Respiratory cycle
One complete inspiration and exhalation
Quiet respiration
Breathing at rest
Passive, energy saving process
Forced respiration
Usually deep or rapid breathing, as in a state of exercise, singing, blowing, coughing, or sneezing
Uses abdominal muscles to pull ribs down-- reduce chest dimensions and expel more air rapidly and thoroughly.
Respiratory muscles
Skeletal muscles of the trunk: diaphragm and intercostal muscles
Diaphragm
Prime mover of ventilation--2/3 of air flow
Relaxed-- bulges upward
Contracted-- flattened
Internal and external intercostal muscles
Synergists to diaphragm
Primary function is to stiffen the thoracic cage during respiration and prevent it from caving inward when diaphragm descends.
Also contribute to enlargement and contraction of the thoracic cafe and add about 1/3 of air that ventil
Valsalva maneuver
Taking a deep breath, holding it, and then contracting abdominal muscles to raise abdominal pressure
Childbirth, defication, urination, and vomiting
Neural control of breathing
Two levels
1. Cerebral/conscious
2. Automatic/unconscious
Automatic, unconscious breathing
Ventral respiratory group (VRG)-- primary generator of respiratory rhythm
1. Elongated nucleus in medulla with inspiratory (I) neurons and expiatory (E) neurons.take turns firing in 2-3 sec intervals to produce 12 breath per minute respiratory rhythm.
Dor
Hyperventilation
Extreme anxiety, leads to dizziness and fainting
CO2 expelled quickly causing a rise in pH
Sensory receptors that provide info to respiratory centers
Central Chemoreceptors in brain stem respond to pH changes in cerebrospinal fluid
Peripheral chemoreceptors in carotid and aortic arteries respond to O2, CO2, and pH of blood and use cranial nerves to report to DRG
Stretch receptors in smooth muscle of br
Voluntary control of breathing
Singing, speaking, holding breath
Output neurons send impulses down corticospinal tracts to integrating centers in spinal cord, bypassing brainstem centers.
Holding breath raises CO2 levels until breaking pt reached and automatic takes over.
Atmospheric/barometric pressure
Governs respiratory airflow
At sea level pressure is 760 mm Hg, 1 atmosphere
Boyles law
At constant temp, pressure is inversely proportional to volume
Lung volume increases, pressure drops (air flows down gradient and fills lungs)
Lung volume decrease, pressure rises (air flows out)
-3 mm Hg means 3 mm Hg below atmospheric pressure
+3 mm Hg
Inspiration
Flow of air into the lungs
As thoracic cage expands, two layers of pleura stick together and this stretches the alveoli within lung. Lung expands and pressure drops (-3 mmHg) and air flows in. Pressure between pleural layers is slight vacuum at -4 mmHg an
Charles's law
Volume of gas directly proportional to its absolute temperature.
16 degrees outside, 21 deg during inspiration, 37 deg by time reaches alveoli.
Expiration
Flow of air out of lungs
Relaxed expiration is passive process achieved mainly by elastic recoil-- compresses the lungs, raises intrapulmonary pressure (+3 mmHg) air flows down its pressure gradient.
Forced breathing, accessory muscles raise pressure as h
Pneumothorax
Presence of air in pleural cavity (puncture in thoracic wall). Without negative intrapleural pressure, the lungs recoil and collapse (atelectasis).
Atelectasis
Without negative intrapleural pressure (I.e. From pneumothorax) the ,ungainly recoil and collapse
Can result from airway obstruction, as blood absorbs gases from the alveoli distal to the obstruction
Resistance
Another determinate of airflow (besides pressure)
Governed by:
1. Diameter of bronchioles
2. Pulmonary compliance
3. Surface tension of alveoli and distal bronchioles
Diameter of bronchioles
Ability of bronchioles to change their diameter makes them t primary means of controlling resistance.
Called bronchiodilation, restriction called bronchoconstriction.
Epinepherine and sympathetic nerves stim dilation.
Histamine, coled air, chemical irrita
Pulmonary compliance
Ease with which the lungs expand, or the change in lung volume relative to a given pressure change.
Thoracic cage may produce the same intrapleural pressure in two diff people, but lungs will expand less in the one with lower pulmonary compliance.
Complia
Surface tension of the alveoli and distal bronchioles
Thin film of water over epithelium if alveoli is necessary for gas exchange, but may be a prob for pulmonary ventilation if hydrogen bonding cause alveolar collapse.
Surfactant
Treat alveolar cells produce surfactant which disrupts hydrogen bonding and reduces surface tension
Composed of amphiphilic proteins and phospholipids which are partially hydrophobic.
Molecules spread over the surface of water like ice cubes.
Surfactants
Anatomical Dead space
Area where no gas exchange can occur
Not all air that gets inhaled get to alveoli--approx 150 ml of it fills the conducting division of the airway
Can vary w circumstances:
Relaxed-- Parasympathetic stim keeps airways somewhat constricted minimizing dead
Physiological dead space
Total dead space
Sum of anatomical and any pathological alveolar dead space.
In healthy people the anatomical and physiological dead spaces are identical
Alveolar ventilation rate
AVR
Amount of air that ventilates the alveoli times the respiratory rate
If 500 ml of air is inhaled, and 150 ml stays in dead space, then 350 ml ventilates the alveoli.
If rate of respiration is 12 breaths per min, then
AVR=350 ml x 12 breaths/min
AVR= 4200
Residual volume
Alveoli never completely empty- leftover air
Typically 1300 ml
Air does mix with fresh air so same air doesn't remain cycle after cycle
Spirometer
Measures ventilation
Recaptures expired breath and records rate and depth of breathing, speed of expiration, and rate of oxygen consumption
Tidal volume
Respiratory volume
Amount of air inhaled and exhaled in one cycle of quiet breathing.
500 ml
Inspiratory reserve volume
IRV
Respiratory volume
Amount beyond the TV that can be inhaled with maximum effort
3,000 ml
Expiatory reserve volume
ERV
Respiratory volume
Amount beyond the TV that can be exhaled with maximum effort
1200 ml
Residual volume
RV
Respiratory volume
Amount remaining after a maximum expiration
1300 ml
Vital capacity
VC
ERV + TV + IRV
Inspirational capacity
TV + IRV
Functional residual capacity
RV + ERV
Total lung capacity
RV + VC
Vital capacity
The maximum ability to ventilate the lungs in one breath
Impt measure of pulmonary health
Respiration all volumes and capacities are gender specific
Gen proportional to body size so gen higher for men than women.
Spirometry
Measurement of pulmonary function and is an aid to diagnosis and assessment of restrictive and obstructive disorders.
Restrictive disorders
Tho set hat reduce pulmonary compliance, limiting the amt to which lungs can be inflated
Show as reduced VC.
Examples are diseases that cause pulmonary fibrosis such as black lung disease and TB.
Obstructive disorders
Interfere w airflow by narrowing or blocking airway-- harder to inhale and exhale.
Asthma and chronic bronchitis
Measured w spirometer-- measure forced expiratory volume (FEV)-- Percentage of vital capacity that can be exhaled in given time period-- 75-85
Minute respiratory volume
MRV
Amt of air inhaled per min
MRV largely det the alveolar ventilation rate.
Measured with spirometer or multiply tidal volume by respiratory rate. 6,000 ml/ minor 6L/min
During exercise: MRV high as 125-170 L/min
Called maximum voluntary ventilation MVV
Respiratory rhythm
Quiet breathing-- eupnea-- Tidal volume 500 ml and respiratory rate of 12-15 breaths per min.
Coughing
Glottis is closed and muscles of expiration contract producing high pressure. Glottis is suddenly opened and air is released in an explosive burst.
Coordinated by center in medulla oblongata
Sneezing
Triggered by irritants in nasal cavity. Glottis is continuously open but soft palate and tongue block the flow of air-- when soft palate is depressed air is directed through the nose.
Coordinated by center in medulla oblongata
Composition of air
78.6% nitrogen
20.9% oxygen
0.04% carbon dioxide
Argon, neon, helium, methane, ozone
Var amt of water vapor (0-4%)
Dalton's law
Total atmospheric pressure is a sum of the contributions of each gas in the mixture.
General pressure
Separate contribution of each gas = partial pressure P
If Sea level pressure is 760 mmHg and nitrogen is 78.6% of this then PN2 is 760 x .786= 597 mmHg
All major gasses in atmosphere added up at sea level are 760 mmHg
Composition of exhaled air
Humidified so PH2O is 10x higher
Oxygen is diluted and enriched w CO2 from residual air left in respiratory system
Alveolar air exchanges O2 and CO2 w the blood so the PO2 of alveolar air is about 65% that of inhaled air and PCO2 is more than 130x higher
Alveolar gas exchange
Back and forth traffic of oxygen and carbon dioxide across respiratory membrane.
Each gas diffuses down its pressure gradient until the partial pressure of each gas I'm the air is equal to the partial pressure in the water film on the surface of alveoli a
Henry's law
Air-water interface, at given temp, the amt of gas that dissolves in water is det by its solubility in water and it's partial pressure in the air.
Greater PO2 in alveolar air, the more O2 the blood picks up; and the greater the PO2 in the blood, the more
Loading O2 and unloading CO2
Greater PO2 in alveolar air, the more O2 the blood picks up; and the greater the PO2 in the blood, the more CO2 is released into alveolar air.
Involves RBCs
Takes .25 sec for gases to reach equilibrium and .75 sec for RBC to pass thru respiratory capillar
Efficacy of alveolar exchange
1. Pressure gradients of gases
2. Solubility of gases
3. Membrane thickness
4. Membrane area
5. ventilation-perfusion coupling
Pressure gradients of gasses
Blood entering lungs has PO2 of 40 mmHg and PCO2 of 46. Blood leaving PO2 95 and PCO2 40
These differ under high elevation and hyperbaric oxygen therapy (treatment of oxygen at greater than 1atm pressure)
Hyperbaric oxygen chamber at 3-4 atm used for gang
Solubility of gases
Gases have different solubility in water. CO2 20xs more soluble than O2, and O2 twice as much soluble as N2.
Even tho pressure gradient of oxygen is higher, equal amts of oxygen and carbon dioxide exchanged because carbon dioxide is so much more soluble
Membrane thickness
Respiratory membrane is only .5 micrometers thick and presents little obstacles to diffusion, but some conditions affect this
Left ventricular failure: blood pressure back up into lungs and causes respiratory membranes to become edematous and thickened, s
Membrane area
Each healthy lung has 70 m-squared of respiratory membrane available.
Several disease decrease area of alveolar surface incl lung cancer, TB, and emphysema
Ventilation-perfusion coupling
Ability to match nentillation and perfusion to each other: Ventilation of the alveolus is required but a good perfusion of its capillaries is also needed.
As whole lungs have ratio of .8--
4.2 L of air and 5.5 L of blood per min at rest.
Poor ventilation:
Gas transport
Process of carrying gases from the alveoli to the systemic tissues and vice versa
Arterial blood carries about 20 ml of oxygen per deciliter
98.5% of oxygen bound to hemoglobin in RBCs and 1.5% dissolved in plasma.
Each hemoglobin carries up to 4 o2 (100%
Oxyhemoglobin
One or more oxygen molecules bound to it
Deoxyhemoglobin
No oxygen bound to it
Oxyhemoglobin dissociation curve
Relationship between hemoglobin saturation and PO2
Not a straight line
Low PO2 curve rises slowly, once first heme group binds O2, second O2 binds quickly, etc, until saturation is met where curve slows again.
Carbon dioxide is transported in three forms
Carbonic acid
Carbamino compounds
Dissolved gas
Carbonic acid
Air to blood--90% of carbon dioxide hydrate to form carbonic acid-- dissociates to form bicarbonate and hydrogen ions
Blood to air-- 70% carbonic acid
Carbamino compounds
5% carbon dioxide binds to the amino groups of plasma proteins and hemoglobin to form Carbamino compounds, chiefly carbaminohemoglobin
No comp with oxygen because different binding site-- attaches to polypeptide chains on hemoglobin not heme group.
Hemogl
Dissolved gas (CO2)
Remaining 5% of carbon dioxide carried in blood as dissolved gas.
Blood to air- 7%
Systemic gas exchange
Unloading of oxygen and loading of carbon dioxide at the systemic capillaries.
Carbon dioxide loading
Occurs because aerobic respiration produces a molecule of carbon dioxide for every molecule of oxygen it consumes and tissue contains a relatively high PCO2.
There is a gradient of 46--> 40 mmHg from fluid to blood, consequently CO2 diffuses into the bloo
Chloride shift
An antiport called the chloride-bicarbonate exchanger pumps most of the HCO3- out of the RBC in exchange for Cl- from the blood plasma, and exchange called chloride shift.
Oxygen unloading
Begins as H+ binds to oxyhemoglobin which reduces the affinity of hemoglobin for O2 and tends to make hemoglobin release it.
Oxygen consumption by respiring tissues keeps PO2 of tissue relatively low so typically there is a pressure gradient of 94--> 40 m
Hypoxia
Deficiency of oxygen in a tissue or the inability to use oxygen
Not respiratory disease but often a consequence of respiratory disease
Indicated by cyanosis (bluish tinge to the skin); its primary effect is necrosis of oxygen starve tissues especially cri
Hypoxemic hypoxia
State of low arterial PO2 and is usually due to inadequate pulmonary gas exchange
Causes: atmospheric deficiency at high elevations, impaired ventilation as in drowning, respiratory arrest, and degenerative lung diseases; and carbon monoxide poisoning
Ischemic hypoxia
Inadequate blood circulation as in congestive heart failure.
Anemic hypoxia
Due to anemia and inability of the blood to carry oxygen
Histotoxic hypoxia
Occurs when a metabolic poison such as cyanide prevents tissues from using oxygen delivered to them
Oxygen toxicity
Can occur when pure oxygen is breathed at 2.5 atm or greater.
Safe to breather pure oxygen at 1 atm for a few hours
Excess oxygen generates hydrogen peroxide and free radicals that destroy enzymes and nervous tissue.
Chronic obstructive pulmonary disease
COPD
Any disorder in which there is long term obstruction of the airflow and a substantial reduction in pulmonary ventillation
Chronic bronchitis and emphysema.
Almost always causes by smoking, but pollution can cause too.
Reduces pulmonary compliance and vita
Chronic bronchitis
Cilia are immobilized and reduced in number while goblet cells enlarge and produce excess mucus.
Smokers cough-- brings up sputum (mucus+cellular debris)
Mucus provides growth medium for bacteria , and cig smoke incapacitates alveolar macrophages and redu
Emphysema
Alveolar walls break down and lungs exhibit larger but fewer alveoli.
Inhale fine, exhale prob:
Less membrane for gas exchange.
Lungs become fibrotic and less elastic.
Air passages open adequately, but tend to collapse and obstruct airflow during expirati
Lung cancer
Follows or accompanies COPD
Cig smoke contains 15 carcinogenic compounds
90% originate in mucous membranes of large bronchi, tumor compresses airway and cause atelectasis(collapse of lung).
Tumor produces cough, but most smokers cough-- metastasizes quick
Squamous-cell carcinoma
Most common.
Arises in basal cells of bronchial epithelium.
Ciliated Pseudostratified epithelium transforms into stratified squamous and invades underlying tissue creating bleeding lesions, keratin appears and replaces functioning tissue.
Adenocarcinoma
Nearly as common as squamous-cell.
Emerges in mucous glands of lamina propria.
Small cell (oat cell) carcinoma
Least common, most dangerous
Originates in main bronchi, invades mediastinum, metastasizes quickly to other organs.
Oxygen loading
As hemoglobin loads oxygen, it's affinity for H+ declines, these ions dissociates from hemoglobin and bind with bicarbonate ions transported into RBCs
Chloride ions transported back out of RBCs (reverse chloride shift)
Reaction of H+ and bicarbonate rever
Oxygen release adjusted to needs of individual tissues
Four factors:
1. Ambient PO2-- active tissue consumes more oxygen, causing low PO2 and more release of oxygen from HbO2
2. Temperature-- elevate temp (active tissue) causes more dissociation and release of oxygen.
3. Bohr effect-- active tissue generate m
Rate of CO2 loading adjusted to needs of tissues--haldane effect
Low level of Hbo2 enables blood to carry more CO2-- haldane effect
Blood gases effect respiratory rhythm
PO2 of systemic arterial blood: 95mmHg
PCO2 of systemic arterial blood:
40 mmHg
pH 7.4
Rate and depth of breathing adjusted to maintain values via chemoreceptors of CNS and peripheral nervous system. CO2 levels most potent stimulus.
Acidosis
Blood pH levels lower than 7.35
Alkalosis
Blood pH levels higher than 7.45
Hypocapnia
PCO2 less than 37 mmHg
Most common cause of alkalosis
*Normal 37-43 mmHg
Hypercapnia
PCO2 greater than 43 mmHg
Most common cause of acidosis
*Normal 37-43 mmHg
Diabetes mellitus and ketoacidosis
Rapid fat oxidation releases acidic ketone bodies causing abnormally low pH called ketoacidosis. Induces form of dyspnea (difficult breathing) called Kussmaul respiration to compensate for increased H+ released by ketone bodies.