10 - LUNG STRUCTURE AND BREATHING Flashcards
External Repsiration
- At rest a normal human breathes 12 to 15 times a minute
- 500 mls of air per breath (6 to 8 litres per minute) are inspired and expired.
- Inhaled air mixes with the gas in the alveoli and by simple diffusion oxygen enters the blood in the pulmonary capillaries
- Carbon dioxide enters the alveoli and is exhaled
Cellular respiration
occurs within tissues and is the breakdown of glucose to produce ATP.
It requires oxygen and releases Carbon dioxide
LUNG STRUCTURE: GROSS ANATOMY
- Right lung has 3 lobes
- Left lung has 2 lobes
- Trachea splits into L and R bronchi.
- Bronchi further subdivide before branching into Bronchioles and terminal Bronchioles
FINAL BRANCHES: FINE ANATOMY
- Respiratory bronchioles form from the terminal bronchioles
- Alveolar system of ducts and alveoli are the final portion of the lung branching system
- Make up 70m2 surface area for gas exchange
- Alveoli double
PULMONARY VENTILATION = BREATHING
- Inhalation and exhalation of air uses the diaphragm and sets of muscles
- During normal quiet breathing the diaphragm, internal and external intercostals are used
- During forceful breathing more muscles are used- Causes the pain of forced breathing on exercise
PULMONARY VENTILATION: PRESSURE CHANGES
• Air moves in response to changes or differences in pressure.
• At rest ie no breathing movements there is no airflow
- Atmospheric pressure = 760mmHg
- Alveolar pressure = 760mmHg
- Intrapleural pressure= 756 mmHg
Intrapleural pressure is always negative. This helps the lungs to expand and stay inflated.
At rest, when the diaphragm is relaxed, alveolar pressure is equal to atmospheric pressure, and there is no air flow.
CREATING AIR FLOW: INHALATION
- Diaphragm contracts, external intercostal muscles contract
- Chest cavity and lung volume expand
- Alveolar pressure drops to 758mmHg
- Atmospheric pressure (760mmHg) is now higher than internal pressure
- Air is drawn in from high to low pressure
CREATING AIR FLOW: EXHALATION
- Diaphragm and external intercostal muscles relax
- Lungs spring back (recoil) and chest cavity contracts
- Contraction increases alveolar pressure to 762mmHg
- Air flows out of lungs towards lower atmospheric pressure (760mmHg)
BOYLE’S LAW
• Volume of a gas varies inversely withpressure = squash it and pressure increases
Ribs falling and diaphragm rising, compresses air and increases pressure.
This drives the flow of air outwards
PULMONARY VENTILATION: FACTORS THAT AFFECT ITS EFFICIENCY
- Compliance: how stretchy are the lungs?
- Surface Tension: surfactant reduces surface tension. Without it, alveoli
would collapse - Airway resistance:airflow = (P alveoli- P atmosphere)/Resistance
Resistance increases on exhalation as bronchiole diameter decreases
NEURAL CONTROL OF BREATHING:
Respiratory centres in the Medulla oblongata and midbrain control breathing.
• Pontine respiratory Centre in mid brain
• Dorsal Respiratory Group in medulla
• Ventral Respiratory Group in medulla
OTHER INFLUENCES ON CONTROL OF BREATHING
- Voluntary control - Useful for communication e.g. speaking, but limited in extent
- Other CNS areas e.g. for emotion - Ventilation can be increased or reduced due to emotion; also transient effects such as gasping, sobbing etc
- Motor cortex e.g. during exercise - Information from motor cortex related to level of effort involved in exercise feeds into respiratory control centre
ANATOMICAL DEAD SPACE
- Part of residual
- Air in conducting zone passages so it is trapped
- Alveoli will have fresh air and o2 is depleted
what is the pleural membrane?
Double wall sac around the lungs
VISCERAL- inner adhering to the lung outside
PARIETAL- outer attached to chest wall
What are the 2 cells lining the epithelium of the lungs?
Goblet cells- secretes mucus
Ciliated cells- mucus escalator that eliminates dust and small particles
