Respiratory System Histology and Anatomy

Respiratory System Histology

• The respiratory system histology lecture, July 2024, was delivered by Prof. Dr. Samia Tayeb Hawisa.
• The lecture covered the histological characteristics of the conducting and respiratory portions of the respiratory system.
• Key objectives included explaining how different components contribute to the overall function of the respiratory system.

Respiratory System Anatomy

• The respiratory tract is anatomically divided into upper and lower tracts.
• The upper respiratory tract includes the nasal cavity, sinuses, pharynx, and larynx.
• The lower respiratory tract comprises the trachea, bronchi, bronchioles, alveolar ducts, and alveoli.

Upper Airway Structure and Function

• The upper airway's structures include nasal passages, pharynx, and larynx.
• Functions include air passage, filtering, heating, and humidification.
• Mucus production and cilia play roles in removing foreign particles.

Lower Airway Structure and Function

• The lower airway consists of trachea, bronchi, bronchioles, alveolar ducts, and alveoli .
• Conducting airways, include trachea, bronchi, and bronchioles, transport air to the respiratory zone.
• The microscopic airways in the respiratory zone carry out gas exchange to the blood.

Respiratory Epithelium

• Most of the respiratory tract is lined with pseudostratified columnar ciliated epithelium.
• The degree of branching influences the epithelium from pseudostratified to simple cuboidal.
• Non-ciliated cells (Clara cells) become more prevalent in bronchioles.
• Alveoli are lined with thin squamous epithelium aiding in gas exchange.

Cellular Transition

• Cells in the trachea and bronchi transition to simpler structures toward the alveoli.
• Cartilage, glands, and smooth muscle are less prominent closer to alveoli.

Cellular Components

• Ciliated columnar cells are abundant in the early portions, important for mucus movement.
• Brush cells, goblet cells, and basal cells are also present.
• Small granule cells and Clara cells contribute to the respiratory epithelium.

Olfactory Epithelium

• In the nasal cavity, specialized olfactory epithelium lines the superior nasal conchae.
• It contains olfactory neurons receiving odor information.
• Supporting cells and basal cells support olfactory neurons.

Sinuses and Nasopharynx

• These are air-filled cavities connected to nasal cavity.
• Lined with respiratory epithelium, containing mucus-producing glands, cilia.
• The sinuses and nasopharynx help regulate air flow and humidity.

Larynx

• The larynx is located in the throat and supports air passage.
• Cartilage and muscles form its structure, including the thyroid, cricoid, and epiglottis.
• The larynx plays a role in voice production and preventing swallowed materials from entering the respiratory tract.
• The epiglottis protects the airway during swallowing.

Trachea

• The trachea is a cartilaginous tube connecting the larynx to the bronchi.
• C Shaped cartilage rings strengthen and maintain the trachea's structure.
• Smooth muscle in the trachea's posterior wall adjusts its diameter during breathing and swallowing.
• The trachea has mucus-secreting glands, and cilia facilitate mucus movement.

Bronchial Tree and Lungs

• The trachea branches into primary bronchi, then to secondary (lobar) bronchi and tertiary (segmental) bronchi.
• Bronchioles progressively decrease in diameter and cartilage.
• They are lined with epithelium and smooth muscle.

Terminal Bronchioles

• The airway's final segment before the respiratory portion.
• They have a thinner wall and smaller diameter.
• Epithelium changes to ciliated cuboidal cells with Clara cells.

Alveolar Wall

• Alveolar walls are thin to facilitate gas exchange.
• Composed of type I pneumocytes and type II pneumocytes important for surfactant production.

Effects of Cigarette Smoking

• Smoking damages epithelial cells and induces inflammation.
• Leads to metaplasia (the replacement of one cell type by another) and increased risk for cancer.

Pulmonary Changes

• Pneumonia involves fluid/pus filling of air sacs.
• Emphysema damages alveolar walls, increasing air volume.

Lung Surfactants

• Lung surfactant is produced by type II pneumocytes..
• Crucial for preventing lung collapse by reducing surface tension in the alveoli..
• Deficiency of surfactant in premature newborns causes respiratory distress syndrome.

ARDS in COVID-19

• COVID-19 can cause ARDS, leading to severe pulmonary inflammation and impairment of alveolar function.
• Surfactant treatment shows potential for improving clinical outcomes in ARDS patients.

Natural Defenses

• Particles are trapped by nasal hairs and mucus for removal from the airways.
• Coughing and sneezing expel foreign materials.

Bronchial Asthma

• Bronchial asthma is a complex response to allergens and irritants including increased mucus in bronchial lining.
• Lung's sensitivity to stimuli may lead to bronchial constriction decreasing air flow.
• Children have higher sensitivity compared to adults.

This quiz explores the histological characteristics and anatomical structures of the respiratory system. Covering both the upper and lower tracts, it addresses their functions, including air filtration and gas exchange. Understand the essential roles of different components in maintaining respiratory health.