CASE 5 Flashcards
Hemoglobin
- globular heme protein
- heme binds oxygen and carbon dioxide
- gives red blood cells their color
- has 4 heme groups which surround globon group
- when bound to oxygen it is called oxyhemoglobin
Hb binding to O2
(H)Hb + O2 –> HbO2 (+ H+) (the H+ is coming from the carbonate buffer; oxygen swaps
places
law of mass action
- concentration of free O2 increases –> more O2 binds to Hb and equation shifts to right
- in pulmonary capillaries, oxygen from alveoli diffuses into RBC where it can bind to Hb until it reaches equilibrium
releasing O2 in tissue
- PO2 of cells determines how much oxygen is unloaded from Hb.
- cells increase metabolic activity –> PO2 decreases –> Hb releases more oxygen
binding of O2 to Hb
- first one binds difficult, after the first one, the protein changes shape and it is easier for the rest.
amount of O2 that binds to Hb
depends on 2 factors:
- the PO2 in the plasma surrounding the RBC’s
- the number of potential Hb binding sites available in RBC’s
- Plasma Po2 is primary factor determining what % of the available binding sites are occupied by oxygen, known as percent saturation of Hb.
- when PO2 decreases –> less oxygen is bound to Hb and transported
establishment PO2
- the composition of inspired air
- the alveolar ventilation rate
- the efficiency of gas exchange from alveoli to blood
mean corpuscular hemoglobin
- total number of oxygen-binding sites depends on number of Hb molecules in RBC’s.
- can be estimated by counting the RBC’s and quantifying the amount of Hb.
percent saturation of Hb
amount of oxygen bound to Hb at any given PO2:
(amount of O2 bound / maximum that could be bound) x 100
Oxyhemoglobin saturation curves
- reflects Hb and its affinity for oxygen.;
- normal alveolar and arterial PO2 (100 mmHg), 98% of Hb is bound to O2.
- as the PO2 stays above 60 mmHG, Hb is more than 90% saturated and is fine
Physiological significance shape of curve
- average value venous blood at rest (PO2 = 40 mmHg), Hb is still 75% saturated.
- remaining oxygen is reserve that cells can draw on in metabolism increase.
- metabolic activity increases –> more O2 is used –> PO2 drops –> more O2 will release from Hb
Factors that affect oxygen-Hb binding
Decrease affinity:
1. higher temperature
2. higher PCO2
shift saturation curve to the right
Increase affinity:
1. lower temperature
2. lower PCO2
shift saturation curve to the left.
Bohr effect
a shift in the saturation curve caused by a change in pH
2,3-diphosphateglycerate (2,3-DPG)
- compound in glycolysis pathway
- affects oxygen-Hb binding
- extended periods of low oxygen triggers an increase in 2,3DPG production in RBC’s -> lowers affinity of Hb -> shifts curve to the right
pH effect on affinity
low pH –> more CO2 –> more CO2 binds to Hb –> Hb less affinity to oxygen because some space is occupied
hypercapnia
- elevated pCO2
- it is important that CO2 is removed from the body because hypercapnia causes pH disturbance –> acidosis.
- can also depress CNS function
CO2 and bicarbonate ions
conversion of CO2 to HCO3- has purpose:
- can transport more CO2 from cells to lungs
- HCO3- can act as a buffer and helps stabilize the body’s pH
Carbonate buffer
- CO2 + H2O –> H2CO3 –> H+ + HCO3-
- continues until equilibrium
- to keep the reaction going end products must be removed from cytoplasm of RBC
Two mechanisms to remove free H+ and HCO3-
- chloride shift
2. respiratory acidosis
Chloride shift
- exchanges HCO3- for Cl-
- makes the cell electrical neutral
- bicarbonate is an extracellular buffer
Respiratory acidosis
- removes free H+ from RBC cytoplasm.
- Hb in RBC acts as a buffer and binds H+ + Hb –> HbH
- prevents large changes in body pH
- if PCO2 is elevated much above normal, the buffer does not work. H+ accumulates in plasma
Acidosis/alkalosis
Metabolic: respiratory system will help maintain homeostasis:
- Alkalosis: vomiting a lot, HCL out of body
- Acidosis: renal system does not remove a lot of acid
Respiratory: the metabolic system will help maintain homeostasis:
- alkalosis: high breath rate
- acidosis: low breath rate
Co2 removal at lungs
- PCO2 of alveoli is lower than that of venous blood in pulmonary capillaries –> Co2 diffuses into alveoli –> plasma PCO2 begins to fall
- allows dissolved CO2 to diffuse out of RBC’s
- removal of CO2 causes the H+ to leave Hb
hyperpnea, increase of breathing depth and rate
- more altitude is thinner air = less oxygen/L
- lower Po2 meand lower saturation of Hb –> sensed in carotid bodies, which cause hyperpnea
- inhibits the respiratory center from enhancing the respiratory rate as much as would be required
