Physiology Flashcards
functions of the respiratory system
*Gas exchange
acid base balance
protection from infection
communication via speech
type 1 pneumocytes
cell type + function
simple squamous epithelium
for gas exchange
type 2 pneumocytes
cell type + function
Cuboidal epithelium
produce surfactant
muscles for inspiration
diaphragm (contracts + lowers)
external intercostal muscles (pull ribs up)
muscles for forced expiration
internal intercostal muscles (force ribs down)
abdominal muscles
Boyle’s law
+ relation to breathing
the pressure exerted by a gas is inversely proportional to its volume
*When you increase the volume in the lungs/ intrapleural cavity, the pressure decreases
steps of inspiration
- contraction of muscles
- decrease in intrapleural pressure
- lungs expand
- decrease in alveolar pressure
- air flows into lungs
Alveolar pressure (P (subscript)A)
pressure inside lungs
changes from slightly +ve to slightly -ve with breathing cycle
intrapleural pressure (P (subscript)ip)
pressure inside pleural cavity always negative (and less than alveolar pressure*) in health due to elastic recoil of lungs and chest wall away from each other
*If not, the lungs would collapse
transpulmonalry pressure (P (subscript)T)
alveolar pressure - intrapleural pressure
always positive in health. if negative, the lungs would collapse due to their elastic recoil.
respiratory minute volume/ pulmonary ventilation
the volume of air inhaled or exhaled from a persons lungs per minute
mechanical factors affecting respiratory minute volume
- difference between atmospheric and alveolar pressures
2. airway resistance (mostly determined by radii of airways)
Alveolar ventilation
volume of fresh air getting to the alveoli (and so available for gas exchange) per minute
alveolar PO2
100mgHg
13.3kPa
Arterial PO2
75mgHg
10kPa
Alveolar PCO2
40mgHg
5.3kPa
Arterial PCO2
46mgHg
6.1kPa
The role of pulmonary surfactant
reduces surface tension on the alveolar surface membrane which…
reduces tendency for alveoli to collapse
increases lung compliance (stretchability)
makes breathing easier
is more effective in smaller alveoli as is more concentrated
surface tension
the attraction between water molecules that occurs at any air-water interface
The law of Laplace
P = 2T/r
P = inwardly directed pressure T = surface tension (reduced by surfactant) r = radius of alveoli
significance of the law of laplace
inwardly directed pressure is equalised in differently sized alveoli
As inwardly directed pressure is greater in smaller alveoli but surfactant is more effective as it’s more concentrated
2,3-DPG
A sugar produced by RBCs in hypoxic conditions. This shifts the oxyhamoglobin dissociation curve to the right (decreases Hb affinity for O2) for more oxygen delivery
factors that affect gas exchange
the partial pressure gradient
gas solubility
available surface area
the thickness of the membrane
distance
the ventilation:perfusion ratio should be…
1 in a healthy lung