BIOC34

• what is the minute ventilation per minute

  6 L per minute of air
• how much of the air reaches the alveoli after some ventilates the dead space

  4.2 L per minute
• how much oxygen does the air contain

  21% oxygen
• how much oxygen reaches the alveoli per minute

  4.2 L > 4200 x 21% =

  882ml of oxygen
• how much out of the 882ml oxygen diffuses to the blood

  250ml
• how many liters does a human consume per day

  250 ml x 1440 (minutes in a day) / 1000 (to get liters) =

  360 L
• haemoglobin contains how much of O2 in the blood

  98.5%
• structure of haemoglobin

  4 globin subunits (2 alpha & 2 beta)

  - each subunit has heme group

  - heme group has a porphyrin ring w iron molecule in the center

  - iron is site of O2 binding
• carbonic anhydrase (CA)

  enzyme that catalyzes the reversible hydration/ dehydration of

  
  

  CO2 + H2O = HCO3 + H+
• where is carbonic anhydrase found

  - in red blood cells

  - in kidney

  - parietal cells lining the stomach & other tissues
• equation of oxygen binding to haemoglobin

  O2 + H+Hb = O2Hb + H+
• O2 movement in the lungs

  - In lungs O2 diffuses into blood then red cell

  - binds to haemoglobin

  - haemoglobin loses H+ ion

  - H+ ion react with HCO3 in the cell to make CO2 + H2O

  - CO2 diffuses out into alveolar gas & lost as we expire
• CO2 movement in the tissues

  - in tissues CO2 diffuses into red cell

  - reacts with H2O to form H+ & HCO3

  - H+ binds to Hb

  - Hb loses its O2

  - O2 free to diffuse into the tissues
• why does PH have a significant effect on oxygen-haemoglobin binding

  both CO2 hydration/ dehydration and the oxygenation/ deoxygenation of Hb are influenced by H+ ions
• what is the form of CO2 in systemic arterial blood

  89.6% as bicarbonate ions

  5.5% dissolved in blood

  4.9% bound to haemoglobin
• oxygen equilibrium (or disassociation ) curve

  *quantifies binding of oxygen to haemoglobin

  
  

  X-axis: partial pressure of oxygen in mmHg on

  Y-axis: level of oxygen-Hb saturation
• what shape is the graph for oxygen equilibrium and why

  sigmoidal due to positive cooperativity
• positive cooperativity

  -binding of 1 O2 molecule to a Hb facilitates binding of a second and so on

  
  

  low partial pressure: Hb does not have a high affinity for oxygen > as 1 molecule becomes bound > other heme groups increase their affinity
• p50 of oxygen

  partial pressure of oxygen at which 50% of haemoglobin is bound with oxygen
• what affects the OEC curve to shift

  - temperature

  - pH

  - CO2

  - small organic ions
• meaning of OEC curve shifting left

  - decrease in p50

  - increase in O2-Hb affinity
• meaning of OEC curve shifting right

  - increase in p50

  - decrease in O2-Hb affinity
• anaemia

  - lower amount of red cells

  - reduced capacity to carry oxygen
• polycythaemia

  - overpopulation of red cells

  - greater capacity to carry oxygen
• sickle cell anaemia

  - point mutation in haemoglobin beta chain > causes Hb to adhere

  - makes blood cell to be 'sickle' shaped

  - abnormal form of Hb makes red blood cells less efficient at O2 transport

  
  

  - symptom: fatigue
• what 5 factors affect oxygen-Hb binding

  - temperature

  - pH

  - partial pressure of CO2

  - 2,3-diphospoglycerate (byproduct of glycolysis)

  - chloride ions
• modification of O2-Hb binding: temperature

  breathing cooler air than 37C: lung gas is cooler > lower p50 > higher binding affinity

  
  

  metabolically active tissues: have elevated temperature (heat is a by-product of metabolism) > higher p50 > lower binding affinity
• modification of O2-Hb binding: pH

  metabolically active tissues: pH is reduced > increase in p50 > decrease in O2-Hb binding affinity

  
  

  lungs: CO2 is excreted > blood pH increases > decrease in p50 > increase in O2-Hb binding affinity
• carbamino effect

  refers to the CO2 produced by tissues to haemoglobin > causes reduction in affinity & increase in p50
• modification of O2-Hb binding: 2,3-DPG

  * normal conditions (high blood-oxygen content): enzymes that produce 2,3-DPG are inhibited

  
  

  hypoxia: 2,3-DPG is produced > causes a decrease in O2-Hb binding affinity
• difference in fetal haemoglobin

  - have different globin molecules

  - have higher affinity for oxygen than mother
• why is exposure to carbon monoxide fatal

  - has a greater affinity for haemoglobin

  - has far lower p50 than O2

  - binds to haemoglobin the same way O2 does & blocks O2 binding
• Haldane effect

  - deoxygenated blood can carry more CO2 than oxygenated blood

  
  

  * reason:

  1) binding of O2 to Hb decreases affinity of Hb for CO2

  2) CO2 is in the form of HCO3 > oxygenation of Hb > decreases bicarbonate ions
• ventilation-perfusion matching

  - relative ratio of air flow in & out of lungs to flow of blood through the lungs

  
  

  V/Q = ventilation perfusion ratio

  V: ventilation

  Q: blood flow

  
  

  *in healthy person; ration should be 1
• ventilation perfusion ratio for obstruction in airways

  - Ventilation decreases

  - Perfusion stays the same

  - ratio decreases
• physiologic shunt

  - even if blood flows through the alveoli, it remains deoxygenated (from dead tissue from smoking prevent air from reaching alveoli)
• ventilation perfusion ratio for capillary blockage

  - ventilation remains same

  - perfusion decreases

  - ratio increases
• physiologic dead space

  alveoli are ventilated but no blood to oxygenate (smoking damaging the alveolar capillaries
• ventilation perfusion ratio of the lung

  bottom of lungs: greater blood flow > some blood isnt oxygenated > physiologic shunt

  
  

  top of lungs: less blood flow > no blood to oxygenate > physiologic dead space

  
  

  *total ventilation perfusion ratio is 1:1 (middle of lungs)
• Partial pressure of gases

  Pressure exerted by a specific gas in a gas mixture