Respiratory: The Thorax L13

Question 1

Simply put, what does the thoracic cavity consist of?

Answer 1

Two pleural cavities with mediastinum separating them.

Question 2

Describe the boundaries of the thoracic cavity.

Answer 2

Superior boundary is the root of the neck (superior thoracic aperture), the inferior boundary is the diaphragm.
Anterior boundary of the thoracic cavity is the sternum, the vertebrae form the posterior boundary.
The lateral boundary is formed by the ribs and the intercostal muscles.

Question 3

What is the function, general location of pleural membranes?

Answer 3

Pleural membranes are serous membranes that line the cavities of the body and secrete serous fluid in order to reduce friction. The serous membranes in the pleural cavity are called pleural membranes.

Question 4

Describe the locations of different types of pleural membranes and the pleural cavity.

Answer 4

The parietal pleura line the entire thoracic cavity: they adhere to the internal surface of the ribs and the superior surface of the diaphragm, and partition off the medistinum.
The parietal pleura fold inward near the primary bronchi and become the visceral pleura which covers the lungs.
In between the parietal and visceral pleura is a potential space called the pleural cavity - contains ~2ml of serous lubricating fluid.

Question 5

What is significant about the pleural cavity in terms of pressure?

Answer 5

Inside the pleural cavity the pressure is lower than the external environment, creating a vacuum that helps to keep the lungs inflated.

Question 6

Do the visceral and parietal pleura come into contact? Explain this.

Answer 6

The function of the pleura is essentially to allow for the low-friction movement of the lungs: when the lungs inflate, the smooth, moist visceral pleura cohere to the smooth, moist parietal pleura.
Because the lungs are covered by the visceral pleura that is attached to the parietal pleura that covers the thoracic wall, movement of the thoracic wall is coupled to the movement of the lungs.

Question 7

Briefly describe Boyle’s Law in terms of the lungs. What are the structures involved in breathing?

Answer 7

Breathing involves changing the dimensions of the thoracic cavity: a change in volume leads to a change in pressure, which results in the movement of air (explain by Boyle’s Law). The sternum, the ribs, the vertebrae, the diaphragm, and the intercostal muscles along with accessory muscles all play a role in the process of breathing.

Question 8

Describe the 3 types of joints made of costal cartilage between the ribs and sternum and what cartilage are made of.

Answer 8

There is cartilage connecting between the sternum and ribs. The cartilage of the ribs are called the costal cartilages and are hyaline cartilage. The first rib joint is the sternocostal joint and is a cartilaginous joint. Only the first seven ribs (known as the ‘true ribs’) articulate with the sternum (through synovial joints). The bottom five are ‘false’ ribs.

The cartilaginous joints between the costal cartilage and the ribs are called costochondral joints.

Cartilage joins the costal cartilage of ribs through 6 to 9 (i.e 6-7, 7-8, 8-9) forming synovial plane joints called interchondral joints.

So only the first rib joint sternocostal and joints between costal cartilage and ribs are cartilaginous, rest are synovial.

Question 9

What are the 11 and 12 ribs commonly called?

Answer 9

Floating ribs, as they have no anterior attachment.

Question 10

Describe the posterior joints of the thoracic cage.

Answer 10

The ribs articulate with the thoracic vertebrae forming synovial joints: each ribs has two articulations with each vertebrae. The most medial of these joins to the vertebral body and is called the costovertebral joint, the second joins with the transverse process of the vertebra and is called the costotransverse joint.
Each thoracic vertebra articulates with the vertebra directly above it via bilateral facet joints (these are synovial joints).

Question 11

What is the primary muscle involved in respiration? Where is this located? How is this innervated? How does the shape change when breathing in and out?

Answer 11

The diaphragm is the primary muscle involved in respiration, it forms the floor or lower boundary of the thoracic cavity.
It is innervated by the phrenic nerve; which has contributions from the cervical nerves C3-5. Summed up as: ‘C3, 4 and 5 keep your diaphragm alive’.
The diaphragm is dome-shaped when relaxed (expiration), but flattens when it contracts (inspiration).

Question 12

What are the secondary muscles involved in respiration? Where are they found? Are they involved in inspiration or expiration?

Answer 12

The muscles found in the spaces between the ribs are called the internal intercostals and external intercostals and are the secondary muscles involved in respiration:
The external intercostals are involved in inspiration.
The internal intercostals are involved with forced expiration (when expiration becomes active).

Question 13

What are the tertiary muscles called? What is their function? Where are they found? When do they get used?

Answer 13

There are many accessory muscles that are capable of moving or stabilising the ribs in some way (technically any and all muscles attached to ribs and clavicle) but that are only recruited in exceptional circumstances. Example: scalene muscles, abdominal muscles.

Question 14

What is required for inspiration in terms of pressure?

Answer 14

Air moves down pressure gradients: from areas of high pressure to areas of low pressure. During inspiration, the alveolar pressure must be lower than the barometric pressure (atmospheric).

Question 15

In general, what does the respiratory system do to create the pressure difference for inspiration (i.e how do the diaphragm, intercostals and accessory muscles move) ?

Answer 15

The respiratory muscles contract, increasing volume of thorax, resulting in a decrease of pressure in alveoli (Boyle’s Law), so air flows in.

Question 16

Describe the movements of the diaphragm in inspiration.

Answer 16

The diaphragm increases the length of the thoracic cavity during inspiration: it contracts concentrically, flattening downward and increasing the vertical dimensions and hence the volume of the thoracic cavity.

Question 17

Describe the movements of the intercostals in inspiration.

Answer 17

The external intercostals increase the diameter of the thoracic cavity during inspiration. They contract concentrically, lifting the ribcage and increasing the width of the thoracic cavity (with a ‘bucket-handle’ motion), and pulling the sternum forward and increasing the depth of the thoracic cavity (with a ‘pump-handle’ motion).

Question 18

When do the accessory muscles get used for inspiration?

Answer 18

Accessory muscles can increase the volume of the thoracic cavity during inspiration and may be used for forced inspiration or when you are short of breath.

Question 19

Is expiration large a passive or active process? What occurs (e.g with the diaphragm) that demonstrates this so?

Answer 19

Expiration is a largely passive process: the respiratory muscles are relaxed, decreasing the volume of the thorax, resulting in an increase in pressure in the alveoli, so air flows out.
The diaphragm returns to its dome shape (no longer pulling on the lungs), and the elastin in the lungs promotes their tendency to recoil elastically.

Question 20

When does active expiration require? What occurs with the muscles when active expiration is required?

Answer 20

Active expiration is required during exercise, hyperventilation, or forced expiration.
The internal intercostals and abdominal muscles can be contracted, resulting in a greater decrease in the volume of the thorax and thus a greater pressure gradient.