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Chapter 16

Respiratory System

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Introduction• The respiratory system consists of tubes that filter

incoming air and transport it into the microscopic alveoli where gases are exchanged.

• Respiration is defined as the process of inhalation of oxygen and the exhalation of carbon-di-oxide with the help of certain organs of the human body. These organs include the nose, pharynx, larynx, trachea, bronchi and the lungs. These organs together make the human respiratory system.

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Functions of the Respiratory System

• RespirationThe most important function of the respiratory system is the process of respiration. • The entire process of exchanging gases between the

atmosphere and body cells is called 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.

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Respiration

How does the respiratory system

function?

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1. InhalationWhen a person breathes air (which contains oxygen), it passes through the nasal passages containing mucous. This mucous helps in filtering out contaminants like dust, pollen and smoke. The nasal epithelium naturally adds moisture and heat to the air. The larynx prevents food or liquid entering the respiratory tract. The air then passes through the larynx and enters the trachea or the windpipe. Here it gets divided into the two bronchi that connect the trachea to the lungs. The bronchi again gets split into many smaller tubes known as bronchioles. These bronchi end in air sacs, also known as alveoli, which contain blood capillaries. These blood capillaries carry blood which comes through veins from all other parts of the body. Here the carbon dioxide from the blood is exchanged for the oxygen in the alveoli. The blood containing oxygen then goes to the heart where it is later pumped to other parts of the body.

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2. Exhalation

Exhalation in human beings is the process of expelling out of air containing carbon dioxide. The movement of the air while exhalation is through the bronchi, then through the airways and then it passes out through the nose. The exhaled air is completely depleted of oxygen.

The lungs are the most important organs of the human respiratory system. There is a muscle located below the lungs known as the diaphragm which also plays an important role in the process of respiration. During inhalation, the diaphragm contracts, creating a vacuum that helps in pulling air into the lungs. On the other hand, during exhalation, the diaphragm relaxes which helps in forcing the air out of the lungs.

How does the respiratory system function?

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3.Vocalization

Vocalization is also one of the major respiratory system functions. Vocalization is the process which enables humans to speak and also to make sound. When the air passes through the pharynx and larynx, it makes the vocal cords in larynx to vibrate which helps in production of sound and speech in humans.

4. Coughing/SneezingWhen any foreign particles enter the nasal passages, it can result into irritation. Therefore, expelling out these foreign bodies or irritants is one of the functions of the respiratory system. These irritants are forced out of the respiratory tract through cough or even sneeze

How does the respiratory system

function?

To Put It Simply…

• The principle functions of the respiratory system are:– Ventilate the lungs– Extract oxygen from the air and

transfer it to the bloodstream– Excrete carbon dioxide and water vapor– Maintain the acid base of the blood– Screen and filter air from foreign

particles

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

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Organs of the Respiratory System

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Nose• supported by bone and cartilage, provides an entrance for air in which

air is filtered by coarse hairs inside the nostrils

Nasal Cavity• space posterior to the nose that is divided medially by the nasal

septum• 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

• 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.

Paranasal Sinuses• Sinuses are air-filled spaces within the maxillary,frontal, ethmoid,

and sphenoid bones of the skull.• These spaces open to the nasal cavity and are lined with mucus

membrane that is continuous with that lining the nasal cavity.• The sinuses reduce the weight of the skull and serve as a resonant

chamber to affect the quality of the voice.

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Pharynx aka Throat

• common passageway for air and food• aids in producing sounds for speech

Larynx• an enlargement in the airway superior to the trachea and inferior to the

pharynx• helps keep particles from entering the trachea and also houses the vocal

cords• composed of a framework of muscles and cartilage bound by elastic tissue

• Note: Epiglottis & vestibular folds prevent swallowed material from moving into larynx (can move to cover trachea)

Larynx continued…• Inside the larynx, two pairs of folds of muscle and

connective tissue covered with mucous membrane make up the vocal cords

• The upper pair is the false vocal cords• The lower pair is the true vocal cords• Changing tension on the vocal cords controls pitch, while

increasing the loudness depends upon increasing the force of air vibrating the vocal cords

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

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

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Trachea • Extends downward

anterior to the esophagus and into the thoracic cavity, where it splits into right and left bronchi

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

• tracheal wall is supported by 20 incomplete cartilaginous rings

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Bronchial Tree• consists of branched tubes leading from the trachea to the alveoli• begins with the two primary bronchi, each leading to a lung• branches of the bronchial tree from the trachea are right and left

primarybronchi; these further subdivide until bronchioles give rise to alveolar ducts which terminate in alveoli

• it is through the thin epithelial cells of the alveoli that gas exchange between the blood and air occurs

Primary bronchi

Secondary bronchi

Tertiary bronchi

bronchioles

Terminal bronchioles

Respiratory bronchioles

Alveolar ducts

Alveolar sacs

alveoli

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Alveoli– Extremely thin-

walled sacs covered w/ capillaries

– CO2 & O2 move by diffusion across the respiratory membrane

– About 300 million alveoli in two lungs

– Size of a tennis court

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Lungs • the right and left soft, spongy, cone-shaped lungs are separated

medially by the mediastinum and are enclosed by the diaphragm and thoracic cage

• the bronchus and large blood vessels enter each lung• A layer of serous membrane, the visceral pleura, folds back to form

the parietal pleura• 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

• the right lung has three lobes, the left has two• Each lobe is composed of lobules that contain air passages, alveoli,

nerves, blood vessels, lymphatic vessels, and connective tissues.

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Breathing Mechanism• Ventilation (breathing), the movement of air in and out of the lungs, is

composed of inspiration and expiration

Inspiration• Atmospheric pressure is the force that moves air into the lungs• When pressure on the inside of the lungs decreases, higher pressure air

flows in from the outside• 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

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

• 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.

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Expiration• The forces of expiration are due to the elastic recoil of

lung and muscle tissues and from the surface tension within the alveoli

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

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Changing Alveolar Volume

• Lung recoil– Causes alveoli to collapse resulting from

• Elastic recoil and surface tension– Surfactant: Reduces tendency of lungs to collapse

• Pleural pressure– Negative pressure can cause alveoli to

expand– Pneumothorax is an opening between

pleural cavity & air that causes a loss of pleural pressure

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Compliance• Measure of the ease with which lungs

& thorax expand– The greater the compliance, the easier it

is for a change in pressure to cause expansion

– A lower-than-normal compliance means the lungs and thorax are harder to expand• Conditions that decrease compliance

– Pulmonary fibrosis– Pulmonary edema– Respiratory distress syndrome

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Respiratory Air Volumes and Capacities • The measurement of different air volumes is called spirometry,

and it describes four distinct respiratory volumes• 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

• During forced inspiration, an additional volume, the inspiratory reserve volume, can be inhaled into the lungs. IRV + TV gives us the inspiratory capacity

• During a maximal forced expiration, an expiratory reserve volume can be exhaled, but there remains a residual volume in the lungs. Adding the two together gives us the functional reservecapacity

• Vital capacity is the tidal volume plus inspiratory reserve and expiratory reserve volumes combined

• Vital capacity plus residual volume is the total lung capacity• Anatomic dead space is air remaining in the bronchial tree

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Control of Breathing• Normal breathing is a rhythmic, involuntary act

even though the muscles are under voluntary control

Respiratory Center • Groups of neurons in the brain stem comprise the

respiratory center, which controls breathing by causinginspiration and expiration and by adjusting the rate and depth of breathing

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Factors Affecting Breathing • Chemicals, lung tissue stretching, an

emotional state affect breathing• Chemosensitive areas (central chemoreceptors)

are associated with the respiratory center and are sensitive to changes in the blood concentration of carbon dioxide and hydrogen ions• If either carbon dioxide or hydrogen ion

concentrations rise, the central chemoreceptors signal the respiratory center, and breathing rate increases

• Peripheral chemoreceptors in the carotid sinuses and aortic arch sense changes in blood oxygen concentration, transmit impulses to the respiratory center, and breathing rate and tidal volume increase

More Factors Affecting Breathing • An inflation reflex, triggered by stretch receptors in the

visceral pleura, bronchioles, and alveoli, helps to prevent over inflation of the lungs during forceful breathing

• Hyperventilation lowers the amount of carbon dioxide in the blood

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Alveolar Gas Exchanges• The alveoli are the only sites of gas exchange between

the atmosphere and the blood.Alveoli

• The alveoli are tiny sacs clustered at the distal ends of the alveolar ducts

Respiratory Membrane• 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.

• Gas exchange occurs across this respiratory membrane

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Hemoglobin and Oxygen Transport• Oxygen is transported by hemoglobin (98.5%) and is

dissolved in plasma (1.5%)

Transport of Carbon Dioxide

•Carbon dioxide is transported as bicarbonate ions (70%) in combination with blood proteins (23%) and in solution with plasma (7%)

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Disorders• Asthma— spasms of smooth muscle in the bronchioles• Lung cancer

– Constant irritation produces excess mucous and puts unnecessary stress on the bronchi

– Alveoli destroyed by WBC’s acting on the irritation– Structural cells disappear and cancer cells take over

• Emphysema— alveolar walls lose their elasticity– Some alveoli merge and reduce volume– Have to work voluntarily to exhale

• Bronchitis— inflammation of the bronchi– Creates site for infection and increases mucous

• Pneumonia— infection or inflammation of the alveoli• Tuberculosis (TB)— bacterial infection that destroys lung tissue and is

replaced by non-elastic connective tissue• Respiratory Distress Syndrome (RDS)

– Lack of surfactant makes breathing difficult – Alveoli are sticking together– Occurs in infants

• Pulmonary Embolism– blood clot obstructs circulation to lung tissue & tissue dies

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Disorders• Respiratory Failure

– Not enough O2 to maintain metabolism

– Cannot eliminate enough CO2

– Caused by:• Drugs• Stroke• CO poisoning• Shock

• Colds and Flu— viral infections• Sudden Infant Death Syndrome (SIDS)

– Crib death– Occurs between 1 week and 12 months– Cause is unknown– Baby stops breathing

• Laryngitis— vocal cords• Pharyngitis— sore throat• Rhinitis— lining of the nose

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Effects of Aging

• Vital capacity and maximum minute ventilation decrease

• Residual volume and dead space increase• Ability to remove mucus from respiratory

passageways decreases• Gas exchange across respiratory membrane is

reduced