<< Chapter < Page Chapter >> Page >

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

i want to improve my study i like this app i interest physiology and anatomy
Su Reply
I also like this app am really interested in learning anatomy and physiology.
Johny
I have this book with my anatomy class it's awesome! also if look at crashcourse anatomy on you tube!
AMY
what the name
isaiah
umesh. rede
Rede
what is heart and long type answer
Lalita Reply
its a organ in the body
ay
describe about hear chambers.. valves.. arteries.. veins.. circulation.. inferior/superior venacava, aorta., tricuspid valve, mitral valve. pulmonary artery/vein, how oxigenation occur,systolic presure diastolic pressure.. stroke volume,cardiac output, ets.. heart located in which place, describe it
Sanjith
if you describe what I cited up, thogh you can write a long type answer about heart
Sanjith
autonomic functions took over
Vanarith Reply
What did they take over?
Eric
what is the average volume of blood in men and why does it varrie from women?
Esther Reply
what is the average volume of blood in men
Esther
5to6liter
Sarita
5to6liter dt
Sarita
umesh. rede
Rede
what is the definition of anatomy
Noriah Reply
Search google
killer
^of
chieng
The study of the structure or internal workings of something. "Machiavelli's anatomy 
Eric
post. communi. artey... this may be true 70% hope correct
vikash Reply
what is the strongest muscle in the human body?
Robiam Reply
masseter muscles
Om
yes masseter..... jaw muscle is the strongest muscle..
Sarita
Kidneys have direct effect on which
The function the loop
function of the loop?
Eric
the function of the loop of henle is to increase surface area for reasorbtion.
Conan
what is an atom and it's functions
Jany
An atom is the basic building block of matter.
Eric
which is the largest digestive gland in our body
Shubu
stomach
Barbara
What is the smallest bone in the body of the human being?
Kelvin
pisiform
Chulit
how many found in the head
obakunmi
4
ayesha
I think stapes is the smallest bone in human body
Sanjith
22
Sanjith
yes stapes is the smallest bone of our body
Sarita
the smallest bone is stapes in the ear
Isaac
smallest bone in human body is stapes or stirrup present in the middle ear ..
Om
stapes yes
Robiam
blood work and purification and it leads to cardiac systen
vikash
explain function of kidney
Noel Reply
filtration
Naqash
Secretagogue hormones
Sa
Organising water
Sa
hi
Jany
they help in the reproduction of sperms
Jany
Their main job is to cleanse the blood of toxins and transform the waste into urine. The kidney have several functions though. I think it is important to know them, but not in depth. But to truly understand the kindney's over all importance.
Eric
I meant to say the kidneys have.
Eric
what us the name of the longest bone in the body
Ohuche Reply
femur
Zaini
femur
AKHILA
anatomical planes of the body
Opio Reply
sagittal plane, transverse plane and coronal plane
Ogechi
the only moveable bone in head
Sewar Reply
the only movable bone in head
Sewar
stapes. in the ear. but one could argue, all three ear bones move. malleus, Incas, and stapes.
Conan
mandible
Ankita
The mandible is.
Eric
The only unattached bone in the body is the hyod bone in the neck.
Eric
The mandible. It's the part that enables us to talk.
chieng
Mandible present in the head
Shubu
how can u protect ur self from corona
Nity Reply
how can u know that u have corona
Nity
with a test
Danielle
can protect by social distancing, following hand hygiene and standard precautions
Danielle
tq very much
sudhakar
as per the CDC incubation period 2 to 14 days. typical symptoms. typical symptoms, fever, cough, malagia, fatigue, and shortness of breath. alcohol based hand sanitizers. 60 to 85% strength, physical barriers, PPE. a face mask with three layers. Keep a physical distance of 6 feet or more.
Conan
a nasal swab test, or a blood test to confirm SARs-cov-19.
Conan
what is corona
Nity Reply
virus
Danielle
It's a virus which causes COVID 19
chieng
The space between the two lungs is called
Zo Reply
Pleural cavity
Jane
No...Mediastinum
Zo
jaundice disease?
Ibrahim
No.. it's a sign
Moses

Get the best Anatomy & Physiology course in your pocket!





Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Anatomy & Physiology' conversation and receive update notifications?

Ask