GI Flashcards
which cells line the intestines?
enterocytes
where does the voluntary phase of swallowing occur?
mouth
describe the voluntary phase of swallowing
food is chewed and pushed into the oropharynx
describe the pharyngeal phase of swallowing
nasopharynx closed
hyoid elevated
epiglottis closed
pharynx shorter and wider (longitudinal muscle)
involuntary
is the pharyngeal phase of swallowing involuntary or voluntary?
involuntary
which sphincter lies between the oesophagus and stomach?
what is it’s function
lower oesophageal sphincter
prevent oesophageal reflux of acid
what is the oesophageal phase of swallowing?
pharynx sequentially contracts (circular muscle)
peristaltic waves along oesophagus towards the lower oesophageal spinchter
hyoid depressed, epiglottis opens, nasopharynx opened
which sphincter prevents oesophageal reflux of acid?
lower oesophageal sphincter
what is reflux into the oesophagus called?
GORD
what can cause acid reflux?
pregnancy, big meals
which sphincter is at the bottom of the stomach?
pyloric sphincter
blood supply to the stomach
coeliac trunk and its branches
a branch of abdominal aorta at T12
branches of the coeliac trunk
common hepatic artery
left gastric artery
splenic artery
blood supply of the lesser curvature of the stomach
left and right gastric arteries, which anastomose
blood supply of the greater curvature of the stomach
left and right gastroepiploic arteries, which anastomose
where does the left gastric arise from?
coeliac trunk
where does the splenic artery arise from?
coeliac trunk
branches of the splenic artery
left gastroepiploic artery
short gastrics
pancreatic branches
appearance of splenic artery
tortuous
sole arterial supply to liver
common hepatic artery
and then also hepatic portal vein supplying venous blood from the GI tract
terminal branches of the common hepatic artery
proper hepatic artery
gastroduodenal artery
branches of the proper hepatic artery
right gastric
right and left hepatic
cystic
last two are intuitive because the proper hepatic artery travels right, towards the liver and obviously gallbladder
branches of the gastroduodenal artery
right gastroepiploic
superior pancreaticoduodenal
blood supply of the fundus
splenic artery - intuitive, as the spleen is near the fundus of the stomach
folds on the stomach lining
rugae
function of rugae
allow expansion of the stomach after the consumption of foods and liquids
differences in the vasa recta and arterial arcades between jejunum and ileum
jejunum
- longer vasa recta, fewer arterial arcades
ileum
- more arterial arcades, shorter vasa recta
vasa recta - straight arteries coming off from arcades in the mesentery of the jejunum and ileum, and heading toward the intestines
arterial arcades - loops of arteries around the jejunum and ileum
function of the colon
absorb water
function of the small intestine
absorb nutrients
retroperitoneal organs
SAD PUCKER
Suprarenal (Adrenal) gland, Aorta and IVC, Duodenum, Pancreas, Ureter, Colon, Kidney, Esophagus, and Rectum
or DADPOK
do mesenteries allow movement?
yes
‘m’ for motile
where do the omenta hang?
off the greater and lesser curvature of the stomach
what is the only natural communication between the lesser and greater sac?
epiploic foramen of Winslow
foregut
mouth to proximal half of duodenum
midgut
distal half of the duodenum to proximal two thirds of the transverse colon
hindgut
distal third of transverse colon to rectum
what does ‘GORD’ stand for?
gastro-oesophageal reflux disease
consequences of GORD
metaplasia
Barret’s oesophagus
epithelium change from stratified squamous non keratinising epithelium (of the oesophagus) to simple columnar (of the stomach)
causes pain, as less protection due to change in epithelium
which cranial nerves are involved in the gag reflex?
which is sensory, and which is motor in this response?
CN IX and CN X
glossopharyngeal (sensory) and vagus (motor)
how much saliva is produced a day?
800ml - 1500ml
what does saliva contain?
water, mucus, antibodies, enzymes e.g amylase
functions of saliva
lubricant, taste (by dissolving), cephalic digestion, mouth hygiene
name the three major salivary glands
parotid, submandibular and sublingual
which is the largest salivary gland?
parotid
which salivary gland are continuous?
submandibular and sublingual
which salivary gland must be stimulated for secretions to occur?
parotid
what type of secretions does the parotid gland secrete?
serous
which duct does saliva from the parotid gland leave?
Stensen’s duct
innervation of the parotid gland
CN IX - glossopharyngeal
not CN XII (facial), this only passes through and divides into 5 terminal branches in the parotid
which cranial nerve passes through the parotid gland?
facial
CN VII
facial DOES NOT innervate the parotid gland
name structures passing through the parotid gland
external carotid artery
retromandibular vein
facial nerve - remember the parotid is not actually innervated by the facial nerve however
is the submandibular gland continuous?
yes
is the parotid gland continuous?
no
is the sublingual gland continuous?
yes
where do secretions from the submandibular gland leave?
Wharton duct
what type of secretions does the submandibular gland secrete?
mixed serous and mucous
subMandibular for mixed
what can we see histologically in submandibular glands?
serous demilunes
serous acini form crescents around mucous
innervation of the submandibular gland
CN VII
7th cranial nerve
facial nerve
which is the smallest salivary gland?
sublingual
which type of secretions does the sublingual gland secrete?
mixed
where do secretions from the sublingual gland leave?
Wharton duct
innervation of the sublingual gland
facial nerve
where is the sublingual gland relative to the submandibular?
anterior
which is the only non mucous secreting (serous) minor gland?
von ebner
from which gland is the main salivary output when stimulated?
parotid
what percentage of salivary flow is by the three major glands?
80
here are minor salivary glands located?
submucosa of oral mucosa
what percentage of saliva is produced by minor salivary glands?
20% approx
compare the contents of serous and mucous secretions
serous
- water and alpha amylase
mucous
- water and glycoproteins
compare the histological appearance of serous and mucous glands
serous
- dark staining
- small central duct
- nucleus in basal third
Mucous
- pale and foamy appearance (Michael Palin - to remember)
- large central duct
- nucleus at base
what is xerostomia?
dry mouth
what can cause xerostomia?
cystic fibrosis
Sjorgen’s syndrome
what causes obstruction in salivary glands?
calcium and phosphate ions in saliva can form salivary calculi
most often in submandibular gland
which gland swells up significantly in mumps?
parotid - capsule does not allow much enlargement
effect of parasympathetic stimulation on salivary glands
saliva stimulated - rest and digest
effect of sympathetic stimulation on salivary glands
saliva inhibited - fight or flight
layers of the GI tract, internal to external
mucosa
submucosa
muscularis externa
serosa
MSMS
name the two large plexuses of the enteric nervous system
submucosal plexus
myenteric plexus
where is the submucosal plexus?
submucosa of the gastrointestinal tract wall
how many layers does the muscularis externa of the stomach have? what are they?
three
inner oblique, intermediate circular, outer longitudinal
how many layers does the muscularis externa of the GI tract (minus the stomach) have? what are there?
two
inner circular, outer longitudinal
where is the myenteric plexus?
muscularis externa of GI tract
which cells are predominantly found in the cardia of the stomach and what do they produce?
foveolar
mucus - for protection
where are parietal cells predominantly found, and what do they produce?
fundus of stomach
HCl and intrinsic factor
what do parietal cells produce?
HCl and intrinsic factor
function of intrinsic factor
absorption of vitamin B12
what is pernicious anaemia?
vitamin B12 deficiency
where are chief cells predominantly found?
fundus of stomach
what do chief cells produce?
pepsinogen
(which is cleaved to pepsin)
what is a zymogen?
inactive precursor of an enzyme
where are ECL cells predominantly found?
fundus of stomach
what do ECL cells produce?
histamine
function of histamine in the stomach
signals the release of HCl for digestion
where are G cells primarily found?
pyloric antrum
what to G cells produce?
gastrin
function of gastrin
stimulates release of HCl into the stomach
directly and via histamine
where are D cells predominantly found? (gastric delta cells)
stomach, duodenum, pancreas
what do D cells produce?
somatostatin
where are I cells found?
duodenum
function of I cells
produce cholecystokinin - CCK
function of cholecystokinin
bile secretion
where are S cells found?
duodenum
what do S cells produce?
secretin
functions of the stomach
digests and sores food
activates enzymes
kill microbes
secrete intrinsic factor for the absorption of B12
protection and lubrication
in which cells is gastric acid produced?
parietal cells
describe gastric acid production, using equations where necessary
water and carbon dioxide combine within the parietal cell cytoplasm to produce carbonic acid
this is catalysed by carbonic anhydrase
carbonic acid spontaneously dissociates into a hydrogen ion and a bicarbonate ion
CO2 + H2O ⇌ H2CO3 ⇌ HCO3- + H+
the hydrogen ion is transported into the stomach lumen via the H+-K+ ATPase ion pump. the pump uses ATP to exchange potassium ions into the parietal cells of the stomach with H+ ions
the bicarbonate ion is transported out of the cell into the blood via an anion exchanger which transports the bicarbonate ion out of the cell in exchange for a chloride ion
the chloride ion is then transported into the stomach lumen via a chloride channel
results in hydrogen and chloride ions being present within the stomach lumen. their opposing charges leads to them associating with each other to form hydrochloric acid
Cl- + H+ —> HCl
what is the pH of the stomach?
pH 2
name the three phases of digestion
cephalic phase, gastric phase, duodenal phase
does the cephalic phase of digestion always stimulate or inhibit gastric acid production?
increase
always stimulatory
does the gastric phase of digestion stimulate or inhibit gastric acid production?
first part
- stimulates
- stomach distends
- triggers gastrin release; activates histamine release
- increases number of H+-K+ ATPase pumps
second part
- low luminal pH
- decrease in gastrin and therefore histamine
- an increase in somatostatin
does the duodenal phase of digestion always stimulate or inhibit gastric acid production?
always inhibitory
what is the mechanism of gastric acid regulation?
an increase in the number of apical H+ K+ ATPase pumps on the parietal cell
what is the cephalic phase of digestion?
stomach responds to the mere sight, smell, taste, or thought of food
what is the gastric phase of digestion?
swallowed food and semi-digested protein ( peptides and amino acids) activate gastric activity
what is the duodenal (also known as intestinal) phase of digestion?
the duodenum responds to arriving chyme and moderates gastric activity through hormones and nervous reflexes
describe the cephalic phase of digestion
vagus nerve uses Ach
induces parasympathetic stimulation of the GI tract
promotes gastrin secretion from G cells
increases histamine secretion from ECL cells
an increase in H+ K+ ATPase pumps
parasympathetic
sight, small, taste of food and chewing
vagus nerve
Ach release
Ach triggers release of gastrin and histamine
net effect is increased acid production
describe the gastric phase of digestion when gastric acid secretion is stimulated
triggered by gastric distension or presence of peptides and amino acids
gastrin release
gastrin acts directly on parietal calls
gastrin triggers release of histamine
histamine acts directly on parietal cells (and mediates effect of gastrin and ACh)
net effect is increased acid production
why do proteins stimulate gastric acid production?
proteins in the lumen act as a buffer and mop up H+ ions
pH rises
gastrin release stimulated
decreased secretion of somatostatin
more parietal cell activity - lack of inhibition
describe the gastric phase of digestion when gastric acid secretion is inhibited
low luminal pH
directly inhibits gastrin secretion
indirectly inhibits histamine release via gastrin
stimulates somatostatin release which inhibits parietal cell activity
what triggers the duodenal phase of digestion?
triggered by
distension of the duodenum
hypertonic luminal contents
a fall in pH
a rise in fatty acid concentration
a rise in amino acid concentration
describe the response in the duodenal phase of digestion
enterogasterones are released
secretin from S cells
- inhibits gastrin release
- promotes somatostatin release
choleocystokinin (CCK) from I cells
- stimulates bile release
what are peptic ulcers?
breaches in mucosal lining
what causes peptic ulcers?
H pylori bacteria
NSAIDS e.g ibuprofen
chemical irritants
gastrinoma
how do gastronomas cause ulcers?
excessive gastrin release attacks gastric mucosa
how does Helicobacter pylori cause peptic ulcers?
secretes urease
splits urea to carbon dioxide and ammonia
ammonia combines with h+ to form ammonium
damaged gastric epithelium
how do NSAIDS cause peptic ulcers?
inhibit Cox-1 which makes prostaglandins
prostaglandins stimulate mucus production
what pH does H pylori thrive at?
low
how are peptic ulcers caused by H pylori treated?
proton pump inhibitors increase pH so conditions are inhospitable to H pylori
antibiotics
how are peptic ulcers caused by NSAIDs treated?
prostaglandin analogues - misoprostol
reduce acid secretion
what do parietal cells produce?
HCl and intrinsic factor
what cell secreted pepsinogen?
chief cell
what two things activates the cleaving of pepsinogen to pepsin?
pepsin itself (positive feedback)
HCl
action of pepsin
protein digestion into peptides
do chief cells produce pepsin?
NO NO NO
they produce pepsinogen, which is converted to pepsin by a low pH and pepsin itself
what vitamin supplements may you need if your stomach is removed?
B12
where do peristaltic waves begin in the stomach? nature of these contractions
gastric body
weak contractions
are contraction in the gastric antrum stronger or weaker than in the body?
stronger
what causes mixing of the contents of the stomach?
antral contents are forced back towards the body
when is the conversion of pepsinogen to pepsin most efficient?
when pH is less than 2
what can irreversibly inactivate pepsin?
HCO3-
what percentage of total protein digestion is pepsin responsible for?
20%
how much chyme is released into the duodenum at a time? what happens to the rest?
3ml
retropulsed - pushed back
nervous control of peristalsis
parasympathetic nervous system acting on enteric nerve plexuses
coordination - afferent input via vagus nerve
what substances mediate receptive relaxation of the GI tract?
nitric oxide and serotonin released by enteric nerves
which cells mediate gastric motility by contracting?
interstitial cells of cajal
how many times does the GI tract contract a minute?
three
what slows gastric emptying?
a decrease in pH
an increase in fatty acids
an increase in amino acids
distension
hypertonicity - high concentration
what is dumping syndrome?
food moves into duodenum too quickly
which has a greater volume, stomach or duodenum?
stomach
rugae can stretch
describe the two responses that mediate the slowing of duodenal emptying
short pathway
- smaller response
- enteric local GI neurons
long pathway
- CNS
- bigger
what is gastroparesis?
too delayed duodenal emptying
water input into the GI tract per day
9000 ml
how much water is secreted and ingested into the GI tract per day?
7000ml secreted
2000ml ingested
where is water secreted in the GI tract?
intestines, saliva, stomach, bile, pancreas
what volume of water is secreted by intestines into the GI tract per day?
1000 ml
what volume of water is secreted in saliva into the GI tract per day?
1500 ml
what volume of water is secreted by the stomach into the GI tract per day?
2500 ml
what volume of water is secreted in bile into the GI tract per day?
500 ml
what volume of water is secreted by the pancreas into the GI tract per day?
1500 ml
what percentage of water is reabsorbed into GI tract, and what volume does this correspond to?
98%
8800 ml
what volume of water is excreted in stool?
200 ml
what does exocrine mean?
secretion into a duct
what volume of water is reabsorbed by the jejunum?
5500 ml
what volume of water is reabsorbed by the ileum?
2000 ml
what volume of water is reabsorbed by the colon?
1300 ml
which ion is most abundant in chyme?
Na+
in which part of the GI tract is iron absorbed?
duodenum
where are vitamin B and C absorbed?
jejunum
but not B12 even though it is water soluble
which are the water soluble vitamins?
B and C
what are the fat soluble vitamins?
ADEK
which vitamins does the ileum absorb?
A,D,E,K and B12
all fat soluble bar B12
which vitamins do the jejunum and ileum absorb?
jejunum - B and C
ileum - A,D,E,K,B12
digestion of starch
alpha amylase in the mouth
pancreatic amylase released at duodenum major duodenal papilla (95% digestion)
broken down into oligo/ disaccharides
membrane bound oligo/ disaccharidases at duodenum converted to monosaccharides
products of carbohydrate digestion
glucose, galactose, fructose
monosaccharides
products of carbohydrate digestion
glucose, galactose, fructose
absorption of glucose and galactose from duodenal lumen into lining cell
secondary active transport with Na+, SGLT-1
where are carbohydrates digested and absorbed?
duodenum
absorption of fructose from duodenal lumen into lining cell
facilitated diffusion using a GLUT 5 transporter
how do glucose, fructose and galactose leave the duodenum?
basolaterally
by GLUT2
diffuse into capillary then portal vein to liver
absorptive state
have eaten
glucose uptake by liver and stored as glycogen and in skeletal muscle
post absorptive state
fasted
glycogen stores broken down to glucose and consumed by skeletal muscle
what is metabolism?
the chemical processes that occur within a living organism in order to maintain life
protein digestion
stomach pepsin cleaves some bonds
in the duodenum, pancreatic endopeptidases
- acts mid chain
- e.g trypsin, chymotrypsin
in the duodenum, pancreatic exopeptidases
- acts on ends
- membrane bound aminopeptidases
protein absorption
secondary active transport with sodium
basolaterally into interstitial fluid then capillaries
fat digestion
starts in mouth with salivary lipase
emulsified by bile salts into small droplets - amphipathic so don’t reaggregate
lipase converts triglycerides to monoglycerides and 2 fatty acids
products packaged into micelles
contents released at intestinal brush border
fat absorption
monoglycerides + 2 FA converted to triglycerides in small intestine SER
packaged into vesicle with cholesterol
vesicles modified by Golgi into chylomicrons
exocytosed basolaterally into lacteals to the lymphatic circulation
where is vitamin A stored?
Ito cells of liver
and space of Diese
what vitamin do the words ‘rhapsodic’, ‘carotenoids’, ‘retinol’ refer to?
A
how is vitamin A absorbed?
as a lipid
function of vitamin A
presentation of vitamin A deficiency
vision
night blindness
source of vitamin A
carrots
what vitamin is ‘calciferol’?
D
what vitamin is required to absorb calcium and phosphate?
D
source of vitamin D
UV B
where is vitamin D stored?
liver
presentation of vitamin D deficiency
rickets
osteomalacia
source of vitamin E
nuts and seeds
where is vitamin E stored?
liver
function of vitamin E
antioxidant
function of vitamin K
activates clotting factors 10, 9, 7, 2 (remember - 1972)
source of vitamin K
synthesised by plants and present in food
presentation of a vitamin K deficiency
bleeding disorders
action of warfarin
inhibits vitamin K
presentation of a lack of vitamin B12
pernicious anamia
function of vitamin B12
cell metabolism
energy
which vitamins does the liver store?
ADEK and B12
fat soluble vitamins and B12
how is vitamin B12 absorbed?
in stomach, binds to R protein transcolbamin-1 which prevents it becoming cleaved
cleaved at duodenum and binds to intrinsic factor
absorbed in ileum as B12-IF complex
source of vitamin B12
poultry and eggs
source of vitamin C
fresh fruit and vegetables
presentation of vitamin C deficiency
scurvy
function of vitamin C
immune system, iron absorption, antioxidant
where is iron stored? and how?
liver as ferritin
how is iron absorbed into the blood
transferrin
storage form of iron
ferritin
where is copper stored?
liver
name two minerals stored by the liver
copper and iron
source sof calcium
dairy
functions of calcium
muscle contraction and synaptic transmission
source of iodine
seafood
function of iodine
key component of thyroid hormone
malnutrition
malabsorption of vitamins and minerals
what is coeliac disease?
gluten intolerance
decrease surface area of intestinal brush border
damaged brush border
equation for BMI
weight/ height2
units of BMI
kg/m2
units of BMR
kcal of energy expended /hr/m2
blood supply of the foregut
coeliac trunk
dorsal mesentery of the foregut
greater omentum
does not seem intuitive because dorsal means on top of
ventral mesentery of the foregut
lesser omentum
does not seem intuitive because ventral means below
sympathetic innervation of the stomach
greater splanchnic nerve
T5-T9
where does the foregut extend to?
mouth to major duodenal papilla
blood supply of the midgut
SMA
sympathetic innervation of the midgut
T10 and 11
lesser splanchnic nerve
where does the midgut extend to?
major duodenal papilla to proximal 2/3 transverse colon
blood supply of the hindgut
IMA
sympathetic innervation of the hindgut?
T12, least splanchnic nerve
where does the hindgut extend to?
distal third of transverse colon to rectum
compare intraperitoneal, primary retroperitoneal and secondary retroperitoneal
viscera with mesentery - intraperitoneal
viscera without mesentery - primary retroperitoneal
viscera that had a mesentery but now does not - secondary retroperitoneal
which layers of the embryo are present in the GI tract?
endoderm - epithelial linings; mucosa
mesoderm - muscle and connective tissue
how and when is the primitive gut tube formed during embryogenesis?
4th week
trilaminar disc folds medially and horizontally
endoderm fuses to form primitive gut tube
how and when does the mouth form during embryogenesis?
end of 4th week
oropharyngeal membrane of primitive gut tube ruptures to form the mouth
how and when do the anus and urogenital openings form during embryogenesis?
7th week
cloacal membrane at the caudal end of the primitive gut tube ruptures
midgut tube development
elongation, herniation, rotation, retraction, fixation
embryological development of the stomach
4th week - fusiform dilation
7th week - 90 degree clockwise longitudinal rotation, creates lesser sac
8th week - ventrodorsal rotation
where do the pharyngeal arches run between?
oropharyngeal membrane to respiratory diverticulum
when do the pharyngeal arches develop?
4th/ 5th week
how many pharyngeal arches are there? which one regresses?
5: 1,2,3,4,6
5th regresses
how are pharyngeal arches formed?
derived from connective mesenchymal tissue (mesodermal) invaded by cranial neural crest cells
what does each pharyngeal arch contain?
its own blood and nerve supply
which cranial nerve is contained in the first pharyngeal arch?
CN V3 (mandibular branch of the trigeminal)
which muscles are associated with the first pharyngeal arch?
mastication, tensor tympani, diagastric, mylohyoid
which bones are associated with the first pharyngeal arch?
maxilla, mandible, incus, malleus
which nerve is associated with the second pharyngeal arch?
CN VII
facial
which muscles are associated with the second pharyngeal arch?
facial expresson, stapedius, stylohyoid
which bones are associated with the second pharyngeal arch?
stapes, styloid, lesser horn of hyoid cartilage
which cranial nerve is associated with the third pharyngeal arch?
CN IX
glossopharyngeal
which muscles are associated with the third pharyngeal arch?
pharyngeal stylopharyngeus
which bones are associated with the third pharyngeal arch?
body and greater horn of hyoid cartilage
which nerve is associated with the 4th pharyngeal arch?
superior laryngeal branch of CN X
vagus
which muscle is associated with the 4th pharyngeal arch?
cricothyroid
which bones are associated with 4th pharyngeal arch?
thyroid and epiglottic cartilages
which nerve is associated with the 6th pharyngeal arch?
recurrent laryngeal branch of CN X
vagus
which muscles are associated with the 6th pharyngeal arch?
all internal larynx muscles except cricothyroid
which bones are associated with the 6th pharyngeal arch?
cricoid, arytenoid, cuneiform, corniculate cartilages
functions of the stomach
secrete proteases
secrete intrinsic factor
kill microbes
store and mix food
how much gastric acid is secreted a day?
2L
why is gastric acid secretion energy dependent
it takes place against a concentration gradient
which nerve regulates gastric acid secretion
vagus
what does ACh release trigger?
release of gastrin and histamine
action of gastrin and histamine
increased gastric acid production
what acts directly but also mediates the effect of gastrin and ACh?
histamine
what happens when there is a low luminal pH?
inhibits gastrin secretion
indirectly inhibits histamine release via gastrin
stimulates somatostatin release
parietal cell activity is inhibited
what are enterogastrones, and give examples
released from duodenal mucosa
secretin and cholecystokinin
which pump regulates gastric acid production?
H+/ K+ ATPase
proton pump
which substances control control gastric acid production?
ACh
gastrin
histamine
somatostatin
secretin
CCK
causes of pepetic ulcers
NSAIDs
H Pylori
Chemical irritants
- alcohol, bile salts
gastrinoma
defences against ulcers
alkaline mucus
tight junctions between epithelial cells
replacement of damaged cells
negative feedback loops to prevent overproduction of acid
how do bile salts cause peptic ulcers?
regurgitated bile strips away mucus layer
what is an inactive form of an enzyme?
zymogen
how is pepsin irreversibly inactivated?
in small intestine by bicarbonate
is the stomach needed for digestion
no
volume of empty stomach
50mL
volume of full stomach
1.5L
what is receptive relaxation?
smooth muscle in body and fundus relax
parasympathetic
vagus
which substances mediate receptive reelaxation?
nitric oxide and serotonin
where do peristaltic waves begin?
body
which cells determine the frequency of peristaltic waves, and where are they located?
pacemaker cells in muscular propria
frequency of peristaltic waves
3 per minute
what increases the strength of peristaltic contractions?
gastrin
gastric distension
what decreases the strength of peristaltic contractions?
duodenal distension
duodenal osmolarity
duodenal luminal pH
sympathetic nervous system action
parasympathetic nervous system action
is the capacity of the stomach or duodenam greater?
stomach
what is gastroparesis?
delayed gastric emptying
are gastric motility and emptying regulated by the same fsctors that regulate HCL production?
pretty much
what pH is saliva? what is the range
7.2
6.2 to 7.4
saliva flow rate
0.3-0.7ml/ minute
content of serous secretions
alpha amylase for starch digestion
content of mucus secretions
mucins for lubrication of mucosal surfaces
are the parotid, submandibular and sublingual glands serous, mucus or mixed?
parotid - serous
the other two are mixed
factors affecting composition and amount of saliva
gender
diet
type and size of gland
how does saliva contrribute to oral health?
lubrication
mechanical cleaning
buffering salts - neutralises acid
remineralisation - calcium and phosphate
proteins for defensive and digestive function
oral defences
mucosa
palantine tonsils
salivary glands
which salivary glands are continuous
submandibular, sublingual and minor glands
which salivary gland must be stimulated?
parotid
which epithelial tissues form the salivary glands?
acinar cells around ducts
have channels and transporters in the apical and basolateral membranes to enable transport of fluid and electrolytes
how are interlobular ducts divided?
intercalated and striated
intercalated
- cuboidal cells
striated
- basal membrane highly folded into microvilli for hydrogencarbonate active transport against concentration gradient
- microvilli filled with mitochondria
- major site of reabsorbtion of NaCl
function of acinar ducts
modify electrolyte composition
ducts secrete K+ and HCO3- and reabsorb Na+ and Cl-
which muscle separates the lobes of thee submandibular?
mylohyoid
what is glucose converted to in erythrocytes?
pyruvate or lactate
what is the only metabolic process RBC use to gain energy and why?
glycolysis
anaerobic
how do triglycerides enter lymphatics?
combine with triglycerides to form chylomicrons
fed state
fuels are oxidised to energy
any excess is stored
triglycerides in adipose tissue
glycogen in liver and muscle
what is gluconeogenesis?
forming new glucose from amino acids, lactate and glycerol
how are fats used for energy?
lipolysis
broken down into glycerol and fatty acids
how are the products of fat breakdown used for energy?
glycerol converted to glucose
fatty acids converted to ketones
which hormones regulates fuel metabolism?
growth hormone somatostatin
thyroxine
adrenaline
noradrenaline
cortisol
insulin
glucagon
is insulin anabolic or catabolic?
anabolic
is glucagon anabolic or catabolic?
catabolic
what processes does insulin stimulate?
glycogen storage, fat storage, protein synthesis
which processes does glucagon stimulate?
glycogenolysis
gluconeogenesis
ketogenesis
effects of cortisol on fuel metabolism
lipolysis
protein breakdown
gluconeogenesis
glycogen storage
what is cortisol and where is it released from?
stress hormone
adrenal glands
effect of thyroxine on fuel metabolism
glycolysis
cholesterol synthesis
glucose uptake
protein synthesis
sensitises tissues to adrenaline
is thyroxine anabolic or catabolic?
normally anabolic but catabolic at high concentrations
effect of growth hormone on fuel metabolism
gluconeogenesis
glycogen synthesis
protein synthesis
lipolysis
decreased glucose use
which hormone increases appetite?
ghrelin
which hormone decreases appetite?
leptin
is leptin high or low with obesity?
high
leptin resistance
which is the only anabolic hormone?
insulin
what do the taste buds detect?
sweet, sour, salty, bitter, umami
why is saliva hypotonic?
duct epithelium does not allow any water movement
what keeps saliva alkaline?
bicarbonate buffering system
what does sympathetic stimulation of salivary glands produce?
secretion of protein and glycoprotein
innervation of the sublingual and submandibular glands
facial
innervation of the parotid
CN V3
are the minor glands continuous?
yes
lipid microvesicles in saliva
exosomes
boundaries of parotid gland
zygomatic arch
sternocleidomastioid
ramus of mandible
muscles layers in the stomach, in to out
oblique, circular, longitudinal
which substances stimulate gastric acid secretion?
gastrin
histamine
which substance inhibits gastric acid production
somatostatin
where in the stomach is intrinsic factor produced?
fundus
basically everything is produced in the fundus
the les and cardia and antrum and pylorus only produce bicarbonate and mucus
stomach epithelium structure and function
invaginates into the mucosa to form tubular glands
upper portion secretes mucus HCL and pepsinogen
lower portion secretes endocrine molecules
which cells are interspersed inthe stomach epithelium?
APUD cells
produce mucus?
mucous neck cells
causes of gastroparesis
idiopathic
abdominal surgery
MS
females
mptoms of gastroparesis
nausea
GORD
abdominal pain
what is the enterogastric reflex?
a nervous reflex whereby stretching of the wall of the duodenum results in inhibition of gastric motility and reduced rate of emptying of the stomach
how to reduce stomach acid pharmacologically
proton pump inhibitors
H2 receptor agonists
where is cholecystokinin released from?
I cells in duodenum, jejunum and less so from ileum
function of choleocystokinin
stimulates release of pancreatic enzymes
increases bicarbonate secretion
liver and gallbladder - sphincter of oddi relaxation
- gallbladder contration
endocrine functions of the pancreas
insulin and glucagon
exocrine functions of the pancreas
bicarbonate secretion
enzyme secretion
what do beta cells of the pancreas secrete?
insulin
hat do alpha cells of the pancreas secrete?
glucagon
which pancreatic cells are endocrine?
islet cells
which pancreatic cells are exocrine?
acini cells
function of centrocinar cells
produce bicarbonate
function of pancreatic duct cells
exchange of bicarbonate and chloride
what activates trypsinogen and chymotrypsinogen?
enterokinase
what activates trypsinogen to trypsin?
trypsin (positive feedback) and enterokinase
how are proteases released?
zymogens
where is enterokinase present?
small intestine wall
amylase function
hydrolyses starch to maltose and dextrin
name other pancreatic enzymes
gelatinise, elastase, ribonuclease, deoxyribonuclease
primary secretion from pancreas
NaHCO3
secondary secretion from pancreas
bicarbonate exchanged for chloride
what happens to the pancreatic fluid composition as flow rate increases?
richer in bicarbonate and lower in chloride
because the faster it flows, less exchange takes place
function of acinar cells
secrete enzyme
which comes first, intercalated or interlobular duct?
intercalated
how much bicarbonate secreted per day
1L
function of bicarbonate secretions
neutralises stomach acid and protects duodenal mucosa
buffers duodenal contents
optimises pH for enzyme digestion
which ions are predominantly in resting flow bicarbonate secretions?
Na+ and Cl-
which ions are predominantly in high flow bicarbonate secretions?
Na+ and bicarbonate
what stimulates bicarbonate secretion from pancreas?
secretin and CCK
what stimulates the reelease of ezymes from the pancreas?
CCK
ACh
what stimulates CCK release?
HCl
proteins and fats in duodenum
action of choleocystokinin
pancreatic enzyme and bicarbonate secretion
gallbladder contraction
inhibition of gastric acid secretion
delayys gastric emptying
what stimulates secretin?
low duodenal pH
where is secretin releaseed from?
upper small intestine
action of secretin
bicarbonate secretion from pancreas
what stimulates gastrin?
gastric distension and irritation
where is gastrin produced?
G cells of stomach
action of gastrrin
HCl secretion
enzyme release from acinar cells
how much peptide does an adult need a day?
40-50g
how many amino acids are used by the body?
20
how many essential amino acids
8
what is an essential amino acid?
cannot be manufactured in the body
which form of amino acid does the body use?
L
what is a zwitterion?
contains positive and negative groups on the same molecule
ncentration of stomach acid
[H+] is greater than 150mM
how much stomach acid is produced a day?
2L
function of stomach acid
activate pepsinogen to pepsin
stomach acid production energy dependent?
yes
what stimulates gastrin?
amino acids/ peptides in stomach lumen
distension of stomach
activation of enteric nervous system
vagus nerve - cephalic reflex
what inhibits gastrin?
decreased pH
what breaks down peptides to amino acids?
peptidases from duodenum
what breaks down proteins to peptides?
pepsin
does pepsin break down proteins to amino acids?
no
to peptides
what percentage of protein digestion is in the stomach by pepsin?
20
types of peptidases in the duodenum
endopeptidases
exopeptidases
action of endopeptidases
split polypeptide internal bonds
name endopeptidases
trypsin, chymotrypsin, elastase
function of exopeptidases
cleave amino acids off ends of polypeptides
name exopeptidases
carboxyl dipeptidases, amino peptidases
can peptides be proken down in cells? how
intracellular peptidases
yes
where can peptides be digested?
intestinal lumen
brush border
intracellularly
which enzyme activates other peptidases?
trypsin
precursors for:
- colipase
- elastase
- carboxypeptidase A
- chymotrypsin
- trypsin
procolipase
proelastase
procarboxypeptidases
chymotrypsinogen
trypsinogen
how are amino acids absorbed?
facilitated diffusion and cotransport
sodium potassium ATPase creates a Na gradient
amino acids are absorbed alongside Na+
peptides can be cotransported with H+
which version of sugars can be used?
D isomer
which is more branched, starch or glycogen?
glycogen
which bonds does cellulose contain?
1-4 beta glycosidic
which bonds do glycogen and starch have?
alpha 1-4 glycosidic and branching by alpha 1-6 glycosidic
in lactose, do OH groups lie above or below the plane of the molecule?
above
what are the constituents of sucrose
glucose and fructose
constituents of lactose
glucose and galactose
constituents of maltose
2 glucose
carbohydrate digestion
starch degraded by ptyalin (alpha amylase in saliva)
small amount of digestion in the mouth
polysaccharides browken down into di and trisaccharides
further digestion by oligosaccharidases and disaccharidases
does amylase produce monosaccharides?
no
oligosaccharides/ disaccharides only
what are oligosaccharides?
several sugar molecules
where is most starch digested?
small intestine especially duodenum
what does alpha amylase break down?
alpha 1-4 linkages, not any others like alpha 1-6
where are disaccharidases located?
intestinal brush border
where are monosaccharides absorbed?
brush border membrane
how are glucose and galactose absorbed?
active transport
Na+ dependent secondary secondary active transport process
low Na conc created intracellularly
monosaccharides cotransported with Na via a sodium glucose linked transported
how is fructose absorbed?
facilitated diffusion
GLUT
how are monosaccharides transported basolaterally from brush border?
facilitated diffusion using GLUT
where does glucose travel from the capillaries in the brush border?
hepatic portal vein
which organs store glucose as glycogen
skeletal muscle and liver
what can glucose be converted into?
glycogen, fatty acids, alpha-glycerol phosphate
which product of glycolysis is required for creation of alpha glycerol phosphate?
dihydroxyacetone phosphate
how is fat made frrom glucose in the liver stored?
with proteins as lipoproteins
how does fat made in the liver reach adipose tissue?
fatty acids from glucose are used to synthesise triglycerides
lipoproteins secreted by hepatocytes into the blood as VLDLs
lipoprotein lipase is present on blood facing surface of capillary endothelial cells, especially in adipose tissue
lipoprotein lipase hydrolyses triglycerides to monoglycerides and fatty acids
free fatty acids diffuse into adipocytes and combine with alpha glycerol phosphate to form triglycerides
what are VLDLs?
very low density lipoproteins
contain more fat than protein, hence low density as fat is lighter
daily fat intake
70-100g
forms of fat
triglycerides, phospholipids, cholesterol
name some fatty acids
palmitic acid, stearic acid, oleic acid
where are proteins digested?
mouth, stomach, small intestine
where are fats digested?
mouth, stomach and small intestine
where are fats predominantly digested/
small intestine
types of lipase
lingual, gastric and pancreatic
what forms fat droplets?
bile salts - amphipathic
what are bile salts synthesised from?
cholesterol
action of colipase
cofactor for pancreatic lipase
what do fats become once emulsified?
miscelles
what is contained inside miscelles?
bile salts, fat soluble vitamins, cholesterol, fatty acids, monoglycerides and phospholipids
where is bile reabsorbed?
ileum
how much bile is excreted?
3%
fate of reabsorbed bile
travels in blood to liver
how many times a day is bile recycled?
8
fat absorbtion and processing
bile salts from liver coat fat droplets
pancreatic lipase and colipase break down fats into monoglycerides and fatty acids stored in micelles
monoglycerides and fatty acids move out of micelles and enter cells by diffusion
chylomicrons are formed as the absorbed fats combine with cholesterol and proteins in the intestinal cell
chylomicrons are removed by the lymphatic system
how are fats formed?
alpha glycerol and fatty acids
systemic handling of fats after absortion
chylomicrons enter lacteals and into the lymphatic system
lymph enters systemic veins
lipoprotein lipase releases fatty acids into circulation
fatty acids diffuse into adipocytes to combine with alpha glycerol phosphate
where is most water reabsorbed?
small intestine
sodium absorbtion
Na/ K ATP ase pumps sodium out of cell to create a low intracellular concentration of Na+
glucose sodium transporter uptakes from luminal side
1 glucose to 2 Na+
glucose moved out via GLUT2
how does luminal glucose enter the epithelial cell?
Na+/ glucose symport protein on the apical membrane
how does enterocyte sodium enter the blood?
sodium potassium pump
sodium secretion
Na/ K ATPase creates low intracellular concentration of Na+
how does intestinal sodium enter the enterocytes?
Na+/ glucose symport protein
how does enterocyte glucose enter the blood?
GLUT 2
how is energy for movement supplied?
sodium and proton gradients
movement of substances in between cells
paracellular pathway
factors increasing intestinal absorption
number and structure of enterocytes
blood and lymph flow
nutrient intake
GI motility
factors increasing intestinal secretion?
irritants
bile
bacterial toxins
neural and hormonal inputs to secretion and GI motility
where can we find gluten?
wheat, rye, barrley
which aspect of the intestines is damaged with coeliac disease?
villi
effect of cholera on small intestine
toxin binds to interstitial cells
stimulates adenylate cyclase to produce more cAMP and increase expression of Cl- channels
dramatic efflux of ions and water
water diarrhoea
what order are fats, carbohydrates and proteins used?
carrbohydrates first, proteins last
how long do glycogen stores last?
12 hours
how long do lipid stores last?
3 months
which sources does brain use for energy?
glucose and ketone bodies
can the liver use ketones for energy?
no
energy in
food and drink
energy out
BMR
diet induced thermogenesis (DIT)
activity
when is weight stable?
energy in = enegy out
what BMI is obese?
over 30 kg/m2
what BMI is overweight?
25-30 kg/m2
normal BMI range
18.5-25 kg/m2
what BMI is underweight?
less than 18.5 kg/m2
what is BMR?
basal metabolic rate
energy required to keep the body alive
how is BMR measured?
oxygen consumption whilst awake, restful and fasted for 12 hours
effect of glucose on VLDL levels
increases
fate of glucose in erythrocytes
converted to pyruvate
pyruvate diffuses out of cell or converted to lactate
lactate released from cell
types of lipoproteins
LDL - low density lipoproteins
HDL - high density lipoproteins
VLDL - very low density lipoproteins
what processes does insulin stimulate?
glycogen storage, fat storage, protein synthesis
what processes does cortisol stimulate?
lipolysis, protein brreakdown, gluconeogenesis, glycogen storage
actions of adrenalise/ noradrenaline
glycogenolysis, gluconeogenesis, lipolysis
actions of thyroxine
glycolysis, cholesterol synthesis, glucose uptake, protein synthesis, sensitises tissues to adrenaline
which hormone controls metabolism?
thyroxine
where is growth hormone produced?
pituitary
actions of growth hormone
gluconeogenesis, glycogen synthesis, lipolysis, protein synthesis, decreased glucose use
where is leptin released from?
adipocytes
where is ghrelin released?
stomach
what do leptin and ghrelin act on?
CNS
what breaks down glycogen?
glucagon
what substances are used for gluconeogenesis?
amino acids, lactate, glycerol
where does gluconeogenesis occur?
liver
how are the components of lipids used for energy?
glycerol transported to liver for gluconeogenesis
fatty acids produce ketones in the liver
is the circular or longitudinal layer of muscle inner?
circular
is the internal sphincter voluntary?
no
external is though
physiology of defecation
basal
pre expulsive
expulsive
termination
basal phase of defecation
segmental contractions of colon - mixing
rectum - motor complexes
tonic contraction of anal sphincter
puborectalis contracted - anorectal angle
pre-expulsive phase
colon - high amplitude propagating contractions
mass movement of stool 8 times a day
gastro-colic reflex
rectum fills causing distension
rectal compliance - adaptive relaxation
EAS maintains contraction
reflex relaxation of IAS for stool sampling
puborectalis contracted
expulsive phase
rectum contracts
3 muscles relax
valsalva manouvre aids emptying
termination phase
traction loss causes sudden contraction of EAS
valsalva ceases
function of pudendal nerve
motor control of external anal sphincter
