A&P Lecture 4: Sturcture Respiratory System

NOTE: The following organ lecture on Anatomy and Physiology will be structured closely to concepts by which nurses must know to be able to have a good foundation in the normal Anatomy and Physiology to know the normal from abnormal findings for Health Assessment and to have a good grasp regarding deviations in the normal functions and structures of the the body in contrast to that during an illness state for advance subjects such as Medical-Surgical Nursing, Maternal and Child Nursing and Psychiatric Nursing.

ANATOMY AND PHYSIOLOGY LECTURE 4

RESPIRATORY SYSTEM

Nurses often encounter disorders of the respiratory system from the community to the intensive care unit. The diversity of respiratory ailments from simple colds to an evolving pulmonary edema necessitates an the development of expert assessment  skills to provide accurate problem identification and prompt treatment to be able to return patients in their optimal level of functioning. In order to differentiate between normal and abnormal assessment findings, an understanding of respiratory function and the significance of abnormal diagnostic test results is essential.

Overview

The respiratory system is composed of the upper and lower respiratory tracts. Together, the two tracts are responsible for ventilation. The upper respiratory tract warms and filters inspired air so that the lower respiratory tract can accomplish gas exchange. Gas exchange involves delivering oxygen to the tissues through the bloodstream and expelling waste gases, such as carbon dioxide, during expiration. The respiratory system works with the cardiovascular system; the respiratory system is responsible for ventilation and diffusion, and the cardiovascular system is responsible for oxygen delivery. 

Upper Respiratory Tract

Nose

Our nose serves as a passageway for air to pass to and from the lungs. It filters impurities and humidifies and warms the air as it is inhaled. The nose is composed of an external and an internal portion. The external portion protrudes from the face and is supported by the nasal bones and cartilage. The anterior nares (nostrils) are the external openings of the nasal cavities.

The internal portion of the nose is a hollow cavity separated into the right and left nasal cavities by a narrow vertical divider, the septum. Each nasal cavity is divided into three passageways by the projection of the turbinates from the lateral walls. The turbinate bones are also called conchae for the name suggested by their shell-like appearance. Because of their curves, these bones increase the mucous membrane surface

of the nasal passages and slightly obstruct the air flowing

through them.

Air entering the nostrils is deflected upward to the roof of the nose, and it follows a circuitous route before it

reaches the nasopharynx. It comes into contact with a large surface of moist, warm, highly vascular, ciliated mucous membrane (called nasal mucosa) that traps practically all the dust and organisms in the inhaled air. The air is moistened, warmed to body temperature, and brought into contact with sensitive nerves. Some of these nerves detect odors; others provoke sneezing to expel irritating dust. Mucus, secreted continuously by goblet cells, covers the surface of the nasal mucosa and is moved back to the nasopharynx by the action of the cilia which are fine hairs.

Paranasal Sinuses

The paranasal sinuses include four pairs of bony cavities that are lined with nasal mucosa and ciliated pseudostratified columnar epithelium. These air spaces are connected by a series of ducts that drain into the nasal cavity. The sinuses are named by their location: frontal, ethmoidal, sphenoidal, and maxillary . A prominent function of the sinuses is to serve as a resonating chamber in speech. The sinuses are a common site of infection.

Pharynx, Tonsils, and Adenoids

The pharynx, or throat, is a tubelike structure that connects the nasal and oral cavities to the larynx. It is divided into three regions: nasal, oral, and laryngeal. The nasopharynx is located posterior to the nose and above the soft palate. The oropharynx houses the faucial, or palatine, tonsils. The laryngopharynx extends from the hyoid bone to the cricoid cartilage. The epiglottis forms the entrance to the larynx. The adenoids, or pharyngeal tonsils, are located in the roof of the nasopharynx. The tonsils, the adenoids, and other lymphoid tissue encircle the throat. These structures are important links in the chain of lymph nodes guarding the body from invasion by organisms entering the nose and the throat. The pharynx functions as a passageway for the respiratory and digestive tracts.

Larynx

The larynx, or voice organ, is a cartilaginous epitheliumlined structure that connects the pharynx and the trachea. The major function of the larynx is vocalization. It also protects the lower airway from foreign substances and facilitates coughing. It is frequently referred to as the voice box and consists of the following:

• Epiglottis: a valve flap of cartilage that covers the opening to the larynx during swallowing

• Glottis: the opening between the vocal cords in the larynx

• Thyroid cartilage: the largest of the cartilage structures; part of it forms the Adam’s apple

• Cricoid cartilage: the only complete cartilaginous ring in the larynx (located below the thyroid cartilage)

• Arytenoid cartilages: used in vocal cord movement with the thyroid cartilage

• Vocal cords: ligaments controlled by muscular movements that produce sounds; located in the lumen of

the larynx. 

Trachea

The trachea, or windpipe, is composed of smooth muscle with C-shaped rings of cartilage at regular intervals. The cartilaginous rings are incomplete on the posterior surface and give firmness to the wall of the trachea, preventing it from collapsing. The trachea serves as the passage between the larynx and the bronchi

Lower Respiratory Tract

The lower respiratory tract consists of the lungs, which contain the bronchial and alveolar structures needed for gas exchange.

Lungs

The lungs are paired elastic structures enclosed in the thoracic cage, which is an airtight chamber with distensible walls. Ventilation requires movement of the walls of the thoracic cage and of its floor, the diaphragm. The effect of these movements is alternately to increase and decrease the capacity of the chest. When the capacity of the chest is increased, air enters through the trachea (inspiration) because of the lowered pressure within and inflates the lungs. When the chest wall and diaphragm return to their previous positions (expiration), the lungs recoil and force the air out through the bronchi and trachea. Inspiration occurs during the first third of the respiratory cycle, expiration during the later two thirds. The inspiratory phase of respiration normally requires energy; the expiratory phase is normally passive, requiring very little energy. In respiratory diseases, such as chronic obstructive pulmonary disease (COPD), expiration requires energy.

Pleura

The lungs and wall of the thorax are lined with a serous membrane called the pleura. The visceral pleura covers the lungs; the parietal pleura lines the thorax. The visceral and parietal pleura and the small amount of pleural fluid between these two membranes serve to lubricate the thorax and lungs and permit smooth motion of the lungs within the thoracic cavity with each breath.

Mediastinum

The mediastinum is in the middle of the thorax, between the pleural sacs that contain the two lungs. It extends from the sternum to the vertebral column and contains all the thoracic tissue outside the lungs (heart, thymus,

certain large blood vessels [ie, aorta, vena cava], and esophagus).

Lobes

Each lung is divided into lobes. The right lung has upper, middle, and lower lobes, whereas the left lung consists of upper and lower lobes. Each lobe is further subdivided into two to five segments separated by fissures, which are extensions of the pleura.

Bronchi and Bronchioles

There are several divisions of the bronchi within each lobe of the lung. First are the lobar bronchi (three in the right lung and two in the left lung). Lobar bronchi divide into segmental bronchi (10 on the right and 8 on the left), which are the structures identified when choosing the most effective postural drainage position for a given patient. Segmental bronchi then divide into subsegmental bronchi. These bronchi are surrounded by connective tissue that contains arteries, lymphatics, and nerves.

The subsegmental bronchi then branch into bronchioles, which have no cartilage in their walls. Their patency depends entirely on the elastic recoil of the surrounding smooth muscle and on the alveolar pressure. The bronchioles contain submucosal glands, which produce mucus that covers the inside lining of the airways. The bronchi and bronchioles are also lined with cells that have surfaces covered with cilia. These cilia create a constant whipping motion that propels mucus and foreign substances away from the lungs toward the larynx.

The bronchioles then branch into terminal bronchioles, which do not have mucus glands or cilia. Terminal bronchioles then become respiratory bronchioles, which are considered to be the transitional passageways between the conducting airways and the gas exchange airways. Up to this point, the conducting airways contain about 150 mL of air in the tracheobronchial tree that does not participate in gas exchange; this is known as physiologic dead space. The respiratory bronchioles then lead into alveolar ducts and alveolar sacs and then alveoli. Oxygen and carbon dioxide exchange takes place in the alveoli.

Alveoli

The lung is made up of about 300 million alveoli, which are arranged in clusters of 15 to 20. These alveoli are

so numerous that if their surfaces were united to form one sheet, it would cover 70 square meters—the size of a tennis court.

There are three types of alveolar cells. Type I alveolar cells are epithelial cells that form the alveolar walls. Type II alveolar cells are metabolically active. These cells secrete surfactant, a phospholipid that lines the inner surface and prevents alveolar collapse. Type III alveolar cell macrophages are large phagocytic cells that ingest foreign matter (eg, mucus, bacteria) and act as an important defense mechanism.