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LSS Alimentary System > small bowel and large intestine > Flashcards

small bowel and large intestine Flashcards

digestive epithelium: explain how the digestive epithelium is specialised for its role in absorption, and describe the source and migration route of newly formed gut epithelia

1
Q

cells of small intestinal mucosa

A

lining mucosa: enterocytes, goblet cells, enteroendocrine cells; in crypts: paneth cells, stem cells

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2
Q

what is the most abundant gut cell

A

enterocytes

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3
Q

shape of enterocytes

A

tall columnar, with microvilli on apical surface (brush border)

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4
Q

where is the nucleus, mitochondria and rough ER located in enterocytes

A

nucleus and mitochondria towards basolateral membrane, rough ER towards apical region

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5
Q

what are enterocytes connected to each other by

A

tight junctions

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6
Q

lifespan of enterocyte

A

1-6 days

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7
Q

how many microvilli per enterocyte

A

2000, about 1um in length

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8
Q

in enterocytes, what is the glycocalyx and where is it located

A

rich network of carbohydrates in apical membrane covering enterocytes

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9
Q

2 functions of glycocalyx in enterocytes

A

trap layer of water, mucus and enzymes on surface of cell to protect it from luminal contents, especially enzymes which may damage cell/membrane; regulate digestion and absorption

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10
Q

what is the glycocalyx layer referred to as

A

unstirred layer

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11
Q

second most abundant cell in gut

A

goblet cells

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12
Q

where is the nucleus, rough ER , Golgi appartus and mucin granules located in goblet cells

A

nucleus and rough ER towards basolateral membrane, Gogli apparatus in middle, mucin granules towards apical region

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13
Q

what distorts goblet cell shape

A

mucin granules

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14
Q

contents and function of mucous, and subsequent abundance of goblet cells along intestine

A

water and glycoproteins, acting as lubricant to facilitate gut passage (useful as water absorbed, so number of goblet cells increase along length of intestine)

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15
Q

what are enteroendocrine cells and where are they

A

hormone secreting epithelial cells, found in bottom of crypts

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16
Q

shape of enteroendocrine cells

A

columnar

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17
Q

where are sensory apparatus located in enteroendocrine cells

A

apical portion

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18
Q

where are collections of manufactured hormones kept in enteroendocrine cells

A

near basolateral membrane ready to secrete into local blood supply

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19
Q

4 examples of enteroendocrine cells and what they secrete

A

G-cells secrete gastrin, I-cells secrete cholecystokinin (CCK), S-cells secrete secretin, D-cells secrete somatostatin

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20
Q

what are closed enteroendocrine cells

A

ones which are not exposed to gut lumen at all

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21
Q

what are paneth cells and where are they located

A

immunological cells located at bottom of crypts near stem cells

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22
Q

what do paneth cells contain

A

acidophilic granules

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23
Q

what 3 things do acidophilic granules contain

A

lysozyme (antibacterial enzyme), glycoproteins (protect local cells from enzymes), zins (cofactor for lysozymes)

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24
Q

why are paneth cells located near stem cells

A

help protect progenitor cells rather than other cells

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25
Q

what do paneth cells do on top of lysozyme granules

A

engulf bacteria, regulate intestinal flora

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26
Q

life span of enterocytes and goblet cells

A

36 hours

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27
Q

significance of stem cell nucleus

A

large, near basolateral membrane; show some form of memory so can’t replace all cells (e.g. can’t go into colon)

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28
Q

journey of energy-intensive pluripotent stem cell (continuous escalator)

A

proliferate in crypts → move up sides towards villus tip → become senescent → naturally slough off → broken down and reabsorbed

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29
Q

what does continuous escalator allow

A

effects of gut-borne toxins/drugs to run course, lesions will be short-lived and repaired quickly

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30
Q

what impairs stem cell activity and hence cause GI dysfunction

A

radiation therapy/exposure

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31
Q

where does first stage of carbohydrate digestion occur

A

mouth via salivary a-amylase, which is destroyed in stomach

32
Q

where does sugar digestion resume and via what

A

duodenum via pancreatic amylase (requires Cl- and alkaline conditions) and brush border enzymes of enterocytes

33
Q

what are complex carbohydrates

A

long polymers in basic chains or branched chains

34
Q

what are simple carbohydrates

A

disaccharides and monosaccharides

35
Q

goal of digestion

A

break the long polymers into simple monomers that can be absorbed by the gut wall

36
Q

3 different disaccharides produced by pancreatic amylase and enzymes used

A

sucrose, maltose, lactose (sucrase, maltase, lactase)

37
Q

what is maltose converted into

A

2 glucose monomers

38
Q

what is sucrose converted into

A

1 glucose, 1 fructose

39
Q

what is lactose converted into

A

1 glucose, 1 galactose

40
Q

what transporter are glucose and galactose absorbed through

A

SGLT-1 transporter (sodium glucose linked transporter 1) in apical surface by secondary active transport (as Na+ allowed into cell, energy released as flows down concentration gradient used to pump glucose or galactose into cell in exchange for Na+)

41
Q

what transporter does fructose undergo facilitated diffusion through

A

GLUT-5 (glucose transporter 5)

42
Q

what channel do all 3 monosaccharides diffuse through in baseolateral membrane

A

GLUT-2 channels

43
Q

what ensures sodium gradient

A

Na+/K+ ATPase pump

44
Q

where are ingested proteins broken down in and by what

A

stomach, by pepsin into smaller peptides

45
Q

why does pepsin stop working effectively into duodenum

A

relies on acidic environment to function

46
Q

where does digestion of proteins continue from stomach

A

duodenal lumen

47
Q

what breaks down smaller peptides in duodenum and what do they become

A

protease-rich pancreatic juice, into tripeptides and dipeptides

48
Q

examples of pancreatic enzymes for protein breakdown

A

trypsin, chymotrypsin, carboxypeptidase

49
Q

where does final stage of digestion of proteins occur and where are the enzymes secreted from

A

brush border by enzymes secreted from epithelial cells

50
Q

what are the typical enzymes

A

tripeptidases and dipeptidases

51
Q

specific enzymes to break down tripeptides and dipeptides

A

endopeptidase, dipeptidase, aminopolypeptidase, carboxypeptidase

52
Q

what transporters does single amino acid absoprtion into enerocytes occur through

A

secondary active transporters such as AA/Na+ symporter

53
Q

what transporters does dipeptide and tripeptide absoprtion into enerocytes occur through

A

secondary active transporters such as AA/H+ symporters

54
Q

what breaks down dipeptides and tripeptides into amino acids

A

cytoplasmic peptidase enzymes in enterocytes

55
Q

how do amino acids move across basolateral transporter

A

facilitated diffusion

56
Q

first stage of fat digestion

A

in mouth where lingual lipase hydrolyses triglycerides

57
Q

what continues fat digestion in stomach

A

ingested lingual lipase, secreted gastric lipase

58
Q

what does gastric lipase do

A

cleaves single fatty acid chains from free triglycerides

59
Q

what increases fat surface area

A

mechanical churning of the stomach (slightly emulsifies)

60
Q

what state are fats in when leaving the stomach

A

largely intact

61
Q

what does bile do to fats in the duodenum

A

provides chemical emulsification with huge increases in SA by creating small fat droplets

62
Q

what is secreted simultaneously with bile

A

pancreatic juices

63
Q

function of pancreatic juices

A

luminal digestion: cleave 2 fatty acid chains from triglycerides to form monoglycerides and free fatty acids (by pancreatic colipase which is activated later - prevents bile salts from displacing lipase from fat droplet)

64
Q

outcome of luminal digestion products

A

reach brush border where combine with bile salts to form micelles which cross aqueous unstirred layer (still fat so must form mixed micelles to get to wall of gut in aqueous solution to increase rate of absorption); absorption of micelle is much quicker than emulsion

65
Q

fate of lipolytic products after passing through brush border

A

diffuse through apical membrane in jejunum while bile salts remain in lumen (travel through small intestine and are reabsorbed in terminal ileum)

66
Q

fate of free fatty acids and monoglycerides in cell

A

resynthesised into triglycerides

67
Q

primary mechanism of triglyceride synthesis

A

monoglyceride acylation pathway (fatty acids bind to apical membrane, FA binding proteins facilitate transfer of fatty acids from apical membrane to smooth ER, where fatty acids esterified into di/tri glycerides)

68
Q

secondary mechanism of triglyceride synthesis

A

phosphatidic pathway (triglycerides synthesised from CoA fatty acid and a-glycerophosphate)

69
Q

outcome of resynthesised triglycerides in enterocytes as emulsion

A

packaged with proteins, phospholipids, cholesterols into chylomicron lipoprotein (80-90% triglycerides, 8-9% phospholipids, 2% cholesterol, 2% protein, trace carbohydrates)

70
Q

fate of chylomicron

A

sent to Golgi, where secreted across basement membrane by exocytosis and enter lymphatics via villi’s lacteal, as too large to enter capillaries

71
Q

reason for rapid turnover of cells

A

first line of defence vs GI pathogens (may be directly affected by toxic substances), effects of agents which interfere with cell function, metabolic rate diminished, lesions will be short-lived, if escalator-like transit of enterocytes interrupted (e.g. radiation), severe intestinal dysfunction

72
Q

effect of cholera on enterocytes, affecting gut and response

A

releases enterotoxin (affects opening of Cl- channel in enterocytes); more open so lose water as can’t retain; treatment is rehydration with salts also as diarrhoea clears bacteria

73
Q

4 stages of fat digestion

A

secretion of bile and lipases, emulsification, enzymatic hydrolysis of ester linkages, solubilization of lipolytic products in bile salt micelles

74
Q

pancreatic cholesterol esterase function

A

hydrolyses cholesterol ester to free cholesterol and fatty acid

75
Q

structure of bile salt

A

flat, amphipathic, hydrophobic face (nucleus and methyl) dissolves fat, hydrophilic face (hydroxyl and carboxyl) dissolves in water

LSS Alimentary System (40 decks)

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