Anatomy of the Thorax and Breathing

Question 1

Describe the body cavities

Answer 1

Our body cavities are lined with serous membranes
- double later of secretory tissue with fluid between the layers
- visceral layer on the organ (visceral serous pleura)
- parietal layer on the body wall (parietal serous pleura)
- thoracic cavity
- pericardium
- pleura x2
- abdominopelvic cavity
- peritoneum

Question 2

Describe the anatomy of the thoracic cavity from the anterior view

Answer 2

Contains:
- mediastinum: heart, vessels, pericardium
- pleural cavities: lungs

Boundaries:
- anterior: sternum
- posterior: thoracic vertebrae
- lateral: ribs
- superior: base of neck
- inferior: diaphragm

Question 3

Describe the anatomy of the thoracic cavity from the transverse view

Answer 3

Mediastinum - heart, vessels, pericardium
Pleural cavities - lungs are separate so if one stops functioning you have another
- visceral pleura
- pleural cavity
- parietal pleura

Question 4

Describe the pressure changes in the thoracic cavity that drive ventilation

Answer 4

• Pressure is inversely proportional to volume
• So if we change the volume of the thorax, we change the pressure

Question 5

What is Boyle’s Law?

Answer 5

P = 1/V (pressure is inversely proportional to volume)
Pressure measured by collisions:
- smaller space = more collisions = increased pressure
- larger space = less collisions = decreased pressure
- air will move to lower pressure space

Question 6

Describe how Boyle’s Law works

Answer 6

• to breathe we need to establish a pressure gradient to make air move
• between breaths - pressure inside cavity = pressure outside (so no gradient)
• increased volume (therefore decreased pressure) - air flows in
• decrease volume (therefore increase pressure) - air flows out

Question 7

Describe the anterior thoracic joints

Answer 7

Sternum to ribs
- via costal cartilage (hyaline)
- synovial joints
- cartilaginous joints
Sternocostal: between sternum and cartilage
- synovial
- EXCEPT 1st (which is cartilaginous)

Costochondral: (between cartilage and rib bones)
- cartilaginous

Interchondral: (between two bits of cartilage)
- synovial

Question 8

Describe the posterior thoracic joints

Answer 8

They produce articulation between thoracic vertebrae and ribs
They are synovial joints

• Costotransverse (between rib and transverse process of vertebrae)
• Costovertebral (between rib and body of vertebrae)

Question 9

Describe the muscles of respiration

Answer 9

• Respiratory muscle move the rib cage to allow us to breathe
• Primary muscles of respiration
  
  • diaphragm
  • intercostals
• accessory muscles
  
  • active only when needed

Question 10

Describe the diaphragm

Answer 10

• Sheet of skeletal muscle
• Separates the thorax from the abdomen
• Dome-shaped when relaxed
• Flattens when contracted
• Contraction expands the thoracic cavity, and compresses abdominopelvic cavity
• Has openings in it for the inferior vena cava, esophagus and aorta to go through

Question 11

Describe the intercostal muscles

Answer 11

• Attach diagonally between neighbouring ribs
  External intercostals:
• lift ribcage and expand cavity
• inspiration - quiet and forced
  Internal intercostals:
• depress ribcage and decrease cavity
• expiration - forced only

Question 12

Describe the accessory muscles

Answer 12

• Several muscles that attach to the thoracic cage
• just know its a group called the accessory muscles (don’t need to know all of their names)
  Need to know their collective functions:
• some accessory muscles increase cavity volume for forced inspiration
• other accessory cycles decrease cavity volume for forced expiration

Question 13

Describe how the muscles of respiration move for inspiration

Answer 13

During normal ‘quiet’ inspiration:
- diaphragm contracts = flattens
- external intercostals contract = lifts ribs
During active ‘forced’ inspiration:
- as above, plus accessory muscles contract to further expand thoracic cavity

Question 14

Describe how the muscles of respiration move for expiration

Answer 14

During normal ‘quiet’ expiration:
- passive process
- diaphragm relaxes = dome shaped
- external intercostals relax = ribs no longer lifted
During active ‘forced’ expiration:
- as above plus:
- internal intercostals contract = depress ribs
- accessory muscles contract to further decrease cavity volume

Question 15

How do the lungs expand as the cavity does?

Answer 15

• Lung tissue is elastic and always trying to recoil
• The pleura make the lungs ‘stick’ to the thoracic wall (the fluid isn’t technically a glue but it helps form a fluid seal and results in sticking)
• Lungs expand during inspiration
• Lungs contract during expiration

Question 16

Describe thoracic movement and the pleura

Answer 16

• Visceral pleura on lungs
• Parietal pleural on thoracic wall
• Pleural fluid in between
  
  • slippery surface for frictionless movement against other structures
  • fluid bond causes lungs to ‘stick’ to thoracic wall
• therefore, thoracic wall movement results in lung movement
  
  • increase volume of thorax -> increase volume of lung -> decrease pressure in lung -> air flows in