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Respiratory > Week 2 - Anatomy and mechanisms of breathing > Flashcards

Week 2 - Anatomy and mechanisms of breathing Flashcards

1
Q

Describe the bony thorax

A
  • Thoracic vertebrae posteriorly
  • The ribs and the intercostal spaces laterally
  • The sternum and costal cartilages anteriorly
  • Above it is continuous with the neck
  • Below the diaphragm separates it from the abdominal cavity
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2
Q

Describe the sternum

A

Has 3 parts:

  • Manubrium (articulates with 1st and part of 2nd costal cartilage)
  • Body (articulates with part of the 2nd and the 3rd-7th costal cartilages)
  • Xiphsternum (remains cartilaginous into adult life)
  • – Junction of manubrium and body = sternal angle
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3
Q

What are the articulations of the ribs?

A
  • The 12 ribs articulate with the vertebral column posteriorly via the costo-vertebral joints
    Anteriorly:
    — ribs 1-7 are connected to the sternum via costal cartilages
    — ribs 8-10 are connected to the costal cartilage above
    — ribs 11-12 end free in the abdominal muscles
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4
Q

What is a ‘typical rib’?

A
  • Ribs 3-9
    Has:
  • Head: 2 articular facets for articulation with the body of the corresponding vertebra and the vertebra above)
  • Neck
  • Tubercle: has 1 articular facet for articulation with the transverse process of the corresponding thoracic vertebra
  • Shaft: thin, flat and curved
    — Has a costal groove close to its lower border which protects the vessels and nerves
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5
Q

What are atypical ribs?

A
  • Ribs 1, 2, 10, 11, 12

- Have only 1 facet on the head for articulation with its corresponding vertebra

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6
Q

What are the costovertebral joints?

A
  • There are 2 synovial joints which connect the ribs with the thoracic vertebrae
  • – Joint of the rib head (the head of the rib articulates with the body of the corresponding vertebra and the vertebra above)
  • – Costo-transverse joint (articular facet on the tubercle of the rib articulates with the transverse process of the corresponding vertebra)
  • Movements of the ribs during respiration take place at these joints
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7
Q

What are the 3 muscles found in the intercostal spaces?

A
  • External intercostal
  • Internal intercostal
  • Innermost intercostal
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8
Q

Describe the external intercostal muscle

A
  • The fibres run downwards and anteriorly
  • From the inferior margin of the rib above to the superior margin of the rib below
  • Responsible for 30% of chest expansion during quiet respiration
  • Elevate the muscles in a ‘bucket handle’ type of movement to increase the antero-posterior and transverse diameters of the chest
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9
Q

Describe the internal intercostal muscle

A
  • The fibres run downwards and posteriorly
  • From the rib above to the rib below
  • Their action pulls the ribs down from the position of chest expansion
  • Active during forced expiration
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10
Q

Describe the innermost intercostal muscle

A
  • Similar to the internal intercostal muscles but less well developed
  • Act along with the internal during forced expiration
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11
Q

What innervates the intercostal muscles?

A

Intercostal nerve

- The anterior rami of thoracic spinal nerves (T1-T12)

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12
Q

Where do you find the intercostal vein, artery and nerve?

A

The intercostal vein, artery and nerve lie in the intercostal groove of the rib

  • In that order
  • Between the internal and innermost intercostal muscles
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13
Q

Describe the intercostal arteries

A
  • Supply the intercostal muscles, parietal pleura and overlying skin
  • Each space has an anterior intercostal artery which anastomoses with a posterior intercostal artery
  • The anterior intercostal arteries arise from the internal thoracic artery (a branch of the subclavian)
  • Posterior intercostal arteries arise from the aorta and the superior intercostal artery
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14
Q

Describe the intercostal veins

A
  • Each space has 2 anterior and 1 posterior vein accompanying the arteries
  • The anterior veins drain via the internal thoracic vein into the subclavian
  • Most posterior intercostal veins drain via the azygos vein on the right and hemiazygos vein on the left, into the SVC
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15
Q

Describe the pleura

A

Pleura = a serous membrane consisting of a single layer of mesothelial cells with a thin layer of underlying connective tissue
- Parietal pleura lines the inside of each hemi thorax
— Continuous at the hilum of the lung with the visceral pleura which lines the outside of the lung
- The visceral pleura extend between lobes of the lung into the depths of the oblique and horizontal fissures
- Pleural space = potential space between the 2 layers of pleura
- Both layers of pleura are covered by a film of fluid
— Allows the 2 parts to slide on one another
— The surface tension of the pleural fluid provides the cohesion that keeps the lung surface in contact with the thoracic wall
— So 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

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16
Q

What is the blood supply to the pleura?

A
  • Parietal pleura is supplied by the intercostal arteries and internal thoracic arteries, and is drained by the corresponding veins
  • Visceral pleura is supplied by the bronchial arteries and drained by the bronchial veins
17
Q

What is the nerve supply to the pleura?

A
  • Parietal: has somatic innervation including pain fibres from intercostal and phrenic nerves, as well as automatic innervation
  • Visceral: has no somatic innervation, only autonomic
18
Q

Describe the trachea

A
  • Commences at the lower border of the cricoid cartilage in the neck
  • Terminates by dividing into the right and left main bronchi
  • – The angle between the right and left main bronchi = the carina
  • Held open by 18-22 U-shaped cartilages
  • Posteriorly where the cartilage is deficient, its wall contains the trachealis muscle
19
Q

Describe the main bronchi

A

Right main bronchus is shorter, wider and more vertical than the left
- 2.5 cm long
- Before it reaches the hilum, the gives off its upper lobar branch
Left main bronchus is 5cm long
- Passes below the arch of the aorta, anterior to the descending aorta and oesophagus

20
Q

Describe the bronchial tree

A
  • The primary (right and left main) bronchi divide into lobar bronchi for each lobe
  • The lobar bronchi in turn divide into segmental bronchi, each destined for a bronchopulmonary segment
  • – Branches of the bronchial arteries accompany the bronchi to the bronchopulmonary segments
  • – Each segment also has its own segmental branch of the pulmonary artery and pulmonary vein
  • – The segments can be isolated and remove without much bleeding, air leakage or interference with other bronchopulmonary segments
  • Segmental bronchi divide further into subsegmental bronchi, which further divide until they become terminal bronchioles
  • These then divide to become respiratory bronchioles, which then become alveolar ducts and then alveoli
21
Q

What is the blood supply to the bronchial tree?

A

Bronchial arteries supply the bronchial tree from the carina up to the respiratory bronchioles, visceral pleura and connective tissue
- Arise from the aorta and the 3rd intercostal artery on the right
Most of the blood supplied by the bronchial arteries is returned via the pulmonary 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 the rest of the bronchi into the main pulmonary vein or directly into the left atrium

22
Q

What do the pulmonary arteries supply?

A
  • Carry mixed venous blood from the right ventricle for gas exchange at the alveoli
  • The main PA divides into the right and left Pas
  • – These enter the lung with the right and left main bronchi
  • PAs divide with the bronchial tree
  • They eventually form the rich capillary network surrounding the alveoli
  • Do not supply the bronchi
  • There are some anastomoses between the bronchial and pulmonary arteries at pre-capillary level and capillary level
  • – Maintain blood supply to lung parenchyma after pulmonary embolism
23
Q

What do the pulmonary veins do?

A
  • Drain the alveoli
  • Tend to run in the intersegmental septa
  • 2 PVs leave each hilum (draining the upper and lower lobes)
24
Q

What is the mediastina?

A

The central compartment of the thoracic cavity

  • Covered on each side by mediastinal pleura
  • Contains all the thoracic viscera and structures, except for the lungs
  • Highly mobile
  • Extends from the superior thoracic aperture to the diaphragm
  • – From the sternum and costal cartilages anteriorly to the bodies of the thoracic vertebrae posteriorly
  • Divide into superior and inferior parts
  • – The middle inferior mediastinum contains the heart
25
Q

How do the bronchioles allow air into the alevoli?

A

Bronchioles dilate, increasing their volume and lowering the pressure inside the lungs, moving air in

26
Q

What muscles are involved in quiet respiration?

A
  • Inhalation: diaphragm and external intercostals
  • Exhalation: none
  • – Passive recoil of lungs
27
Q

What is the resting expiratory level?

A

Equilibrium formed when the inward force of the elastic recoil of the lungs is balanced by the outward recoil of the chest wall

28
Q

Which muscles are involved in forced breathing?

A 
Inhalation:
- Diaphragm
- External intercostals
- Scalene
- Pectoralis major
- Sternocleidomastoid
- Serratus anterior
Exhalation:
- Internal intercostals
- Innermost intercostals
- Abdominal muscles
29
Q

What is compliance?

A

The stretchiness of the lungs = the volume change per unit pressure change

  • Depends on the starting volume from which it is measured, even with constant elasticity of lung structures
  • Specific compliance = (volume change per unit pressure change) / (starting volume of lung)
30
Q

What is surface tension?

A
  • Makes the surface resist stretching
    — The higher the surface tension, the harder the lungs are to stretch
    The airways and alveoli of the lungs are lined with a film of fluid which is increased in area as the lungs expand
    — The force required to expand the alveoli, to stretch the fluid lining the alveoli, is elastic recoil
  • Surface tension is reduced by surfactant
    — Produced by type 2 alveolar cells
    — Disrupts interactions between surface molecules
    — Reduces surface tension when the lungs are deflated
    — Quiet breathing uses little energy
    — Does not reduce surface tension as much when the lungs are fully inflated
    — .: big breaths are hard
    — As alveoli get bigger, the surface tension in their walls increases because surfactant is less effective
    — So pressure stays high and stops them collapsing
    — It equalizes the pressure between different size alveoli so that they do not collapse into each other
31
Q

What are the factors that affect airway resistance?

A

Poiseulle’s law: The resistance of a tube increases sharply with a falling radius

  • However, the combined resistance of the small airways is normally low, because they are connected in parallel
  • Most of the resistance to breathing resides in the upper respiratory tract
  • At rest, the work of breathing only consumes 0.1% of total oxygen consumption (so very efficient!)

Respiratory (8 decks)

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