Lecture 16 - Respiratory system III - Anatomy of the thorax and breathing (ventilation)

Question 1

Which cell type is not associated with the respiratory membrane?

Answer 1

Type II pneumocystis

Question 2

Which cells remove debris from the alveoli?

Answer 2

Macrophages

Question 3

Body cavities

Answer 3

Our body cavities are lined with serous membranes.
Double layer of secretory tissue with fluid between layers. Visceral layer on the organ. Parietal layer on the body wall.

Thoracic cavity - Pericardium and pleura (membrane that surrounds the lungs that allows them to move smoothly and frictionlessly as they expand

Abdominopelvic cavity - peritoneum

Question 4

The thoracic cavity contains

Answer 4

Mediastinum - heart, vessels, pericardium

Pleural cavities - lungs are separate so if one stops functioning you have another

Question 5

Hilum of lung

Answer 5

Where primary bronchus vessels enter

Question 6

Thoracic cavity boundaries

Answer 6

Anterior = sternum 
Posterior = thoracic vertebrae (12) 
Lateral = ribs 
Superior = base of neck 
Inferior = diaphragm

Question 7

Pleura

Answer 7

The function of the pleura is to allow optimal expansion and contraction of the lungs during breathing. The pleural fluid acts as a lubricant, allowing the parietal and visceral pleura to glide over each other friction free.

Question 8

Visceral pleura

Answer 8

Sits on the lungs themselves

Question 9

Parietal pleura

Answer 9

Sits against the thoracic wall, right up against the ribs and those muscles

Question 10

What is ventilation driven by…?

Answer 10

Pressure changes in the thoracic cavity

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

Question 11

Volume in inhalation and exhalation

Answer 11

Volume increases during inspiration

Volume decreases during expiration

Question 12

Boyle’s law equation

Answer 12

P= 1/V

Question 13

Boyle’s law

Answer 13

Pressure is inversely proportional to volume

Pressure is measured by collisions …
Smaller space = more collisions = increased pressure
Bigger space = less collisions = decreased pressure

Air will move to lower pressure space

Question 14

Boyle’s law and the thoracic cavity

Answer 14

To breathe, we need to establish a pressure gradient to make air move

Between breaths … pressure inside cavity = pressure outside therefore there is no gradient and this no reason for air to move

Increase volume and therefore a decrease in pressure means that air flows in. (inspiration)
Decrease volume and therefore increase in pressure - air flows out (expiration)

Question 15

Thoracic joints - anterior

Answer 15

Sternum to ribs via costal cartilages (hyaline) - hyaline cartilage because it extends the size a little more so there is a little more space and it is a little bit more moveable than bone whilst still giving us protection
Synovial joints
Cartilaginous joints

Sternocostal - between sternum and the ribs
Synovial (2-7)
Except first one which is cartilaginous since the cartilage is directly united with the sternum
7 on each side

Costochondral
Cartilaginous
The costochondral joints are the joints between the ribs and costal cartilage in the front of the rib cage. They are hyaline cartilaginous joints
Not much movement is able to occur here

Interchondral
Synovial - need to be moveable
Interchondral joints are synovial joints between the tips of adjacent costal cartilages of ribs 6-10.
Between the cartilage
As you get further down the ribs they get smaller and some don’t directly attach to the sternum instead attach to the cartilage of neighbouring ribs

Majority of the joints on the anterior side are synovial so that we can lift the ribs up

Question 16

Sternocostal

Answer 16

Sternocostal - between sternum and the ribs
Synovial (2-7)
Except first one which is cartilaginous since the cartilage is directly united with the sternum
7 on each side

Question 17

Costochondral

Answer 17

Costochondral
Cartilaginous
The costochondral joints are the joints between the ribs and costal cartilage in the front of the rib cage. They are hyaline cartilaginous joints
Not much movement is able to occur here

Question 18

Interchondral

Answer 18

Interchondral
Synovial - need to be moveable
Interchondral joints are synovial joints between the tips of adjacent costal cartilages of ribs 6-10.
Between the cartilage
As you get further down the ribs they get smaller and some don’t directly attach to the sternum instead attach to the cartilage of neighbouring ribs

Question 19

Thoracic joints - posterior

Answer 19

Articulation between thoracic vertebrae and ribs - 12 pairs of ribs with 12 thoracic vertebrae
Synovial joints - joints allow movement but we need muscles to create the environment.

Costotransverse = between rib and transverse process of vertebrae 
Costovertebrae = between rib and body of vertebrae 

Each rib actually articulates twice with the vertebrae as stated above

Question 20

Which of the thoracic joints are NOT synovial joints?

Answer 20

1st sternocostal joint

Costochondral joint

Question 21

What is the name of the law that describes the relationship between pressure and volume of gas?

Answer 21

Boyle’s Law

Question 22

Muscles of respiration

Answer 22

Respiratory muscles (change the volume of the ribcage) move the rib cage to allow use to breathe

Primary inspiratory muscles - diaphragm and intercostals (these sit in between the ribs)
Accessory muscles - active only when needed

Question 23

The diaphragm

Answer 23

Sheet of skeletal muscle
Separates the thorax from abdomen
Dome shaped when relaxed
Flattens when contracted - so it elongates the thoracic cavity which causes an increase in volume also compresses abdominopelvic cavity to help with things like urination and child birth
Contraction expands thoracic cavity, compresses abdominopelvic cavity

Question 24

Intercostal muscles

Answer 24

Attach diagonally between neighbouring ribs

External intercostals
Lift ribcage and expand cavity
Inspiration - quiet (normal breathing) and forced

Internal intercostals
Depress ribcage and decrease cavity
Expiration - forced only (e.g. during exercise)

Question 25

Accessory muscles

Answer 25

Several muscles that attach to the thoracic cage

Increase cavity volume for forced inspiration
Decrease cavity volume for forced expiration

Question 26

Muscles of respiration - inspiration

Answer 26

Inspiration is about increasing volume and therefore decreasing pressure so that air is going to flow in

During normal ‘quiet’ inspiration…
Diaphragm contracts = flattens
External intercostals contract = lifts ribs

During active ‘forced’ inspiration…
As above, plus accessory muscle contract to further expand thoracic cavity

Question 27

Muscles of respiration - expiration

Answer 27

Expiration is about decreasing the volume for breathing out

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 muscle contract to further decrease cavity volume

Question 28

How do the lungs expand as the cavity does?

Answer 28

Lung tissue is elastic and always trying to recoil

The pleura make the lungs ‘stick’ to the thoracic wall so it means that when the walls move so does the lungs

Lunges expand during inspiration and lungs decrease during expiration

Question 29

Thoracic movement - pleura

Answer 29

Visceral pleura on lungs
Parietal pleura on thoracic wall

Pleural fluid in between…
Slippery surface for frictionless movement against other structures
Fluid bond causes lungs to ‘stick’ to thoracic wall which ensures that we can have the lungs expanding

Therefore, thoracic wall movement results in lung movement ….increase volume of thorax, increase volume of lung, decrease pressure in lung, air flows in

Question 30

Describe what muscles will be contracting to allow you blow out the candles on a cake

Answer 30

Need to take a big breath in - diaphragm, external intercostals and accessory muscles contract to increase thoracic cavity volume as much as possible

Need to force a big breath out - internal intercostals and accessory muscles contract (and diaphragm relaxes) decrease thoracic cavity volume as much as possible, to force air out

Question 31

Summary - what are the key anatomical features of the thoracic cavity?

Answer 31

Bones, joints and muscles form the thoracic wall. Inside the cavity is the mediastinum, plus the lungs within a double layer of pleura

Question 32

How do the anatomical features of the thoracic cavity change thoracic volume?

Answer 32

Inspiration - diaphragm and external intercostals contract. Accessory muscles contact for forced breathing

Expiration - Diaphragm relaxes. Internal intercostals and accessory muscles contract for forced breathing

Question 33

How does our anatomy facilitate breathing?

Answer 33

Muscles move bones at joints to increase volume/decrease pressure for inspiration and to decrease volume/increase pressure for expiration. Pleural fluid adheres lungs to thoracic wall to ensure lungs expand and recoil as the cavity volume changes

Question 34

Describe the structures of the respiratory tract that help maintain a patent airway, and explain the anatomical structures that draw air in and out of the lungs

Answer 34

A patent, unobstructed airway is needed to ensure air is able to flow through the respiratory tract to the site of gas exchange.
The airway of the nose is kept patent by external cartilage around the external nares, and by nasal cavity walls made of bone. Although passage of air through much of the URT is shared with food, during swallowing food is given right of way into the esophagus by the closure of the epiglottis, preventing food from entering the larynx. The vestibular folds in the glottis also prevent food from obstructing the LRT.
Cartilage ensures an open airway for most of the LRT, starting with complete rings of cartilage in the larynx, becoming C shaped in the trachea due to the presence of the trachealis muscle, which can contract to force blockages out. In the primary bronchi the rings return to complete circles, with cartilaginous support decreasing along the bronchial tree, becoming plates by the tertiary bronchi and disappearing in the bronchioles. At this point the airway is small enough to not require cartilaginous support.
Most of the tract is lined with respiratory epithlium, with goblet cells to produce mucus to trap debris. To ensure mucus does not block airways, ciliated cells push the mucus to the pharynx to be swallowed, via the mucocilary escalator.

Air is drawn into and out of the lungs by pressure changes driven by the volume of the thoracic cavity. As pressure is inversely proportional to volume, increasing the size of the cavity results in air flowing into the lungs for inspiration, and decreasing the size of the cavity result in air flowing out for expiration. The pleura adhere the lungs to the thoracic wall, ensuring their volume changes with the thoracic cavity
Synovial joints of the ribs at the sternum and vertebrae allow the cavity volume to change
For quiet inspiration, the diaphragm and external intercostals contract, increasing the volume of the cavity. For forced inspiration, accessory muscles further increase the cavity volume, pulling more air in.
For quiet expiration, the diaphragm and external intercostals relax, decreasing the cavity size. For forced expiration, internal intercostals relax, decreasing the cavity size. For forced expiration, internal intercostals and accessory muscles contract to further decrease the cavity volume, forcing more air out.

Question 35

Diaphragm

Answer 35

The diaphragm separates the thoracic cavity, containing the heart and lungs, from the abdominal cavity and performs an important function in respiration: as the diaphragm contracts, the volume of the thoracic cavity increases, creating a negative pressure there, which draws air into the lungs.