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z:Physl 210A/B > GIT Lec 6: Small Intestine > Flashcards

GIT Lec 6: Small Intestine Flashcards

1
Q

small intestine is between

A

stomach + large intestine

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2
Q

size of small intestine

A
  • tube of 2.4 cm diameter

- 3m length (doubles during autopsy–> loss of tone)

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3
Q

small intestine sections

A

duodenum- 30 cm - close to stomach
jejunum - 1 m
ileum - 1.7 m - close to large intestine

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4
Q

small intestine functions

A

-digestion + absorption of protein, fat, carbohydrates, electrolytes, H2O, minerals, vitamins

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5
Q

functions of duodenum

A
  • mixing pancreatic digestive enzymes + bile with food
  • absorption of nutrients, iron, calcium
  • release of endocrine hormones–> secretin, CCK
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6
Q

functions of jejunum

A
  • digestion + absorption

- most chyme digested + absorbed in first 25% of small intestine

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7
Q

functions of ileum

A

-digestion + absorption (bile acids, vitamin B12)

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8
Q

large SA is important because

A

absorption, exposure to enzymes needs to be increased

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9
Q

folds of small intestine increases

A

SA (epithelial layer)

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10
Q

folds of small intestine (largest to smallest)

A

folds of kerckring –> villi + crypts —> microvilli

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11
Q

type of cells in villus

A
  • stem cells in crypts
  • paneth cells in crypts
  • enterocyte (absorptive) cells -villus stalk
  • goblet cells -villus stalk
  • enteroendocrine cells -villus stalk
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12
Q

paneth cells

A

secrete antibacterial proteins

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13
Q

enterocyte (absorptive) cells

A

absorption , brush-border enzymes

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14
Q

goblet cells

A

secretion of mucus

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15
Q

enteroendocrine cells

A

release of hormones

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16
Q

brush border

A

-small projections (microvilli) at epithelial cells –> major absorptive surface

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17
Q

brush border enzyme

A
  • enzyme anchored to brush border, catalytic activity in lumen
  • breakdown of carbohydrates, pep–> sugars, aa before transport into enterocyte
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18
Q

starch (amylose +amylopectin) products by salivary + pancreatic amylase

A

maltose, maltotriose, a-limit dextrins

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19
Q

enzymes that turn maltose, maltotriose to glucose

A

maltase
sucrase
a-dextrinase

20
Q

enzymes that turn a-limit dextrins to glucose

A

a-dextrinase

21
Q

sucrose enzyme + products

A
  • sucrase

- glucose + fructose

22
Q

lactose enzyme + products

A
  • lactase

- glucose + galactose

23
Q

SGLT

A

sodium -glucose linked transporter

24
Q

GLUT2/5

A

glucose transporter 2/5

25
Q

intestinal absorption of glucose/galactose

A

apical: glucose/galactose and 2Na+ from lumen into cytosol through SGLT
basolateral: glucose/galactose from cytosol into blood through GLUT2
Na+/K+ ATPase– 3 Na+ out/ 2 K+ in

26
Q

intestinal absorption of fructose

A

apical: fructose from lumen into cytosol through GLUT5
basolateral: fructose from cytosol into blood through GLUT2

27
Q

lactose intolerance

A
  • all mammals lose some lactase expression
  • can’t completely digest lactose -
  • decreased water absorption
  • more water in gut (osmotic gradient into lumen)
  • bacteria in large intestine digest lactose
    consequence: pain, diarrhea
28
Q

major pancreatic proteases

A

trypsin + chymotrypsin

29
Q

further protein digestion (breakdown)

A
  • carboxypeptidase (pancreatic protease)

- aminopeptidase (brush border)

30
Q

protein absorption (apical/basolateral)

A

apical: free aa coupled with Na+ absorbed (2 active transport)
small peptides absorbed by 2 active transport coupled with H+ then peptidases in cytosol: peptides to a.a

basolateral: Na+/K+ ATPase, a.a facilitated diffusion across basolateral surface

31
Q

fat absorption

A
  • fatty acids+ monoglycerides processed by ER to make triglycerides= maintains diffusion gradient
  • aggregate into lipid droplets coated by amphipathic proteins
32
Q

chylomicrons

A
  • extracellular fat droplets
  • triglycerides, phospholipids, fat soluble vitamins, cholesterol
  • larger ones enter lymphatic system through lacteals (leakier)- enter systematic circulation through thoraic duct
33
Q

lipoprotein lipase on endothelial cells (blood vessels)

A

break down of chylomicrons for uptake

34
Q

absorption of iron for the intestine

A
  • Fe2+ actively transported into enterocyte and stored in ferritin protein
  • not stored: transported into blood + stored in transferrin (plasma protein)
  • increase iron in body stores –> increase ferritin expression –> decrease absorption of iron
  • decrease iron i body stores –> decrease ferritin expression –> increase absorption of iron
35
Q

no iron excretion

A
  • iron is toxic

- increase skin pigmentation/heart failure

36
Q

iron deficiency anemia

A

-decrease number/size in RBC
symptoms-tiredness, light-headness, headaches
cause: decrease iron /blood loss, poor iron abs. , intestinal disease

37
Q
  • Water amount absorbed by small intestine vs feces?

- why water in intestine?

A
  • 8-9 L –> majority absorbed by small intestine – 100 ml in feces
  • water in intestine – permits contact food + enzymes, diffusion of digested nutrients to absorption site, prevents damage to epithelial layer
38
Q

water absorption

A

determined by Na+ gradients out of cell, apical side

-at villi

39
Q

water secretion

A

depends on Cl- gradients by 2 active Na+/K+/2Cl- transporter (NKCC1)- basolateral side into cell
Cl- (+cAMP) out of cell - apical side
increasing cAMP, increasing Cl-

40
Q

Cholera

A
  • ingesting food+water vibrio cholerae bacteria – produces toxin that increase cAMP, Cl- channel secretion of Cl- into small intestine, increase water in lumen
  • 20 L of stool causes: vomiting + excessive diarrhea
    treatment: clean water +electrolytes, intravenous fluids
41
Q

motility (small intestine)- during digestion

A
  • “segmentation” - mechanical breakdown of food, digestive enzymes mixes
42
Q

contractions per min (duodenum)

A

12

43
Q

contractions per min (ileum)

A

9

44
Q

motility (small intestine)- after digestion

A
  • segmentation stops, MMC (migrating myoelectric complex) starts
  • starts lower stomach then 2 feet in small intestine (overlapping waves starts further down - 2hrs then repeat)
45
Q

purpose of MMC

A
  • pushes any undigested material from small to large intestine
  • removal of bacteria in small intestine
46
Q

Regulation of MMC

A
  • motilin hormone secretion by cells of small intestine – initiate MMC
  • feeding inhibits motilin

z:Physl 210A/B (28 decks)

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