Respiration- 3 separate but related functions

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Respiration- 3 separate but related functions

Ventilation or breathing- uses diaphragm & internal/external intercostals muscles

Gas exchange- between air/blood in lungs and between blood/tissues of body

Oxygen utilization- tissues use oxygen during cellular respiration

External respiration- ventilation/exchange of gases in lungs

Internal respiration- exchange of gases at tissues; cells need oxygen & get rid of carbon dioxide

Adults breathe about 15 times/min moving about 6 L of air

In strenuous exercise the rate increases to 100 times/min

Without breathing 4-5 min you lose consciousness; 7-8 min there is brain damage & more than 10 min means death


Upper respiratory system

Nose, pharynx, & associated structures

Lower respiratory system

Larynx, trachea, bronchial tree, pulmonary alveoli & lungs

Functionally system is divided into 2 parts

Conducting division- all cavities/structures to transport gases to/from pulmonary alveoli

Respiratory division- pulmonary alveoli

Nose External nose

Made of cartilage & supported by nasal bones

Nasal cavity

Septal cartilage forms nasal septum along with vomer/ethmoid bones

2 halves or nasal fossa formed with the nasal vestibule found behind the nostril

Roof of nasal cavity formed by frontal, nasal, ethmoid & sphenoid bones

Floor made of palatine/maxillary bones

Turbinate or nasal conchae form lateral walls & passageway between conchae are called nasal meatuses

Jobs: warms, moistens & cleanses air (ciliated mucous lining)


Resonating chamber for voice

Paranasal sinuses

Found in & named for the maxillary, frontal, sphenoid, & ethmoid bones

Connected to nasal cavity by drainage ducts

Helps to warm/moisten air as well as some resonating function

Reduces weight of skull


Funnel shaped passageway between nasal/oral cavities

Nasopharynx- top portion that is only passageway for air

Uvula closes off this area when swallowing

Auditory or Eustachian tubes connect from here to middle ear

Adenoids found here

Oropharynx- middle between soft palate & level of hyoid bone

Used for both food & air

2 pairs of tonsils found here

Laryngopharynx- lowest part that extends below level of hyoid bone

Opens into esophagus & larynx
Larynx Positioned in anterior midline of neck at level of 4-6 cervical vertebrae

Two jobs- keeps food/fluid from entering trachea & produces sound

Made of cartilage structures

Laryngeal prominence (Adam’s apple)- on anterior side of thyroid cartilage

Male sex hormone makes it more prominent in males than females

Epiglottis- hyaline cartilage behind base of tongue

Closes off larynx during swallowing so it routes food/air where they should go

Cricoid cartilage- ring at lower end of larynx

Aretenoid cartilages- above cricoids & are the back attachments of vocal cords

Muscles in larynx

Extrinsic- responsible for elevating larynx during swallowing

Intrinsic- change length, position & tension of vocal cords

Vocal cords

2 pair of strong connective tissue bands stretched across upper opening of larynx

Connected to aretenoid/thyroid cartilages

True vocal cords- vibrate to produce sound

Ventricular folds- support true cords; males have thicker/longer folds so they vibrate slower & have lower pitches

Trachea (windpipe)

Rigid tube 4”x1” going from larynx to bronchi

C shaped hyaline cartilage “rings” form supporting walls & ensure airway stays open

Lining has pseudostratified ciliated columnar epithelial to sweep particles our of air passage

Goblet cells also present

Bronchial tree

Composed of respiratory tubes that branch into smaller/smaller tubes going to the lungs

Trachea branches into principle bronchi which branch into secondary bronchi & then tertiary Bronchioles- smaller tubules with little cartilage; lined with simple cuboidal epithelial; continues to branch into smaller tubes that end in alveolar sacs

Pulmonary alveoli

Functional units of respiratory system

350 million/lung

Provides large surface area for gas exchange

Walls are 1 cell layer thick (0.5-1 micrometer)

Sac structure surrounded by capillaries

Moistened by surfactant for ease of exchange of gases by diffusion

Lungs Large spongy paired organs

Extend from clavicle to diaphragm

Enclosed by ribs

Left lung is slightly smaller & has cardiac impression

Left has 2 lobes (superior/inferior) Right has 3 lobes(superior, middle, inferior)

Pleura Epithelial membranes surrounding lungs & lining thoracic cavity

Separates thoracic viscera

Protects/lubricates lungs, secretes serous fluid & help form a pressure chamber for breathing

Visceral pleura- adheres to outer surface & extends in between lobes

Parietal pleura- lines thoracic walls & surface of diaphragm

Pleural cavity- very small cavity between visceral/parietal membranes; contains liquid to lubricate; pleuras stuck together by fluid

Respiratory system designed for gas exchange

Functions of respiratory system

Provides tissue with oxygen that is needed for metabolic processes that fuel body’s activities

Provides for excretion of waste carbon dioxide produced during metabolism

Movements of the respiratory muscles necessary for oral communication

Breathing- mechanical process of taking air into lungs & expelling carbon dioxide

Respiration- exchange of gases between living organism & its environment

External respiration- involves exchange of gases between atmosphere/blood; occurs in lungs

Internal respiration- exchange of gases that takes place between blood/cells; occurs in capillaries of body

How do we breathe?

As long as nasal passages aren’t blocked, pressure equilibrium is maintained between environment & lungs

Inspiration- act of taking air into lungs

When atmospheric pressure is higher than lung pressure, air is pushed into lungs

Diaphragm/intercostals muscles contract to enlarge the thoracic cavity around lungs (both top to bottom & front to back); larger volume means less pressure in lungs & so air flows into lungs to equalize pressure; these muscles are stimulated by phrenic/intercostals nerves; diaphragm moves about 15 mm down

The inward movement of air does not inflate lungs like a balloon but rather the expansion of the lungs causes the air to rush in

Those who take voice lessons sing with hand at base of rib cage to be sure that they fully expand (open up) their lungs

Expiration- act of expelling air from lungs

When atmospheric pressure is lower than lung pressure, air leaves the lungs

Diaphragm/intercostals muscles relax, size of thoracic cavity decreases all the way around so air pressure inside is greater than outside & air flows out of lungs to equalize pressure

How much air are you moving?

Total lung capacity- 5-6 L (volume that both lungs hold)

Tidal volume- volume of air moved in/out of respiratory passage during normal breathing

About 0.5 L

Inspiratory reserve volume- volume of air that can be inhaled by deepest possible inspiration in excess of tidal; above tidal volume

About 3 L

Expiratory reserve volume- volume of air that can be exhaled by deepest possible expiration in excess of tidal

About 1.2 L

Vital capacity- volume of air that can be exhaled by deepest possible expiration after deepest possible inspiration; inhale/exhale with greatest possible effort

Residual air- amount of air remaining in lungs after deepest possible expiration

About 1.2 L

Eliminated only by collapse of lung

Minimal air- air remaining in lungs after lungs have collapsed

Blood gases

Diffusion of gases occurs from area of high concentration to area of low concentration

A difference in the amount of oxygen present in alveoli & the amount of oxygen present in blood of pulmonary vessel causes oxygen to diffuse from alveoli to blood (concentration gradient of gases)

Oxygen is carried by RBC as well as blood plasma- each hemoglobin molecule can carry 8 oxygen atoms

At the body tissues there is again a difference in the amount of oxygen present there as compared to the bloodstream so oxygen diffuses into the tissues

Carbon dioxide diffuses from tissue cells into bloodstream

In blood, carbon dioxide

7% stays in gaseous form & dissolves in plasma

20% binds to the hemoglobin to be carried

73% is carried in blood in form of bicarbonate ions in plasma

At lungs, carbon dioxide diffuses from the blood into the alveoli

People breathe at rate of 16-24 cycles/min but it can be altered voluntarily

Breathing is controlled by nerves (phrenic/intercostals) as well as chemically

Respiratory musculature is stimulated by nerves regulated by respiratory centers in brain stem

In medulla oblongata are inspiratory/expiratory centers that stimulate the phrenic/intercostals nerves; rhythmicity center helps to control breathing

Cyclical activity of inspiratory center is all that is needed to sustain resting breathing (most of the lung volume changes now attributed to movements of diaphragm)

Expiratory center becomes active when the body’s activity level increases & passive expiration is not rapid or deep enough; now intercostals nerves are added to stimulate intercostals muscles ot move

Breathing also influenced by apneustic center & pneumotaxic center of pons

Apneustic center prolongs inspiration (taking a deep breath)

Pneumotaxic center has an inhibitory effect on inspiration (holding your breath)

Respiration is chemically controlled by carbon dioxide in blood

An increase in carbon dioxide stimulates respiratory center; this is most powerful stimulus

Chemical regulation is responsible for maintaining breathing at day/night without conscious thought

Chemoreceptors in medulla oblongata are stimulated by changes in hydrogen ion level & as pH of blood/cerebrospinal fluid drops there is an increase in respiratory rate

Other chemoreceptors are found in aortic arch & carotid arteries which respond to changes in oxygen/carbon dioxide levels in blood

Some Disorders of Respiratory System

Cystic fibrosis

Most common lethal inherited disease affecting Caucasians (1 birth in 2500)

Gene defect on chromosome 7

Seldom survive past age 30 & death usually due to bacterial infection of lungs & heart failure

Symptoms: thick gooey secretions from mucus glands of respiratory tract, pancreas, salivary glands & digestive tract

Treatment: usually symptoms are treated with supportive care & antibiotic therapy but there is no cure


Affects 2-6% of US population Exhalation affected more than inhalation

Symptoms: constriction of smooth muscles along bronchial tree, edema, swelling of mucus pathways, accelerated production of mucus, inflammation

Treatments: treated with use of bronchiodilators during attacks, glucocorticoids that inhibit inflammation, epinephrine promotes bronchodilation


Airborne pathogens spread by coughing, sneezing or speaking

Infects 8-10 million worldwide annually

As disease progresses, masses of fibrous tissue distort conduction pathways which increases resistance & decreases air flow; also in alveoli surface area for gas exchange is reduced

Treatment difficult but includes use of drugs but bacteria can become antibiotic resistant easily

Twice as common among blacks as whites


Inflammation of bronchial lining which leads to overproduction of mucus & frequent coughing Can be caused by smoking or environmental irritants


Chronic progressive condition characterized by shortness of breath & inability to tolerate physical exertion

Due to destruction of alveoli by inhaling particles/vapors

Alveoli break down & this increases the size of the air spaces & decreases surface area

Reduces ability of bronchioles to stay open during expiration

All smokers will develop at least some emphysema by age 35-40

Permanent/irreversible but can be slowed if smoking is stopped

Sleep apnea- stopping breathing while asleep

Acute respiratory distress syndrome

Reduced surfactant due to accumulation of protein-rich fluid in lungs

May occur when person has systemic infection that leads to septic shock

Blood leaving lungs has normally low oxygen concentration

COPD (chronic obstructive pulmonary disease)

5th leading cause of death in US

Chronic inflammation with narrowing of airways & destruction of alveoli

Most patients are smokers & stopping smoking does not stop progression of disease

May develop pneumonia, traveling blood clots or heart failure

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