Chapter 19 - Respiratory System



Chapter - Respiratory System

Respiratory System - This is the system responsible for gas (oxygen and carbon dioxide) exchange.

A. Basic Anatomy

1. Nose/Nasal Cavity - As air enters the nose, dust and debris is trapped by mucus and nostril hairs. Air is warmed and moisturized as well.

a. Smell receptors - Although part of your sensory system, smell receptors are located at the top of the nasal cavity.

b. Sinuses - Mucus-lined cavities in the skull bones communicate with the nasal cavity. They aid in filtering and moisturizing the air, as well as being a cavity for resonance of sound. Unfortunately, infections and allergies can cause sinuses to become filled with a lot of mucus, they may become infected, and may even become clogged from draining into your nasal cavity. This condition is termed sinusitis, and certainly causes much discomfort.

2. Pharynx - Next, air passes into your throat (this is an open space)

3. Larynx - Next, air passes into your larynx. This is the structure that is the opening into your airways and you may have referred to it as your "Adam's apple" or your "voice box". It is made out of cartilage so that it is semi-rigid yet flexible enough for you to be able to turn your neck.

a. Epiglottis - The epiglottis is an important component of the larynx. It is a triangular flap that operates like a door opening and closing. When swallowing, it closes so that you don't choke. When breathing or speaking, it opens so that air can go back and forth in the airways.

Thought question: Why did your mother always tell you not to talk while eating?

b. Vocal cords - Your elastic vocal cords are housed within the larynx. They vibrate as air moves passed them. You have tiny muscles that can shorten and lengthen the cords. Short and tightly stretched vocal cords provide for high tones and long and loose vocal cords provide for low tones.

Thought question: Why does the larynx enlarge as a boy goes through puberty? Hint: The vocal cords lengthen and thus their "housing" must enlarge.

4. Trachea - This is your windpipe. This airway is made of cartilaginous rings and carries air from the larynx down towards your lungs. It is lined with cilia, or tiny hairs, that function as an escalator to lift debris and dirt upward towards the throat, rather than into the lungs.

5. Bronchi and Bronchioles - Once the trachea reaches the level of your lungs, it branches into smaller and smaller branches that enter and spread out in each of your lungs. The larger branches are called bronchi and the smaller ones are bronchioles. The bronchi still have cartilage in their walls to prevent collapsing, but the bronchioles do not have cartilage, and could collapse during an asthma attack.

6. Lungs - You have two lungs within your chest cavity. The lungs are elastic and filled with all of the bronchi and bronchioles. The bronchioles finally terminate on millions of tiny air sacs called alveoli. These alveoli have very thin walls (one cell layer) and are surrounded by numerous blood capillaries. THIS IS THE SITE WHERE GAS EXCHANGE OCCURS.

B. Respiratory Physiology

1. Ventilation = Breathing

a. Inhalation=Inspiration - This is the process of bringing air IN to the airways. The diaphragm (your breathing muscle located at the floor of the chest cavity) lowers and the ribcage moves up and out. This enlarges the chest cavity and the lungs and allows air to flow into the lungs. You bring oxygen into your lungs from the atmosphere during inhalation.

b. Exhalation=Expiration - This is the process of breathing OUT. As the diaphragm raises, and your ribcage moves down and inward, air is forced out of the lungs. You move carbon dioxide out into the

atmosphere during exhalation.

2. Diffusion - Diffusion occurs at the level of the alveoli and capillaries. Oxygen is in high concentration in the alveoli after inhalation. It diffuses from the alveoli into the bloodstream. Carbon dioxide is high in the bloodstream, as it is metabolic "waste", and low in the alveoli. Therefore, carbon dioxide diffuses out of the bloodstream and into the alveoli to be exhaled.

3. Gas transport in body ---As you recall from the blood section, the red blood cells have hemoglobin that carries oxygen around the body in the bloodstream.

4. Respiratory Control Centers - Although you do have voluntary control over your breathing muscles (they are skeletal muscle), you don't have to think about breathing. The reason is, that the base of your brain, called your brainstem, controls breathing. It tells you when to breathe, how rapidly and how deeply to breathe.

C. Respiratory Pathology

1. Carbon monoxide poisoning - Carbon monoxide is a gas released from burning combustible fuel such as a running car or a gas furnace. The poisonous nature of carbon monoxide is that is readily attaches to hemoglobin, even faster than does oxygen. Thus oxygen cannot attach to hemoglobin because it is clogged by the carbon monoxide. The cause of death is lack of oxygen to your body tissues.

2. Laryngitis - Since the vocal cords are housed in the larynx, inflammation of the larynx leads to voice loss.

3. Bronchitis -As the bronchi become irritated and inflamed, a deep and chronic cough develops. It typically results in mucus being coughed up. Although a cold or flu viral infection can move on down the airways and results in bronchitis, 75% of all chronic bronchitis cases are due to cigarette smoking.

4. Emphysema - As bronchitis becomes chronic, it can result in inflammation of the tiniest airways, the bronchioles. If these airways are inflamed for a long period of time, they can scar closed, trapping any air in the alveoli. The alveoli then become nonfunctional and eventually are destroyed. This change describes emphysema and unfortunately is an irreversible change. Luckily, you have millions of alveoli, and hopefully enough are functional to stay alive. This condition [sometimes called chronic obstructive pulmonary disease (COPD)] is the fourth leading cause of death in the U.S. Guess what the most common cause of emphysema is? 80% of the cases are due to smoking.

5. Cancer - Lung cancer tends to be a difficult cancer to treat. The prognosis is often poor, with estimates showing a 13% five year survival rate after lung cancer is diagnosed. Again, about 83% of all cases of lung cancer are due to smoking. This makes smoking the single major cause of cancer mortality in the U.S.!

6. Asthma - Most cases of asthma are due to allergies. Exposure to the allergens (substances to which you are allergic such as pollen, molds, pet dander, peanuts, strawberries...) results in increased mucus secretion in the airways and spasms of the smooth muscle in the wall of the airways. Of course, the larger airways have cartilage in their walls to prevent collapse. The bronchioles, however, have no

cartilage support in their walls and can collapse. As airways get smaller, the person has difficulty breathing and makes a wheezing sound while breathing. It can become a life-threatening situation when bronchioles constrict too much, preventing oxygen from entering the alveoli. Medical inhalants contain medicines that open the airways. If a person is unconscious from an asthma attack the

paramedic will administer epinephrine, or adrenaline, to open up the airways and restore any heart or blood pressure complications.

7. Pneumonia - Normally, alveoli are filled with air. If they become infected and fill with fluid, gas exchange becomes difficult or impossible. That is why pneumonia can be a life-threatening illness. Most cases of pneumonia are caused by infection deep within the lungs - in the alveoli.

Introduction

A. The respiratory system consists of tubes that filter incoming air and transport it into the microscopic alveoli where gases are exchanged.

B. The entire process of exchanging gases between the atmosphere and body cells is called respiration and consists of the following: ventilation, gas exchange between blood and lungs, gas transport in the bloodstream, gas exchange between the blood and body cells, and cellular respiration.

16.2 Organs of the Respiratory System

A. The organs of the respiratory tract can be divided into two groups: the upper respiratory tract (nose, nasal cavity, sinuses, and pharynx), and the lower respiratory tract (larynx, trachea, bronchial tree, and lungs).

B. Nose

1. The nose, supported by bone and cartilage, provides an entrance for air in which air is filtered by coarse hairs inside the nostrils.

C. Nasal Cavity

1. The nasal cavity is a space posterior to the nose that is divided medially by the nasal septum.

2. Nasal conchae divide the cavity into passageways that are lined with mucous membrane, and help increase the surface area available to warm and filter incoming air.

3. Particles trapped in the mucus are carried to the pharynx by ciliary action, swallowed, and carried to the stomach where gastric juice destroys any microorganisms in the mucus.

D. Paranasal Sinuses

1. Sinuses are air-filled spaces within the maxillary, frontal, ethmoid, and sphenoid bones of the skull.

2. These spaces open to the nasal cavity and are lined with mucus membrane that is continuous with that lining the nasal cavity.

3. The sinuses reduce the weight of the skull and serve as a resonant chamber to affect the quality of the voice.

E. Pharynx

1. The pharynx is a common passageway for air and food.

2. The pharynx aids in producing sounds for speech.

F. Larynx

1. The larynx is an enlargement in the airway superior to the trachea and inferior to the pharynx.

2. It helps keep particles from entering the trachea and also houses the vocal cords.

3. The larynx is composed of a framework of muscles and cartilage bound by elastic tissue.

4. Inside the larynx, two pairs of folds of muscle and connective tissue covered with mucous membrane make up the vocal cords.

a. The upper pair is the false vocal cords.

b. The lower pair is the true vocal cords.

c. Changing tension on the vocal cords controls pitch, while increasing the loudness depends upon increasing the force of air vibrating the vocal cords.

5. During normal breathing, the vocal cords are relaxed and the glottis is a triangular slit.

6. During swallowing, the false vocal cords and epiglottis close off the glottis.

G. Trachea

1. The trachea extends downward anterior to the esophagus and into the thoracic cavity, where it splits into right and left bronchi.

2. The inner wall of the trachea is lined with ciliated mucous membrane with many goblet cells that serve to trap incoming particles.

3. The tracheal wall is supported by 20 incomplete cartilaginous rings.

H. Bronchial Tree

1. The bronchial tree consists of branched tubes leading from the trachea to the alveoli.

2. The bronchial tree begins with the two primary bronchi, each leading to a lung.

3. The branches of the bronchial tree from the trachea are right and left primary bronchi; these further subdivide until bronchioles give rise to alveolar ducts which terminate in alveoli.

4. It is through the thin epithelial cells of the alveoli that gas exchange between the blood and air occurs.

I. Lungs

1. The right and left soft, spongy, cone-shaped lungs are separated medially by the mediastinum and are enclosed by the diaphragm and thoracic cage.

2. The bronchus and large blood vessels enter each lung.

3. A layer of serous membrane, the visceral pleura, folds back to form the parietal pleura.

4. The visceral pleura is attached to the lung, and the parietal pleura lines the thoracic cavity; serous fluid lubricates the “pleura cavity” between these two membranes.

5. The right lung has three lobes, the left has two.

6. Each lobe is composed of lobules that contain air passages, alveoli, nerves, blood vessels, lymphatic vessels, and connective tissues.

16.3 Breathing Mechanism

A. Ventilation (breathing), the movement of air in and out of the lungs, is composed of inspiration and expiration.

B. Inspiration

1. Atmospheric pressure is the force that moves air into the lungs.

2. When pressure on the inside of the lungs decreases, higher pressure air flows in from the outside.

3. Air pressure inside the lungs is decreased by increasing the size of the thoracic cavity; due to surface tension between the two layers of pleura, the lungs follow with the chest wall and expand.

4. Muscles involved in expanding the thoracic cavity include the diaphragm and the external intercostal muscles.

5. As the lungs expand in size, surfactant keeps the alveoli from sticking to each other so they do not collapse when internal air pressure is low.

C. Expiration

1. The forces of expiration are due to the elastic recoil of lung and muscle tissues and from the surface tension within the alveoli.

2. Forced expiration is aided by thoracic and abdominal wall muscles that compress the abdomen against the diaphragm.

D. Respiratory Air Volumes and Capacities

1. The measurement of different air volumes is called spirometry, and it describes four distinct respiratory volumes.

2. One inspiration followed by expiration is called a respiratory cycle; the amount of air that enters or leaves the lungs during one respiratory cycle is the tidal volume.

3. During forced inspiration, an additional volume, the inspiratory reserve volume, can be inhaled into the lungs.

4. During a maximal forced expiration, an expiratory reserve volume can be exhaled, but there remains a residual volume in the lungs.

5. Vital capacity is the tidal volume plus inspiratory and expiratory reserve capacities combined.

6. Vital capacity plus residual volume is the total lung capacity.

7. Anatomic dead space is air remaining in the bronchial tree.

16.4 Control of Breathing

A. Normal breathing is a rhythmic, involuntary act.

B. Respiratory Center

1. Groups of neurons in the brain stem comprise the respiratory center, which controls breathing by causing inspiration and expiration and by adjusting the rate and depth of breathing.

2. Neurons in the pneumotaxic area control the rate of breathing.

C. Factors Affecting Breathing

1. Hyperventilation lowers the amount of carbon dioxide in the blood.

16.5 Alveolar Gas Exchanges

A. The alveoli are the sites of gas exchange between the atmosphere and the blood.

B. Alveoli

1. The alveoli are tiny sacs clustered at the distal ends of the alveolar ducts; some alveoli have pores between them to assist in air exchange between alveoli.

C. Respiratory Membrane

1. The respiratory membrane consists of the epithelial cells of the alveolus, the endothelial cells of the capillary, and the two fused basement membranes of these layers.

2. Gas exchange occurs across this respiratory membrane.

D. Diffusion across the Respiratory Membrane

1. Gases diffuse from areas of higher pressure to areas of lower pressure.

2. In a mixture of gases, each gas accounts for a portion of the total pressure; the amount of pressure each gas exerts is equal to its partial pressure.

3. When the partial pressure of oxygen is higher in the alveolar air than it is in the capillary blood, oxygen will diffuse into the blood.

4. When the partial pressure of carbon dioxide is greater in the blood than in the alveolar air, carbon dioxide will diffuse out of the blood and into the alveolus.

5. A number of factors favor increased diffusion; more surface area, shorter distance, greater solubility of gases, and a steeper partial pressure gradient.

16.6 Gas Transport

A. Gases are transported in association with molecules in the blood or dissolved in the plasma.

B. Oxygen Transport

1. Over 98% of oxygen is carried in the blood bound to hemoglobin of red blood cells, producing oxyhemoglobin.

2. Oxyhemoglobin is unstable in areas where the concentration of oxygen is low, and gives up its oxygen molecules in those areas.

3. More oxygen is released as the blood concentration of carbon dioxide increases, as the blood becomes more acidic, and as blood temperature increases.

4. A deficiency of oxygen reaching the tissues is called hypoxia and has a variety of causes.

C. Carbon Dioxide Transport

1. Carbon dioxide may be transported dissolved in blood plasma, as carbaminohemoglobin, or as bicarbonate ions.

2. Most carbon dioxide is transported in the form of bicarbonate.

3. When carbon dioxide reacts with water in the plasma, carbonic acid is formed slowly, but instead much of the carbon dioxide enters red blood cells, where the enzyme carbonic anhydrase speeds this reaction.

4. The resulting carbonic acid dissociates immediately, releasing bicarbonate and hydrogen ions.

5. Carbaminohemoglobin also releases its carbon dioxide which diffuses out of the blood into the alveolar air.

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