Chapter 18b

Gas Exchange and Transport

15

16

ExpirationInspiration

Sensoryreceptors

Integratingcenters

Efferentneurons

Effectors

Afferentneurons

Stimuli

KEY

Afferent sensoryneurons

Carotid and aorticchemoreceptors

Externalintercostals

Internalintercostals

Abdominalmuscles

Diaphragm

Somaticmotor neurons

(inspiration)

Somaticmotor neurons

(expiration)

Medullarychemoreceptors

Emotionsand voluntary

control

Medulla oblongataand pons

Scalene andsternocleidomastoid

muscles

CO2 O2 and pH

Limbicsystem

Higherbrain

centers13

14

1

2

3

4

5

6

12

11

10

7

8

9

Reflex Control of Ventilation

Figure 18-16

PRG

PRG = Pontine respiratory group

DRG

VRG

Output to expiratory,some inspiratory,

pharynx, larynx, andtongue muscles

Outputprimarily toinspiratory

muscles

Sensory inputfrom CN IX, X

(mechanical andchemosensory)

Medullarychemo-

receptors

Higherbrain

centers

NTS

pre-Bötzingercomplex

Pons

Medulla

KEY

DRG = Dorsal respiratory group

VRG = Ventral respiratory group

NTS = Nucleus tractus solitarius

Regulation of Ventilation

Figure 18-17

Regulation of Ventilation

• Respiratory neurons in the medulla control inspiration and expiration• Rhythmicity center Inspiration and Expiration• VRG and DRG of medulla

• Rhythmic pattern of breathing arises from a network of spontaneously discharging neurons

Neurons in the pons modulate ventilation• Ventilation is subject to modulation by

chemoreceptor-linked reflexes and by higher brain centers

• Apneustic and Pneumotaxic• Apenustic – inspiration• Pneumotaxic – anatagonistic – inhibit

inspiration

Rhythmicity of breathing

Regulation of Ventilation

• Neural activity cycles during quiet breathing

Figure 18-18

Regulation of Ventilation

• Peripheral chemoreceptors• Located in carotid and aortic arteries• Specialized glomus cells

• Sense changes in PO2, pH, and PCO2

central

chemoreceptors

• Changes in CO2

Regulation of Ventilation

• Carotid body oxygen sensor releases neurotransmitter

when PO2 decreases

Figure 18-19

7

6

5

4

3

21

K+ channels closeLow PO2

Blood vessel

Voltage-gated Ca2+

channel opens

Ca2+

entry

Celldepolarizes

Exocytosis ofneurotransmitters

Receptor onsensory neuron

Glomus cellin carotid

body

Signal to medullarycenters to increaseventilation

Action potential

Low PO2

H+

CO2 + H2O

Cerebral capillary

Blood-brainbarrier

Cerebrospinalfluid

Medulla

Central chemoreceptor

PCO2

Respiratorycontrolcenters

Ventilation

CAH2CO3 H+ + HCO3

–

Regulation of Ventilation

• Central chemoreceptors monitor CO2 in cerebrospinal fluid

Figure 18-20

Regulation of Ventilation

• Chemoreceptor response to changes in plasma CO2

Figure 18-21

Plasma PO2

Stimulatescentral

chemoreceptor

PCO2 in CSF Arterial PCO2

inplasma

PlasmaPCO2

Stimulatesperipheral

chemoreceptor

Plasma PO2

< 60 mm Hg

Ventilation

CO2

inCSF

HCO3–H+ + HCO3

–CO2 H+ +

Plasma PCO2

Negative feedback

Control of Ventilation

PLAY Interactive Physiology® Animation: Respiratory System: Control of Respiration

Regulation of Ventilation

• Protective reflexes• Irritant receptors • Bronchoconstriction• Sneezing• Coughing

• Hering-Breuer inflation reflex• Don’t over stretch and damage

Summary

• Diffusion and solubility of gases• Gas exchange• Gas transport• Transport of oxygen and carbon dioxide• Factors affecting oxygen-hemoglobin binding• Carbonic anhydrase and chloride shift

Summary

• Regulation of ventilation• Central pattern generator• Dorsal versus ventral respiratory groups• Peripheral versus central chemoreceptors