5 - Airways Function

Question 1

What happens to the size of the airways as they branch and get to the periphery

Answer 1

They get narrower

Question 2

Why are the cartilage rings C chaped?

Answer 2

it allows food to pass down the oesphagus with ease

Question 3

What does the cross section of the airways (trachea) look like?

Answer 3

• cartilage on the outside (cant see a complete C because the rings are offset)
• beneath the cartilage is a layer if smooth muscle
• there are submucosal glands present (that secrete mucus onto the airways surface). The lower part is embedded in the smooth muscle- when the SM contracts, it squeezes the submucosal gland
• the epithelium has ciliated cells and mucus producing goblet cells

Question 4

Why is there lots of mitchondrion in the epithelium?

Answer 4

the cells are highly metabolically active so they can keep pumping the cilia

Question 5

How is mucus stored in goblet cells?

Answer 5

in a highly condensed form- as mucin granules

Question 6

What happens to the mucin granules as they are secreted?

Answer 6

• fuse with apical surface

- combines with water and expands rapidly (up to 100 fold)

Question 7

What are the functional units of the submucosal glands?

Answer 7

Acini

Question 8

How do the airway submucosal glands secrete mucus?

Answer 8

• secrete into the collecting duct
• this then moves to the ciliated duct
• the cilia then waft the mucus out of the gland

Question 9

What are the 2 types of acini in humans?

Answer 9

serous and mucus

Question 10

What is the arrangement of airway submucosal gland in the human bronchial gland?

Answer 10

there are serous cells peripheral to the mucus cells

• the serous cells produce a watery mucus (containing enzymes)
• the watery secretions wash over the mucus secretions and washes into the collecting duct

Question 11

What is meant by metachronal rhythm?

Answer 11

• one field of cilia beat and then the field behind it beats
• meanwhile, the first field is on the backstroke

this allows the cilia to move the mucus sequentially along

Question 12

What is the function of airway epithelium?

Answer 12

• secretion of mucin, water and electrolytes
• movement of mucus by cilia - MUCOCILIARY CLEARANCE
• physical barrier
• production of mediators

Question 13

What enzyme produces NO?

Answer 13

nitric oxide synthase (NOS)

Question 14

What are the 3 main functions of airway smooth muscle?

Answer 14

STRUCTURE
- in respiratory disease of the airways (e.g. asthma), you get inflammation and smooth muscle hypertrophy
TONE
- the SM is not entirely relaxed, so it can contract much quicker if something (e.g. food) is inhaled
SECRETIONS
- increases when the mass of smooth muscle increases (asthma also increases the amount of secretions)
- produces lots of cytokines etc, and it changes its function and phenotype

Question 15

What happens to the amount of secretions when there is inflammation?

Answer 15

• cytokines are produced
• in response to this, NOS gets upregulated
• COX enzymes produce more histoglandins
• Chemokines lead to the recruitment of inflammatory cells
• the smooth muscle then gets involved in inflammotory processes

Question 16

Where do the bronchial arteries arise from:

Answer 16

• aorta
• intercostal arteries
• other sites

Question 17

How does blood return from the tracheo-branchial circulation?

Answer 17

• returns form the tracheal circulation via systemic veins

- returns from the bronchial circulation to both sides of the heart via the systemic and pulmonay veins

Question 18

Describe the autonomic innervation of the airways in humans and in animals

Answer 18

• both have a parasympathetic pathway (cholinergic is the most important)- causes bronchoconstriction
• animals other than humans have sympathetic pathway causing relaxation once the thing has been removed out of the airways
• HUMANS DO NOT HAVE THE SYMPATHETIC PATHWAY, we rely on adrenaline from the adrenal gland which relaxes the airways

Question 19

In addition to adrenaline, what helps to relax the airways?

Answer 19

There is a neuronal pathway (NOT SYMPATHETIC) that produces NO
NO is the

Question 20

In addition to adrenaline, what helps to relax the airways?

Answer 20

There is a neuronal pathway (NOT SYMPATHETIC) that produces NO
NO is the neurotransmitter of the neuronal pathway that causes the opening up of the airways

Question 21

What is the cholinergic mechanism in the airways?

Answer 21

• irritants cause an impulse to pass up the sensory fibre
• this causes a cholinergic reflex, which contracts the smooth muscle and causes secretion of mucus (makes airways slippier so object can be removed)
• may also get a small amount of vasodilation

Question 22

What is airway remodelling?

Answer 22

the airway changes in structure over a long period of time