Lecture 16: Anatomy of the Thorax and breathing Flashcards
What are our body cavities lined with?
serous membranes:
- Double layer of secretory tissue with fluid between
layers - Visceral layer on the organ
- Parietal layer on body wall
What are the boundaries of the thoracic cavity and what does it contain?
Boundaries
* Anterior: Sternum
* Posterior: Thoracic vertebrae
* Lateral: Ribs
* Superior: base of neck
* Inferior: diaphragm
Contains
* Mediastinum (Heart, vessels, pericardium)
* Pleural cavities (Lungs)
How does breathing work?
- Pressure is inversely proportional to volume (Boyle’s Law)
- So, if we change the volume of the thorax, we change the pressure
- To breathe, we need to establish a pressure gradient to make air move
- Between breaths- pressure inside cavity = pressure
outside. No gradient - Increase volume of lungs (therefore decrease pressure) – air flows in (inhale)
- Decrease volume of lungs (therefore increase pressure) - air flows out (exhale)
What are the anterior joints of the thoracic cavity?
Sternocostal (cartilage to sternum)
- Synovial joints (allows more movement)
- Except 1st = cartilaginous
Costochondral (cartilage to rib bone)
- cartilaginous (more rigid for structural integrity)
Interchondral (cartilage to cartilage)
- synovial (4 of them on the lower portion of ribs) (allows movement)
What are the posterior joints of the thoracic cavity?
Both are synovial joints that can allow some movement
Costotransverse:
between rib and transverse process of vertebrae
Costovertebral:
between rib and body of vertebrae
Describe the diaphragm, include shape when contracted/relaxed:
- Sheet of skeletal muscle
- Separates thorax from the abdomen
- Dome-shaped when relaxed
- Flattens when contracted
- Contraction expands the thoracic cavity, and compresses abdominopelvic cavity
What are the two types of intercostal muscle and what do they do?
- Attach diagonally between neighbouring ribs
External intercostals
* Lift ribcage and expand cavity
* Allows Inspiration - quiet and forced
Internal intercostals
* Depress ribcage and decrease cavity
* Allows Expiration- forced only
What are the functions of accessory muscles?
- Some accessory muscles increase cavity volume for
forced inspiration - Other accessory muscles decrease cavity volume for
forced expiration
Describe the process of inhalation including the muscles:
During normal ‘quiet’ inspiration
* Diaphragm contracts = flattens
* External intercostals contract = lifts ribs
* This increases the volume of the lungs allowing air to rush in
During active ‘forced’ inspiration
* As above, plus accessory muscles contract to further
expand thoracic cavity
Describe the process of exhalation including the muscles:
During normal ‘quiet’ expiration
* Passive process
* Diaphragm relaxes = dome shaped
* External intercostals relax = ribs no longer lifted
* This decreases the volume of the lungs allowing air to leave the body
During active ‘forced’ expiration
* As above plus:
* Internal intercostals contract = depress ribs
* Accessory muscles contract to further decrease cavity volume
How do the lungs expand as the cavity
does?
- Lung tissue is elastic and always trying to recoil
The Visceral pleura on lungs and Parietal pleura on thoracic wall has fluid in between them. This fluid acts like glue to the lungs and thoracic wall causes the lungs to stick to the walls. This allows the lung to expand and deflate with the thoracic wall.
The pleural fluid also allows for slippery, frictionless movement.
