15.2 Adrenal Glands, Parasympathetic Division, and Enteric Plexus

adrenal (suprarenal) glands

paired glands located on superior poles of kidneys; each is two glands with different functions; includes adrenal cortex and adrenal medulla

adrenal cortex

outer layer; secretes steroid hormones

adrenal medulla

inner core; essentially a sympathetic ganglion; Consists of modified postganglionic neurons without dendrites or axons; Stimulated by preganglionic sympathetic neurons; Secretes a mixture of hormones into bloodstream called catecholamines

catecholamine

85% epinephrine (adrenaline) and 15% norepinephrine (noradrenaline)

sympathoadrenal system

collective name for adrenal medulla and sympathetic nervous system; closely related in development and function

parasympathetic pathways

arise from the brain and sacral regions of the spinal cord (so also called craniosacral division); Relatively long preganglionic and short postganglionic fibers

preganglionic neurons of parasympathetic division

cell bodies are found in the midbrain, pons, and medulla, or sacral spinal cord segments S2 to S4

preganglionic fibers of parasympathetic division

travel through cranial or sacral nerves, end in terminal ganglia in or near target organs; Synapse with postganglionic neurons in ganglia

terminal ganglia

intramural ganglion— embedded within organ wall

postganglionic fibers of parasympathetic division

cover rest of the (short) distance to target organ

parasympathetic division

relatively selective in stimulation of target organ—very little neural divergence

parasympathetic fibers of CN III

thicken lens and narrow pupil of eye; allow for exit out of brainstem

parasympathetic fibers of CN VII

regulate tear, nasal, and salivary glands; allow for exit out of brainstem

parasympathetic fibers of CN IX

regulate parotid salivary gland; allow for exit out of brainstem

parasympathetic fibers of CN X

innervate viscera as far as proximal half of colon; cardiac, pulmonary, and esophageal plexuses in chest give off anterior and posterior vagal trunks; allow for exit from brainstem

parasympathetic fibers outside the brainstem

arise from S2 to S4 of spinal cord; travel in anterior rami of spinal nerves, then form pelvic splanchnic nerves that lead to inferior hypogastric plexus; some synapse while others travel through to terminal ganglia

target organs of parasympathetic fibers outside the brainstem

distal half of colon, the rectum, urinary bladder, and reproductive organs

enteric plexus (enteric nervous system)

the nervous network of the digestive tract; Composed of 500 million neurons found in the walls of the digestive tract and doesn’t arise from brain or spinal cord; has its own ganglia and reflex arcs

enteric plexus innervates

smooth muscle and glands

enteric plexus regulates

motility of esophagus, stomach, and intestines and secretion of digestive enzymes and acid

enteric plexus and the (para)sympathetic systems

requires regulation for digestive function

hirschsprung disease

hereditary defect causing absence of enteric plexus; No innervation in sigmoid colon and rectum; Constricts permanently and will not allow passage of feces

megacolon

massive dilation of bowel accompanied by abdominal distension and chronic constipation

peritonitis

infection of peritoneum

hirschsprung disease is most common in

newborns who fail to have their first bowel movement 33

causes of hirschsprung disease

colonic gangrene, perforation of bowel, and peritonitis