1 Anatomy of the Parenchyma, Airways, and Blood Vessels Flashcards Preview

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Flashcards in 1 Anatomy of the Parenchyma, Airways, and Blood Vessels Deck (23)
1

The airways

  • Symmetry
  • Trachea
  • L lung
  • R lung

  • 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

Lobe segments

  • R upper lobe
  • R middle lobe
  • R lower lobe
  • L upper lobe
  • L lower lobe

  • 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
  • L lower lobe (4)
    • Superior
    • Antero-medial basal
    • Lateral basal
    • Posterior basal

3

Cilia

  • 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

Clinical pearls

  • Kartagener's syndrome
  • L vs. R mainstem bronchus

  • 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

Conducting airways (conducting zone)

  • Consist of...
  • Trachea
  • Bronchi
  • Terminal bronchioles
  • Alveolar ducts
  • Alveolar sacs
  • Acinus

  • 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)
  • 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

Conducting airways (conducting zone): IMPORTANT

  • Bronchi vs. bronchioles
  • Trachea & bronchi
    • Epithelium
    • Have...
  • Bronchiole
    • Epithelium
    • Non-ciliated cells
  • Alveolus
    • Epithelium

  • 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

Total airway cross-sectional area vs. airway generation

  • 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

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

  • 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

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 

  • 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

Alveoli & the alveolar-capillary interface

  • Type I epithelial cells
  • Type II epithelial cells

  • 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

Capillary (& pulmonary capillary) endothelium

  • 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

Alveolar-capillary membrane

  • Alveolar-capillary membrane
  • In order to get to the red cell, a moleucle of oxygen needs to traverse...
  • Alveoli factoids

  • 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

Surfactant

  • Production
  • Action
  • Components
  • Apoproteins
  • Visible as...
  • Lack of surfactant

  • 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

Clinical pearl: congenital alveolar proteinosis

  • 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

Pulmonary circulation blood supplies

  • Pulmonary arteries
  • Bronchial arteries
  • Important points
    • Venous blood
    • Pulmonary capillary blood
  • Clinical pearl: transplanted lungs

  • 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

Pulmonary lymphatics & interstitium

  • Lymphatics
  • Interstitium

  • 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
  • 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

Pleural space

  • 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

Respiratory muscles: main points

  • Inspiratory muscles
    • Primary muscle
    • Accessory muscles
  • Expiratory muscles
    • Expiration
    • Expiratory muscles

  • 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

Respiratory muscles

  • 2 kinds of respiratory muscles
  • Diaphragm
  • Accessory muscles of inspiration
  • Normal respiratory system is like a spring

  • 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

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

  • 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

Innervation of the respiratory system:
Motor

  • Diaphragm
  • Intercostals

  • Diaphragm
    • Phrenic nerve (C3 C4 C5)
    • "3-4-5 keeps the diaphragm alive"
  • Intercostals
    • Intercostal nerves (thoracic segmental nerves)

22

Innervation of the respiratory system:
Autonomic

  • Sympathetic
  • Parasympathic
  • Non-adrenergic, non-cholinergic pathway

  • 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

Innervation of the respiratory system:
Sensory receptor types

  • Pulmonary stretch receptors (slowly adapting)
  • Irritant, rapidly adapting
  • C-fiber receptors

  • 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

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