the lungs

Answer 2

• Remember innate vs. adaptative response
• Innate:
• Mucociliary system
• Reflexes: cough, sneeze
• Resident macrophages and dendritic cells
• Neutrophils
• TLR in antigen presenting cells (against fungi, virus, bacteria)
• Adaptative:
• Specific response (cellular and humoural responses)

Question 3

T cells (adaptative immune response)

Answer 3

• Cytotoxic (CD8+) and helper (CD4+), helper are divided in Th1 and Th2
• Th1 produce IFN-ɣ and are involved in delayed hypersensitivity
• Th2 activate B cells (IgE)
• There is sometimes cross immunity against different pathogens

Question 4

B cells (adaptative immune response)

Answer 4

• Antibodies on surface specific to antigens
• B cells act as antigen presenting cells like macrophages or neutrophils (they engulf pathogens
and present the antigen through a MHC II receptor to CD4+ T helper)
• T helpers activate B cells to either “memorise” the pathogen (memory B cell) or plasma cells
• Activated B cells turn into:
• Plasma cells - the ”army”, produce antibodies
• Memory cells prepare for long term immunity

Question 5

Immune response in the lungs: mechanics

Answer 5

• Barrier to harmful substances
• Stopping aerosols and inhalable particles (10
microns) and respirable particles (2.5 microns)
• The smaller the more harmful!
• Stopped by mechanics and chemistry:
• Impaction against turns of the airway and handled by tonsils and bronchus-associated lymphoid tissue (inertial deposition)
• Airflow – rapid and shallow enhances inertial deposition
• Concentration gradient and solubility (toxic gases)
8

Question 6

Mucociliary system

Answer 6

• Double layer of mucus (sol and gel) that traps particles
• Cells have cilia and they move the mucus with the particles upwards (head down helps!)
• Mucus produced by Clara cells and goblet cells (regulated by autonomic system)
• Changes in viscosity impairs clearance – importance of hydration level and repetitive insult

Question 7

Cough and sneezing

Answer 7

• Subepithelial receptors in respiratory epithelium of the larynx, trachea and larger bronchi (the deeper we get, the less of them!!) respond to particles or lumps of mucus
• Initiates cough reflex – vagus nerve – medulla oblongata →
• Younger animals and certain drugs inhibit this reflex (careful when intubating or passing a nasogastric tube!!)

Question 8

Immune response: cytokines

Answer 8

• Remember: communication components from the immune system
• Examples: tumor necrosis factor (TNF) and interleukin 1 (IL-1) from macros, which attract more neutros, and trigger local inflammatory response (endothelial cells: IL-8)

Question 9

What does the lymphatic system do?

Answer 9

1. Return tissue fluid to the circulation
2. Filter potentially damaging material
3. Produce antibodies and lymphocytes for the defense of the body
4. Transport digested fat from the intestine to the liver/storage sites around the body
   Lungs produce lymph as a result of the pressure changes in the interstitial environment

Question 10

Lymphatic role in the lungs

Answer 10

• Remember how lymph is made and that there is extra fluid around cells (interstitial fluid) which is collected by the lymphatic vessels
• The lower BP in the lungs and higher permeability of the pulmonary endothelium means this is enhanced compared to other tissues
• Alveolar epithelium (logically!!) is not as permeable so if fluid builds up it does not go in the alveoli
• Fluid is then filtrated into lymphatic vessel

Hence why retrograde blood flow affect lungs more than other organs

Question 11

Metabolic role in lungs

Answer 11

• pH balance→respiratory acidosis (homeostasis lesson)
• O2 and CO2 balance
• Temperature: evaporation (panting dog!!) by moving small tidal volume quickly over to the dead space
• BP
• Metabolism of internal substances (serotonin, norepinephrine, prostaglandins)

Question 12

Hormonal control of BP.

Answer 12

RAAS cascade

Angiotensinogen -> Renin-> Angiotensin 1-> ACE. (Angiotensin-converting enzyme) ->Angiotensin II-> Vasoconstriction, Release of aldosterone (adrenal gland), Increased blood pressure

Question 13

Tidal air

Answer 13

The air that goes in and out of the lungs with each normal breach at rest

Question 14

Tidal volume

Answer 14

The volume of air that goes in and out in one normal breath. Small dog/cat: 15 ml/Kg; med/large dogs: 10 ml/kg

Question 15

• Residual volume

Answer 15

Volume of air that remains in the lungs after maximum expiration

Question 16

• Total lung capacity

Answer 16

As it name states! Maximum volume of air that can be within the lungs. Vital capacity + residual volume

Question 17

• Vital capacity

Answer 17

The maximum volume of air that can be exhaled during maximal expiration (deepest breath possible)

Question 18

• Functional residual capacity

Answer 18

Volume of air left in the lungs after one normal breath, useful left over air – allows oxygen exchange during exp

Question 19

• Anatomical dead space

Answer 19

Volume of air that goes in and out and never reaches the alveoli (volume in the trachea, bronchi and bronchioles)

Question 20

-

• Functional dead space

Answer 20

Anatomical dead space + volume of air in any non-working alveoli

Question 21

• Respiratory rate

Answer 21

Number of breath per minute