18-20 Flashcards
What is physiologic dead space?
the sum of anatomic and alveolar dead space
- anatomic = air left in conducting airways
- alveolar = alveoli with no blood flow
What is gill dead space?
the water that flows through gills but not between lamellae consitutes anatomic dead space
- Lamellae dead space is if water passes between and then no exchange of gases
What is the expired minute volume?
volume of air moved out of the lungs in a minute
Ve = Vt x Breathing Frequency
- based on assumption that the volume inspired is equal to the volume expired
- not quite true
The volume of fresh air that actually reaches alveoli is the alveolar ventilation
Va = (Vt - Vd) x f
- Vt is the tidal volume
- Vd is the dead space volume
- f is breathing frequency
How can the alveolar ventilation be measured directly?
- volume of expired CO2/fractional concentration of CO2 in the alveolar gas x K (to account for BTPS and STPD conversion)
K usually = 0.865
= alveolar ventilation equation
VeCo2 from spirometer measurements
What happens during hyperventilation?
doubling alveolar ventilation
arterial Pco2 reduces (halves)
- P02 must increase
Palveolar O2 increases but not double
What happens during hypoventilation? halving of alveolar ventilation
double arterial Pco2
- alveolar P02 must decrease
What is the respiratory exchange ratio?
R = volume CO2 exhaled/ volume of O2 taken up
What is the alveolar gas equation?
- work out alveolar oxygen partial pressure
PICTURE OF EQUATION
- pg 18
Where is the central pattern generator of breathing in the brain?
brain stem
- both frequency and tidal volume alteration
- probably the medulla
What is the negative feedback system if differs from 40mmHg PCO2 or 100mmHg PO2?
detected by sensors
- fed to controller
- superimposed on regular cyclic pattern
- arterial O2 conc is achieved by regulating arterial blood CO2 content
What happens when CO2 dissolved in blood?
How to get HCO3- ions
- react with water to get carbonic acid which dissociates
- reaction to carbonic acid by carbonic anhydrase
How is CO2 level measured in blood?
Proton content (pH)
- chemoreceptive cells
Carotid and aortic
- outside of brain
What are the chemosensitive cells of the carotid body?
glomus cells
- same in aorta
- inhibition of potassium channel activity with increase H+
Formula for calculating partial pressure
P = fraction of mixture occupied by gas x total pressure exerted by mixture
how to calculate the partial pressure of gas in a liquid
Pgas = [conc]/Solubility coefficient of gas
How to calculate the concentration of oxygen at the surface in fractions of an atmosphere?
FO2 = (VO2 x r^2)/6K
- VO2 = rate of oxygen consumption as cm3 of oxygen per cm3 tissue per minute
- r = radius of sphere in centimetres
- K = diffusion constant in cm2 per atmosphere per minute
What is the respiratory organ of insects?
Tracheal system
- exploits fact that oxygen and carbon dioxides diffuse 10,000 faster in air than in water
Structure of tracheal system
Spiracle Trachea Tracheoles - air filled tubes - access to all cells - At various intervals - small air sacs - increase tracheal volume and so oxygen storage capacity
How can insect tracheal system in water work ->
Diffusion gill
- Notonecta
- Have bubbles
Attached to the ventral surface of the abdomen
- basically the same pressure as atmospheric pressure as doesnt dive very deep
- 6 hours
- though dependent
1. Insect metabolic rate
2. Initial size of bubble
3. Depth at which bubble taken
Way to stabilise bubble?
Plastrons
- hairs = hydrophobic
- not like diffusion gill
Comparison as air and water - respiratory medium
- O2 concentration
- 1:30 ratio water-air - Viscosity
- 50:1 - Heat Capacity
- 3000:1 - Diffusion coefficient
- 1:300,000
How have the lungs and gills evolved for gas exchange?
- maximise gas exchange
- minimise work associated with it
- as evolved in air and water respectively - different ways of doing that
Structure of the lung
DIAGRAM
- airway branches
- narrower, shorter and more numerous
CONDUCTING ZONE = first 17 generations
- Warm and humidify air
- Distribute air to the depths of the lungs
- Defence against bacteria and dust
Trachea —> bronchi —>lobar bronchi —> segmental bronchi —>all the way till the terminal bronchioles
- no exchange in this region —>anatomic dead space
First 4 = U shaped cartilage
then plates before disappearing
