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Chapter 22 (Respiratory System)

Terms in this set (91)

Conducting division of pulmonary ventilation
Nostrils --> Major Bronchioles
Respiratory division of pulmonary ventilation
alveoli and other gas exchange regions of the distal airway
Ventilation, the forced movement of air in and out of the respiratory system, is achieved through the action of __________ muscles.
skeletal
Which principal muscle is responsible for most of the airflow?
diaphragm and intercostal muscles
How does its contraction & relaxation drive inflow and outflow - how is this driving pressure changes?
When the diaphragm flattens, it pushes outward on the sternum and ribs and enlarges the area.
- enlargement of the thoracic cavity lowers its internal pressure and produces and inflow of air.

- when diaphragm relaxes, it bulges upward and compresses the lungs and expels air.
How do the internal intercostals contribute to inflow?
- synergist to the diaphragm

- they stiffen the thoracic cage during respiration and prevent it from caving inward when the diaphragm descends.
- also contribute to enlargement and contraction of the thoracic cage and add about 1/3rd of the air that ventilates the lungs.
Forced Expiration
- rectus abdominis pulls down on sternum and lower ribs which reduce chest dimensions and expel air more rapidly
Breathing is controlled in two ways by the brain:
1) conscious, cerebral control
2) unconscious, automatic, control mediated by the 3 pair of respiratory centers in the brainstem:
a. ventral respiratory group (VRG)
b. dorsal respiratory group (DRG)
c. pontine respiratory group (PRG)
two classes of neurons
inspiratory and expiratory, generate action potentials to achieve this
Breathing ceases if the nerve connections in the ______ muscles are severed or if the ____ ___ is severed high on the neck
- thoracic

- spinal cord
Breathing is dependent on the brain because 2 reasons
1) skeletal muscles, unlike cardiac muscles, cannot contract without nervous stimulation
2) breathing invovles well-orchestrated action of multiple muscles and thus require a central coordinating mechanism
Ventral respiratory group (VRG)
primary generator of breathing rhythm; output to spinal integrating centers
- elongated nucelus in medulla with 2 neurons:
a. inspiratory neurons
b. expiratory neurons

when I neurons fire, they inhibit the E neurons and vice versea
Inspiratory Neurons
- VRG
- generate action potentials during inspiration
- quiet breathing lasts 2 seconds
- when I neurons fire, it inhibits E neurons
Expiratory Neurons
- VRG
- generate action potentials during expiration
- E neurons fire when I neurons wane, they inhibit the I neurons allowin the inspiratory muscles to relax
Dorsal respiratory group (DRG)
- integrating center that receives input from several, higher brain centers: PRG, medullary chemoreceptors, peripheral chemoreceptors & stretch receptors

- DRG issues output to the VRG that modifies the respiratory rhythm to adapt to varying conditions
Pontine respiratory group (PRG)
- modifies the rhytmn of the VRG as well
- receives input from higher brain centers including the: hypothalamus, limbic system, and cerebral cortex
- issues output to both DRG and VRG
- hastens or delays the transition from inspiration to expiration
Spinal integrating centers (SIC)
- receives output from VRG, then issues output --> intercostal and phrenic nerves --> intercostal muscles & diaphrgam

- receive output directly from higher brain centers and then issue motor commands to accessory muscles of respiration
Neural Control of Breathing by Motor Neurons: quiet breathing
breathing cycle consists of contraction of inspiratory muscles, then relaxation of the same muscle during expiration
Neural Control of breathing by Motor Neurons: active breathing
expiratory muscles contract during the expiration phase
Central Chemoreceptors
- brainstem neurons that respond to changes in pH of the CSF
- indicator of blood pH
- regulation of stable pH ensures stable blood CO2
Where are these central chemoreceptors located?
concentrated on each side of the medulla oblongata
Peripheral Chemoreceptors
- respond to the O2 and CO2 content of the blood but mostly the pH
- sensory fibers enter the medulla and synapse with neurons of the DRG
Which cranial nerves carry signals to the DRG?
Glossopharyngeal nerves communicate with the brainstem and aortic bodies by way of the vagus nerve
Stretch receptors
- smooth muscle of bronchi and bronchioles and in visceral pleura
- respond to inflation of the lungs
- signal the DRG by ways of vagus nerves
Irritant Receptors
- nerve endings in epithelial cells of airway
- respond to smoke, dust, pollen, cold air, excessive mucus
- transmit signals to vagus nerves to DRG which signal the respiratory and bronchial muscle
- results in protective reflexes such as shallower breathing, breath holding or coughing
For both stretch receptors and irritant receptors, which cranial nerve carries their fibers to the brain, and which of the three respiratory centers do they project to?
- they project to the DRG
- the vagus nerve carries their fibers to the brain
total atmospheric pressure
sum of the contributions of individual gases in the air
- Dalton's Law
Partial pressure in atmosphere
separate contribution of each gas in a mixture
- signaled by letter P
How is it that a gas, say an O2 molecule, exerts force, expressed as a pressure?
Because the total atmospheric pressure is a sum of the contributions of individual gasses
Atm. pressure at sea level is 760 mm Hg: Partial pressure of N2 at sea level is __% of 780 mm Hg
78.6%

because
0.786 x 760 mm HG = 597 mm Hg
The composition of inspired and alveolar air differs because of three influences
1) Humidification
2) Mixture with residual alveolar air
3) O2 & CO2 is exchagned between blood and alveolar
Humidification
- air is humidified by contact with the mucous membranes
- so PH2O is more than 10x higher than that of inhaled air
Mixture with residual alveolar air
- freshly inspired air mixes with residual air left from precious respiratory cycle
- oxygen is diluted and is enriched with CO2 from residual air
Air exchanges O2 and CO2
alveolar air exchanges O2 and CO2 with the blood
- thus PO2 of alveolar air is about 65% of inhaled air and the PCO2 is much higher
Alveolar Gas Exchange
- air in alveolus is in contact with a film of water covering the alveolar epithelium
- for oxygen to get into the blood it must dissolve in the water and pass through respiratory membrane

- when air and water are in contact, gases diffuse down their gradients until the partial pressure of each gas in the air is equal to the partial pressure in the water
What's the functional significance of the aqueous (surfactant) layer of the alveolar epithelium ?
regulates exchange by allowing each gas to diffuse down/up it's own partial pressure gradient
Why does O2 diffuse into, and CO2 diffuse out of, pulmonary capillaries?
each gas diffuses down its own partial pressure gradient
- gasses diffuse down their gradients until the partial pressure of each gas in teh air is equal to its partial pressure in the water
- if gas has greater partial pressure in the water than the air, then it diffuses into the air
At any given temperature, the amount of a particular gas in solution is directly _____ to the partial pressure of that gas
proportional
Differences in pressure....
move gas molecules from one place to another, and also affect the movement of gas molecules into and out of solution
The actual concentration of gas in solution at any given temperature and partial pressure dpeends on the....
solubility of the gas in the solution
___ is highly soluble in water ___ les so
- CO2
- O2
O2 in alveoli diffuses into alveoloar capillaries, from high partial pressure air to low partial pressure liquid ( plasma) , eventually reaching equilibrium. Does that mean that, at partial pressure equilibrium, the concentration of O2 in alveolar air and alveolar capillaries are equal?

Why? (The answer is related to solubility of O2 in air vs water)
...
In an alveolus and across it's wall to the pulmonary capillary, how much time does it take for respiratory gases (O2, CO2) to reach equilibrium?
It takes 0.25 s to reach equilibrium
O2 loading and CO2 unloading depends on...
RBC time spent on alveolar capillaries
Why is O2 loading and CO2 unloading related to RBC time in capillaries?
loading and unloading of O2 and Co2 involve RBC, therefore processes depend on how long an RB spend sin an alveolar capillary compared with how long it takes for each gas to be fully loaded or unloaded
Blood circulates at it's slowest speed when the body is at rest; at rest it takes ~ 0.__ s to pass through an alveolar capillary
rest takes: 0.75 s
During heavy exercise, it takes ~ 0.__ s to pass through an alveolar capillary
exercise takes: 0.3 s
Henry's law
states that at the air-water interface for a given temperature, the amount of gas that dissolves in the water is determined by its solubility in water and its partial pressure in the air
Five factors significantly affec tthe efficiency of alveolar gas exchange
1) pressure gradients of gases
2) solubility of the gases
3) membrane thickness
4) membrane area
5) ventilation-perfusion coupling
Pressure gradients of gases
Factors affecting gas exchange
- Blood entering the lungs has a PO2 of 40 mm Hg and a PCO2 of 46 mm Hg; blood leaving has a PO2 of 95 mm Hg and a PCO2 of 40 mm Hg. These gradients differ under circumstances such as high elevation and hyperbaric oxygen therapy (treatment with oxygen at greater than 1 atm of pressure. Treatment in a hyperbaric oxygen chamber at 3 or 4 atm is used for conditions such as gangrene and carbon monoxide poisoning.
Solubility of gases
Factors affecting gas exchange
- gases differ in their ability to dissolve in water which affects the speed of solubility
Membrane thickness
Factors affecting gas exchange
- obstacle for diffusion because gases will have to travel farther between blood and air and cannot equilbrate fast enough to keep up with pace of bloodflow
membrane area
Factors affecting gas exchange
- surface area of respiratory membrane available for gas exchange
ventilation-perfusion coupling
Factors affecting gas exchange
- gas exchange requires good ventilation of alveoli and good perfusion of their capillaries
- refers to physiological responses that match airflow to blood flow and vice versa

- poor ventilation leads to low PO2 in that region of lung which stimulates rerouting the blood to better ventilated areas of the lung where it can pick up more oxygen
Gas transport
process of carrying gases from the alveoli to the systemic tissues and vice versa
Oxygen
- arterial blood carries about 20 mL/L of O2
- most bound to hemoglobin in RBC
Hemoglobin
specialized in RBCs for oxygen transport
Is the oxyhemoglobin fully loaded?
Oxyhemoglobin has 1 or more molecules of O2 bound to it.
Deoxyhemoglobin
hemoglobin with no oxygen bound to it
If 10 million Hb leaving an areaolar capillary each carry 4 O2, and 10 million carry 3 O2, what is the saturation of these 20 million Hb?
100% saturted for the 10 mil Hb with 4 O2
75% satured for the 10 mil Hb with 3 O2
oxyhemoglobin dissociation curve
- the relationship between hemoglobin saturation and PO2
- Relationship between available oxygen and amount of oxygen carried by hemoglobin.
Hb-O2 binding and dissociation is a _____ reaction
reversible
____ is a function o8f PO2
saturation
O2 binding is ______
cooperative
- binding of one O2 makes binding of the next one easier
Why does the binding of one O2 makes binding of the next one easier?
hemoglobin changes shape in a way that facilitates uptake of the second O2 hence causing a rapidly rising midportion of curve
What does the 22% indicated on the graph signify?
As oxygen passes through the alveolar capillaries where the PO2 is high, hemoglobin becomes saturated with oxygen. As it passes through the systemic capillaries where PO2 is low, it typically gives up about 22% of its oxygen.
Carbon Dioxide
CO2 is transported in 3 forms:
1) carbonic acid:
- transported 90% exchanged 70%
2) carbamino compounds:
- transported 5%, exchanged 23%
3) dissolved gas
- transported 5%, exchanged 7%

the relative amount of CO2 exchanged between blood and alveolar air differs from where and its transported
System gas exchange: CO2 loading
Co2 gradient ~ 46-->40 mm Hg from tissue fluid to blood
- most CO2 reacts with water to produce bicarbonate (HCO3-) and hydrogen (H+)
- most CO2 made in RBC's is transported in the blood
Why is the P CO2 so high in the tissues?
aerobic respiration produces a molecule of CO2 for every molecule of O2 it consumes. the tissue fluid therefore contains relatively high PCo2.
CO3 reaction with water occurs much faster in RBC's than in blood. Why?
in RBC, CO2 is catalyzed by the enzyme carbonic anhydrase. An antiport called the chloride-bicarbonate exchanger then pumps most of the HCO3- out of the RBC in exchange for Cl- from the blood plasma
Most H+ in RBC's binds to ____ or ____
- hemobolbin
- oxyhemoglobin

most of H+ binds to these buffers the intracellular pH
System gas exchange: O2 unloading
O2 gradient 95-->40 mm Hg from the arterial blood to the tissue fluid
Utilization coefficient
Hb saturation on arrival to system capillaries ~97% on departure is ~75%
- gives up ~22% of oxygen load
Venous resserve
oxygen remaining in the blood after it passes through the capillary bed
- can sustain life for 4-5 minutes even in event of respiratory arrest
As Hb loads O2, its affinity for H+ ____
declines
- : H+ dissociate from the Hb and bind with HCO3− transported from the plasma into the RBCs.

- aveolar gas exchange
H+ dissociate from the Hb and bind with
HCO3 transported from the plasma to the RBC's

- aveolar gas exchange
Reverse chloride shift
- chloride ions are transported back out of the RBC
- aveolar gas exchange
Reaction of H+ and HcO3+ ....
reverses the hydration reaction and generates free CO2. This diffuses into the alveolus to be exchaled as does the CO2 released from carbaminohemoglobin and CO2 gas that was dissolved in the plasma.
4 factors that adjust the rate of oxygen unloading to the metabolic rates of different tissues
1) ambient PO2
2) Temperature
3) Bohr Effect
4) Bisphosphoglycerate (BPG)
Ambient PO2
- rate of oxygen unloading to metabolic rates

- active tissue consumes oxygen rapidly, PO2 of tissue fluids remain low
Temperature
- rate of oxygen unloading to metabolic rates

- elevated temperature promotes oxygen unloading
- active tissues are warmer than less active ones and thus extract more oxygen from blood passing through them
The Bohr Effect
- rate of oxygen unloading to metabolic rates

- hydrogen ions weaken the bond between hemoglobin and oxygen and therefore promote oxygen unloading
Bisphosphoglycerate
- rate of oxygen unloading to metabolic rates

- binds to hemoglobin and promotes oxygen unloading
- hormones, temperature also promote oxygen unloading in tissues
Rate of CO2 loading is also adjusted to varying needs of tissues by ___ effect
Haldane
Haldane effect
low level of oxyhemoglobin enables the blood to transport more CO2

occurs for 2 reasons
1) HbO2 does not bind oxyhemoglobin (HBO2) as well as deoxyhemoglobin (HHb)
2) HHb binds more hydrogen ions than HbO2 does and by removing H+ from solution HHb shifts the carbonic acid reaction to the right.

- high metabolic rate keeps oxyhemoglobin levels relatively low and thus allows more CO2 to be transported by these two mechanisms
Blood gases and the respiratory rhythmn
breathing depth and rate are adjusted to maintain arterial blood at:
1) PO2 ~ 95 mm Hg
2) PCO2 ~ 40 mm Hg
3) pH ~ 7.40 _ 0.05
Brainstem respiratory centers receive input from ____ and ______ that monitor the composition of blood and CSF
- central
- peripheral chemoreceptors
Hydrogen Ions (pH)
- blood and CSF
- H+ does not cross the BBB easily. Most of H+ remains free and strongly stimulates the central chemoreceptors.
- also a potentent stimulus to peripheral chemoreceptors

-
How do you know that is it the H+ that stimulates the central chemoreceptors and not primarily the Co2 that diffuses into the CSF?
When pH alone changes, there is a strong effect on respiration. When PCO2 changes alone, the effect is weaker.
Carbon Dioxide
- blood and CSF
- indirect influence on respiration
- CO2 has some effect when pH remains stable
- may directly stimulate the peripheral chemoreceptros and trigger an increase in ventilation more quiclky than the central chemoreceptors do
Oxygen
- blood and CSF
- usually ha slittle effect on respiration
- arterial PO2 affects respiration only if it drops below 60 mm Hg
- moderate drop in PO2 does stimulate theperipheral chemoreceptors but can be overrided
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