Respiration During Exercise

Why Do We Breath?

gas exchange - O2 in, CO2 out

maintain pH balance

support increased ATP demand

Cellular Respiration

utilization and CO2 production by the tissues (think about the krebs cycle)

Pulmonary Respiration

exchange of O2 and CO2 in the lungs

helps remove H+ via CO2 exhalation

Inspiration

the diaphragm pushes downward, ribs lift outward

lung volume goes up

pressure goes down

Expiration

diaphragm relaxes, ribs pulled downward

lung volume goes down

pressure goes up

Inspiration Muscles

sternocleidomastoid

scalenes

external intercostals

internal intercostals

diaphragm

Expiration Muscles

internal intercostals

external abdominal oblique

transverse abdominis

rectus abdominis

Dalton’s Law

the total pressure of a gas mixture is equal to the sum of the pressure that each would exert independently

P v air (dry atmosphere) = PO2 + PCO2 + PN2

Fick’s Law of Diffusion

the rate of gas transfer is proportional to the tissue area, the diffusion coefficient of the gas, and the difference in the partial pressure of the gas on the two sides of the tissue, and inversely proportional to the thickness

O2 Transport in the Blood

99% of O2 is transported bound to hemoglobin

the amount transported per unit volume of blood is dependent on the Hb — each gram of Hb can transport 1.34 ml O2

Oxyhemoglobin

Hb bound to O2 ( 4 O2 bound to 1 Hb)

Deoxyhemoglobin

Hb not bound to O2 (O2 dissolved in plasma)

Shifts in the O2-Hb Dissociation Curve

increase in temperature, 2-3 DPG, and decrease in pH = right shift

enhances O2 unloading at working muscle

Myoglobin

higher O2 affinity

present in slow twitch fibers

O2 reserve in muscle

CO2 Transport in Blood

10% dissolved in plasma

20% bound to Hb - carbamino

70% bicarbonate

1) dissolved CO2

2) CO2 combined with hemoglobin (HbCO2)

3) bicarbonate (HCO3) diffuses out of the RBC and Cl- moves into the RBC to avoid electrochemical imbalance (chloride shift)

Medulla Oblongata

controls breathing

home to respiratory rhythm centers: preBotzinger complex and retrotrapezoidal nucleus

Somatic Motor Neurons

controls the diaphragm

Pons

home to the pneumotaxic center and caudal pons

Central Command

motor cortex signals increase ventilation

Humoral (blood-borne) Chemoreceptors

located in the medulla

PCO2 and H+ concentration in cerebrospinal fluid

Peripheral Chemoreceptors

aortic and carotid bodies

PO2, PCO2, H+, and K+ in blood

Rest to Work Transitions

VE rises quickly, then slower adjustment

PO2, PCO2 remain relatively stable

lag between metabolism and ventilation = slight decrease in PO2 and increase in PCO2

Causes of Ventilation Upward Drift

increase core temperature

increase of breathing frequency

NOT driven by increase in CO2

Exercise in Heat

little change in arterial PCO2

ventilation drifts upward - higher blood temp that affect respiratory control center

Hypoxemia

decrease in PO2 in elite endurance athletes

ventilation hits the threshold at much higher rate, not leaving enough time for gas exchange

Ventilation and Acid-Base Balance

pulmonary ventilation removes H+ from blood by the HCO3 reaction

CO2 + H2O ←→ H2CO3 ←→ H+ + HCO3

Increase Ventilation results in CO2 __________

exhalation

reduces PCO2 and H+ concentration — pH increases

Decreased Ventilation results in CO2 __________

buildup

increases PCO2 and H+ concentration — pH decreases

Ventilatory Threshold

reflects buffering of H+ via CO2 exhalation

training shifts will move threshold to the right, improving performance