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GI > Digestion and Absorption > Flashcards

Digestion and Absorption Flashcards

1
Q

What is the main function of the small intestine?

A

Major site for digestion and absorption

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2
Q

What is the length of the small intestine?

A

Approx. 6m long with a 3.5cm diameter

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3
Q

What does the small intestine recieve?

A

Chyme from the stomach via the pyloric sphincter
Pancreatic juice from the pancreas (sphincter of oddi)
Bile from the gall bladder (sphincter of oddi)

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4
Q

Generally what does the small intestine secrete?

A

Intestinal juices (succus entericus)

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5
Q

What valve does the small intestine move residues thorough?

A

The ileocaecal vale which opens in response to proximal pressure and in response to gastrin

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6
Q

How has the small intestine adapted to be good at absorption?

A

Circular folds
Villi
Microvilli

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7
Q

What peptide hormones are secreted into the blood via endocrine cells within the mucosa of the small intestine?

A 
Gastrin 
Cholecystokinin (CCK) 
Secretin
Motilin
Glucagon-like insulinotropic peptide (GIP) and incretin 
Glucagon-like peptide-1 (GLP-1)
Ghrelin
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8
Q

What cell secretes gastrin?

A

G cells of the gastric antrum and duodenum

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9
Q

What cell secretes CCK?

A

I cells of the duodenum and jejunum

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10
Q

What cell secretes secretin?

A

S cells of the duodenum

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11
Q

What cell secretes motilin?

A

M cells of the duodenum and jejunum

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12
Q

What cell secretes GIP and incretin?

A

K cells of the duodenum and jejunum

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13
Q

What cell secretes GLP-1 and incretin?

A

L cells of the gut

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14
Q

What cell secretes ghrelin?

A

Gr cells of the gastric antrum, small intestine and elsewhere (pancreas)

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15
Q

What do all the peptide hormones from the small intestine act on except from incretin?

A

G-protein coupled receptors

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16
Q

What does incretin act on?

A

Beta cells of the pancreas in essentially a feed-forward manner to stimulate the release of insulin

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17
Q

What are the positive control mechanisms for the release of succus entericus?

A 
Distension/irritation
Gastrin
CCK
Secretin
Parasymp 
ALL enhance
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18
Q

What is the negative control mechanism for the release of succus entericus?

A

Symp nerve activity

Decreases

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19
Q

What does the succus entericus contain?

A

Mucus for protection (goblet cells)
Aqueous salt - enzymatic digestion (crypts of lieberkuhn)
NO digestive enezymes

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20
Q

What occurs during segmentation (mixing) of chyme?

A

The chopping action moves chyme back and forth - very vigorous after a meal
Alternating contraction and relaxation of segments of circular muscle

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21
Q

What initiates segmentation?

A

Small intestine pacemaker cells causing the BER which is continous. At threshold, it activates segmentation which in the duodenum is primarily due to distension by entering chyme

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22
Q

How is segmentation in the empty ileum triggered?

A

By gastrin from the stomach (gastroileal reflex)

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23
Q

How is the strength of segmentation altered?

A

It is enhanced and decreased by parasympathetic and sympathetic activity

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24
Q

What is the migrating motor complex (MMC)?

A

Occurs between meals every 90-120 mins and is a strong peristaltic contraction passing the length of the intestine (stomach - ileocaecal valve)

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25
Q

What is the function of the migrating motor complex?

A

Clears the small intestine of debris, mucus and sloughed epithelial cells between meals

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26
Q

What inhibits the MMC?

A

Feeding and vagal activity

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27
Q

What triggers the MMC?

A

Motilin, suppressed by gastrin and CCK

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28
Q

What are the endocrine pancreatic secretions?

A

Insulin and glucagon - secreted to the blood

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29
Q

What are the exocrine pancreatic secretions?

A

Digestive enzymes (acinar cells), aqueous NaHCO3- solution (duct cells) which are secreted to the duodenum as pancreatic juice

30
Q

What is the purpose of the duct cells producing alkaline fluid?

A

To neutralise the acidic chyme entering the duodenum, this provides optimum pH for the pancreatic enzyme function and protects the mucosa from erosion by acid

31
Q

What are the proteases stored within the acinar cells?

A

Trypsinogen, chymotrypsinogen and procarboxypeptidae A and B

32
Q

What are the amylases stored within the acinar cells?

A

Pancreatic amylase

33
Q

What are the lipases stored within the acinar cells?

A

Pancreatic lipase

34
Q

Where are the enzyme stored within the acinar cells?

A

In zymogen granules and released in response to elevated calcium

35
Q

Where are the proteases activated?

A

Within the duodenum

36
Q

What are the 3 phases to pancreatic secretion?

A

Cephalic
Gastric
Intestinal

37
Q

What occurs during the cephalic phase?

A

Mediated by the vagal stimulation of mainly the acinar cells

38
Q

What occurs during the gastric phase?

A

Gastric distension evokes a vasovagal reflex resulting in parasymp stimulation of acinar and duct cells

39
Q

What occurs during the neutralisational intestinal phase?

A

Acid in duodenual lumen, increased secretin release, secretin carried to pancreaetic duct cells resulting in increased secretion of alkaline fluid

40
Q

What occurs during the digestion part of intestinal pancreatic secretion?

A

Fat and protein in duodenal lumen
Increased CCK release from I cells which is carried by the blood to the pancreatic acinar cells. This results in an increased secretion of digestive enzymes into duodenal lumen

41
Q

What are the main constituents of carbohydrates?

A

Starch (amylose and amylopectin)
Cellulose
Glycogen
Disaccharides (sucrose, lactose)

42
Q

What are the main constituents of lipids?

A 
Triacylglycerols 
Phospholipids
Cholesterol and cholesterol esters 
Free fatty acids 
Lipid vitamins
43
Q

What are the main constituents of proteins?

A

Ingested plus some from endogenous sources such as digestive enzymes and dead cells from GI tract

44
Q

What is digestion?

A

The enzymatic conversion of complex dietary substances to a form that can be absorbed

45
Q

What do most digestive proccesses occur in the small intestine as?

A

Luminal digestion - mediated by pancreatic enzymes secreted into the duodenum
Membrane digestion - mediated by enzymes situated at the brush border of epithelial cells

46
Q

What is absorption?

A

The proccesses by which the absorbable products of digestion are transferred across both the apical and basolateral membranes of enterocytes (absorptive cells of the intestinal epithelium)

47
Q

What are the different types of digestible carbohydrates?

A

Polysaccharides
Oligosaccharides
Monosaccharides

48
Q

What are the 2 different types of polysaccharides?

A

Starch (amylose, amylopectin), glycogen (animal)

49
Q

What are the different types of oligosaccharides?

A

Sucrose (glucose and fructose)

Lactose (glucose and galactose)

50
Q

What are the different types of monosaccharides?

A

Glucose and fructose and galactose

51
Q

What do carbohydrates need to be converted to to be digested?

A

They need to be converted to monosaccharides

52
Q

How are starch converted to oligosaccharides?

A

Alpha-amylase by salivary and pancreatic

53
Q

How are oligosaccharides converted to monosaccharides?

A

Via oligosaccharidases (lactase, maltase and sucrase-isomaltase)

54
Q

What is alpha-amylase?

A

Endoenzyme

55
Q

What does alpha-amylase break down?

A

It breaks down linear internal alpha-1,4 linkages but not terminal alpha-1,4 linkages and therefore there is no production of glucose

56
Q

What are the products when alpha amylases break down amylose or amylopectin?

A

Products are thus linear glucose oligomers (maltotriose, maltose) and alpha limit dextrins

57
Q

What are the role of oligosaccharidases?

A

They are integral membrane proteins with a catalytic domain that faces the lumen on the GI tract

58
Q

What is the substrate of lactase?

A

Has only one substrate, breaks down lactose to glucose and galactose

59
Q

What do all other oligosaccharides do (apart from lactase)?

A

Cleave the terminal alpha-1,4 linkages of maltose, maltotriose and alppha limit dextrins (to yield glucose)

60
Q

What is sucrose responsible for?

A

It is specifically responsible for hydrolysing sucrose to glucose and fructose

61
Q

How can lactose intolerance result?

A

Primary lactase deficiency
Secondary lactase deficiency
Congenital lactase deficiency

62
Q

Where does absoprtion of the final products of carbohydrate digestion occur?

A

In the duodenum and jejunum via the apical and basolateral membranes.

63
Q

What receptor absorbs glucose and galactose?

A

Seconadry active transport mediated by SGLT1

64
Q

How is fructose absorbed?

A

Facilitated diffusion mediated by GLUT5

65
Q

How do all monosaccharides exit the small intestine?

A

Facilitated diffusino via GLUT

66
Q

How does SGLT1 work?

A

2 Na+ bind increasing the affinity for glucose. Na+ and glucose translocate from extracellular to intracellular where the Na+ dissociate and the affinity for glucose decreases

67
Q

How must protein be digested before it can be absorpbed?

A

To oligopeptides and amino acids by pepsin and pancreatic proteases

68
Q

What do pepsidases do?

A

They further hydrolyse oligopeptides to amino acids at the brush border

69
Q

How are amino acids transported across the apical membrane?

A

Via a variety of amino acid transporters, some of which are Na+ dependent and others Na+ independent

70
Q

How are oligopeptides transported across the apical membrane?

A

Via H+/oligopeptide co-transporter PepT1

71
Q

What happens to oligopeptides once they cross the apical membrane/

A

Within the cytoplasm they are further hydrolysed to amino acids by pepsidases within the enterocyte

72
Q

How do amino acids exit the enterocyte?

A

By crossing the basolateral membrane by several Na+ independent transporters

GI (42 decks)

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