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BIOLOGY 206: THE RESPIRATORY SYSTEM; LAUREL: SPRING 2007
I.
II.
Introduction
A.
Functions
1.
obtain oxygen and release carbon dioxide
2.
Filter, moisten and warm incoming air
3.
Produce sounds
4.
Play role in sense of smell
5.
Role in regulation of body pH
B.
Terms
1.
Pulmonary ventilation/breathing = movement of air in and out of lungs
2.
External respiration = gas exchange between pulmonary capillaries and
alveoli of lungs
3.
Internal respiration = gas exchange between systemic capillaries and
tissue cells
4.
Cellular respiration = metabolic process in the mitochondria of cells to
produce ATP.
a.
Aerobic respiration requires oxygen and produces 38 ATPs, water
and carbon dioxide.
b.
Anaerobic respiration does not require oxygen and only produces
2 ATPs/glucose as well as lactic acid
Anatomy of the Respiratory system
A.
Zones
1.
Respiratory zone involves areas where gas exchange occurs
2.
Conducting zone includes all the passageways to get air to the respiratory
zone
3.
More details later
B.
Nose and nasal cavity
1.
Nose = External part supported by nasal, frontal, and maxillary bones as
well as hyaline cartilage.
2.
Nostrils/external nares provide entrance to nasal cavity
3.
Nasal cavity = hollow space behind external nose
4.
Nasal septum divides nose medially
a.
vomer, perpendicular plate of ethmoid, and hyaline cartilage
5.
Hard palate (palatine process of maxilla & horizontal plates of palatine)
& soft palate form the floor of the nasal cavity
6.
Mucous membrane lines nose.
a.
Respiratory mucosa filters, warms, and moistens incoming air
b.
Particles trapped in mucus are carried to pharynx and swallowed or
removed by sneezing/coughing
c.
Secrete lysozymes and defensins to combat microorganisms
d.
Olfactory mucosa on superior aspect contain olfactory receptors
7.
Conducts air to pharynx and separated from pharynx by posterior nasal
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aperture
C.
D.
E.
F.
Paranasal Sinuses
1.
Space in the bones of the skull that open into the nasal cavity
a.
Frontal, ethmoid, sphenoid, and maxillary bones
2.
Lined with mucous membrane that is continuous with lining of nasal
cavity
3.
Reduce the weight of skull and serve as resonant chambers
Pharynx (throat)
1.
Located behind nose and mouth and is between nasal cavity and larynx
2.
Functions as a common passage for air and food and aids in sounds of
speech
3.
Composed of skeletal muscle and has 3 subdivisions:
4.
Nasopharynx is area behind nose - down to uvula
a.
Uvula hangs off soft palate and closes nasopharynx during
swallowing
b.
Holds adenoids /pharyngeal tonsils
c.
Contains openings for auditory/eustachian tubes into middle ear
5.
Oropharynx is area behind mouth from uvula to epiglottis
a.
holds palatine and lingual tonsils
b.
Fauces is archway from oral cavity into pharynx
6.
Laryngopharynx extends behind epiglottis to esophagus
Larynx (voice box)
1.
Enlargement at the top of the trachea & attached superiorly to hyoid
2.
Serves as a passageway for air and helps prevent foreign objects from
entering trachea
3.
Composed of cartilage and smooth muscle. Three major cartilages:
a.
Thyroid cartilage with Adam's apple as its midsagittal ridge
b.
Cricoid cartilage is smaller one under thyroid
c.
Epiglottis = covers opening of larynx during swallowing
4.
Contains vocal ligaments of elastic fiber
a.
False cords (vestibular folds) are superior to true and don't
function in sound production
b.
True cords are inferior to false and produce sounds by vibrating as
air passes over them
c.
Increased tension --> increased pitch; increased force of air over
cords --> increased intensity of sound
5.
Glottis = opening between true vocal cords
6.
Laryngitis is inflammation of the vocal cords
Trachea (windpipe)
1.
Extends into thoracic cavity ventrally to esophagus
a.
Approximately 4-5 inches (10-12 cm) long
b.
1 inch (2.5 cm) in diameter
2.
Extends from larynx into mediastinum and divides at carina into right and
2
G.
H.
I.
left primary bronchi.
3.
Composed of c-shaped cartilaginous rings separated by smooth muscle
4.
Mucous lining warms, filters, and moistens air
a.
Smoking inhibits action of cilia and inhibits removal of debris for
swallowing
Bronchial tree: The Conducting Zone
1.
Consists of branched air passages, each successively smaller that lead from
the trachea to the respiratory zone
a.
functions to distribute air to all parts of the lungs
2.
Primary bronchi are extra-pulmonary (outside of lung) and enter lung at
its hilus.
a.
Right bronchus is shorter, wider, and steeper
3.
Primary bronchi branch into secondary bronchi that lead into discrete
lobes of the lung.
4.
Secondary branch into tertiary bronchi which branch into tiny
bronchioles which are entirely lacking in cartilage
5.
The smallest bronchioles are terminal bronchioles
6.
Composition of bronchi mimics trachea but as one descends:
a.
Cartilage support decreases to zero
b.
Epithelium changes from pseudostratified ciliated columnar
epithelium to simple cuboidal
c.
Amount of smooth muscle increases
7.
Review of passageway:
Primary Bronchi  secondary bronchi tertiary bronchi 
bronchioles  terminal bronchioles.
The Bronchial Tree: The Respiratory Zone
1.
Respiratory zone begins where Terminal bronchioles  respiratory
bronchioles (have some out-pockets where gas exchange occurs) 
alveolar ducts  alveoli which are surrounded by capillary beds
2.
Alveoli are functional units of lung.
3.
Clusters of alveoli at end of alveolar ducts are called alveolar sacs
4.
300,000,000 alveoli in lungs with 70 sq. meters of internal respiratory
surface!
a.
Size of a tennis court!
Respiratory membrane
1.
= alveolar-capillary membrane
2.
= area across which gases are exchanged by simple diffusion
3.
Consists of:
a.
Simple squamous epithelium and basement membrane of alveoli
b.
Interstitial fluid
c.
Simple squamous epithelium and basement membrane of
pulmonary capillary
4.
Membrane is moistened by surfactant secreted by alveolar cells inside the
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alveoli which enhances exchange by reducing surface tension of fluids
lining alveoli
Dust cells or alveolar macrophages consume microorganisms
III.
5.
J.
Lungs
1.
Each lung is within one pleural cavity of the thoracic cavity separated by
the mediastinum
2.
Primarily composed of air spaces and elastic connective tissue
3.
Apex: superior pointed surface of lung
4.
Base: broad inferior surface of lung that rests on diaphragm.
5.
Hilus is medial indentation where vessels and bronchi enter and leave
lungs
6.
Right lung has 3 lobes (superior, middle and inferior), the left lung 2
(superior/inferior)
a.
Each lobe divided into bronchopulmonary segments and lobules
b.
These divisions help contain disease
7.
Recall vascular pattern of deoxygenated pulmonary arteries entering
lung, pulmonary capillaries around alveoli and oxygenated pulmonary
veins exiting lungs
8.
Each pleural cavity is lined by a serous membrane (no exit to outside)
called the pleura which has 2 components:
a.
parietal pleura lies on thoracic walls, diaphragm and lateral walls
of mediastinum
b.
Visceral pleura lies on outside of lungs
9.
Pleural cavity (intrapleural space) is potential space between 2 pleura and
is filled with pleural fluid
a.
Lubricant so membranes slide by each other
b.
At same time prevents them from separating from each other and
creates a slight vacuum. Important in breathing.
10.
Pleurisy is inflammation of the pleura.
a.
Caused by infection (bronchial pneumonia) or injury
b.
Coughing, shallow breathing, fever, chills, and pain.
c.
Often a complication of another pulmonary disease.
Mechanics of breathing
A.
Terms
1.
Inspiration/inhalation = period of time air is rushing into lungs
2.
Expiration/exhalation = period of time air is rushing out of lungs.
B.
Relationships in Thoracic Cavity
1.
Atmospheric pressure at sea level = 760 mm Hg = supports a column of
Hg to that height (Patm)
a.
A negative pressure, e.g., -4 mm Hg, indicates a pressure 4 mm
less than 760 and vice versa for positive pressure
2.
Intrapulmonary pressure is pressure in alveoli. It rises and falls with
breathing, but it always eventually equalizes with atmospheric pressure
4
IV.
because it is continuous with the atmosphere.
3.
Intrapleural pressure: pressure between visceral and parietal pleura.
a.
Fluctuates with breathing but always 4 mm less than alveoli
4.
Intrapleural pressure is created by opposing forces:
a.
Elasticity of alveoli causes them to recoil
b.
Surface tension of alveolar fluid pulls alveoli in
c.
Elasticity of chest wall pulls out to enlarge lung
5.
Volume changes  Pressure changes  flow of gases to equalize pressure
6.
Recall the inverse relationship between volume and pressure:
a.
Increase in volume  decreased pressure
b.
Decrease in volume  increased pressure
C.
Inspiration
1.
Diaphragm contracts and flattens and external intercostals contact and
raise ribs
a.
Both action  increase in size of thoracic cavity
b.
Surface tension holds parietal and visceral pleura together, so lungs
also expand
c.
Expansion produces a decreased intrapleural pressure (754 or -6)
and decreased intrapulmonary pressure (758 or -2) relative to
atmospheric pressure
2.
Result = air rushes into lungs from atmosphere: greater pressure to lesser
pressure.
3.
Sequence of events in inspiration:
a.
Diaphragm and external intercostals contract.
b.
Intrapleural volume increases and intrapleural pressure decreases.
c.
Intrapulmonary volume increases and intrapulmonary pressure
decreases.
d.
Now intrapulmonary pressure is < atmospheric pressure so air
rushes into lungs and inhalation occurs.
D.
Expiration
1.
Quiet expiration is passive: Inspiratory muscles relax  decreased
intrapleural volume  increased intrapleural pressure lungs recoil 
decreased intrapulmonary volume  increased intrapulmonary pressure 
air moves out of lungs (> to < pressure).
2.
Forced expiration is an active process involving contraction of internal
intercostals, latissimus dorsi, abdominal muscles etc. to greatly decrease
size of thoracic cavity
Physical Factors Influences Pulmonary Ventilation
A.
Airway Resistance
1.
Decreased bronchi diameter  increased resistance to airflow
2.
Bronchial asthma
a.
may result from an allergic reaction accompanied by a reduction in
the diameters of the bronchioles, increased mucus secretion, and
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V.
inflammation. Breathing is difficult and wheezing is present.
B.
Alveolar Surface Tension
1.
At gas-liquid boundary, liquid molecules attracted more to each other than
the gas and creates surface tension such that alveoli tend toward collapse
and resists stretching in inhalation.
2.
The surfactant produced by alveoli reduces this tension and reduces the
energy required to stretch such that only use 1-2% of total body energy to
breathe when resting. (3-5 for heavy work).
C.
Compliance
1.
refers to lung distensibility
2.
diminished by disease and scar tissue, mucus, decreased surfactant and
decreased ability of the thorax to expand.
Alveolar Gas Exchanges
A.
Gas laws
1.
Total pressure exerted by a mixture of gases is the sum of the individual
pressures
2.
Partial pressure = pressure exerted by an individual gas and is equal to its
percentage in the total gas mixture
3.
One can determine partial pressure of gas by multiplying the % present X
760 mm Hg.
4.
When a mixture of gases is in contact with a liquid, each gas will dissolve
in the liquid in proportion to its partial pressure and its solubility in the
liquid
5.
Solubility of any gas in water increases with increasing partial pressure
and decreases with increasing temperature of water
B.
External respiration (gas exchange between alveoli and pulmonary capillaries)
1.
PO2 in alveoli = 104 mm Hg
PO2 in pulmonary capillaries before gas exchange is 40 mm Hg
a.
O2 moves out of lungs and into capillaries until equilibrium is
reached in capillaries at 104 mm Hg.
b.
Equilibrium is reached in 0.25 sec and RBCs stays in capillary
exchange area for 0.75 sec.
2.
PCO2 in pulmonary capillaries before exchange is 45 mm Hg
PCO2 in alveoli is 40 mm Hg
a.
CO2 moves out of capillaries into lungs until equilibrium is
reached and capillaries are at 40 mm Hg
b.
gradient is lower with CO2 and still reaches equilibrium because
CO2 is 20 X more soluble than O2 in plasma
3.
Arterial blood therefore has PO2 of 104 mm Hg and PCO2 of 40 mm Hg
C.
Internal respiration (gas exchange between systemic capillaries and body cells)
1.
Tissues continually use up O2 to produce ATP and produce CO2 as a by
product such that:
a.
Tissue PO2 = 40 mm Hg or less
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b.
Tissue PCO2 = 45 mm Hg or more
3.
Results are that
a.
oxygen diffuses into tissues from greater (104) to lesser (40)
until equilibrium is reached and
b.
CO2 diffuses into capillaries from greater (PCO2 45) to lesser
(PCO240) until equilibrium is reached
3.
Consequently venous blood has PO2 of 40 mm Hg and PCO2 of 45 mm Hg
VII. Transportation of respiratory gases
A.
Oxygen transport
1.
Carried
a.
Bound to Hb as oxyhemoglobin (98.5%).
b.
Dissolved in plasma (1.5%)
2.
Amount dissolved in plasma determines the PO2
a.
O2 on Hb has no affect on PO2 as it has been pulled out of solution
3.
When O2 is removed from plasma and attached to Hb:
a.
Process is called loading
b.
PO2 drops because amount dissolved O2 in plasma decreases
4.
When O2 is removed from Hb:
a.
Process is called unloading
b.
PO2 increases because dissolved O2 in plasma increases
5.
Loading occurs at external respiration
a.
PO2 in alveoli = 104 and PO2 in capillaries is 40
b.
O2 diffused into plasma and increases PO2, but as PO2 rises O2 is
loaded onto Hb and PO2 drops. Therefore more O2 diffuses into
plasma and process repeats itself until Hb is saturated.
6.
Unloading occurs at internal respiration
a.
PO2 in tissues is 40 mm Hg and PO2 in capillaries is 104 mm Hg
b.
O2 diffuses into tissues, PO2 drops and HbO2 unloads O2 to raise
PO2 again and procedure repeats itself.
B.
Hypoxia
1.
= state of inadequate amount of O2
2.
In CO poisoning CO out competes O2 for heme binding sites
a.
affinity 200 X > than O2s, so effective at very low PCO
b.
= silent killer
c.
treated with 100% O2 until all CO removed
C.
CO2 transportation
1.
10% dissolved in plasma.
2.
20% bound to Hb as carbaminohemoglobin (HbCO2)
a.
Binds to globin part of Hb and does not compete with O2 which
binds to Fe.
b.
Loading and unloading influenced primarily by PCO2
3.
70% transported as bicarbonate.
a.
CO2 + H2O  H2CO3 (carbonic acid)  H+ + HCO37
VIII.
(bicarbonate)
b.
Most of this occurs within RBC because RBC contains enzyme
carbonic anhydrase that catalyzes the formation of carbonic acid
4.
Step 1: CO2 diffuses into the plasma then in the RBC.
5.
Step 2: Carbonic anhydrase catalyzes the formation of H+ and bicarbonate
ion.
a.
H+ cannot remain as a free ion because it will lower the pH of the
blood.
b.
However, once H+ is attached to another molecule, it can no longer
effect the pH.
6.
Step 3: H+ kicks the K+ off the Hb- and joins with the Hb-.
a.
Now it can no longer effect the blood pH.
7.
The salt Na+Cl- is abundant in the plasma.
8.
Step 4: In a process called the chloride shift, the Cl- diffused into the
RBC and the bicarbonate diffuses into the plasma.
a.
The bicarbonate joins with the Na+ in the plasma to form sodium
bicarbonate and
b.
the K+ joins with the Cl- to form the salt potassium chloride
(K+Cl-).
9.
Reverse reaction occurs in pulmonary capillaries.
D.
Carbonic Acid-bicarbonate buffer system
1.
Bicarbonate produced in the way mentioned above forms an important part
of the carbonic acid-bicarbonate buffer system
2.
If H+ concentration rises, it can be removed by the HCO3- to form
carbonic acid, and if the H+ concentration drops, the carbonic acid
dissociates to release H+.
3.
Respiratory rates play a major, fast-acting role in acid-base balance
a.
Slow, shallow breathing  increased CO2 in blood  increased
HCO3- and decreased pH.
b.
Rapid, deep breathing removes CO2 by decreasing H2CO3 and
increasing pH
Acidisos and Alkalosis
A.
Overview
1.
Recall blood’s pH range is 7.35 to 7.45
2.
Any value below 7.35 (excess H+) creates a condition known as acidosis
3.
Any value above 7.45 (loss of H+) creates a condition known as alkalosis
4.
How can a condition be called acidosis if the pH is not below 7?
B.
Respiratory Acidosis
1.
Occurs as a result of problem with the respiratory system
2.
P CO 2 becomes greater than 45
3.
Common in pneumonia, cystic fibrosis and emphysema
C.
Metabolic Acidosis
1.
Acidic conditions in blood caused by anything other than a problem with
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IX.
X.
the respiratory system.
2.
Too much alcohol which is metabolized to acetic acid which lowers the
pH
3.
Excess loss of bicarbonate ion as in diarrhea
4.
High levels of lactic acid from overexertion
5.
Increase in ketones which come from the metabolism of fats
a)
Starvation
b)
Diabetic crisis (lack of insulin)
D.
Respiratory Alkalosis
1.
Cause by difficulty somewhere in the respiratory system
2.
PCO2 becomes less than 35 mm Hg
3.
Primary cause is hyperventilation
4.
This condition is not usually caused by a pathological condidtion as in
respiratory acidosis
E.
Metabolic Alkalosis
1.
Any cause other than the respiratory system which produces a situation of
too high a H+ concentration
2.
Less common than metabolic acidosis
3.
Vomiting: lose H+ from stomach and then stomach pulls H+ out of blood
to maintain the stomach’s pH
4.
Excess consumption of antacids
5.
Constipation: excess absorption of bicarbonate, so there is too much
buffer in the blood stream and the pH rises
Control of breathing
A.
Medullary Respiratory Centers
1.
Ventral respiratory group (VRG)
a.
rhythm-generating and integrative center
b.
some neurons fire to create inspiration via the phrenic and
intercostals nerves to excite the diaphragm and external
intercostals muscles.
c.
others fire to produce exhalation which stops inhalation and results
in a passive exhalation
d.
Produces a rhythm of 12-15 breaths per minute. This normal
breathing is called eupnea
2.
Dorsal respiratory group (DRG) used to be thought of as the inspiration
center, but no longer.
a.
integrates input from peripheral stretch and chemoreceptors, and
communicates this information to the VRG
B.
Pontine Respiratory Centers
1.
smooths out the transitions from inspiration to expiration and vice versa.
2.
modifies breathing rhythms during activities such as vocalization, sleep
and exercise.
Factors affecting rate and depth of breathing
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A.
B.
C.
D.
E.
F.
Overview
1.
Increased # motor units stimulated  stronger contractions and increased
depth of respiration and vice versa
2.
Rate determined by how long the I.C. is active or how quickly it is shut
off.
Pulmonary Irritant Reflexes
1.
Variety of irritants stimulate vagus nervecough/sneeze
Inflation Reflex
1.
Stretch receptors (baroreceptors) in lungs are stimulated when lungs are
stretched vigorously.
2.
Receptors send inhibiting impulses via the vagus nerve to the medullary
respiratory centers to promote exhalation
a.
Action potentials no longer sent down intercostal and phrenic
nerves and corresponding muscles relax.
b.
Protective, not involved in normal breathing
Hypothalamic controls
1.
Strong emotions and pain acting through the limbic system activate
sympathetic centers in hypothalamus which influences Respiratory centers
2.
Laughing, crying, gasping when touch cold/clammy.
Cortical Controls
1.
We can exert conscious control over breathing
2.
However, medulla takes over when CO2 levels become critical
a.
why drowning victims have water in their lungs
Chemical factors
1.
Changing levels of O2, CO2 and H+ in arterial blood have strongest effect
on the respiratory centers.
3.
Measured by
a.
Central chemoreceptors in medulla and
b.
peripheral chemoreceptors large neck vessels.
2.
PCO2 has strongest effect
a.
Peripheral chemoreceptors only weakly sensitive to PCO2.
b.
Primary effect is on cerebrospinal fluid surrounding brain stem.
c.
CO2 + H2O H2CO3 H+ + HCO3d.
CSF lacks proteins to buffer H+, so when hypercapnia occurs
(increased CO2 levels) decreased pH of CSF  excites central
chemoreceptors increased depth (and rate) of breathing =
hyperventilation which removes excess CO2 and increased blood
pH.
c.
Increased PCO2 of only 5 mm Hg 100% increase in alveolar
ventilation.
d.
Anxiety attacks  hyperventilation where you blow out lots of
CO2. Hypocapnia (low CO2) results.
e.
A person feels faint because low CO2 causes vasoconstriction of
10
3.
4.
cerebral blood vessels cerebral ischemia.
f.
Breathing into a paper bag causes one to rebreathe expired air that
increases the CO2.
g.
When CO2 levels are abnormally low hypoventilation occurs (low,
shallow breathing), and this can even lead to apnea or cessation of
breathing until CO2 levels rise enough to restimulate breathing.
Influence of PO2
a.
Peripheral chemoreceptors in aortic bodies of aortic arch and
carotid bodies of bifurcation of common carotid.
b.
PO2 must fall below 60 mm Hg before chemoreceptors stimulate
increased ventilation because Hb still very saturated
c.
For people with chronically elevated PCO2 (emphysema and
chronic bronchitis) central chemoreceptors become unresponsive.
It is the PO2 mechanism which provides principal respiratory
stimulus = hypoxic drive
Influence of arterial pH
a.
Changes in arterial pH can modify rate/rhythm even if PCO2 and
PO2 are normal
b.
H+ diffuses poorly into CSF from blood so primary effect is on
peripheral chemoreceptors.
c.
Recall acidosis can be from metabolic causes as well as respiratory
causes
d.
Decreased pH increased rate and depth of breathing (compensate
by eliminating CO2)
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