H.6 Gas ExchangeH.6 Gas Exchange

HemoglobinHemoglobin

Hemoglobin is a protein found in Hemoglobin is a protein found in RBC’s composed of 4 polypeptides, RBC’s composed of 4 polypeptides, each polypeptide containing a heme each polypeptide containing a heme group. Each heme group contains an group. Each heme group contains an iron atom. Each iron atom can bind iron atom. Each iron atom can bind with one oxygen molecule (Owith one oxygen molecule (O22))

Each time an oxygen molecule binds to a Each time an oxygen molecule binds to a hemoglobin molecule the molecule hemoglobin molecule the molecule changes shape.changes shape.

The shape changes the hemoglobin’s The shape changes the hemoglobin’s affinity for oxygen.affinity for oxygen.

A hemoglobin with no oxygen molecules A hemoglobin with no oxygen molecules has the least affinity for oxygen.has the least affinity for oxygen.

A hemoglobin with 3 oxygen has the A hemoglobin with 3 oxygen has the highest affinity for oxygenhighest affinity for oxygen

A hemoglobin with 4 oxygen has no A hemoglobin with 4 oxygen has no affinity for oxygen.affinity for oxygen.

HbHb44 is used as an abbreviation for is used as an abbreviation for hemoglobin. A hemoglobin with one hemoglobin. A hemoglobin with one oxygen would be written as Hboxygen would be written as Hb44OO22

How hemoglobin’s affinity for How hemoglobin’s affinity for oxygen changesoxygen changes

(No affinity)

H.6.1H.6.1

Partial pressure – the pressure Partial pressure – the pressure exerted by a single type of gas when exerted by a single type of gas when it is found in a mixture of gases.it is found in a mixture of gases.

PPtotaltotal= P= P11+P+P22+P+P33…..….. Can be calculated by taking the total Can be calculated by taking the total

pressure of a mixture of gases within pressure of a mixture of gases within which a gas occurs, multiplied by the which a gas occurs, multiplied by the percentage of the total volume the percentage of the total volume the gas occupies.gas occupies.

H.6.2 Dissociation CurvesH.6.2 Dissociation Curves

An oxygen dissociation curve is a An oxygen dissociation curve is a graph that shows how various forms graph that shows how various forms of hemoglobin and myoglobin of hemoglobin and myoglobin perform under various conditions.perform under various conditions.

X axis is partial pressure of oxygenX axis is partial pressure of oxygen Y axis is percent hemoglobin Y axis is percent hemoglobin

saturationsaturation

Adding oxygen to hemoglobin is Adding oxygen to hemoglobin is referred to as loading/associationreferred to as loading/association

Removing oxygen to hemoglobin is Removing oxygen to hemoglobin is referred to as unloading/dissociationreferred to as unloading/dissociation

Hemoglobin is fully saturated when it Hemoglobin is fully saturated when it is bound to 4 oxygen moleculesis bound to 4 oxygen molecules

Dissociation curveDissociation curve

As the partial pressure of oxygen increases so the Hb becomes more saturated with oxygen.

There is high affinity by each haem group and oxygen at high partial pressures.

There is low affinity between each haem group and oxygen at low partial pressures.

The oxygen dissociation curves show The oxygen dissociation curves show the tendency of hemoglobin to bind the tendency of hemoglobin to bind to oxygen (affinity) and separate to oxygen (affinity) and separate from oxygen (dissociation).from oxygen (dissociation). RememberRemember: Oxygen can only move : Oxygen can only move in and out of blood in either the lung in and out of blood in either the lung capillaries or the tissue capillaries. As capillaries or the tissue capillaries. As blood circulates its % saturation blood circulates its % saturation does notdoes not change, except in the two change, except in the two instances illustrated belowinstances illustrated below

Oxygen LoadingOxygen Loading

Blood in the pulmonary artery has a Po2 = 5 kPa. This blood goes to the alveoli of the lung.

The Alveoli has a Po2 = 16 kPa

Hb is 100% saturated at 10kPa.

The fully saturated Hb will be carried away from the lung in the pulmonary vein

Oxygen UnloadingOxygen UnloadingThe demand for oxygen within the tissues changes and haemoglobin responds to meet the demand for oxygen.Blood leaves the lung/ pulmonary vein/ aorta at 100% saturation Blood arrives at the tissues 100% saturated with oxygen since to exchange is not possible up to that point (thickness of the walls of blood vessels + flow rate) A typical respiring tissue would have a low Po2 = 5-7 kPa. .Oxygen dissociates from the haemoglobin and diffuses into the cell.

MyoglobinMyoglobin

An oxygen binding protein found. in An oxygen binding protein found. in muscle. Myoglobin makes muscle muscle. Myoglobin makes muscle “dark” “dark”

Myoglobin has one polypeptide and 1 Myoglobin has one polypeptide and 1 heme group so can bind to one heme group so can bind to one oxygenoxygen

Myoglobin allows oxygen to be Myoglobin allows oxygen to be stored in muscle tissue in case of stored in muscle tissue in case of anaerobic situations at which time anaerobic situations at which time the oxygen will dissociate and be the oxygen will dissociate and be used for cellular respirationused for cellular respiration

This delays the onset of lactic acid This delays the onset of lactic acid fermentationfermentation

Myoglobin has a higher affinity for oxygen than haemoglobin and retains its oxygen until very low partial pressures occur.

Such low partial pressures occur when the muscle is working very hard and the oxygen is used up in aerobic respiration.

Myoglobin unloads its oxygen when there is a high rate of respiration such as during intense exercise.The oxygen is replaced during rest as excess post-exercise oxygen consumption

Fetal HemoglobinFetal Hemoglobin

Fetal hemoglobin has a higher Fetal hemoglobin has a higher affinity for oxygen than adult affinity for oxygen than adult hemoglobin.hemoglobin.

In the capillaries of the placenta In the capillaries of the placenta adult hemoglobin dissociates oxygen adult hemoglobin dissociates oxygen and fetal hemoglobin loads that and fetal hemoglobin loads that same oxygen.same oxygen.

At a partial pressure of Po2 = 5 kPa. Adult Hb can retain less than 50% Hb but Fetal HB can associate with a much higher 80 + %. The oxygen dissociates from the adult Hb and is loaded up to the fetal haemoglobin.The Po2 in fetal tissues is very low due to the high metabolic rate associated with fetal growth rates. Therefore although fetal Hb has a higher affinity for oxygen in such a low partial pressure environment of the fetal tissue it unloads oxygen readily. At birth the fetal Hb is replaced with adult Hb

6.3 Carbon Dioxide Transport6.3 Carbon Dioxide Transport

COCO22 is the waste product of ATP is the waste product of ATP production/cellular respirationproduction/cellular respiration

It diffuses out of cells into capillary beds It diffuses out of cells into capillary beds where it enters the circulatory system.where it enters the circulatory system.

It may be transported 3 ways: dissolved It may be transported 3 ways: dissolved in plasma (5%), bound to hemoglobin in plasma (5%), bound to hemoglobin (10%, forms carbaminohemoglobin), or (10%, forms carbaminohemoglobin), or as bicarbonate ions in the RBC’s (85%)as bicarbonate ions in the RBC’s (85%)

To summarize!To summarize!

H.6.4 The Bohr EffectH.6.4 The Bohr Effect

Oxygen carrying capacity varies with Oxygen carrying capacity varies with blood pHblood pH– Low pH lowers the affinity of Hb for Low pH lowers the affinity of Hb for

oxygen, oxygen is unloadedoxygen, oxygen is unloaded– High pH has increases the affinity of Hb High pH has increases the affinity of Hb

for oxygenfor oxygen

Increased blood acidity is associated Increased blood acidity is associated with increasing carbon dioxide levels with increasing carbon dioxide levels in the blood.in the blood.

More COMore CO22 lower pH lower pH lower Hb lower Hb affinity for Oaffinity for O2 2 more O more O2 2 released to released to tissuestissues

Most is transported as bicarbonate.Most is transported as bicarbonate. The RBC cytoplasm contains carbonic The RBC cytoplasm contains carbonic

anhydrase that catalyzes the anhydrase that catalyzes the reaction between COreaction between CO22 and water to and water to form carbonic acid. form carbonic acid.

Carbonic acid then dissociates into Carbonic acid then dissociates into hydrogen ions and bicarbonatehydrogen ions and bicarbonate

Bicarbonate ions are pumped out of Bicarbonate ions are pumped out of the RBC and chloride ions enter the RBC and chloride ions enter (purpose? I am not sure yet!)(purpose? I am not sure yet!)

HbOHbO8 8 acts as a buffer and absorbs acts as a buffer and absorbs hydrogen ions (reducing blood hydrogen ions (reducing blood acidity) which reduces hemoglobin’s acidity) which reduces hemoglobin’s affinity for oxygen. Oxygen is affinity for oxygen. Oxygen is released to the cytoplasm of a cellreleased to the cytoplasm of a cell

In the mitochondria, oxygen acts as a In the mitochondria, oxygen acts as a proton (Hproton (H++) acceptor for the oxidation ) acceptor for the oxidation of NADH and FADHof NADH and FADH

(a) The partial pressure of oxygen in the tissue

(b) At Pco2 = 3kPa Hb has 50% unloaded its oxygen.

(c) At Pco2= 4kPa Hb has approx 80% unloaded its oxygen.

(d) At Pco2= 6kPa Hb has approx 90 % unloaded its oxygen.

From: Click4biology.info

H.6.5 Effects of exercise on H.6.5 Effects of exercise on ventilation rateventilation rate

Exercising muscles produce more Exercising muscles produce more COCO22which decreases blood pH. (a)which decreases blood pH. (a)

Changes in blood pH are detected by Changes in blood pH are detected by the breathing center in the medulla of the breathing center in the medulla of the brain (b)the brain (b)

Chemoreceptors in the aorta and the Chemoreceptors in the aorta and the carotid arteries detect the changes in carotid arteries detect the changes in pH and send impulses to the brain pH and send impulses to the brain stem medulla (c)stem medulla (c)

The cardiac center responds to the The cardiac center responds to the same stimuli and increases heart same stimuli and increases heart rate (d)rate (d)

The breathing center stimulates the The breathing center stimulates the diaphragm and the intercostal diaphragm and the intercostal muscles (e)muscles (e)

To illustrate:To illustrate:

H.6.6 AsthmaH.6.6 Asthma

In as asthma attack, smooth muscle In as asthma attack, smooth muscle of the bronchi constrict, restricting of the bronchi constrict, restricting airflow to the lungairflow to the lung

May be triggered by allergy, May be triggered by allergy, exercise, or a variety of other causesexercise, or a variety of other causes

Check this out for more information Check this out for more information about asthma! about asthma! http://www.nhlbi.nih.gov/health/dci/Diseases/Asthma/Asthma_Causes.html

H.6.7 High AltitudeH.6.7 High Altitude

At higher altitude the atmospheric At higher altitude the atmospheric pressure decreasespressure decreases

The partial pressure of oxygen The partial pressure of oxygen decreasesdecreases

Hb is less saturated than at sea levelHb is less saturated than at sea level Tissues receive less oxygenTissues receive less oxygen Respiration cannot provide sufficient Respiration cannot provide sufficient

ATPATP

These factors cause altitude sickness These factors cause altitude sickness which can cause headache, nausea, which can cause headache, nausea, weakness and rapid pulseweakness and rapid pulse

This can be treated with tylenol, This can be treated with tylenol, hydration and sometimes oxygen!hydration and sometimes oxygen!

Physiological changes due to Physiological changes due to altitudealtitude

After an extended period at altitude an After an extended period at altitude an individual may adapt to the lower individual may adapt to the lower atmospheric pressure in a variety of atmospheric pressure in a variety of ways:ways:– Increased red cell number in bloodIncreased red cell number in blood– Increased vascularisation of the muscleIncreased vascularisation of the muscle– Increases in of myoglobinIncreases in of myoglobin– Increase in number of mitochondria per Increase in number of mitochondria per

muscle cellmuscle cell

– Increases in the concentration of Increases in the concentration of respiratory enzymesrespiratory enzymes

– Improved buffering of pH and utilization Improved buffering of pH and utilization of lactate ions (lactic clearance)of lactate ions (lactic clearance)

Athletes often train at high altitude Athletes often train at high altitude to develop some of these changes in to develop some of these changes in order to enhance performance at order to enhance performance at lower altitudeslower altitudes

It is the recovery period when It is the recovery period when changes take place so by sleeping in changes take place so by sleeping in a hyperbaric chamber, athletes have a hyperbaric chamber, athletes have the benefit of being at high altitude the benefit of being at high altitude without relocating.without relocating.

Those who live at high altitude are Those who live at high altitude are genetically different from the rest of genetically different from the rest of us!us!– Larger thoracic cavityLarger thoracic cavity– Denser alveoli (more per bronchiole)Denser alveoli (more per bronchiole)– More hemoglobinMore hemoglobin– Hemoglobin has a higher affinity for Hemoglobin has a higher affinity for

oxygenoxygen