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
ANATOMY
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)
Smell
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
Pharynx
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
PHYSIOLOGY
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
Asthma
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
Tuberculosis
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
Bronchitis
Inflammation of bronchial lining which leads to overproduction of mucus & frequent coughing
Can be caused by smoking or environmental irritants
Emphysema
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