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Gas Exchange in Humans


The gas exchange surface of a mammal is the alveolus.

There are numerous alveoli - air sacs, supplied with gases via a system of tubes (trachea, splitting into two bronchi - one for each lung - and numerous bronchioles) connected to the outside by the mouth and nose.

These alveoli provide a massive surface area through which gases can diffuse. These gases diffuse a very short distance between the alveolus and the blood because the lining of the lung and the capillary are both only one cell thick.

The blood supply is extensive, which means that oxygen is carried away to the cells as soon as it has diffused into the blood. Ventilation movements also maintain the concentration gradients because air is regularly moving in and out of the lungs.
This breathing in (inspiration) and breathing out (expiration) is controlled via nervous impulses from the respiratory centre in the medulla of the brain.

Both the intercostal muscles (in between the ribs) and the diaphragm receive impulses from the respiratory centre. Stretch receptors in the lungs send impulses to the respiratory centre in the brain giving information about the state of the lungs.



Process of inspiration (breathing in)
1.
external intercostal muscles contract

2.
ribs and sternum move up and out

3.
width of thorax increases front to back and side to side

4.
diaphragm contracts

5.
diaphragm moves down, flattening

6.
depth of thorax increases top to bottom so the...


volume of thorax increases.


pressure between the pleural surfaces decreases.


lungs expand to fill thoracic cavity.


air pressure in alveoli is less than atmospheric pressure.


air is sucked in.



As the lungs fill with air the stretch receptors send impulses to the expiratory part of the respiration centre to end breathing in.



Process of expiration (breathing out)
1.
External intercostal muscles relax

2.
ribs and sternum move down and in

3.
width of thorax decreases front to back and side to side

4.
diaphragm relaxes

5.
diaphragm moves up

6.
depth of thorax decreases top to bottom. So the …


volume of thorax decreases.


pressure between the pleural surfaces increases.


lung tissue recoils from sides of thoracic cavity


air pressure in alveoli is more than atmospheric pressure.


air is forced out.



As the air leaves, the stretch receptors are no longer stimulated. The inhibition of breathing in (via the expiratory part of the centre) stops so breathing in can start again.


History plan for essay question
‘How important were the terms of the treaty of Brest-Litovsk, March 1918, in explaining the start of the civil war in Russia?’
Introduction
-Important to a certain extent for several reasons.
-The Civil war had begun before the treaty.
-Yet humuliating terms intensified conflict
-Treaty: Germany received Land: Russian Poland, Baltic provinces, Finland, Ukraine and southern Transcaucasian
Germany received also: 27% Russian arable land, 26% Russian population, 74% Russian coal and iron ore. Reparations of
-National humiliation encouraged ppl to fight to abandon the treaty
-But there was other causes for civil war.
Main Answer!
1 cause: Some groups wanted to restore Tsarist Regime.
-officer class were outraged by treaty and sought to put army in field.
-officer frustrated that peasants in army returned home to gain land who wanted to stay with their land therefore no fighting desire and then received Bolshevik backup. Army officers wanted to fight so takeout Bolsheviks for resuming war therefore land owners also have similar desires.
2 cause: Some groups aimed to restore democratic Russia.
-frustrated by Bolshevik undemocratic take-over.
-Bolshevik used terror tactics against potential rivals therefore boost intention for democracy and end brutality
-Bolshevik passed: land decree, workers control decree & rights of people of Russia decree = frustrated middle/upper class & imperialists. They want government that appeals.
-Civil war = counter revolutionary movement for various groups to defeat Bolsheviks. Many who opposed tsar rule also opposed idea of a Marxist volume.
-Treaty also affected view towards Bolsheviks. Lost support of left wing of SR who wanted war, patriotic Russians horrified.
-many believed Bolshevik strengthened German empire which opposes ideals of ‘right of people of Russia decree’ of self determination. Also gave away many ppl to Russia.
3 cause: some groups intended to gain a long waited independence from Russia.
-Minor nationalities were promised self determination by the people of Russia decree yet Bolsheviks wasn’t powerful enough to enforce it so needed to consolidate their power.
-but Lenin wasn’t willing to loose the resources and population of the minority areas from the Bolsheviks where when national parties were established themselves the Bolsheviks had attacked them.
-caused various groups to revolt. They were: Ukrainian separatists, Baltic separatists and Transcaucasian separatists. Ukraine had German backup since it had great resources.
-Treaty provoked allied intervention aiming to reconstruct the eastern front by getting russia to return to the war. The entente powers needed them so they wanted to abandon the treaty therefore eliminate Bolsheviks
- They helped many minorities in their attempts to gain independence including the Czech Legion who had recently join the western European Siberia after the collapse of Austria and Hungary empire.
- After the betrayal that the allies suffered of the Russian withdrawal, allies intended to inflict some revenge by helping the various groups including the minorities.
- even intended to fight ideological crusade against Bolsheviks
4 cause: land owners wanted to get their land back.
-Peasants take land which got Bolsheviks backing in land decree.
-Before Bolsheviks land owners had their land so crushing Bolsheviks will regain land. Therefore intention is also to bring back democracy
-since land owners are middle/upper class they are bound to be middle/upper class who were wither conservative or nationalists where treaty annoyed these political groups who wanted to continue the battle at the eastern front.
-economic problems caused by war weakened Russia a lot where land owners wanted land back to survive and therefore help the economy by distributing grain unlike the kulaks. Treaty threatened economy to become more corrupt therefore making it more urgent for them to gain land.
5 cause: Peasants wanted food after suffering the risk of famine
-war caused uncontrollable inflation and collapsed economy. Too expensive for peasants to purchase things. Also grain supplies were 13 mill tons short of national need. NO FOOD, CORRUPT ECONOMY provoked the peasant revolt.
-Bolsheviks had to distribute food so try to look innocent by creating myth about Kulaks that they were hoarding grain provoking land war between Kulaks and the land owners and the hungry peasants.
-Later on the Kulaks demanded for fair price for grains but economy made it hard for the gov to accomplish the aims therefore making the peasants fight without gov assistance therefore strengthening desire for democratic gov that would be more reliable
but treaty made situation worse due to terms affecting economy. With worse economy the grain situation was threatened to be worse therefore making it more urgent for peasants to obtain the grains.
Conclusion
Brest Litovsk surely intensified each cause but the Bolsheviks were faced with a number of problems limiting the importance of the brest litovsk treaty.
Each cause had contributed significantly to the war where if one of them was missing then the war wouldn’t of had such a huge impact eg if there was no minorities fighting then Bolsheviks power would of appeared more secure.



Chemoreceptors
There are also chemoreceptors in the medulla and certain blood vessels that are sensitive to changes in carbon dioxide levels in the blood.

If the level is too high (the pH would drop, enzyme action would be affected with serious results), impulses are sent from these cells to the inspiratory part of the centre so that breathing rate increases.

This means that carbon dioxide is got out of the body as quickly as possible and more oxygen comes in.

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