Respiratory System

  1. What's the main functional component of all aspects of the respiratory tract?
    • the epithelium
    • mostly what's described
  2. Conducting Portion
    • includes structures that carry air to & from sites of gas exchange while warming, moistening, & cleansing it
    • no gas exchange takes place IN the conducting portion because the walls of the structures are too thick
  3. What is the path air flows through in the conducting portion of the respiratory system?
    nasal cavity → nasopharynx → larynx → trachea → (intrapulmonary) bronchi → bronchioles → terminal bronchioles
  4. Respiratory (Conducting) Epithelium
    • the epithelium that covers the surfaces of the conducting portion of the respiratory tract
    • it's a pseudostratified, ciliated, columnar epithelium with goblet cells
    • very deep in the lung this epithelium will no longer be ciliated
  5. Respiratory Portion
    where gas exchange takes place, specifically in the thin-walled alveoli

    order: respiratory bronchioles → alveolar ducts → alveolar sac → alveoli
  6. What are the 3 types of cells in the respiratory portion (where gas exchange takes place) of the tract?
    • type I pneumocytes
    • type II pneumocytes
    • alveolar macrophages
  7. Olfactory Epithelium
    • not a huge region, comprises part of the upper lateral wall & septum of the nose
    • is pseudostratified 
    • has stem cells (basal cells) that sit on the basal lamina
    • bipolar neurons (olfactory cells) pass through the basal lamina
    • they have cilia at the top of the epithelium that's bathed in serous fluid from Bowman's glands
  8. olfactory nerve cells
    • bipolar neurons with modified, non-motile cilia present at knob-like endings
    • receptors for odorants are present on the surface of the CILIA - such cells turn over constantly (unusual for CNS)
  9. How is something smelled?
    • odors/molecules have to dissolve in the fluid from the Bowman's glands at the surface of the epithelium
    • they then bind to odorant binding proteins
    • the compound then binds to receptors on the olfactory cell (bipolar neuron) cilia
  10. What do axons from the olfactory cells become?
    • CN I (cranial nerve I)
    • any cells associated with these olfactory cell axons are Schwann cells (because they're part of the peripheral nervous system)
  11. Why are the bipolar neurons in the olfactory epithelium unusual?
    • because they divide / turn over (@ ~the same rate as skin, olfactory epithelium)
    • the capacity is diminished in Parkinson's & Alzheimer's - patient early on complain of anosmia
  12. Image Upload 1
    • olfactory epith. is quite thick (especially compared to respiratory epithelium)
    • upper most nuclei belong to the sustentacular (supportive) cells
    • nuclei right along the basement membrane = basal cells
    • all other nuclei in the middle belong to the bipolar neurons
    • can see nerve bundles with the nuclei of associated Schwann cells
    • everything else below = Bowman's glands
  13. Respiratory (Conducting) EpitheliumImage Upload 2
    • can see pseudostratified, columnar epithelial cells
    • can see the cilia at the top
    • dark line under cilia = basal bodies; anchor them & organelles from which they develop
    • also see goblet cells
    • no respiration takes place where there is respiratory epithelium (too thick for gas exchange)
  14. Where would basal bodies not be visible?
    it isn't present on villi
  15. Image Upload 3
    • goblet cells visualized in respiratory epithelium
    • goblet cells don't have cilia b/c they open up & exocytose their contents (mucus granules
  16. Kulchitsky (Enteroendocrine) Cells
    Image Upload 4
    • made lots of products, eg. NTs like catecholamine, serotonin, hormones like calcitonin
    • are part of the DNES (diffuse neuroendocrine system)
    • can't be observed using H&E
  17. CF as it relates to Respiratory Epithelium Cilia
    • muco-cilliary 'escalator' doesn't work well
    • CFTR is located ~ where the basal bodies are (found at the apical end of ciliated cells, not goblet cells)
    • when CFTR doesn't properly transport Cl-, Cl- can't exit the cell, meaning Na+ stays in the cell to maintain electroneutrality, & WATER also goes into the cell FROM the mucus
    • this dehydrates the mucus making it THICK
    • thick mucus is hard for cilia to move, so pathogens that'd normally be cleared won't be
  18. Larynx
    Image Upload 5
    • this portion of conducting pathway isn't covered by respiratory epithelium
    • - larynx contains stratified squamous epithelium (SSNKE)
    • contains vocal chords & vocalis muscle that controls the vocal chords
    • several cartilages (most hyaline, a few elastic) anchor the vocalis muscle
  19. epiglottis
    • directs food away from the airway during swallowing
    • has non-keratinized stratified epithelium on its superior surface and has respiratory epithelium on its inferior surface
    • lamina propria contains some seromucous glands + an elastic cartilage plate
  20. vocal apparatus
    • consists of:
    • vestibular folds (false vocal cords) - respiratory epith.
    • true vocal cords - stratified squamous epith, control phonation
    • each true vocal cord has a large elastic fiber bundle, vocal ligament, & a parallel SKELETAL muscle bundle, the vocalis muscle
  21. Trachea
    long tube extending from the larynx down to the point where it bifurcates into the 2 main-stem bronchi
  22. Trachea X-Section
    • sits anterior to the esophagus
    • lined by Respiratory (Conducting) Epithelium [pseudostratified ciliated columnar w/ goblet cells]
    • Lamina Propria is the next layer after epithelium; it contains elastic fibers
    • there is NO muscularis mucosa proximal to the lamina propria in the trachea
    • instead there's Adventitia with Hyaline Cartilage that's C-shaped
    • Trachealis Muscle connects the 2 ends of the C-shaped Hyaline Cartilage Adventitia
    • Image Upload 6
  23. What are the 2 functions of the Trachealis Muscle?
    1. to contract when you cough & generate a lot of intrathoracic pressure that causes the trachea to expand (this muscle prevents over-expansion)

    2. it allows the esophagus to expand into the trachea when you're swallowing something
  24. What happens to the hyaline cartilage of the trachea in older individuals?
    it gets transformed into bone tissue
  25. Trachea Mucosa + Submucosa
    • Mucosa (innermost layer, closest to lumen):
    • - covered by respiratory epithelium
    • - has a PROMINENT basement membrane
    • - & underlying lamina propria

    • Submucosa:
    • - contains MANY mixed seromucous glands
    • - is separated from mucosa by a layer of elastic fibers

    *there is no muscularis mucosa separating the mucosa & submucosa in the trachea

    Image Upload 7
  26. How are the mainstem bronchi different from the trachea?
    • they're not - they're histologically identical to the trachea
    • can identify changes once you get into the lung proper
  27. Which lung do aspirated foreign materials tend to enter more readily?
    • the RIGHT one
    • because the right primary bronchus is wider, shorter & more VERTICAL than the left, & it makes a smaller angle with the axis of the trachea than the left (more room for things to enter)
  28. Intra v. Extra Pulmonary
    • Intra-anything means it's actually in the substance of the lungs
    • everything before/outside of the lungs = extra pulmonary (trachea + main bronchi)
  29. How does cartilage exist in the lung?
    • cartilage in the intra-pulmonary areas won't be C-shaped like it was extra-pulmonarily
    • instead it'll exist as 'plates' in the aventitia
  30. Intrapulmonary (Secondary) Bronchi
    • cartilaginous airways that arise from subdivisions of the primary bronchi via branching
    • intrapulmonary bronchi themselves divide to give rise to lobar & segmental bronchi
    • as bronchial diameter ↓ → thickness & complexity of the wall ↓
  31. Intrapulmonary (Secondary) Bronchi Characteristics
    • prominent muscularis mucosa (folds - also characteristic of bronchioles & larger bronchi due to preparation)
    • hyaline cartilage plates
    • Image Upload 8
    • *anytime you see hyaline cartilage in the adventitia in any level, the passageway is an intrapulmonary bronchus
    • (once the plates disappear the passageway is called a bronchiole)
  32. What causes asthma?
    • the thick smooth muscle of intrapulmonary bronchi
    • histamine release from mast cells due to an allergic reaction causes constriction of the smooth muscle layer, narrowing the passageway
  33. Bronchiole
    • a passageway is by definition a bronchiole if it lacks hyaline cartilage in its adventitia
    • Image Upload 9
    • still too thick for gas exchange
    • are typically 1mm or less
    • has no glands in the submucosa, lacks cartilage altogether 
    • contains only a few goblet cells
    • epithelium is no longer really pseudostratified, mostly cuboidal at this point; most nuclei lie basally & a clear apical cytoplasm can be seen
    • a muscularis mucosa is present
  34. Club cellsImage Upload 10
    • non-ciliated, dome-shaped apex, with the ultrastructure of a protein secreting cell
    • 1. make surfactant so bronchioles don't collapse in on themselves
    • 2. act as progenitor stem cells of the bronchiole epithelium during regeneration & repair
    • 3. protect against inflammation & oxidative stress

    Image Upload 11
  35. How can club cells be used clinically?
    proteins - such as CC16 - can be measured & if present in serum are indicative of epithelial damage in the lung
  36. Terminal Bronchioles
    • you know a bronchiole is terminal because the region downstream has out-pouchings known as alveoli
    • you can't differentiate a terminal from standard bronchiole via cross-section only 
    • is the smallest, last portion of the conducting pathway
    • the epithelium contains Club cells & some cuboidal ciliated cells (to remove any mucous which might move this far)
    • muscular layer is made up of an incomplete circular layer of smooth muscle
    • each terminal bronchiole divides into 2 or more respiratory bronchioles
    • Image Upload 12
  37. Where is there both gas exchange & conducting epithelium?
    • Respiratory Bronchiole
    • once you get passed the terminal bronchiole you can have regions with thin walls (alveoli, where gas exchange occurs) & thick walls (conducting)
    • Image Upload 13
  38. Respiratory Bronchiole
    • make up the first part of the respiratory portion
    • has a cuboidal epithelium (with ciliated cells, goblet cells & clara/club cells) is similar to that of a terminal bronchiole BUT the wall is interrupted by alveoli
    • Image Upload 14
    • can see smooth muscle (conducting) & out-pocketing (alveoli that contain capillaries in their walls for gas exchange)
  39. as the respiratory bronchioles divide, the # of alveoli in the walls _______, & the number of goblet & ciliated cells _______
    • alveoli increase in number
    • goblet cells disappear
    • frequency of ciliated cells decreases
  40. Alveolar Duct
    • lies downstream of respiratory bronchioles
    • entire wall is composed of alveoli out-pocketings (thin not thick wall with no smooth muscle)
    • ANY place along the duct is thin enough to have gas exchange
    • Image Upload 15
  41. Alveolar Sac
    • where the alveolar ducts end
    • multiple alveoli wrapped in elastic fibers
  42. How do you prevent alveoli surfaces from atelectasis (collapsing) & sticking to each other?
    • surfactant, which reduces the surface tension of surface membranes 
    • surfactant is amphipathic: made up of lipids [dipalmitoylphosphatidylcholine, DPPC] & proteins [surfactant protein A - D]
    • it also makes lungs more compliant
  43. What type of cell makes surfactant?
    type II pneumocyte
  44. Respiratory Distress Syndrome
    • non-functional lungs is a big problem for premature infants because surfactant production starts at 6 months in the fetus
    • RDS may occur in premature babies that have insufficient surfactant
    • can treat with corticosteroids to ↑ surfactant or just give exogenous surfactant
  45. Cells of the Alveoli
    type I pneumocyte: stretch a lot; gas exchange takes place over them

    type II pneumocyte: cover a smaller SA than type I; usually found in alveoli corners

    Macrophages (Dust cells)

    Image Upload 16
  46. Where are capillaries present in alveoli?
    • in the middle of alveolar cell walls (septa)
    • the barrier for gas exchange is between capillary endothelium & type I pneumocytes
    • gas must traverse both cells + their shared basement membrane for exchange
  47. Caveolae
    • take up inhaled molecules via pinocytosis
    • can then be transported through to capillary endothelial cells & subsequently transported through the blood
    • Image Upload 17
  48. Type II Pneumocytes
    chunkier, have microvilli extending out

    Image Upload 18

    contain lamellar bodies* in cytoplasm that contain surfactant (are lipid rich)

    Image Upload 19

    histologically type II cells/lamellar bodies look like little clearings
  49. Which pneumocytes are capable of division & which aren't?
    • type II can divide
    • type I cannot
    • renewal of type I pneumocytes requires proliferation of type II cells
  50. Alveolar Pores (of Kohn)
    • small pores that may interrupt alveolar septum & connect one alveolus to another
    • they equalize pressure & allow collateral air flow
    • are important when small airways are blocked
    • can also play a role in the spread of infection from one alveolus to another
  51. Arteries v. Veins
    • Veins bring blood back to the heart (usually deoxygenated)
    • Arteries pump blood away from the heart (usually oxygenated)
  52. Lung Blood Vessels
    1. Pulmonary Arteries: carry deoxygenated blood from the heart/pulmonary trunk; run with conducting airways (share adventitia); are a thin walled low pressure/resistance system that end as capillary networks (for gas exchange)

    2. Pulmonary Veins: carry oxygenated blood back to the heart; usually run by themselves in the substance of the lung, aren't connected to the conducting airway (separated by a sea of alveoli)

    Image Upload 20
  53. What do pulmonary arteries always follow?
    • the bronchiole tree
    • Image Upload 21
  54. Image Upload 22
    • pulmonary veins
    • carrying oxygenated blood in isolation (sea of alveoli) back to the heart
  55. What makes up the lungs' own blood supply?
    Bronchial Arteries & Veins

    • arteries are small, branch directly off the aorta & supply the bronchiole tree itself
    • Image Upload 23
    • have no function in gas exchange, just supply the lung organ
Card Set
Respiratory System
Histology Exam 4