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Respiratory Respiratory SystemSystem

Andrew McCaskillAndrew McCaskill

ICSICS

In humans the respiratory system consists of the airways, the lungs, and the respiratory muscles that mediate the

movement of air into and out of the body. Within the lungs, molecules of oxygen and carbon dioxide are

passively exchanged, by diffusion, between the gaseous environment and the blood. The system also helps to

maintain the acid-base balance of the body through the efficient removal of carbon dioxide from the blood.

In humans the respiratory system can be conveniently subdivided into an upper respiratory tract (or conducting zone) and lower respiratory tract

(respiratory zone), trachea and lungs.

Air moves through the body in the following order:1. Nostrils 2. Nasal cavity 3. Pharynx (naso-, oro-, laryngo-) 4. Larynx (voice box) 5. Trachea (wind pipe) 6. Thoracic cavity (chest) 7. Bronchi (right and left) 8. Alveoli (site of gas exchange)

Upper respiratory tract/conducting zoneThe conducting zone starts with the nares (nostrils) of the nose, which open into the nasopharynx (nasal cavity). The primary functions of the nasal passages are to: 1) filter, 2) warm, 3) moisten, and 4) provide resonance in speech.

The nasopharnyx opens into the oropharynx (behind the oral cavity). The oropharynx leads to the laryngopharynx, and empties into the larynx

(voicebox), which contains the vocal cords, passing through the glottis, connecting to the

trachea (wind pipe).

The Progression

A nostril (or naris, pl. nares) is one of the two channels of the nose. In humans the nasal cycle is the normal

ultradian cycle of each nostril's blood vessels becoming engorged in swelling, then shrinking. During the course of

a day they will switch over approximately every four hours or so. Meaning that only one nostril is used at any

one time.

The nasal cycle is the rhythmic, alternating

side-to-side fluctuation in nasal airflow. It is known to be regulated by the

autonomic nervous system probably from the

centers located in brainstem.

The nasal cavity (or nasal fossa) is a large air-filled space above and behind the nose in the middle of the

face. The nasal cavity is important in warming or cooling and cleaning the air as it is inhaled. The nasal cavity is

enclosed by the nasal bone above and by the maxilla and ethmoid bone on the sides. The palate separates the

nasal cavity from the mouth.

The nasal cavity is divided in two by a vertical fin called the nasal septum. Cilia and mucus along the inside wall

of the nasal cavity trap and remove dust and germs from the air as it flows through the nasal cavity. The cilia move the mucus down the nasal cavity to the pharynx,

where it can be swallowed.

The pharynx (plural: pharynges) is part of the digestive system and respiratory system in humans. Because both food and air pass through the pharynx,

special care is necessary to prevent choking or aspiration when food or liquid is swallowed. In humans

the pharynx is important in vocalization.

The larynx (plural larynges), colloquially known as the voicebox, is an organ in the neck of humans involved in protection of the

trachea and sound production. The larynx houses the vocal cords, and is situated just below where the tract of the pharynx splits into the trachea and the esophagus. Sound is generated in the larynx, and that is where pitch and volume are manipulated. The strength

of expiration from the lungs also contributes to loudness, and is necessary for the vocal cords to produce speech.

During swallowing, the larynx (at the epiglottis) closes to prevent swallowed material from entering the

lungs; the larynx is also pulled upwards to assist this process. Stimulation of the larynx by ingested matter produces a strong cough reflex to protect the lungs

The trachea, or windpipe, is a tube extending from the larynx

to the bronchi in humans, carrying air to the lungs. It is lined with ciliated cells which

push particles out, and cartilage rings which reinforce the trachea and prevent it from collapsing on

itself during breathing.These numerous cartilaginous

half-rings, located one above the other along the trachea, have

open ends adjacent to the esophagus. The rings are

connected by muscular and fibrous tissue, and they are lined

inside with a ciliated mucous membrane. Drawn by Theresa Knott

Lower respiratory tract/respiratory zone

The trachea leads down to the thoracic cavity (chest) where it

divides into the right and left "main stem" bronchi. The subdivision of

the bronchus are: primary, secondary, and tertiary divisions (first, second and third levels). In

all, they divide 16 more times into even smaller bronchioles.

The bronchioles lead to the respiratory zone of the lungs which consists of respiratory bronchioles, alveolar ducts and the alveoli, the multi-lobulated sacs in which most of the gas exchange occurs.

A bronchus (plural bronchi) is a caliber of

airway in the respiratory tract that conducts air into the lungs. No gas

exchange takes place in this part of the lungs. A

bronchopulmonary segment is a division of a

lung that is separated from the rest of the lung by a connective tissue septum. This property

allows a bronchopulmonary

segment to be surgically removed without affecting other segments. Smooth

muscle and hyaline cartilage is present

continuously around the bronchi.

An An alveolusalveolus (plural: (plural: alveolialveoli, from Latin , from Latin

alveusalveus, "little cavity"), , "little cavity"), is an anatomical is an anatomical

structure that has the structure that has the form of a hollow form of a hollow

cavity. In the lung, the cavity. In the lung, the pulmonary alveolipulmonary alveoli

are are spherical spherical outcroppingsoutcroppings of the of the

respiratory bronchioles respiratory bronchioles and are the primary and are the primary

sites of gas exchange sites of gas exchange with the bloodwith the blood. . The lungs contain about 700 million alveoli, representing a total

surface area of 70-90 square meters, each wrapped in a fine mesh of capillaries.

The alveoli consist of an epithelial layer surrounded by capillaries. In some alveolar walls there are pores between

alveoli.

Gas ExchangeThe major function of the respiratory system is gas exchange. As gas exchange occurs, the acid-base balance of the body is maintained as part of homeostasis. If proper ventilation is not maintained two opposing conditions could occur: 1) respiratory acidosis, a life threatening condition, and 2) respiratory alkalosis.

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InhalationInhalation is initiated by the

diaphragm and supported by the external intercostal muscles. Normal

resting respirations are 10 to 18 breaths per minute. Its time period is

2 seconds. During vigorous inhalation (at rates exceeding 35

breaths per minute), or in approaching respiratory failure,

accessory muscles of respiration are recruited for support. These consist

of sternocleidomastoid and platysma muscles of the neck.

Inhalation is driven primarily by the diaphragm. When the diaphragm contracts, the ribcage expands and the

contents of the abdomen are moved downward. This results in a larger thoracic volume, which in turn causes a decrease in intrathoracic pressure. As the pressure in the

chest falls, air moves into the conducting zone.

Drawn by Theresa Knott

ExhalationExhalation is generally a passive

process.The lungs have a natural elasticity; as they recoil from the stretch of inhalation, air flows back out until the pressures in the chest and the

atmosphere reach equilibrium.During forced exhalation, as when blowing out a candle, expiratory muscles including the abdominal muscles and internal intercostal

muscles, generate abdominal and thoracic pressure, which forces air

out of the lungs.

Review: Upon inhalation, gas exchange occurs at the alveoli, the tiny sacs which are the basic functional component of the

lungs. The alveolar walls are extremely thin (approx. 0.2 micrometres), and are permeable to gases. The alveoli are lined

with pulmonary capillaries, the walls of which are also thin enough to permit gas exchange. All gases diffuse from the

alveolar air to the blood in the pulmonary capillaries, as carbon dioxide diffuses in the opposite direction, from capillary blood to alveolar air. At this point, the pulmonary blood is oxygen-rich, and the lungs are holding carbon dioxide. Exhalation

follows, thereby ridding the body of the carbon dioxide and completing the cycle of respiration.

In an average resting adult, the lungs take up about 250ml of oxygen every minute while excreting about 200ml of carbon

dioxide. During an average breath, an adult will exchange from 500 ml to 700 ml of air. This average breath capacity is called

tidal volume.

Disorders of the respiratory system can be classified into four general areas:

Obstructive Conditions (e.g., Emphysema, Bronchitis, asthma attacks)

Restrictive Conditions (e.g., Fibrosis or other genetic conditions)

Vascular Diseases (e.g., Pulmonary Hypertension) Infectious, Environmental and Other "Disease"s (e.g.,

Pneumonia, Tuberculosis, Asbestosis, Particulate Pollutants)

Disorders of the respiratory system are usually treated internally by a Pulmonologist.

Coughing is of major importance, as it is the body's main method to remove dust, mucus, saliva, and other

debris from the lungs. Inability to cough can lead to infection.

Acute respiratory distress syndrome (ARDS) is a severe inflammatory disease of the lung. Usually triggered by other pulmonary pathology, the uncontrolled inflammation leads to impaired gas exchange,

alveolar flooding and/or collapse, and systemic inflammatory response syndrome.

In asthma, the bronchioles, or the "bottle-necks" into the sac are restricted causing the amount of air flow into the lungs to be greatly reduced.

Emphysema is another disease of the lungs, whereby the elastin in the walls of the alveoli is broken down (elevated by cigarette smoke) The resulting loss of elasticity in the lungs leads to prolonged times for

exhalation, which occurs through passive recoil of the expanded lung. This leads to a smaller volume of gas exchanged per breath.

Chronic bronchitis occurs when an abundance mucus is produced by the lungs. The production of this substance occurs naturally when the lung tissue is exposed to irritants. In chronic bronchitis, the air passages into the alveoli, the broncholiotes, become clogged with mucus. This causes increased coughing in order to

remove the mucus, and is often a result of extended periods of exposure to cigarette smoke.

Cystic fibrosis is a genetic condition caused by the dysfunction of a transmembrane protein responsible for the transport of chloride ions. This causes huge amounts of mucus to clog the bronchiolites, similar to chronic

bronchitis. The result is a persistent cough and reduced lung capacity.

Lung cancer is a common form of cancer causing the uncontrolled growth of cells in the lung tissue. It is often difficult to prevent once started, due to the sensitivity of lung tissues.

Pneumonia is an infection of the alveoli, which can be caused by both viruses and bacteria. Toxins and fluids are released from the virus causing the effective surface area of the lungs to be greatly reduced. If this

happens to such a degree that the patient cannot draw enough oxygen from his environment, then the victim may need supplemental oxygen.

Quiz #1

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