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PA10315 > GI physiology - Digestion and absorption > Flashcards

GI physiology - Digestion and absorption Flashcards

1
Q

What is digestion?

A

How ingested nutrients are broken down.

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2
Q

What is absorption?

A

How ingested nutrients are taken up in the GI tract.

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3
Q

What initiates digestion?

A

The salivary glands.

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4
Q

What are the glands that secrete saliva?

A

The sublingual salivary gland the submandibular salivary gland.

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5
Q

What cells are present in the salivary glands?

A

Serous cells.

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6
Q

What do the cells in the salivary glands secrete?

A

Alpha amylase, lingual lipase, mucin, lgA and lysozyme.

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7
Q

What is the function of alpha amylase in the saliva?

A

It breaks down complex carbohydrates (starch) in the mouth. However, it is inactivated by the low pH in the stomach.

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8
Q

What is the function of lingual lipase in the saliva?

A

Breakdown of triglycerides. Its optimal pH is 405 and its activity is persistant throughout the GI tract.

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9
Q

What is the function of mucin in the saliva?

A

A lubricant.

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10
Q

What is the function of lysozyme?

A

It is an anti-microbial.

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11
Q

What is the function of lgA in the saliva?

A

It is an immunoglobin (antibody).

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12
Q

How does the concentration and composition of saliva differ to that of plasma?

A

It is hypotonic and alkaline.

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13
Q

What is the purpose of bicarbonate in the saliva?

A

It is a buffering function to minimise acid decay and damage from acid reflux.

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14
Q

How much saliva is produced each day?

A

Between 1000 and 1500ml.

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15
Q

Why is taste produced in the mouth?

A

Saliva moistens and lubricates the food and also solubilises a small amount of it which releases molecules that activate taste receptors.

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16
Q

What percent of total lipid digestion does lipase account for?

A

10-30%.

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17
Q

How is protein broken down in the stomach?

A

Chief cells secrete pepsinogen that is a precursor for pepsin that partially breaks down the proteins.

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18
Q

What cells secrete HCl?

A

Parietal cells.

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19
Q

What do mucous cells do in the stomach and what is their function?

A

They secrete mucous that is essential for protection and lubrication.

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20
Q

What is the purpose of G cells in the stomach?

A

They produce gastrin which controls motility and production of HCl, pepsinogen and mucous.

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21
Q

How does pepsin work?

A

It is an exopeptidase that clips amino acids from the end of polypeptide chains.

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22
Q

How much HCl is secreted by the stomach per day?

A

Around 2 litres.

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23
Q

What is the origin of hydrogen ions in the stomach?

A

CO2 in the parietal cells.

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24
Q

How is CO2 converted to hydrogen ions?

A

Carbonic anhydrase causes the CO2 to react with water to produce carbonic acid which dissociates into HCO3- and H+.

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25
Q

How do hydrogen ions reach the lumen of the stomach?

A

Primary H+/K+ - ATPases in the luminal membrane of the parietal cells pump the ions into the lumen actively, against a steep electrochemical gradient.

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26
Q

What happens to the K+ in this process?

A

The K+ leaks back into the lumen through K+ channels.

uptake of K+ ionis into the parietal cell, which are passed on into the blood

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27
Q

What happens to the HCO3-?

A

It is secreted on the opposite side of the cell into the blood in exchange for Cl-, at the baselateral membrane.

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28
Q

What chemical messengers regulate acid secretion?

A

Gastrin, acetylcholine, histamine and somatostatin.

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29
Q

What is the difference between protein digestion by chief cells and parietal cells?

A

Pepsin from chief cells acts as an exopeptidase whereas acid from parietal cells acts an endopeptidase.

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30
Q

What is the difference between exopeptidases and endopeptidases?

A

Exopeptidases clip amino acids from the end of polypeptides whereas endopeptidases catalyse the cleavage of internal peptide bonds.

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31
Q

How is pepsin produced from pepsinogen?

A

Pepsinogen is only activated by the low pH in the stomach.

32
Q

Which function of the pancreas is utilised in digestion?

A

The exocrine function.

33
Q

What is the significance of the bicarbonate in the pancreatic fluid?

A

It acts as a buffer to ensure chyme is not acidic and the enzymes can remain active.

34
Q

Where is bile stored?

A

The gall bladder.

35
Q

How is bile injected into the lumen of the small intestine during feeding?

A

The gall bladder muscle contracts and the bile enters via the common bile duct.

36
Q

What is the function of bile?

A

It is alkaline and neutralises gastric acid entering the duodenum. It is also important for digestion and absorption of fats along with acting as a surfactant to reduce surface agent.

37
Q

What are zymogens?

A

Enzymes precursors that require some change to become active.

38
Q

What do the enzymes secreted from the pancreas digest?

A

Fat, polysaccharides, proteins, nucleic acids, sugars, amino acid and nucleotides.

39
Q

What is the role of enterokinase?

A

It is a proteolytic enzyme that splits off a peptide from pancreatic trypsinogen to form the active trypsin.

40
Q

What is the function of trypsin?

A

It activates other pancreatic zymogens and also digests proteins.

41
Q

How is pancreatic sections controlled?

A

By the hormones secretin and CCK (cholecystokinin).

42
Q

What is the role of secretin?

A

It is the primary stimulant for HCO3- secretion.

43
Q

What is the role of CCK?

A

It stimulates enzyme secretion.

44
Q

What is the brush border of an epithelial cell?

A

It contains a variety of protein carriers that facilitate the uptake of free amino acids.

45
Q

What do peptidases do on the brush border?

A

Break large peptides (too big to get through the brush border) into small peptides or free amino acids that can then enter the cell via carriers.

46
Q

What happens when small peptide enter the epithelial cell?

A

They are hydrolysed into small amino acids by intracellular peptidases.

47
Q

What happens when amino acids are inside the epithelial cell?

A

They converge on the basal lateral membrane to be transported into the bloodstream.

48
Q

How are carbohydrates digested?

A

Salivary and pancreatic amylase to reduce the complex carbohydrates into smaller sections.

49
Q

How are maltase, sucrose and lactose digested?

A

On the brush border, maltase, sucrase and lactase are present to digest the carbohydrates into fructose or glucose and galactose.

50
Q

How do glucose and galactose enter the cell?

A

There are transporters that are specialised for their uptake into the cell.

51
Q

How does sodium affect the transport of glucose and galactose?

A

Sodium travels down an electrochemical gradient (from high to low) that drives the uptake by cotransporters of glucose and galactose.

52
Q

Why is ATPase present intracellularly?

A

It is needed to maintain the intracellular concentrations of sodium low - it removes Na+ to maintain the gradient.

53
Q

How do oral rehydration solutions work?

A

They need to be sweet so that sugar is present so sodium can be transported across the membrane,

54
Q

Why can sucrose, lactose or maltose not enter the epithelial cell?

A

They are too large and the correct transporters are not present.

55
Q

What happens when cholesterol is broken down?

A

It forms cholic acid and chenodeoxycholic acid which are primary bile acids.

56
Q

What happens to primary bile acids?

A

They are stored in the gall bladder.

57
Q

What happens to cholic acid?

A

It undergoes bacterial hydroxylation and deoxycholic acid is formed (secondary bile acid)

58
Q

What happens to chenodeoxycholic acid?

A

It undergoes bacterial hydroxylation to form lithocholic acid (secondary bile acid)

59
Q

What happens to these secondary bile acids?

A

They are released into the duodenum.

60
Q

please look at bile salts properly

A

this is very unprofessional

61
Q

What are triglycerides broken down into?

A

Monoglycerides and two molecules of FFA.

62
Q

What are phospholipids broken down into?

A

Lysophosphatides and FFA.

63
Q

What is colipase?

A

A protein co-enzyme required for optimal pancreatic triglyceride lipase activity.

64
Q

How is colipase activated?

A

It is secreted by the pancreas in an inactive form which is then activated in the intestinal lumen by trypsin.

65
Q

What happens after colipase is activated?

A

It binds to the bile-salt covered triacylglycerol interface of micelles, allowing the access of the PTGL to its substrates at the water-lipid interface.

66
Q

pepsin function

A

initiates protein digestion, breaks them up into peptides and amino acids

67
Q

what converts pepsinogen into pepsin

A

hcl

68
Q

where are zymogens produced

A

pancreatic bulb

69
Q

How are zymogens released into lumen of pancreatic duct

A

exocytosis

70
Q

By what process do amino acids enter epithelial cells

A

active transport or by Na+ dependent active transport

71
Q

transport of sugars into blood overview

A

facilitated diffusion transports fructose into epi cells

secondary active transport moves glucose and galactose in, using Na+ ions

72
Q

How do bile slats digest lipids

A

Cling to mono, di and triglycerides of fat molecules and break them up into triglyceride emulsion droplets

73
Q

lipases action

A

cleave off fatty acids from glycerol and generate monoglycerides
FFAs bind to phosphates

74
Q

Why emuslify fats with bie

A

forms lipid droplets which increase the surface area for lipases

75
Q

how does co-lipase act as a co enzyme

A

lodges on lipid droplet surface, binds lipase

76
Q

why can bile salts and and lipids form micelles

A

amphipathic

PA10315 (47 decks)

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