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Tuesday, March 30, 2010

Respiration in human beings

Tuesday, March 30, 2010
Respiration is process of taking in oxygen to oxidise the food and release carbondioxide,energy and water.Energy is used to perform metabolic activities whereas carbondioxide and water is exhaled during expiration.
Respiratory tract includes the passage through which air reach up to lungs.Respiratory tract consists of following part:
1)External nares:
The external nares are a pair of slit at the lower end of the nose.They open into the nasal chamber.Air enters into the nasal chamber through these nares.
2)Nasal chamber:
The nasal chambers are the pair of passage in the head above the palate.Each chamber show three region.They are:
a)Vestibular region:
It has hair which filter the air.
b)Respiratory region:
it is thin walled and highly vascular.It makes the air warm.It also bear mucus gland which secrete mucus.
c)Olfactory region:
It detect the smell.It open into internal nare.
3)Internal nares:
The nasal chamber open into nasopharynx by internal nares.The inhaled air passes into nasopharynx through internal nares.
The pharynx is short funnel like tube behind the buccal cavity.The food and air passage cross here.Its upper part is nasopharynx in which the internal nares and eustachian tube open.The middle part is oropharynx which receives the buccal cavity.The lower part is laryngopharynx.It leads to two tubes :the one in front is wind pipe or tarchea and the one at the back is the food pipe or osopharynx.
larynx is the upper part of the trachea.It is short,tubular chamber which is often called Adam's apple or voice box.
Trachea is a long tube which is 25 cm long and 2.5cm in diameter.It runs through the neck and enters into the anterior region of thorax and divide into right and left bronchus.Trachea and bronchus are supported by incomplete cartiliginous ring.It provide free passage to air.
Each bronchus open into lung.After entering into lung,it divide into primary,secondary,tertiary and finally into bronchioles.Bronchioles open into terminal duct which open into alveoli.Each alveolus is surrounded by cappilaries of vein and cappilaries of artery for exchange of gases.Bronchial tree include the bronchus which divide repeatedly inside the lung and end into alveoli.
8)Repiratory organ:The lung
Lung is spongy,pink colour moist organ which lie in anterior thoracic cavity inside the pleural cavity.It is covered by double layered pleural membrane.Between the pleural membrane is pleural fluid which keep the lungs moist and reduces friction.The left lung is slightly smaller than left lung.Between the left lung and right lung there is a space known as mediasternum.Towards the posterior end of left lung has cardiac notch which provide space for heart.The left lung is divided by oblique fissure into anterior lobe and small posterior lobe.In right lobe the horizontal and oblique fissure divide into anterior lobe,posterior lobe and median lobe.The lung is completely filled by alveoli.Each alveolus is surrounded by cappilaries of vein and cappilaries of arteries.
Mechanism of lungs include mainly two process and they are inspiration and expiration.Inspiration is taking in of oxygen to lungs and expiration is releasing carbon dioxide from lungs to external environment.
The lung is located in thoracic chamber which has dorsally verterbrae,ventrally sternum and on the sides has rib.Anteriorly vertebrae and sternum is joinged;and posteriorly there is dome shaped diaphragm.Between the rib has two set of muscle i.e external intercostal muscle and internal intercostal muscle.Conraction and relaxation of intercostal muscle increase and decrease thoracic valve.
#During inspiration,external intercostal muscle contract and internal intercostal muscle relax so that ribs move forward and downward.
#Due to movement of ribs,sternum move downward so that dome shaped diaphragm stretch and become flat.
#So,that the thoracic volume is increased and lungs expand.
#The air pressure inside the lung is lower than external environment.
#Due to difference in air pressure ,the air rush from external environment into lung through respiratory tract where gaseous exchange take place.
#During expiration,internal intercostal muscle contract and external intercostal muscle relax so that the ribs move backward and upward.
#Due to movement of ribs,the sternum move upward and return to original position.
#Due to this the diaphragm become dome shape.
#Thoracic volume decreases and increases pressure in the lungs.
#As a result,air pressure inside the lung is higher than that of external environment.So,the air rush outside from lung to external environment.
The amount of air exchanged during breathing is measured by appratus called Spirometer.The quantities of air the lung can receive,hold or expel under different conditions are called pulmonary volumes.The following are the terms used to express pulmonary volume:
1)Tidal Volume(TV):
It is the volume of air that is breathed in and out during effortless normal breathing.In a normal adult person this volume is about 500ml.
2)Inspiratory Reserve Volume(IRV):
It is the total volume of forced inspired air inn addition to normal inspired air(tidal volume).It is approximately 1500-2500ml.
3)Expiratory Reserve Volume(ERV):
It is the total volume of air expired forcefully in addition to normal expired air.It is approx. 1500ml.
4)Vital Capacity:
It is the volume of air,which can be maximum inspired and also maximum expired.It is about 4500ml in males and 3000 ml in females.
Vital capacity=IRV+ERV+TV
5)Residual Volume:
The volume of air that remains in the lungs after maximum forced expiration is called residual volume.It is about 1500ml.
6)Total lung capacity:
The volume of air in lungs and respiratory passage afer a maximum inspiratory effort is called total lung capacity.
Total lung capacity=vital capacity + Residual volume
7)Dead space:
It is the volume of air trapped in respiratory passage during inspiration is called dead space.It is about 150 ml
8)Respiratory Quotient:
It is the ratio of carbon dioxide evolved to oxygen absorbed.Some of the value of respiratory quotient of subsatances are:
Protein :0.9
fat :0.7

The exchange of Carbondioxide and oxygen between fresh air of alveolus and carbondioxide containing blood of alveolar cappillary by diffusion is called external respiration.It takes place mainly due to partial pressure of Carbon dioxide and oxygen.

3% of oxygen is carried by blood plasma whereas 97% of oxygen is carried by Haemoglobin as Oxyhaemoglobin.When the partial pressure of oxygen is high,more oxy hRESPIRATION:VOLUME OF AIRaemoglobin is formed.15 gm of Hbis present in 100ml of blood.One molecule of iron of haemoglobin can bind four molecules of oxygen.the amount of oxy haemoglobin formed is called percent saturation of Haemoglobin.
The relation between percent saturation of haemoglobin and Partial pressure of oxygen in mm is expressed by dissociation which is of sigmoid shape.
When the partial pressure of oxygen is 70 mm Hg the blood bceome completely saturated with the oxygen.When the partial pressure of oxygen decreses that means partial pressure of carbondioxide increases the oxyhaemoglobin dissociates into haemoglobin and oxygen.Therefore the partial pressure of carbondioxide is directly pressure to percent dissociation of oxy haemoglobin.This is known as Bohr's effect.

By the dissociation of oxy haemoglobin,free oxygen is produced which diffuses into cell, tissue or organ due to concentration gradient.The oxygen is used to oxidise the food to give energy,carbon dioxide and water.This is known as internal respiration.Energy is used to perform different metabolic activity of body whereas carbon dioxide and water is carried by blood in different form upto alveolar cappilaries.

Blood carry carbon dioxide and water in different forms upto alveolar cappilaries:
5-10% Of carbon dioxide is carried by bllod plasma as carbonic acid .
H20 +cO2----H2CO3
The respiratory enzyme carbonic anhydrase acts as catalyst during the formation of carbonic acid.

About 15% of CO2 is transported as carbamine compound.Amino group of haemoglobin also carbon dioxide in the form of carbamine compound upto alveolar coppilaries.
3)ABOUT 30-35% OF co2 IS CARRIED AS NaHCO3 and KHCO3:
RBC carry carbondioxide in the form of potassium bicarbonate(KHCO3) and plasma carry carbon dioxide in the form of sodium bicarbonate(NaHCO3).There is the excess carbon dioxide and water which diffuse in RBC and makes carbonic acid(H2CO3).As the RBC can not carry carbonic acid,so it dissociates into H+ and HCO3-.
Excess CO2 + H2O---------H2CO3-------H+ + HCO3-
Now the potassium haemoglobin(KHb)begins to dissociates into K+ ion and Hb.K+ ion together with HCO3- ion makes KHCO3 and H+ion together with haemoglobin makes KHb.Excess KHCO3 begins to dissociate K+ ion and KCO3- ion.The HCO3- diffuse from RBC into plasma because RBC is permeable to negatively charged ion.Plasma has NaCl.Due to the deposition of HCO3- ion,NaCl dissociate into Na+ and Cl-.The Na+ together with HCO3 make NaHCO3.To make ionic balance,chloride shift from plasma to RBC and with K+ makes KCl.
The mutual exchange of Cl- and HCO3- between plasma and RBC to make ionic balance is called chloride shift.In this way,NaHCO3 and the KHCO3 is carried by plasma and RBC to alveolar cappilaries.The HHb dissociates into H+ and Hb.The KCl also dissociates into K+ and Cl-.Now the K+ with Hb makes KHb so that Cl- shift back into the plasma.Now,NaHCO3 dissociates into Na+ and HCO3-.SO,Na+ and HCO3-.SO,Na+ with Cl- makes Nacl.Hco3- also move back to RBC and with H+ ion make H2Co3.Similarly,H2CO3 dissociate into water and carbon dioxide which diffuse from alveolar cappilaries into alveoli and exhaled during expiration.


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