Week 20: (A) Respiratory Physiology Flashcards
What branches are the conductive zone?
1-16
What branches are the respiratory zone (acinus)?
17-23
How do we measure how much of a gas is in a space?
partial pressure
What is partial pressure?
The notional pressure of a constituent of gas if it alone occupied the entire volume of the original mixture at the same temp.
What percent room air is oxygen?
0.21/ 21%
What is the pressure of air at room temp?
760mm Hg
Does concentration of oxygen change with what state the has is in?
YES, room air has a higher concentration that water and blood (both the same)
Why do we use partial pressure?
Partial pressure refers to a number of gasses in an area
Tells us the direction which has moves, Conc does not!
Is partial pressure and Concentration proportional?
YES
What is the partial pressure exchange when O2 enter the alveolus?
atmospheric pressure = 156mm Hg to alveolar 100 mmHg
Where does the O2 in the airways dissolve?
Airway surface liquid (ASL) lining the alveolus
What is the O2 solubility in the ASL?
0.003ml O2/100ml/1mmHg
What is PO2 at 100mmHg in the ASL?
- 003ml X 100
0. 3ml O2/100ml ASL
how much oxygen does blood contain?
contains 0.003ml O2/100ml/1mmHg Po2
PLUS
All the O2 bound to haemoglobin (1.39ml O2/g Hb x Hb conc x %Hb saturation/ 100)
What is the PO2 of mixed venous blood that arrives at the lungs?
40 mmHg
What is the O2 conc of mixed venous blood arriving at the lungs with PO2 40mmHg ?
(40 x 0.003) + (1.39 x 15 x 75/ 100) = 0.12 + 15.64
–> 15.8 ml O2/100ml blood
What has higher O2 concentration, venous or ASL?
venous
venous= 15.8 ml
ASL = 0.3 ml
What has higher partial pressure, ASL or venous?
ASL
ASL= 100 mmHg
Venous = 40 mmHg
What would happen if O2 moved according to Conc gradients?
move from bloods to ASL out of the body.
what is the pathway of O2 entering the body? from dry room air to Cytochrome C oxidase…
Dry room air- 159 Tracheal gas- 149 Alveolar gas- 100 Pulmonary venous blood-98 Systemic arterial blood-96 mixed venous- 40 mitochondria-2 Cytochrome C oxidase -~0
What drives the surface area of alveoli?
the number of alveoli
What percent of the lungs is the respiratory zone?
95%
What is the surface area of the respiratory zone?
130m^2 packed into a 6L volume
What are 2 consequences to airway branching for lung function?
1) increase SA for gas exchange
2) Dissipates resistance to airflow as airway diameter narrows towards the respiratory zone
Why is it that we are able to respire as the airway diameter decreases?
down generations…
According to Poiseuille’s Law
It is about the total surface area for has exchange not just the individual alveolus
Combined cross-sectional area of the airways
Compare branch generation 1 to branch generation 17 about; No. of airways, total cross-sectional area (cm2) and Airflow Resistance factor (&)?
BG 1; 1, 2.5, 100*%
BG 17; 23630, 300, 0.9%
What is the upper airways ?
Nose, nasal cavity, pharynx
What is the lower airways?
Larynx; trachea, bronchial tree and the lungs
What is a definition of Poiseuille’s Law?
A doubling of total airway diameter at each branch generation reduces resistance 16 fold.
What drives the bulk gas into the conductive zone?
Driven by difference in net pressure caused by the expansion and relaxation of chest cavity
What is the movement of gas form the atmosphere to airways?
CONVECTION
What is the movement of gas from the airways to the blood called?
DIFFUSION
What is required for gas to move into the airways from the atmosphere?
Open airways
Will move into lung if pressure is below the atmospheric
What is needed for has to move out of the lungs to the atmosphere?
relaxation; lung deflated shape due to the elastic recoil
this causes the pressure on the walls of alveoli
This causes the pp of the lungs to be above atmospheric
CONVECTION OCCURS
What is the alveolar pressure the sum of?
elastic recoil pressure (airways collapsing)
Also, variable by muscular effect (Pleural P)
What muscles are used in inspiration of the lungs?
external intercostal muscles between rib cages
What direction do the ribs move in inspiration?
upwards and outwards
What happens when the diaphragm contracts?
diaphragm moves down, pressure decreases inside airways, creating more space –> gas moves into airways
What are the 3 categories of the main inspiratory muscles?
Diaphragm
External intercostals
Accessory muscles
what are the key features of the diaphragms during inspiratory?
- dome shaped, sits above liver
- Phrenic nerves, C3-5
- Flattens on contraction
- Moves 1cm in quiet breathing, up to 10cm
what are the accessory muscles and key features?
sternocleidomastoid, scalene, plus some others
Chest expands, intrapleural pressure falls
How do the lungs expire air?
mostly by elastic recoil (at rest)
What muscles in the lungs cause expiration?
internal intercostal muscles (slope down riband back)- exercise
What way motion do the lungs move when expiration occurs?
depressing lower rib. against lung
When does forced expiration occur?
exercise, voluntary (cough, sneeze, defection)
What are the main expiratory muscles used in forced expiration occurs?
abdominal wall - push guts up against diaphragm
internal intercostals
define partial pressure
The pressure of a gas in a mixture of gases is equivalent to the percentage of that particular gas in the entire mixture multiplied by the pressure of the whole gaseous mixture.
Example:
Atmospheric Pressure = 760mmHg
Pressure of air we breathe therefore = 760mmHg
21% of air we breath = O2
Partial pressure of O2 in air we breath = 21% x 760mmHg
= 160mmHg
Calculate the partial pressure…
O2 = 21%
Atmospheric pressure = 760 mmHg
percent of Oxygen X atmospheric pressure 760 mmHg
21 x 760
= 160 mmHg
Why is the partial pressure of oxygen lower in the alveolar space compared to atmospheric pressure (160mmHg)
diluted by anatomical dead space and residual volume
saturated by water vapour, needs to be in solution.
It is constant equilibrium with gas in the blood
What is the normal partial pressure of CO2 in the alveoli?
40mmHg
5.3 kPa
In health, are the partial pressure of CO2 and O2 the same in the alveoli and systemic arterial blood?
yes
What are the values of alveolar ventilation in hypo-ventilation?
PO2 falls to 30 mmHg and PCO2 rises to 100 mmHg.
What are the values of alveolar ventilation in hyper-ventilation?
PO2 rises to about 120 mm Hg and PCO2 falls to about 20 mmHg.
What is the alveolar partial pressure of oxygen?
100mmHg
13.3 kPa
For any given change in pressure in the lung, where has the biggest change in volume?
at the base of the lung and less at the apex
alveolar ventilation greatest at the base.
Where is compliance greatest in the lung?
most compliance at the base
