gas exchange and transport Flashcards
what is total gas pressure
the sum of all partial pressures
Ptotal = P1 + P2 + P3 + … Pn
what does partial pressure depend on
Fractional concentration of the gas
Total pressure of gas mixture
what percentage of the air is nitrogen
79%
what percentage of the air is oxygen
21%
how do you calculate partial pressure
Pgas = % gas x Ptotal
e.g.
P air = 760 mm Hg = PN2 + PO2
– PN2 = 0.79 x 760 mm Hg = 600 mm Hg
– PO2 = 0.21 x 760 mm Hg = 160 mm Hg
what does fick’s law calculate
rate of diffusion
what do the letters stand for in fick’s law
A - surface area
T - thickness
AP - pressure difference
D - diffusion constant
S - gas solubility
MW - melecular weight
at rest how long does blood spend in a capillary
0.75 secs
what is pulmonary oedema
fluid accumulation in alveoli or interstitial space
what are the effects of pulmonary oedema
impairs diffusion
increased work breathing
leakage in unprotected capillaries
what are the causes of pulmonary oedema
Increased capillary pressure
– Via left heart failure
Reduced atmospheric pressure
what is treatment for pulmoary oedema
Administering oxygen and diuretics
how is oxygen transported
dissolved in plasma or bound to haemoglobin
what is the function of haemoglobin
to provide greater oxygen carrying capacity
how much oxygen does haemoglobin transport
98.5%
what is the structure of haemoglobin
Tetrameric globular protein
how much haemoglobin is in a person
150 g.litre-1 in men
* 130 g.litre-1 in women (13 g.dl-1
how many haemoglobin groups are there
4 (each contain 1 Fe2+ ion)
what is the Haemoglobin-Oxygen Dissociation Curve
describes how oxygen binds to hemoglobin in red blood cells and how easily it is released into tissues.
what does the Haemoglobin-Oxygen Dissociation Curveshow
S shape shows that as one oxygen molecule binds, haemoglobin’s affinity for oxygen increases, making it easier for additional oxygen to bind.
what does the x and y axis on the Haemoglobin-Oxygen Dissociation Curve represent
X-Axis (Pₒ₂ of blood, mm Hg): Represents the partial pressure of oxygen in the blood.
Y-Axis (% Hemoglobin Saturation): Indicates the percentage of hemoglobin molecules bound to oxygen.
what is the average resting pressure of oxygen and saturation at Systemic Capillaries
40 mm Hg Pₒ₂, ~75% saturation
Oxygen is released into tissues during rest.
what is the average resting pressure of oxygen and saturation at Pulmonary Capillaries
100 mm Hg Pₒ₂, ~97% saturation
Oxygen binds to hemoglobin in the lungs.
what factors cause a right shift (Reduced O₂ Affinity) in the Haemoglobin-Oxygen Dissociation Curve
Increased CO₂ (Bohr effect)
Lower pH (more acidic)
Higher temperature
what factors cause a left shift (Increased O₂ Affinity) in the Haemoglobin-Oxygen Dissociation Curve
Decreased CO₂
Higher pH (more alkaline)
Lower temperature
how is carbon dioxide transported
dissolved in plasma- 10%
bound to haemoglobin - 30%
As bicarbonate ions (in plasma) - 60%
what is hypoxia
insufficient cellular O2
name the types of hypoxia
Hypoxic Hypoxia (Low Oxygen in Blood)
Anemic Hypoxia (Low Hemoglobin or Oxygen-Carrying Capacity)
Histotoxic Hypoxia (Cells Can’t Use Oxygen)
Circulatory hypoxia (low supply of oxygenated blood)
what are Abnormal PaCO2 conditions
Hypercapnia
* Excess PaCO2
Hypocapnia
* Below normal PaCO2
where are respiratory control centres
in brainstem
what is in the pons respiratory centre
pneumotaxic center
apneustic center
what is in the medullary respiratory center
dorsal and ventral respiratory groups
what respiratory control centers are in the brainstem
pons respiratory center
medullary respiratory center
pre-Botzinger complex
what are the steps of Respiratory Control During Quiet Breathing
- chemoreceptors, pons and cortex
- central pattern generator (medulla)
- inspiratory neurons in dorsal and ventral respiratory group
- breathing rhythm
what are Pulmonary stretch receptors (Hering-breuer reflex) responsible for
Inflation and deflation
what are chemoreceptors responsible for
oxygen and carbon dioxide pressure changes
where are peripheral chemoreceptors found
carotid bodies and aortic bodies
what is the function of peripheral chemoreceptors
responds to low arterial oxygen pressure
responds to high arterial carbon dioxide pressure
aortic bodies respond ro low total arterial oxygen content
where are central chemoreceptors
medulla
what is the function of central chemoreceptors
provide 80% respiratory drive
detect changes in CO₂ (carbon dioxide) and pH in cerebrospinal fluid (CSF
when does arterial O2 effect ventilation
when PO2 < 60 mm Hg
describe carbon transport in haemoglobin
CO₂ binds to the globin (protein) portion of hemoglobin (Hb) to form carbaminohemoglobin (HbCO₂).
This binding is reversible, allowing CO₂ to be released in the lungs for exhalation
how does the presence of oxygen effect carbon transport
When oxygen levels are high (like in the lungs), O₂ binds to hemoglobin, reducing hemoglobin’s affinity for CO₂. This promotes CO₂ release into the lungs, where it is exhaled.
describe carbon transport through bicarbonate ions
Inside red blood cells (RBCs), CO₂ reacts with water (H₂O) under the action of the enzyme carbonic anhydrase, forming carbonic acid (H₂CO₃)
Carbonic acid then dissociates into bicarbonate ions (HCO₃⁻) and hydrogen ions (H⁺)
Bicarbonate ions leave RBCs and enter plasma in exchange for chloride ions (Cl⁻) to maintain electrical neutrality.
describe carbon transport in plasma
CO₂ is directly dissolved in plasma due to its relatively high solubility in water compared to oxygen.
This dissolved CO₂ is readily available for diffusion into the lungs for exhalation.
