Resp S2 - Anatomy & Lung Ventilation

Question 0

What is the sternal angle?

Answer 0

Where the manubrium meets the body of the sternum, there is a change in angle which is useful for locating the level of the 2nd rib and the arch of the aorta

Question 1

What does the sternum consist of?

Answer 1

Manubrium - articulates to 1st & 2nd costal cartilages
Body - articulates to 2nd to 7th costal cartilages
Xiphersternum - remains cartilaginous to adult life

Question 2

Describe ribs and their articulation

Answer 2

There are 12 ribs, all of which articulate posteriorly to the vertebral column. Anteriorly, their joints are as follows:
1-7 are connected to the sternum via the costal cartilages
8-10 are connected to the costal cartilage above
11-12 are “floating ribs” which end free in the abdominal muscles

Question 3

What are the intercostal muscles?

Answer 3

External intercostal muscles
Internal intercostal muscles
Innermost intercostal muscles

Question 4

Describe the external intercostal muscles

Answer 4

Outermost layer. Run anteriorly and inferiorly to the rib below. “Bucket handle” type movement. Responsible for ~30% of chest expansion during quiet breathing.

Question 5

Describe inner intercostal muscles

Answer 5

Run posteriorly and inferiorly to the rib below

Active during forced expiration

Question 6

Describe innermost intercostal muscles

Answer 6

Similar to the inner intercostal muscles but less developed

Act with the inner intercostal muscles during forced expiration

Question 7

Where does the intercostal neurovascular bundle run and why is this clinically relevant?

Answer 7

They run along the lower border of the ribs, in the intercostal grooves between the internal and the innermost intercostal muscles.
Clinically relevant when inserting a chest drain or doing a pleural aspiration because we want to avoid damaging neurovascular bundles

Question 8

Describe the intercostal arteries

Answer 8

Supply the intercostal muscles, parietal pleura and overlying skin
Each intercostal space (except the last two) have anterior intercostal arteries which arise from the musculophrenic->internal thoracic-> subclavian arteries and anastomose with the posterior intercostal arteries. These arise from the aorta and superior intercostal artery->costo-cervical trunk-> subclavian artery

Question 9

Describe the intercostal veins

Answer 9

Each intercostal space has two anterior and one posterior intercostal vein. The anterior drain into the internal thoracic->subclavian arteries. The posterior drain into the azygous vein on the right and the hemiazygous vein on the left into the IVC

Question 10

Describe the intercostal nerves

Answer 10

From the anterior rami of the thoracic spinal nerves (T1-T12)
They supply the intercostal muscles, parietal pleura and overlying skin

Question 11

Describe the diaphragm

Answer 11

A dome shaped muscle which divides the thoracic cavity from the abdominal cavity
The dome lies at ~5th rib, lower on the LHS
Consists of central tendon and peripheral muscular parts.
Responsible for 70% of chest expansion
Innervated by the phrenic nerve (C3, 4, 5)

Question 12

What is the peripheral muscular part of the diaphragm comprised of?

Answer 12

Sternal part (from xiphisternum)
Vertebral part (from arcuate ligament & crura)
Costal part (from 7-12th costal cartilages)

Question 13

What are the arcuate ligaments?

Answer 13

Thickening of fascia over the muscles of the posterior abdominal wall

Question 14

What are the crura?

Answer 14

Strong tendons attached to the anterolateral surfaces of the upper 3 vertebral bodies (2 on the left)

Question 15

Where and for what structures are the openings in the diaphragm?

Answer 15

T8 - inferior vena cava
T10 - oesophagus
T12 - aorta

Question 16

What makes up the thoracic cavity?

Answer 16

2 lateral pulmonary cavities

1 central compartment called the mediastinum

Question 17

How is the mediastinum sub-divided?

Answer 17

Divided into sub compartments:
Superior
Middle
Anterior
Posterior

Question 18

Describe the pleura

Answer 18

Serous membrane consisting of a single layer of mesothelioma cells and a thin underlying layer of connective tissue
The parietal pleura lines the inside of each hemi thorax and is continuous at the hilum with the visceral pleura which lines the outside of the lung

Question 19

Describe the pleural space

Answer 19

Space between the parietal and visceral layers of the pleura
Contains a small amount of pleural fluid to allow the layers to move against each other and to maintain surface tension so the lung is pulled with the ribs whilst breathing
Fluid produced by parietal surface and drains into parietal lymphatic vessels

Question 20

What are the costodiaphragmatic recesses?

Answer 20

The pleural-lined gutters at the base of the diaphragms upward convexities

Question 21

Describe the blood supply to the pleura

Answer 21

Parietal: intercostal and internal thoracic arteries and veins
Visceral: bronchial arteries and veins

Question 22

Describe innervation of the pleura

Answer 22

Parietal: somatic, including pain fibres from the intercostal and phrenic nerves, as well as autonomic
Visceral: autonomic only

Question 23

Describe the trachea

Answer 23

Commences at the lower border of the cricoid cartilage and terminates by dividing into the right and left bronchi at the level of the sternal angle, called the carina.
18-22 U-shaped cartilages with trachealis muscle posteriorly where the cartilage is lacking
Lined with pseudostratified ciliated columnar epithelium

Question 24

Describe the bronchi

Answer 24

Right: shorter, wider and more vertical. 2.5cm long. Gives off first branch (the upper lobar branch) before the hilum Left: 5cm long. Passes under the arch of the aorta, anterior to the descending aorta and oesophagus

Question 25

Briefly describe the bronchial tree

Answer 25

The primary bronchi divide into the lobar bronchi (one for each lobe of the lung) These divide into segmental bronchi, one for each bronchopulmonary segment Segmental bronchi divide into subsegmental bronchi -> terminal bronchioles -> respiratory bronchioles -> alveolar ducts -> alveoli

Question 26

What is a bronchopulmonary segment and why are they clinically relevant?

Answer 26

An area of lung supplied by a segmental bronchus and accompanying bronchial artery and segmental branches of the pulmonary artery and vein. Important in surgery because they can be isolated and removed with little bleeding, air leakage or interference with other segments

Question 27

Describe a bronchoscopy

Answer 27

Can be used to visualise the inner trachea, carina, main bronchi, lobar bronchi and origins of the segmental bronchi Used in diagnosis of bronchial carcinoma for histology sampling and visualisation

Question 28

Describe the arterial blood supply to the bronchial tree

Answer 28

Bronchial arteries arise from the aorta on the left and the 3rd intercostal artery on the right Supply visceral pleura, connective tissue and bronchial tree from the carina to the respiratory bronchioles

Question 29

Describe the venous blood supply to the bronchial tree

Answer 29

Most blood drains into the pulmonary veins Superficial bronchial veins drain visceral pleura & hilar region bronchi to the azygous vein (RHS) & the hemiazygous accessory vein (LHS) Deep bronchial veins drain drain the rest of the bronchi to the pulmonary vein or directly into the left atrium

Question 30

Briefly describe lung divisions

Answer 30

Left: two lobes (upper and lower) which are separated by the oblique fissure Right: three lobes (upper, middle and lower) which are separated by the oblique fissure (middle from lower) and the horizontal fissure (middle from upper)

Question 31

What is the hilar region of the lung?

Answer 31

Where almost everything enters and leaves the lung: air in bronchi, blood in bronchial and pulmonary arteries and veins, lymphatics and nerves

Question 32

Describe pulmonary artery

Answer 32

Divides into right and left pulmonary arteries which enter the lung with the main bronchi. These further subdivide with the bronchi to the alveolar level to supply the alveoli, NOT the bronchi Some anastomoses with bronchial arteries at capillary and precapillary level which maintain blood supply after pulmonary embolism

Question 33

Describe the pulmonary veins

Answer 33

Tend to follow the inter segmental septa Drain the alveoli Leave at the hilum

Question 34

Describe nerve supply to the lung

Answer 34

Parasympathetic fibres from the vagus for bronchial smooth muscle (bronchoconstriction), vasodilation in the pulmonary artery and secremotor in mucous glands Vagal afferent fibres for cough reflex and some subserving pain Sympathetic efferents for bronchodilator and vasoconstrictor

Question 35

Describe pulmonary lymphatics

Answer 35

Sub pleural lymphatic plexus drains lung parenchyma and visceral pleura along the surface to the hilar lymph nodes Deep bronchopulmonary plexus lies in the submucosa of the bronchi and peribronchial tissue and eventually drains to the hilar region too Enlarged tracheobronchial nodes may cause widening of the carina

Question 36

What are the normal values for CO2 and O2 in alveolar gas?

Answer 36

CO2: 5.3 kPa O2: 13.3 kPa

Question 37

What factors affect gas exchange?

Answer 37

Available exchange area Resistance/distance to diffusion Partial pressure gradient

Question 38

Discuss exchange area as a factor for gas exchange

Answer 38

Lungs contain many alveoli, which total ~80m^2 of exchange area, therefore area available is rarely a limiting factor for gas exchange

Question 39

Discuss diffusion distance as a factor for gas exchange

Answer 39

Gases must diffuse through: alveolar cell, interstitial fluid, capillary cell, plasma and a red blood cell membrane However, overall this is less than 1 micron in distance

Question 40

Discuss resistance as a factor for gas exchange

Answer 40

The resistance is not the same for the two gases. CO2 diffuses 21x as fast as O2 because it is more soluble. Therefore anything affecting diffusion will only affect O2 because this is limiting

Question 41

Discuss partial pressure gradient as a factor for gas exchange

Answer 41

O2 and CO2 must be kept very close to their normal values. This occurs through a process called ventilation

Question 42

Describe ventilation

Answer 42

Fresh atmospheric air does not enter the alveoli: diffusion of gases occurs in terminal and respiratory bronchioles This means that alveolar gases remain at a very constant level, so blood gases remain constant

Question 43

How can the movement of air during breathing be measured?

Answer 43

With spirometry

Question 44

Define "tidal volume"

Answer 44

A certain volume enters the lungs with each breath - the tidal volume

Question 45

Define inspiratory reserve volume

Answer 45

The difference between normal (tidal) breathing and maximal inhalation

Question 46

Define expiratory reserve volume

Answer 46

The different between normal 'tidal' breathing and maximal exhalation

Question 47

What is residual volume?

Answer 47

We cannot completely empty our lungs, so the remainder after we exhale as much as we can is known as the residual volume

Question 48

Define inspiratory capacity

Answer 48

From quiet respiration to maximum respiration | Aka inspiratory reserve + tidal volume

Question 49

Define functional inspiratory capacity

Answer 49

The volume of air in the lungs at the end of quiet respiration

Question 50

Define vital capacity

Answer 50

Inspiratory capacity + expiratory reserve OR Tidal volume + inspiratory reserve + expiratory reserve

Question 51

Define total lung volume

Answer 51

Vital capacity + reserve volume

Question 52

Describe anatomical dead space

Answer 52

The volume of the conducting airways is called dead space because the air in these parts of the lung at the end of inspiration isn't available for gas exchange. This volume is usually ~150ml and can be measured by the nitrogen washout test

Question 53

Describe alveolar dead space

Answer 53

The volume of air contained by alveoli which do not take part in gas exchange for any reason (eg poor blood supply, damage due to accident or disease)

Question 54

Describe physiological dead space

Answer 54

Anatomical dead space + alveolar dead space | May be determined by measuring the pCO2 (or pO2) of expired and alveolar air

Question 55

Define the pulmonary ventilation rate

Answer 55

Comprised of two components: alveolar ventilation and dead space ventilation

Question 56

Define empyema

Answer 56

Pus in the pleural space