respiratory system physiology - external respiration for A + P II

what process of movement do oxygen and carbon dioxide use to move between the lungs and the blood

simple diffusion

according to Fick’s law of diffusion, what is the diffusion rate equation

(surface area * concentration gradient * membrane permeability) / membrane thickness

according to Fick’s law of diffusion, what is the membrane permeability equation

lipid solubility / molecular size

assuming that membrane permeability is constant, what are the factors that influence the diffusion of gases in the lungs

• surface area

• membrane thickness

• diffusion distance

• concentration gradient

* the solubility factor is based on the gas itself, so oxygen’s solubility and carbon dioxide’s solubility are different from each other but are constant

what is the relationship of surface area regarding the diffusion of gases in the lungs

• the rate of diffusion is directly proportional to the available surface area

• the larger the amount of surface area is, the faster the rate of diffusion

what is the relationship of membrane thickness regarding the diffusion of gases in the lungs

• the rate of diffusion is inversely proportional to the thickness of the membrane

• the thicker the membrane is, the slower the rate of diffusion

what is the relationship of diffusion distance regarding the diffusion of gases in the lungs

diffusion is rapid over short distances and slow over long distances

what factor of diffusion rate is affected with emphysema

the destruction of the alveoli reduces the surface area available for gas exchange

what factor of diffusion rate is affected with fibrotic lung disease

• the thickened alveolar membrane slows gas exchange

• loss of lung compliance may decrease alveolar ventilation as well

what factor of diffusion rate is affected with pulmonary edema

• the fluid in the interstitial space increases diffusion distance

• arterial partial pressure of carbon dioxide may be normal due to the higher solubility of carbon dioxide in water

what is the relationship of concentration gradient regarding the diffusion of gases in the lungs

• the rate of diffusion is directly proportional to the concentration (partial pressure) gradient

• the more drastic the partial pressure gradient, the faster the rate of diffusion

what is the most importance factor for gas exchange in a healthy respiratory system and why

• the most important factor for gas exchange in a healthy respiratory system is concentration (partial pressure) gradient

• this is because, in a healthy respiratory system, membrane permeability, surface area, membrane thickness, and diffusion distance are constant

what is solubility

it is defined as the ease with which a gas dissolves in a solution

if a gas is very soluble, what does this mean

large numbers of gas molecules go into solution at low partial pressures

if a gas is less soluble, what does this mean

even high partial pressure may cause only a few molecules of the gas to dissolve

what is the difference in solubility between carbon dioxide and oxygen and what does this mean

• carbon dioxide is 20 times more soluble in water than oxygen

• even if the partial pressures in air/water were the same for the two gases, the amount of each gas that dissolves in water is different

• carbon dioxide would dissolve much more than water

what is a partial pressure used to describe

partial pressures are used to describe gas concentration in air and solution

what is the solubility of gases in liquid/the movement of gases from air into solution directly proportional to

• solubility of the gas in a given liquid (carbon dioxide is more soluble in water than oxygen)

• pressure gradient of the individual gas (partial pressure of oxygen is higher than the partial pressure of carbon dioxide)

• temperature (considered relatively constant in the body)

what happens in a beaker when oxygen is placed in contact with water while there is a pressure gradient

• a container of water is exposed to air that has a partial pressure of oxygen at 100 mmHg

• initially, the water has no oxygen dissolved in it, meaning it has a partial pressure of oxygen equal to 0 mmHg

• as the gaseous phase stays in contact with the water, the oxygen molecules in the gas diffuse into the water and dissolve

• this process continues until equilibrium is reached

what does it mean if the water beaker with oxygen has reached equilibrium

• if the gaseous phase has a partial pressure of oxygen of 100 mmHg at equilibrium, the water will also have a partial pressure of oxygen of 100 mmHg

• this does not mean that the concentration oxygen is the same in the air and the water

• the concentration of dissolved oxygen also depends on the solubility of oxygen

• when the partial pressure of oxygen of both air and water is 100 mmHg, the concentration of oxygen in air is 5.2 mmol/L while the concentration of oxygen in water is only 0.15 mmol/L

• this disparity is due to oxygen’s low solubility in water

what happens in a beaker when carbon dioxide is placed in contact with water while there is a pressure gradient

• a container of water is exposed to air that has a partial pressure of carbon dioxide at 100 mmHg

• initially, the water has no carbon dioxide dissolved in it, meaning it has a partial pressure of carbon dioxide equal to 0 mmHg

• as the gaseous phase stays in contact with the water, the carbon dioxide molecules in the gas diffuse into the water and dissolve

• this process continues until equilibrium is reached

what is the partial pressure of oxygen in the alveoli

the partial pressure of oxygen in the alveoli is 100 mmHg

what is the partial pressure of oxygen in arterial blood

the partial pressure of oxygen in arterial blood is 100 mmHg

what is the partial pressure of oxygen in cells

the partial pressure of oxygen in cells is 40 mmHg

what is the partial pressure of oxygen in venous blood

the partial pressure of oxygen in venous blood is 40 mmHg

what is the concentration gradient of oxygen between the alveoli and venous blood and what does this mean

• normal alveolar partial pressure of oxygen is 100 mmHg

• normal venous blood partial pressure of oxygen is 40 mmHg

• therefore, oxygen moves down its partial pressure gradient from the alveoli into the capillaries

• diffusion continues to equilibrium

• after diffusion goes to equilibrium, the blood is considered arterial blood

• the partial pressure of oxygen of the new arterial blood which leaves the lungs is now 100 mmHg, the same as in the alveoli

what is the concentration gradient of oxygen between arterial blood and cells and what does this mean

• a cell at rest has a partial pressure of oxygen of 40 mmHg

• arterial blood entering the systemic capillaries has a partial pressure of oxygen of 100 mmHg

• since the partial pressure of oxygen is lower in the interstitial fluid/cells (40 mmHg), oxygen diffuses down its pressure gradient from plasma into interstitial fluid/cells

• diffusion continues to equilibrium

• after diffusion goes to equilibrium, the blood is considered venous blood

• the partial pressure of oxygen of the new venous blood which enters the lungs is now 40 mmHg, the same as the cells

what is the partial pressure of carbon dioxide in cells

the partial pressure of carbon dioxide in cells is 46 mmHg

what is the partial pressure of carbon dioxide in venous blood

the partial pressure of carbon dioxide in venous blood is 46 mmHg

what is the partial pressure of carbon dioxide in the alveoli

the partial pressure of carbon dioxide in the alveoli is 40 mmHg

what is the partial pressure of carbon dioxide in arterial blood

the partial pressure of carbon dioxide in arterial blood is 40 mmHg

why is the partial pressure of carbon dioxide higher in cells than in blood

the partial pressure of carbon dioxide is higher in cells than in blood due to carbon dioxide production by cells

what is the concentration gradient of carbon dioxide between the resting cells and arterial blood and what does this mean

• a resting cell’s partial pressure of carbon dioxide is 46 mmHg

• arterial blood’s partial pressure of carbon dioxide is 40 mmHg

• this gradient causes carbon dioxide to diffuse out of cells/interstitial fluid and into the capillaries/arterial blood

• after this diffusion goes to equilibrium, the arterial blood becomes venous blood

• the partial pressure of carbon dioxide of the new venous blood is 46 mmHg

what is the concentration gradient of carbon dioxide between venous blood and alveoli and what does this mean

• in the lungs, venous blood bringing waste carbon dioxide from the cells has a partial pressure of carbon dioxide of 46 mmHg

• alveolar partial pressure of carbon dioxide is 40 mmHg

• the partial pressure of carbon dioxide is lower in the alveoli so carbon dioxide moves from the blood into the alveoli

• after this diffusion goes to equilibrium, the venous blood becomes arterial blood

• by the time arterial blood leaves the alveoli, it has a partial pressure of carbon dioxide of 40 mmHg, the same as the alveoli

what is hypoxia and what is hypoxemia

• hypoxia is too little oxygen in the air, blood, interstitial fluid, and/or cells

• hypoxemia is a type of hypoxia in which the arterial oxygen content is low

what is hypercapnia

• elevated concentrations of carbon dioxide in the blood

• often occurs along side hypoxia

are hypoxia and hypercapnia signs/symptoms or conditions/disease

they are signs/symptoms, not conditions/diseases

what is hypoxic hypoxia and what are the typical causes of it

• it is low arterial partial pressure of oxygen

• typical causes include high altitude, alveolar hypoventilation, decreased lung diffusion capacity, abnormal ventilation-perfusion ratio

what is anemic hypoxia and what are the typical causes of it

• it is a decreased total amount of oxygen bound to hemoglobin

• typical causes include blood loss, anemia (low hemoglobin or altered hemoglobin-oxygen binding), carbon monoxide poisoning

what is ischemic hypoxia and what are the typical causes of it

• it is reduced blood flow

• typical causes include heart failure (whole-body hypoxia), shock (peripheral hypoxia), thrombosis (hypoxia in a single organ)

what is histotoxic hypoxia and what are the typical causes of it

• it is the failure of cells to use oxygen because the cells have been poisoned

• typical causes include cyanide and other metabolic poisons

what are the causes of hypoxemia (low arterial oxygen content)

• inadequate oxygen reaching the alveoli (ventilation or exchange I problem)

• poor oxygen exchange between alveoli and blood (exchange II problem)

what does a decrease in alveolar partial pressure of oxygen result in and what is this caused by regarding altitude

• decrease in alveolar partial pressure of oxygen results in less oxygen entering the blood

• this is caused by abnormal composition of inspired air

how does altitude affect oxygen content

• the main factor that affects oxygen content of inspired air is altitude

• partial pressure of oxygen decreases, along with total atmospheric pressure, when someone goes from sea level (760 mmHg) to high altitudes

• Denver, which is above sea level, has a dry atmospheric pressure of 628 mmHg

• unless a person is traveling, however, altitude remains constant

what does a decrease in alveolar partial pressure of oxygen result in and what is this caused by regarding alveolar ventilation

• decrease in alveolar partial pressure of oxygen results in less oxygen entering the blood

• this can be caused by inadequate alveolar ventilation/hypoventilation

what is hypoventilation and what can cause this

• characterized by less fresh air entering the alveoli

• alveolar hypoventilation can be caused by increased airway resistance (i.e. asthma), decreased lung compliance (i.e. fibrotic lung disease), and drug/alcohol overdose

• an overdose depresses the central nervous system and slow ventilation rate/depth

what does normal gas exchange between the alveoli and blood look like (solubility, rate of gas exchange, rate of blood flow, and diffusion speed)

• since oxygen and carbon dioxide are water and lipid soluble, they easily diffuse across the respiratory membrane

• gas exchange in the lungs is rapid

• blood flow through pulmonary capillaries is slow

• diffusion reaches equilibrium in less than a second

what is suggested as the issue when the amount of oxygen in the alveoli is normal but the partial pressure of oxygen of the arterial blood is low

this suggests that a gas exchange problem between the alveoli and the blood has occurred

what factors can cause poor oxygen exchange between alveoli and blood

• decrease in the amount of alveolar surface area

• increase in thickness of the alveolar membrane

• increase in diffusion distance between the alveoli and the blood

what causes a decrease in the amount of alveolar surface area and how does this affect alveolar surface area

• loss of alveolar surface area is seen in emphysema, a degenerative lung disease that is caused by exposure to environmental smoke

• irritating effects of smoke in the alveoli activates alveolar macrophages that release enzymes

• enzymes destroy the elastic fibers of the lungs, kill cells, and break down the walls of the alveoli

• results in high compliance/low elastic recoil in the lungs with fewer and larger alveoli, meaning less surface area for gas exchange

what can cause an increase in the thickness of the alveolar membrane and how does this affect gas exchange

• in fibrotic lung disease, the deposition of scar tissues thickens the alveolar membrane

• diffusion of gases through scar tissue is much slower than normal

• any change to the alveolar membrane that alters its properties will slow gas exchange

what can cause an increase in diffusion distance between the alveoli and the blood and how does this affect gas exchange

• in pulmonary edema, the diffusion distance between the alveoli and the blood increase - this is characterized by excessive interstitial fluid volume in the lungs and shortness of breath

• oxygen is not very soluble in body fluids so it takes longer to cross the increased diffusion distance, resulting in decreased arterial partial pressure of oxygen

• since carbon dioxide is more soluble in fluids, the increased diffusion distance may not affect carbon dioxide exchange

what can cause pulmonary edema

• normally, only small amounts of interstitial fluid are found in the lungs, due to low pulmonary pressure adn effective lymphatic system drainage

• if pulmonary blood pressure increases due to left heart failure, the normal filtration/absorption balance in the lung capillaries is disrupted

• when capillary hydrostatic pressure increases, more fluid filters out of the capillary and the lymphatic system is unable to remove it

• excess fluid accumulates in the pulmonary interstitial space creating pulmonary edema

how much of the total oxygen diffused into blood is dissolved into the plasma

less than 2 percent

how much of the total oxygen diffused into blood is bound to hemoglobin

more than 98 percent

how much of the total carbon dioxide diffused into blood is dissolved into the plasma

7 percent

how much of the total carbon dioxide diffused into blood enters erythrocytes

70 percent which is then converted to bicarbonate ion

how much of the total carbon dioxide diffused into blood is bound to hemoglobin

23 percent

what is the structure of hemoglobin and what does this mean for oxygen binding to it

• one hemoglobin molecules has four globin subunits

• each globin subunit centers around a heme group whose central iron atom binds reversibly with an oxygen molecule

• since there are four iron atoms per hemoglobin, one hemoglobin molecule has the potential to bind four oxygen molecules

what is the strength/nature of an iron-oxygen bond and what does this mean

• iron-oxygen interaction is a weak bond

• can be easily broken without altering the hemoglobin or oxygen

what does hemoglobin do with oxygen when in the lungs versus in the cells

• in the lungs, where oxygen concentrations are high, hemoglobin binds to oxygen

• at the cells, where oxygen is being used and concentrations are lower, hemoglobin gives up its oxygen

what does the amount of oxygen that binds to hemoglobin depend on

• partial pressure of oxygen of plasma surrounding the erythrocytes

• number of potential oxygen binding sites available within the erythrocytes

what is the primary factor that determines how many hemoglobin binding sites are occupied by oxygen

the partial pressure of oxygen of plasma surrounding erythrocytes

what is the correlation/relationship between the partial pressure of oxygen of plasma and the amount of hemoglobin binding sites that are occupied by oxygen

• the higher the partial pressure of oxygen of plasma, the more hemoglobin binding sites that are occupied by oxygen

• the lower the partial pressure of oxygen of plasma, the less hemoglobin binding sites that are occupied by oxygen

what does the amount of oxygen that binds to hemoglobin depend on

the number of potential oxygen binding sites available within the erythrocytes

what does the number of potential oxygen binding sites available within the erythrocytes depend on

depends on the number of hemoglobin molecules in the blood

how can the number of hemoglobin molecules in the blood be determined

• number can be estimated by counting the erythrocytes and quantifying the amount of hemoglobin per red blood cell

• number can be estimated by determining the blood hemoglobin content

• any pathology that decreases the number of erythrocytes or the amount of hemoglobin in each erythrocyte will lessen the blood’s oxygen transporting capacity

how is the amount of oxygen bound to hemoglobin expressed

• the amount of oxygen bound to hemoglobin is expressed as a percentage

• percent saturation of hemoglobin is the percentage of available binding sites that are bound to oxygen

• if all binding sites of all hemoglobin molecules are occupied by oxygen molecules, the hemoglobin is 100 percent oxygenated or saturated with oxygen

• if half the available binding sites are occupied by oxygen molecules, the hemoglobin is 50 percent saturated

what is PaO2

partial pressure of oxygen in blood

what is PaCO2

partial pressure of carbon dioxide in blood

what is SaO2

• percentage of available hemoglobin that is saturated with oxygen

• saturation level of oxygen in hemoglobin, as measured by samples obtained from arterial puncture

what is SpO2

• estimate of arterial oxygen saturation

• measured using a pulse oximeter

• considered the 5th vital sign (4 others are pulse rate, respiration rate, temperature, and blood pressure)

how does a pulse oximeter work and what does it measure

• device emits small beams of light that pass through the blood in the finger

• it measures changes in light absorption in oxygenated or deoxygenated blood

• this way, it can measure the amount of oxygen in the blood

what are normal ranges for arterial blood and for a pulse oximeter reading

• normal partial pressure of oxygen in arterial blood is 75-100 mmHg

• values under 60 mmHg usually indicate the need for supplemental oxygen

• normal pulse oximeter readings range from 95-100 percent

• values under 90 percent are considered low

what treatment is given to patients who have lost a lot of blood and why

• patients who have lost a lot of blood have decreased erythrocytes/hemoglobin for oxygen transport

• blood transfusion is the ideal replacement for blood loss

• in emergencies, saline solutions will replace lost blood volume

• saline (like plasma) cannot transport sufficient quantities of oxygen to support cellular respiration which is why it is less ideal and used primarily for emergencies

what is the equation for the binding of oxygen and hemoglobin and how does this equation work

• hemoglobin + oxygen = oxyhemoglobin

• if the partial pressure of oxygen increases on the left side of the equation, more oxygen binds to the hemoglobin and the balance of the equation shifts to the right

what is the equation for the unbinding of oxygen and hemoglobin and how does this equation work

• oxyhemoglobin = hemoglobin + oxygen

• if the partial pressure of oxygen decreases on the left side of the equation, hemoglobin releases some of its bound oxygen and the balance of the equation shifts to the left

what is depicted in the oxyhemoglobin dissociation curve

depicts how hemoglobin binds to oxygen with varying partial pressure oxygen levels

what does the oxyhemoglobin dissociation curve look like and what does this mean

• the curve is nearly flat at higher partial pressure oxygen levels

• above 100 mmHg, large changes in partial pressure oxygen cause only minor changes in percent saturation

• this means that alveolar partial pressure of oxygen can fall a good bit below 100 mmHg without having significant effect on hemoglobin saturation

what are the “key points” and their values on the oxyhemoglobin dissociation curve

• alveoli partial pressure-oxygen = 100 mmHg at 98 percent O2 saturation of hemoglobin (arterial blood saturation)

• percent of O2 saturation of hemoglobin is still at 90 percent when alveoli pressure reaches 60 mmHg

• resting cell partial pressure-oxygen = 40 mmHg at 75 percent saturation of hemoglobin (venous blood saturation)

• 75 percent saturation means that every hemoglobin still has 3 out of 4 oxygen binding spots that are bound with oxygen

what does a steeper slope on the oxyhemoglobin dissociation curve mean

a steep slope means that a small decrease in partial pressure of oxygen causes a relatively large release of oxygen

what does the 75 percent of the oxygen that remains bound to hemoglobin after reaching equilibrium with a cell (40 mmHg) serve as in venous blood

the 75 percent of the oxygen that remains bound to hemoglobin serves as a reservoir that cells can draw upon if metabolism increases

what factors can affect oxygen-hemoglobin binding

• temperature

• partial pressure of carbon dioxide in blood

• pH

• anything that changes the structure of the hemoglobin molecules may affect its ability to bind with oxygen

• changes in binding ability will change the shape of the oxyhemoglobin dissociation curve

if temperature increases, what is the affect on oxygen-hemoglobin binding and oxyhemoglobin dissociation curve

• increased temperature decreases the binding of hemoglobin with oxygen

• shifts the oxygen-hemoglobin dissociation curve to the right

• worse

if temperature decreases, what is the affect on oxygen-hemoglobin binding and oxyhemoglobin dissociation curve

• decreased temperature increases the binding of hemoglobin with oxygen

• shifts the oxygen-hemoglobin dissociation curve to the right

• better

if partial pressure of carbon dioxide in the blood increases, what is the affect on oxygen-hemoglobin binding and oxyhemoglobin dissociation curve

• increased partial pressure of carbon dioxide in the blood decreases the binding of hemoglobin with oxygen

• shifts the oxygen-hemoglobin dissociation curve to the right

• worse

if partial pressure of carbon dioxide in the blood decreases, what is the affect on oxygen-hemoglobin binding and oxyhemoglobin dissociation curve

• decreased partial pressure of carbon dioxide increases the binding of hemoglobin with oxygen

• shifts the oxygen-hemoglobin dissociation curve to the left

• better

if pH of blood increases, what is the affect on oxygen-hemoglobin binding and oxyhemoglobin dissociation curve

• increased pH increases the binding of hemoglobin with oxygen

• shifts the oxygen-hemoglobin dissociation curve to the LEFT

• BETTER

if pH of blood decreases, what is the affect on oxygen-hemoglobin binding and oxyhemoglobin dissociation curve

• decreased pH decreases the binding of hemoglobin with oxygen

• shifts the oxygen-hemoglobin dissociation curve to the RIGHT

• WORSE

how do the factors of oxygen-hemoglobin binding change the degree of their effects depending on the location in the body and what does this look like on the oxygen-hemoglobin dissociation curve

• when the curve shifts in either direction, the changes are more pronounced in the steep part of the curve

• oxygen binding to hemoglobin at the lungs is not greatly affected by changes in temperature, partial pressure of carbon dioxide, or pH

• oxygen delivery at the tissues is significantly altered by changes in temperature, partial pressure of carbon dioxide, or pH

what is the equation for carbon dioxide in the blood

CO2 + H2O = H2CO3 = H+ + HCO3

what causes the unbinding of carbon dioxide from hemoglobin within the erythrocytes in the lungs

• since the partial pressure of carbon dioxide of alveoli is lower than that of venous blood in pulmonary capillaries, carbon dioxide diffuses out of plasma into the alveoli

• plasma partial pressure of carbon dioxide then begins to fall

• the decrease in plasma partial pressure of carbon dioxide causes the unbinding within the erythrocytes and carbon dioxide then diffuses out of erythrocytes

what is respiratory acidosis and what can this cause

• increased partial pressure of carbon dioxide (hypercapnia) in the blood causes a pH decrease known as respiratory acidosis

• abnormally high partial pressure of carbon dioxide levels depress central nervous system function and causes confusion, coma, and death

• carbon dioxide is a toxic waste product that must be removed by the lungs

what can the hypothalamus and cerebrum do for ventilation and how might higher brain center control not be necessary for ventilation

• the hypothalamus and cerebrum can alter the activity of the central pattern generator network and change ventilation rate/depth

• voluntary control of ventilation falls into this category

• higher brain center control is not a requirement for ventilation

• even if the brainstem above the pons is severely damaged, normal respiratory cycles continue

how might ventilation be affected by the limbic system

• emotional and autonomic activities such as fear and excitement may affect the rate/depth of ventilation

• in some of these situations, neural pathway goes directly to the somatic motor neurons, bypassing the central pattern generator cells in the brainstem

how can individuals affect their respiratory performance

• individuals can temporarily alter their respiratory performance, but cannot override the chemoreceptor reflexes indefinitely

• voluntarily holding our breath is possible only until elevated partial pressure of carbon dioxide in the blood and cerebrospinal fluid activate the chemoreceptor reflex, forcing us to breathe

• small children having temper tantrums can hold their breath until they turn blue and pass out from hypoxia, but once they are unconscious, normal breathing automatically resumes

what does a protective reflex do

responds to physical injury, irritation of the respiratory tract, and over inflation of the lungs

what are the protective reflexes of respiration

• bronchoconstriction

• coughing, sneezing

• Hering-Breuer inflation reflex

what mediates bronchoconstriction and how does it act as a protective reflex in the respiratory tract

• mediated through parasympathetic neurons that innervate bronchiolar smooth muscle

• inhaled particles or noxious gases stimulate irritant receptors in the airway mucosa

• irritant receptors send signals through sensory neurons to the central nervous system that trigger bronchoconstriction

what does the Hering-Breuer inflation reflex do in the respiratory tract

• prevents overexpansion of the lungs during strenuous exercise

• if tidal volume exceeds one liter, stretch receptors in the lungs signal the brainstem to terminate inspiration

• since normal tidal is 500 mL, this reflex does not operate during quiet breathing