Chapter 18: Gas Exchange and Transport Flashcards
remain relatively constant
Arterial blood O2 and CO2 levels
how much oxygen does the body consume at rest?
250 mL of O2 each minute
how much CO2 does the body produce at rest?
200 mL of CO2 each minute
how much air does the average adult inhale and how much reaches the alveoli?
- 6000mL/min
- 4200mL reaches alveoli
what are the steps of the pulmonary gas exchange?
1. Oxygen enters the blood at alveolar- capillary interface 2. Oxygen is trans- ported in blood dissolved in plasma or bound to hemoglobin inside RBCs. 3. Oxygen diffuses into cells 4.CO2 diffuses out of cells 5. CO2 is trans- ported dissolved, bound to hemoglobin, or as HCO3- 6. CO2 enters alveoli at alveolar-capillary interface.
states that the pressure exerted by a mixture of gasses is equal to the sum of the pressures exerted by the individual gases occupying the same volume.
Dalton’s Law-partial pressure of gases
are mixtures of different molecules
many gases
= proportion of pressure of entire gas that is due to presence of the individual gas
partial pressure of a gas
Ptotal=
P1 + P2 + P3 + … Pn
depends on fractional concentration of the gas
partial pressure of a gas
what is the equation for the total pressure of a gas mixture?
Pgas = %gas × Ptotal
what is the composition of air?
-79% nitrogen
21% oxygen
-Trace amounts of carbon -dioxide, helium, argon, and other gases
-Water can be a factor depending on humidity
Pair=
760 mm Hg = PN2 + PO2
PN2=
0.79 × 760 mm Hg = 600 mm Hg
PO2=
0.21 × 760 mm Hg = 160 mm Hg
how much of the air is CO2?
0.03%
PCO2=
0.0003 × 760 mm Hg = 0.23 mm Hg
what is the composition of air at 100% humidity?
Pair = 760 mm Hg = PN2 + PO2 + PH2O
what is PN2 at 100% humidity?
PN2 = 0.741 × 760 mm Hg = 563 mm Hg
what is PO2 at 100% humidity?
PO2 = 0.196 × 760 mm Hg = 149 mm Hg
what is PH2O at 100% humidity?
PH2O = 0.062 × 760 mm Hg = 47 mm Hg
what is PCO2 at 100% humidity?
PCO2 = 0.00027 × 760 mm Hg = 0.21 mm Hg
can exist in gas form or dissolved in a liquid
gas molecules
affects the amount of gas that goes into solution
partial pressure of a gas
what happens if a gas exists over a liquid?
the gas will dissolve in the liquid until equilibrium is reached
are the concentration of gas (moles/L) in the air and in the liquid at equilibrium?
no
20 times more soluble in blood than O2
CO2
what is involved in the exchange of oxygen and carbon dioxide?
- gas exchange in lungs
- gas exchange in respiring tissue
differ from atmospheric pressures
alveolar gas pressures
mixes with air rich in CO2 and relatively poor in O2 in dead space of conducting zone
fresh air
saturated with water vapor
air in alveoli
form a diffusion barrier between lung and blood
cells
- diffuse down pressure gradients
- high pressure–> low pressure
gases
- diffuse down partial pressure gradients
- High partial pressure → low partial pressure
gases in gas mixtures
- diffuses down its own partial pressure gradient
- Presence of other gases is irrelevant
a particular gas
how does gas exchange occur in respiring tissue?
Gases diffuse down partial pressure gradients
diffuses from blood to cells
oxygen (respiring tissue)
- Oxygen diffuses from blood to cells
- PO2 systemic veins = 40 mm Hg
PO2 cells ≤ 40 mm Hg
PO2 systemic arteries = 100 mm Hg
- Carbon dioxide diffuses from cells to blood
- PCO2 systemic veins = 46 mm Hg
PCO2 cells ≥ 46 mm Hg
PCO2 systemic arteries = 40 mm Hg
depends on metabolic activity of the tissue
mixed venous blood
Amount of O2 and CO2 that is exchanged in a vascular bed
what does greater rate of metabolism lead to?
greater exhcange
vary in different systemic veins
PO2 and PCO2
returns to the right atrium and is pumped out of the right ventricle and into the pulmonary artery
All systemic venous blood
- blood in pulmonary artery=?
- PO2=40mmHg
- PCO2=46 mmHg
mixed venous blood
determine systemic arterial PO2 and PCO2
Alveolar PO2 and PCO2
What are the factors affecting alveolar partial pressures?
- PO2 and PCO2 of inspired air (altitude)
- Minute alveolar ventilation (the volume of fresh air reaching the alveoli each minute)
the volume of fresh air reaching the alveoli each minute
Minute alveolar ventilation
- increased ventilation due to increased demand
- Minimal changes in arterial PO2 and PCO2
hyperpnea
- ventilation does not meet demands
- Arterial PO2 decreases
- Arterial PCO2 increases
Hypoventilation
a state of too little oxygen
hypoxia
elevated concentrations of CO2
hypercapnia
-Inadequate alveolar ventilation
-Decreased lung compliance
Increased airway resistance
CNS depression
hypoventilation
what can depress the CNS?
- Alcohol poisoning
- Drug overdose
what are the factors influencing gas exchange?
- Surface area
- Diffusion distance
- Diffusion barrier permeability
=surface area x barrier permeability/ distance^2
diffusion
- destruction of alveoli means less surface area for gas exchange
- PO2 normal or low in alveoli
- arterial PO2 low
emphysema
- thickened alveolar membrane slows gas exchagne
- loss of lung compliance may decrease alveolar ventilation
- PO2 normal or low in alveoli
- arterial PO2 low
fibrotic lung disease
- fluid in interstitial space increases diffusion distance
- arterial PCO2 may be normal due to higher CO2 solubility in water
- exchange surface normal
- arterial PO2 low
pulmonary edema
- increased airway resistance decreases alveolar ventilation
- bronchioles constricted
- alveolar PO2 low
- alveoalr PO2 low
asthma
what is involved in adequate perfusion of alveoli?
- Local control of ventilation and perfusion
- Matching of ventilation to perfusion
- Local control diverts blood away from the under-ventilated region to better-ventilated regions of the lung
rate of air flow
Ventilation (V)
rate of blood flow
Perfusion (Q)
what happens if ventilation to certain alveoli decreases?
- Increased PCO2 and decreased PO2 in blood and air
- Increased PCO2 in bronchioles → bronchodilation
- Decreased PO2 in P. arterioles → vasoconstriction
what happens if perfusion to certain alveoli decreases?
-Increased PO2 and decreased PCO2 in blood and air
Increased PO2 in P. arterioles → vasodilation
Decreased PCO2 in bronchioles → bronchoconstriction
what is ventilation-perfusion mismatch caused by?
under-ventilated alveoli
what gases are transported in the blood?
oxygen and carbon dioxide
- composed of 4 protein globin chains, each centered around a heme group
- contains 2 alpha chains and two beta chains
hemoglobin molecule
consists of a porphyrin ring with an iron atom in the center
heme group
how many erythrocytes per cubic millimeter of blood?
5 million erythrocytes
how many hemoglobin molecules per erythrocytes?
250 million hemoglobin molecules
how much oxygen does every liter of arterial blood contain?
200 mL of oxygen
how much oxygen do cells require at rest?
250 mL/ minute at rest
what is oxygen transport done by?
hemoglobin
is O2 soluble in plasma?/
not really
how much arterial O2 is dissolved in plasma?
- Only 3.0 mL of every 200 mL of arterial blood O2
- 1.5% of plasma
what happens to other 197mL of arterial O2 that is not dissolved in plasma?
it is transported by hemoglobin
when is the blood able to the supply almost 1000mL of oxygen to respiring tissues each minute?
when the CO is 5L/min
- Hb + O2 –> Hb*O2 (oxyhemoglobin)
- Hb = deoxyhemoglobin
oygen binding to hemoglobin
when does alveolar PO2= arterial PO2?
when oxygen is transported in the blood without hemoglobin
when is oxygen transport at normal PO2 in the blood?
with hemoglobin
what does the amount of oxygen bound to hemoglobin depend on?
- plasma O2
- amount of hemoglobin
- %saturation of Hb x total # of Hb binding sites
what does plasma O2 determine?
% saturation of hemoglobin
what does the amount of hemoglobin determine?
total number of hemoglobin binding sites
what is the total # of Hb binding sites calculated from?
Hb content per RBC x # of RBCs
how many oxygen molecules can hemoglobin bind?
4
what law does the binding of oxygen to hemoglobin follow?
**the law of mass action
-More oxygen → more binds to hemoglobin
-Binding of O2 to one subunit increases the affinity of
remaining subunits
a measure of how much oxygen is bound to hemoglobin
saturation of hemoglobin
what does 100% saturation of hemoglobin mean?
all four binding sites on hemoglobin have oxygen bound to them
what does a shift right on a Hb*O2 dissociation curve mean?
- Decrease in affinity, oxygen is unloaded more easily from hemoglobin (more available to the tissue)
- Less loading and more unloading
what does a shift left on a Hb*O2 dissociation curve mean?
- Increase in affinity, oxygen is loaded more easily onto hemoglobin
- More loading and less unloading
how does a higher temperature affect a Hb*O2 dissociation curve?
- Active tissues
- Shift right
- More O2 unloading in tissues
- More O2 delivery to tissues
- decreased affinity
what is the Bohr effect?
- lower pH increases O2 unloading
- decreased affinity
- **Active tissues
- Produce more acid; pH decreases in tissues
- Decreased pH causes shift right in saturation curve
- More O2 is unloaded to tissues
- CO2 reacts with hemoglobin to form carbaminohemoglobin
- Hb + CO2 –> HbCO2
- HbCO2 has lower affinity for oxygen than Hb
- Increased metabolic activity → increases CO2
- Increased oxygen unloading in active tissue
- higher PCO2=decreased affintiy
- lower PCO2=increased affinity
carbamino effect (effects of CO2)
- Produced in red blood cells under conditions of low O2 such as high altitude
- Synthesis inhibited by oxyhemoglobin
- decreases affinity of hemoglobin for O2, enhancing O2 unloading
2,3-DPG (2,3-diphosphoglycerate)
how does carbon monoxide affect oxygen transport?
- Hemoglobin has greater affinity for carbon monoxide (CO) than for O2
- Prevents O2 from binding to hemoglobin
- more soluble in plasma than O2, but still not very soluble
- 7% transported dissolved in plasma
carbon dioxide
what does CO2 form when it binds to hemoglobin?
- carbaminohemoglobin
- 23% transported bound to hemoglobin
what is CO2 converted to by erythrocytes?/
*converted to bicarbonate, then transported to plasma
-70% of transported CO2 dissolved in the plasma as
bicarbonate
-Hemoglobin also binds H+
- Enzyme that converts carbon dioxide and water to carbonic acid
- Law of mass action: an increase in CO2 causes an increase in bicarbonate and hydrogen ions
carbonic anhydrase
what are the steps of carbon dioxide transport?
- CO2 diffuses out of cells into systemic
capillaries. - Only 7% of the CO2 remains dissolved in plasma
- Nearly a fourth of the CO2 binds to
hemoglobin, forming carbaminohemoglobin - 70% of the CO2 load is converted to
bicarbonate and H+. Hemoglobin buffers H+. - HCO3- enters the plasma in exchange for
Cl- (the chloride shift). - At the lungs, dissolved CO2 diffuses out of
the plasma. - By the law of mass action, CO2 unbinds from
hemoglobin and diffuses out of the RBC - The carbonic acid reaction reverses, pulling
HCO3- back into the RBC and converting it
back to CO2.
what is the neural control of breathing facilitated by?
motor neurons
where does the generation of breathing rhythm occur?
the brainstem
where does peripheral input go to?
respiratory centers s
respiratory muscles=
skeletal muscles
what are respiratory muscles controlled by?
motor neurons
what is involved in inspiration?
- Phrenic nerve → diaphragm
- External intercostal nerve → external intercostal muscles
what is involved in expiration?
Internal intercostal nerve → internal intercostal muscles
what components are involved in generating the breathing rhythm?
- Respiratory control centers of medulla
- Respiratory control centers of pons
- Central pattern generator
what are the two respiratory control centers located on each side of the medulla?
- Ventral respiratory group (VRG)
- Dorsal respiratory group (DRG)
2 expiratory, 1 inspiratory region
Ventral respiratory group (VRG)
Primarily inspiratory neurons
Dorsal respiratory group (DRG)
hypothesized to control motor neurons to inspiratory muscles, neurons show ramp like activity in frequency of action potentials
inspiratory neurons
hypothesized to control motor neurons to expiratory muscles and/or inhibit inspiratory neurons
Expiratory neurons
what do medullary chemo-receptors monitor?
CO2
PRG
pontine respiratory group
VRG
- ventral respiratory group
- in medulla
DRG
- dorsal respiratory group
- in medulla
NTS
nucleus tractus solitarius
- Contains inspiratory, expiratory, and mixed neurons
- May regulate transitions between inspiration and expiration
pontine respiratory group
- establishes respiratory cycle
- -located in thee per-Bötzinger complex
- mechanism unknown
central pattern generator
what is the sensory input for quiet breathing?
- Central chemoreceptors
- Peripheral chemoreceptors
- Pulmonary stretch receptors
- Proprioceptors
what is the peripheral input to respiratory centers?
-Chemoreceptors
-Pulmonary stretch receptors
I-rritant receptors
-Muscle and joint proprioceptors
-Detect blood levels of O2 and CO2
-two types
-Peripheral chemoreceptors in
carotid bodies
-Central chemoreceptors in
medulla oblongata
chemoreceptors
- Located in carotid bodies near carotid sinus
- Direct contact with arterial blood
- Communicate with afferent neurons via chemical messenger
- Afferent neurons project to medullary respiratory control areas
- Respond mainly to changes in blood pH
peripheral chemoreceptors
-Located on the ventral surface of medulla
-Respond to changes in pH of the CSF
-Not directly responsive to CO2
-Respond indirectly to CO2
via pH
-Increased CO2 decreases
pH
-Not responsive to changes in [O2]
central chemoreceptors
monitor CO2 in cerebrospinal fluid
central chemoreceptors
monitor CO2, O2, and H+
carotid chemoreceptors
