Lung volume and its capacities 

Hello students and friends, today we going to learn lung volume and capacities. So, let's start with the basics-

>Lung volumes are directly measured.

>Lung capacities are inferred from lung volumes.

>The average total lung capacity of an adult male= 6 liters of air.

Lung volumes:

1)Tidal volume

2) Inspiratory reserved volume

3) Expiratory reserved volume

4) Residual volume

1) Tidal volume

•Tidal volume is defined as the normal volume of air inspired or expired during quiet breathing.

•Tidal volume = 500 ml.

2) Inspiratory reserve volume

•Extra volume of air inhaled after tidal volume by maximum inspiratory effort.

•Inspiratory reserve volume = 3000 ml in an adult male.

•3300/1900= male/female.

3) Expiratory reserved volume

•Extra volume of air that can be exhaled after tidal volume by maximum expiratory efforts.

•1100 in a normal adult male.

•1200/700=male/female.

4) Residual volume

•Volume of air left out in the lungs after forceful expiration or complete expiration.

•1200/1100=male/female.

Lung capacities:

Lung capacities are the combination of two or more lung volumes

1) Inspiratory capacity

2) Expiratory capacity

3) Functional residual capacity

4) Vital capacity

5) Total lung capacity

1) Inspiratory Capacity:

• Inspiratory volume of air is defined as the maximum volume of air that can be inspired after normal tidal expiration.

• Inspiratory capacity = Tidal Vol. + Inspiratory Reserve Vol.

                                    IC= TV+IRV

                                        = 500+3000

                                        = 3500 ml

2) Expiratory capacity:

• Expiratory capacity is defined as the maximum volume of air that can be expired after normal tidal inspiration.

• Expiratory Capacity = Tidal Volume + Expiratory Reserve Vol.

                                  EC= TV + ERV

                                      = 500+1100

                                      = 1600 ml

3) Functional residual capacity:

• Functional residual capacity is defined as the volume of remaining in the lungs after normal tidal expiration.

• Functional residual capacity= Expiratory Reserve Vol. + Residual Vol.

                                              FRC= ERV+RV

                                                     =1100+1200

                                                     = 2300 ml

4) Vital capacity:

• Maximum amount of air expelled after the deepest possible inspiration.

• Vital capacity= Tidal Vol. + Inspiratory Reserve Vol. + Expiratory Reserve Vol.

                     VC=TV+IRV+ERV

                          =500+3000+1100

                          =4600ml

5) Total lung capacity:

• Total lung capacity is the volume of air present in the lungs after a maximum inspiration.

• Total Lung Capacity=Vital Capacity + Residual Vol.

                               TLC=VC+RV

                                     =4600+1200

                                     = 5800 ml

The partial pressure of Oxygen and carbon dioxide in the body

Alveoli:

Partial pressure of oxygen(PO2)= 104 mmHg

Partial pressure of carbon dioxide(PCO2)= 40 mmHg.

Alveolar capillaries:

PO2= 40 mmHg

PCO2= 45 mmHg

In alveolar capillaries, the partial pressure of oxygen is relatively low because blood has just returned from systemic circulation and has lost much of its oxygen and the partial pressure of carbon dioxide is relatively high because the blood returning from the systemic circulation has picked up carbon dioxide from the tissue.

Hope you all find this helpful for you, if you have any query related to this topic or any other topic then you all are free to contact me via contact us or you can also ask your doubts on the comment box. Thank you! 

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