B) Vagal receptors
Stretch receptors – localized in the smooth muscles of the airways –
-
the
Hering-Breuer inflation reflex
.
Stimulation:
lung inflation
Effects:
termination of inspiration, systemic hypotension
(mechanical limitation of the venous return + reflex vasodilatation),
tachycardia.
Juxtapulmonary capillary receptors –
the pulmonary chemoreflex
.
Stimulation
by interstitial pressure ( pulmonary edema), chemical substances (PDG, NaS,
hypertonic solution)...
Effects:
biphasic – inhibition/stimulation reaction: apnoe/hyperpnoe;
hypotension/hypertension + bradycardia (through baroreceptors).
C-fiber endings in the coronary circulation –
the coronary chemoreflex
Stimulation:
by chemical substances (veratridine, serotonin, capsaicin, metabolites ...)
Effects:
rapid shallow breathing, hypotension, bradycardia = depressor reflex (during myocardial
infarct?)
The Coronary Circulation
Anatomy:
The right and the left coronary
artery
- the anterior descending
- the circumflex branch
Smaller branches (epicardial arteries) give off tiny arteries that course at right angles through the
myocardium = intramural vessels
Capillary number:
1 capillary/1 myofiber (3000/mm
3
)
Venules
converge to the coronary sinus – into the RA
The veins
from the right side of the heart drain directly at multiple site within the RA and RV.
Blood Flow
BF = 250 ml/min
;
(60 ml/min/100 g heart w.) = 5% of CO
Pressure – Flow Paradox:
BF falls during systolic BP and it rises with the onset of diastole when BP is low – mainly in
LV coronary intramural vessels
Explanation: Contraction of the LV squeezes the intramural vessels.
The flow dependence on the cardiac cycle phases – on differential pressure between BP
ao
– P
in
myocardial ventricular wal (intraventricular P).
Pressure
Gradient (dif. P)
Aorta LV
RV
Ao – LV
Ao – RV
_______________________________________________________
Systole 120
121
25
-1
95
Diastole
80
Ø
Ø
80 80
________________________________________________________