structure and function of the airways

Question 1

What is dichotomous branching

Answer 1

trachea dividies into 2 etc

Question 2

What are the types of cells in and around the alveoli

Answer 2

type 1 cells: 95% of the surface area (like fried eggs) 
very thin, and have delicate barrier (to increase gas exchange) 
type 2 cells: 
turn into type 1 cells when they are damaged
secretes surfactant (to reduce surface tension) and antiproteases 
xenobiotic metabolism (metabolises noxious particles that may get down into the alveolus 
macrophage: clear up debris 
capillary endothelim- in intimate contact with type 1 cells so you can have efficient gas exchange 
Fibroblasts: produces matrix that holds the whole thing together

Question 3

What is the function of nasal conchae

Answer 3

filtered, warm humidified air

Question 4

What % of surface area AND number of cells relatively are type 1 and type 2 cells

Answer 4

epithelial type 1 cells cover 95% of SA but are a minority

type 2 cells cover 5% but are a majority

Question 5

whats basic function of airways and how is this facilitated

Answer 5

-to get air efficiently to the gas exchange region (and keeping the pipework clean) 
facilitated by: 
1) mechanical stability from cartilage 
2) control of calibre by smooth muscle 
3) protections and 'cleansing'

Question 6

What is a goblet cell filled with

Answer 6

mucin granules - contain mucin in a highly condensed form

Question 7

What is there a lot of in cilia

Answer 7

mitochondria to keep cilia beating

Question 8

What is the pharynx

Answer 8

a common pathway for food, liquids and air

Question 9

Describe the structure of the airway from a transverse view

Answer 9

airway lumen surrounded by ciliated and goblet cells that secrete mucus
in the lower level, have blood vessels and sub mucosal glands (and nerves)
sub mucosal glands attach to smooth muscle
which is surrounded by cartilage

Question 10

What could happen if you swallow a peanut

Answer 10

• smooth muscle distal to swallowing contracts

- squeezes the mucous from the sub mucusal gland onto the lumen

Question 11

what happens to the mucus we secrete

Answer 11

-wafted back and we swallow it (ab 10ml/day)

Question 12

In what form do the mucin granules store mucus

Answer 12

in a highly condensed form

Question 13

Describe how mucus is released from the mucin granules

Answer 13

1) granules come to the apical surface of the cell and fuse with it
2) you get a double pore ( a omega profile)
3) airway liquid comes into the granule
4) and makes the highly condescended mucin expand and become decondensed
5) causing a massive release of mucin onto the airway surface

Question 14

What 2 things secrete mucus into the airway

Answer 14

goblet cells and sub mucosal glands

Question 15

Describe the structure of sub mucosal glands

Answer 15

there are acini at the end, then the collecting duct then the ciliated duct, which wafts mucus out of the end of the gland

Question 16

what is the anatomical relationship between the serous and visceral collecting ducts
(and why must the evidence leading to this be treated with caution)

Answer 16

1) serous acini are distal
2) mucousal acini secrete more viscous substance but serous acini are more watery
3) so the watery serous scini wash out the viscous mucousal acini
4) But this structure of a human sub mucousal gland was only found from a cancer patient BUT this was also replicated in other animal studies

Question 17

What else do serous cells in the sub mucosal gland secrete

Answer 17

anti bacterial enzymes (eg lysozymes)

Question 18

Describe the structure of a human cilium

Answer 18

1) apical hooks (cilia) that engage with the mucous
2) then have axonemes that slide over each other to push the cilia one way and then the other
3) then have intracellular anchoring proteins

Question 19

Describe the transverse section through a human cilium

Answer 19

1) 9+ 2 arrangement of microtubules ( 9 on the outside and 2 in the middle)
2) nexin link between each of the doublets
3) radial spoke into the centre
4) inner and outer arm from each microtubule forms the dynein

Question 20

What rhythm do the cilia beat in

Answer 20

metachronal

Question 21

Name 6 inflammatory and regulatory mediators secreted by the airway epithelium

Answer 21

1) proteases
2) cytokines (eg GM-CSF)
3) nitric oxide (via nitric oxide synthase)
4) chemokines (eg IL 6)
5) Archidonic acid metabolites (eg prostaglandins via COX)
6) carbon monoxide

Question 22

What could be a possible function of nitric oxide on the airway epithelium

Answer 22

1) if you put nitric oxide donors onto cilitated cells, their cilia speed up
2) so could be used in regulating the rate of movement of cilia

Question 23

What are 3 functions of the airway smooth muscle

Answer 23

1) structural (integral to epithelia)
2) tone (airway calibre by constriction and relaxation)
3) secretion (mediators, cytokines and chemokines)

Question 24

When and how does the structure of airway smooth muscle change

Answer 24

1) during inflammation

2) smooth muscles hypertrophy and proliferate

Question 25

What else happens to the airway smooth epithelium during inflammation

Answer 25

increased secretion of cytokines and chemokines

Question 26

Specifically what does smooth airway muscle upregulate during inflammation

Answer 26

1) nitric oxide synthase (NOS) to increase nitric oxide production
2 ) cyclo-oxygenase to increase prostaglandin production
3) cytokines
4) chemokines
5) adhesion molecules
3,4 and 5 recruit immune cells

Question 27

What is the paradox of tracheo-bronchial circulation

Answer 27

1) only 1-5% of cardiac output goes to it

2) But blood flow to airway mucosa is among the highest of any tissue (100 to 150 ml/min/100g tissue)

Question 28

How is this paradox solved

Answer 28

massive plexus of subepithelial microvasculature just below the airway surface

Question 29

What are 7 functions of tracheo bronchal circulation

Answer 29

1) warming of inspired air
2) humidification of inspired air
3) clears inflammatory mediators
4) clears inhaled drugs ( can be good or bad)
5) supplies inflammatory cells
6) supplies with proteinaceous plasma)

Question 30

Describe 4 ways to control airway function

Answer 30

1)  Nerves 
Parasympathetic (cholinergic) 
Maybe some sympathetic 
sensory 
2) Regulatory and inflammatory mediators 
histamines 
arachidonic metabolites (prostaglandins, leukotrienes) 
cytokines 
chemokines 
3) proteases ( neutrophil elastase ) 
4) reactive gas substances (eg NO)

Question 31

Describe in detail how contraction of the airways happens

Answer 31

1) sensory neurons go via the vagus nerve and then via the NoDose ganglion to the brainstem
2) Then there goes a parasympathetic motor pathway back via the vagus nerve to constrict the airway
3) mucous secretion by sub mucosal glands

Question 32

How are we different from other animals when it comes to the sympathetic pathway

Answer 32

1) We dont have it instead we have NO which sends nerve signals to the spinal cord to relax
2) Adrenaline also causes relaxation