The Respiratory System rev 11-11

Respiratory System-BIO 102 1

The Respiratory System rev 11-11

• The primary function of the respiratory system is to deliver oxygen (O2) to and remove carbon dioxide (CO2) from the blood.

• The respiratory system also plays a role in maintaining the blood pH (acid-base balance).

• Additionally, in humans and most animals, the respiratory system also produces sounds.


Anatomy of the Upper Respiratory Tract:• Nose, nasal cavities, sinuses and pharynx

(throat) (everything above the Adam’s apple)– The nose, nasal cavities and sinuses provide a

large area of highly vascularized tissues which warm, filter and add moisture to air.

– As air comes into contact with the warm, moist tissue of the nasal passages, it is warmed and moistened. The sinuses also add moisture to the air.

– Your nose contains receptors for smell


– The pharynx (throat) connects the nasal cavity and mouth to the larynx (voice box).

– The tract provides a resonating chamber that gives your voice its characteristic tone

Other structures which enter or are located in the pharynx are:– 2 tear ducts which carry fluid away from the

eyes (this is why excess tears also make your nose runny)

– the esophagus--this makes it possible to breathe through your mouth.


– The 2 Eustachian tubes that drain the middle ear and equalize air pressure between the middle ear and outside air.

– Food• Below the throat, the air passage crosses in front of

the esophagus. This makes it possible for food or liquids to be accidentally sucked into the air passages and can cause us to cough or choke. These actions attempt to clear the food or liquid.


– Epiglottis-a flap of cartilage located in the back of the throat.

• During swallowing, the epiglottis forms a tight seal over the trachea so food can’t go down it.

– The Uvula-a flap of tissue in the back of the mouth that hangs from the roof of your mouth.

• This closes the upper air passages so food does not come out your nose. (This is also the part of the body that causes snoring when air passes over it.)


The lower respiratory tract includes– the larynx, trachea, 2 bronchi, 2 lungs

(including the bronchioles and alveoli)– the larynx or voice box is below the epiglottis

and pharynx and is protected by the thyroid cartilage (nicknamed the Adam’s apple).

– Functions of the larynx • maintains an open airway• route food and air into their appropriate tubes• assist in the production of sound


– The vocal cords consist of 2 folds of connective tissue that extend across the airway. The opening of this airway is called the glottis.• Vocal cords are supported by ligaments.

Sound is produced as we expel air past the stretched cords causing them to vibrate.


– The trachea (or windpipe) is a tube below the larynx and transports air on its way into the lungs. • It is about 4 1/2 inches long, • is composed of C-shaped rings of cartilage

(to ensure that it stays open), and carries air to the bronchi and through them to the lungs

• The trachea branches into airways which are called the right and left bronchi (sometimes called the primary bronchi). These further subdivide into smaller and smaller bronchi.


– The walls of the bronchi contain fibrous connective tissue and smooth muscle reinforced with cartilage. As the branches get smaller, the amount of cartilage declines. When they have no cartilage, their name changes into bronchioles.

– Surrounding the bronchi are the lungs. These fill the thoracic cavity and extend from the clavicles to the diaphragm (a thin sheet of muscle).

– Bronchioles lead to alveoli which are the air sacs of the lungs. Alveoli are composed of a single layer of flat, simple squamous cells and this is where gas exchange takes place.


• Breathing– Involves repetitive cycles of getting air into and

out of the lungs.– This requires muscular effort.– Since the lungs themselves do not have any

skeletal muscle tissue, expansion and contraction occurs because the surrounding bones and muscles expand the size of the chest cavity.


• Inspiration:– As the diaphragm contracts and flattens, the

external intercostal muscles contract and lift the ribcage. This causes a pressure drop in the thoracic cavity.

– The scalene and sternocleidomastoid (SCM) muscles also contract to help expand the thoracic cavity space.

– As the volume (space) in the thoracic cavity increases, air rushes in to fill this space.


• Other things that help inspiration:– The lungs and chest cavity are surrounded by a

membrane called “pleura”. There is fluid between the layers of the pleura (pleural cavity) so the lungs can stretch and contract with minimum friction.

• There is also a partial vacuum between the 2 pleural layers. This causes the lungs to stick to the chest wall as it expands.

• Alveolar surfactant, a chemical within the lungs, decreases the surface tension so the lung tissue doesn’t stick to itself.


• Expiration or Exhalation:– The diaphragm relaxes and intra-abdominal

pressure pushes the diaphragm up. The internal intercostal muscles and gravity help to drop the ribcage and thoracic cavity back to its smaller size. This increases pressure within the lungs and forces the air out of them.


Respiratory Volumes• Tidal volume is the amount of air an individual

normally inhales and exhales. • Our body's normal breathing strategy is to

ventilate the air sacs and also keep a minimal residual volume in the lungs. This allows us to keep some air for the blood passing through the lungs between breaths. This air is referred to as dead space volume.


• The amount of air that can be forcibly inhaled after a normal inspiration (tidal volume) is called inspiratory reserve volume.

• The amount of air that can be forcibly exhaled after a normal expiration (tidal volume) is called expiratory reserve volume.

• The vital capacity is the maximal volume that you can forcibly exhale after a maximal inhalation.

• After you forcibly exhale, there is always some air left in the lungs. This is called the residual volume.


• These lung capacities are measured with a spirometer.

• Gases are transported from the lungs to the body primarily by hemoglobin. They can also be dissolved in the plasma. In plasma, carbon dioxide dissolves and becomes carbonic acid or bicarbonate.


Gas Exchange and Transport: A Passive ProcessGases diffuse according to their partial pressures (pressure

exerted by 1 particular gas in a mixture of gases). No ATP is used.

• External respiration: gases exchanged between air and blood• partial pressure of O2 is higher in alveoli-- CO2 is

higher in the capillaries, so gases passively diffuse; – O2 carried to the blood and then to the body, CO2

exhaled

• Internal respiration: gases exchanged with tissue (interstitial) fluids/space

• partial pressure of O2 is lower in blood and CO2 is higher in the extracellular space, so gases passively diffuse;

– O2 goes into the cell, CO2 diffuses into capillaries


Gas Exchange and Transport: A Passive Process cont’d

• Oxygen transport: either bound to hemoglobin in red blood cells (primary method or dissolved in blood plasma – Forms oxyhemoglobin; depends on partial pressure of O2

(when P O2 rises, oxygen attaches to hemoglobin; when PO2 falls, oxygen detaches), temperature (likes lower

temperature) & pH (likes neutral pH)• Hemaglobin’s affinity for oxygen is decreased by

carbon monoxide

• Carbon dioxide transport: dissolved in blood plasma in the form of plasma bicarbonate (primary method by which CO2 is transported) or bound to hemoglobin– Carbaminohemoglobin, can dissolve into carbonic acid

or bicarbonate

Respiratory System BIO 006 19


Regulation of Breathing: Nervous System Involvement

The nervous system regulates the rate and depth of breathing in order to maintain homeostasis.

• The respiratory center in the medulla oblongata establishes basic breathing pattern including the rate at which we breathe.

Chemical receptors monitor carbon dioxide, hydrogen ions, and oxygen levels:

• The medulla is sensitive to hydrogen ions in cerebrospinal fluid as a result of more carbon dioxide in the blood.

• Carotid and aortic bodies in the blood are sensitive to carbon dioxide, pH, and oxygen levels

• Conscious control of breathing resides in higher brain centers (primarily the cortex)--ability to modify breath


Disorders of Respiratory SystemReduced air flow: • Asthma: chronic inflammatory disorder of the

airways characterized by inflammation, bronchial hyperresponsiveness and airflow obstruction– causes constriction of the bronchi, edema and increased

production of mucus with possible mucus plugs. • COPD-Chronic Obstructive Pulmonary Disease

– Emphysema is caused by damage to the alveoli due to damage in the connective tissue in the bronchioles. The airways tend to collapse and this causes increased pressure in the lungs which eventually damage the alveoli.

• Bronchitis is an inflammation of the bronchi which causes increased mucus which causes coughing.• Can be acute or chronic• Chronic bronchitis is considered a form of COPD



Infections: • Pneumonia is an infection which causes inflammation of

the lungs. The alveoli secrete excess fluid so gas exchange is impaired.

• Tuberculosis is a bacterial infection causing lung scars.• Botulism is a poisoning by bacterial toxin. The toxin

blocks the transmission of nerve signals to the respiratory muscles.

• Lung cancer• Congestive heart failure impairs lung functioning.• Cystic fibrosis is an inherited condition which causes

mucus producing cells in the lungs to produce a very thick, sticky mucus which causes frequent infections. Other organs of the body are also involved.

The Respiratory System rev 11-11

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