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Questions and Answers

What is the primary function of the conducting portion of the respiratory system?

Oxygen storage

Conduction of air (correct)

Regulation of blood flow

Gas exchange

Which type of epithelium predominantly lines the conducting portion of the respiratory tract?

Stratified squamous epithelium

Simple cuboidal epithelium

Simple squamous epithelium

Pseudostratified columnar ciliated epithelium (correct)

What structure primarily facilitates the opening of the trachea?

Seromucous glands

Smooth muscle fibers

C-shaped hyaline cartilage rings (correct)

Elastic connective tissue

Which of the following cell types is NOT found in the epithelium of the conducting portion?

Type I alveolar cells Signup and view all the answers

Which part of the bronchial tree is considered the conducting portion?

Terminal bronchioles Signup and view all the answers

What characterizes the layers of the tracheal wall?

Mucosa, submucosa, and adventitia Signup and view all the answers

What is the main function of the alveoli in the respiratory system?

Gas exchange Signup and view all the answers

Which structure connects the larynx to the primary bronchi?

Trachea Signup and view all the answers

Which component is found in the submucosa of the trachea?

Seromucous glands Signup and view all the answers

What type of connective tissue forms the adventitia of the trachea?

Fibroelastic connective tissue Signup and view all the answers

What is the primary function of Clara cells in the bronchiolar wall?

To protect against harmful inhaled substances Signup and view all the answers

Which type of pneumocyte is primarily involved in gas exchange?

Type I pneumocytes Signup and view all the answers

What characterizes the bronchiolar wall from its musculoskeletal composition?

Layer of smooth muscle arranged circularly Signup and view all the answers

What structure separates adjacent alveoli in the respiratory portion of the bronchial tree?

Inter-alveolar septa Signup and view all the answers

Which statement about type II pneumocytes is accurate?

They secrete pulmonary surfactant. Signup and view all the answers

What is a key structural feature of the blood-air barrier?

Includes reticular fibers for support Signup and view all the answers

Which cells are responsible for forming a film over the alveolar epithelium?

Type II pneumocytes Signup and view all the answers

What type of epithelium lines the mucosa of the bronchioles?

Simple columnar ciliated epithelium Signup and view all the answers

Which layer is absent in the bronchioles compared to larger bronchi?

Adventitia with hyaline cartilage Signup and view all the answers

What contributes to the structure of inter-alveolar septa?

Blood capillaries and reticular fibers Signup and view all the answers

Study Notes

Respiratory System Histology

The respiratory system is divided into two functional portions: a conducting portion and a respiratory portion.
The conducting portion connects the external environment with the respiratory portion and performs functions like air conduction, conditioning (cleaning, moistening, and warming inspired air), and warming.
The respiratory portion, including respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli, facilitates gas exchange.
The conducting portion includes the nasopharynx, larynx, trachea, bronchi, and terminal bronchioles.
The walls of the respiratory portion enable gas exchange.

Respiratory Epithelium

Most of the conducting portion of the respiratory tract has pseudostratified columnar ciliated epithelium with goblet cells.
Five cell types are recognized in this epithelium:
- Ciliated columnar cells (most abundant)
- Mucous goblet cells (next most abundant)
- Brush cells (sensory receptors)

Trachea

A flexible tube, approximately 10 cm long, extending from the larynx and bifurcating into the primary bronchi.
It's maintained open by 16-20 C-shaped hyaline cartilage rings.
Its wall has three layers:
- Mucosa: Contains respiratory epithelium and lamina propria (loose connective tissue with elastic fibers).
- Submucosa: Contains seromucous glands and lymphoid nodules.
- Adventitia: Contains fibroelastic connective tissue and 20 C-shaped hyaline cartilages.

Bronchial Tree

The conducting portion of the bronchial tree includes extrapulmonary (primary) bronchi, intrapulmonary (secondary) bronchi, bronchioles, and terminal bronchioles.
The respiratory portion of the bronchial tree includes respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli.
Extra-pulmonary bronchi have the same structure as the trachea.
Intrapulmonary bronchi have;
- A pseudostratified columnar ciliated epithelium with goblet cells
- Connective tissue with elastic fibers
- No submucosa
The walls of the bronchioles have spiral smooth muscle, and the outer layer is composed of connective tissue.
- No cartilage, glands, or lymphatic nodules are present in bronchioles.

Clara Cells

Tall, dome-shaped, non-ciliated cells found in the bronchiolar wall.
Functions include protecting against inhaled harmful substances and acting as stem cells for other types of bronchiolar epithelium.

Alveoli

The structural and functional units of gas exchange in the lungs.
Separated by inter-alveolar septa.
Lined with alveolar epithelium, consisting of type I and type II pneumocytes.
- Type I pneumocytes are the most numerous, consisting of flat, simple squamous cells with connections via tight junctions. They form a very thin membrane for gas exchange.
- Type II pneumocytes are fewer in number, cuboidal cells with round nuclei. They secrete pulmonary surfactant, reducing surface tension and preventing alveolar collapse during expiration.
The inter-alveolar septa have abundant blood capillaries and a network of reticular fibers.

Blood-Air Barrier

The blood-air barrier is a layer of cells allowing gas exchange.
Consist of four layers:
- Pulmonary surfactant lining
- Cytoplasm of type I pneumocytes
- Fused basal lamina of type I alveolar cells and capillary endothelial cells
- Endothelial cells of blood capillaries.