1 Anatomy of the Parenchyma, Airways, and Blood Vessels Flashcards
1
Q
The airways
- Symmetry
- Trachea
- L lung
- R lung
A
- Not symmetric
- Trachea
- Divides at the carina into R & L mainstem bronchi
- L lung
- Slightly smaller due to the heart
- Only has 2 lobes (upper & lower)
- L upper lobe divides into an upper division + lingula
- R lung
- 3 lobes: upper, middle, & lower
2
Q
Lobe segments
- R upper lobe
- R middle lobe
- R lower lobe
- L upper lobe
- L lower lobe
A
- R upper lobe (3)
- Apical
- Posterior
- Anterior
- R middle lobe (2)
- Medial
- Lateral
- R lower lobe (5)
- Superior
- Anterior basal
- Medial basal
- Lateral basal
- Posterior basal
- L upper lobe (4)
- Upper division
- Apical-posterior
- Anterior
- Lingula
- Superior
- Inferior
- Upper division
- L lower lobe (4)
- Superior
- Antero-medial basal
- Lateral basal
- Posterior basal
3
Q
Cilia
A
- Critical for clearance of the lungs
- Lungs are essentially blind ended tubues
- 9+2 ultrastructure
- Primary ciliary dyskinesia (PCD) –> chronically infected lungs (Kartagener’s) & airway destruction
- Cystic fibrosis: similar to Kartagener’s
4
Q
Clinical pearls
- Kartagener’s syndrome
- L vs. R mainstem bronchus
A
- Kartagener’s syndrome
- Aka primary ciliary dyskinesia
- Often have a mirror image of a normal chest
- Dextrocardia
- Reversal of the normal branching pattern of the lungs (“L middle lobe” + “R lingula”)
- L vs. R mainstem bronchus
- L is longer than the right
- L is more acutely angled at the trachea, so most aspirated foreign bodies end up in the R lung
5
Q
Conducting airways (conducting zone)
- Consist of…
- Trachea
- Bronchi
- Terminal bronchioles
- Alveolar ducts
- Alveolar sacs
- Acinus
A
- Consist of…
- Airways w/o alveoli directly attached
- Trachea
- Have C-shaped rings of cartilage in their walls
- Bronchi
- Mainstem bronchi have C-shaped rings of cartilage in their walls
- Segmental & lower bronchi have plates of cartilage in their walls
- Give way to bronchioles
- Distinguished by having no cartilage in their walls
- Terminal bronchioles
- Develop by 16 weeks gestation
- There are 16 generations of conducting airways
- Give way to respiratory bronchioles that have alveoli budding directly off their walls (transitional zone)
- Develop by 16 weeks gestation
- Alveolar ducts
- Final 3 generations of airways (respiratory zones)
- Made up of alveoli w/ bands of smooth muscle in their walls
- Bands of smooth muscle distinguish alveolar ducts from alveoli
- Alveolar sacs
- Primary site of gas exchange
- Acinus
- Repiratory bronchiole + all of its branches & alveoli
6
Q
Conducting airways (conducting zone): IMPORTANT
- Bronchi vs. bronchioles
- Trachea & bronchi
- Epithelium
- Have…
- Bronchiole
- Epithelium
- Non-ciliated cells
- Alveolus
- Epithelium
A
- Bronchi vs. bronchioles
- Test question: what differentiates a bronchus vs. a bronchiole? Cartilage
- Cartilage –> bronchus
- No cartilage –> bronchiole
- Alveolar ducts
- Bands of smooth muscle distinguish alveolar ducts from alveoli
- Trachea & bronchi
- Epithelium: columnar, pseudostratified, ciliated
- Have cartilage & glands
- Bronchiole
- Epithelium: cuboidal, ciliated
- Non-ciliated cells
- Clara cells: secrete “clara cell secretory protein”
- Goblet cells: make mucus
- Serous cells: submucosal glands that secrete 2 kinds of fluids (mucins & bicarb-rich serous fluid dense w/ CFTR)
- Alveolus
- Epithelium: flat, squamous, mostly type I (in area), non-ciliated
7
Q
Total airway cross-sectional area vs. airway generation
A
- Total airway cross-sectional area goes up exponentially with airway generation
- Important for how various parts of the airway contribute to total airway resistance
- Explains why the small (peripheral) airways contribute relatively little to total resistance
- The vast majority of cross-sectional area is in the peripheral airways
- Largely silent on exam
8
Q
Microscopic anatomy of the airway
- Microscopic anatomy of the airway changes w/…
- The entire airway is covered by…
- Lining in the trachea & bronchi
- Lining in the bronchioles
- Lining in the alveoli
- Lining between the bronchioles & the trachea
- Sub-mucosal glands
- Goblet cells
A
- Microscopic anatomy of the airway changes w/…
- Airway generation
- The entire airway is covered by…
- Epithelium
- Lining in the trachea & bronchi
- Pseudostratified columnar epithelium
- Lining in the bronchioles
- Cuboidal epithelium
- Lining in the alveoli
- Squamous epithelium
- Lining between the bronchioles & the trachea
- Cilia sweep in an organized fashion to continuoulsy push a thin layer of mucus outward from the peripheral airways (“mucociliary escalator”)
- Sub-mucosal glands
- Glands in the trachea & bronchi that secrete water, electrolytes, & mucins into the airway lumen
- Goblet cells
- Mucin secreting epithelial cells present at all airway levels down to the terminal bronchiole
9
Q
Clinical pearl: impaired mucus clearance
- The clearance of mucus from the lung is impaired in…
- Impaired mucus clearance results in…
- Other factors that impede mucociliary clearance
A
- The clearance of mucus from the lung is impaired in…
- Primary ciliary dyskinesia
- Cystic fibrosis
- Impaired mucus clearance results in…
- Chronic lower airway infection
- Inflammation of the airways
- Eventual destruction of the normal airway structure leading to bronchiectasis
- Other factors that impede mucociliary clearance
- Smoking
- Infection
10
Q
Alveoli & the alveolar-capillary interface
- Type I epithelial cells
- Type II epithelial cells
A
-
Type I epithelial cells
- There are more in surface area of Type I cells
- Aka squamous pneumocytes
- Cover the majority (~93%) of the alveolar surface (~100 M2, the size of a tennis court)
- Terminally differentiated cell
- Flat
-
Type II epithelial cells
- There are more in number of Type II cells
- Aka granular pneumocytes
- Cover the remaining 7%
-
Can differentiate into Type I cells in cases of lung injury
- Ex. ARDS
- Rounded with granular cytoplasm
- More numerous than the Type I cells
- Take up little of the alveolar surface area due to their rounded shape
- Produce surfactant
11
Q
Capillary (& pulmonary capillary) endothelium
A
- Thin surface keeping blood within the vascular space
- Metabolically active
- Converts AI to AII
- Produces factor 8
- Inactivates prostaglandins E2 & F2a, leukotrienes, & serotonin
- Pulmonary capillary endothelium
- Principal site of liquid & solute filtration
- Net outward flow of 10-20 ml/hr in adults
- Fluid is removed via the pulmonary lymphatics
12
Q
Alveolar-capillary membrane
- Alveolar-capillary membrane
- In order to get to the red cell, a moleucle of oxygen needs to traverse…
- Alveoli factoids
A
- Alveolar-capillary membrane
- Barrier b/n the alveolar gas & capillary blood
-
In order to get to the red cell, a moleucle of oxygen needs to traverse…
(test question: what layers does a molecule of oxygen have to walk through to get into the red cell?)- Surfactant
- Type I pneumocyte (epithelial cell)
- Fused basement membrane
- Endothelial cell
-
Plasma / RBC
- Red cell doesn’t march along the capillary
- Red cells actually deform & form sheets to maximize surface area that’s exposed to capillaries
- This allows them to take up the most oxygen
- Job of lung (1): give oxygen to red cells so muscles, brain, etc. has oxygen
- Job of lung (2): get rid of CO2
- Alveoli factoids
- We are born with ~50 million alveoli and have ~300 million alveoli as adults
- We continue to develop alveoli (and alveolar ducts) until age 5 to 8
- The blood-gas barrier is 0.5 μm thick
- Avg diameter of an alveolus is 250 μm
- Total alveolar surface area is about that of a tennis court, an average of 126 M2
13
Q
Surfactant
- Production
- Action
- Components
- Apoproteins
- Visible as…
- Lack of surfactant
A
- Production
- Produced by type II cells
- Produced starting ~24 weeks gestation but more is prodocued later
- Why premies born that early don’t do as well
- Action
- Lower surface tension at the alveolar surface
- Components
- 90% lipid & 10% protein
- Main lipid component: phospholipid (principally phosphotidyl choline, PC)
- Most PC is in the form of dipalmitoyl phosphotidyl choline (DPPC, 80%)
- Other fatty acids: myristate, stearate, palmitoylate, & oleate
- Apoproteins
- Surfactant proteins: A, B, C, & D
-
Critical to the function of surfactant
- Esp surfactant apo B, w/o which an infant will die shortly after birth
- –> respiratory failure w/o lung transplant (awful on babies)
-
Role in defense
- Esp apo A & C
- Visible as…
- Lamellar inclusion bodies seen on EM of Type II epithelial cells
- Looks like a sliced onion
- Lack of surfactant
- Incompatible w/ life
14
Q
Clinical pearl: congenital alveolar proteinosis
A
- Congenital deficiency of surfactant apoprotein B
- Fatal w/o a lung transplant
- More commonly: deficiency in surfactant in premature infants
- Administor exogenous surfactant (e.g., Exosurf, Survanta) to improve gas exchange
15
Q
Pulmonary circulation blood supplies
- Pulmonary arteries
- Bronchial arteries
- Important points
- Venous blood
- Pulmonary capillary blood
- Clinical pearl: transplanted lungs
A
- Like the liver, the lung has 2 cirulations
-
Pulmonary arteries
- Carry desaturated (systemic venous) blood to the capillary bed for re-oxygenation
- Pulmonary arteries follow bronchial anatomy
- They follow bronchi & bronchioles & branch into the capillaries
- Pulmonary capillaries are structured to allow maximal contact of blood with alveolar gas
- Blood flows as if in a continuous sheet through the lungs
- Blood returns to the left atrium via 4 pulmonary veins (L, R, superior, & inferior)
-
Bronchial arteries
- Since the larger airways require arterial blood, they receive systemic arterial blood from the bronchial arteries
- Carry systemic (arterial) blood to nourish the bronchi
- Bronchial blood supply arises from the aorta and nourishes the bronchi
- Most bronchial venous blood returns to the left atrium via the pulmonary veins, contributing to the normal shunt of approximately 3%
- The other contributor to shunt is the thebesian veins, which drain the left ventricle
- Important points
- Venous blood from bronchial artery returns to the LEFT heart & contributes to normal shunt
- Think of pulmonary capillary blood flowing as a SHEET through the lung
- Clinical pearl: transplanted lungs
- Have no bronchial circulation
- Surgeons reanastomose the airways and pulmonary arteries only, leaving bronchial arteries alone
- After a few months the vascular supply returns via collateral growth from nearby systemic vessels
16
Q
Pulmonary lymphatics & interstitium
- Lymphatics
- Interstitium
A
- Lymphatics
- Fluid entering the interstitium via the alveolar capillaries enters lymphatic vessels, which follow the airways and pulmonary arteries and drain into the mediastinal lymph nodes
- Lymphatics follow septae & bronchovascular bundles
- Lymph then enters the venous circulation via the thoracic duct
- Lymph flow from the lungs is ~20 ml/hr
- Interstitial fluid is formed as the net result of fluid filtration through the capillary endothelium, which is predicted by Starling forces
- Fluid entering the interstitium via the alveolar capillaries enters lymphatic vessels, which follow the airways and pulmonary arteries and drain into the mediastinal lymph nodes
- Interstitium
- More a potential space than a real space
- Portion of the lung between the alveolar epithelium and the capillary endothelium
-
Primarily composed of non-cellular components
- Collagen fibrils and elastin fibers
- Occasional fibroblasts and macrophages
17
Q
Pleural space
A
- Potential space
- 2 pleural surfaces
- Lung is covered by a layer of visceral pleura
- Inner surface of the thorax is covered by a layer of parietal pleura
- Surfaces are in continuous contact, and are constantly sliding over one another as we breathe
- There must be a small amount of pleural fluid present to lubricate the system
- Fluid enters the pleural space through the parietal pleura and is removed by the pulmonary lymphatics after traversing the visceral pleura
- Pressure in the pleural space is negative relative to atmospheric pressure
- Pleural surfaces are richly innervated & sense pain & stretch
- Most commonly involved as a bystander in human disease (parapneumonic effusion, etc.)
18
Q
Respiratory muscles: main points
- Inspiratory muscles
- Primary muscle
- Accessory muscles
- Expiratory muscles
- Expiration
- Expiratory muscles
A
-
Inspiratory muscles
- Primary muscle: diaphragm
-
Accessory muscles: SCM, external intercostals
- Raise bucket handle of sternum
-
Expiratory muscles
- Expiration is usually passive, but we use the muscles of expiration for coughing & w/ increased respiratory work
- Expiratory muscles: rectus abdominus, obliques, transverse abdominal muscles, & the internal intercostals
19
Q
Respiratory muscles
- 2 kinds of respiratory muscles
- Diaphragm
- Accessory muscles of inspiration
- Normal respiratory system is like a spring
A
- 2 kinds of respiratory muscles
- Those for inhaling
- Those for coughing/breathing out
- Diaphragm
- Main muscle of inspiration
- Musculotendonous sheet that functions as a piston
- Comprised of skeletal muscle and is under a combination of voluntary and autonomic control via the phrenic nerves
- Arises from the 7-12th ribs laterally/posteriorly and from the xiphoid anteriorly
- Accessory muscles of inspiration
- External intercostals
- Scalene muscles (which elevate the first 2 ribs)
- Sternomastoid muscles (which serve to elevate the sternum like a bucket handle) to increase the volume in the ribcage
- Normal respiratory system is like a spring
- It takes work to stretch the spring (inhale) but the spring recoils automatically without any effort (exhaling)
20
Q
Respiratory muscles
- In order to cough or breathe forcefully…
- If the airway is open…
- If the glottis is closed…
- Clinical pearl: patients with weak respiratory muscles
A
- In order to cough or breathe forcefully…
- We use our accessory muscles of expiration (rectus abdominus, obliques, transverse abdominal muscles, and the internal intercostals)
- These act to increase intra-abdominal and intra-thoracic pressure
- If the airway is open…
- This causes an upward displacement of the diaphragm and expiration
- If the glottis is closed…
- This leads to increased intra-thoracic pressure, which is required for coughing
- Clinical pearl: patients with weak respiratory muscles
- E.g. muscular dystrophy
- At increased risk of pneumonia because of a weak and ineffective cough
- Inability to clear secretions from the chest can lead to mucous plugging, growth of bacteria, and pneumonia
21
Q
Innervation of the respiratory system:
Motor
- Diaphragm
- Intercostals
A
- Diaphragm
- Phrenic nerve (C3 C4 C5)
- “3-4-5 keeps the diaphragm alive”
- Intercostals
- Intercostal nerves (thoracic segmental nerves)
22
Q
Innervation of the respiratory system:
Autonomic
- Sympathetic
- Parasympathic
- Non-adrenergic, non-cholinergic pathway
A
- Sympathetic (upper throacic ganglia)
- Stimulation results in bronchodilation, constriction of pulmonary blood vessels, inhibition of glandular secretion
- Parasympathetic (vagus nerve)
- Stimulation results in airway constriction, dilatation of pulmonary circulation, increased glandular secretion
- Non-adrenergic, non-cholinergic pathway (NANC)
- Possibly mediated via NO
23
Q
Innervation of the respiratory system:
Sensory receptor types
- Pulmonary stretch receptors (slowly adapting)
- Irritant, rapidly adapting
- C-fiber receptors
A
- Pulmonary stretch receptors (slowly adapting)
- Found associated with smooth muscle of intra-pulmonary airways
- React to lung inflation and increased transpulmonary pressure
- Irritant, rapidly adapting
- Epithelial, larynx and intrapulmonary
- React to irritants, mechanical stimulation, etc.
- C-fiber receptors
- (1) pulmonary C-fiber receptors
- Found in alveolar wall
- Sense increased pulmonary interstitial congestion, chemical injury, microembolism
- (2) bronchial C-fiber receptors
- Stimulation of these results in bronchoconstriction
- In general, C-fibers are responsible for the sensation of dyspnea in many pulmonary diseases
- (1) pulmonary C-fiber receptors
