# 39.2 Gas exchange across respiratory surfaces

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By the end of this section, you will be able to:
• Name and describe lung volumes and capacities
• Understand how gas pressure influences how gases move into and out of the body

The structure of the lung maximizes its surface area to increase gas diffusion. Because of the enormous number of alveoli (approximately 300 million in each human lung), the surface area of the lung is very large (75 m 2 ). Having such a large surface area increases the amount of gas that can diffuse into and out of the lungs.

## Basic principles of gas exchange

Gas exchange during respiration occurs primarily through diffusion. Diffusion is a process in which transport is driven by a concentration gradient. Gas molecules move from a region of high concentration to a region of low concentration. Blood that is low in oxygen concentration and high in carbon dioxide concentration undergoes gas exchange with air in the lungs. The air in the lungs has a higher concentration of oxygen than that of oxygen-depleted blood and a lower concentration of carbon dioxide. This concentration gradient allows for gas exchange during respiration.

Partial pressure is a measure of the concentration of the individual components in a mixture of gases. The total pressure exerted by the mixture is the sum of the partial pressures of the components in the mixture. The rate of diffusion of a gas is proportional to its partial pressure within the total gas mixture. This concept is discussed further in detail below.

## Lung volumes and capacities

Different animals have different lung capacities based on their activities. Cheetahs have evolved a much higher lung capacity than humans; it helps provide oxygen to all the muscles in the body and allows them to run very fast. Elephants also have a high lung capacity. In this case, it is not because they run fast but because they have a large body and must be able to take up oxygen in accordance with their body size.

Human lung size is determined by genetics, gender, and height. At maximal capacity, an average lung can hold almost six liters of air, but lungs do not usually operate at maximal capacity. Air in the lungs is measured in terms of lung volumes and lung capacities ( [link] and [link] ). Volume measures the amount of air for one function (such as inhalation or exhalation). Capacity is any two or more volumes (for example, how much can be inhaled from the end of a maximal exhalation).

Lung Volumes and Capacities (Avg Adult Male)
Volume/Capacity Definition Volume (liters) Equations
Tidal volume (TV) Amount of air inhaled during a normal breath 0.5 -
Expiratory reserve volume (ERV) Amount of air that can be exhaled after a normal exhalation 1.2 -
Inspiratory reserve volume (IRV) Amount of air that can be further inhaled after a normal inhalation 3.1 -
Residual volume (RV) Air left in the lungs after a forced exhalation 1.2 -
Vital capacity (VC) Maximum amount of air that can be moved in or out of the lungs in a single respiratory cycle 4.8 ERV+TV+IRV
Inspiratory capacity (IC) Volume of air that can be inhaled in addition to a normal exhalation 3.6 TV+IRV
Functional residual capacity (FRC) Volume of air remaining after a normal exhalation 2.4 ERV+RV
Total lung capacity (TLC) Total volume of air in the lungs after a maximal inspiration 6.0 RV+ERV+TV+IRV
Forced expiratory volume (FEV1) How much air can be forced out of the lungs over a specific time period, usually one second ~4.1 to 5.5 -

#### Questions & Answers

what is cell?
The smallest structure and functional unit
vinod
Hydra reproduce through which process
which is smallest organ in our body
Techi
pineal gland
Himangshu
Yh in the ears...
Mozua
who is the father of mycology
Heinrich Anton de Bary
Delissa
describe the similarities and differences between cytokinesis mechanism found in animal cells versus in plant cells
are humans beings considered to have the eukaryotic cells
yes.....
Delissa
eukaryotes are organisms that possess cells with a nucleus enclosed in a membrane, humans, and all complex organisms are eukaryotes.
Delissa
so humans and animals also have cell membranes.... cause I did this test prep and they said plants...I just want to be sure
success
success
eu= "perfect", "good", karyon= nut, amound, nucleus
Tiago
you're welcome. Plants are also eukaryotes.
Delissa
plants, like animals, possess a nucleus bound by a membrane.
Delissa
similarities and differences between cytokinesis mechanism found in animal cell vs cell division
what is the name of a male flower?
staminate means flower containing only stamen
Falak
what is the definition of evolution in a population?
the slow changing of a species to adapt to any changes in the environment or how it feeds/hunts. im not good at explaining things lol.
Eclipse
the organ which is sensitive to light in euglena
the organ which is sensitive to light in euglena is
Fatimah
all chlorophyll containing motile cells are sensitive to light
Himangshu
there is no more other chapter
Give tow examples for nutritional deficiency Diseases-
How does a plant cell look like
in a sleepers form
David
what do you mean ? I could not understand
Gul
they have a regular shape and a large vacoule
Fatimah
I thought it looked like rectangle
Abrahán
a stage in mitosis wherein in spindle fibers begin to shorten to pu the sister chromatids away from each other towards the opposite ends of the cell
a stage in interphase where chromosome s are duplicated
Earl
What is biodiversity
Hmm
Hele
Name two secretions of Golgi apparatus