Respiratory Physiology Flashcards
Explain the role of peripheral chemoreceptors in respiration. What are they are more responsive to?
o More responsive to changes in the oxygen content of blood but also respond to changes in pH and carbon dioxide.
o Carotid bodies: bilaterally @ bifurcation of common carotids; pass from Hering’s nerves to the glossopharyngeal nerves and onto the dorsal respiratory group
o Aortic bodies: @ aortic arch; pass from the vagus nerve to the dorsal respiratory group
o These bodies are constantly exposed to only arterial blood
Based on the oxygen-hemoglobin dissociation curve, what is the PO2 when 50% of Hb is saturated?
PO2 at 27 mmHg when Hb 50% saturated (P50 = 27mmHg)
The oxygen dissociation curve plots the % saturation against the partial pressure of oxygen, and its contribution to the total oxygen content. This is an S shaped curve due to the alterations in hemoglobin’s affinity for oxygen in response to other physiologic factors such as pH and temperature.
A reduction of PO2 below 60 mm Hg causes a rapid decrease in amount of O2 bound to hemoglobin. However, diffusion of oxygen from hemoglobin to tissue cells is enhanced by this process.
The P50 represents the partial pressure at which hemoglobin is 50 percent saturated with oxygen. P50 provides a means of quantifying the hemoglobin’s affinity with oxygen and reflects the dissociation curves.
Right shift – hemoglobin has decreased affinity, increased P50 – takes more oxygen to reach 50% (higher partial pressure to get 50% saturated)
Left shift – increased affinity, decreased P50 – less oxygen to reach 50% (less partial pressure to get 50% saturated)

Describe the cough reflex.
Bronchi and trachea are very sensitive to light touch (larynx and carina especially sensitive) Afferent signals pass from the respiratory passageways to the medulla by way of the vagus nerve. The initiates an influx of air and subsequent closure of the epiglottis and vocal folds to trap the air in the lungs. The abdominal muscles contract and forcefully expel the air.
Describe the sneeze reflex.
Irritants in the nose send afferent signals to the medulla by way of CN V
Describe what occurs with control of normal breathing (nervous control).
Normal quiet breathing is controlled by repetitive inspiratory signals from dorsal respiratory group transmitted to diaphragm; expiration is passive elastic recoil of lungs and thorax.
Dorsal respiratory group come from the IX and X CN.

Describe when oxygen therapy will be effective in hypoxemia.
- 100% effective with decreased atmospheric oxygen
- Pretty effective (5x O2 delivery) with hypoventilation hypoxia
- Pretty effective with a decreased alveolar membrane diffusion because the increased PaO2 facilitates diffusion at a higher partial pressure
- Minimally effective in hypoxia caused by anemia, abnormal hemoglobin transport of oxygen, circulatory deficiency, or physiologic shunt
• Normal amounts of oxygen are already available to the alveoli • Small amount of increased O2 transport in the dissolved state may make a difference
5, Not effective in hypoxia caused by inadequate tissue use of oxygen
Explain the dissociation of carbonic acids into bicarbonate and hydrogen ions.
Carbonic acid (in RBC, H2CO3) dissociates into hydrogen and bicarbonate ions (H+ and HCO3-) = Faster with carbonic anhydrase o About 70% CO2 transported to lungs from tissue • H+ combine with Hgb (powerful acid-base buffer)
What ocurrs at the BBB with H+ and CO2 to stimulate respiration?
Effect of blood PCO2 in stimulating the chemosensitive area
- CO2 + H2O → carbonic acid → HCO3- + H+ → H+ after CO2 has diffused across BBB
- Chemosensitive region is stimulated much more rapidly if the CO2 enters via the CSF rather than the brain interstitial water (less protein buffers for the hydrogen in the CSF)
- The excitation of the respiratory center to the increased CO2 is great within the first few days but subsequently declines over the next 1-2 days
o Due to renal compensation for acidosis by retaining bicarb, AND bicarb diffusing across BBB to buffer H+ there
How does alveolar ventilation occur?
• Alveolar ventilation: rate at which air reaches the gas-exchange regions
o The gas in the air really only goes down to the terminal bronchioles and not into the alveoli during normal inspiration. It makes it the rest of the way by simple diffusion.
How does oxygen reversibly bind to hemoglobin?
O2 combines loosely/reversibly with heme portion of hemoglobin
o PO2 high = O2 binds to hemoglobulin (pulmonary capilaries)
o PO2 low = O2 is released (tissue capilaries)
How many molecules of oxygen can be bound by 1 Hemoglobin?
4 molecules of Oxygen per 1 Hb
Name 5 major categories of hypoxemia?
Extrinsic problems •
- Low FIO2 (high altitude) •
- Hypoventilation (neuromuscular disease) Pulmonary disease • 2. Hypoventilation (increased airway resistance, decreased lung compliance) •
- Diffusion impairment •
- V/Q mismatch o High V/Q: physiologic dead space o Low V/Q: physiologic R-L shunt Anatomic shunts •
- Right-to-left cardiac shunts Inadequate O2 transport to tissues •
- Anemia or abnormal Hgb •
- Hypovolemic shock Inadequate capability of the cells to use oxygen (uncoupling of oxidative phosphorylation) •
- Metabolic abnormalities, cyanide toxicity
Name the 4 major factors that will shift the oxygen-hemogloblin dissociation curve to the right.
Situations when there is a decreased affinity of Hb to oxygen → Unloading of O2 (great in tissue)
- Increased PCO2
- Decreased pH (more acidic)
- Increased temp
- Increased 2,3-DPG (byporduct of glycolysis)
Name the factors that can affect the oxygen-hemoglobin dissociation curve?
• pH Changes:
o Acidic (7.4 → 7.2): Shifts curve to right (about 15%)
o Basic (7.4 → 7.6): Shifts curve to left
- ↑ CO2 concentration → Shifts curve to right
- ↑ Blood Temperature → Shifts curve to right
- ↑ 2,3-biphosphoglycerate (BPG) → Shifts curve to right
o Phosphate compound in blood
Parasympathetic stimulation to airways leads to ….
Bronchoconstriction via acetylcholine release (muscarinic)
Sympathetic stimulation to airways leads to…..
Bronchodilation (B2 adrenergic)
What are factors that affect the diffusion of gas through the respiratory membrane?
- Thickness of membrane (edema, fibrosis)
- Surface area of membrane (↓ by lung removal, emphysema)
- Diffusion coefficient of gas in membrane (CO2 20x faster than O2)
- Partial pressure difference of gas btwn 2 sides of membrane (PP> alveoli than in blood (O2)
Net diffusion from alveoli into blood
PP> blood (CO2), net diffusion from blood to alveoli)
What are the effects of emphysema and pulmonary fibrosis on lung compliance?
Emphysema = Increased lung compliance (loss of elastic fibers) Pulmonary Fibrosis = Decreased lung compliance (increased stiffness of the lungs)
What are the layers of the respiratory membrane?
o Layer of fluid lining alveolus (containing surfactant: surface tension of alveolar fluid)
o Alveolar epithelium composed of thin epithelial cells o Epithelial basement membrane
o Thin interstitial space btwn alveolar epithelium and capillary membrane
o Capillary basement membrane (fuses with alveolar epithelial basement membrane)
o Capillary endothelial membrane
What are the main forms that CO2 travels in the body?
- Dissolved in solution
- Bicarbonate (Major form)
- Combined with hemogloblin (o CO2 reacts with water, amine radicals of Hgb → carbaminohemoglobin (CO2Hgb)
o Reversible reaction – slow!!
o Only small amount of CO2 reacts this way (1/4th quantity of Hgb)
o Carbamino + Hgb and plasma protein: 30% total amount transported
What are the two extremes of V/Q mismatches?
Ventilation-perfusion ratio (V/Q): Respiratory exchange when imbalance btwn alveolar ventilation and alveolar blood flow
o No exchange f gases V/Q = 0 → Ventilation zero, yet there is still perfusion V/Q = infinity →Ventilation adequate, but zero perfusion
What are the two qualities controlled in the inspiratory ramp?
- Rate of increase of ramp signal
- Limiting point at which ramp stomp sudddenly decreases
Rate of increase of ramp signal - during heavy respiration, ramp increases rapidly, fills the lungs rapidly
Limiting point of ramp cessation - earlier ramp ceases the shorter the duration of inspiration – and ultimately, increases respiration frequency.
Ramp - weak and stead increase of action potential to inspirator muscle, then ceases.
What controls the mechanism of pulmonary hypoxic vasconstriction?
Direct action of alveolar PO2 on the vascular smooth muscle of pulmonary arterioles
HYPOXIC pulmonary vasoconstriction (HPV) is a reflex contraction of vascular smooth muscle in the pulmonary circulation in response to low regional partial pressure of oxygen (Po2). This vasoconstriction by the pulmonary vasculature represents its fundamental difference from the systemic circulation, which typically vasodilates in response to hypoxia.
What determines tissue PO2?
Tissue PO2 determined by rate of O2 transport to tissue in blood and rate at which O2 is used by tissues


