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Physical factors affecting ventilation

In addition to the differences in pressures, breathing is also dependent upon the contraction and relaxation of muscle fibers of both the diaphragm and thorax. The lungs themselves are passive during breathing, meaning they are not involved in creating the movement that helps inspiration and expiration. This is because of the adhesive nature of the pleural fluid, which allows the lungs to be pulled outward when the thoracic wall moves during inspiration. The recoil of the thoracic wall during expiration causes compression of the lungs. Contraction and relaxation of the diaphragm and intercostals muscles (found between the ribs) cause most of the pressure changes that result in inspiration and expiration. These muscle movements and subsequent pressure changes cause air to either rush in or be forced out of the lungs.

Other characteristics of the lungs influence the effort that must be expended to ventilate. Resistance is a force that slows motion, in this case, the flow of gases. The size of the airway is the primary factor affecting resistance. A small tubular diameter forces air through a smaller space, causing more collisions of air molecules with the walls of the airways. The following formula helps to describe the relationship between airway resistance and pressure changes:

F = P / R

As noted earlier, there is surface tension within the alveoli caused by water present in the lining of the alveoli. This surface tension tends to inhibit expansion of the alveoli. However, pulmonary surfactant secreted by type II alveolar cells mixes with that water and helps reduce this surface tension. Without pulmonary surfactant, the alveoli would collapse during expiration.

Thoracic wall compliance is the ability of the thoracic wall to stretch while under pressure. This can also affect the effort expended in the process of breathing. In order for inspiration to occur, the thoracic cavity must expand. The expansion of the thoracic cavity directly influences the capacity of the lungs to expand. If the tissues of the thoracic wall are not very compliant, it will be difficult to expand the thorax to increase the size of the lungs.

Pulmonary ventilation

The difference in pressures drives pulmonary ventilation because air flows down a pressure gradient, that is, air flows from an area of higher pressure to an area of lower pressure. Air flows into the lungs largely due to a difference in pressure; atmospheric pressure is greater than intra-alveolar pressure, and intra-alveolar pressure is greater than intrapleural pressure. Air flows out of the lungs during expiration based on the same principle; pressure within the lungs becomes greater than the atmospheric pressure.

Pulmonary ventilation comprises two major steps: inspiration and expiration. Inspiration is the process that causes air to enter the lungs, and expiration    is the process that causes air to leave the lungs ( [link] ). A respiratory cycle    is one sequence of inspiration and expiration. In general, two muscle groups are used during normal inspiration: the diaphragm and the external intercostal muscles. Additional muscles can be used if a bigger breath is required. When the diaphragm contracts, it moves inferiorly toward the abdominal cavity, creating a larger thoracic cavity and more space for the lungs. Contraction of the external intercostal muscles moves the ribs upward and outward, causing the rib cage to expand, which increases the volume of the thoracic cavity. Due to the adhesive force of the pleural fluid, the expansion of the thoracic cavity forces the lungs to stretch and expand as well. This increase in volume leads to a decrease in intra-alveolar pressure, creating a pressure lower than atmospheric pressure. As a result, a pressure gradient is created that drives air into the lungs.

Questions & Answers

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Natarajan Reply
3 longitudinal bands of smooth muscles found in large intestines
what's is sutures
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Roy Reply
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anatomy mins
when two or more bones meet.
I am interested in learning but it is a little threatening corona virus covid 19
Samnang Reply
I don't know about Corona virus
what would you like to know?
what is a peripheral protien
Ayesha Reply
actually its located in between the lipid layer, it does not specify if it's closer to the inside or the outside of the cell
It is protein found in lipid bilayer but found attached with Cytoplasm aspect
what are the collection of blood.?
sunshine Reply
Effect of exercise on different body systems?
Rania Reply
what is ambroylogy
kashif Reply
embryology..is the biological studing of embryos
I know biological study but embryology mean any pic, example?
I like to learn about medical and more
what is the function of the blood
Yolanda Reply
Transporting of oxygen,fighting against germs, forms clotting ,distribution of nutrients and minerals through out the body ,
Transportation of gases such as oxygen and water blance and carrei metabolites to the exit organ and Acid base equilibrium and clotting blood and Immune
What are Gross and microscopicAnatomy
Waiswa Reply
study of the internal structures of a human being
gross anatomy is the study of body parts that can be seen with our naked eyes while micro anatomy involves the study of body parts that cannot be seen with our naked eyes but with the aid of a microscope
gross means examination of specimen or tissue with bare (unaided ) eye while microscopic means examination of same with the help of microscope
what is physiology
Waiswa Reply
what are blood pressure
physiology is the study of the normal functions of organs
Blood pressure is a when systolic phase is 190 and diastolic phase 90.
systolic phase is 180.not 190
explain the anatomy of the human heart
Maia Reply
is the scientific study of the body structure ie like structure very small which can be only observed.
where can I find the muscle organization
Taonga Reply
what is the physiology?
Josoph Reply
the study of functioning of body organs
In other words... Physiology is the study of normal function within living creatures. It is a sub-section of biology, covering a range of topics that include organs, anatomy, cells, biological compounds, and how they all interact to make life possible.
which part of the heart supply blood to all parts of the body
left heart supply all the body.
what analysisof an anatomy
Okay thanks distinguish between blood pressure and body organs
branch of anatomy which deal with the life process and function
how oxygen and carbondioxide are transported in the body.
riddon Reply
Through the lungs as we inhale oxygen it diffuses into the alveoli while carbon dioxide diffuses out of the blood and from our bodies
from lungs o2 diffuses into blood capillaries from where it is bound to heam part of hb there after it is transported to different parts of body ...co2 that is produced during respiration in cells gets transported to lungs from lungs it gets exhalated
o2 is mainly transported by hb present in blood while co2 is transported main as bicarbonate.. detailed topics

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