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Figure 31.1 Respiratory System

Conchae Diaphragm Horizontal fissure Larynx Parietal pleura Pleural cavity Primary bronchus

Naris Nasopharynx Oblique fissure Oropharynx Rib Secondary bronchus Trachea Visceral pleura cartilage. It is attached to the first segment of the trachea.

The paired cartilages of the larynx are much smaller than the single cartilages. The arytenoid cartilages are located superior to the posterior portion of the cricoid cartilage. The arytenoid cartilages are attached to the vocal folds and pharyngeal muscles. Action of the muscles controls the tension in the vocal folds and thereby the pitch of sounds produced by vibration of the folds.

On top of each arytenoid cartilage is a horn-shaped cor-niculate cartilage. The paired cuneiform cartilages are anterior to the corniculate cartilages. These four cartilages are not of great concern to our study of the respiratory system.

The larynx opens into the trachea, anterior to the esophagus. The trachea is composed of a series of incomplete cartilaginous rings. The rings are MCW- shaped and are open in the rear. The esophagus expands into the open part of the ring during swallowing. The last ring of the trachea has an internal projection of cartilage called the carina which is particularly sensitive and plays an important role in the cough reflex.

Inferiorly the trachea divides into two primary bronchi (sing. - bronchus). The right primary bronchus is shorter and straighter than the left. Each primary bronchus divides into one secondary bronchus for each lobe of the lungs. The secondary bronchi divide into ever smaller branches connected to the microscopic air sacs where the exchange of gases takes place.

The lungs are separated from each other by the organs of the mediastinum (Figure 1.6). Each lung is surrounded by a serous membrane, the pleura, which is folded to give the appearance of having two distinct layers (see Figure 1.8). The layer closest to a lung is termed the visceral pleura. The outer layer is the parietal pleura. There is a potential space between the layers termed the pleural cavity. The larger, right lung has three lobes, while the smaller, left lung only has two lobes. The lobes of the right lung are divided by oblique and horizontal fissures. The horizontal fissure is superior to the angled oblique fissure. The left lung has only an oblique fissure.

Layers The Lung Horizontal
Figure 31.2 Larynx

Arytenoid cartilage Corniculate cartilage Cricoid cartilage Epiglottis Hyoid Parathyroid gland Thyroid cartilage Thyroid gland Trachea

Each lobe is composed of small functional units called lobules. Inside each lobule are numerous air sacs termed alveoli (sing. - alveolus). The walls of the alveoli are only one squamous cell thick. Gases can freely exchange between the alveoli and the blood vessels beneath.

The primary muscle of breathing is the diaphragm which is assisted by the action of the external and internal intercostals (Figure 16.1) and other muscles.

Exercise 312

Examine the models of the respiratory system. Identify:

Thorax: Bronchioles, cricoid cartilage, diaphragm, epiglottis, esophagus, heart, hyoid bone, larynx, lungs, thyroid cartilage, thyroid gland, and trachea.

Larynx: arytenoid cartilages, comiculate cartilage, cricoid cartilage, epiglottis, hyoid bone, glottis, thyroid cartilage, trachea, and vocal folds.

Midsagittal section of head: cricoid cartilage, epiglottis, esophagus, hard palate, inferior nasal concha, laryngopharynx, larynx, medial nasal concha, nares, nasopharynx, oral cavity proper, oropharynx, soft palate, superior nasal concha, thyroid cartilage, tongue, uvula, and vocal folds.

Exercise 313

Examine the larynx of the cat. Identify the cricoid cartilage, thyroid cartilage, and thyroid gland. Cut into the larynx to see the epiglottis and glottis. Trace the trachea down into the lungs. Note that there are different number of lobes in the cat lungs than in the human.

Cut across the trachea to examine the shape of the cartilaginous rings.

Exercise 31.4

Examine a microscopic slide of a lung. Note the alveoli and their thin walls. Identify the visceral pleural membrane.

Examine a prepared slide of the trachea. Notice the epithelial lining of the airway and the hyaline cartilage in the ring.





1. _ How many secondary bronchi are in the right lung?

2. _ How many secondary bronchi are in the left lung?

3. _ How many lobes does the right lung have?

4. Why are the tracheal cartilage rings open in the back?

5. How is an inferior nasal concha different from a superior concha?

6. __Into which cavity does the Eustachian tube open?

7. __Which cartilages attach to the vocal folds?

8. __What is the primary muscle for breathing?

9. __Name the serous membrane surrounding a lung.

10. _ What structure prevents aspiration?

11. _ Name the inferior, internal ridge of cartilage in the trachea which acts in the cough reflex.

13. _ Name the three parts of the pharynx in alphabetical order.



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Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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  • bo
    What is the inferior internal ridge of cartilage in the trachea which acts in the cough reflex?
    3 years ago

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