Question

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how does the Autonomic nervous system affect circulation, respiration, digestion and excretion?

Answer 1

Autonomic nervous system: It is a division of the peripheral nervous system that controls and regulates the internal organs without any conscious recognition or effort by the organism. The autonomic nervous system is a control system that acts largely unconsciously and regulates bodily functions

• It is formed by collections of motor neurons (ganglia) situated in the head, neck, thorax, abdomen, and pelvis, and to the axonal connections of these neurons.
• The organization of ANS is on the basis of the reflex arc and it has an afferent limb, efferent limb, and a central integrating system.
• The afferent limb transmits information from the periphery to the central nervous system (CNS). The receptors are present in the abdominal and thoracic viscera.
• The efferent limb is made up of preganglionic and post-ganglionic fibres and an autonomic ganglion.
• The efferent limb is further subdivided based on its anatomic and physiological differences into sympathetic and parasympathetic components.

Sympathetic Nervous system: It connects the internal organs to the brain by spinal nerves. When stimulated these nerves prepare the organism for stress. The sympathetic division typically functions in actions requiring quick responses and is thus known as "fight or flight" system

Parasympathetic nervous system: The nerve fibers of the parasympathetic system are the cranial nerves, primarily the vagus, and the lumbar spinal nerve when stimulated to increase digestion and reduces heartbeat. The parasympathetic system is often considered the "rest and digest" or "feed and breed" system.

Circulation:

SNS:

• When stimulated it increases the circulation.
• It increases the heart rate by stimulating the (β1, β2) adrenergic receptors.
• It increases the contractility by stimulating the (β1, β2) adrenergic receptors.
• The SNS acts on β1 adrenergic receptors to increase chronotropy, dromotropy, and inotropy of the heart
• It also increases conduction velocity.
• By stimulating Adrenergic receptors α1, α2 it stimulates the vasoconstriction of arterioles and systemic veins.
• It diverts blood flow away from the GI and skin by vasoconstriction in their vessels.
• By stimulating β receptors it brings the vasodilation of the coronary vessels of the heart.
• It increases blood flow to the skeletal muscles and lungs by vasodilatation.

PNS:

• When stimulated it decreases the circulation.
• Decrease heart rate.
• Decrease contractility
• Decrease conduction velocity
• The parasympathetic fibers are responsible for decreasing chronotropic, dromotropy, and inotropy via cholinergic action on cardiac M2 receptors.
• stimulates vasodilation
• increases blood flow to the GI.

Respiration:

SNS:

• It increases the respiratory rate to meet with the increased demand of oxygen by the muscles.
• Increased vascular resistance is mediated by α-adrenoreceptors upon sympathetic nerve stimulation.
• stimulation of (β2) brings the Bronchodilatation
• It dilates bronchioles through circulating epinephrine and this allows for greater alveolar exchange.
• Chemoreceptors respond to decreased arterial PO2 levels to increase sympathetic nerve stimulation by the sympathetic chain neurons

PNS:

• It decreases the respiratory rate.
• Parasympathetic activation via vagal stimulation results in cholinergic-mediated relaxation of pulmonary arteries.
• It stimulates the constriction of the bronchiolar diameter when the need for oxygen has diminished

Digestion:

SNS:

• It decreases the blood flow to the GI.
• Decrease activity of the digestive system
• Inhibits peristalsis and decreases intestinal tone.
• Decreases amount of secretion by digestive glands
• It causes glucose to be released to blood from the liver.
• Constricts all the intestinal sphincters by stimulating α receptors.
• It increases Basal metabolism.

PNS:

• It stimulates GI by dilating blood vessels leading to the GI tract, increasing the blood flow.
• Stimulates salivary gland secretion.
• Accerates peristalsis.
• Increases the tone
• stimulates increased digestion of food and, indirectly, the absorption of nutrients.
• Stimulates relaxation of the sphincter

Excretion:

SNS:

• Stimulates to produce perspiration
• Decreases urine output by Increasing renin secretion by stimulation of (β1) receptors
• Constricts urethral sphincter by stimulation of α1 receptors.
• Brings Detrusor relaxation by stimulation of β2 receptors.

PNS:

• Brings Detrusor contraction
• Stimulates Sphincter relaxation
• No effect on preparation or urine output.