S2 Physiology Flashcards
How is the gut controlled ?
Autonomic NS
Enteric NS
Hormones
Paracrine substances
How does the ANS control the gut ?
Preganglionic fibres synapse with an autonomic ganglia outside the CNS and postganglionic fibres synapse on peripheral effector organs
Where do the cell bodies reside in ANS ?
CNS
How many neurones does the ANS pathway have ?
2
What preganglionic fibres release ?
Ach
What do post-ganglionic fibres release ?
Ach, neuropeptides and noradrenaline
How does the Sympathetic NS control the gut ?
Pass through sympathetic trunk without synapsing
Form presynaptic splanchnic nerves which synapse with prevertebral ganglia
Mainly innervate blood vessels, shuts down the gut by reducing blood flow there and increasing blood flow to skeletal muscle
Short pre ganglionic and long post gnaglionic.
What are the sympathetic nerve roots that control the gut ?
T5-L3
What do the post ganglionic fibres release in the sympathetic NS ?
NA
What presynaptic splanchnic nerves formed ?
Greater (t5-T9)
Lesser (t10-11)
Least (t12)
What are the prevertebral ganglia that the splanchnic nerves synapse with
Coeliac
Renal
Superior mesenteric
Inferior mesenteric
what is the sympathetic NS role in GI physiology
mainly innervate blood vessels, shuts down the gut by reducing blood flown there and increasing blood flow to skeletal muscle
short pre, long post ganglionic fibre
describe the nature of the parasympa NS wrt to GI physiology
craniosacral outflow. composed broadly of the vagus nerve and the pelvic splanchnic nerves (S2-S4)
stimulates the gut
post ganglionic release ACH. pre ganglionic synapse in the walls of the viscera
long pre, short post ganglionic fibre
what is enteric NS
one of the divisions of the NS, which can operate independently but has extensive connection with the ANS
exists from oesophagus to anus and has two main plexuses
- submucosal (Meissner’s) plexus in the submucosa. this controls things near the epithelia such as blood flow and secretions
- myenteric (Auerbach’s) plexus, in between circular and longitudinal muscle. this controls motility
- communicates with the para (via vagus and pelvic nerves) and sympa NS (via prevertebral ganglia)
what cells release hormones in the gut
enteroendocrine cells in the krypts of the gut release hormones
enterochromafin like cells produce paracrine subtances such as histamines
describe visceral pain in the gut
fore gut - epigastric
mid gut - peri umbilical
hind gut - suprapubic
describe motility of the GI tract
contraction and relaxation of the GI tract in order to move mix or grind contents. All muscle is smooth except the pharynx, upper 1/3 oesophagus, anal sphincter
epithelia in the GI tract is mainly squamous in the upper and lower parts and simple columnar in between
peristalsis - propel contents in one direction
segmentation - contraction splits contents then relaxes
mass movement - occurs in distal colon, rapid movement of contents into rectum. gastrocolic reflex
sympa NS reduces motility, para increases motility
describe some motility problems of the GI tract
paralytic ileus - loss of GI contractility
achalasia - failure of lower oesophagus to relax causing dysphagia
hirshsprungs disease - lack of myenteric and submucosal plexuses, new borns cant pass their digestion
describe some major GI secretions
stomach acid
- barrier to infection, prepares proteins for digestion and activates enzymes
HCO3
- neutralises acid (saliva,pancreas, Liver[in bile])
waste products
- mainly from the liver in the form of bile e.g cholesterol and bilirubin
Emulsifiers
- increase SA of lipids, aids lipase digestion
Mucus
- protects against acids in stomach
-protects against bacteria in small intestine
- harbours bacteria in large intestine
Enzymes
- break down proteins, fats and carbohydrates. Found in saliva, stomach , pancreas
Secretions come from ; Acini of salivary glands, Gastric glands, Brunner’s glands (duodenum)
summarize absorption in the GI tract
movement after digestion across enterocyte (apical/basolateral membrane) or paracellular (tight junction). Large SA of gut provided by folds and villi. Anything which affects this such as diarrhoea or Crohns shall reduce absorption. Absorbed substances include water, electrolytes and nutrients such as carbs, proteins and vitamins
