Lecture 16 - Respiratory system III - Anatomy of the thorax and breathing (ventilation) Flashcards
Which cell type is not associated with the respiratory membrane?
Type II pneumocystis
Which cells remove debris from the alveoli?
Macrophages
Body cavities
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
The thoracic cavity contains
Mediastinum - heart, vessels, pericardium
Pleural cavities - lungs are separate so if one stops functioning you have another
Hilum of lung
Where primary bronchus vessels enter
Thoracic cavity boundaries
Anterior = sternum Posterior = thoracic vertebrae (12) Lateral = ribs Superior = base of neck Inferior = diaphragm
Pleura
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.
Visceral pleura
Sits on the lungs themselves
Parietal pleura
Sits against the thoracic wall, right up against the ribs and those muscles
What is ventilation driven by…?
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
Volume in inhalation and exhalation
Volume increases during inspiration
Volume decreases during expiration
Boyle’s law equation
P= 1/V
Boyle’s law
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
Boyle’s law and the thoracic cavity
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)
Thoracic joints - anterior
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
Sternocostal
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
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
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
Thoracic joints - posterior
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
Which of the thoracic joints are NOT synovial joints?
1st sternocostal joint
Costochondral joint
What is the name of the law that describes the relationship between pressure and volume of gas?
Boyle’s Law
Muscles of respiration
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
The diaphragm
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
Intercostal muscles
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)
Accessory muscles
Several muscles that attach to the thoracic cage
Increase cavity volume for forced inspiration
Decrease cavity volume for forced expiration
Muscles of respiration - inspiration
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
Muscles of respiration - expiration
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
How do the lungs expand as the cavity does?
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
Thoracic movement - pleura
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
Describe what muscles will be contracting to allow you blow out the candles on a cake
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
Summary - what are the key anatomical features of the thoracic cavity?
Bones, joints and muscles form the thoracic wall. Inside the cavity is the mediastinum, plus the lungs within a double layer of pleura
How do the anatomical features of the thoracic cavity change thoracic volume?
Inspiration - diaphragm and external intercostals contract. Accessory muscles contact for forced breathing
Expiration - Diaphragm relaxes. Internal intercostals and accessory muscles contract for forced breathing
How does our anatomy facilitate breathing?
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
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
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.
Diaphragm
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.
