Physiology 1 (Week 1) Flashcards
What is internal respiration?
The intracellular mechanisms which consume O2 and produce CO2
What is external respiration?
The sequence of events involved in gas exchange of O2 and CO2 between the external environment and body cells
Describe the four stages of external respiration.
Ventilation - gas exchange between atmosphere and air sacs in the lungs
Gas exchange between alveoli and blood
Transport of gases between lungs and tissue
Exchange of gases between blood and tissue
Explain Boyle’s Law.
At a constant temperature, the pressure exerted by a gas is inversely proportional to the gas volume
Air flows down a ______ gradient.
pressure
During inspiration, the intra-alveolar pressure is ___ ___atmospheric pressure.
less than
Why do the thorax and lungs expand during inspiration?
Contraction of inspiratory muscles
Name two forces which hold the thoracic wall and the lungs together.
- Intrapleural fluid cohesiveness (water molecules attracted to one another)
- Negative intrapleural pressure (transmural pressure gradient - lungs forced to expand, chest forced to squeeze inwards)
Name three pressures important in preventing lung collapse.
- Atmospheric pressure
- Intra-alveolar pressure
3, Intrapleural pressure
Inspiration is an ____ process.
active
What does inspiration depend on?
Muscle contraction
What is the major inspiratory muscle?
The diaphragm
When the diaphragm contracts, ____ volume increases vertically.
thorax , vertically
Which muscles are responsible for lifting the ribs and moving the sternum anteriorly during inspiration?
External intercostal muscles
How does an expansion of the lungs help during inspiration?
Expansion of the lungs –> greater lung volume –> decrease in intra-alveolar pressure by Boyle’s Law –> air travels into the alveoli down the pressure gradient
Expiration is a ____ process.
passive
What brings about expiration?
Relaxation of inspiratory muscles
What name is given to the size reduction of the lungs and chest wall ‘back to normal’?
Recoil
Recoil causes the intra-alveolar pressure to ____.
increase
Why does recoil cause an increase in intra-alveolar pressure?
Decrease in volume –> Increase in pressure (Boyle’s Law)
During expiration, air leaves the lungs ___ the pressure gradient.
down
What is a pneumothorax?
Air in the pleural space
Name a possible cause of a pneumothorax.
Disease
Stab wound
A pneumothorax abolishes the ____ pressure gradient.
transmural
What is a common consequence of a pneumothorax?
Lung collapse
Why do the lungs recoil during expiration?
- Elastic connective tissue in the lungs
2. Alveolar surface tension
What is alveolar surface tension?
Attraction between water molecules at the air-liquid interface of an alveolus
Alveolar surface tension produces a force which ____ the stretching of the lungs.
resists
Why aren’t alveoli lined with water alone?
Surface tension would be too strong –> alveolar collapse
Explain LaPlace’s Law.
Smaller alveoli have a greater tendency to collapse
What is pulmonary surfactant?
A mixture of lipids and proteins which lines the alveoli.
What type of alveoli secrete pulmonary surfactant?
Type II
Pulmonary surfactant ___ alveolar surface tension.
lowers
When do developing fetal lungs synthesise pulmonary surfactant?
Late in pregnancy
Name the syndrome in which premature babies do not have enough pulmonary surfactant.
Respiratory distress syndrome of the newborn
How would you tell a newborn had respiratory distress syndrome?
Strenuous inspiratory efforts
A newborn with respiratory distress syndrome struggles to overcome ____ ____ ___ ___ and inflate their lungs.
high alveolar surface tension
Explain alveolar interdependence.
If an alveolus starts to collapse, the surrounding alveoli STRETCH and then RECOIL to expand and open the collapsing alveolus.
Name three forces which keep alveoli open.
- Transmural pressure gradient
- Pulmonary surfactant
- Alveolar interdependence
Name two forces which promote alveolar collapse.
- Elasticity of connective tissue
2. Alveolar surface tension
