gastrointestinal tract Flashcards
what are the 8 parts of the gastrointestinal tract/system
oral cavity
oesophagus
small intestine
liver
pancreas
gall bladder
large intestine
what is the total length of the GIT
6m
due to what can increase the SA of the intestinal lumen to almost 200 square meters
villi
what are the 5 things that make up the structure of the oesophagus
- stratified squamous epithelium
- muscular mucosa
(1 and 2 together are simply considered as mucosa) - submucosa
- circular muscle
- longitudinal muscle
what are the 3 pairs of salivary glands and where in the mouth are they found
- sublingual (under the tongue)
- parotid (overlying the cheek)
- submandibular gland (close to jawline)
why is saliva able to dissolve soluble food components
it is made of mostly water
what found in saliva can aid in digesting starch
amylase
how is the chewed food/bolus of food carried down into the stomach?
carried by the peristalsis (involuntary muscle movement) to stomach via cardiac sphincter (upper portion of stomach/lower oesophageal)
what prevents food from falling into the lungs
epiglottis covers the trachea
why is the oesophagus lined by squamous epithelium
to protect it from food which is abrasive
what makes the oesophagus squamous lining resilient
larger surface area attachment and long periphery attaching it to its neighbours
what role does the submucosa play when the squamous cells aren’t working well
- they are relatively loose with many elastic fibres so can swell (due to pressure) during passage of food
- they also contain small seromucous glands which aid lubrication
why is the oesophagus muscle layer thick
it undergoes waves of muscular contractions (peristalsis) to move food towards the stomach
what are the 3 sections of the stomach?
- fundus (dome shaped section at top of stomach)
- body ( main section that stored food till passing to small intestine)
- pylorus ( part of stomach that connects to small intestine/duodenum)
protein and fat are not acted on enzymatically
what 2 food groups are acted on in the stomach
lipids and protein
why is there mucosa in the folds/rugae of the stomach
to give stomach extra capacity when food distends it
where can the gastric glands of the stomach be found and what do they do?
found in the epithelium (simple columnar) of stomach which extends to open into stomach lumen via gastric pits
they secrete gastric juice (HCL, pepsinogen etc)
describe the 5 structural components of stomach
- mucosa
- submucosa
- (inner) oblique
- (inner) circular muscle
- (outer) longitudinal muscle
why does the stomach need an extra oblique layer compared to the oesophagus>
it provides strong musculature enabling the stomach to effectively churn food
what are the 4 structural components of the small intestine/ ileum
- villi
- submucosa
- circular muscle
- longitudinal muscle
what 3 additional structural components can be found within the small intestine
- goblet cells
- brunners glands
- crypt/ intestinal glands
what 3 things in the epithelium of the villi allow the digestion of lipids
pancreatic fluid
bile
enzymes
what specifically does pancreatic fluid contain to allow the breakdown of lipids and what does it breakdown into
lipase
breakdown into monoglycerides
how does bile acid aid in digestion of lipids
it acts as a detergent (emulsifies) lipid droplets down to 1micrometer diameter
once the monoglycerides pass through the epithelial cell of villi, what do they resynthesises into and using what
smooth endoplasmic reticulum resynthesises it into triglycerides
after triglycerides are resynthesises in the villi, what happens
- Golgi surrounds it with protein coat forming chylomicron
- chylomicrons discharged via exocytosis into lymph vessels, lacteals draining the villi
what proportion of ingested fats fail to breakdown and get digested hence released in feaces
1/3
what is a zymogen
proteins that contain an inactive enzyme
explain how proteins are further broken down in the duodenum
- further digested by 4 zymogens (produced by pancreas)
- zymogens are activated in duodenum to form various endopeptidase
- different endopeptidases cut at different places on peptide chain as they target different sequences
what are the 4 different endopeptidases used to digest proteins
- trypsin
- chymotrypsin
- elastase
- carboxypeptidase
what also the short peptide chains to further digest into amino acids
exopeptidase
where are exopeptidase found
in the membrane of the ileum epithelial cells
explain how 3 types of exopeptidase form amino acids
- carboxypeptidase work on c-terminal end
- aminopeptidases work on N-terminal end
- dipeptidases cut dipeptides in half
what transport mode is amino acids absorbed by
active transport via co-transport with sodium ions
describe how further digestion of disaccharides occur in iileum
- in general, dissachridases convert disaccharides into their monosaccharide units
- maltase hydrolyses maltose into glucose
- lactase hydrolyses lactose into glucose and galactose
- sucrase hydrolyses sucrose into glucose and fructose
how do each monosaccharide get absorbed
- fructose simply diffuses into villi
- glucose and galactose absorbed via active transport with co-trasport of sodium
symbiotic (friendly) bacteria in ileum occur but less numerous than in colon
what is the function of villi
maximise surface area for absorption of nutrients (mainly occurring in small intestine)
what additional feature does the duodenum have compared with the proximal jejunum and ileum
burners glands
what is the function of brunners glands and where is it found
- lies in submucosa deep to the muscular mucosae
- secrete alkaline mucus which neutralises the acidic chyme passing down from the stomach
what are paneth cells + function
- secretory cells in the crypt
- can occur in duodenum and provide host defence against microbes
what is the only difference between the jejunum and ileum
jejunum has no aggravated lymph nodes (Peyers patches)
why are the villi in the ileum shorter than int he duodenum
most absorption happens here so faster
what is the function of goblet cells in the mucosa
produce mucin for lubrication of intestinal contents and protection of epithelieum
explain the role of the gallbladder and pancreas in digestion
- chyme enters duodenum
- hormones secretin and cholecystokinin stimulates pancreas and gall bladder to discharge pancreatic fluid and bile into duodenum
what is the role of liver in digestion
- detoxifies foreign compounds in foods and drugs
- secretes bile
- veins draining intestine lead to 2nd set of capillary beds in liver and here the liver removes many of the materials absorbed by intestine
how do the liver and gall bladder work together in digestion
- bile released by the liver accumulates in the gallbladder
how does bile aid in digestion
- contains salts derived from cholesterol
- salts help emulsify fats
what makes poo brown
- breakdown of haemoglobin from old RBC makes bile pigments which form brown colour
how does the liver aid in digesting non-nutritive molecules
liver screens blood reaching it in the hepatic portal system (removes and detoxifies) so blood composition when leaving liver is close to normal
how does the liver deal with excess amino acids
- removed and deaminated
- amino group is converted to urea
- residue enters pathway of cellular respiration and oxidised for energy
glucose is removed from the blood in liver and converted into glycogen.
other monosaccharides are removed and converted into glucose
how is pancreatic fluid moved into the duodenum?
- pancreas consists of endocrine cells (islets of langerhand) and exocrine cells
- their secretion drains into duodenum
what 4 types of things is pancreatic fluid consisted of
- sodium bicarbonate (neutralise acid)
- pancreatic amylase
- lipase
- 4 zymogens
why does pancreatic fluid consist of inactive enzymes (zymogens)
protease enzymes are dangerous so synthesised by RER as inactive forms
how/what are the 4 different zymogens activated
- trypsinogen activated to trypsin by enterokinase (secreted from duodenum epithelium)
- trypsin activates chymotrysinogen to chymotrypsin
- proelastase to elastase
- procarbozypeptidase to carboxypeptidase
what are the 2 main structures of large intestine
- circular muscle
- longitudinal muscle
what 2 additional structures does the large intestine/colon have
goblet cells
lymphoid
what does the residue from ileum consist of in the colon
- mainly water
- non digested materials
what is there a large population of in the colon
bacteria (mainly harmless)
what can the intestinal flora/bacteria do
- capable of fermenting indigestible carbohydrates to short-chain fatty acids e.g acetate
- acids formed can be energy source for host
- they can also produce vitamin k, biotin, folic acid, thiamine, vitamin b12 (absorbed in colon)
what 5 beneficial components can the bacteria in our colon produce
- folic acid
- vitamin b12
- vitamin k
- biotin
- thiamine
what causes diarrhoea
irritation of large intestine causing discharge of contents before water reabsorption
what causes constipation
colon retains contents for too long, fecal matter dries out and compresses
what is the main function of the colon
reabsorption of water
what 2 types of cells does the mucose epithelium of the colon contain
- absorptive cells
- mucus-secreeting goblet cells
absorptive cells decrease in number from proximal to distal while goblet cells increase in number
what is particular about the structure of goblet cells in the colon
arranged in closely packed straight tubular glands/crypts which extend to muscular mucosa
why does mucus because increasingly important as faeces pass along the colon
faeces become progressively dehydrated so mucus required to protect mucosa from trauma
the anus has stratified squamous mucosa
the appendix is located in which area of the GI tract
small intestine
