The Repary Sys 2 Flashcards
Why is the resistance the highest in medium sized bronchi
- diameters of the early conducting are huge
- progressive branching of smaller airways increase total cross-sectional area
- known as the transition point which is thought to be about 4th-8th generation of bronchi
True or Fakse
Since the respiratory passageway from the nasal cavity to the terminal bronchioles serves merely as access or exit routes for air, it is also referred to as anatomical dead space
True
The lungs
Are soft, spongy organs that occupy the entire thoracic cavity minus the mediastinum
- it’s divided by fissures into lobes: 3 on the right and 2 on the left
- the root of each lung starts at an indentation called the hilum
- it receives the primary bronchi; pulmonary arteries and pulmonary vein
The medial surface of the left lung has a cardiac impression for the heart
Each lung
Is enclosed on a double layered serous membrane called pleura(e)
- the parietal pleura is attached to the thoracic walls and diaphragm
- viscera pleura is attached to the lung tissues
The pleural space
Between the membranes contains pleural fluid
- reduces friction when the lungs inflate and deflate during breathing
Alveoli
99% of the lungs are made up of alveoli(around 480 million per lung)
- each alveolus is a pouch about 0.2 to 0.5 mm in diameter
- simple squamous epithelium
- the external surface is covered with the capillary network and together form the respiratory membrane
Alveoli are composed of 3 cell types
Type 1: simple squamous epithelial cells that form the mechanical barrier if the alveolus
Type 2: cells that secrete alveolar fluid containing surfactant
Dust cells: phagocytes that defend against foreign materials not removed by mucus and cilia
Pulmonary surfactant
is a mixture of phospholipids and proteins that coats the inner surface in contact with air
Surfactant
The surface tension of alveolar fluid arises from the cohesive forces between the water molecules, which collapses the alveolar wall
Surfactant disrupts this cohesive forces between by:
- allowing alveoli and respiratory bronchioles to stay inflated
- reducing the work of breathing(lungs are easier to inflate)
Clinical Application:
Infant respiratory distress syndrome (IRDS) is a condition where insufficient surfactant is produced in premature babies.
What does this lead to?
• increased surface tension in alveoli from alveolar fluid, which can collapse the terminal reparatory pathway (during expiration)
• greater effort to reinflate the alveoli
• use of mechanical ventilators
Ventilation
Pulmonary ventilation(breathing) occurs due to differences in air pressure between the atmosphere and and the alveoli
It consists of 2 phases:
Inspiration(inhalation): air flows into lungs
- Expiration(exhalation): air exits the lungs
One complete breath, in and out is called a respiratory cycle
Ventilation can be quiet or forced
Quiet ventilation: relaxed, unconscious and automatic breathing
Forced ventilation: unusually deep or rapid breathing
- occurs during exercise, singing, playing a wind instrument, blowing up a balloon sneezing or in a diseased state
- uses accessory respiratory muscles
What doesn’t happen during inspiration?
Pressure inside the lungs is increased
Inspiration
- is always active
This means that it requires energy(ATP) input
During quiet inspiration, only the diaphragm and external intercostal muscles contract - the diaphragm increases vertically
- the external intercostal muscle increases laterally and in anterior/posterior dimensions
Expiration
Quiet expiration is an energy saving passive process
- inspiration muscles relax
- natural tendency of lung tissue recoil
Forced expiration becomes active
- abdominal and pelvic muscles, and muscles and internal intercostal muscles to contract to reduce thoracic dimension and increase pressure
External intercostal muscles
External intercostal muscles are inspiratory muscles.
• located on the outer surface of the ribs
• directed downward and forward
• contract to pull the ribs upward and outward
Internal Intercostal Muscles
Internal intercostal muscles are expiratory muscles. located deeper and run perpendicular to the external intercostal muscles
• contract to pull the ribs downward and inward
Lung Volume and caps
Lung capacities- different combinations of lung volumes
Tidal volume(TV)- respiratory volume inhaled or exhaled during normal breathing
Vital capacity(VC)- total amount of exchangeable air
Inspiration reserve volune(IRV)- amount of air that can be forcefully inhaled after a normal tidal wave
Expiratory reserve volune(ERV)- amount of air that can still be exhaled(forcibly) after a normal exhalation
Residual volume(RV)- reaming in the lungs after a forceful exhalation
Mechanics of breathing
Describes how breathing occurs
- involves pressure changes in the thoracic cavity
- based on Boyles law: pressure and volume are inversely related: P1V1=P2V2
Volume changes lead to pressure changes which lead to the flow of gases
Atmospheric pressyre(Patm): the air pressure surrounding the body
- 760mmHg at sea level is 1 atmospheric pressure
Respiratory pressures are defined relative to Patm
- (-) less than
- (+) greater than
- 0 is equal to
Air moves out of the lungs when the pressure inside the lungs is
Greater than the pressure in the atmosphere
Charc of each pressure
Atmospheric:
- the pressure of air around us
- 760 mmHg at sea level
Intrapleural:
- always slightly below atmospheric pressure
- if this pressure equals the atmospheric pressure, the lungs collapse
Intrapulmonary pressure:
- as it decreases, the lungs collapse
- fluctuates below and above atmospheric pressure during breathing
- Rises wells over atmospheric pressure during a forceful cough
Trans pulmonary pressure
= intrapulmonary pressure- intramural pressure
At rest is 4mmHg
This pressure gradient determines the size of the lungs, the greater this is, the larger the lungs become
Gas exchange
Occurs at the site of the lungs or peripheral tissues
- covered by simple diffusion
In blood
, the concentration of gases is expressed as its partial pressure(PO2 or CO2)
- according to Daltons Law, the partial pressure of each gas is directly proportional its percentage in a gas mixture
Pulmonary gas exchange
Oxygen
O2 has a steep partial pressure gradient from 100mmHg in alveoli to 40 mm in blood
The diffusion of O2 occurs much faster than the speed of blood flow
- this ensures adequate oxygenation if blood flow increases a lot
Pulmonary gas exchange
Carbon diode
Has a smaller partial pressure gradient from 45mmHg in blood to 40mm in the alveoli
However CO2 is much more soluble in plasma and alveolar fluid than O2
- it diffuses quickly and in equal amount to oxygen
Once diffused across the pulmonary membrane, O2 is carried in blood on 2 ways
1-2% is dissolved in plasma
The rest is bound to hemoglobin in erythrocytes
CO2 is transported 3 ways in blood
-7-10% is dissolved in plasma
- about 20% is bound tit he globin part of hemoglobin
- the rest is transported as bicarbonate ions in plasma;part of the blood buffer system)
True or False
A drop in blood ph is likely to cause a slower breathing rate
False
It causes a faster and deeper breathing rate
Drivers of Breathibg
The respiratory centres(medulla and pons) adjust the rests, rhythm, and depth of breathing to maintain normal blood gas levels
- receives input from central and peripheral chemoreceptors that monitor the composition of blood and CSF
- the 3 chemical stimuli: O2, CO2, and H(ph)
Drivers of breathing; PCO2
Is the most important factor influencing respiration
- CO2 enters CSF which increases CSF H concentration
- detected by central chemoreceptors
For PO2, the respiratory centres are triggered when it falls below 100mHG
A hyperventilating person is asked to breathe into a paper bag because it
Helps retain CO2 in the blood
