digestive system Flashcards
what is the name of the cavity in which abominopelvic viscera reside
peritoneum
describe how the 9 regions are derived from surface anatomy of bony landmarks
the trans-tubercular plane is formed along L5
the subcostal plane is formed along L3
two sagittal planes are formed along the two mid-clavicular lines
what are the 4 divisions of the abdominal cavity that can be used instead of the usual 9
right upper and lower quadrants
left upper and lower quadrants
where does the transpyloric plane sit
along L1
what viscera sits along the transpyloric plane
pylorus of the stomach (D1 and D-J flexure)
what are the four main layers of the GI tract
mucosa
submucosa
muscularis propria
serosa
what are the 3 ‘regions’ of the GI tract
foregut
midgut
hindgut
what blood vessel supplies the foregut
coeliac artery
what blood vessel supplies the midgut
superior mesenteric artery
what blood vessel supplies the hindgut
inferior mesenteric artery
from where to where does the foregut run
mouth to mid-duodenum
from where to where does the midgut run
mid-duodenum to 2/3 along transverse colon
from where to where does the hindgut run
2/3 along transverse colon to anus
where does pain in the foregut localise to
epigastric area
where does pain in the midgut localise to
periumbilical area
where does pain in the hindgut localise to
suprapubic area
what is the upper GI tract comprised of
oesophagus
stomach
duodenum
what is the function of the mouth in the upper GI tract
mastication/chew/mechanical breakdown
what is the function of the oesophagus in the upper GI tract
conduit
what is the function of the stomach in the upper GI tract
mechanical digestion (absorption)
what is the function of the duodenum in the upper GI tract
digestion (bile and pancreatic juice)
absorption
describe the oesophagus
muscular tube for peristalsis
mostly squamous epithelium
more distally = columnar epithelium
has the lower oesophageal sphincter
what three areas does the oesophagus run through
neck, thorax and abdomen
what is the gastro-oesophageal junction (GOJ)
oesophagus through diaphragm > enters cardia of the stomach
anatomically important to prevent reflux
histologically important as it goes from squamous to columnar epithelium
what can causes reflux
hiatal hernia
here, part of the stomach essentially goes through the diaphragm due to it being weakened > reflux
describe the stomach
4 regions
highly variable in shape and size
mechanical digestion
2 openings/curvature surfaces
what are the 4 regions of the stomach
cardia, fundus, body, pyloric region/antrum
what does the stomach do
digestion (pepsin/HCL acid)
absorption (H20, alcohol, aspirin)
what supplies blood to the stomach
it is part of the foregut so it is supplies by the coeliac trunk
it has two networks:
- R/L gastric artery of lesser curve
- R/L gastro-omental artery of greater curve
what are the 3 branches of the coeliac trunk
left gastric artery
common hepatic artery
gastroduodenal artery
what is superior and inferior to the stomach
omentum
what is anterior to the stomach
abdominal wall, diaphragm, liver left lobe
what is posterior to the stomach
pancreas, left kidney, spleen
what does the duodenum do
digestion (1L of bile which is produced by the liver and stored by the gall bladder and 1L of pancreatic juice)
describe the duodenum in relation to the peritoneum
1st and 4th parts are within the peritoneum
2nd and 3rd parts hide behind the peritoneum
describe the duodenum
starts at the Pylorus of the stomach
- superior part in line with L1
-descending part in line with L2
-inferior part in line with L3 - ascending part curves back up towards L2
ends at duodenojejunal junction
what is anterior to the duodenum
stomach
what is posterior to the duodenum
portal vein
super mesenteric artery
gastroduodenal artery
what is medial to the duodenum
pancreas
bile duct
what is lateral to the duodenum
right kidney
what can duodenal ulcers lead to
peptic ulcer disease > upper GI bleeding / perforation / peritonitis
describe the small bowel
consists of duodenum, jejunum, ileum
villi > increase SA
major site for digestion / absorption
what is the small bowel structurally comprised of
muscular tube
peristalsis (linked w the enteric NS)
slow progress of content
circular folds
what are the two junctions found in the small bowel
duodeno-jejunal junction to show the start of the Jejunum
ileo-caecal junction to show the start of the ileum
what supplies blood to the jejunum and ileum
SMA
- jejunal and ileal branches
- form arcades
what are the differences between the jejunum and ileum
jejunum has long vasa recta whereas ileum has short
jejunum has few large hoops of arcades whereas ileum has lots of small hoops
how does blood get drained from jejunum and ileum
jejunal/ileal veins >
drains into SMV >
joins splenic vein to form portal vein
what can cause small bowel obstruction
lumen - gallstones
wall - inflammation
extrinsic - adhesions / trapped in hernia
what is the large bowel comprised of
caecum and appendix
ascending colon, transverse colon, descending colon, sigmoid colon, anus
describe the appendix
blind ending tube connected to caecum
embryological remnant > no function
what is gastroenteritis
diarrhoea w or without abdominal pain, possibly w vomiting and fever
what is the primary function of the digestive system
transfer nutrients, water, and electrolytes from food into the internal environment
what are the accessory digestive organs
salivary glands
liver
gallbladder
pancreas
what is the function of salivary glands
secretions help in lubrication, anti bacterial and begin digestion
what is the function of the pancreas
vital for digestion, enzymes for all food categories and alkaline solution
what is the function of the liver
secretes bile continuously
what is the function of the gallbladder
bile storage
what is the function of the small bowel
digestion and most absorption
what is the function of the large bowel
completes absorption of water and electrolytes
describe the mucosa
3 layers:
mucous membrane - protective surface barrier, epithelial tissue w exocrine, endocrine and absorptive cells
lamina propria - middle layer of CT containing gut associated lymphoid tissue
muscularis mucosa - smooth muscle > contract > expose diff areas of surface folding
describe the submucosa
CT containing larger blood and lymph vessels and a nerve network (submucosal plexus)
describe the muscularis externa
major smooth muscle coat (circular and longitudinal layers
contains myenteric plexus
describe the serosa
outer CT which secretes serous fluid
what are the 4 physiological aspects of digestion
motility
secretion
digestion
absorption
what is motility
muscular contractions > propel and mix food
phasic smooth muscle
tone (constant low level contraction)
2 types of phasic digestive motility
what are the 2 types of phasic digestive motility
propulsive (peristalsis) which is a forward mvmt
mixing (segmentation) which mixes food in with digestive juices and exposes to absorptive surfaces
what is secretion
exocrine glands secrete digestive juices and endocrine glands secrete hormones
e.g salivary glands > amylase
stomach > pepsin
liver > bile
what is digestion
food is both mechanically and biochemically broken down into smaller units
this is done through hydrolysis in digestion of proteins, fats and carbs
what is absorption
small units are transferred into blood and lymph
carbs and proteins > Na+ dependent symport > blood
fats > passive process > lymph
what are the four regulatory functions of motility and secretion
autonomous smooth muscle function
intrinsic nerve plexuses
extrinsic nerves
gut hormones
what is the process behind autonomous smooth muscle function
non contractile interstitial cells of Cajal (‘pacemakers’) > est rhythmic and slow wave potentials that spread to smooth muscle
depolarisation = increase permeability to Ca2+
depolarisation = increase permeability to K+
what happens during smooth muscle contraction
increase intracellular Ca2+ conc > calmodulin > MLCK > myosin > actin myosin interaction > cross bridge cycling > contraction
what happens during smooth muscle relaxation
NO is released from enteric neurons > triggers cyclic GMP > stimulates PKG > myosin dephosphorylated > relaxation
what are intrinsic nerve plexuses
myenteric plexus - located b/w longitudinal and circular layers of muscles > control of digestive tract motility
submucosa plexus - main role of sensing luminal environment, regulating GI blood flow and controlling epithelial cell function
what are extrinsic nerves
originates from outside digestive system from ANS
acts on intrinsic nerves, hormone secretion and acting directly on effector cells
what are GI hormones
enteroendocrine cells in mucosa release hormones into blood > excite/inhibit smooth muscle and exocrine cells
e.g gastrin, secretin, motion
what happens during mastication
grind and break up food into smaller sizes
mix w saliva
stimulate taste buds
what does saliva do
washes particles away and acts as a solvent for taste
what does saliva contain
mucus, amylase, lingual lipase, lysozyme, bicarbonate buffer
what 2 reflexes causes an increase in salivation
pressure and chemoreceptors in the mouth > simple reflex
thinking of food, seeing food, smelling food > conditioned reflex
what is the pathway for increased salivation
salivary centre in medulla > autonomic nerves > salivary glands > increased salivation
what are the three stages of swallowing
oral stage (voluntary)
pharyngeal stage (involuntary)
oesophageal (involuntary)
what happens during the oral stage
tongue pushes portion of food to the back of the oral cavity
what happens during the pharyngeal stage
breathing stops and airways close
soft palate and uvula lifted to close nasopharynx
epiglottis is bent over airway as larynx is elevated
what happens during the oesophageal stage
pharynx muscles contract to force bolus into oesophagus
upper oesophageal sphincter opens when larynx is lifted and then closes as soon as bolus passes
peristalsis to push food down
what 2 sphincters are in the oesophagus
pharyngo-oesophageal (upper) which prevents excess air entering the GIT
gastro-oesophageal (lower) which keeps out stomach contents
what is primary peristalsis
preceded by pharyngeal phase, controlled by swallowing centre
what is secondary peristalsis
can occur without pharyngeal phase if oesophagus is distended
describe the anatomy of the stomach
muscular antrum
oxyntic mucosa (acid producing) in the body
pyloric gland area (mucus secreting)
pyloric sphincter is a barrier to small bowel
what are the functions of stomach
store food > release into SI at appropriate rate
secrete HCL and enzymes
create chyme (mix food w secretions)
how does gastric filling occur
the interior of the stomach has deep folds (rugae) which flatten during meals > increase from 50ml to 1L
what is receptive relaxation and when does it occur
relex relaxation of the stomach as it receives food where the folds flatten out > happens during gastric filling
what happens during gastric mixing
ICC create slow wave potentials > threshold in smooth muscle cells > peristalsis > mixing
pyloric sphincter closes tightly
contractions > mix food w secretions > liquid chyme
what happens during gastric emptying
constant tonic contraction of pyloric sphincter keeps it almost closed but open enough for fluids to pass through
small portion of chyme enters duodenum w each contraction
chyme hits closed pyloric sphincter and tumbles back into antrum to continue mixing and digesting
what factors increase antral motility and rate of emptying
volume of chyme and fluidity
distension
what factors inhibit antral motility
fat in the duodenum (slowly digested)
acid in the duodenum (chyme must be neutralised)
hypertonicity of duodenum
distension of duodenum
intrinsic nerve plexuses, autonomic nerves (neural response) and secretin and CCK (hormonal response) in duodenum
external e.g pain and emotion
what is the process behind emesis (vomiting)
deep respiration > glottis closed > uvula raised > stomach, oesophagus and gastroesophageal sphincter is relaxed > respiratory muscles contract > stomach squeezed b/w descending diaphragm > increased intra-abdominal pressure > salivation, sweating , rapid HR
what can cause vomiting
chemical factors
tactile stimulation at back of throat
irritation or distension of stomach and duodenum
visual cues
what are the 2 areas of gastric mucosa that secrete juices
oxyntic mucosa in the body and fundus
pyloric gland area in the antrum
what do exocrine cells in the oxyntic mucosa secrete
mucous cells (stimulated by contents) > alkaline mucus > lubricating, pepsin inhibited, alkaline secretion
chief cells (stimulated by ACh and gastrin) > pepsinogen > protein digestion
parietal cells (stimulated by ACh, gastrin, histamine) > HCL and intrinsic factor > HCL activates pepsinogen, kills microorganisms / intrinsic factor binds w vitamin b12 which is essential for normal function of RBC
what do endocrine cells in the pyloric gland area secrete
enterochromaffin-like cells (stimulated by ACh, gastrin) > histamine > stimulates parietal cells
G cell (stimulated by protein products, ACh) > gastrin > stimulates ECL, parietal and chief cells
D cell (stimulated by acid) > somatostatin >inhibits gastrin and acid secretion
what are the 3 phases of gastric secretion
cephalic phase
gastric phase
intestinal phase
what happens during the cephalic phase
sight, smell , taste or though of food > cerebral cortex stimulates parasympathetic NS > vagus nerve stimulates gastric secretion and motility by increasing muscle and gland activity
what happens during the gastric phase
stretch and chemoreceptors provide info (e.g distension or semi digested protein) > activates short and long reflexes and G cells
what happens during the intestinal phase
gastric secretion decreases as protein in the stomach is removed, pH falls very low in stomach, and food enters duodenum
digestion
body - semi solid mass of food > salivary amylase digestion of carbs can continue
antrum - food mass well mixed w HCL and pepsin
absorption
no food or water absorbed
SMALL amount of lipid soluble compounds can diffuse across cell membranes e.g ethanol
the small intestine is made of what 3 regions
duodenum (25cm)
jejunum (1-2m)
ileum (2-4m)
what two factors affect S.I motility
segmentation and migrating motility complex
what is segmentation
primary method of motility during digestion
circular smooth muscle contract for few seconds at a time and then relax (not move like a wave similar to peristalsis)
mixes and slowly propels chyme forward > ample time for digestion and absorption (decreased frequency of seg. along length of SI)
how is segmentation controlled
initiated by ICC (pacemaker) > threshold > contract
segmentation = slight/absent b/w meals but vigorous right after a meal
increase strength of contraction due to parasympathetic and decrease strength of contraction due to sympathetic
what is smooth muscle responsiveness altered by
distension, gastrin, nerve activity
how can neural control lead to contractions
ACh > binds to M3 receptors (which can be blocked by atropine) on ICCs and smooth muscle > open more ca+ channels > increased strength of contraction
what is the gastroileal reflex
chyme in stomach > gastrin secreted > gastrin acts on ileum smooth muscle > segmentation initiated at the same time as duodenum
what is migrating motility complex (MMC)
after meal mostly absorbed > repetitive peristaltic waves behind (seg. ceases)
what are the 3 phases of MMC
1 - 40-60 mins of relative quiet and few contractions
2 - 20-30mins w some contractions
3 - 5-10 mins of intense peristaltic contractions from upper stomach to end of SI
what is the overall function of MMC
sweeps meal remnants, mucosal debris and bacteria to colon
what controls MMC
b/w meals > SI endocrine cells secrete motilin (inhibited by feeding) > peristalsis
fasting continues > MMC repeats the phases again
what is the ileocaecal juncture
barrier b/w LI and SI
contains ileocaecal valve and ileocaecal sphincter
what does the ileocaecal sphincter do
under neural and hormonal control > relaxation on SI side > prevents contamination of small intestine by bacteria from colon
what does the ileocaecal valve do
colon contents push it closed > pressure makes sphincter contract more forcefully
what secretions occur in the SI
exocrine cells > succus entericus
mucus > lubrication
H2O > hydrolysis + liquid chyme
how can secretion be increase
hormone secretin and enteric neutron stimulation
what are the adaptations of the SI
all carbs, proteins, fats and most electrolytes, vitamins and water are absorbed indiscriminately
most absorption occurs in duodenum and jejunum
ileum > transport mech > absorption of bile salts + vitamin b12
mucosal > larger SA
epithelial cells > enzymes + transport mech
how is SA increased of small bowel
circular fold > 3 fold
villus > 10 fold
microvilli (brush border) > 20 fold
describe the structure of the villus
epithelial cells on surface
CT core > lamina propia
capillaries network + central lacteal
what are crypts of lieberkuhn
invaginations > water + electrolyte secreted
crypt base > paneth cells > lysozymes and defensins
describe the brush border structure
cores of microvilli extend into apical cytoplasm > cross linked w myosin
integral proteins > enzymes + channels > digestion + absorption of carbs + protein
what enzymes exist in the brush border
enterokinase > activates proteolytic enzyme trypsinogen to trypsin
disaccharidases > digest disaccharides into monosaccharides
aminopeptidases > digest small peptide fragments into amino acids
what is linked to Na+ absorption
absorption of h2o, nutrients and electrolytes
how does Na+ transport occur
passive
> b/w cells thru tight junctions
>thru Na+ channel in membrane
active
> accompany another ion e.g Cl-
> accompany nutrient molecules e.g glucose
> exchange for another ion e.g H+
what are the steps of CARB digestion and absorption
- polysaccharides > salivary amylase and pancreatic amylase > disaccharides >
- lactase, maltase, sucrase > monosaccarides >
- glucose/galactose enters cell by 2 Na+ and SGLT symporter
- fructose enters by facilitated diffusion (GLUT-5)
- glucose/galactose/fructose leaves cell by facilitated diffusion (GLUT-2)
- glucose/galactose/fructose diffuses into capillary
what are the steps of PROTEIN digestion and absorption
- exogenous and endogenous proteins > pepsin + pancreatic proteolytic enzymes > small peptides and amino acids
- amino acids enter cells
- small peptides enter cell
- broken down into amino acids within cell (intracellular peptidases)
- exits cell by facilitated diffusion
- diffuses into capillary
what are the steps for FAT digestion and absorption
1.large globes of dietary fat > emulsified by bile salts > small droplets
- lipase > hydrolyses triglycerides > free fatty acids + monoglycerides
- water-insoluble products > carried to epithelial surface in micelles
- monoglycerides + FFA passively diffuse thru cell membrane
- mono. + FFA resynthesised into triglycerides
- triglycerides > coated w lipoprotein > water soluble-chylomicrons
- chylomicrons leave cell by exocytosis
- chylomicrons enter central lacteal as they cannot fit in capillary due to size
what is an example of disordered digestion
lactose intolerance
what happens in lactose intolerance
absence of lactase in SI brush border
> undigested lactose in lumen creates osmotic drag for water > diarrhoea
> colonic bacteria > gas > distension and pain
does pancreas have endocrine or exocrine tissue
it has both
exocrine > duct cells and acinar cells
endocrine > islets of langerhans
what do duct cells secrete
sodium bicarbonate rich aqueous alkaline solution
what do acinar cells secrete
pancreatic enzymes
what are the 3 types of pancreatic enzymes and what do they act on
proteolytic > protein digestion
pancreatic amylase > carbs digestion
pancreatic lipase > fat digestion
what are the major pancreatic proteases
trypsinogen (which is converted into trypsin by enterokinase)
chymotrypsinogen (which is converted into chymotrypsin by trypsin)
procarboxypeptidase (which is converted into carboxypeptidase by trypsin)
what are some protective mechanisms of the pancreas
enzymes stored + release in inactive form
trypsinogen is activated to trypsin in duodenum
pancreas produces trypsin inhibitor
duodenum secretes mucus
what does pancreatic amylase do
hydrolyses polysaccharides into disaccharides
what does pancreatic lipase do
hydrolyses triglycerides into monoglycerides and FFA
what is steatorrhoea
excess fat in faeces resulting from pancreatic insufficiency
what does alkaline solution secreted from duct cells do
neutralises chyme by secreting NaHCO3- and absorbing H+
outline the neutralisation regulation of pancreatic exocrine secretions
acid in duodenum > secretin released from duodenal mucosa > secretin carried by blood > stimulates pancreatic duct cells > increase secretion of NaHCO3 into duodenum > neutralised
outline the digestive regulation of pancreatic exocrine secretions
fat and protein products in duodenum > CCK released from duodenal mucosa > CCK carried by blood > stimulates pancreatic acinar cells > increase secretion of pancreatic digestive enzymes into duodenum > digestion
what is the digestive role of liver
secretion of bile salts
describe the blood flow to the liver
2 sources of reception: hepatic artery (from aorta) and hepatic portal vein
liver sinusoids - large expanded capillary spaces
hepatic vein leads from liver to IVC
describe a hepatic lobule
blood flows from periphery to sinusoids to central vein (central veins converge to form hepatic vein)
bile secreted from hepatocytes to bile canaliculus to peripheral bile duct (bile ducts converge to form common bile duct)
what is bile
secreted by liver continuously
contains bile salts, cholesterol, lecithin, bilirubin, aqueous alkaline fluid
diverted to gallbladder b/w meals
what does the gallbladder do
storage of bile b/w meals
how do gallstones form
crystals that have precipitated from components of bile
too much cholesterol, not enough bile
how does bile get to duodenum
gallbladder/liver > bile duct > sphincter of oddi (regulates when contents from bile duct is released into duodenum > duodenum
how doe bile salts facilitate fat digestion and absorption
emulsification (digestion)
micelles (absorption)
how does emulsification work
hydrophobic heads of bile salts bury into lipid droplet while hydrophilic tails stick out > electrical repulsion > lipid emulsion
how do micelles work
bile salts and lecithin aggregate in small clusters > water soluble > enable lipid digestion products to be transported to the small intestinal surface for absorption
how does bile salt recycling work
most bile salts are reabsorbed by active transport in the terminal ileum and are returned by hepatic portal system to the liver > enterohepatic circulation
what regulates bile secretion
choleretics (substances that increase bile secretion)
what are the 3 types of choleretics
chemical - bile salts stimulate own secretion
hormonal - secretin stimulates aqueous NaHCO3 bile secretion to neutralise chyme
neural - vagal stimulation liver increase bile flow during cephalic phase
what does CCK do in relation to bile release
CCK stimulates contraction of gallbladder and relaxation of sphincter of oddi > release bile into duodenum
what is bilirubin
yellow pigment
modified by bacterial enzymes > makes faeces brown
can be excreted in urine if modified
can accumulate > jaundice
what is hepatitis
inflammatory disease of the liver that can arise from viruses, obesity or toxic agents
repeated inflammation (e.g from alcoholism) can lead to cirrhosis, which results in decrease in active liver tissue and liver failure
what is hydrolysis
addition of a molecule of water
what are micelles
water soluble carrier vehicle
what is SGLT1
it is a symport carrier that uses sodium conc gradient by Na/K ATPase pump to move sodium into a cell
what happens when there is an overconsumption of fructose
fructose escapes into larger bowel and liver > bowel microbes utilise fructose via hexokinase to generate amino acids and SCFAs
how does uptake of glucose happen in hepatocytes
glucose enters liver cell via GLUT2 > converted into glycogen for storage
how does uptake of glucose happen in skeletal and adipose tissue
insulin > GLUT4 inserts into membrane to allow glucose to enter cell
how does transport from GIT to lymph happen
- thoracic duct joins left subclavian vein
- gives plasma milky appearance
- chylomicrons bypass portal circulation and liver
- enter systemic circulation downstream of liver
how does uptake of lipids occur
adipose cells - recombined to TAG for storage
muscle cells - stored or oxidised to acetyl-CoA
how are lipids transported if they are insoluble in water (plasma)
non polar lipids binds with amphipathic lipids (phospholipids and cholesterol) and proteins to water-miscible lipoproteins
what is the structure of lipoproteins
non polar core
single surface layer of amphipathic lipids
how does the degree of lipid in a lipoprotein affect density
the more lipid it contains, the lower the density
what are the four major types of lipoproteins
chylomicrons
VLDL
LDL
HDL
what two types of lipoproteins are TAG rich
chylomicrons and VLDL
what is the function of chylomicrons and VLDL
deliver energy rich TAG to cells in the body
what does LDL do
delivers cholesterol to cells, which is taken up by receptor-mediated endocytosis
what does HDL do
involved in reverse cholesterol transport
> travels in circulation to gather excess cholesterol > returns to liver > eliminated in bile or converted to bile salts
what is the role of the liver in the transport of lipoproteins
removes LDL and other lipoproteins from circulation by receptor-mediated endocytosis
receives excess cholesterol from HDL
why are LDLs considered bad
deposit in sub endothelial space in arterial walls
why are HDLs considered good
prevents accumulation of cholesterol in blood
however, the link between HDL and cardioprotection is weakening as research advances
what are the main functions of the LI
drying and storage
what does faeces contain
bacteria, mucus, undigested fibre, unabsorbed biliary components, fats
what is the LI comprised of
appendix, caecum, ascending colon, transverse colon, descending colon, rectum, anal canal
what are haustra
divided pouches of the colon
not fixed in place > contractile activity of circular muscle layer (similar to segmentation)
what are taeniae coli
3 separate bands of longitudinal muscle > layers gathered into haustra
myenteric plexus concentrated beneath
what is the internal anal sphincter made of
circular smooth muscle
what is the external anal sphincter made of
skeletal muscle
what is the main difference in mucosal architecture of LI compared to SI
Li has no villi > smother/decrease SA
what are haustral contraction
main motility of colon
initiated by ICC
segmental
slow and non propulsive
shuffles chyme back and forth for absorption of salt and water
what are mass movements
another method of motility of colon
propulsive (ascending > transverse colon)
large segments of LI contract > drives faeces 1/3 to 3/4 way through colon in few seconds
how is the LI innervated
taeniae coli > intrinsic innervation (myenteric plexus)
extrinsic - parasympathetic > proximal colon = vagus nerve / distal colon = pelvic nerve
extrinsic - sympathetic > proximal colon = superior mesenteric ganglion / distal colon = inferior mesenteric ganglion / rectum and anal canal = hypogastric plexus
what controls haustral contractions
locally mediated reflexes which changes the likelihood of slow wave reaching threshold
what control mass movements
neural and hormonal stimuli in response to a meal
what is gastrocolic reflex
food enters stomach > release of gastrin + activate extrinsic autonomic nerves (parasympathetic) > stimulate colon motility > mass mvmt
what causes defecation reflex
mass mvmt > distension of rectum (internal anal sphincter relaxes which opens anal canal) > defecation reflex > external anal sphincter can be relaxed voluntarily
how is defecation neurally controlled
short reflex (myenteric plexus) > contraction of muscle in rectum and sigmoid colon > relaxation of internal sphincter
long reflex (spinal cord) > action reinforced by parasymp neurons
sensation to defecate = mediated by cerebral cortex
what voluntary components can assist in defecation
ab contractions
expiration against closed glottis
pelvic floor muscles relax
what happens during constipation
abnormal transit thru colon
delayed transit > increase H2O absorbed > hard dry faeces
can occur due to obstruction, decrease def. reflex, emotion, age
what is hirschsprung’s disease
congenital megacolon
absence of enteric NS in distal colon involving internal anal sphincter and rectum > area has increased tone and narrow lumen > no propulsive activity
what does LI absorb
actively absorbs Na+
Cl- passively absorbed
absorbs water osmotically
absorbs electrolytes and vitamin K
what does LI secrete
protective alkaline mucus to neutralise acids and lubricate passage
what does the microbiome in the colon do
synthesise vitamin K, promote calcium, magnesium, zinc absorption
contribute to host metabolism through fermentation
> produce enzymes to break down nutrients that the host cant (e.g cellulose)
> produce gases (flatulence), SCFA, heat
> SCFA used as energy source for colonocytes
> products influence colon motility
what two bacteria are the leading causes of food poisoning
salmonella and campylobacter
how does food poisoning occur
bacteria passes epithelium > inflammatory response > diarrhoea
what is metabolism
chemical reactions in living organisms that maintain life
what is intermediary (fuel) metabolism
reactions that involve degradation, synthesis, and transformation of energy rich organic molecules
what is anabolism
synthesis of larger macromolecules
what is catabolism
degradation of larger macromolecules
what are our fuel intakes
dietary protein, carbs, an triglyceride fat
what are the absorbable units of our fuel intake
amino acids, glucose, monoglycerides and fatty acids
what is the metabolic pool
absorbable units that can either be used anabolically to store energy for later or catabolically for fuel use
amino acids, glucose, fatty acids
what molecules do we store fuel as
proteins, glycogen, triglycerides
how do we use fuels
oxidation of pool to form ATP
how are fuels lost
urea formed from amino acids and CO2 formed from oxidation of AA, glucose, and FA
amino acids to protein is called…
protein synthesis
protein to amino acids is called…
proteolysis
amino acids to glucose is called…
gluconeogenesis
glucose to glycogen is called…
glycogenesis
glycogen to glucose is called…
glycogenolysis
glucose to FA is called…
lipogenesis
fatty acids to triglycerides is called
lipogenesis
triglycerides to FA is called…
lipolysis
glucose to ATP is called…
glycolysis
what happens during glycolysis
glucose converted to 2 pyruvate
ADP forms ATP
2 ATPs per glucose molecule
no o2 required
what happens during citric acid cycle
acyl unit from acetyl CoA (from pyruvate when sufficient O2) combines w oxaloacetate to form citrate > further reactions form ATP, NADH and FADH2
what happens in the electron transport chain
energy from e- of NADH and FADH2 is transferred to ATP
o2 required
what happens in the absorptive state
just fed by meal so…
insulin > increase glucose oxidation / increase glycogen synthesis / increase fat synthesis / increase protein synthesis
what happens in postabsorptive state
fasting so…
glucagon > increase glycogenolysis / increase gluconeogenesis / increase ketogenesis / increase protein breakdown
what are the main nutrient classes
macronutrients (proteins, carbs, fats)
micronutrients (vitamins, minerals, trace elements)
what is energy required for
voluntary activity
maintenance of life (BMR) e.g breathing, body temp, HR
growth e.g children and body builders
what does energy requirement depend on
body size and composition
age
activity
what are dietary fats
primarily composed of triglycerides
saturated, monounsaturated, polyunsaturated
what does saturated fats mean
no double bonds (found in animal and dairy fats)
what does monounsaturated fats mean
one double bond (found in olives and nuts)
what does polyunsaturated mean
several double bonds (found in plant oils, fish oils
what are the functions of dietary fats
provision of energy
component of membranes
precursors of prostaglandins
precursors of cholesterol
absorption of fat soluble vitamins
essential fatty acids (linoleic, alpha linoleic)
what are omega 3 fatty acids
double bond 3 carbons from the methyl end of fatty acid chain
DHA, EPA, and alpha linolenic acid (which converts to EPA)
oily fish > DHA and EPA
walnuts and canola oil > alpha linolenic acid
what are trans fatty acids
trans double bond
found in animal products
can be manufactured
increased LDL cholesterol > CVD link
what are the 4 types of carbs
sugars
starches
oligosaccharides
dietary fibres
what are the 3 types of sugars
monosaccharides
disaccharides
sugar alcohols e.g sorbitol, mannitol
what are the functions of mono and disaccharides
energy
formation of glycoproteins formation of glycosaminoglycans and proteoglycans
what are the health effects of sugars
obesity and weight gain > risk of DM and CVD
what is starch
alpha glucan polysaccharides
amylose and amylopectin
no adverse general health effects
what are maltodextrins and glucose syrups
made from hydrolysis of starch
chains of 3 or more glucose units w some mono and disaccharides (glucose polymers)
used as energy supplements
potentially cariogenic
what are the 3 classes non digestible carbs in dietary fibre
resistant starch
non starch polysaccharides
resistant oligosaccharides
what is resistant starch
starch that is not digested (e.g they are physically enclosed in cell wall)
what is non starch polysaccharides (NSP)
comprises cellulose, pectins, hemicelluloses
not digested in upper GU
insoluble NSP adds to stool bulk and aids peristalsis and reduces toxin conc
soluble NSP increase in blood lipids and glucose so it is important for glucose homeostasis and lipid metabolism
NSP increase satiety
what are resistant oligosaccharides
resistant or partially resistant to digestion in upper GI tract
encourage growth of bifidobacteria and lactobacilli in colon
potentially cariogenic
what are the functions of dietary proteins
growth and repair
maintenance of muscle
hormones and enzymes
why is protein required
it is needed fro nitrogen balance
positive N-balance in growth and pregnancy
negative N-balance in starvation and trauma
define basal metabolic rate
amount of energy your body needs to maintain homeostasis
What disorders affect the oral cavity and swallowing
Xerostomia
Dysphagia
What happens during Xerostomia
Hyposalivation or excessive clearance due to things like damage to salivary glands, cancer treatment and dehydration
Most common cause in medication related
How can Xerostomia be treated
Saliva substitutes
Pilocarpine (muscarinic receptor agonist)
Why would a muscarinic receptor agonist be helpful for Xerostomia
Increase secretion by exocrine glands
Cholingeric action mimics the release of ACh from parasympathetic nerve endings > acts on muscarinic receptors in salivary glands
What happens during Dysphagia
Disruption in swallowing process > aspiration, pneumonia, malnutrition, dehydration, airway obstruction
Can occur at any stage of swallowing
Why is Dysphagia common in neurological conditions
The swallowing centre is in the brain stem so it is affected by things like strokes or traumatic brain injuries or other degenerative neurological disorders
What disorders affect the oesophagus and stomach
Reflux
Peptic ulcers
In reflux oesophagitis, how can acid defy gravity and move into the oesophagus to cause injury
Lower oesophageal sphincter relaxed > inspiration > subatmospheric intrapleural pressure favours backward mvmt > lower pressure in oesophagus compared to stomach > acidic stomach contents move into oesophagus
How can reflux be treated
Antacids, histamine receptor inhibitors, proton pump inhibitors
How can bacteria such as H.pylori lead to peptic ulcers
Secrete toxins > gastritis at site of infection > disruption tight junctions b/w epithelial cells > acid penetrate > increase gastric release by keeping pH high in antrum (low pH is an inhibitor for gastrin)
What disorders affect the accessory organs
Biliary obstruction
Pancreatitis
What happens during biliary obstruction
Blockage of any duct that carries bile from the liver or gallbladder to the SI
Can occur from choleiths, malignancy, infection, biliary cirrhosis
Jaundice occurs bc bilirubin can’t be eleimated in faeces
What happens during pancreatitis
Pancreatic enzymes irritate + damage pancreas > premature activation of trysinogen due to excessive CCK, low pH, and dysregulated exocytosis > tissue loss, necrosis, pain
Results mainly from alcoholism, certain drug use and duct blockage
What disorders affect the SI
Gluten allergy
What happens during celiac disease (gluten enteropathy)
Autoimmune inflammatory disease
T Cells mediate injury > dev IgA and IgG antibodies directed against gluten peptides
Villi/microvilli damaged > decreased SA of SI > impaired nutrient absorption
Can results in malnutrition and bone loss
Duodenal biopsy is good for diagnosis
What disorders affect the large intestine
Diverticula disease
What is diverticula
Herniations protrude through smooth muscle at openings created by vasa recta in wall of colon > create small pouches lined by mucosa (most often found in sigmoid colon)
What is diverticulosis
Having the condition of uninflamed diverticula
What is diverticulitis
Inflammation of one or more diverticula, associated with fever, leukocytosis and pain
Can be caused by trapped fecal material > obstruction > distension, mucus secretion and bacterial overgrowth > vascular compromise and perforation > peritonitis
Which blood vessels are the most likely source of bleeding in diverticulosis
Vasa recta, which branch from marginal and colic arteries
What does RDI stand for
Recommended daily intake
What does EAR stand for
Estimated average requirements
What does AI stand for
Adequate intakes
What does SDT stand for
Suggested dietary targets
What does EER stand for
Estimated energy requirement
What does AMDR stand for
Acceptable macronutrient distribution range
What is the RDI of protein in men and women
Men = 0.84g/kg body weight
Women = 0.75g/kg body weight
Over 70 years:
Men = 1.07g/kg
Women = 0.94g/kg
What is the AMDR for protein
12-25% of energy intake
What is the upper limit of protein
25% of energy as protein
What is the AMDR for fat
20-35% of energy intake
8-10% of energy intake as saturated fat
What is the Omega 3 RDI of fat
Men = 0.6g/day
Women = 0.4g/day
Needs 1-2 fish meals per week
What is the RDI of essential fatty acids
Men = 160mg/day
Women = 90mg/day
What is the SDT of carbs as fibres
Men = 30g/day
Women = 25g/day
What is the AMDR for carbs
Total CHO 45-65% of energy
What is the energy intake of free sugars recommended by WHO
<10%
What is outlined by Aus dietary guideline 1
Be physically active and eat nutritious foods to meet energy need
Children + adolescents = sufficient nutritious foods + active every day to grow
Older ppl = nutritious foods + active to maintain muscle strength + weight
What does Aus dietary guideline 2 outline
Foods from veg, fruit, grains + fibres, lean meats, dairy and plenty of water
What does Aus dietary guidelines 3 outline
Limit saturated fat, added salts and sugars and alcohol
What does Aus dietary guideline 4 outline
Encourage, support and promote breastfeeding
