Human Body Function HBF 102 - Sympathetic Nervous System II

Faculty of Medicine

• Academic Year: 2024-2025
• Year: 1
• Semester: 1
• Module: Human Body Function (HBF) 102

Sympathetic Nervous System - II

• Lecturer(s): Dr. Maessa M. Elnhas (Professor of Physiology, Tanta University), Dr. Mohamed abo El Hassan (Professor of Physiology, Al-Azhar University)
• Department: Clinical Physiology

Objectives

• Describe the functions of sympathetic nerves on the thoracic part (heart and lungs).
• Describe the organs supplied by the greater splanchnic nerve and their functions.
• List the structures supplied by the lesser splanchnic nerve and discuss their functions.

Sympathetic Division

• Preganglionic neurons are located in the lateral gray horn of T1-L2 segments of the spinal cord (thoracolumbar outflow).

Divisions of the Sympathetic Nervous System

• Cervical
• Cardio-pulmonary
• Splanchnic
• Somatic

Functions of Sympathetic Division

• Heart: Stimulates all properties of cardiac muscle (increase rhythmicity, contractility, conductivity, and excitability). Positive inotropic effects = increased contractility, positive chronotropic effects = increased heart rate. Increased conductivity and excitability. Indirectly increases coronary blood vessel diameter due to increased cardiac metabolism. Direct effect is coronary vasoconstriction. Increases oxygen consumption of the heart.
• Lungs: Relaxation of smooth muscles in bronchi and bronchioles (bronchodilation), decreased bronchial secretions. Constriction of pulmonary blood vessels preventing lung congestion.
• Gastrointestinal Tract: Inhibition (relaxation) of wall and motor (contraction) of sphincters. Reduced gastric and intestinal secretions and motility. Vasoconstriction of stomach, small intestine, proximal colon, kidney, pancreas and liver arterioles.
• Gall bladder: Relaxation of plain muscles of the wall but contraction of the sphincter of Oddi.
• Liver: Stimulates glycogenolysis (increase blood glucose levels)
• Spleen: Contraction of smooth muscles of the splenic capsule (especially during hemorrhage), aiding the squeezing of stored blood into circulation.
• Pancreas: Reduces insulin hormone and pancreatic juice secretion.
• Kidney: Vasoconstriction of renal vessels leading to decreased renal blood flow and urine output. Stimulates renin secretion
• Adipose tissue: Promotes lipolysis
• Adrenal medulla: Stimulates secretion of adrenaline (80%) and noradrenaline (20%) hormones. Supplied by preganglionic sympathetic fibers (greater splanchnic nerve). Circulating catecholamines have the same, but more prolonged, effects as direct sympathetic stimulation.

Structures Supplied by Sympathetic Divisions

• Includes various structures throughout the body, including organs such as the heart, lungs, intestines, kidneys, and adrenal glands, along with blood vessels and glands associated with them.

2 - Cardio-Pulmonary Division (Thoracic Division)

• Preganglionic fibres originate in the upper four thoracic segments, relaying in the cervical and upper four thoracic lateral ganglia.
• Postganglionic fibres form the cardiac and pulmonary plexuses to supply thoracic viscera.

3 - Splanchnic Division

• Greater splanchnic nerve: Preganglionic fibres arise from the lower 6 thoracic segments, forming the greater splanchnic nerve. They relay in coeliac and superior mesenteric collateral ganglia, and some preganglionic fibers reach the adrenal medulla directly. Postganglionic fibres reach abdominal viscera along their blood vessels.
• Lesser splanchnic nerve: Preganglionic fibres originate in upper 3 lumbar segments. The fibres form the lesser splanchnic nerve. These fibers relay in inferior mesenteric (hypogastric) ganglia. Postganglionic fibres extend through blood vessels to supply the pelvic viscera.

Functions of Divisions

• Urinary bladder: Relaxation to the wall and contraction to the internal urethral sphincter, aiding retention of urine.
• Distal colon and rectum: Inhibitory action on the wall and motor action to the internal anal sphincter, promoting retention of feces.
• External genitalia (males): Inhibition of erection (vasoconstriction of erectile tissue), and ejaculation of semen (contraction of vas deferens, prostate, and ejaculatory ducts).
• External genitalia (females): Contraction or relaxation of female genital organs based on menstrual cycle stage and hormonal levels.

Summary

• Vasoconstriction of blood vessels to the gastrointestinal tract.
• Increased heart rate
• Increased blood pressure
• Inhibition of gastrointestinal secretion and motility.
• Increased metabolism
• Ejaculation of semen

Long-term Control

• Norepinephrine (NE) is slowly inactivated
• Adrenal medulla releases epinephrine (EP) and norepinephrine (NE) which act for longer periods.
• Maintain vasomotor tone.

Interactive Questions

• These are provided for self-assessment of knowledge gained from the notes.

This quiz focuses on the functions and structure of the sympathetic nervous system, particularly as it relates to the thoracic region, including the heart and lungs. It covers the roles of the greater and lesser splanchnic nerves, as well as the preganglionic neuron locations within the spinal cord. Test your understanding of this fundamental aspect of physiology in the context of your first semester studies.