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SI Flashcards

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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

Study These Flashcards
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

Study These Flashcards
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

Study These Flashcards
A

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

25
closed enterocytes
not exposed to the lumen at all
26
Paneth cells
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
Stem cells
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
proteins digestion
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
protein absorption
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
fat digestion
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
fat absorption
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
microvilli
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
epithelial life span
cells sort lifespan 36hrs | replaced by dividing stem cells
34
why rapid turnover
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
cholera
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
digestion in the duodenum
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
primary and secondary active transport
primary - hydrolysis of ATP secondary - energy 2nd hand, gradient set up previously eg Na 17 days ago
38
digestion of carbs
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
carbohydrate structure
simple carb = monosaccharides, glucose and fructose, and disaccharides, sucrose and maltose complex carb = starch, cellulose, pectins - sugars joined
40
absorption of carb
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
digestion of proteins
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
absorption of proteins
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
digestion of lipids
``` in SI secretion of bile and lipases emulsification enzymatic hydrolysis of ester linkages solubilisation of lipolytic products in bile salt micelles ```
44
emulsification of lipids
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
lipid enzymes
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
bile salt molecule
``` steroid nucleus planar - 2 phases, amphipathic hydrophobic face (nucleus and methyl) dissolves in fat hydrophilic phase (hydroxyl and carboxyl) dissolves in water ```
47
bile salt micelles
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
Absorption of lipids
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
lipid metabolism
monoglycerides and FFA absorbed by enterocytes | resynth into triglycerides by monoglyceride acylation (major) and phosphatidic acid pathway (minor)
50
monoglyceride acylation
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
phosphatidic acid pathway
triglycerides synth from CoA FA and glycerophosphate
52
chylomicrons
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
separation between ileum and colon
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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