Esa 3 - Respiration Session 2

Front 1

Describe the structure of the bony thorax and its function.

Back 1

The bony thorax comprises of 12 pairs of ribs with costal hyaline cartilage, the sternum and the 12 thoracic vertebrae with intervertebral discs in-between them.
The thoracic cage is rigid which enables it to protect the thoracic viscera and some abdominal organs, resist the negative internal pressure created during inspiration by contraction of diaphragm and accessory muscles, provide a site of attachment for many muscles that move the upper limb, neck, back and abdomen and provide attachment for and support the weight of the upper limb.

Front 2

What are the benefits for the thinness and flexibility of the ribs?

Back 2

The thinness and flexibility of the ribs along with the joints allow the thoracic cage to absorb many external blows and compressions without fracture.

Front 3

State the features of a typical rib

Back 3

A typical rib eg 3-9
- A head - with an inferior and a superior facet, separated by the crest of the head, to articulate with the numerically corresponding vertebrae and the one superior to it eg rib 3 will articulate with vertebrae 2 and 4.
- A neck
- A tubercle - with a smooth articular facet to join to the transverse process of the vertebrae and a rough non-articular part which is the attachment site for costotransverse ligament.
- A body - thin flat and curved, particularly at the costal angle where the rib turns anterolaterally. On the internal inferior surface lies the costal groove where the neurovascular bundle runs. Therefore during pleurocentesis, a needle must be placed superior to the rib and NOT inferior.

Front 4

State the features of a typical thoracic vertebrae.

Back 4

A typical thoracic vertebrae:
- Large Vertebral body which increases in size down the vertebral column
 On body lies 2 pairs of superior and inferior articular facets (demifacets) for articulation with head of rib at numerical level and the one below ie T3 will articulate with ribs 3 and 4.
- Vertebral arch – comprised of 2 left and right pedicles joining at flat lamina
 On arch lies 2 pairs of superior and inferior articular facets for zygopophysial joints between adjacent vertebrae
- Transverse processes – left and right which have articular facets for articulation with tubercle of rib
- Spinous process – posterior to vertebral column, on lamina and descends inferiorly and covers the region between the lamina, preventing sharp objects from damaging the vertebral canal

Front 5

Describe how ribs 1&2 and 11 & 12 are atypical.

Back 5

1st rib
- The broadest, widest and most sharply curved body.
- It has a single inferior demifacet for binding to T1 vertebrae.
- It has 2 transverse grooves within which lie the subclavian artery and vein, separated by the attachment of the anterior scalene muscle to the scalene tubercle. It does not have a costal groove.
2nd rib
- Thinner, less curved and longer vertebral body
- Tuberosity for the serratus anterior muscle on upper surface. (Long thoracic nerve ( c5,c6,c7) -> winged scapula. Elevation, supports shoulder girdle, upward rotation, abduction after 90 degree with trapezius)
11th -12th ribs
- Only one costal facet to articulate with one vertebrae
- Are short and have no neck or tubercle

Front 6

Define true, false and floating ribs.

Back 6

True ribs, 1-7, attach directly to the sternum via associated costal cartilage.
False ribs, 8-10, attach indirectly to the sternum via their cartilage attaching to the cartilage above.
Floating ribs, 11-12 ( sometimes 10), don’t attach to the sternum at all and instead end in the posterior abdominal musculature.

Front 7

Describe the relations and arrangement of muscles in the thoracic wall and diaphragm and state briefly their functions and nerve supply.

Back 7

The thoracic wall comprises of the thoracic rib cage, the muscles that extend between the ribs, the skin, subcutaneous tissues, muscles and fascia covering the anterolateral aspect. The posterior aspect is considered the back. The thoracic wall recieves innervation from intercostal nerves

Front 8

Which muscles are involved in forced expiration?

Back 8

Expiration is usually passive recoil of lungs and diaphragm however during forced expiration accessory muscles are used, which are mainly the abdominal muscles. Also Internal intercostal muscles ( interosseous part) and innermost muscles which extend from inferior border of rib to superior border of below in inferolateral direction. They are innervated by the intercostals nerve, depresses the ribs to help expiration

Front 9

Which muscles are involved in forced inspiration?

Back 9

In silent respiration, the diaphragm moves down to increase the vertical dimensions and external intercostals move in a bucket handle movement to raise ribs to increase the antero-posterior and transverse diameters of the thorax. In forced inspiration when ventilation is increased or resistance to respiration is present, accessory muscles are used such as scalene, sternocleidomastoids, serratus anterior and pectoralis major ( when patients arm is fixed by grasping the edge of a table)

Front 10

What is the main role of intercostal muscles?

Back 10

The main role of the intercostals muscles is to support the intercostal space, preventing paradoxical movement during inspiration when internal thoracic pressures are the most negative. The other roles are in elevation and depression of ribs during forced respiration. The external intercostals and the interchondral part of internal intercostals contract during inspiration to elevate the ribs.The internal intercostals contract to depress the ribs during expiration.

Front 11

Describe the role of the diaphragm in respiration.

Back 11

The diaphragm is a thin, double domed, musculotendinous sheet comprised of striated skeletal muscle and dense connective tissue. It separates the thoracic cavity from the abdominal cavity. The convex surface faces the thorax and the concave surface faces the abdomen.
The diaphragm is the main muscle of quiet respiration. Its descent increases the volume of the thoracic cavity. It also controls the intra-abdominal pressure during defecation, micturition and child birth. The diaphragm must work harder when the abdomen is protuberant – 6 FS: fat, faeces, foetus, fluid, flatus and food.
.

Front 12

Describe the structure of the diaphragm

Back 12

The diaphragm is the muscle which separates the thorax from the abdomen and consists of a muscular peripheral part, a central tendon which is partly fused with the pericardium and has 2 hemidomes ( the right is higher than the left due to the liver) . the muscular diaphragm takes origin from the vertebrae and arcuate ligaments, the rib cage and the sternum. The right crus arises from the upper 3 lumbar vertebrae and the left crus from the upper 2 lumbar vertebrae. Their fibrous medial borders form the median arcuate ligament over the front of the aorta. The medial and lateral arcuate ligaments are thickenings of the fascia overlying the psoas major and quadratus lumborum respectively. The costal part is attached to the inner aspects of the 7th-12 ribs and associated costal cartilages. The sternal part originates as 2 slips from the posterior xiphoid process. The phrenic nerves ( c3,4,5) supply motor fibres and carries sensory fibres from the central diaphragm. Pain from irritation of the diaphragm is often referred to C4 dermatome at the shoulder eg inflammatory fluid in peritoneal cavity can irritate the inferior surface of the diaphragm, usually at the subphrenic recesses causing should pain. When the patient stands up the shoulder pain disappears as diaphragm is no longer being irritated.
The lower intercostals nerves supply sensory fibres to the peripheral diaphragm. The aorta, thoracic duct and azygos vein pass through the diaphragm at the aortic hiatus at T12. The oesophagus, branches of the left gastric artery and vein and both vagi pass through the oesophageal hiatus at T10. The inferior vena cava and right phrenic nerve pass through the vena cava opening in the central tendon at T8.

Front 13

Describe the domes of the diaphragm.

Back 13

There is a right and a left dome comprised of the costal muscle part of the diaphragm and separated by the central tendon, which is slightly depressed due to the presence of the pericardium above.
The right dome is slightly higher than the left dome due to the presence of the liver. During full expiration the right dome can rise as high as the 5th rib and the left reaches the 5th intercostal space.
The levels of the domes vary according to the phase of respiration, posture and size and degree of distension of abdomen. The domes are present due to the attachment of the parietal pleura pulling the diaphragm up.
The costodiaphragmatic recess is the region between the costal parietal pleura covering the thoracic wall and the diaphragmatic parietal pleura covering the diaphragm. Blunting of this angle on an x ray should be noted. .

Front 14

Describe the movements of the thoracic cage during respiration

Back 14

During inspiration the transverse thoracic diameter, the sagital thoracic diameter and the infrasternal angle increase( the angle between the xiphoid process and the costal cartilage - on the left, it is the site of pericardiocentesis). This is achieved by the diaphragm contracting and thus compressing the abdominal cavity. Pregnancy and obesity can make it difficult to inspire as the abdominal cavity is much harder to compress.
During expiration all of the above decrease

Front 15

Describe the non-respiratory functions of the diaphragm.

Back 15

The diaphragm as well as being the main respiratory muscle also is involved in other functions. By increasing the intra-abdominal pressure, it is involved in expelling vomit, faeces and urine from the body. It also prevents acid-reflux by exerting pressure on the oesophagus as it passes through the oesophageal hiatus.

Front 16

Describe the distribution of the intercostals nerves arteries and veins.

Back 16

The neurovascular bundles lies on the inferior surface of the rib in the subcostal groove.
The subclavian artery gives of the internal thoracic artery. The internal thoracic artery in turn gives off the anterior intercostals artery. The thoracic aorta gives off the posterior intercostals artery. The anterior and posterior intercostals arteries form anastomoses which supply the thoracic wall.
The anterior and posterior intercostals veins anastomose and drain into the azygos vein on the right and the hemiazygos vein on the left which empty into the superior vena cava.
There are 12 intercostal nerves that run in the subcostal groove and supply the skin, intercostals muscles, parietal pleura and margins of diaphragm.

Front 17

What is the sternal angle?

Back 17

T4/t5 – junction between manubrium and sternum – angle of Louis
It marks the end of the aortic arch and the bifurcation of the trachea into primary bronchi. It also marks the boundary between the superior and inferior mediastiunum.

Front 18

Describe the pleural cavity and pleura.

Back 18

Each lung is invested by a pleural sac with the lungs being surrounded by a visceral serous membrane and a paretial membrane which surrounds the pulmonary cavity. The pleural cavity is found between the 2 membranes and contains very little serous fluid in a healthy person. The visceral membrane is continuous with the mediastinal parietal layer at the hilum of the lung where the bronchus and pulmonary vessels enter and leave.
There are 4 parts of the parietal pleura
- Costal pleura – which is in contact with the thoracic wall, lying on top of the endothoracic fascia – surgical access!!
- Mediastinal pleura- which is in contact with the central mediastinum and continues superiorly to be cervical pleura
- Diaphragmatic pleura – covers the superior surface of the diaphragm except where the pericardium attaches. Phrenicopleural fascia connects the diaphragmatic pleura to the muscular fibres of the diaphragm.
- Cervical pleura – covers the apex of the lung where is extends through the superior thoracic aperture into the root of the neck.

Front 19

State and describe the lines of pleural reflection.

Back 19

The lines of pleural reflection are the abrupt lines along which the parietal pleura changes direction as it passes from one wall of the pleural cavity to the next. They are the sternal, costal and diaphragmatic lines.
The pulmonary cavities are asymmetrical due to the deviation of the heart to the left.
- The apex of the pleural cavity extends 3 cm above the medial part of the clavicle.
- The anterior borders of the pleural cavity descend infero medially, posterior to the sternoclavicular joint until reaching..
- The sternal angle at T4/t5 ( 2nd rib). The 2 pleura are so close they are nearly touching and can easily communicate.
- The right sternal line then continues vertically to reach 6th costal cartilage
- The left pleural cavity deviates to the edge of the sternum at rib 4 before descending vertically to reach 6th costal cartilage.
- They both pass round the back on either side crossing..
- the mid clavicular line at 8th rib
- the mid axillary line at 10th rib
- The scapular line at the 12th ribs.

Front 20

What is the fascia that surrounds the apical pleura called and what happens if it does not function properly.

Back 20

The suprapleural membrane, fascia, covers the apical pleura and attaches to the first rib.
If the suprapleural fascia doesn’t prevent the lung from extending into the neck, then there is a bulge in the supra-clavicular fossa. But this is harmless.

Front 21

Describe the surface markings of the lobes of the lung.

Back 21

The left lung comprises of upper and lower lobes separated by the oblique fissure. It also has a lingula which is where the middle lobe should be.
The right lung comprises of upper, middle and lower lobes. The upper and middle lobes are separated from the lower lobe by the oblique fissure and the upper and middle lobes are separated by the horizontal fissure.
The oblique fissure runs from spinous process of T2 posteriorly to the 6th costal cartilage anteriorly.
The horizontal fissure extends from the oblique fissure at the midaxillary line and runs anteriorly along the 4th rib to the anterior edge of the lung.
The lungs fill the pleural cavity except for the lower margin of the lungs where it is about 2 ribs above the parietal pleura. The right lung reaches 6th costal cartilage and moves horizontally to the right so that at the midclavicular point it is at the 6th rib ( parietal pleura is at the 8th), at the midaxillary line it is at the 8th rib ( parietal pleura is at the 10th) and at the scapular line it is at the 10th ribs ( parietal pleura is at the 12th).
The left lung has a cardiac notch where the pericardium is exposed. It extends from the sternal angle at 4th rib and nearly reaches the midclavicular line before curving around the pericardium to the heart’s apex in the 5th intercostals space and then moves horizontally along at the level of 6th rib and follows the same markings as the right lung.

Front 22

Describe the structure and arrangement of airways and blood vessels in the lungs.

Back 22

The trachea bifurcates at T4/T5 into the primary bronchi which enter the right and left lungs at the hila. They further divide into the lobular bronchi ( 3 right lung lobes and 2 left lung lobes) which divide into segmental bfronchi. Generations 5-11 are small bronchi. Bronchioles start at 12th generation and terminal bronchioles ( 16) lead to respiratory bronchioles > alveolar ducts -> alveolar sacs -> alveoli.
The right and left pulmonary arteries branch from the pulmonary trunk at the angle of Louis and enter the lungs via the hila. The pulmonary arteries divide into lobar arteries and segmental arteries which provide de-oxygenated blood to the lungs to be oxygenated. The oxygenated blood returns to the heart via segmental veins, lobar veins and pulmonary veins into the left atrium. The bronchi and airways down to the respiratory bronchioles recieve blood supply from bronchial arteries which are branches of the descending thoracic aorta. The respiratory bronchioles, alveolar ducts and sacs are supplied by the pulmonary circulation.

Front 23

What part of the lungs do the bronchial arteries supply?

Back 23

The bronchial arteries supply blood for nutrition to the structures making up the root of the lungs, the supporting tissue of the lungs and the visceral pleura. 2 left bronchial arteries branch directly from the thoracic aorta and the single right bronchial artery may also arise from the aorta directly. Usually the right bronchial artery arises indirectly from the aorta by a branch of the upper posterior intercostals arteries or from the left superior bronchial artery.
The bronchial arteries branch to provide the upper oesophagus branch and then pass along the posterior aspects of the main bronchi, supplying them and their branches until the respiratory bronchioles. Distally the bronchial arteries anastomose with pulmonary arteries in the walls of the bronchioles

Front 24

Describe the mediastina and their contents.

Back 24

The thoracic cavity is divided into 3 compartments: the right and left pulmonary cavities containing the lungs and the pleura and in between these cavities is the central mediastinum which contains all other thoracic viscera – heart, thoracic parts of great vessels, thoracic parts of oesophagus and trachea, thymus, thyroid etc.
The mediastinum extends from the superior thoracic aperture to the diaphragm inferiorly and from the sternum and costal cartilages anteriorly to the vertebral column posteriorly.
The superior mediastinum is the region from the superior thoracic aperture to the angle of Louis at T4/T5 (transverse thoracic plane). It contains thymus, trachea, oesophagus, great vessels and thoracic duct.
The inferior mediastinum is the region between the transverse thoracic plane and the diaphragm. It is further divided by the pericardium into the anterior, middle and inferior compartments.
- The anterior compartment houses fat, loose connective tissue, lymphatic vessels, lymph nodes.
- The middle compartment houses the pericardium and the heart and roots of great vessels
- The posterior compartment houses DATES – descending aorta, azygos and hemiazygos veins, thoracic duct, oesophagus, sympathetic branches.

Front 25

Describe the structure of the pulmonary circulation and the characteristics that distinguish it from the systemic circulation.

Back 25

The pulmonary artery contains deoxygenated blood whereas in the systemic circulation all arteries contain oxygenated blood and all veins contain deoxygenated blood. The pulmonary circulation has low resistance vessels (short wide vessels in parallel, arterioles with little smooth muscle) as opposed to the systemic circulation which has high resistance vessels, capacitors and low resistance vessels. The pulmonary circulation functions at much lower pressures than the systemic. The systemic circulation is demand lead whereas pulmonary is supply driven.

Front 26

Describe the innervations of the lungs and pleurae.

Back 26

The pulmonary nerve plexus lies behind each hilum, receiving fibres from both vagi and 2nd-4th thoracic ganglia of sympathetic trunks. Each vagus contains sensory afferents from lungs and airways, parasympathetic bronchonconstrictor (MI) and secretomotor efferents and NANC nerves.
Sympathetic noradrenergic fibres supplying airway smooth muscle are sparse in humans and the B2 adrenergic receptors are stimulated by circulating catecholamines from the adrenal medulla.

The parietal pleura is segmentally innervated by intercostals nerves and by the phrenic nerve and so pain from pleural inflammation ( pleurisy) is often referred to chest wall or shoulder. The visceral pleura lacks sensory innervations.