Respiratory System

Question 1

Comparative Anatomy of Respiratory System

Answer 1

• Elephant is the only mammal without a pleural space
• Birds have air sacs, lack a diaphragm and a pleura cavity
• In amphibians, both the lungs and skin are respiratory organs
  
  • Skin is rich in microcirculations, mechanism of respiration is the same as the lung
• Fish breathe through gills. Lungfish have lungs

Question 2

Respiratory Learning Objectives

Answer 2

• Be able to relate the gross and microscopic anatomy of the respiratory system
• Describe the organization of the olfactory and respiratory epithelium of the nasal cavity
• Descibe the progressive devisions of the airways from the trachea to the level of the alveolus. Describe the organization of each division, including layers, cells and glands present.
• Recognize/ientify examples fo each portion of the respiratory system
• Describe the structure and significance of the blood-air barrier
• Discuss the similarities and differences between the mammalian and avian respiratory systems

Question 3

Progression of Airways

Answer 3

1. Primary Bronchus - cartilage
2. Secondary Bronchus - cartilage
3. Tertiary Bronchus - cartilage
4. Priamary Bronchioles - no cartilage
5. Secondary Bronchioles - no cartilage
6. Tertiary (terminal) Bronchioles - no cartilage
7. Respiratory Bronchioles - alveoli
8. Alveolar sacs - alveoli
9. Alveoli - 02/CO2 exchange

Question 4

Layers in the Upper Airway

Answer 4

• Mucosa: the lining layer of the wall of a mucosal organ; consists of epithelium, lamina propria, and muscularis mucosa (not always present )
  
  • Lamina propria (LP): the connective tissue component of the lining of amucosal organ
  • Muscularis mucosa: a thin layer of smooth muscle; not present in all mucosa
• Submucosa (SM): connective tissue layer deep to the mucosa
• Adventitia: outermost layer of an organ vessel, or other structure; composed of connective tissue
• Serosa: membrane lining body cavities and various organs. Secretes serous fluids
  
  • ​Ex: the Vesceral pleura is the serosal layer of the lung

Question 5

Layers of Upper Airway

Answer 5

Question 6

Nasal Cavity

Answer 6

• Has Respiratory and Olfactory regions
• Nasal Vestibule: transition from the skin of the nose to the mucosa of the nasal cavity. The transition is called mucocutaneous junction.

Question 7

Respiratory Region of the Nasal Cavity Mucosa

Answer 7

• Respiratory epithelium
  
  • pseudostratified columnar cilitated with goblet cells
    
    • found in the nasal cavity and paranasal sinuses; extends down into the airway divisions
  • Lamina propria is higly vscular
    
    • functions in heat exchange
  • Serous and mucus glands are located in the submucosa

Question 8

Mucosa of the Olfactory Region of the Nasal Cavity

Answer 8

• Found in patches inthe nasal cavity
• Epithelium is a much thicker pseudostratified columnar, with Bowman’s glands
  
  • No gobetcells
  • Sustentacular cells - most superficial
  • nuclei with cilia
  • Basal cells - at base; germinal cell layer
  • Olfactory cells - intraepithelial bipolar neurons whose axons become cranial nerve 1
• Bowman’s glands - Serous Olfactory Glands
  
  • Serous glands in the lamina propria
  • Secretions dissolve inhaled substances for detection by olfactory cells
• Picture:
• Olfactory Cells - various odor receptors (blue)
• Sustentacular cells - (pink)

Question 9

Olfactory Epithelium

Answer 9

• Sustentacular Cells - most superficial nuclei with cilia
• Olfactory Cells - pale round nuclei
• Basal Cells - at base; germinal cells
• Thickre, nuclei throughout epithelium
• Very uniqe to have neurons in an epithelium exposed to the environment

Question 10

Nasal Cavity - Vomeronasal Organ

Answer 10

• Tubular gland in nasal cavity - located on either side of nasal septum
• Has both olfactory and respiratory epithelium
• Functions in olfction related to pheramones
  
  • (Ex: Flehmen reaction in cats and horses)
• Picture:
  
  • Thick layer (olfactory epithelium)
  • Thin layer (respiratory epithelium)

Question 11

Olfactory Bulb

Answer 11

• Dorsal and Ventral neurons
• Olfactry neurons in the Dorsal domain transmit innate fear responses to the brain, wherea the neurons in the ventral domain convey learned aversion
  
  • No fear to predators scents was recognized when a specific area of olfactory epithelium is ablated by targeted expression of diphtheria toxin gene; the dorsal domain of the olfactory bulb was depleted
    
    • Technique to make target gene inoperative is targeted gene knockout (disruption).

Question 12

Nasopharynx

Answer 12

Part of the pharynx located dorsal to the soft palate

• Large mass of lymphoid tissue asociated for defense mechanism

Question 13

Larynx

Answer 13

Complex cartilagenous structure lined by respiratory epithelium and in some places by stratified squamous epithelium

• Contains Vocal fold

Question 14

Lung Overview

Answer 14

• Stroma: Mainly elastic fibers; some collagen
• Parenchyma:
  
  • Divided into lobes and lobules. The lobular pattern is readily apparent in species with well-developed interlobular septae (ruminants and pigs)
  • The alveoli are the major parenchyma and are contained in respiratory bronchioles, alveolar ducts and alveolar sacs
• Visceral Pleura:
  
  • ​Tunica Serosa of the lung; covers the external surface of the lung
  • Consists of epithelium (mesothelium) plus some connectve tissue (collagens)

Question 15

Layers of the Tubular Airways

Answer 15

• Trachea and Bronchi have a Mucosa, submucosa, cartilage, and an adventitia
• Muslce in the trachea is not continuous around the airway, and is called the Trachealis muscle
• A muscularis mucosa is NOT present in the trachea. It appears in the bronchi and persists to the alveolar duct
• Bronchioles essentially only have a mucosa with a thickened muscularis mucosae (submucosa becomes extremely thin)

Question 16

Trachea

Answer 16

• Bifurcates into primary cronchi to supply each lung
• Contains c-shaped pieves of hyaline cartilage
  
  • _​_opens dorsally
  • ends of the rings connected by the tracheali muscle (smooth)
• Mucosa: the lining layer
  
  • consists of respiratory epithelium, plus the underlying connective tissue (lamina propria)
    
    • Lamina Propria: contain numerous elastic fibers arranged paralll to the ong axis of the tracheas
      
      • Stain acidophilically and are seen in cross section
      • helpful in recognizing the lamina propria

Question 17

Tracheal Epithelium

Answer 17

• Several cell types are distiguishable in the repiratory epithelium
  
  • Ciliated columnr cell
  • Basal (germinal) cell
  • Goblet cell
  • Diffuse neuroendocrine system (DNS)
    
    • ​Cells that seccrete polypeptides (calcitonin, bombesin, CCK, etc.) and biologcally active amines (serotonin) into localblood vessels s local hormones.
    • Regulates tracheal air flow (relevant to asthma)
    • In fetus, associated with lung development

Question 18

Submucosal Glands

Answer 18

Located in the submucosa of the trachea are seromucous glands (mixed secretion of mucin, defense peptides, etc)

Question 19

Bronchi

Answer 19

• Respiratory epithelium continues into the bronchi, but its cells are shorter than in the trachea and there are fewer goblet cells
• Muscularis mucosae appears between the lamina propria and the submucosa
• The seromucous glands in the submucosa become more scattered
• Cartilage rings are replaced by plates or plaques

Question 20

Changes in the Bronchi

Answer 20

• Progressve changes with successive divisions of the Bronchi:
  
  • Overall airway diameter decreases
  • Mucosa and submucosa become thinner
    
    • epithelium is shorter with less pseudostratifications
    • fewer goblet cells
  • Cartilage plates become smaller
  • Muscle layer becomes progressively a more prominent component of the airway

Question 21

Bronchioles

Answer 21

• Smaller than Bronchi
  
  • Less than 1 mm diameter
  • No cartilage
  • Simple epithelium (height of the cells varies; columnar in the largest bronchioles, cuboidal in tertiary)
  • No goblet cells,
  • Relatively larger smooth muscle in submucosa
• Changes occurring with each division of bronchioles:
  
  • Diameter decreases
  • Walls of aiway become thinner
  • progessively lose glands and cilia
• Cell Types:
  
  • Ciliated epithelial cells
  • non-ciliated Club Cells (bronchiolar cells)
  • neuroendocrine cells
• Primary and Secondary Bronchioles:
  
  • Ciliated simple columnar epithelium
  • Mucosa highly folded
• Tertiary (terminal)
  
  • Partially ciliated simple columnar or cuboidal epithelium
  • Thinner lamina propria
  • One layer of spiral smooth muscle

Question 22

Club Cells

Answer 22

• “Clara cells”
• Tall, non-ciliated cells with apical granules
• Produce componens of surfactant
• Contain P450 enzymes to detoxify some substances
• Act as reserve cells (stem cells) for differentiation to other types
• Neoplastic differentiation leads to lung cancer

Question 23

Cancers in Veterinary Medicine

Answer 23

Canines:

• 1/4 develop some type
  
  • 1/2 that possess cancer are older than 10
• Most common: lymphoma, breast cancer, soft tissue sarcoma

Felines:

• Not as prevalent, but higher incidence in older cats
• Most common: lyphoma, breast cancer

*humans have 25% of cancers are lung/bronchus

Question 24

Respiratory Bronchiole

Answer 24

• Level at which Gaseous exchange begins
• These resemble tertiary bronchioles in structure, except for the alveoli opening to the lumen of these bronchioles
• Wall of the bronchiole appears incomplete because of the alveoli that interrupt it; it appears “broken”
  
  • otherwise has the same cells/layers as a tertiary bronchiole
  • appearance quite different in cross section compared to longitudinal section

Question 25

Alveolar Duct

Answer 25

* A duct composed of numerous adjacent alveoli * Alveoli have simple squamous epithelium * _Smooth muscle bundles (knobs)_ found at tips of interalveolar septae (entrances of alveoli) * Leads to a blind-end alveolar sac

Question 26

Alveoli

Answer 26

* Site of **gaseous exchange** * Alveolar wall is very thin * walls of alveolar epithelium, pluss endothelial cells, form the "alveolar wall" * Filled with capillaries * Epithelial cells: * **Type 1 pneumocyte (P1):** Looks like an endothelial cell * lines the alveolus * **Type 2 pneumocyte (septal cell, P2):** Produces _surfactant_, is cuboidal, and appears vacuolated or granular due to the _lamellar bodies_ in its cytoplasm. * Also a stem cell for the alveolar lining * **​Lamellar bodies:** surfactant (phospholipids) containing vesicles

Question 27

Alveolar Septum

Answer 27

* Lining between 2 adjacent alveoli * Contains capillaries and small amount of loose connective tissue (**Interstitium)** * **​Elastic fibers** are important * Septal wall may contain: * Type 1 and 2 pneumocytes * macrophages * endothelial cells * pericytes * fibroblast * cells normally found in loose connective tissue (transient cells) and capillaries

Question 28

Alveolar Macrophages

Answer 28

* 2 types in the alveoli: * **Septal** - the tissue macrophage of the septum; located in the interstitium * **Free macrophage -** in the alveolar lumen, or on thesurfce. called "pulmonary alveolar macrophage" (PAM) * Large amount of elastic fiber present

Question 29

Blood-Air Barrier

Answer 29

* Variable thickness, but has 3 main components at minimum: * **Endothelial cell-** lining a capillary * **Basement membrane** - May be fused * from 2 epithelial layers (from capillary and alveolus) * **Alveolar Type 1 pneumocyte** - Lining the alveolus * In some areas the barrier is thicker, with the basal laminae of the 2 epithelial layers separated by some connective tissue

Question 30

Blood Supply to the Lung

Answer 30

* **Systemic Vessels:** * ​Nutritional supply is the **bronchoesophageal artery,** from the aorta * **Pulmonary Vessels:** * ​Functional supply is the **Pulmonary artery** * Pulmnary vessels are a low pressure system. They generally follow the airways, and divide into a capillary bed located surrounding the alveoli * find many of the same cells with these capillaries that you find with other capillaries

Question 31

Avian Respiratory System

Answer 31

* Lung smallar than mammals * Do not change size with inspiration/expiration * lack a diaphragm * Air passageway system: * Bronchi (primary and secondary) * Parabronchi (tertiary bronchi) * Atria = similar to terminal bronchiole * Air capillaries = similar to alveolar sac * Air sacs move the air in an out of the lungs * _Unidirectional air flow_ (explanation is in the figures next page) * Are extremely thin-walled (act like billows) * Most air sacs (approx 8) connected to bronchi and parabronchi * More efficient gas exchage due to _thin walls, smaller alveoli and rich capillary system_

Question 32

Key Points

Answer 32

* Airways branc repeatedly, becoming smaller and simpler with each division. Divisions of the airways that have alveoli (respiratory bronchioles, alveolar ducts, alveolar sacs and alveoli) are referred to as the respiratory portion * Transitional changes in the airways (gradual and sometimes overlapping): * change from the relatively rigid tubular structure ofthe trachea, to that of the bronchioles whose diameter is regulated via its higher proportion of smoot muscle * Glands and goblet cells diminish. Clia persist deeper in the airway thamucus-producing elements * Transitions from _respiratory epithelium_ (for defense) _to simple squamous_ (for gaseous exchange) across the blood-air barrier between alveoli and the capillary beds that surround them * Muscosal system is one that has an inner wet lining (mucosa) and communcates with the external environment. * defensive cells are usually found in its connective tissue layer due to its vulnerability * Has an epithelium and loose connective tissue layer **(Lamina propria)** gets progressively thinner and is filled with defensive cells * Beginning at the Bronchi, a muscular laryer is present in the mucosa * Submucosa is connective tissue underthe lamina propria. Contains fewer cells and thicker fibers, may contain glands * Adventitia is a connective tissue around a tubular organ that is NOT in a body cavity * Serosa is the outer layer if it is in a body cavity * Serosa of the lungs and of the pleural cavity is called **"Pleura"** * Respiratory epithelium is named for the specific epithlium of the respiratory tract * Pseudostratified columnar ciliated with goblet cells. * has basal cells and diffuse neuroendocrine system cells that secrete hormones for local effect * begins at the nasal cavity and extends into the airways * replaced by simple epithelium in the bronchioles * Olfactory epithelium contains bipolar neruon for cranial nerve 1 * basal cells that aregerminal for the other cell types * sustentacular cells that are support cells * pesudostratified with a thicker layer of nuclei than respiratory epithelium

Question 33

Key Points 2

Answer 33

* Trachea has cartilage rings and smooth muscle (**Trachealis muscle)** give it rigidity. * Muscle does not encircle the trachea - dorsal side only * Superficial to the cartilage ring - trachealis muscle layer is the submucosa, containing seromucous glands * Superfcial to this layer is the mucosa with typicl respiratory epithelium and a lamina propria (elastic fibers) * Bronchi have respiratory epithelium that is getting shorter, a smooth muscle layer (**lamina muscularis mucosae)** completely encircles the broncus and cartilage plaques. Lamina propia is thinner nd submucosa is very thin, with some glands * Bronchioles have simple solumnar or cuboidal epithelium. * **Club cells** are multi-functional cells that assist in defense, serve as **stem cells,** and produce some components of **surfactant** * **Terminal bronchioles** are the smallest-diameter airways that do not have alveoli. * have cuboidal epitelium and smooth muscle * **Respiratoy bronchioles** have the structure of terminal brnchioles, but have alveoli opening into them * **Alveolar ducts** have alveoli lining thei walls and "knobs" of smooth muscle at the luminal ends of the alveolar septae. * **Alveolar sacs** are clusters of blind-ended alveoli * Alveoli have cuboidal surfactant-producing cells (Type 2 pneumocytes) and squamous lining cells (Type 1 pneumocytes). * Type 2 are also stem cells for bth epithelial cell types * **Interalveolar septae** contain elastic connective tissue stroma and a capillary bed * **Macrophages** are a feature of the alveoli an their interalveolar septae