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Can someone please explain to me the exchange of gases in the lungs, especially what happens in this process. Also what the role of alveoli is. I am really struggling with this so any help will be greatly appreciated.
Original post by cricketman
Can someone please explain to me the exchange of gases in the lungs, especially what happens in this process. Also what the role of alveoli is. I am really struggling with this so any help will be greatly appreciated.


Gas exchange system consists of:

1) The trachea which is supported by incomplete rings of cartilage.
2) The trachea which divides into two bronchi the repeatedly spit into smaller tubes; the bronchioles.
3) At the ends of the bronchioles are alveoli, which is where gas exchange occurs.

How alveoli are adapted for efficient gas exchange:
- Their shape and large number provides a large surface area.
- There is a fluid which lines the alveoli which allows gases to dissolve in it and diffuse across it.
- There are only 2 layers that seperate the blood and the air(in the alveoli) which provides a small diffusion pathway. (The 2 layers consist of 1) An alveolar wall; single layer of flattened epithelial cells. 2) A capillary wall; single layer of endothelial cells).
- Blood capillaries surround each alveolus providing a large surface area for absorbing oxygen and releasing carbon dioxide.
- A circulatory system which maintains a high diffusion gradient by transporting deoxygenated blood to the lungs and removing oxygenated blood from the lungs. (Think of it like taking oxygen to the cells, bringing it back to be replenished to take it back again)
- A ventilation mechanism which again maintains a high diffusion gradient by continually providing air with high oxygen concentration and removing air with high carbon dioxide concentration.

The role of the alveoli for gaseous exchange:
1) Oxygen enters the alveoli into the alveolar air space.
2) This oxygen diffuses into the fluid which is lining the epithelium of the alveolus.
3) Oxygen then difusses across the alveolar wall (flattened epithelial cells lining the alveolus) and then across the capillary wall (flattened endothelial cells lining the blood capillary) and into the blood.
4) Oxygen combines with haemoglobin to create oxyhaemoglobin and the oxygenated blood is transported away from the lungs.

If you need to talk about how carbon dioxide enters the alveolus, just reverse it.
So deoxygenated blood (CO2) diffuses into capillary wall -> into alveolar wall -> dissolves into fluid lining into the alveolar air space.

All of this maintains a high diffusion gradient so gaseous exchange is efficient.



(Sorry if its too much but I hope it helped :colondollar:)
(edited 12 years ago)
Reply 82
Original post by Mocking_bird

Gas exchange system consists of:

1) The trachea which is supported by incomplete rings of cartilage.
2) The trachea which divides into two bronchi the repeatedly spit into smaller tubes; the bronchioles.
3) At the ends of the bronchioles are alveoli, which is where gas exchange occurs.

How alveoli are adapted for efficient gas exchange:
- Their shape and large number provides a large surface area.
- There is a fluid which lines the alveoli which allows gases to dissolve in it and diffuse across it.
- There are only 2 layers that seperate the blood and the air(in the alveoli) which provides a small diffusion pathway. (The 2 layers consist of 1) An alveolar wall; single layer of flattened epithelial cells. 2) A capillary wall; single layer of endothelial cells).
- Blood capillaries surround each alveolus providing a large surface area for absorbing oxygen and releasing carbon dioxide.
- A circulatory system which maintains a high diffusion gradient by transporting deoxygenated blood to the lungs and removing oxygenated blood from the lungs. (Think of it like taking oxygen to the cells, bringing it back to be replenished to take it back again)
- A ventilation mechanism which again maintains a high diffusion gradient by continually providing air with high oxygen concentration and removing air with high carbon dioxide concentration.

The role of the alveoli for gaseous exchange:
1) Oxygen enters the alveoli into the alveolar air space.
2) This oxygen diffuses into the fluid which is lining the epithelium of the alveolus.
3) Oxygen then difusses across the alveolar wall (flattened epithelial cells lining the alveolus) and then across the capillary wall (flattened endothelial cells lining the blood capillary) and into the blood.
4) Oxygen combines with haemoglobin to create oxyhaemoglobin and the oxygenated blood is transported away from the lungs.

If you need to talk about how carbon dioxide enters the alveolus, just reverse it.
So deoxygenated blood (CO2) diffuses into capillary wall -> into alveolar wall -> dissolves into fluid lining into the alveolar air space.

All of this maintains a high diffusion gradient so gaseous exchange is efficient.



(Sorry if its too much but I hope it helped :colondollar:)

Your explanation for the adaptation lacks depth. You need to specifically say that the alveoli walls are folded to increase surface area, also the squamous epithelium and thin alveolar walls .. (diffusion distance etc)
Original post by EffKayy
Your explanation for the adaptation lacks depth. You need to specifically say that the alveoli walls are folded to increase surface area, also the squamous epithelium and thin alveolar walls .. (diffusion distance etc)


Diffusion distance was mentioned - only 2 single layers, thus short diffusion pathway.

Other 2 aren't in the notes given by my teacher, so I presume its a bit of waffle :P
Reply 84
Original post by Mocking_bird
Diffusion distance was mentioned - only 2 single layers, thus short diffusion pathway.

Other 2 aren't in the notes given by my teacher, so I presume its a bit of waffle :P


It isn't waffle. It was in a previous markscheme ... Awkward
Learn them!
Reply 85
Original post by EffKayy
It isn't waffle. It was in a previous markscheme ... Awkward
Learn them!


I agree with the thin alveoli walls, but haven't heard of 'squamous epithelium' :confused:
Original post by EffKayy
It isn't waffle. It was in a previous markscheme ... Awkward
Learn them!


:rolleyes:
It's not awkward at all.

& I just had a quick google for some mark schemes:

"Through alveolar epithelium;
Through capillary epithelium/endothelium;

Accept: Through lining / wall of alveolus and
capillary for 1 mark
Accept: squamous epithelial cells for
‘epithelium’
Neutral: alveolar endothelium
Neutral: references to diffusion"

It's a case of just having different wording.
(Can't think of a biology example right now, but for example in chemistry calling "VDW forces" something like london forces or temporary dipole).
Reply 87
Original post by Mocking_bird
:rolleyes:
It's not awkward at all.

& I just had a quick google for some mark schemes:

"Through alveolar epithelium;
Through capillary epithelium/endothelium;

Accept: Through lining / wall of alveolus and
capillary for 1 mark
Accept: squamous epithelial cells for
‘epithelium’
Neutral: alveolar endothelium
Neutral: references to diffusion"

It's a case of just having different wording.
(Can't think of a biology example right now, but for example in chemistry calling "VDW forces" something like london forces or temporary dipole).


NO! You are missing the point, I assume that question is asking you about the pathway. Go onto AQA and look at the June 2010 markscheme , you need to say squamous
Original post by EffKayy
NO! You are missing the point, I assume that question is asking you about the pathway. Go onto AQA and look at the June 2010 markscheme , you need to say squamous


"Flattened / squamous epithelium;"
http://store.aqa.org.uk/qual/gce/pdf/AQA-BIOL1-W-MS-JUN10.PDF
7b.

I think you're the one missing the point. :P
wait so, if you dont have exactly the same wording, although it means the same thing, you dont get the mark???
and do we need to know the HWS cases or cn we just learn the bio info and apply?
Reply 91
At the end of the day, its a 5 mark question and there were ten available points that could be made so you're both correct but Kayy was right to say a Flattened / Squamous Epithelium would grab a mark.
Original post by cheesecake11
wait so, if you dont have exactly the same wording, although it means the same thing, you dont get the mark???


It depends.
Sometimes, the mark scheme will have a certain word underlined and you MUST say that word to get the mark. E.g "Water enters lumen by osmosis;" (Noy sure what the question was, just scrolled through a mark scheme)

Or sometimes the mark scheme will be seperated by dashes which allow different wording, e.g "Low(er) water potential in lumen / intestine / gut;"

But as for everything else, as long as its going along the same lines as the mark schemes then it doesn't have to be exact word for word.

Original post by cheesecake11
and do we need to know the HWS cases or cn we just learn the bio info and apply?


Its mostly just application of knowledge, (as far as im aware) you can't really revise for the exact question besides just practice and looking at the mark schemes to see what they usually want for the answers.
Anyone else hate the water potential/osmosis HSW bits?:sigh:
when meausring a distance , so you round to the nearest whole number? january 2009 measured 20 micrometres(2cm) but the actual distance was 18micrometres (ie 1.8 cm)
Does anybody understand antigenic variabilty and monoclonal antibodies. The book doesnt really explain in much detail :s-smilie:
Can someone give me their notes of diffusion, active transport and osmosis because the nelson thornes book doesn't really explain it, it just gives examples of scenarios where each of the types of transports takes place. I cant really use that in the exam can i?
Also can someone give me a good image of the heart, in case there is a question on labeling the heart. Like which parts are oxygenated and deoxygenated, pulmonary veins, vena cava etc. There was a question on labeling it in January 2011.

Any help will be greatly appreciated
guys does anybody know where to get the june 2011 paper?? Please if somebody could kindly help me out.
Original post by cricketman
x


Feel as if these notes should come with a disclaimer now :rolleyes:
Trying to remember them off the top of my head so some stuff may be missing, feel free to ask if something doesnt make sense.
(& I didnt put the examples like.. through the phospholipid bilayer and all of those as you said you have them and that would have made this post huge haha :smile: )

Spoiler




Heart:

Spoiler

(edited 12 years ago)
Original post by khalidpatel
guys does anybody know where to get the june 2011 paper?? Please if somebody could kindly help me out.


http://www.thestudentroom.co.uk/showthread.php?p=35372851&highlight=biology%20june%202011
I hope this links to the right post.. but just incase it doesnt, its page 23, theres a QP, MS and grade boundaries :smile:

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