Peripheral circulation II

Autoregulation

If the blood flow increases due to higher pressure, the basal tone of resistance vessels increases, so the vascular resistance increases in proportion to the increase in arterial mean pressure and the intensity of blood flow is constant.

Vasomotor centers

There are two vasomotor centers controlling blood pressure in the medulla.

• Pressor centers

• Depressor centers

Pressor centre

increasing blood pressure is characterized by having its own intrinsic activity. Activity can be increased or decreased by carbon dioxide concentration in the blood.

It is continuously blocked by the depressor center so no intrinsic activity, blood pressure is lowered.

Its activity is governed by nerve afferentation and not by CO2

Carbon dioxide role in vasomotor centers

detected by central chemoreceptors but hypoxia (low oxygen tension) is not an adequate stimulus for chemoreceptors

Nerve afferentation of the pressor center

peripheral chemoreceptors found in glomus caroticum and glomus aorticum.

hypercapnia are the adequate stimulus of the chemoreceptors.

Pressor response

increases heart rate, stroke volume and cardiac output, resistance vessels contract, peripheral resistance increases, constriction of veins leads to increase of venous return and cardiac output

Depressor center

inhibits the pressor center.

Depressor response

decrease of heart rate, cardiac output, resting vasoconstrictor tone, decreases total peripheral resistance but capacity of vein increases, venous return and blood pressure decrease.

Nerve afferentation of the depressor center:

baroreceptors that detect blood pressure in the sinus caroticus and aortic wall.

Loven reflex

painful stimuli affecting the skin produce a generalized blood pressure increase (pressor reflex), but local vasodilation (axon reflex)

Bainbridge reflex

stretch-sensitive receptors in the large vein walls and right atrium, baroreceptors set the optimal heart rate and is therefore called a buffer reflex.

Goltz reflex

extero- and interoceptors located in the abdominal wall and in the abdominal cavity. Strong mechanical stimulus to abdomen or pathological process in the abdomen cause increased vagus tone, decreasing heart rate and decreasing blood pressure.

Effects of High heart rate in the heart

decrease in coronary circulation

Skin at low temperatures

sympathetic vasoconstrictor tone increases, perfusion and heat loss decrease

Skin at high temperatures

resting vasoconstrictor tone decreases, the blood flow increases, heat loss increases.