PHYS - Gut Autonomics and Motility

Question 1

4 functions of the GIT

Answer 1

• nutrition
• excretion
• water and electrolyte balance
• protection

Question 2

types of muscle in small intestine wall: orientation, appearance on cross section and function

Answer 2

• circular muscle (inner layer) - orientated in a circular direction around the wall so look spindle shaped on a cross section - CONSTRICTION of gut BEFORE the bolus
• longitudinal muscle (outer layer) - orientated in the same direction as the tube so look circular in a cross section - SHORTENING of gut AFTER the bolus

Question 3

all GIT sphincters and are they smooth or skeletal

Answer 3

• upper oesophageal - skeletal
• lower oesophageal (gastroesophageal)- smooth
• pyloric - smooth
• oddi (hepatopancreatic: merging of bile and pancreatic ducts) - smooth
• iliocaecal - smooth
• internal anal - smooth
• external anal - skeletal

Question 4

3 types of nerves in the gut and what do they supply?

Answer 4

• sensory afferent: chemoreceptors and mechanoreceptors send info re: stretch to CNS
• autonomic (+ enteric) efferent: glands and smooth muscle (lubrication + contraction)
• somatic efferent: skeletal muscle sphincters i.e. “swallowing and shitting” - Julia Choate

Question 5

varicosity (nerve context)

Answer 5

• swelling of GIT nerves

Question 6

two parts of the enteric nervous system
- where are they located
- what do they control

Answer 6

• myenteric plexus: between circular and longitudinal muscle along the whole gut, controls motility
• submucosal plexus: underneath mucosa only in SOME regions, controls secretion of glands and absorption of nutrients

Question 7

main excitatory/inhibitory NTs of the GIT

Answer 7

• excitatory: ACh = increased motility
• inhibitory: NO = relaxation of smooth muscle

Question 8

describe the PARAsympathetic innervation of the gut

Answer 8

• parasympathetic nerves synapse on target organs
• vagus nerve (CN X): innervates gut proximally to splenic flexure
• pelvic splanchnics (S2-S4): innervates gut distally to splenic flexure

Question 9

describe the SOMATIC innervation of the gut

Answer 9

• pudendal n. (S2-4) controls external anal sphincter

Question 10

describe the SYMPATHETIC innervation of the gut

Answer 10

• greater splanchnics (T5-9): synapse at coeliac trunk (coeliac plexus innervates foregut)
• lesser splanchnics (T10-11): synapse at coeliac trunk (coeliac plexus innervates foregut) or SMA (SMA plexus innervates midgut)
• lumbar splanchnics (L1-2): synapse on IMA (IMA plexus innervates hindgut)
• sacral splanchnics (L1-2): synapse on superior or inferior hypogastric plexus (superior/inferior to aorta bifurcation) > innervate pelvic cavity

Question 11

type of epithelium in the mucosal layer throughout the GIT

Answer 11

• oropharynx + oesophagus: stratified squamous (for protection)
• stomach: simple columnar
• small intestine: simple columnar with microvilli (absorption)
• large intestine: simple columnar with goblet cells (secretion and absorption)
• rectum: simple columnar > stratified squamous (protection)

Question 12

segmental contractions

Answer 12

• not the same as peristalsis
• helps with churning and mixing in the small intestine
• 2 steps forward, 1 step back
• replaced with peristalsis (migrating myoelectric complex) when most of the meal has been absorbed

Question 13

what is the migrating myoelectric complex

Answer 13

• peristaltic contractions of adjacent segments from stomach to large intestine
• initiated by increasing chyme pH (alkaline) or motilin hormone concentration in plasma
• moves undigested remains to large intestine and prevents overgrowth of bacteria
• stops when another meal enters stomach because then we go back to the mixing/segmental contractions

Question 14

function of the small intestine

Answer 14

• chyme mixed with digestive juices = chemical digestion completed
• nearly all nutrient absorption occurs
• undigested remains move to large intestine

Question 15

functions of the large intestine

Answer 15

• mixing contractions and propulsive actions
• chemical digestion by enteric bacteria
• absorption of water and electrolytes
• excretion (anus)

Question 16

2 types of contractions in the large intestine

Answer 16

• haustral (mixing) contractions: very slowly mix contents to allow time for absorption of water and electrolytes
• mass movements (peristalsis): move from caecum to sigmoidal colon, forms a constrictive ring and loss of haustra. facilitated by gastrocolic and duodenocolic reflexes (i.e. activated by stretch of stomach or duodenum)

Question 17

circular vs longitudinal muscle in the large intestine

Answer 17

• circular muscle works together with myenteric plexus to form haustra (bulbs)
• longitudinal muscle formed into 3 strips called teniae coli which run continuously from caecum to sigmoid colon

Question 18

what happens if gut motility is too fast or too slow?

Answer 18

• too fast = less time for absorption of water and electrolytes = diarrhoea
• too slow = too much time for absorption of water and electrolytes = constipation

Question 19

what is constipation?
- what are the 2 types
- what are some causes
- Tx

Answer 19

• pass stools <2 times per week, hard stools, incomplete evacuation
• 2 types: slow transit, obstructive
• causes: inadequate fibre, pregnancy, IBS, drugs, neurological, psych, metabolic
• Tx: treat the underlying cause e.g. increase fibre or laxative if severe

Question 20

what is diarrhoea
- what are the 2 types
- causes
- Sx
- Tx

Answer 20

• rapid movement of faeces thru the large intestine
• types: organic (e.g. inflammation) or functional (damage to nerves/muscle)
• causes: osmotic (e.g. intolerance), secretory, inflammatory, abnormal motility e.g. diabetes
• Sx: cramps, fever, blood-stained (inflammatory)
• Tx: treat the underlying cause + fluid and electrolyte replacement

Question 21

retrograde peristalsis

Answer 21

• if the external (skeletal) anal sphincter doesn’t relax (i.e. you choose not to defaecate), faeces can go back up to the sigmoid colon

Question 22

defaecation reflex

Answer 22

• triggered by mass movement of faeces from sigmoidal colon to rectum
• detected by stretch receptors in rectum send signals via sensory nerves to spinal cord
• efferent parasympathetic and enteric nerves cause rectal contraction, internal sphincter relaxation, and mucus secretion for lubrication
• somatic motor nerves from cerebral cortex allow for relaxation of external anal sphincter

Question 23

3 phases of swallowing (deglutition)

Answer 23

• buccal (voluntary): food is chewed and moved to back of mouth
• pharyngeal (involuntary): food passes thru pharynx and upper oesophageal sphincter
• oesophageal: food passes thru oesophagus and lower oesophageal sphincter into stomach

Question 24

role of uvula and epiglottis during pharyngeal phase of swallowing

Answer 24

• uvula: rises to close off nasal passage
• epiglottis: lowers to closes off trachea
• therefore respiration is temporarily inhibited

Question 25

neuronal control of the 3 phases of swallowing

Answer 25

- voluntary (buccal): cerebral cortex + somatic motor nerves (efferent) - involuntary (pharyngeal and oesophageal): swallowing centre in medulla of brainstem + vagus nerve (efferent)

Question 26

composition of pharynx and oesophagus re: muscle

Answer 26

- skeletal muscle: pharynx, upper oesophageal sphincter, top 1/3 of oesophagus - (middle 1/3 of oesophagus is overlapping smooth and skeletal muscle) - smooth muscle: bottom 1/3 of oesophagus, lower oesophageal sphincter

Question 27

causes of dysphagia

Answer 27

- diseases of mouth, tongue or salivary glands - oesophageal diverticulum (outpouchings) - neuromuscular disorders, CVA, Parkinson's

Question 28

achalasia - what is it - cause - Tx

Answer 28

- type of dysphagia where lower oesophageal sphincter can't fully open (relax) - due to degeneration of myenteric plexus therefore can't be corrected - Tx: endoscopic dilation of sphincter with balloon or botox