18 - anatomy of ventilation Flashcards
pulmonary ventilation definition:
the physical movement of air into and out of the respiratory tract
function of breathing:
to ensure constant supply of oxygen
to prevent build up of CO2 and therefore maintain pH
inspiration
expiration
inhilation
exhalation
what two principles does pulmonary ventilation rely on?
- Boyles law (pressure of a gas is inversley proportional to its volume (and so the containers volume) at a constant temperature)
- Air flows from an are of low pressure to an area if high pressure
In a syringe
- plunger pulled back
- volume inside increases
- pressure decreases
- fluid/gas moves in
air will enter the lungs when
atmospheric pressure is greater than pressure within the lungs (intraalveolar pressure or intrapulmonary pressure)
air will leave the lungs when
atmospheric pressure is less than pressure in the lungs
how do we change the pressure in the lungs?
by changing the volume of the lungs and thoracic cavity
atmospheric pressure is
760mmHg
pressure in the lungs differs by how many mmHg during inspiration and expiration
-1=759
+1=761
Thoracic volume can be increased by:
-increasing the vertical diameter (diaphragm)
-increasing the anterior posterior diameter (ribs)
-increasing the transverse diameter (up and out) (ribs)
not horizontal diameter
contracting the diaphragm
- flattens the diaphragm
- causes vertical diameter to increase
- increases thoracic capacity by 75%
Elevation of the ribs
- increases the AP diameter and the transverse diameter
- responsible for 25% of thoracic capacity increase
How is AP diameter increased
- pump handle action of the ribs
- elevation of the ribs at the sternal end causes them to become horizontal instead of B\F
How is the transverse diameter increased
The bucket handle - ribs tend to dip in the middle like a sagging bucket handle - during inspiration pick the bucket handle up so its horizontal - this increases the diameter from left to right
How does the thoracic cavity size effect lung size?
The parietal pleura is stuck to the thoracic wall and diaphragm.
the visceral pleura is stuck to the surface of the lungs and moves with the parietal pleura due to surface tension cause by the serous fluid (fills cavities) in the cavity between the two membranes
the pressure in the pleural cavity is
always lower than atmospheric and intrapulmonary pressure because the elastic fibres in the lung tissue are always trying to pull back and cause recoil, causing negative pressure in the pulmonary cavity
If air gets between lung and _____ pleura
- parietal pleura the lung will succeed on pulling back and come free from the pleura and collapse - pneumothroax
- occurs as a result of injury - disease or puncture wound
what causes pneumothorax
- accumulation of air in pleural cavity resulting from disease or puncture wound
- loss of negative intrapleural pressure
- lung collapse
on x-rays what is
- black
- white
- imbetween
- air is black
- connective tissues come up faintly grey
- if the whole lung space is a solid black colour the lung has collapsed
- bone is white
- everything else is imbetween
when one lung collapses
it can push the mediastinum to the other side and cause the other lung to collapse
what to do when someones lung collapses
put a tube into the pleural cavity and put the other end of the tube into water so the air from the space will start bubbling into the water and the lung will re-inflate
what is used in quiet inspiration
active process
- diaphragm 75%
- external intercostal muscles 25%
what is used in forced inspiration
- pectoralis major
- pectoralis minor
- scalenes
- serratus anterior
- sternacloidamastoids
-used by unhealthy people as normal inspiration
external intercostal muscles
go downwards and forwards. start on one rib and go down onto the next one. lift the ribs like you would lift weights from squats
pec minor
pec minor is attached on the shoulder and comes down to the ribs - it pulls ribs 3-5 up and down to help with AP diameter
scalenes
are in the neck come from the cervical vertebra onto the ribs
fixes the first rib in place so the external intercostal muscles can work more effectively
serratus anterior
comes round the side from the spine and helps pull ribs out at the side
sternocleidomastoid
is between the sternum and the clavicle
helps fix the first rib and pulls the sternum out at the front
pec major
fixes your humorous so you can move the ribs up and out
whats used in quiet expiration
nothing its a passive process
relax the diaphragm and external intercostal muscles
whats used in forced expiration
- active process
- internal intercostal muscles
- abdominal muscles - compress contents of abdomen and therefore push them up against the diaphragm to force air out
neural control of ventilation
chemoreceptors
-central and peripheral
chemoreceptors
- detect changes in pH ppO2 and ppCO2
- send information via afferent pathways to the brain via the vagus nerve and glossopharyngeal nerves
where do the signals from the chemo receptors get sent
- through afferent pathways through vagus and glossopharangeal nerve
- to the respiratory centres in the brain stem
- down the efferent pathways down the the phrenic and intercostal nerves
which nervous system controls the diaphragm
signals sent to skeletal muscle so somatic nervous sytsem
central chemo receptors
- respond to changes in pH and CO2
- DONT RESPOND TO O2
- found in the medulla in the brain stem
peripheral chemoreceptors
- respond to ppO2 ppCO2 and pH
- found near baroreceptors
- some called aortic bodies found in aortic arch
- stimulate? vagus nerve
- some called carotid bodies found in the common carotid artery
groups of neurons in the respiratory centres
- medullary rhythmicity area
- pneumotaxic area (pons)
medullary rhythmicitary area
dorsal (back) respiratory group - sets rhythm, stimulates muscles of quiet inspiration
ventral (front) respiratory group - involved in forced expiration and inspiration
pneumotaxic area
influences the dorsal respiratory group by regulating the duration of inspiration
Hering breuer reflex
prevents the over inflation of the lungs
- stretch receptors in the visceral pleura, bronchioles and alveoli
- impulses sent to the pneumotaxic area via the vagus nerve
- duration of inspiration shortened
