The Respiratory System: Functions, Processes, and Structures, Study notes of Voice

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THE RESPIRATORY SYSTEM

COMPILED BY HOWIE BAUM

Through breathing,

inhalation and exhalation,

the respiratory system

facilitates the exchange of

gases between the air and

the blood and between

the blood and the body’s

cells.

The respiratory system

also helps us to smell

things and create sound.

The following are the five

key functions of the

respiratory system.

Inside the lungs, oxygen is

exchanged for carbon dioxide waste

through the process called external

respiration.

This respiratory process takes place

through hundreds of millions of

microscopic sacs called alveoli.

Oxygen from inhaled air diffuses

from the alveoli into pulmonary

capillaries surrounding them.

It binds to hemoglobin molecules in

red blood cells and is pumped

through the bloodstream.

Meanwhile, carbon dioxide from

deoxygenated blood diffuses from

the capillaries into the alveoli and is

expelled through exhalation.

The bloodstream delivers oxygen to cells and removes waste carbon dioxide through internal respiration, another key function of the respiratory system.

In this respiratory process, red blood cells carry oxygen absorbed from the lungs around the body, through the vasculature.

When oxygenated blood reaches the narrow capillaries, the red blood cells release the oxygen.

It diffuses through the capillary walls into body tissues. Meanwhile, carbon dioxide diffuses from the tissues into red blood cells and plasma.

The deoxygenated blood carries the carbon dioxide back to the lungs for release.

OLFACTION (SMELLING)

The nasal cavities are chambers of the internal nose.

In front, the nostrils, or nares, create openings to the outside world.

Air is inhaled through the nostrils and warmed as it moves further into the nasal cavities. Scroll-shaped bones, the nasal conchae, protrude and form spaces through which the air passes.

The conchae swirl the air around to allow the air time to humidify, warm, and be cleaned before it enters the lungs.

Epithelial cilia (commonly called “nose hair”) and a mucous membrane line the inside of the cavities.

The cilia, along with mucus produced by seromucous and other glands in the membrane, trap unwanted particles.

Finally the filtered, warmed air passes out of the back of the nasal cavities into the nasopharynx, the uppermost part of the pharynx.

The paranasal sinuses are four paired, air-filled cavities found inside bones of the skull.

These sinuses are named for the skull bones that contain them:

Frontal

Ethmoidal

Sphenoidal

Maxillary

Mucosae line the paranasal sinuses and help to warm and humidify the air we inhale.

When air enters the sinuses from the nasal cavities, mucus formed by the muscosae drains into the nasal cavities.

The larynx connects the lower part of the pharynx, the laryngopharynx, to the trachea.

It keeps the air passages open during breathing and digestion and is the key organ for producing sound.

This larynx is comprised of nine cartilages.

One, the epiglottis, is a lifesaver: Located on the posterior side of the larynx, the epiglottis closes like a trap door as we swallow.

This action steers food down the esophagus and away from the windpipe.

Inside the larynx are the vocal folds (or true vocal cords), which have elastic ligaments at their core.

When we speak, yell, or sing, air coming up from the lungs and trachea vibrates the

folds, producing the sound.

Phonation is the creation of sound by structures in the upper respiratory tract of the respiratory system.

During exhalation, air passes from the lungs through the larynx, or “voice box.”

When we speak, muscles in the larynx move the arytenoid cartilages.

The arytenoid cartilages push the vocal cords, or vocal folds, together.

When the cords are pushed together, air passing between them makes them vibrate, creating sound.

Greater tension in the vocal cords creates more rapid vibrations and higher-pitched sounds.

Lesser tension causes slower vibration and a lower pitch.

The process of olfaction begins with

olfactory fibers that line the nasal

cavities inside the nose.

As air enters the cavities, some

chemicals in the air bind to and

activate nervous system receptors on

the cilia.

This stimulus sends a signal to the

brain: neurons take the signal from the

nasal cavities through openings in the

ethmoid bone, and then to the

olfactory bulbs.

The signal then travels from the

olfactory bulbs, along cranial nerve 1,

to the olfactory area of the cerebral

cortex

The respiratory system, in close

conjunction with the circulatory

system, is responsible for supplying

all body cells with essential oxygen

and removing potentially harmful

carbon dioxide from the body.

The mouth and nose channel air from

outside the body through a system of

tubes of diminishing size that

eventually reach the two lungs

situated on either side of the heart

within the chest cavity.

Bronchial cast

By filling a lung’s airways with

a resin that hardens, a cast

such as this can be made of

the bronchial tree.

Each color indicates an

individual bronchopulmonary

segment aerated by a tertiary,

or segmental, bronchus.

ALVEOLI - The lungs’ microscopic air sacs,

alveoli, are elastic, thin-walled structures arranged in clumps at the ends of respiratory bronchioles.

They resemble bunches of grapes, although the alveoli are partly merged with each other.

White blood cells known as macrophages are always present on their inner surfaces, where they ingest and destroy airborne irritants such as bacteria, chemicals, and dust.

Around the alveoli are networks of capillaries. Oxygen passes from the air in the alveoli into the blood by diffusion through the alveolar and capillary walls

Carbon dioxide diffuses from blood into the alveoli. There are more than 300 million alveoli in both lungs, providing a huge surface area for gas exchange – about 40 times greater than the body’s outer surface.

Without surfactant

Molecules in the watery fluid lining

attract and cohere to each other, making

the alveolar wall pull inwards and

collapse.

With surfactant

Molecules of surfactant flow between

the fluid molecules and reduce their

cohesive forces, allowing the alveoli to

stay inflated.

Cellular respiration

Glucose (blood sugar) is the body’s main energy source.

Cellular respiration occurs in every body cell when oxygen reacts with glucose to free its energy in chemical form.

The end products are carbon dioxide and water, which is known as metabolic water and amounts to about 300ml (10fl oz) daily throughout the body.

The whole process is called aerobic (oxygen-requiring) cellular, or internal, respiration.