Session 2 Flashcards
Describe the structure of the bony thorax
- The bony thorax is made up by the thoracic vertebrae posteriorly, the ribs and the intercostal spaces laterally, and the sternum and costal cartilages anteriorly.
- Above, at the thoracic inlet (aka the superior thoracic aperture – the superior opening the thoracic cavity), it is continuous with the neck
- Below, the diaphragm separates it from the abdominal cavity.
Describe the sternum and the sternal angle
The sternum consists of 3 parts:
- The manubrium which articulates with the 1st and part of the 2nd costal cartilage
- The body which articulates part of the 2nd and the 3rd-7th costal cartilages
- The xiphersternum which remains cartilaginous into adult life.
The junction of the manubrium and body is known as the sternal angle and is felt as a transverse ridge on palpation of the sternum
- The fact that the 2nd costal cartilage articulates with the sternum at the level of the sternal angle enables the 2nd rib to be identified and the other ribs to counted during clinical examination to accurately surface mark intra thoracic structures.
Describe the 12 ribs
The 12 ribs articulate with vertebral column posteriorly via the costal-vertebral joints. Anteriorly,
- Ribs 1-7 are connected to the sternum via costal cartilages
- Ribs 8-10 are connected to the costal cartilage above (connection with sternum is indirect – known as false ribs)
- Ribs 11 and 12 (and sometimes 10th) end free in the posterior abdominal muscles (aka ‘floating ribs’)
NB: Superior Thoracic Aperture is aka Thoracic Inlet (anatomically) and Thoracic Outlet (clinically)
Describe a typical rib
A ‘typical’ rib (ribs 3-9) has a head, a neck, a tubercle and a shaft.
- the head has two articular facets for articulation with the body of the corresponding vertebra and the vertebra above
- the tubercle has one articular facet for articulation with the transverse process of the corresponding thoracic vertebra.
- The shaft is thin, flat and curved. At the angle, the shaft twists forward to form its characteristic curve.
- The shaft has a costal groove close to its lower border which protects the intercostal vessels and nerve
Describe the typical features of thoracic vertebrae
- Typical thoracic vertebra features: independent, have bodies , vertebral arches and seven processes for muscular and articular connections. Characteristics include:
- Bilateral costal facets (demifacets): on the vertebral bodies, usually occurring in inferior and superior pairs for articulation with the heads of the rib inferior to it.
- Costal facets: One the transverse processes for articulation with the tubercles of corresponding ribs (except the inferior two or three thoracic vertebrae – atypical ribs)
- Spinous (processes: long slanting inferiorly and anteriorly. Offers increased protection to the spinal cord, preventing an object like a knife entering the spinal canal through the intervertebral discs.
- Vertebral foramen is circular.
What are costovertebral joints?
there are 2 synovial joints, which connect the ribs with the thoracic vertebrae.
- Joint of the rib head – the head of rib articulates with body of the corresponding vertebra and the vertebra above.
- Cost transverse joint – the articular facet on the tubercle of the rib articulates with the transverse process of the corresponding vertebra.
Describe how ribs 1&2 different to typical ribs.
- The 1st rib is the broadest (i.e. its body is widest and nearly horizontal), shortest and most sharply curved of the 7 true ribs. It has a single facet on its head for articulation with the T1 vertebra only and two transversely directed grooves crossing its superior surface for the sub-clavian vessels. The two grooves are separated by a scalene tubercle and ridge, to which the anterior scalene muscle is attached.
- The 2nd rib has a thinner, less curved body and is substantially longer than the 1st rib. It’s head has two facets fir articulations with the bodies of the T1 and T2 vertebrae. Its main atypical feature is a rough area on its upper surface, the tuberosity for serratus anterior and has a poorly marked costal groove.
Describe how ribs 10, 11 and 12 are atypical ribs
- 10th - 12th ribs have a single facet on their heads and articulate with a single vertebra.
- 11th-12th are short and have no neck or tubercle.
Describe the intercostal muscles
Each intercostal space contains 3 muscles, innervated by the intercostal nerves. From superficial to deep they are:
- The external intercostal muscles: fibres run downwards and anteriorly from the inferior margin of the rib above to the superior margin of the rib below. These muscles are responsible for 30% of chest expansion during quiet respiration. Contraction elevates the upper ribs increasing the anterior-posterior diameter of thorax and elevation of the lower ribs, increasing the lateral (transverse) diameter of the thorax.
- Internal intercostal muscles: fibres run downwards and posteriorly from the rib above to rib below. Hence, their action pulls the ribs down (depress) from the position of chest expansion. They reduce the AP and lateral diameters of the chest. They are active during forced expiration. (quiet expiration is passive).
- Innermost intercostal muscles are similar to the internal costal muscles but are less well-developed. They act along with the internal intercostal muscles during forced expiration.
Describe the structure of the diaphragm
The diaphragm is a dome-shaped muscle which divides the thoracic cavity from the abdominal cavity. The shape of the diaphragm (marked convexity) means the thoracic cavity is much smaller than the bony thorax would suggest.
- The liver, spleen, parts of the stomach and upper kidneys, which lie in the abdominal cavity, are covered by the ribs.
- The right dome of the diaphragm lies at the level of the 5th rib, and left dome is slightly lower at the level of the 5th intercostal space.
- The diaphragm consists of a peripheral muscular part and a central tendon. The muscle fibres insert into central tendon.
What is the peripheral muscular part of the diaphragm? What are the arcuate ligaments and crura?
The peripheral muscular part is made up by:
- A sternal part arising from the deep surface of the xiphisterum
- A costal part arising from the inner aspects of the 7-12 costal cartilages
- A vertebral part arising from the arcuate ligament and crura.
The arcuate ligaments are thickenings of fascia over the muscles of the posterior abdominal wall.
The crura are strong tendons attached to the antero-lateral surfaces of the upper 3 lumbar vertebral bodies The right crus arises from bodies and intervertebral discs of L1, 2 &3.
What openings does the diaphragm have for? What action is it involved in? Innervation?
The diaphragm has openings for:
- Inferior vena cava (T8 level)
- Oesophagus (T10 level)
- Aorta (T12 level – aortic hiatus)
The diaphragm is the main muscle of inspiration being responsible for 70% of chest expansion in quiet respiration. On contraction of the diaphragm, it moves downwards (flattens) to increase vertical diameter of thoracic cavity.
The diaphragm is innervated by phrenic nerve (C3,C4,C5). It provides a motor supply to the diaphragm and sensory supply to both surfaces of the diaphragm, pericardium mediastinal part of parietal pleura and diaphragmatic part of parietal pleura.
- Margins of the diaphragm receive innervation from intercostal nerves.
- It is the mediastinal/diaphragmatic part of the parietal pleura.
Describe the distribution of the intercostal nerves, arteries and veins
VAN: the intercostal vein, artery and nerve (in order from above to below) lie in the intercostal groove of the rib, between the internal and innermost intercostal muscles.
They run along the lower border of the rib – important to remember when carrying out a pleural aspiration or insertion of a chest drain, when the needle (or tube) should be inserted at the upper border of the rib to avoid injury.
Describe the intercostal arteries
Intercostal arteries:
- Supply the intercostal muscles, parietal pleura and overlying skin
- Each intercostal space has an anterior intercostal artery (except the last two), which anastomoses with a posterior intercostal artery.
- The anterior intercostal arteries arise from the internal thoracic artery (a branch of the subclavian) and its continuation, the musculophrenic artery.
- Brachiocephalic / Aortic arch -> Subclavian -> Internal thoracic/musculophrenic (later) -> anterior intercostal
- Posterior intercostal arteries arise from the aorta
- Brachiocephalic / Aortic arch -> subclavian -> costocervical trunk - > superior intercostal -> posterior intercostal (1st/2nd spaces).
- Thoracic aorta -> posterior intercostal (other spaces)
Describe the intercostal veins and nerves
- The intercostal veins: each intercostal space has two anterior and one posterior vein accompanying the arteries.
- The anterior veins drain via the internal thoracic vein into the subclavian vein.
- Most posterior intercostal veins drain via the azygos vein on the right and hemiazygos vein on the left, into the superior vena cava.
- The intercostal nerves: the anterior rami (formed as soon as the mixed spinal nerves leave the intervertebral foramina) of thoracic spinal nerves (T1-T12) supply the intercostal muscles, the parietal pleura and the overlying skin.
What are the 3 compartments of the thoracic cavity? Describe the pleura
The thoracic cavity has 3 compartments: 2 lateral pulmonary cavities that contain the lungs and one central compartment known as the mediastinum.
- The pleura is a serous membrane consisting of a single layer of mesothelial cells with a thin layer of underlying connective tissue. Each lung is enclosed in a pleural sac consisting of 2 continuous membranes.
- The parietal pleura line the inside of each hemi-thorax (the bony thoracic cage, diaphragm and mediastinal surface) and is continuous at the hilum of the lung with the visceral pleura which lines the outside of lung, forming the pleural cavity – a pleural space.
- The visceral pleura extend between lobes of the lung into the depths of the oblique and horizontal fissures.
What is the pleural space? What does the pleural fluid allow?
- Pleural space (cavity) is in fact a potential space between the two layers of pleura Both layers of pleura are covered with a common film of fluid produced from the parietal surface and absorbed by the parietal lymphatic vessels.
- The pleural fluid allows parietal and visceral parts to slide on one another. Thus in a healthy person, the pleura allows movement of the lung against the chest wall with breathing. The surface tension of the pleural fluid provides the cohesion that keeps the lung surface in contact with the thoracic wall (forms a pleural seal – which can be broken by leakage of air -> lung collapse). As a result, when the thorax expands in inspiration, the lung expands along with it and fills with air.
The lungs do not occupy all the available space in the pleural cavity, even in deep inspiration.
The costodiaphragmatic recesses are the pleural lined-gutters that surround the upward convexities of the diaphragm.
Describe the supply to the parietal and visceral pleura?
- The parietal pleura are supplied by the intercostal arteries and internal thoracic arteries and is drained by the corresponding veins.
- The visceral pleura is supplied by the bronchial arteries and drained by the bronchial veins.
- Parietal pleura: has somatic (voluntary) innervation including pain fibres from intercostal and phrenic nerves, as well as autonomic innervation.
- Visceral pleura: has no somatic innervation, only autonomic innervation
What are the 4 parts of the parietal pleura?
- Cervical pleura: extends into the root of the neck
- Mediastinal pleura: covers the lateral aspects of mediastinum
- Costal pleura: covers the internal surfaces of the thoracic wall (inside of the rib cage)
- Diaphragmatic pleura: covers the superior/thoracic surface of the diaphragm
What are the lines of pleural reflection?
The lines of pleural reflection are the relatively abrupt lines along which the parietal pleura changes direction (reflects) as it passes from one wall of the pleural cavity to another. There are 3 lines of pleural reflection on each side: sternal, costal and diaphragmatic (vertebral)
What makes the Lower Respiratory Tract? Describe the lungs? What is the hilum of the lung?
- Lower Respiratory Tract: trachea, primary bronchi and lungs
- Each lung has an apex (extends above the level of 1st rib into the neck), a base (concave inferior surface, resting on the diaphragm), three surfaces (costal, mediastinal and diaphragmatic) and three borders (anterior, inferior and posterior)
- The convex costal surface and the concave diaphragmatic surface are separated by a sharp inferior border; the posterior border is rounded to fit the paravertebral gutter, the anterior border is thin and on the left side shows the cardiac notch.
- Lingula – is an area on the left upper lobe which corresponds to the right middle lobe.
- The hilum of the lung is a wedge-shaped area on the mediastinal surface of each lung through which the structures forming the roots of the lung pass to enter or exit. The roots of the lung consist of the bronchi, pulmonary arteries, superior and inferior pulmonary veins, the pulmonary plexus of nerves and lymphatics.
Describe the structure of the trachea
The trachea commences at the lower border of the cricoid cartilage in the neck and terminates by dividing into the right and left main bronchi (at the level of the sternal angle/ Angle of Louis).
- The angle between the right and left main bronchi is known as the carina.
- The trachea is held open by 18-22 U/C-shaped cartilages.
- Posteriorly, where the cartilage is deficient, its wall contains the trachealis muscle
- The trachea is lined by pseudo-stratified columnar ciliated epithelium (with goblet cells)
- It descends anterior to the oesophagus and enters the superior mediastinum, inclining a little to the right of the median plane. The posterior surface of the trachea is flat where it is applied to the oesophagus.
Describe the bronchial tree. What’s a bronchopulmonary segment?
The bronchial tree: the primary (left and right main)bronchi divide into lobar bronchi for each lobe (3 on right – upper, middle and lower lobar bronchi; 2 on left – upper and lower lobar bronchi). The lobar bronchi in turn divide into segmental bronchi, each destined for a bronchopulmonary segment.
- The part of the lung supplied by a segmental bronchus is known as a bronchopulmonary segment.
- A bronchopulmonary segment is a pyramid shaped area of lung with its apex facing towards hilum and base toward lung surface. Each is supplied by a segmental bronchus and by its own segmental branch of the pulmonary artery and pulmonary vein. Branches of the bronchial arteries also accompany the bronchi, supplying them.
- Knowledge of bronchopulmonary segments is surgically important because they can be isolated and removed without much bleeding, air leakage or interfering with other bronchopulmonary segments.
- Segmental bronchi divide further -> subsegmental bronchi -> which further divide on and on until they become terminal bronchioles -> respiratory bronchioles -> alveolar ducts -> alveoli.
Describe the bronchial arteries. What do they supply? How does the blood return?
Bronchial arteries supply the bronchial tree from the carina up to the respiratory bronchioles, visceral pleura and connective tissue.
They arise from the thoracic aorta on the left, and the 3rd intercostal artery (branch of the thoracic aorta) on the right.
The two left Bronchial arteries arise directly from the thoracic aorta
The single right bronchial arterial arises from the 3rd intercostal artery.
Most of the blood supplied by the bronchial arteries is returned via the pulmonary veins rather than the bronchial veins The superficial group of veins drain the visceral pleura and the bronchi in the hilar region to azygous vein on the right, and the accessory hemiazygous on the left.
The deep group of veins drain rest of the bronchi (deep in lung) into the main pulmonary vein or directly into left atrium.
Explain about diffusion resistance
Resistance to diffusion: The diffusion pathway from alveolar gas to alveolar capillary blood is short, but there are several structures between the two. First gas must diffuse through the gas in the alveoli then through: (liquid diffusion)
- The alveolar epithelial cell
- Interstitial fluid
- Capillary endothelial cell
- Plasma
- Red cell membrane (to get to Hb to which O2 binds)
Despite all of this the overall barrier is less than 1 micron – 0.6μm thick
What is Spirometry? And define the Tidal Volume, the Inspiratory Reserve Volume and the Expiratory Reserve Volume
- The movement of air during breathing can be measured by Spirometry. The subject breathes from a closed chamber (has constant pressure) whose volume changes with ventilation.
- A certain volume enters and leaves the lungs with each breath – the Tidal Volume. [The lung volume that represents the amount of air that is displaced between normal inspiration and expiration, when extra effort is not applied].
- During normal respiration the increase in lung volume is not maximal – it can be increased to the extent of the Inspiratory Reserve Volume (the extra volume that can be breathed in when extra effort is applied). We can also breathe out more than at the rest, by using the Expiratory Reserve Volume (the extra volume that can be breathed out when extra effort is applied).
Lung Volumes change. What are better measurements?
Lung volumes change with changes in tidal volume (changes in breathing pattern) but LUNG CAPACITIES do not change with tidal volume, as they are measured from fixed points in the breathing cycle. These are:
- Maximum Inspiration
- Maximum Expiration
- End of a quiet expiration
Inspiratory Capacity is: end of quiet expiration to maximum inspiration (i.e. inspiratory reserve + tidal volumes). [The biggest breath that can be taken from resting expiratory level – lung volume at end of quiet expiration – and is often ~3L].
Functional residual capacity is the volume of air in the lungs at the end of a quiet expiration (At resting expiratory level). [Expiratory reserve volume + residual volume]. ~2L
Vital Capacity = Inspiratory Capacity + Expiratory Reserve OR Inspiratory Reserve Volume + Tidal Volume + Expiratory Reserve Volume. The biggest breath that can be taken in, measured from the max inspiration to max expiration. It often changes in disease and is ~5L.
Total Lung Volume = Vital Capacity + Residual Volume
Describe the nitrogen washout test
- The patient takes a maximum inspiration of 100% oxygen
- The oxygen that reaches the alveoli will mix with alveolar air and the resulting mix will contain Nitrogen (there is 79% Nitrogen in air)
- However the air in the conducting airways (dead space) will still be filled with pure oxygen.
- The person exhales through a one-way valve that measures the percentage of Nitrogen in and volume of air expired.
- Nitrogen concentration is initially zero as the patient exhales the dead space oxygen.
- As alveolar air begins to move out and mix with dead space air, nitrogen concentration gradually climbs until it reaches a plateau where only alveolar gas is being expired.
- A graph can be drawn to determine the dead space, plotting Nitrogen % against Expired Volume.
