2) Humoral regulation:
Increase in PaCO
2
decreases in PaO
2
, pH – vasodilatation
Cerebral tissue PO
2
– normal 35-40 mm Hg at PO
2
below 20 mm Hg – coma in 5 – 10 s.
Inhalation of CO
2
– increase in CBF by 75%
Inhalation of O
2
– decrease in CBF by 15 %
3) Nervous regulation:
Sympathetic innervation from the superior cervical sympathetic ganglia.
Vasoconstriction. During streuous exercise – prevention againsthigh pressure and cerebral stroke
(a vascular hemorrhage intothe brain).
Parasympathetic innervation: n. facialis. Vasodilatation. Mild importance.
Circulation in Skeletal Muscles
Flow – during rest 3-4 ml/min/100g
- during exercise – the increase more than 20-fold
Regulation
1) Local:
Mechanical: Muscle contractions → the decrease in BF (the importance rhythmic
contractions). Between contractions – BF is increased.
Temperature: the increase - vasodilation
2) Humoral:
Vasodilators: Hypoxia, hypercapnia, lactic acid, K
+
,acetylcholine, epinephrine
Vasoconstrictor: Norepinephrine
3) Nervous control of muscle blood flow
- Sympathetic NA system – vasoconstriction
- Special – Sympathetic cholinergic system – vasodilation (activation before the
start of muscular exercise)
The Skin Circulation
Anatomy: Blood vessels in the fatty subcutaneous tissue.-
Important for the thermoregulation:
- venous plexus supplied by inflow of blood from the skin
capillaries
- arteriovenous anastomoses (in hands, feet, ears)
The Skin Blood Flow
F = 250 ml/min = 1-3 ml/min/100 g = 5% of CO – at rest
F = 150 ml/min/100 g – in response to thermal stimuli
Blood is shunted through the anastomoses.
Higher skin BF causes the conduction of the heat from the core to the skin – higher radiation of
the heat.
Flow of blood to the skin is a most effective heat transfer from the body core to the skin.