Respiratory Histology

Describe the cells that lines the Respiratory System

Lined by respiratory epithelium – pseudostratified columnar ciliated epithelium

• Mucus producing cells (Goblet)

  • Mucus traps particles

• Ciliated cells

  • Moves thin layer of mucus

Describe how the cellular composition changes as you go from conducting to respiratory zone

1. Describe what happens to the Respiratory Epithelium as you go from the start towards the end of the conduction zone

2. Where are Nonkeratinized stratified squamous epithelium present?

Transition:

• as you go towards the respiratory zone:

  • Pseudostratified columnar ciliated with goblets → simple columnar → simple cuboidal epithelium

---

Nonkeratinized stratified squamous epithelium:

• In areas exposed to rapid airflow (ex: Vocal Folds)

• In areas prone to other abrasions (Ex: epiglottis)

Describe the characteristics of these cells associated w/ respiratory
epithelium:

• Ciliated columnar cell

• Goblet (mucous) cell

• Brush Cell

• Basal Cell

• Neuroendocrine Cell

Ciliated columnar cell:

• Each cell has hundreds of cilia on its apical surface that move mucus along the epithelial surface.

• Cillia is attached to microtubules

---

Goblet (mucous) cell:

• apical region of the cell is filled with polysaccharide-rich mucus droplets

---

Brush cell:

• apical surface is covered with microvilli.

• Acts as sensory receptors

---

Basal (stem) cell:

• rounded cells that sit on the basal lamina

• regenerative cells, capable of dividing and differentiating into other cell types of the epithelium

---

Neuroendocrine cell: 

• cells of diffuse endocrine system that are located on the basal lamina and have numerous granules

• may regulate the mucous and serous secretions of other cells

1. Define Squamous Metaplasia

2. How can this occur

3. consequences?

DEF: reversible process in which an epithelial tissue transforms to a different type of epithelial tissue

---

Cause:

• chronic presence or accumulation of toxins that occur with heavy cigarette smoking or industrial air pollution

---

Consequences:

• Immobilization of cilia → failure to clear mucus containing filtered material → exacerbates problem → squamous metaplasia of the epithelium

• change from pseudostratified ciliated columnar to stratified squamous epithelium →  precancerous cell dysplasia

Describe the Nasal Mucosa:

• Cells of Respiratory epithelium

• Basement Membrane

• What happens to the mucus

• Respiratory epithelium = pseudostratified, ciliated, columnar

  • Contains Goblet Cells

• Lamina propria rich in blood vessels, serous and mucus glands

• Mucus is propelled to pharynx by cilia where it is swallowed or expelled

Describe the Olfactory Epithelium:

• Location?

• What does it lacks?

• Describe Olfactory cells

  • Type of Cells

  • What kind of receptors?

  • Where does it send signals to?

Location:

• Superior nasal concha and superior portion of the nasal septum

---

Cellular Composition:

• Lacks goblet cells and motile cilia

---

Olfactory cells (OC):

• Specialized sensory bipolar neurons

  • Dendrites extends to epithelial surface ending in a knob with cilia

• Non-motile cilia contains olfactory receptors that bind odor molecules

• Axons project from the cell base to olfactory bulb forming Cranial Nerve 1

In the olfactory epithelium, Describe:

• Sustentacular cells

  • Characteristic/Function

• Basal cells

Sustentacular cells:

• has microvilli on apical surface and form junctional complexes w/ each other and w/ OC

• Function: Support & electrically insulate olfactory cells

---

Basal Cells:

• Replace and proliferate both olfactory cells and sustentacular cells

  • ***one of the few instances in adult where nerve cells can be replaced***

Describe Olfactory Glands

• AKA?

• Function?

Olfactory Glands (Bowman’s Glands):

• Produce a serous secretion that traps and dissolves odiferous substances → Constant Flow = remove
  old scents and permits detection of new scents

  • secretory portion found in basement membrane, deep to olfactory epithelium and their ducts open on the epithelial surface

Describe the Lymphoid tissue in the nasal pharynx

• Function?

• Bulge?

• Component of…?

• Function: acts as immune surveillance against inhaled antigens

• May bulge into lumen (that is called adenoid)

• Component of Waldeyer ring of lymphoid tissue protecting openings of respiratory and GI

1. Describe the two folds of the larynx; Seperated by?

2. What is the function of vocalis muscles

Folds:

• Upper false vocal cord

• Lower true vocal cord

• Separated by ventricle – narrow cleft

Vocalis muscle controls pitch of sound by moving true cord

Describe the epiglottis:

• Lining?

• Core?

• During respiration/swallowing

• Lining = Stratified squamous epithelium; changes to respiratory epithelium at base of laryngeal surface

• Elastic cartilage core

• Respiration: epiglottis is in a vertical position and uncovers the laryngeal opening

• Swallowing: epiglottis moves to a horizontal position covering the larynx

Describe the Trachea:

• Basal Cells Function?

• Components of Basement Membrane?

• Submucosa contains?

• What is more common in upper trachea

• Basal cells

  • Part of diffuse neuroendocrine system

  • Stem cells can divide and replace other cell types

• Lamina propria – loose, vascular supporting tissue
  

• Submucosa contains numerous serous and mucinous glands
  

• Goblet and basal cells more common in upper trachea

Describe Tracheal rings:

• Composed of?

• Cartilage prevents?

• Function of Trachealis Muscle?

Tracheal rings:

• Composed of fibroelastic tissue and C shaped rings of hyaline cartilage

• Cartilage prevents collapse during inspiration

• Trachealis muscle: joins rings posteriorly

  • Contraction during coughing

Describe the changes as we move towards:

• Main Bronchus 

• Segmental Bronchus

• Bronchiole

• Terminal Bronchiole

Changes in Main Bronchus:

• contains less goblet cells

• Submucosa contains fewer glands

• Upper lamina propria contains more elastin

  • SM seperates Lamina propia and submucosa

• Cartilage support by plates not rings

---

Segmental Bronchus:

• Sparse submucosal glands

• Occasional cartilage plates

• Completely encircled by smooth muscle

---

Bronchiole:

• No cartilage or submucosal glands

• Abundant smooth muscle

• Neuroendocrine cells secrete serotonin

  • Regulates muscle tone in bronchial and vessel wall

---

Terminal Bronchiole:

• Goblet cells replaced by Clara (club) cells-columnar cells

  • Produce components involved in maintaining alveolar patency

  • Act as stem cells

  • Synthesis of enzymes believed to degrade certain inhaled toxins

Differentiate between Pulmonary Lobule/acinus

Pulmonary lobule:

• Terminal bronchiole

• Respiratory bronchioles

• Alveolar ducts

• Alveolar sacs

• Alveoli

---

Pulmonary acinus:Functional unit of gas exchange

• Respiratory bronchiole

• Alveolar duct

• Alveolar sac

• Alveoli

Describe Respiratory bronchiole:

• Structure?

• Composition

Respiratory bronchiole:

• initial segment of the respiratory portion

• Structurally: similar to terminal bronciole

  • except for the presence of a few alveoli projections

• Composition:

  • cuboidal cells and Clara cells

Describe Alveolar ducts:

• Divides into?

• Composed of?

Alveolar ducts:

• Divides into alveolar ducts (AD) that ends in alveolar sacs (AS)

• Composition:

  • bundles of smooth muscle, collagen and elastin fibers form alveolar rings

  • Smooth Muscles function:

    • Regulates air movements

1. What is the alveolus

2. Lining?

3. Cell types?

Alveolus:

• Functional unit of the pulmonary acinus

• has a thin wall lined by simple squamous epithelial cells forming a part of air – blood barrier

• Cell Types:

  • Type 1 alveolar cells

  • Type 2 alveolar cells

Describe Alveolar Capillaries

• Describe its lining

• What does its endothelial cells contain?

Alveolar Capillaries:

• Lined by continuous endothelial cells juxtaposed to Type I alveolar cells through a dual basal lamina produced by these two cells

• Endothelial contains: ACE

  • Angiotensin II constricts blood vessels

Describe the Alveoli:

• What does it provide?

• Describe the characteristics of Type1 and Type2 cells

• What is Kohn?

Alveoli:

• Provide a large surface area for gas exchange

• Consists of pocket lined by pneumocytes

  • Type1: Flat

  • Type2: Rounded- typically at branch points

    • Secrete surfactant

    • has Lamellar bodies

      • membrane bound vesicles of concentric surfactant

    • Can divide and replace type 1 cells

• Kohn:

  • Alveolar pore between each alveoli → equalizes pressure between air sacs

1. What is the function of surfactant

2. What is it composed of

Function:

• Decreases surface tension of alveoli

• Allows normal inflation of alveoli at birth

• Allows reinflation of alveoli which collapse after airway obstruction

• Keeps alveoli open

---

Composition:

• phospholipids, particularly palmitoyl phosphatidylcholine

[REVIEW] NRDS

Describe Alveolar wall:

• Composed of?

• Elastin Forms?

Composed of:

• simple squamous epithelium, capillaries and fibroelastic
  supporting meshwork

---

Elastin forms supportive ring at opening of alveoli

What three membrane forms the Blood-Air barrier

• Alveolar epithelial cells

• Basement membrane formed by fusion of epithelial cell basal lamina + capillary endothelial cell basal lamina.

• Capillary endothelial cells

Describe Pulmonary macrophage:

• Location

• Function

Pulmonary macrophage

• Found in alveolar spaces and connective tissue of alveolar septum

• Remove foreign material (mostly carbon from exhaust and smokers and bacteria)

  • Carbon is expelled into mucus or remains in lung

    • Recognized as anthracotic pigment

[REVIEW] Pulmonary vs Bronchial vasculature

****Bronchial Arterial branches follow the bronchial tree until the level of the respiratory bronchioles, at which point the network of continuous capillaries is formed****

[REVIEW] Parietal vs Visceral Pleura

How can lymph vessels cause pleural effusion

• pulmonary lymphatics run in fibrous septa and empty into the pleural cavity

• If lungs = edematous (heart failure, cirrhosis) → lymphatics can move fluid into pleural space causing pleural effusion

  • it can also carry bacteria that cause this as well