physiology Flashcards
why is ingested food essential
as an energy source
what are the 4 basic processes of the digestive system
- motility
- secretion
- digestion
- absorption
what is motility
muscular contractions that mix and move forward the contents
what are the 2 types of motility
- propulsive
- mixing movements
what is propulsive movements
propel or push the contents forward through the digestive tract
function of small intestine
main site of digestion and absorption
is movement in the small intestine fast or slow
slow to allow time for absorption
what muscle controls movement in small intestine
smooth
what is mixing movements
mixing food with digestive juices
where does motility involve skeletal muscle
mouth through oesophagus into stomach
external anal sphincter
what is secreted
a number of digestive juices excreted by exocrine glands
what is in digestive secretions
- water
- electrolytes
- specific organic constituents
are digestive excretions reabsorbed
yes
what happens if digestive excretions are not reabsorbed
- vomiting
- diarrhoea
what are the 3 biochemical categories of food stuff
- carbohydrate
- protein
- fats
can carbohydrate cross plasma membrane
no
what is digestion
breakdown of complex food stuff into smaller absorbable units
examples of monosaccharide
- glucose
- fructose
- galactose
are monosaccharides found in diet
rarely
how are most carbohydrates ingested
as polysaccharides
what is the most common polysaccharide consumed
starch
where is starch derived
plant sources
what carbohydrate do meats contain
glycogen
what carbohydrate is found in plant cell walls
cellulose
examples of disaccharides
- sucrose
- lactose
what is lactose
milk sugar
how are carbohydrates absorbed
monosaccharides
what makes up proteins
amino acids
what are proteins broken down into
small polypeptides
what is the form of dietary fat
triglyceride
what makes up triglyceride
glycerol with three fatty acids molecules
what is end product of fat digestion
monoglycerides and free fatty acids
how is digestion accomplished
hydrolysis
where does absorption occur
in small intestine
what are the accessory digestive organs
- salivary glands
- exocrine pancreas
- biliary system (liver and gallbladder)
what does digestive tract include
- mouth
- pharynx
- oesophagus
- stomach
- small intestine
- large intestine
- anus
what makes up small intestine
- duodenum
- jejunum
- ileum
what makes up large intestine
- caecum
- appendix
- colon
- rectum
what are the layers of the digestive tract
- mucosa
- submucosa
- muscularis externa
- serosa
what does the mucosa line
the luminal surfaces of the digestive tract
what are the 3 layers of mucosa
- epithelium
- lamina propria
- muscularis mucosa
what does epithelium contain
- exocrine glands
- endocrine glands
- epithelial cells
what do epithelial cells do
absorb digested nutrients
what layer is the lamina propria
middle layer
what does lamina propria house
the gut associated lymphoid tissue
what is the muscularis mucosa
smooth muscle
it is outer most
where in the digestive tract is there the most folding
small intestine
what occurs in mouth
chewing
what occurs in pharynx
swallowing
what occurs in stomach
relaxation
what occurs in small intestine
segmentation
migrating motor complex
what is the submucosa
thick layer of connective tissue
what does submucosa provide
distensibility and elasticity
what does submucosa contain
blood and lymph vessels
what nerve network is in submucosa
submucosal plexus
what is the muscularis externa
smooth muscle coat
what are the layers of muscularis externa
- inner circular
- outer longitudinal
what network is in muscularis externa
myenteric plexus
what is the outer layer
serosa
what does serosa secrete
watery, slippery fluid that lubricates and prevents friction between organs
what is the serosa continuous with
mesentery
what does the electrical activity occur as
slow wave
what is another name for the slow waves
basically electrical rhythm
what are the pacemaker cells called
interstitial cells of cajal
where are the insterstitial cells of cajal located
in-between longitudinal and circular smooth muscle layers
slow waves are action potentials
true or false
false
slow waves are rhythmic, wavelike fluctuations in membrane potential that bring the membrane closer to threshold potential
how are interstitial cells of cajal connected
via gap junctions
how are smooth muscle cells connected
by gap junctions
do muscle contract in sync
yes
what does the intensity of the contractions depend on
number of action potentials that occur when the slow wave reaches threshold
what happens at threshold
voltage gated calcium channels are activated
how does sympathetic affect GI tract
inhibits or slow down digestive tract contraction and secretions
what dominates under resting conditions
parasympathetic
how does parasympathetic reach
vagus nerve
what does parasympathetic stimulation do
increase smooth muscle motility and promote secretions of digestive enzymes and hormones
what are mechanoreceptors sensitive to
stretch or tension within the wall
where is entry to the digestive tract
the mouth or oral cavity
what does palate form
the arched roof or oral cavity
what is tongue controlled by
skeletal muscle
what is at the side walls of the pharynx
tonsils
what are tonsils
lymphoid tissues
what is mastication
chewing
where do jaw bones articulate
temporomandibular joint
what are the most important salivary proteins
- amylase
- mucus
- lysozyme
how does saliva being digestion
through salivary amylase
what does saliva amylase break down
polysaccharides into maltose
how does saliva provide lubrication
through mucus
how does saliva provide antibacterial action
through lysozyme
what immunoglobulin is present in saliva
IgA
does saliva neutralise acids
yes through bicarbonate buffers
is saliva essential for breakdown of food
no
what is xerostomia
difficulty in chewing and swallowing
why is saliva constantly produced
through low level stimulation of parasympathetic nerve endings
what are the 2 salivary reflexes
the simple
conditioned
when does simple saliva reflex occur
when chemoreceptors and pressure receptors within the oral cavity respond to presence of food
where is salivary centre
medulla
when does conditioned salivary reflex occur
without oral stimulation
by thinking, seeing, smelling food
what autonomic innervation is dominant in salivary excretion
parasympathetic
what type of saliva is produced in response to parasympathetic
abundant flow of watery saliva that is rich in enzymes
what type of saliva is produced in response to sympathetic
smaller volume of thick saliva that is rich in mucus
what does digestion in the mouth involve
hydrolysis of polysaccharide into disaccharide by amylase
where is most digestion achieved
in stomach
what does acid inactivate
amylase
does absorption occur in the mouth
no
what drug can be absorbed by oral mucosa
nitroglycerin
what is nitroglycerin
vasodilator drug used in angina
what movement is associated with pharynx and oesophagus
swallowing
when is swallowing initiated
when a bolus of chewed or liquid food is forced by the tongue to the rear of the mouth
Where is swallowing centre located
in medulla
what does swallowing centre inhibit
respiratory centre in the brain
what prevents food from entering nasal passage
uvula
what prevents food from entering airways
epiglottis
does food enter trachea or oesophagus
oesophagus
what prevents food re entering the mouth
tongue against hard palate
what is the first part of the trachea
larynx (voice box)
what aligns the vocal folds
contraction of laryngeal muscles
what contracts to force the bolus into the oesophagus
pharyngeal muscles
where does oesophagus extend between
pharynx and stomach
does oesophagus penetrate diaphragm
yes
what guards the oesophagus
sphincter
how many sphincter in oesophagus
2
is the upper oesophageal sphincter usually open or closed
closed
to prevent air entering stomach
what happens if air enters stomach
burping
what does swallowing centre trigger
primary peristaltic wave
what is peristalsis
ringlike contractions of circular smooth muscle that move progressively forward
what innervates peristalsis
parasympathetic
if food gets lodged how does it get moved
second more forceful peristaltic wave is initiated
does the second peristaltic wave involve the swallowing centre
no
patient is usually oblivious this happens
what does lower oesophageal sphincter prevent
reflux of acidic gastric contents
what is the symptoms when gastric contents flow back through
heartburn
what does oesophagus excrete
mucus
what are the 3 parts of the stomach
- fundus
- body
- antrum
where is the fundus
part of the stomach above the oesophageal opening
where is body
middle part (main)
where is the antrum
lower part
what makes up the antrum
heavier musculature
what separates stomach from duodenum
pyloric sphincter
what is stomachs main function
stores ingested food until it can be emptied
what does the stomach secrete
hydrochloric acid and enzymes
what odes hydrochloric acid do
starts protein digestion
what does stomach produce
chyme
can the stomach expand throughout a meal
yes
where are interstitial cells of cajal in the stomach
upper fundus region
what are the slow waves like in fundus and body
weak
what are the slow waves like in atrium
much stronger
what keeps the pyloric sphincter closed
tonic contraction
what factors in stomach controls rate of stomach emptying
- volume of chyme
- stomach distension
- intrinsic plexuses
- consistency of chump
what intrinsic mechanisms control gastric emptying
vagus and gastrin
what factors in duodenum control rate of stomach emptying
- duodenum must be empty and have room
- presence of fat, acid
what are enterogastrones
hormones in small intestine mucosa
what do enterogastrones do
reduce gastric emptying
examples of enterogastrones
CCK
secretin
what produces secretin
S cells
what produces CCK
I cells in duodenum and jejunum
what does fat in the duodenum do
inhibit gastric emptying
what neutralises chyme
sodium bicarbonate
how do sadness and fear affect gastric motility
decrease it
what does anger and aggression affect gastric motility
increase it
does the stomach control vomiting
no
why is someone sick
contraction of diaphragm and abdominal muscles
where is vomiting centre
medulla
what begins vomiting
deep inspiration and closure of glottis
what is lost during vomiting
secreted fluids and acids
what are the 2 areas of gastric secretions
- oxyntic mucosa
- pyloric gland area
where is oxyntic mucosa
lines body and fundus
where is pyloric gland area
lines the antrum
where are gastric glands
in gastric pits
what cells line gastric pits
mucous cells
what do parietal cells secrete
HCl
intrinsic factor
what cells are in oxyntic mucosa
- mucous
- chief
- parietal
- enterochromaffin cell
what cells are in pyloric gland area
- G cell
- D cell
what do chief cells secrete
pepsinogen
what does hydrochloric acid do
activates pepsinogen
denatures proteins
what does intrinsic factor do
facilitate absorption of vitamin B12
what does enterochromafin cell secrete
histamine
what do G cells secrete
gastrin
what do D cells secrete
somatostatin
what does histamine do
stimulates parietal cells
what does gastrin do
simulate parietal cells
what does somatostatin do
inhibit parietal cells, G cells
what does HCl do
- activates pepsinogen to an active enzyme pepsin
- denatures protein
- kills microorganism ingested with food
what produces pepsinogen
chief cells
how is pepsinogen stored in chief cells
in vesicles known as zymogen granules
how does pepsin initiate protein digestion
splitting certain amino acid linkages in proteins to yield peptide fragments
what is the surface of the gastric mucosa covered by
layer of mucus
what secretes intrinsic factor
parietal cells
why is intrinsic factor important
absorption of vitamin B12
what is vitamin B12 important for
formation of red blood cells
what results when vitamin B12 is reduced
anaemia
where are G cells found
gastric pits
where are D cells more numerous
duodenum
what is somatostatin released in response to
acid
what are the 3 phases of gastric secretion
- cephalic
- gastric
- intestinal
when does cephalic occur
by stimuli in the head before food even reaches the stomach
what happens first in cephalic
vagal stimulation promotes ACh which intern leads to increased HCl secretion and pepsinogen
what else does the vagus nerve stimulate in cephalic phase
G cells
what does increased gastrin stimulate
enterochromaffin cells
when does gastric phase occur
when food enters the stomach
what does distension, caffeine and alcohol do to gastric secretion
increase it
what is the intestinal phase
inhibitory
what is released in response to high gastric acid
somatostatin
how often is the entire stomach lining replaced
every 3 days
what disease is caused when gastric barrier is exposed
peptic ulcer
what 2 substances are absorbed by the stomach
- ethanol
- aspirin
where are most drugs absorbed
small intestine
what is the endocrine part of the pancreas
Islets of Langerhans
what are the 2 cell types of exocrine pancreas
- acinar
- duct
what does duct cell secrete in the pancreas
aqueous solution
what do acinar cells of the pancreas secrete
digestive enzymes
what is the alkaline component of the pancreas rich in
sodium bicarbonate
where are pancreatic enzymes stored
in zymogens
what is important about pancreatic enzymes
they can digest food in the absence of all other enzymes
what are the 3 types of enzymes secreted by acinar cells
- proteolytic enzyme
- pancreatic amylase
- pancreatic lipase
what do proteolytic enzymes do
protein digestion
what do pancreatic amylase do
carbohydrate digestion
what does pancreatic lipase do
fat digestion
what are types of proteolytic enzyme
- trypsinogen
- chymotripsinogen
- procarboxypeptidase
what is trypsinogen active form
trypsin
what does trypsin then activate
the other 2 enzymes
what does pancreatic amylase convert
polysaccharide into disaccharide (maltose)
what is the only enzyme in the digestive tract that can break down fat
pancreatic lipase
what is main symptom of pancreatic insufficiency
steatorrhoea
what de-acidifies the chyme from stomach
alkaline fluid secreted by pancreatic duct cells
what is pancreatic exocrine secretion regulated by
- secretin
- CCK
what is primary stimulus for secretin release
acid in duodenum
what does secretin do when acid in duodenum
transported by the blood to the pancreas where it stimulated duct cells to increase secretion
what does CCK regulate
pancreatic digestive enzymes secretions
what causes release of CCK
presence of fat
what transports CCK
circulatory system
what does CCK do once it reaches the pancreas
stimulates acing cells to increase enzyme secretion
are all pancreatic enzymes released at same rate
yes it doesn’t matter what you eat they are all together in the zymogen granules
other than pancreas what other secretory product is emptied into the liver
bile
what does biliary system included
liver and gallbladder
what is the largest organ in the body
liver
what do bile salts aid in
fat digestion and absorption
what secretes bile salts
liver
what organ secrete blood clotting factors
liver
what organ stores glycogen, fats, iron, copper
liver
what are liver cells called
hepatocytes
what are macrophages in the liver called
Kupffer cells
how do hepatocytes receive arterial blood
from hepatic artery
how does venous blood enter the liver
hepatic portal system
what are sinusoids
space for blood flow in the liver
what are the functional units of the liver
lobules
what shape are lobules
hexagonal
what is at each corner of the lobule
3 vessels
- branch of hepatic artery
- branch of hepatic portal vein
- bile duct
what lines the sinusoids
Kpffer cells
what do Kupffer cells do
engulf and destroy old red blood cells and bacteria that pass through the blood
what is bile into the duodenum stopped by
sphincter of oddi
where is bile stored
in gallbladder
where is bile synthesised
liver
what does bile contain
- bile salts
- cholesterol
- lecithin
- bilirubin
- alkaline fluid
what is bile important in
digestion and absorption of fats (mainly through bile salts)
what are bile salts
derivatives of cholesterol
are bile salts reabsorbed
yes in the ileum and transported back to the liver
how do bile salts help in absorption
formation of micelles
how do bile salts help in digestion
increase the surfaces area for attack by pancreatic lipase
what digests fat
lipase
are triglycerides soluble in water
no
how do bile salts increase area for attack
the movement in small intestine breaks up the triglycerides and bile salts join on to their surface before the triglycerides join together which repels them and increases the surface area for lipase to break them down
can lipase penetrate the bile salts layer
no
what is secreted so lipase can bind
colipase
where is bilirubin
main constitution of bile
does bilirubin help with digestion
no
how is bilirubin derived
from breakdown of red blood cells
what part of red blood cells is bilirubin derived form
heme (iron containing)
what type of cell is bilirubin
anti-oxidant
what colour is bilirubin
yellow
what are faeces like if patient has gallstone
greyish white
how is bilirubin excreted
in faeces
what happens if bilirubin accumulates in body
jaundice
what are the 3 ways jaundice can be brought about
- prehepatic
- hepatic
- post hepatic
what is prehepatic
before the liver
what causes pre-hepatic jaundice
excessive breakdown of red blood cells so more bilirubin is in the liver than it can excrete
what causes hepatic jaundice
when the liver is disease and cannot deal with the normal load of bilirubin
what cause post hepatic jaundice
when bile duct is obstructed e.g. by a gallstone so bilirubin cannot be eliminated in the faeces
how do bile salts affect bile secretion
increase it
where is bile stored
gallbladder
how does secretin affect bile secretion
increase it
how does vagus nerve affect bile secretion
increases it
if gallbladder is removed where is bile stored
common bile duct
what is hepatitis
inflammatory disease of the liver
what can hepatitis lead to
cirrhosis
what are fibroblasts
connective tissue cells
what is the function small intestine
site where most digestion and absorption occur
what are the parts of the small intestine
- duodenum
- jejunum
- ileum
what is motility in the small intestine
- segmentation
- migrating motor complex
what is the small intestine’s primary method of motility
segmentation
what is segmentation
oscillating, ring like contraction of circulate smooth muscle along the small intestine
what initiates segmentation
small intestine pacemaker cells
does segmentation occur in-between meals
no
affect of parasympathetic on segmentation
enhances it
affect of sympathetic on segmentation
depresses it
when segmentation ceases what occurs
migrating motor complex
where does migrating motor complex wave start
stomach and moves down
when does migrating motor complex stop
start of next meal
how is migrating motor complex regulated between meals
motilin
where does ileum empty into
caecum
when causes ileocaecal sphincter to relax
increased gastrin
what is small intestine juice called
succus entricus
are digestive enzymes secreted by small intestine
no
what forms the brush border in small intestine
microvilli
what enzymes are present at the brush border of small intestine
- enterokinase
- disaccharides
- aminopeptidase
what does enterokinase do
activate the pancreatic proteolytic enzyme trypsinogen
what do disaccharide enzymes do
hydrolyse the disaccharides into monosaccharides
what do amino peptidase do
hydrolyse the small peptide fragments into their amino acid component
where are carbohydrate and protein digestion completed
at brush border
what is there a lack of in lactose intolerance
lactase
symptoms of lactose intolerance
- cramping
- diarrhoea
- malnutrition (in infants)
where does most absorption occur in the small intestine
duodenum and jejunum
what does ileum specifically absorb
- vitamin B12
- bile salts
the small intestine has a small surface area
true or false
false
has a large surface area
what enzymes breaks down carbohydrates
amylase
where enzyme breaks down protein
pepsin
what enzymes breakdown fat
lipase
what increase surface area in small intestine
villi
why can malabsorption occur
due to damage or reduction in small intestine surface area
what covers the surface of the villus in small intestine
epithelial cells
how are epithelial cells joined
tight junctions
what is the core of that villi in small intestine
connective tissue core
what forms the core
lamino propria
what supplies the villi of small intestine
arteriole that breaks up into capillary network
what is the lymphatic vessel of villus called
central lacteal
what are between the villi of small intestine
crypts of Lierberkuhn
do crypts of Lierberkuhn secrete digestive enzymes
no
what do crypts of Lieberkuhn secrete
water and electrolytes
succus enterocus
are the small intestine cells always changing
yes
where are Paneth cells found
in the villi crypts
what do Paneth cells do
defensive function
what 2 chemicals do Paneth cells secrete
- lysozyme
- defensins
how are both carbohydrates and proteins absorbed
by Na symport
how are glucose and galactose absorbed
by SGLT1
where is SGLT1
at luminal membrane
how does fructose enter the cell
via GLUT-5
how do glucose, galactose and fructose exit the cell
via GLUT-2
where is GLUT-2
basal border
how are proteins presented for absorption
as amino acids
how are amino acids absorbed
across the intestinal cells by symporters
where do amino acids enter the capillary network
within the villus
are micelles water soluble
yes
what os produced when lipase hydrolyses triglycerides
monoglycerides and fatty acids
how are monoglycerides and fatty acids transported to the luminal surface of small intestine epithelial cells
in water soluble micelles formed by bile salts
how do monoglycerides and fatty acids diffuse through the lipid layer
they leave the micelles and passively diffuse through the luminal membrane
what happens to monoglycerides and fatty acids once they cross the membrane of the bvilli
resynthesised into triglycerides
what coats the triglycerides
lipoprotein which makes them water soluble
what synthesises lipoprotein
endoplasmic reticulum of epithelial cell
what is the large coated fat droplet called
chylomicron
can chylomicron enter the capillaries
no due to their basement membrane
what must vitamin B12 be bound to for absorption
intrinsic factor
what type of iron can be absorbed
ferrous (Fe2+)
what is iron that is absorbed needed for
red blood cell production
how is absorbed iron transferred into the blood
ferroportin (membrane iron transporter)
once in the blood where does the absorbed iron go
to the bone marrow
what is absorbed iron bound to in the blood
transferrin
what form of iron is stored
ferritin
can ferritin be transferred into the blood
no
where does the unused iron go
into the faeces
what is iron essential for
haemoglobin production
what can increase iron absorption
vitamin C
what is iron absorption controlled by
hormone hepcidin
where and when is hepcidin released
from the liver when iron levels in the blood get too high
how does calcium enter the luminal membrane
down its electrochemical gradient
how does calcium exit a cell
Ca ATPase
what vitamin enhances calcium absorption
vitamin D
where is vitamin D enhanced
liver
where do the venules that leave the small intestine drain into
hepatic portal vein
what carries absorbed fat
systemic circulation
what is the only secretory product that escapes from the body
bilirubin
what makes up the large intestine
- colon
- caecum
- appendix
- rectum
what is at the bottom of the caecum
appendix
what does appendix house
lymphocytes
what makes up the colon
- ascending
- transverse
- descending
what is at the end of the descending colon
sigmoid colon
what comes after the sigmoid colon
rectum
what does the large intestine do
extracts more H2O and salts from the chyme contents
where does the remainder of the chyme go
eliminated as faeces
how is the outer longitudinal smooth muscle arranged in large intestine
in 3 strips known as taeniae coli
what are the pouches or sacs in large intestine
haustra
can haustra change location
yes due to contraction
what is large intestine main motility
haustration
is haustration a fast or slow process
slow
what moves the contents into the rectum
colonic mass movement
when does defecation occur
when the external anal sphincter relaxes
what type of muscle is the external anal sphincter
skeletal muscle
when does constipation occur
when faeces becomes too dry
what happens if hard faecal matter becomes lodged in the appendix
appendicitis
does the large intestine secrete digestive enzymes
no
why could bacteria grow in large intestine
as contents move so slowly it can become a ‘breading; ground
what is the main waste product excreted in the faeces
bilirubin
what causes gas
- swallowed air
- gas produced by bacterial fermentation
what is eructation
burping
where is gastrin produced
in the stomach
what does gastrin increase the secretion of
HCl and pepsinogen
what does gastrin enhance
gastric motility
what inhibits gastrin release
accumulation of acid in the stomach
what stimulates secretion of secretin
presence of acid in duodenum
what does secretin inhibit
gastric emptying
what does secretin stimulate
pancreatic duct cells to produce more aqueous secretions
and
secretion of bile from liver
what causes release of CCK
fat in duodenum
what does CCK inhibit
gastric motility and secretion
what does CCK stimulate
pancreatic acinar cells to increase pancreatic enzymes
what does CCK cause to contract
gallbladder
what does CCK cause to relax
sphincter of oddi (so bile is emptied into duodenum)
what does GIP help promote
metabolic processing of nutrients once they are absorbed
what does GIP stimulate
insulin release
what stimulates GIP
presence of a meal, especially glucose
