– inhale – oxygen travels down the bronchi and bronchioles – into the alveoli – oxygen strikes the moist coating of the alveolar wall – dissolves in this liquid –  moves by diffusion through the cells of the alveoli, and into the cells of the capillaries – enters the red blood cells which will transport it to the rest of the body.

– the component of the red blood cells that is able to carry the oxygen is called hemoglobin.  This is a red coloured molecule that consists of two parts:

1) heme – an organic molecule that contains iron.

2) globin – a protein that wraps itself around the heme.

– oxygen forms a loose chemical bond with hemoglobin by attaching to the iron in the heme portion of the hemoglobin.

– when oxygen is bound to the hemoglobin, the molecule is called oxyhemoglobin

– this bond between the oxygen molecule and the hemoglobin is easily formed and also easily broken –  ensures that the oxygen can be easily picked up by the red blood cell, and also easily released when the oxygen reaches a destination that requires oxygen.

Hb   + O2 ->   Oxyhemoglobin

in area where O2 concentration is high:   Hb +  O2 -> OxyHb

in area where O2 concentration is low:    OxyHb  ->  Hb +  O2

– Red blood cells circulate at a very fast rate within the blood stream – pass through the capillaries that come in contact with every cell in our bodies

– When red blood cells with oxyhemoglobin pass through tissues with lower concentration of oxygen lower than theirs –  oxygen is released from the iron molecule – oxygen moves by diffusion from the blood, through the capillary walls and into the tissue cells – enters the mitochondria where cellular respiration occurs

– the red blood cells that now do not carry oxygen circulate back to the lungs so that more oxygen can be picked up by the hemoglobin and circulated once again

– most of oxygen is picked up by Hb in RBC, but small amount dissolves in water portion of plasma (to depend on this – must circulate 130X more blood per minute)

NOTE: remember that rate of diffusion depends on

1.  Large exchange area

2.  High concentration difference

3.  Short diffusion distance

Carbon Dioxide Transport

– Cellular respiration uses oxygen and produces carbon dioxide as a waste product – carbon dioxide diffuses from areas in our bodies where it is in high concentration to the liquid part of the blood and the red blood cells, where its concentration is lower

– There are three ways that carbon dioxide can be transported:

1) A small portion (5%) is carried as dissolved gas molecules in the water part of the blood

2) A small portion (5%) combines with hemoglobin and is carried to the lungs

3) The largest amount (90%) reacts with water to produce bicarbonate ions (HCO3).  – this reaction is accelerated by enzymes that found exclusively in the red blood cells

– bicarbonate ions diffuse out into the liquid part of the blood and is transported to the lungs

– at the lungs, the carbon dioxide diffuses from the blood into the air spaces in the lung alveoli and is excreted during exhalation

CO2 +   H2O   ->   H2CO3 ->   HCO3–   +   H+

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