38. Control of circulation. Characteristic and localization of receptors, Vasomotor centre. Supramedular control of the circulation

blood flow/control of circulation

• Blood flow adapts locally and systemically to meet organ demands.

• During exercise, skeletal muscle receives increased blood flow.

• Muscle contraction leads to:

  • ↑ Lactic acid, adenosine, CO₂, and heat

  • ↓ O₂
    → These changes cause local vasodilation in muscles.

• To maintain mean arterial pressure (MAP), vasoconstriction occurs in less active regions (e.g., gastrointestinal tract).

During exercise, sympathetic activation leads to vasoconstriction in non-essential areas via norepinephrine binding to α₁ receptors, preserving blood pressure.
At the same time, epinephrine from the adrenal medulla binds to β₂ receptors in skeletal muscle vessels, promoting vasodilation and increasing blood flow to active muscles.

RECEPTORS

1.Baroreceptors à receptors which respond to the stretching of the blood vessels; they detect

the mean arterial blood pressure. These are found in the aortic arch, and carotid artery.

2.Chemoreceptors à detects the composition of arterial blood (CO2, O2 and pH is the

blood). These can be found in the carotid artery and aortic arch.

3.Osmoreceptors à detect the changes in osmotic pressure (osmolarity). Controls the

secretion of ADH by hypothalamus. Found in the hypothalamus

4.Volume receptors à detect the volume of blood, these receptors are found in the atria, and

carotid arteries. Decrease in volume sends signals to hypothalamus which produces

vasopressin

Vasomotor centre

- portion of the medulla oblongata which together with cardiovascular

centre and respiratory centre, regulates the blood pressure by regulating the vessel tone and

contraction of smooth muscle in the tunica media. It consists of 3 parts:

1.Vasoconstrictor area

2.Vasodilator area

3.Sensory area

à Baroreceptors à if there is an increase in arterial blood pressure, the glossopharyngeal

and vagus nerve sends impulses to the medullary vasomotor centre and causes activation of

parasympathetic nervous system which decreases the heart rate and leads to vasodilation and

inhibits the sympathetic nervous system

à Chemoreceptors à if there is hypoxia (low O2), hypercapnia (high CO2), OR acidosis

(lowered pH), they send the impulses to the vasomotor centre by vagus and glossopharyngeal

nerves which stimulates the sympathetic nervous system. This will then lead to

vasoconstriction to increase the blood pressure

Aortic arch sends signal through à vagus nerve

Carotid artery sends signal through à glossopharyngeal nerve

Supramedular control of the circulation

• The higher levels of organization in the ANS are the supramedullary networks of neurones.

• These networks coordinate the cardiovascular centre.

• Proprioceptors detect the changes in muscle contraction and body position which then sends information to the supramedullary areas.