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ailmentary > SI > Flashcards

SI Flashcards

1
Q

structure small intestine

A 
6m 
3.5cm in diameter 
originate immediately after stomach 
coils around abdomen 
meets L intestine at lower R quadrant
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2
Q

3 portions

A

duodenum - digestion and gut regulation
jejunum - absorption
ileum - absorption

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3
Q

features of the small intestine

A

finger like projections - villi (motile, rich blood and lymph supply)
mucosa arranged in folds
invaginations - crypts of lieberkuhn

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4
Q

duodenum

A

coiled mucus secreting submucosal gland
secrete bicarb rich alkaline solution - open up into base of crypt
neutralise acid chime
protect lining of proximal SI and provide optimum pH for enzymes

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5
Q

jejunum

A

large submucosal folds - plicae circularis or valves of kerckring
taller and thinner than in the rest of the intestine

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6
Q

ileum

A

100 payers patches - aggregates of lymphoid tissue
prime immune system against aggregates of intestinal bacteria
initiate leukocyte and immunoglobulin responses
contain M cells - don’t have microvilli

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7
Q

motility functions

A

mix ingested food with digestive secretions and enzymes
facilitate the contact between contents and mucosal surface
propel the contents

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8
Q

how is motility achieved

A

segmentation, peristalsis, migrating motor complex

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9
Q

migrating motor complex

A

periodic contractions from stomach to distal ileum during fasting state
restart once complete
in fed state - less ordered
it prevents colonic flora travelling back and to help cleanse SI

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10
Q

digestion of macronutrients

A

secretions are derived from the liver, panc and SI
enzymes work optimally in alkaline env
enzymes that cleave big nutrients - in gut lumen from glandular organs
enzymes cleave dimeric nutrients into monomers for absorption are in brush border of enterocytes

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11
Q

digestion of carbs

A

first stage occurs in the mouth - salivary amylase
then duodenum- panc amylase and brush border enz
amylase = sucrose, maltose, lactose
maltose = 2x glucose
sucrose = glucose and fructose
lactose = glucose and galactose

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12
Q

absorption of carbs

A

glucose and galactose absorped by secondary active tranbsport through SGLT-1 transporter and fructose goes throigh fascilitated diffusion through GLUT-5
all go down conc grad down basolateral membrane using GLUT-2 channels

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13
Q

SGLT-1

A

transporters transport 1 carb and 1 glucose into a cell at a time
Na pumped out of basolateral surface by Na ATPase to ensure Na gradient

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14
Q

mesentery

A

fan shaped
throws SI into folds
supports the blood supply

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15
Q

the digestive epi

A

outside have the serosa surface - stop sticking
external walls - longitudinal and circular muscles - important for motility
internal mucosa - arranged in circular folds
submucosa - layer of tissue and bv
mucosa covered in vili
invaginations - crypts of lieberkuhn

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16
Q

vili

A 
increase SA 
in SI 
motile 
rich blood supply and lymph 
innervation from submucosal plexus 
simple columnar enterocytes
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17
Q

duodenum lecture

A

brunner’s glands - secreting alkaline fluid
submucosal coiled tubular mucosal glands secreting alkaline fluid
open into base of crypts
alkaline: neutralise acid chime for protection and optimise pH for pancreatic enzymes

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18
Q

segmentation

A

mix contents
stationary contraction of circular muscles
more frequent in duodenum than ileum - allow panc enz and bile to mix with chime
net movement towards colon

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19
Q

peristalsis

A

sequential contraction of adjacent rings of sm

propel chime to colon

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20
Q

migrating motor complex - lecture

A 
fasting - circular contraction
contraction of adjacent segments 
move down the gut 
prevent migration of colon bacteria to 
fed = less ordered and less frequent
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21
Q

enterocytes

A 
most abundant in the gut 
columnar epithelia 
microvilli on apical surface 
basal nucleus 
specialised for absorption
lifespan 1-6 days 
approx. 2000 microvilli oin each cell = the brush border 
glycocalyx - rich network of carbs = trap water mucous and enzymes on surface to protect it from luminal contents and reguklate digestion and absorbtion = unstirred layer
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22
Q

goblet cells

A

2nd most abundant
apical part packed with mucin granules - distort shape of cells
mucus consists of water and glycoproteins - lubricant
useful because water is absorbed from the lumen which dehydrates the contents therefore number of goblet cells increases along the lumen

23
Q

enteroendocrine cells

A 
secreting 
in bottom of crypts 
columnar 
sensory apparatus is in apical portion 
hormones are in basolateral membrane to secrete into the blood supply
24
Q

examples of enteroendocrine cells

A

G cells - gastrin
S - secretin
D cells - somatostatin
I cells - secretin

25
Q

closed enterocytes

A

not exposed to the lumen at all

26
Q

Paneth cells

A

immunological cells
at the bottom of crypts
near stem cells
help protect progenitor cells
conatin acidophilic granules
granules contain: lysozyme, glycoproteins, zinc - act as cofactor
enguld bacterua and regulate intestinal flora

27
Q

Stem cells

A

enterocytes and stem cells have a short lifespan - 36hours
replaced by stem cells by apoptosis
pluripotent stem cells proliferate in crypts, move up the villus towards the tip
when they reach the top they become senescent and naturally slough off
energy intensive
allows: gut born toxins to run their course, lesions to be short lived
following radiation stem cell activity is impaired = sever GI dysfunction

28
Q

proteins digestion

A

degraded by pepsin in stomach
pepsin requires acidic environment to func
continues in duodenal lumen 0 pancreatic juice breaks peptides
pancreatic enzymes: trypsin, chymotrypsin and carboxypeptidase
final digestion - brush border by enzymes secreted from epithelial cells - endopeptidase, dipeptidase, aminopolypeptidase, carboxypeptidase

29
Q

protein absorption

A

single AA absorbed onto enterocytes by secondary AT

short peptides 2/3 AA can be absorbed via apical surface - cytoplasmic peptidase enzymes break them into AA

30
Q

fat digestion

A

mouth - lingual lipase hydrolyses triglycerides
stomach - ingested lingual lipase and secreted gastric lipase - cleaves single FA chains from free triglycerides
mechanical churning of stomach - emulsifies fat
bile in duodenum = emulsification= increase in SA
pancreatic lipase and colipase cleave triglycerides to monoglycerides and free FA
trhis is luminal digestion - and as the digestion products reachborder - combined with bile salts to form micelles - soluble enough to cross aqueous unstirred layer

31
Q

fat absorption

A

lipolytic enzymes diffuse through the apical membrane
bile salts remain in the lumen
in cell monoglycerides and FFA resynthesized into triglycerides
monoglyceride acylation pathway - primary pathway
phosphatidic pathway - secondary mechanism
triglycerides package with proteins, phospholipids and cholesterols into chylomicrons
chylomicrons are exocytosed as they’re too large to leave the capillaries

32
Q

microvilli

A

make up brush border
covered with glycocalyx - carb layer protection against lumen, trap layer water and mucosa - unstirred layer regulates rate of absorption
glycocalyx

33
Q

epithelial life span

A

cells sort lifespan 36hrs

replaced by dividing stem cells

34
Q

why rapid turnover

A

enterocytes 1st line of defence
also need to be able to absorb
any lesions will be short lived
if interfered by radiation - escalator stop = intestinal dysfunction - unable to retain water = diarrohea

35
Q

cholera

A

endotoxin = prolonged opening of chloride channels = uncontrolled secretion of H2O = dehydration
treatment - rehydration
only need to live 2-3 days because epithelium will be replaced

36
Q

digestion in the duodenum

A

alkaline environment
digestive enzymes and bile enter duodenum from pancreatic and bile duct
digestion occurs in lumen and in contact with membrane
enzymes in middle make large molecules smaller, enzymes at brush border make small molecules smaller

37
Q

primary and secondary active transport

A

primary - hydrolysis of ATP
secondary - energy 2nd hand, gradient set up previously eg Na
17 days ago

38
Q

digestion of carbs

A

begin in mouth - salivary a-amylase (reward because tastes sweet)
most in SI
pancreatic a-amylase acts in lumen, some in brush border
forms disaccharides and oligosaccharides
digestion to monosaccharides occurs on the membrane by maltase, lactase, sucrase

39
Q

carbohydrate structure

A

simple carb = monosaccharides, glucose and fructose, and disaccharides, sucrose and maltose
complex carb = starch, cellulose, pectins - sugars joined

40
Q

absorption of carb

A

secondary active transport
using SGLT-1 on apical membrane
pump Na in down conc grad - energy released allows you to pump monosaccharide into the cell
then travels into the blood through GLUT-2 by facilitated diffusion

41
Q

digestion of proteins

A

begins in the stomach by pepsin
inactivated in the alkaline duodenum
trypsin is activated by enterokinase on duodenal brush border
trypsin activates other proteases and self activatesb

42
Q

absorption of proteins

A

brush border peptidases break down larger peptides before absorption
AA absorbed by facilitated diffusion and secondary AT
di and tri peptides absorbed by carrier proteins distinct from AA
cytoplasmic peptidases break di and tripeptides down before cross basolateral membrane

43
Q

digestion of lipids

A 
in SI 
secretion of bile and lipases 
emulsification 
enzymatic hydrolysis of ester linkages 
solubilisation of lipolytic products in bile salt micelles
44
Q

emulsification of lipids

A

bile and lipases secreted into the duodenum
bile salt = emulsification of fat into lipid droplets
increase sa and allow pancreatic lipase to split triglycerides
broken into 2x FA and a monoglyceride at a fat/water interface
pancreatic lipase complexes with colipase
colipase prevents bile salts from displacing lipase from fat droplet

45
Q

lipid enzymes

A

phospholipase A2 - hydrolyses FA at 2 position in many phospholipids = lyso-phospholipids and free FA
pancreatic cholesterol esterase - hydrolyses chol ester to free chol and FA

46
Q

bile salt molecule

A 
steroid nucleus planar - 2 phases, amphipathic 
hydrophobic face (nucleus and methyl) dissolves in fat 
hydrophilic phase (hydroxyl and carboxyl) dissolves in water
47
Q

bile salt micelles

A

hydrophilic head regions in contact with solvent
hydrophobic tail regions are in centre
water insol monoglycerides from lipolysis are solubilised forming a core stabilised by bile salts

48
Q

Absorption of lipids

A

micelles are absorbed quicker than emulsion
allow transport across the unstirred layer and present FA and monoglycerides to brush border
micelle not absorbed together - bile salts are absorbed in ileum, fully absorbed by jejunum
bile salts transported back to liver for recycling - enterohepatic circulation

49
Q

lipid metabolism

A

monoglycerides and FFA absorbed by enterocytes

resynth into triglycerides by monoglyceride acylation (major) and phosphatidic acid pathway (minor)

50
Q

monoglyceride acylation

A

FA bind to apical mem
fatty acid binding protein fasciliate transfer FA from apical membrane to smooth ER
in smooth ER FA esterified into triglycerides and triglycerides

51
Q

phosphatidic acid pathway

A

triglycerides synth from CoA FA and glycerophosphate

52
Q

chylomicrons

A

lipoprotein particles synthesised in enterocytes
chylomicrons transported to the Golgi and secreted across the BM by exocytosis
too big to enter the blood capillaries/villi
enter lacteals of lymph instead

53
Q

separation between ileum and colon

A

by ileocaecal sphincter (also moves food when it is digested)
relaxation and contraction controls the passage of material into the colon and prevents backflow of bacteria into the ileum

ailmentary (15 decks)

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