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Phsyiology 210 B > Gastrointestinal Tract 6 - Small Intestine > Flashcards

Gastrointestinal Tract 6 - Small Intestine Flashcards

1
Q

Small intestine divided into three sections

A
  • Duodenum (closest to stomach) - 30cm
  • Jejunum-~1 m
  • Ileum-~1.7 m (closest to large intestine)
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2
Q

Does the small intestine do absorption AND digestion?

A

YES

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3
Q

Duodenum functions

A
  • Mixing of pancreatic digestive enzymes and bile with food
  • Absorption of nutrients, iron and calcium.
  • Release of secretin and CCK
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4
Q

Jejunum function

A
  • Digestion and absorption
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5
Q

Ileum function

A
  • Digestion and absorption

- Bile acids, vitamin B12

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6
Q

How is SA increased in the small intestine?

A

By Folds of Kerckring/ Circular folds

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7
Q

Structure of a villus in the small intestine contain:

A
  • cells enterocyte (absorptive cell)
  • goblet cell (mucus)
  • endocrine cell
  • paneth cell
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8
Q

Potential cell types derived from stem cells

A
  • Absorptive cells: absorption, brush-border enzymes
  • goblet cell: secrete mucus
  • endocrine cell: release hormones
  • paneth cell: secrete antibacterial proteins
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9
Q

Brush border

A

small projections (microvilli) of epithelial cells covering the villi of the small intestine, major absorptive surface of the small intestine

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10
Q

Brush border enzyme

A

enzyme anchored to the brush border with catalytic activity in the lumen

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11
Q

Brush border enzymes are Important for breaking down

A

carbohydrates and peptides into sugars and amino acids prior to transport across the enterocyte

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12
Q

Digestion of carbohydrates

A
  • Starch (amylose and amylopectin) is broken down into maltose, maltotriose, and α-limit dextrins by salivary and pancreatic amylases
  • These are broken down to the monosaccharide glucose by brush border enzymes
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13
Q

Other sugars broken down by brush border enzymes

A
  • Sucrose broken by sucrase into (glucose + fructose)

- lactose broken by lactase into
glucose +galactose

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14
Q

Intestinal absorption of glucose/galactose

A

Glucose/galactose from intestinal lumen goes into epithelial cells (low Na+, high K+) via transport protein (SGLT) and leaves through another one (GLUT2) into the blood (high Na+, low K+)

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15
Q

Intestinal absorption of fructose

A

Fructose from intestinal lumen goes into epithelial cells (low Na+, high K+) via transport protein (GLUT5) and leaves through another one (GLUT2) into the blood (high Na+, low K+)

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16
Q

When lactose cannot be completely digested:

A

Results in decreased water absorption in the gut (presence of lactose produces an osmotic gradient)

Lactose containing fluid passes on to large intestine and bacteria digest lactose
- Gas (colon distension and pain), diarrhea

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17
Q

Proteins are broken down by

A

pepsin in the stomach, and in the small intestine by pancreatic proteases (major ones are trypsin and chymotrypsin)

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18
Q

Once proteins are broken down in the stomach or small intestine, they are then further broken down by:

A
  • Carboxypeptidase (pancreatic protease)
  • Aminopeptidase (brush border enzyme in the small intestine)
  • Other brush border enzymes (>20 different peptidases)
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19
Q

Once digested, free amino acids are absorbed by

A

secondary active transport coupled to Na+ (multiple transport proteins)

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20
Q

Small peptides can also be absorbed by different secondary active transport proteins coupled to H+, after …

A

Peptidases within the cytosol then hydrolyze peptides to amino acids

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21
Q

After the Peptidases hydrolyze peptides to amino acids, the amino acids then undergo

A

facilitated diffusion across the basolateral surface of the enterocyte

  • different facilities transporters between the two surfaces, each for a specific amino acid.
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22
Q

Products of lipase are incorporated into

A

micelles which are in a dynamic state- breaking down and reforming

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23
Q

As micelles breakdown they will release

A

fatty acids and monoglycerides that can then diffuse across the small intestine epithelium

24
Q

Once fatty acids and monoglycerides are absorbed by the enterocyte, they are

A

Processed by the ER back into triglycerides.

- This maintains diffusion gradient

25
Q

Within the ER triglycerides aggregate into

A

lipid droplets coated with amphipathic proteins

26
Q

The lipid droplets are packaged into the ______ and secreted via exocytosis

A

Golgi

27
Q

Extracellular fat droplets secreted are known as

A

“chylomicrons”

28
Q

Chylomicron contains

A

triglycerides, phospholipids, fat soluble vitamins and cholesterol

29
Q

The large chylomicrons enter into the

A 
lymphatic system (rather than the capillaries in the intestine
- Lacteals are leakier

Lymphatics eventually enter into the systemic circulation through the thoracic
duct

30
Q

Lipoprotein lipase on endothelial cells of blood vessels release

A

triglycerides from chylomicrons as monoglycerides and free fatty acids which can be taken up by tissues

31
Q

Iron (as Fe2+) is actively transported into the enterocyte and incorporated into the protein

A

ferritin, a protein iron complex that acts as a storage form of iron

32
Q

Iron that is not stored is released on the blood side of the enterocyte and transported through the blood attached to the plasma protein

A

transferrin

33
Q

Iron that remains in the enterocyte bound to ferritin is excreted from the body when the enterocytes

A

slough off of the villi tips

34
Q

When iron stores are ample in the body expression of ferritin protein is

A

upregulated resulting in a reduced absorption of iron

35
Q

When iron stores are depleted the production of

A

intestinal ferritin decreases resulting in increased absorption

36
Q

Is there a mechanism for the excretion of iron, if so what’s it called?

A

NO, it accumulates in the tissue = toxicity = skin pigmentation and hear failure.

37
Q

Causes for iron accumulating in tissue

A
  • Genetic defects in absorption control pathways
  • Adult males/post-menopausal women excessively supplementing
  • Poisoning-often children accidentally consuming supplements
38
Q

Iron-deficiency anemia

A
  • Reduced number and/or size of red blood cells
  • Symptoms: tiredness, light-headedness, headaches,
  • Causes: not enough iron in diet, iron loss via blood loss, poor iron absorption, intestinal disease
39
Q

Water and electrolyte absorption and

secretion in the intestine is critical for GI function

A
  • Permits contact between food and digestive enzymes
  • Diffusion of digested nutrients to absorption site
  • Fluidity provides for transit without damage to the epithelium
40
Q

Intestine handles large quantities of fluids each day

A
  • Some from diet
  • Majority from intestine and organs that drain into the intestine (e.g., liver and pancreas)
  • Majority is “reclaimed” or reabsorbed by the small intestine
41
Q

How much fluid is handled by the GI tract each day ?

A
  • 8-9 L
  • Majority is reabsorbed in the small intestine.
  • 100 ml lost in feces.
42
Q

Villi does what and crypts do what?

A

absorption at the villi, secretion from the crypts

43
Q

Intestinal epithelium establishes an osmotic gradient and water

A

follows through tight junctions (paracellular transport).

44
Q

Na+, Cl-, HCO3- are important electrolytes for

A

water transport

45
Q

Absorption of water in the small intestine Predominantly depends on

A

Na+ gradients generated during secondary active nutrient uptake (e.g., glucose and amino acids)

46
Q

Secretion of water in the small intestine Predominantly depends on

A

Cl- gradients generated by secondary active Na+/K+/2Cl- transporter (NKCC1)

47
Q

Cholera Occurs after eating food or drinking water contaminated with

A

Vibrio cholerae bacteria, which produces a toxin that INCREASES cAMP in crypts of small intestine = activation of the Cl- channel and excessive secretion of Cl- into the gut lumen, water follows (diarrhea)

48
Q

Treatment to cholera

A
  • Consumption of clean water containing salt and glucose (fluid
    replacement)
  • Intravenous fluids
49
Q

Most common motion in small intestine during digestion is

A

“segmentation”

50
Q

Segmentation is continuous

A

division and subdivision of intestinal contents

  • Mechanical breakdown of food (increases surface area)
  • Mixing of food with digestive enzymes
51
Q

During segmentation, Frequency of contraction set by

A

basic electrical rhythm

  • 12 contractions/min in duodenum
  • 9 contractions/min in ileum
52
Q

Contraction force during segmentation is determined by

A

neurohormonal input

  • Slow net migration towards the large intestine
  • Allows digestion and absorption of food
53
Q

Segmentation occurs in the small intestine

A

during digestion

54
Q

After digestion, segmentation stops and is replaced by

A

a pattern of peristaltic activity called the migrating myoelectric complex (MMC)

55
Q

MMC Begins in the

A

lower portion of the stomach travels about 2 feet along the small intestine and then dies out, next wave starts further down SI, this is repeated
(takes -2hrs, then repeats)

56
Q

Purpose of MMC

A
  • Pushes any undigested material from the small to the large intestine
  • Prevents bacteria from remaining in the small intestine
57
Q

Regulation of MMC

A
  • Intestinal hormone motilin (released by cells in the small intestine) thought to initiate MMC
  • Feeding inhibits the release of motilin
  • MMC ceases when next meal is consumed

Phsyiology 210 B (24 decks)

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