Respiration Respiration

Control of BreathingControl of BreathingDynamics of BreathingDynamics of Breathing

External/Internal RespirationExternal/Internal RespirationGas Transport in BloodGas Transport in Blood

Control of BreathingControl of BreathingPRIMARY MECHANISMPRIMARY MECHANISM• [CO[CO22] and [H] and [H++] within the blood are the primary ] within the blood are the primary

stimuli that affect a person’s breathing rate/depth.stimuli that affect a person’s breathing rate/depth.• COCO22 and H and H++ levels in the blood (including levels in the blood (including allall ways ways

that they are carried) are detected by that they are carried) are detected by chemoreceptors chemoreceptors (chemical-sensitive nerve (chemical-sensitive nerve endings) in the endings) in the Respiratory Center Respiratory Center of the of the MEDULLA OBLONGATA MEDULLA OBLONGATA in the brainstem (top of in the brainstem (top of spinal cord).spinal cord).• The The Medulla OblongataMedulla Oblongata is the part of the brain that is the part of the brain that

controls the body’s organ systems. (p.334-335)controls the body’s organ systems. (p.334-335)• The The respiratory center respiratory center is a cluster of nerve cells that is a cluster of nerve cells that

trigger inspiration through automatic, fairly rhythmic trigger inspiration through automatic, fairly rhythmic discharges. discharges.

COCO22 and H and H++ ions are also detected by ions are also detected by Carotid Carotid BodiesBodies (chemoreceptors) in the carotid arteries, and (chemoreceptors) in the carotid arteries, and by by Aortic Bodies Aortic Bodies (chemoreceptors) located in the (chemoreceptors) located in the aorta.aorta.

-- these bodies communicate (via nerves) with -- these bodies communicate (via nerves) with the Respiratory Center when COthe Respiratory Center when CO22/H/H++ levels are too levels are too high/low.high/low.

• When the levels of COWhen the levels of CO22/H/H++ increase in the blood increase in the blood (usually coupled with decreased O(usually coupled with decreased O22), the RATE and ), the RATE and DEPTH of breathing increases. Vice versa too…DEPTH of breathing increases. Vice versa too…

• The Respiratory Center receives signals from the The Respiratory Center receives signals from the Carotid/Aortic Bodies and sends a nerve message to Carotid/Aortic Bodies and sends a nerve message to the diaphragm and intercostal muscles to contract the diaphragm and intercostal muscles to contract more often and for longer (fig. 15.6 p. 290).more often and for longer (fig. 15.6 p. 290).

*** An increase of 0.3% CO*** An increase of 0.3% CO22 in the blood DOUBLES the in the blood DOUBLES the breathing rate!!!breathing rate!!!

SECONDARY MECHANISMSECONDARY MECHANISMo OO22 levels in the blood are detected by the same levels in the blood are detected by the same

Carotid and Aortic Bodies. Carotid and Aortic Bodies. o Oxygen levels have little effect on the Oxygen levels have little effect on the

respiratory center, unless there exists an respiratory center, unless there exists an extremeextreme deficiency. deficiency.

o Cases could be:Cases could be:o High Altitudes, CO poisoning, extreme blood loss.High Altitudes, CO poisoning, extreme blood loss.o The Carotid/Aortic Bodies detect the extreme O2

deficiency and signal the Respiratory Center to increase the rate/depth of breathing (again, low O2 is usually coupled with high CO2/H+, but not necessarily in extreme cases – some anaerobic respiration can produce CO2 as a byproduct).

Hyperventilation lowers CO2 levels to below normal increases blood pH constricts blood vessels in brain lowers O2 levels in brain faint. Breathing into paper bag? Increases CO2 levels to keep pH nearer to normal…

Synchronicity!!!Synchronicity!!!

The respiratory center responds to a The respiratory center responds to a variety of nervous and chemical signals, variety of nervous and chemical signals, adjusting the rate/depth of breathing adjusting the rate/depth of breathing accordingly.accordingly.

Control of breathing is only effective if it Control of breathing is only effective if it is synchronized with the circulatory is synchronized with the circulatory system.system.eg. During exercise, cardiac output is aligned eg. During exercise, cardiac output is aligned

with the increased breathing rate, thus with the increased breathing rate, thus enhancing the Oenhancing the O22 supply and CO supply and CO22 removal. removal.

Dynamics of Breathing -- Dynamics of Breathing -- InspirationInspiration

The respiratory center signals the diaphragm and The respiratory center signals the diaphragm and the intercostal (rib) muscles to the intercostal (rib) muscles to contractcontract..

Results: normally ‘dome-shaped’ diaphragm Results: normally ‘dome-shaped’ diaphragm flattens out; intercostals contract to move ribcage flattens out; intercostals contract to move ribcage up and out.up and out.

* during ‘rest’ (normalcy), only the diaphragm contracts; * during ‘rest’ (normalcy), only the diaphragm contracts; intercostals contract during stressful/exertive situations.intercostals contract during stressful/exertive situations.

- Both of these contractions/movements serve to Both of these contractions/movements serve to increase the size of the thoracic cavity.increase the size of the thoracic cavity.

- Since the lungs are attached to the diaphragm and Since the lungs are attached to the diaphragm and the intercostals/ribs by the intercostals/ribs by pleural membranespleural membranes, the , the contraction of each (and the increased thoracic contraction of each (and the increased thoracic cavity volume) increases the size of the lungs (and cavity volume) increases the size of the lungs (and the alveoli, themselves) as well.the alveoli, themselves) as well.

So, the air pressure within the lungs So, the air pressure within the lungs decreases to a point where it is less than decreases to a point where it is less than atmospheric air pressure (ie. the air atmospheric air pressure (ie. the air pressure pressure outsideoutside the body). the body).A notable pressure A notable pressure gradientgradient has now has now

been created and air flows from a been created and air flows from a region of higher pressure (outside of region of higher pressure (outside of body) to a region of lower pressure body) to a region of lower pressure (inside lungs/alveoli).(inside lungs/alveoli).

Result: Air rushes into lungs/alveoli.Result: Air rushes into lungs/alveoli.Fig. 15.7a p. 291.Fig. 15.7a p. 291.

Humans breathe due to Humans breathe due to negative pressurenegative pressure – air does not force the lungs open, they are – air does not force the lungs open, they are opened up before air enters; a negative opened up before air enters; a negative (relative to the ‘outside’ of the body) pressure (relative to the ‘outside’ of the body) pressure induces this.induces this.

In other words, a partial In other words, a partial vacuumvacuum is created in is created in the lungs/alveoli – air flows into this vacuum-the lungs/alveoli – air flows into this vacuum-like region of space.like region of space.

Inspiration is an Inspiration is an activeactive process since muscles process since muscles must must contractcontract in order for it to occur. in order for it to occur.

The stretch receptors in the alveolar walls The stretch receptors in the alveolar walls signal the respiratory center to stop signal the respiratory center to stop stimulating the diaphragm/intercostals – end stimulating the diaphragm/intercostals – end of inspiration.of inspiration.

Dynamics of Breathing -- Dynamics of Breathing -- ExpirationExpiration

Upon ceased stimulation from the Upon ceased stimulation from the respiratory center, the diaphragm and the respiratory center, the diaphragm and the intercostals relax and return to their intercostals relax and return to their resting positions:resting positions:The diaphragm resumes its dome shape by The diaphragm resumes its dome shape by

pushing upward;pushing upward;The intercostals relax, dropping the ribcage The intercostals relax, dropping the ribcage

down and inward. See fig. 15.7b p. 291.down and inward. See fig. 15.7b p. 291.Both of these actions serve to decrease Both of these actions serve to decrease

the size of the thoracic cavity, decrease the size of the thoracic cavity, decrease the size of the lungs (the lungs the size of the lungs (the lungs recoilrecoil), ), and increase the air pressure in the lungs and increase the air pressure in the lungs to greater than that of atmospheric air.to greater than that of atmospheric air.

Air, once again, flows from a region of Air, once again, flows from a region of higher pressure (the lungs/alveoli) to a higher pressure (the lungs/alveoli) to a region of lower pressure (the ‘outside’).region of lower pressure (the ‘outside’).

Expiration is a Expiration is a passivepassive process in that it process in that it simply involves the simply involves the relaxationrelaxation of muscles. of muscles.

That said, expiration, at times, may be That said, expiration, at times, may be activeactive in nature when breathing is deeper in nature when breathing is deeper and/or more rapid (eg. during exercise).and/or more rapid (eg. during exercise).Intercostal muscle contractions can FORCE the Intercostal muscle contractions can FORCE the

ribcage down and in with more vigor;ribcage down and in with more vigor;Contraction of abdominal muscles can push Contraction of abdominal muscles can push

diaphragm upwards with more force.diaphragm upwards with more force.Thus, more air might be expelled at a faster Thus, more air might be expelled at a faster

rate.rate.

Lung Air CapacityLung Air Capacity The volume of air a human inhales and exhales The volume of air a human inhales and exhales

with each breath is called with each breath is called tidal volumetidal volume (avg = (avg = 500 mL).500 mL).

The The maximummaximum volume of air that can be volume of air that can be inhaled/exhaled during forced breathing is known inhaled/exhaled during forced breathing is known as as vital capacityvital capacity (avg = 4-5 L). (avg = 4-5 L).

The lungs are actually able to hold more air than The lungs are actually able to hold more air than the vital capacity, but since it is impossible to the vital capacity, but since it is impossible to completely empty (and thus, collapse) the alveoli, completely empty (and thus, collapse) the alveoli, a a residualresidual volumevolume of air remains in the lungs of air remains in the lungs after active expiration (avg = 1.2 L). This air after active expiration (avg = 1.2 L). This air plays no role in gas exchange. Certain plays no role in gas exchange. Certain respiratory disorders increase the residual volume respiratory disorders increase the residual volume of the lungs (more useless air = less chance to of the lungs (more useless air = less chance to get useful air get useful air weak, short of breath, etc). weak, short of breath, etc).

Avg total lung capacity = 6 L.Avg total lung capacity = 6 L. See fig. 15.5 p. 288See fig. 15.5 p. 288

Some inspired air (in Some inspired air (in allall people) never reaches people) never reaches the lungs; instead it fills the respiratory tract the lungs; instead it fills the respiratory tract where there exists no gas exchange where there exists no gas exchange functioningfunctioning

Known as ‘dead space’ air…Known as ‘dead space’ air…To increase the chances of inspired air To increase the chances of inspired air

reaching the lungs, and expired air actually reaching the lungs, and expired air actually reaching the ‘outside’, it is better to breathe reaching the ‘outside’, it is better to breathe slowly & deeplyslowly & deeply – luckily, the medulla – luckily, the medulla promotes this.promotes this.This idea is evident when getting a cramp while This idea is evident when getting a cramp while

running (the cramp is indicative of anaerobic running (the cramp is indicative of anaerobic respiration taking place in certain muscles (usually respiration taking place in certain muscles (usually the abs)) – it is better to exhale deeply to rid body the abs)) – it is better to exhale deeply to rid body of dead space air so that the next inhalations of dead space air so that the next inhalations contain mainly ‘fresh’ air with a higher % of Ocontain mainly ‘fresh’ air with a higher % of O22..

External Respiration (Location: External Respiration (Location: Lungs)Lungs)

Refers to the exchange of ORefers to the exchange of O22 and CO and CO22 between the alveoli and the blood in the between the alveoli and the blood in the alveolar (pulmonary) capillaries.alveolar (pulmonary) capillaries.

Recall that the two structures are, at Recall that the two structures are, at most, 0.2 micrometers apart and that most, 0.2 micrometers apart and that each of them possess walls that are only each of them possess walls that are only one cell thick – excellent conditions for one cell thick – excellent conditions for efficient exchange.efficient exchange.

Transfer occurs via simple Transfer occurs via simple diffusiondiffusion, but , but the gradient is based on gas pressures.the gradient is based on gas pressures.

All gases exert pressure (proportional to All gases exert pressure (proportional to their concentrations); each indiv. gas their concentrations); each indiv. gas exerts its own exerts its own partialpartial pressure (PP). pressure (PP).

The PPThe PPO2O2 in the alveoli (due to the inspiration in the alveoli (due to the inspiration of Oof O22-laden air) is higher than the PP-laden air) is higher than the PPO2O2 in the in the lung capillaries (due to the usage of/transfer lung capillaries (due to the usage of/transfer of Oof O22 by/to the tissue cell capillaries in the by/to the tissue cell capillaries in the body).body).

Thus, OThus, O22 flows (via the principles of diffusion) flows (via the principles of diffusion) from a region of higher PP (alveoli) to a from a region of higher PP (alveoli) to a region of lower PP (blood).region of lower PP (blood).

COCO2 2 follows a similar gradient, except that it follows a similar gradient, except that it moves, via diffusion (higher PP to lower PP), moves, via diffusion (higher PP to lower PP), from the lung capillaries into the alveoli for from the lung capillaries into the alveoli for expiration.expiration.COCO2 2 is produced as a byproduct of cellular is produced as a byproduct of cellular

respiration by the body’s cells – high blood PPrespiration by the body’s cells – high blood PPCO2CO2

PPPPCO2CO2 in inhaled air is quite low. in inhaled air is quite low.

Internal Respiration (Location: Body Internal Respiration (Location: Body Cells)Cells)

Gas exchange that occurs at the tissue cell level Gas exchange that occurs at the tissue cell level is between the blood in the capillaries and the is between the blood in the capillaries and the ECF (tissue fluid) – the material entering the ECF ECF (tissue fluid) – the material entering the ECF eventually enters cells; the material ‘waiting’ in eventually enters cells; the material ‘waiting’ in the ECF to enter the blood originated within the the ECF to enter the blood originated within the cells.cells.

PPPPO2O2 in blood > PP in blood > PPO2O2 in ECF in ECF O O22 diffuses into ECF diffuses into ECF for eventual entry into cells.for eventual entry into cells.

PPPPCO2CO2 in ECF > PP in ECF > PPCO2CO2 in blood in blood CO CO22 diffuses into diffuses into blood (in order to reach lungs for exhalation).blood (in order to reach lungs for exhalation).

**Both external and internal respiration involve the **Both external and internal respiration involve the movement of water and other substances as well movement of water and other substances as well (Capillary-Tissue exchange) – but here, in the (Capillary-Tissue exchange) – but here, in the Respiration Unit, we are focusing primarily on the Respiration Unit, we are focusing primarily on the driving force (gradient) behind the movement of driving force (gradient) behind the movement of gases.gases.

Transport of Gases in BloodTransport of Gases in BloodOXYGENOXYGEN:: Oxygen binds loosely and therefore reversibly Oxygen binds loosely and therefore reversibly

to hemoglobin (Hb) in RBCs.to hemoglobin (Hb) in RBCs. One Hb molecule can bind up to 4 OOne Hb molecule can bind up to 4 O22 molecules molecules Once this occurs, and it is Once this occurs, and it is saturated, saturated, it is it is

referred to as referred to as oxyhemoglobin oxyhemoglobin ((HbOHbO22).). Hb + OHb + O22 HbO HbO22 (at lungs) (at lungs) HbOHbO22 Hb + O Hb + O22 (at tissue cells) (at tissue cells) Hb = Hb = DeoxyhemoglobinDeoxyhemoglobin (purplish) whereas (purplish) whereas

HbOHbO22 = = Oxyhemoglobin Oxyhemoglobin (bright red).(bright red). Within the lung capillaries, 98% of OWithin the lung capillaries, 98% of O22 joins Hb joins Hb

whereas 2% simply dissolves in the plasma whereas 2% simply dissolves in the plasma (oxygen is fairly non-polar).(oxygen is fairly non-polar).

Hb binds more readily to oxygen at a relatively Hb binds more readily to oxygen at a relatively cooler temperature (37cooler temperature (3700 C) and a higher pH C) and a higher pH (7.40) – conditions that exist in the lung (7.40) – conditions that exist in the lung capillaries (since they are ‘closer’ to the outside capillaries (since they are ‘closer’ to the outside of the body). (See fig. 15.9 p. 294)of the body). (See fig. 15.9 p. 294)

Once Hb has 1, 2, or 3 OOnce Hb has 1, 2, or 3 O22 molecules bound to it, molecules bound to it, its ‘attraction’ (affinity) for the 2its ‘attraction’ (affinity) for the 2ndnd, 3, 3rdrd, and 4, and 4thth molecule increases exponentially. Thus, all Hb molecule increases exponentially. Thus, all Hb molecules are saturated with Omolecules are saturated with O22..

Conditions at the tissue cells are warmer (38Conditions at the tissue cells are warmer (3800 C) and more acidic (7.38 pH) than those in the C) and more acidic (7.38 pH) than those in the lung capillaries.lung capillaries.

Hb tends to release an appreciable amount Hb tends to release an appreciable amount (~28%) of its O(~28%) of its O22 in these conditions. in these conditions.

The difference in the affinity of Hb for OThe difference in the affinity of Hb for O2 2 under under different temp./pH conditions = the different temp./pH conditions = the Bohr ShiftBohr Shift..

The ‘freed’ OThe ‘freed’ O22 then diffuses across the capillary walls then diffuses across the capillary walls into the ECF, and eventually into cells, following its PP into the ECF, and eventually into cells, following its PP gradient and traveling with water and other stuff gradient and traveling with water and other stuff (recall Tissue/Capillary Exchange). *label Bohr shift!(recall Tissue/Capillary Exchange). *label Bohr shift!

TISSUES

LUNGS

During exercise, muscles heat up and produce lactic During exercise, muscles heat up and produce lactic acid (decr. pH) which promotes Hb to give up even acid (decr. pH) which promotes Hb to give up even more of its Omore of its O22 to the cells (sometimes up to 75%). to the cells (sometimes up to 75%).

INTERNAL SUFFOCATIONINTERNAL SUFFOCATION – Carbon monoxide (CO) – Carbon monoxide (CO) binds to Hb 200x more readily than Obinds to Hb 200x more readily than O22..

Thus, oxygen is prevented from reaching the tissue Thus, oxygen is prevented from reaching the tissue cells on any RBC ‘infested’ with CO.cells on any RBC ‘infested’ with CO.

Therefore, the cells ‘suffocate’.Therefore, the cells ‘suffocate’.

CARBON DIOXIDE (COCARBON DIOXIDE (CO22))

COCO22 is transported through the blood in three ways: is transported through the blood in three ways:

1. 70% is transported as the 1. 70% is transported as the bicarbonate ionbicarbonate ion (HCO (HCO33--) )

in the plasma (more on this in a moment).in the plasma (more on this in a moment).

2. 23% attaches directly to Hb to form 2. 23% attaches directly to Hb to form carbaminohemoglobincarbaminohemoglobin (HbCO (HbCO22))

COCO22 + Hb HbCO + Hb HbCO22

The lower temp./higher pH in the lungs The lower temp./higher pH in the lungs promotes COpromotes CO22 release by Hb. release by Hb.

The higher temp./lower pH at the tissue The higher temp./lower pH at the tissue cells promotes COcells promotes CO22 uptake by Hb. uptake by Hb.3. 7% simply dissolves in the plasma (as 3. 7% simply dissolves in the plasma (as molecular COmolecular CO22).).

** Metaphor: Hb likes O** Metaphor: Hb likes O22 in the winter (O in the winter (O22 is is like a snowman) and hates Olike a snowman) and hates O22 at the beach. at the beach. CO CO22 is opposite…when Hb likes O is opposite…when Hb likes O22, it hates , it hates COCO22, and vice versa…, and vice versa…

@ TISSUES

@ LUNGS

The ‘Beach’:

Higher temperature, Lower pH

‘Winter’:

Lower temperature, Higher pH

O2

“snowman”

Bicarbonate Ion Transport of COBicarbonate Ion Transport of CO22

As mentioned previously, 70% of the tissue cell-As mentioned previously, 70% of the tissue cell-produced COproduced CO22 is transported in the plasma is transported in the plasma (dissolved) as HCO(dissolved) as HCO33

--. HCO. HCO33-- acts as a acts as a blood blood

bufferbuffer.. Once COOnce CO22 leaves tissue cells and enters the ECF, leaves tissue cells and enters the ECF,

the blood, and eventually the RBCs, it reacts the blood, and eventually the RBCs, it reacts with water to form carbonic acid (Hwith water to form carbonic acid (H22COCO33) which ) which then dissociates slightly to form HCOthen dissociates slightly to form HCO33

-- and H and H++..

COCO22 + H + H22O O H H22COCO33 H H++ + HCO + HCO33--

- The RBC enzyme - The RBC enzyme carbonic anhydrasecarbonic anhydrase acts to acts to catalyze the first portion of this reaction and the catalyze the first portion of this reaction and the higher tissue temperature promotes the 70% higher tissue temperature promotes the 70% production of the final products.production of the final products.

The HCOThe HCO33-- diffuse out of the RBCs (Cl diffuse out of the RBCs (Cl-- ions move ions move

into RBCs to balance the charge) and are carried in into RBCs to balance the charge) and are carried in the plasma to the lungs, leaving Hthe plasma to the lungs, leaving H++ behind. behind.

The remaining HThe remaining H++ are picked up by Hb (or else the are picked up by Hb (or else the pH would severely drop – blood proteins would be pH would severely drop – blood proteins would be denatured, as would vessel walls) to form denatured, as would vessel walls) to form reduced reduced hemoglobin (HHb)hemoglobin (HHb), which is carried within RBCs , which is carried within RBCs to the lungs.to the lungs.

HH++ + Hb + Hb HHb (at tissues, within RBCs). HHb (at tissues, within RBCs). Thus, Hb acts to Thus, Hb acts to bufferbuffer the blood and keep it at, or the blood and keep it at, or

near, its optimal pH.near, its optimal pH. FYI: optimal blood pH = 7.4 due to the fact that FYI: optimal blood pH = 7.4 due to the fact that

HCOHCO33-- is a better base than it is an acid and that is a better base than it is an acid and that

there is a much higher concentration of it in the there is a much higher concentration of it in the blood than COblood than CO22 and H and H22O (which, in combo, produce O (which, in combo, produce HH22COCO33).).

Once blood reaches the lungs, the HCOOnce blood reaches the lungs, the HCO33- - and and

HH++ must be converted back to CO must be converted back to CO22 and water and water so that the majority of the COso that the majority of the CO22 can be expired. can be expired.

At the lower temp. and higher pH conditions in At the lower temp. and higher pH conditions in the lung capillaries, Hb gives up Hthe lung capillaries, Hb gives up H++ (so that Hb (so that Hb can pick up Ocan pick up O22), HCO), HCO33

-- diffuses back into the diffuses back into the RBC (ClRBC (Cl-- ions diffuse back out), reacts with H ions diffuse back out), reacts with H++ to form Hto form H22COCO33, which then forms CO, which then forms CO22 and and water; the COwater; the CO22 then diffuses into the alveoli then diffuses into the alveoli from the blood.from the blood.

Carbonic anhydraseCarbonic anhydrase helps again, but this helps again, but this time catalyzes the reverse reaction at the time catalyzes the reverse reaction at the cooler temperature. Also, the diffusion of the cooler temperature. Also, the diffusion of the other 30% of the COother 30% of the CO2 2 into the alveoli drives the into the alveoli drives the following reaction to the right:following reaction to the right:

HH++ + HCO + HCO33-- H H22COCO33 CO CO22 + H + H22OO

See fig. 15.8 p. 293 for summary See fig. 15.8 p. 293 for summary diagramdiagram

Read pp. 295-298 (for interest only) – Read pp. 295-298 (for interest only) – Respiratory Disorders…including figs. Respiratory Disorders…including figs. 15.10 p. 295 and 15.11 p. 296.15.10 p. 295 and 15.11 p. 296.

Finished!!!Finished!!!