Lecture 6 Respiratory System 2
Lecture 6 Respiratory System 2
Lecture 6 Respiratory System 2
PHYSIOLOGY I
RESPIRATORY SYSTEM 2
INTRAPLEURAL PRESSURE
• Pressure in pleural cavity (Pip)
• Fluctuates with breathing phases
• 4 mm Hg less than Ppul – Pip is always negative relative to Ppul
PRESSURE RELATIONSHIPS IN THORACIC CAVITY
2 opposing forces – to pull lungs away from thorax wall & cause lung
collapse:
BUT….
If not…immediate lung
collapse
Transpulmonary pressure –
difference between Ppul & Pip
keeps air spaces in lungs
open
PHYSICAL FACTORS INFLUENCING PULMONARY
VENTILATION
1) Airway resistance
2) Lung compliance
• Due to water in the alveoli acts to draw the walls of the alveoli
together
• Presenting a force that must be overcome in order to expand
the lungs.
• Reduce by surfactant produced by type II alveolar cells –
decreases cohesiveness of water molecule.
• Without surfactant – alveoli can collapse between breaths.
• Pulmonary Surfactant is a phospholipids & protein (know as
phophatidil choline) that produce maximum at 34-36 of
pregnancy. Thus baby born premature may die of hyaline
membrane disease / Respiratory Distress Syndrome.
RESPIRATORY VOLUMES
4 respiratory volumes:
• Tidal volume is the amount of air that moves in and out of the
lungs with each breath during quiet breathing.
• At higher plasma partial pressures of oxygen, The PO2 gradient required to unload one
hemoglobin unloads little oxygen, but if plasma oxygen from partially saturated HbO2 is
partial pressure falls dramatically, i.e. during substantially less, and decreases with
vigorous exercise, much more oxygen can be each successive oxygen removed.
OTHER FACTORS INFLUENCING HEMOGLOBIN
SATURATION
Temperature
• Increased temperature, a by-product of increased
metabolic activity, pushes Hb from its high affinity
structure toward its low affinity structure, from
which oxygen unloads more easily.
• Increased temperature also increases the metabolic
rate of RBCs, increasing the production of BPG,
which also facilitates oxygen unloading from HbO2.
OTHER FACTORS INFLUENCING HEMOGLOBIN
SATURATION
pH
• As H+ ions bind to Hb, the affinity for O2 decreases; as O2 is released from Hb H+ ions can
more easily bind, which further facilitates the release of O 2.
• In the lungs the increased PO2 favors oxygen binding to HHb, which drives H+ ions off Hb
and into solution and increases the affinity of Hb for O2; the complete oxygen saturation
of HbO2 achieved in the lungs stabilizes the high affinity structure of Hb.
• This interaction, which facilitates oxygen unloading where it is needed and oxygen
loading where it is plentiful, is known as the Bohr effect.
OTHER FACTORS INFLUENCING HEMOGLOBIN
SATURATION
PCO2
• Increased blood PCO2, the result of metabolic activity of
tissues, decreases the affinity of Hb for oxygen and
facilitates oxygen unloading.
BPG (Bisphosphoglycerate)
• A by product of glycolysis in RBCs, BPG binds to Hb and
stabilizes the low affinity structure.
CARBON DIOXIDE
TRANSPORT
• Carbon dioxide is transported
in the blood in 3 ways:
1) 7–10% is dissolved in plasma
2) 20% is carried on hemoglobin
bound to globins
3) 70% exists as bicarbonate, an
important buffer of blood
pH.
• The Haldane effect
encourages CO2 exchange in
the lungs and tissues: when
plasma partial pressure of
oxygen and oxygen saturation
of hemoglobin decrease,
more CO2 can be carried in
the blood.
• Carbonic acid-bicarbonate
buffer system – resisting
shifts in blood pH
HYPOXIA
1) Influence of PCO2
• CO2 is hydrated in CSF – liberate H+ - detected
• Increase breathing rate & depth – enhance alveolar ventilation
• To flush out CO2 – to restore normal level
2) Influence PO2
• Slight influence – limited to enhancing peripheral receptors to increase PCO2
• To be major stimulus – drop below to at least 60mmHg.
• O2 reservoir – bound to hemoglobin.
FACTORS INFLUENCING BREATHING RATE
& DEPTH
3) Influence of Arterial pH
• Ventilation occurs is mediated through peripheral
chemoreceptors
• Drop in blood pH – CO2 retention & metabolic causes
• Declines in pH – elimination of CO2
• So, respiratory & depth increase