Anatomy of thorax and breathing

Question 1

Thoracic cavity

Answer 1

The thoracic cavity starts at the base of your neck and extends all the way down until your last rib
It contains the mediastinum which is a region containing the heart, vessels, pericardium and on either side there are the lungs covered by the pleura

Question 2

Boundaries of thoracic cavity

Answer 2

Anterior wall- sternum
Posterior wall - thoracic vertebrae
Lateral wall- ribs
Superior wall- base of neck
Inferior wall- diaphragm (at bottom of ribs)

Question 3

Pleural Cavity

Answer 3

Pleural cavities contain the lungs, the lungs are separate so if one stops functioning the other will continue to work. Blood vessels go from heart into lungs via hilum and this is where the trachea splits into two, one into each lung
Two layers of pleural cavity, visceral pleura (on top of the lungs) and parietal pleura (attached to thoracic cavity)

Question 4

How does ventilation relate to pressure?

Answer 4

Ventilation is driven by pressure changes in thoracic cavity, pressure is inversely proportional to volume, if we change the volume we change the pressure

Inspiration (breathe in): volume increases, pressure decreases
Expiration (breathe out): volume decreases, pressure increases

Question 5

What is Boyle’s Law?

Answer 5

Boyle’s Law is P=1/V
Pressure inversely proportional to volume
Pressure is measured in collisions, smaller the space (decrease volume), more collisions, increased pressure or bigger the space (increased volume,) less collisions, decreased pressure. Air will move to lower pressure space

Question 6

What is the pressure gradient?

Answer 6

To breathe we need to establish pressure gradient to make air move. Between breathes pressure inside cavity = outside cavity, no gradient. Increased volume (decreased pressure) air flows in, decreased volume (increased pressure) air flows out

Question 7

Thoracic Joints - Anterior

Answer 7

Connection between sternum to ribs, ribs are not directly attached to sternum itself, hyaline cartilage links ribs to sternum (synovial joints and cartilaginous joints)

Question 8

Three joints in anterior thoracic cavity

Answer 8

Sternocostal - joint between sternum and ribs, all ribs, synovial joint, except 1st which is cartilaginous (more stable)
Costochondral - joint between ribs and cartilage, found on all ribs, cartilaginous joint
Interchondral - joint between chondral cartilage, synovial joints (allows for movement)

Question 9

What are the two joints in the posterior thoracic cavity?

Answer 9

Costotransverse joint: between rib and transverse process of vertebrae, found between each rib and vertebrae
Costovertebral joint: between rib and body of vertebrae, found between each rib and vertebrae
Allows for articulation between thoracic vertebrae and ribs, both are synovial joints, help lift and lower ribs during breathing

Question 10

What are the muscles involved in respiration?

Answer 10

Respiratory muscles move the rib cage to allow us to breathe. The primary muscles are diaphragm and intercostals, and the accessory muscles are only activated when needed

Question 11

What is the diaphragm?

Answer 11

Diaphragm is a sheet of skeletal muscle (voluntary) which separate thorax from abdomen. It is dome shaped when relaxed and flattens when contracted. Contraction expands thoracic cavity, compresses abdominopelvic cavity
There are three openings in the diaphragm, one for the aorta, one for the inferior vena cava and one for the oesophagus

Question 12

What is intercostal muscles?

Answer 12

Intercostal muscles attach diagonally between neighbouring ribs. External intercostals lift rib cage and expand cavity, inspiration (quiet and forced). Internal intercostals depress rib cage and decrease cavity, expiration (forced only)

Question 13

What are accessory muscles?

Answer 13

Accessory muscles are muscle that attach to the thoracic cage. Some increase cavity volume for forced inspiration and others decrease cavity volume for forced expiration

Question 14

Inspiration

Answer 14

During normal quiet inspiration diaphragm contracts (flattens), external intercostals contract (lifts ribs). During active forced inspiration diaphragm and external intercostals contract as well as accessory muscles to further expands thoracic cavity

Question 15

Expiration

Answer 15

During normal quiet expiration which is a passive process diaphragm relaxes (dome), external intercostals relax (lowering ribs). During active forced expiration diaphragm and external intercostals relax, internal intercostals contract to depress ribs and accessory muscles contract to further decrease cavity volume

Question 16

How do lungs expand as the cavity does?

Answer 16

Lung tissue is elastic (allows lungs to expand in volume) and always tries to recoil. The pleura makes the lungs stick to the thoracic wall, lungs expand during inspiration and contract during expiration

Question 17

Pleura involved in thoracic movement

Answer 17

Visceral pleura found on lungs, parietal pleura on thoracic wall, pleural fluid in between (allows for frictionless movement against other structures, fluid bond causes lungs to stick to wall) therefore thoracic wall movement results in lung movement