Air flow and gas exchange Flashcards
What is the resting respiratory rate in
- domestic species
- horses
- 20-30 brpm
2. 10-12 brpm
Define the following:
- normal resting breathing
- increased RR
- increased respiratory depth
- laboured breathing
- absence of breathing
- Eupnoea
- Tachypneoa
- Hyperpneoa
- Dysponea
- Apnoea
What is the purpose of breathing?
Ventilate the alveoli at which gas exchange occurs
How are pressure differences created during inspiration?
- diaphragm contracts, flattening caudally
- external intercostal muscles contract
- lift ribs out and cranially
- size of the thoracic cavity is increased
Describe how active expiration occurs
- uses abdominal wall muscles to push the abdominal contents cranially
- forces the relaxed diaphragm to dome upwards
- costal portions of the internal intercostal muscles pull the ribs caudally and inwards
- size of thorax decreases and pressure in the alveoli increases
What does the compliance of the lungs depend on?
- elasticity in the lung tissue
- surface tension in the alveoli
What creates surface tension?
At any interface between water and air, the hydrogen bonds between water molecules create surface tension.
What makes up surfactant?
Phospholipids, proteins and calcium ions
How does surfactant reduce surface tension?
Reduce the formation of H-bonds between water molecules. The hydrophilic heads of the phospholipids dissolve in the liquid lining the alveoli, and the tails remain on the inside of this liquid layer preventing H-bond formation.
What is atelectasis?
Collapse of alveoli if insufficient surfactant is released
The pressure (P) inside an alveolus is dependent on which two factors?
Its radius and surface tension
How is the pressure alveoli maintained to be the same as larger alveoli?
The concentration of surfactant is higher in smaller alveoli
Resistance to movement through a tube is governed by which 3 factors?
- length of the tube
- radius of the tube
- viscosity of the substance traveling through it
How does turbulence affect air flow?
- greatly increases resistance as there is greater friction between molecules in turbulent air.
By which system is the smooth muscle in the walls of the airways innervated and how does this affect them?
Autonomic NS
Activation of the sympathetic limb of the ANS, the smooth muscle cells relax due to stimulation of β2 adrenoreceptors, causing an increase in the radius of the airways and a reduction in resistance to flow and increased lung ventilation to allow for an increased oxygen demand
What is tidal volume?
The volume of air moved during a respiratory cycle
How is minute ventilation calculated?
Tidal volume x number of breaths
What is the fraction of oxygen in normal room air?
21% = 0.21
What is the partial pressure of a gas and how is it calculated?
The pressure exerted by an individual gas within a gas mixture
e.g. PO2 in normal room air = 0.21 x atmospheric pressure = 0.21 x 760mmHg
What does inspired air consist of?
Air + water (it has been humidified in the airways)
Describe how the partial pressure of oxygen and carbon dioxide are in the blood entering the lung capillaries from the right ventricle?
- low PO2
- high PCO2
How are the pressure gradients enabling movement of O2 and CO2 maintained?
Constant consumption of O2 and production of CO2 by respiration in the tissues
Which two factors need to be balanced for correct exchange of gases?
Ventilation and perfusion
What is dead space?
Regions of the respiratory tract which are ventilated but which do not participate in gas exchange
