pulmonary week 2 histo learning objectives

8/6/2019 Pulmonary Week 2 Histo Learning Objectives

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Pulmonary Week 2: Airways Disease

Pulmonary Week 3: Gas ExchangeLearning Objectives (Histology)

1. Describe both the conducting and respiratory components of the respiratorytree including their histological appearance and explain the functionalsignificance of each of these components.

CONDUCTING:

Delivers warm moist air from outside to lungsIncludes:

y Nasal cavities and sinuses

y Pharynx

y Larynx

y Trachea

y Bronchi

y Bronchioles

RESPIRATORY

Provides most efficient mechanism for O2 and CO2 exchange between pulmonary alveoli

and blood in lung capillaries

Includes:

y Respiratory bronchioles

y Pulmonary alveoli (alveolar ducts, sacs and alveoli proper)


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2. Describe the embryological development of both components of therespiratory tree

Foregut endoderm all epithelium

Splanchnic mesoderm surrounding stroma, smooth muscle and cartilage

3. Describe the composition and histological appearance of the respiratorymucosa and explain how it provides the muco-ciliary clearance mechanism.

The upper respiratory tract is lined by a

typical respiratory mucosa, consisting of:

y Respiratory epithelium(pseudostratified epithelium):- Columnar ciliated cells (cilia on apical

surfaces sweep mucus and debris

towards oral cavity= muco-ciliary

clearance mechanism)

- Mucus secreting goblet cells

- Small rounded basal cells serve as stem

cells that continually replace epithelium

y Basement membrane

y Underlying lamina propria: looseconnective tissue, highly cellular and

richly vascular

Cilia have 9+2 microtubule pattern that

moves mucus and trapped matter to

naso-pharynx for elimination.

3 concentric layers of upper resp. tract:

- Mucosa- Submucosa (mostly loose CT)- Adventitia (outer protectice CT)

4. In microscopic sections, differentiate between the trachea, bronchi,bronchioles and pulmonary alveoli.

a. Trachea: 15-20 cm long semi-rigid tube- 1. Mucosa: respiratory epithelium and

goblet cells and underlying lamina propria

- 2. Submucosa: seromucous glands deliver

secretions to mucosal surface.Seromucus glands: large pale-staining mucous

secreting and smaller dark-staining serous

secreting cells augment mucus produced by

goblet cells

- 3. Adventitia: 12-20 hyaline cartilagehorseshoe rings keep airway open; smooth

muscle (trachealis) bridges gap and controls

lumen size


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b. BronchiRespiratory epithelium reduced in height, gradual reduction of # of goblet cells

Elastic fibers and lymphoid nodules in lamina propria

Sero-mucus glands connect to surface

Smooth muscle complete encircles lumen

Irregular hyaline cartilage plates

c. BronchiolesConducting passages < 1 mm


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No cartilage or submucosal glands

Simple columnar cuboidal ciliated epitheliumGoblet cells replaced by Clara cells (secretory & non-ciliated)

- Ciliated cells: columnar to cuboidal, sweep debris upward- Clara cells: dome shaped, degrade toxins, reduce surface tension, mitotic stem cells

Lamina propria rich in elastic fibers

Smooth muscle- arranged helically and completely encircles lumenRespiratory bronchioles: smaller bronchioles with alveolar outpocketings

d. Pulmonary alveoliSmall (200 um) air sacs (300 x 10^6 in each lung)

Lined by simple epithelium: pneumocytes

Th

in wallsSeveral alveoli are in contact and form an interalveolar septum


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5. Describe the muco-ciliary clearance mechanism and factors that affect it indisease states

= Movement of mucus and trapped matter to naso-pharynx for elimination by the ciliated

cells in respiratory mucosa in upper respiratory tract.

From Wikipedia:

The main bronchi down to the alveoli are lined with a respiratory epithelium. On that,cilium is present, bearing hair-shaped structures on its surface (cilia). The cilia aresurrounded by a thin fluid film of mucus. On top of that is a second viscous film ofmucus, in which foreign particles and microorganisms get stuck. Within the thin fluid filmof mucus the cilia act out movements coordinated in direction towards the pharynx.Thereby the viscous film of mucus including its freight is transported off in directiontowards the mouth, where it is either swallowed or expelled via coughing.

Important for good mucociliary clearance are the number of cilia, their structure, activity,and coordinated movement. Optimum functionality of mucociliary clearance presuppose

a temperature of 37 C and an absolute humidity of 44 mg/dm corresponding to arelative humidity of 100 %. Under the condition of insufficient temperature and humidity,after a short time the ciliary cells suspend their transport function. Under suchcircumstances, bacterial germinal colonization is facilitated. Pulmonary infections anddamaging of the pulmonic tissues may be the consequence.

6. Describe the structure and ultra structure of the two types of pneumocytesand the alveolar macrophage cells and their roles in health and disease states.

y Type I Pneumocytes: thin and flattened (80 nm wide)o Line 95% of alveolar surfaceo Linked by tight junctions

y Type II Pneumocytes: more numerous but line only 5% of alveolar surfaceo Secrete surfactant- reduces surface tension and prevents alveolar collapse


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7. Describe the key features of the blood-air barrier and indicate the functionalsignificance of surfactant.

Minimal thickness (0.5 um) provides rapid gaseous exchange

i. Type 1 Pneumocytes and tight junctions (covered by thin layer of surfactant)ii. Capillary endothelium and tight junctions (prevent indiscriminate fluid

leakage)iii. Dual basal laminae (often fused)

14.Compare and contrast the histological sections of the auditory tube, olfactorymucosa, epiglottis and larynx.

Auditory tube:

- Lined by respiratory mucosa (see above) which is composed to respiratoryepithelium, basement membrane and lamina propria

Olfactory mucosa:

- Pseudo stratified epithelium highly specialized for sensory reception of odoriferoussubstances

- 3 types of cells:


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o Olfactory receptor cells: bipolar neuronsw/ apical process w/ non-motile cilia receptive toodoriferous stimuli

o Supportive cells: mechanically supportreceptor cells

o Basal cells: progenitor cells with 30 day

turnover- Lamina propria (underneath):o nerve fascicles of unmyelinated axons that

have emanated from receptor cells

o serious glands ofBowman that produce awatery secretion that dissolves odoriferous

substances on the epithelial surface

o thin-walled veins that become engorged inresponse to infection or the common cold, causing

swelling of mucosa


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Epiglottis:

- Flap-like structure that guards upper opening of larynx- Supported by a central core of elastic cartilage- Covered externally by mucous membrane- Upper lingual surface faces tongue, lower laryngeal faces larynx, and tip- Stratified squamous non-keratinizing epithelium on lingual surface and tip

- Stratified columnar on laryngeal surface- Eventually becomes pseudostratified epithelium- Seromucous glands underly epithelium and deliver secretions to surface

lingual surface

Central core of elastic cartilage

laryngeal surface

Larynx:


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- Upper false vocal cord lined by stratified squamous non-keratinizing epithelium;beneath lie many seromucous glands

- Laryngeal ventricle- True vocal cord lined by stratified squamous non-keratinizing epithelium, protects

against abrasion caused by rapidly moving air stream

o Has elastic connective tissue in its core and skeletal muscle (vocalis) which

regulates tension for phonationo Changes to pseudostratified epitheliumo Mixed seromucus glands underlie lamina propria

Upper vocal cord:

True vocal cord:


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15.Describe the histological features of the trachea with special reference tomucosa, submucosa and adventitia.

Three concentric layers:

- Mucosa- Submucosa- Adventitia (see above)

*Squamous metaplasia occurs in chronic bronchitis and is a common feature of cigarette

smoking

16.Discuss the hilus of the lung with special reference to the histologicalappearance of the main bronchi

Major blood vessels, bronchi, nerves and lymphatics enter or emerge from lung:

- Main bronchus:o Similar to trachea but cartilage is arranged into small plates and circular

arrangement of smooth muscle completely envelops lumen


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17.Describe the essential histological features of the lung with special referenceto intrapulmonary bronchi and bronchioles

Intrapulmonary bronchus:

- Lined by respiratory epithelium

- Underlying lamina propria is highly cellular with occasional solitary lymphoidnodules

- Prominent circular layer ofhyaline cartilage- Surrounded by pulmonary alveoli

Bronchioles:

- Small airways < 1 mm in diameter- Lack cartilage, tinner- Simple columnar to simple cuboidal epithelium- Devoid of goblet cells- Bronchiolar smooth muscle is partially contracted = star-shaped, crinkled

appearance of mucosa

- Smaller bronchioles with alveolar outpocketings = respiratory bronchioles


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bronchus

respiratory bronchiole

18.Contrast the main cell types in the respiratory epithelium of the bronchuswith those of the bronchiole.

Respiratory Epithelium:- Pseudostratified columnar epithelium with goblet cells- Goblet cells decrease in number in the more distal airways (less in bronchus)- Ciliated columnar cells are interspersed with mucus secreting goblet cells- Small basal cells rest on a basement membrane- Mixed seromucous gland in underlying lamina propria

Bronchiole:

- Clara cells (non-ciliated, 75-80% of these airways) interspersed amongst ciliatedepithelial cells

- Clara cells:o Detoxify many inhaled noxious substances via SERo Secrete surfactant like protective material that coats bronchilar epithelial

surface

o Secrete growth factors, antimicrobial peptides and proteolytic enzymeso Serve as progenitor cells for normal renewal of nonciliated and ciliated

bronchiolar epithelial cells


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WEEK 3 LOWER RESPIRATORY TRACT

1. Describe the anatomic organization of respiratory bronchioles, pulmonaryalveoli and the inter-alveolar wall septum.

y Respiratory bronchioles: transitional zone of the respiratory system concerned withboth conduction of air and gaseous exchange; very thin walls, lack cartilage, gobletcells and glands. Simple lining epithelium, with Clara cells and ciliated cells, and

small amount of smooth muscle; alveolar outpocketings in wall.

y Pulmonary alveoli: air sacs with extremely thin walls; lined by type 1 and type 2pneumocytes

y Interalveolar septum: shared wall of alveoli; contains many red blood cells in anextensive network of pulmonary capillaries

2. Relate the ultrastructure of the alveolar-capillary barrier to its function ingaseous exchange.

Blood-air barrier is formed by type 1 pneumocytes, capillary endothelium and fused

basement membrane (see #7 from week 2)

3. Relate the ultrastructure of the type 2 pneumocyte to the synthesis andfunction of surfactant.

See #6 from week 2


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4. Describe how alveolar macrophages (dust cells) keep the lungs free ofparticulate matter.

Dust cells = alveolar macrophages. Found within walls of alveoli or free in alveolar air

spaces. Derived from blood monocytes. Function by phagocytosing inhaled particulate or

foreign matter.

5. Outline the importance of elastin in the walls of air spaces.There is a huge amount of elastic tissue in the walls of bronchioles, arteries, and pulmonary

alveoli in the lung. When the lungs are expanded during inspiration, they provide sufficient

elasticity to return to their original volume during expiration. 3

pulmonary week 2 histo learning objectives

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