GI Flashcards
what is the foregut
lower end of hypopharynx - 1/3 down duodenum
what is the midgut
1/3 down duodenum - 2/3 along transverse colon
what is the hindgut
2/3 way along transverse colon - anal canal
which embryological part is the liver, biliary apparatus, pancreas etc located in
foregut
what is the arterial n nerve supply of foregut
coeliac trunk
- greater splanchnic nerve (T6-9)
what is the arterial n nerve supply of midgut
sup mesenteric artery
- lesser splanchnic nerve (T10-11)
what is the arterial n nerve supply of hindgut
inf mesenteric artery
- least splahnic nerve (t12-l1)
what is swallowing initiated by
pressure receptors in pharynx walls stimulated
what is the diff btwn proximal 1/3 of oesophagus and distal 1/3
striated muscle
vs
smooth muscle
what are the 3 stages of swallowing
1 - voluntary (food compressed against much roof, pushed to oropharynx by tongue)
2 - involuntary (nasopharynx closed by soft palate, pharynx shortened n widened, hyoid elevates, epiglottis closes trachea)
3 - involuntary (contraction of constrictor muscles followed by depression of hyoid bone n pharynx, bolus pushed to oesophagus)
which muscles manipulate food during chewing n elevate hyoid bone/flatten floor of mouth during s1
buccinators
in s2, what is the pharynx shortened n widened by
elevation of hyoid bone (via actions of muscles of the floor of the palate)
what raises the larynx n closes glottis to prevent food from entering trachea
swallowing centre
how many seconds does it take 1 oesophageal peristaltic wave to reach stomach
9 seconds
what is the upper oesophageal sphincter
ring of skeletal muscle surrounds oesophagus jus below pharynx
- before food enters oesophagus, immediately after food has passed, sphincter closes, glottis opens n breathing resumes
what is the gag reflex
reflex elevation of pharynx
what are true vocal cords
vocal folds
what are false vocal cords
vestibular folds
name some properties of saliva
- lubricant for mastication, speech etc
- oral hygiene, maintains pH around 7.2
- release digestive enzymes
which glands secrete serous
patotid
submandibular n sublingual secrete serous and mucous
which glands secrete mucous
minor glands
submandibular n sublingual do both
what is diff btwn mucous and serous secretion
mucous - mucins for lubricant of mucosa
serous - alpha amylase for starch digestion
what are 3 components of defence of oral cavity
mucosa (physical) salivary glands (washes away) palatine tonsils (surveillance system for immune system)
what is structural of salivary glands
2 diff types of epithelia:
- acinar cells (functional unit)
- ducts (surrounded by acinar cells - have channels enabling transport of fluid etc)
what are interlobular duct divided into
intercalated (connect acini to larger striated ducts) n striated (major site of reabsorption of NaCl)
where are some minor salivary glands located
lips, cheeks, hard/soft palate etc
which strucs pass through parotid gland
external carotid artery
facial nerve CN VII
thus, parotid capsule is very tough
what is PS innervation of the 3 major salivary glands
parotid - CN IX glossopharyngeal
submandibular/sublingual - CN VII facial
list some functions of the stomach
- store/mix food
- digestion
- kill microbes
- secrete intrinsic factor
name the 5 main diff stomach cells
- parietal cells
- chief cells
- g cells
- ecl cells
- d cells
what do parietal cells secrete
HCl/gastric acid
intrinsic factor
what do chief cells secrete
pepsinogen
gastric lipase
what do g cells secrte
gastrin
what do ecl cells secrete
histamine
what do d cells secrete
somatostatin
what is the role of parietal cells (hcl, instrinc factor)
- kill microbes
- activate pepsinogen
- intrinsic factor binds to vit B12
what is the role of chief cells (pepsinogen, gastric lipase)
protein and fat digestion
what is the role of G cells (gastrin) and ECL cells (histamine)
stimulate gastric acid secretion
what is the role of D cells (somatostatin)
inhibits gastric acids ecretion
what stimulates and inhibits gastric acid secretion
stimulates - G cells (gastrin) and ECL cells (histamine)
inhibits - D cells (somatostatin)
what does ECL stand for
enterochromaffin-like cell
what is gastric acid
mainly HCl, pH 2
energy dependant
neurohormonal reg
from parietal cells
how is gastric acids secreted/prod (4)
- H2O in parietal cells break down –> OH- & H+
- H+ pumped into stomach via H+/K+ ATPase pumps in membrane of parietal cells (1K+ into parietal cell for every 1H+ pumped out of stomach)
- HCO3- from H2CO3 breakdown secreted into capillary for exchange of Cl-
- In stomach, H+ and Cl- react to form HCl
how is gastric acid secretion regulated initially
turning it on (cephalic phase)
- PS NS
- sight, smell triggers
- ACh triggers gastrin release (from G cells) and histamine (from ECL cells)
- Both of these incr number of H+/K+ ATPase pumps on parietal cell
thus increased acid production
what happens once food has reached stomach (in terms of gastric acid secretion)
turning it on (gastric phase)
- initiated by gastric distension
- same things happen as cephalic phase (gastrin n histamine release, incr pumps, incr acid production)
how do proteins in the stomach stimulate gastric acid release
direct stimulus
- proteins in lumen act as buffer, cause pH to rise
- less secretion of somatostatin - more acid produced
how is gastric acid secretion turned off (gastric phase)
gastric phase
- low luminal pH directly inhibits gastrin secretion
- stimulates somatostatin release - inhibits parietal cell activity
how is gastric acid secretion turned off (intestinal phase)
in duodenum: - duodenal distension - low luminal pH - presence of amino acids - release of enterogastrones eg CCK - reduces ACh release and secretin which reduces gastrin release n incr somatostatin release
what 3 factors help regulate gastric acid secretion
brain
duodenum
stomach
which PS neurotransmitter is involved in gastric acid reg
ACh - turning it on, cephalic phase
what are peptic ulcers
breach in mucosal surfce
how does gastric mucosa defend itself
- alkaline mucus (lie on gastric pit surface)
- tight junctions btwn epithelial cells
- replacement of damaged cells
how does ammonia affect gastric mucosa
toxic, less mucous produced
what does the secretion of pepsinogen parallel
HCl secretion
what are the 3 steps of protease secretion
- chief cells secrete pepsinogen
- pepsinogen converted to pepsin in stomach lumen - low pH
- speeds up protein digestion - neutralised by bicarb in duodenum
what is the role of pepsin in protein digestion
- not essential but no vit B12 can occur
- accelerates protein digestion
what is vol of empty stomach
50mL
what is vol of stomach when eating
1.5L
the smooth muscle in the stomach undergoes receptive relaxation - what do this mean
reflex in which the gastric fundus dilates when food passes down the pharynx and the esophagus
what is receptive relaxation is mediated by
PNS
with co-ord from stomach by Vagal nerve n brain’s swallowing centre
Vagus nerve causes NO n serotonin release
where do peristaltic waves begin
in the body of the stomach - prod a ripple as it proceeds towards antrum
what does the pyloric sphincter do as peristaltic waves reach it
close
what is pyloric sphincter
ring of smooth muscle n connective tissue btwn atrium n duodenum
what is the freq of peristaltic waves detrained by
pacemaker cells in muscular propria of fundus undergo slow depolarisaiton-repolarisation cycles (3/min)
what can increase strength of peristaltic waves
gastrin
gastric distension
what can decrease strength of peristaltic waves
duodenal distension
incr duodenal fat
incr duodenal osmolarity
what is the most abundance substance in chyme
water
which part of s intestine reabsorbs most water
jejunum
what is the most abundant solute in chyme
Na+
how can diarrhoea affect K+ levels
decreases
what are the 2 functional states the body undergoes in providing energy for cellular activities
- absorptive state:
- ingested nutrients enter blood from GI tract
- some nutrients provide energy requirements of body remainder added to body’s energy stores to be called upon in the next postabsorptive state - post absorptive state:
GI tract empty of nutrients
body’s own supply must store energy
does the brain store glucose
no
how are excess triglycerides stored
adipose tissue
how is excess glycogen stored
in liver and muscle
what process happens in a short fast
glycogenolysis
what process happens in a long fast
gluconeogenesis
what is a fuel source of muscles
ketones
what is the process of breaking down triglyceride stores
lipolysis
what is lipolysis promoted by
glucagon
what happens when body goes into starvation state (4-5 days)
muscles use less ketones - needed for brain
liver can’t make new glucose
brain relies on ketones so glucose is available for rbc
what is diff btwn ghrelin n leptin
ghrelin is hunger hormone whereas leptin suppresses hunger
in obesity, would leptin or gremlin levels be high
leptin (leptin resistance may also occur)
which hormones are involved in metabolism control
insulin is anabolic
the rest are catabolic
what is the most abundant fatty acid absorbed
palmitic acid
where is lipase synthesised
pancreas
what do triglycerides split into
monoglyceride n 2 fatty acids
what do serous acini secrete
water n amylase
what do mucous acini secrete
mucous
what is the diff btwn primary n mature saliva
primary - high in NaCl
mature - high in KCO3
what is the BMR
rate of energy expenditure in body for vital processes at rest (related to ATP use, measured by oxygen consumption)
what are the energy requirements of brain
glucose
ketone bodies
what are the energy requirements of liver
amino aicds
fatty acids
glucose
alcohol
what are the energy requirements of muscles
glucose
triglycerides
amino acids
what are the energy requirements of rbc
glucose
what is vit A involved in
immune system
vision
what is vit B involved in
RBC prod
what is vit C involved in
collagen prod
haemostasis
what is vit D involved in
bone formation n maintenace
what is vit E involved in
free radical protection
what is vit K involved in
blood clotting
what are the 3 phases of gastric acid secetion
- cephalic phase
- gastric phase
- duodenal phase
what are the 4 steps of water absorption
- Na absorbed (cotransported) by enterocytes
- Na/K pump transports 3Na out and 2K in (electrochemical grad)
- high intercellular Na conc, low intracellular conc
- water diffuses into enterocytes through aquaporins
where is iron absorbed
duodenum
what does the jejunum absorb
most other vitamins
what does ileum absorb
b12 n bile salts
what are the steps of carb digestion n absorption
- pancreatic n salivary amylase break down poly –> disaccharides
- maltase, sucrose, lactase etc cleave di –> monosaccharides
- sodium binds to hexose transporter
- glucose binds - glucose n Na invaginated into enterocyte
- hexose transporter on basolateral membrane transports monosaccharides into capillaries down conc gradient
what are enterocytes
intestinal absorptive cells
what does an amino acid consist of
central C atom
NH2, COOH, H group
variable R group
forms zwitterions - H from COOH moves to NH2
4 structure of proteins?
1 - aa sequence
2 - alpha helix n beta pleated sheet
3- disulphide bridges, polar interactions, hydrogen bonding
4- multiple tertiary structures
what are the 5 steps of protein digestion n absorption
- dietary proteins broken down by pepsin (stomach) n proteases (pancreas) –> polypeptides
- polypeptides broken down by peptidases in villi of enterocyte - amino acids
- sodium binds to sodium dependant amino acid transporters –> aa bind
- transporter undergoes conformational change - aa and Na enter cell
- aa transported into blood via basolateral membrane transporter
what are the 5 steps of lipid digestion and absorption
- pancreatic lipase breaks down triglycerides –> glycerol n 3 date acids
- bile salts emulsify fats - micelles absorbed by enterocytes
- triglycerides + cholesterol + lipoproteins = chylomicrons
- chylomicrons transported into lymphatic system
- lipoprotein lipase oxidises triglycerides - used for energy or storage
what is the equation for BMI
weight in kg/height in m^2
