Which Of The Following Is/Are Part(S) Of The Respiratory Zone Structures?

The respiratory zone corresponds to the lung parenchyma and includes the respiratory bronchioles, alveolar ducts, and alveoli. It is also called the terminal airspaces of the lungs because they are at the end of the bronchial tree. The lower respiratory system is a hierarchical system that can be divided into two functional and structural components: the conducting tract (airways) and the respiratory zone.
The conducting airway consists of three parts:
Bronchi
Bronchioles
Alveolar ducts
In contrast, the respiratory zone structures include the following components:
Respiratory Bronchioles
Alveolar Ducts
Alveoles
These zones have different functions but work together to provide adequate ventilation for gas exchange in the lungs. In other words, each zone has its own job to do, but all of them must function properly if you want your body to breathe normally.
So now we know what the respiratory zone is, how does it help us breathe better? How would you describe the structure of this part of our bodies? What makes these parts so important in breathing? And why do people get shortness of breath when their respiratory zone is compromised?
Let’s take a look at some of the things that make up the respiratory zone:
1. Alveolar Ducts – These are the smallest air sacs within the lungs that connect one set of alveoli with another set through which oxygenated blood flows. They serve as a pathway between the pulmonary capillaries and alveoli, allowing waste products to exit from the lungs. Their walls consist of type I cells, which are responsible for producing surfactants for foaming action on the surface of the alveolus. Surfactant prevents protein-coating of the alveolar wall and helps keep the lining fluid moist. Without surfactant, the alveolus becomes dry and collapses. This causes a condition known as Adult Respiratory Distress Syndrome (ARDS).
2. Alveolar Cells – These are the main cell types found in the lungs that produce surfactant proteins, mucins, and white blood cells. Type II cells line the inner layer of the alveolar septum separating the alveolar space from the pulmonary capillary. Type II cells secrete pulmonary surfactant, which lowers the surface tension of the alveolar liquid film. Another type of cell, the type III cell secretes hyaluronic acid, an organic molecule that keeps the airspace open, thus preventing collapse of the alveolus.
3. Air Spaces – Also called lamellae or acini, these are microscopic cavities separated by thin sheets of tissue called interstitial fibers made of collagen and elastin filaments. Each air space contains many tiny pores or fenestrations. Blood vessels pass through the interstitium along with nerves and lymphatics.
4. Lymphatic Vessels – Found throughout the body, these are closed tubes that bring back fat droplets and wastes from the tissues where they were produced. When they reach the subcapsular sinuses, lymph nodes filter out any foreign particles, bacteria, viruses, and tumor cells that may enter the circulation. After filtering, the filtered lymph fluid is sent back to the bloodstream via larger lymphatic vessels.
5. Pulmonary Artery – This artery carries deoxygenated blood toward the heart from the right ventricle of the heart. At the same time, the left common carotid artery delivers oxygenated blood from the superior vena cava and enters the left side of the heart. Oxygenated blood then travels to the lungs via smaller arteries called arterioles.
6. Venous Return Veins – These veins collect blood returning from the lungs and carry it back to the heart. One vein leads directly back to the right atrium while others return to the left atrium and pump the blood forward to the rest of the body.
7. Capillary Network – Made up of millions of tiny capillaries, the network works like a highway system transporting nutrients and oxygen to every cell in the human body. A major component of the circulatory system, the capillary bed regulates the distribution of oxygen and carbon dioxide throughout the body.
8. Lung Parenchyma – The largest organ in the human body; 80% of the total internal surface area of the chest cavity is occupied by lung tissue. Within the lung parenchyma there are several distinct layers including the pleural membrane, the visceral pleura, the parietal pleura, and finally the underlying lung parenchyma. The latter is divided into lobules, which contain air spaces, and alveolar ducts, which lead to the air spaces.
9. Pleura – Located just below the thoracic diaphragm, the pleura forms the outermost covering of both the lungs and the chest wall. Its primary function is to act as a lubricant between the two organs.
10. Peribronchial Layer – This layer surrounds the entire bronchiole and extends inward until it reaches the smooth muscle layer. Here it splits into two branches: one branch continues down the trachea and divides again to form cartilage rings around the trachealis muscle at the entrance to the larynx. The second branch ends at the level of the first branching point of the bronchus.
11. Smooth Muscle Layer – Connected above to the peribronchial layer, the smooth muscle layer surrounds the bronchioles and attaches to the adventitia of the surrounding fascia. Its function is to constrict the bronchioles during inspiration and dilate the airways during expiration.
12. Cartilage Rings – Formed by the perichondrial sheath, these are tough elastic bands composed of collagen fibers that separate the bronchioles from the bronchus.
13. Adventitia – This is the innermost layer of the media and adventitia. Together, the media and adventitia form the tunica muscularis of the bronchus.
14. Subpleural Space – Between the pleura and the visceral and parietal pleuras is the subpleural space, which contains loose connective tissue that separates the lungs from the rib cage.
15. Rib Cage – This is formed by 12 pairs of ribs connected by joints making up the skeletal framework of the chest.
16. Diaphragm – This is the central tendon of the abdominal muscles that divide the abdomen into upper and lower sections. The diaphragm is attached to both sternum and spine and serves as a natural partition between the chest and the abdomen. During inspiriration, the diaphragm moves downward and presses against the bottom of the chest cavity creating negative pressure in the chest cavity. Negative pressure draws air into the chest cavity and provides thrust for respiration.
17. Intercostal Nerve – An autonomic nerve that originates from the medulla oblongata and terminates in the thorax near the middle of the third costal cartilage. The intercostal nerves supply sympathetic innervation to the intercostal muscles.
18. Thorax – This is the protective cover over the chest and abdomen. Both regions are protected by the ribcage and the abdominal contents.
19. Mediastinal Fibrosis – This is scar tissue caused by previous trauma, inflammation, infection, radiation, surgery, thymoma, etc., resulting in adhesions between organs such as the heart and chest.
20. Thymus – Located in front of the neck and behind the breastbone, the thymus is a small glandular mass consisting of lymphoid elements, Hassall corpuscles, epithelial cells, fibroblasts, and macrophages. The thymus produces hormones that control the immune response, especially T cells.
21. Thyroid Gland – Located in the anterior region of the neck, this is the only endocrine gland in the body. It is composed of three lobes and is surrounded by four membranes.
22. Esophagus – This is the tube connecting the pharynx to the stomach. It begins at the intersection of the hard and soft palates and ends at the top of the aorta. It is lined by stratified squamous nonkeratinized epithelium.
23. Trachea – Also called the windpipe, this is the long curved passage that connects the mouth with the glottis. It is located in the neck, midway between the chin and collar bone. The trachea opens into the larynx forming the vocal cords.
24. Glottis – This is the opening in the larynx where sound waves leave the vocal folds.
25. Eustachian Tube – See the ear section.
26. Pharyngoesophageal Valve – This valve, named after Greek physician Galen, is located at the junction between the tongue and esophagus. Its purpose is to prevent food particles and gastric juices refluxing upward into the esophagus.
27. Hypoglossal Canal – This is a narrow

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