Phgy 210: Digestion 9

Front 1

What has broken down enough for absorption?

Back 1

Fats --> mono, diglycerides, FA

Front 2

Which molec still need to be broke down more?

Back 2

Polysac-> disac -->need to still be broken down to monosac
Ptns -> small peptides ---> need to be broken to aa, di and tri-peptides

Front 3

What characterizes all of the intestinal muscosa?

Back 3

Crypts
Villi

Front 4

What do the cells in the crypt do?

Back 4

Secrete large amounts (3L/day) of ALKALINE fluid (SUCCUS ENTERICUS) into the lumen (that's all they can do, can't digest)

Front 5

Where do crypt cells go?

Back 5

Divide and migrate up along the villi and are shed at the tip of the villus
->covering is replaced every 3-5 days

Front 6

What do villi do?

Back 6

ABSORB nutrients and fluid (don't secrete fluid)
SYNTHESIZE enzymes, retain them in brush border (.: get complete digestion)

Front 7

Which enz are synthesized in the villi and what do they do?

Back 7

Enterokinase: activation of trypsinogen to trypsin
Amylase: Breaks carbs down to disac
Lipase: If some lipids aren't digested yet
Aminopeptidase and Dipeptidases can break down residual ptns toaa and di/tri peptides
DISSACHARASES: only sunthesized in villi cells of SMALL intestine
Sucrase,maltase, isoaltase, lactase

Front 8

What does the colonic secretion consist of?

Back 8

-Small volume
-Alkaline [HCO3] = 100-150mEq/L
[K+] 100-150 mEq/L
-Mucin (lots)
-**No digestive enzymes
-Bacterial Activity

Front 9

What is the result of secretory activity of salivary, gastric, pancreatic, hepatic and INTESTINAL secretions?

Back 9

Get monosacs (due to intestinal disaccharases)
Get aa, di/tripeptides ( due to intesinal peptidases)
Mon/di-glycerides and FA: doesn't really require intestine

Front 10

Describe the secretions in SI.

Back 10

Crypts: succus entericus
Volume: 3L/day
Isotonic: Na+, K+, Cl-, **HCO3-
pH: 7.5-9
No enzymes!!!

Front 11

Why doesn't the colon secrete any digestive enz?

Back 11

All digestion and secretion must be completed in the small intestine

Front 12

What is involved in the daily intake?

Back 12

Water (2000mL)
Solids (500g)

Front 13

What is the daily output?

Back 13

Solids: 50 g (includes 30% bacteria, 30% undigested fiber, 10-20% lipids, 10-20% inorganic matter)
Water: 100 ml

Front 14

How much is ingested compared to secretions?

Back 14

2L ingested
7L secreted throughout the body
Total of 9L absorbed by the GI
->Small intestine: 7L
-> Colon: 2L

Front 15

What else is reabsorbed from the lume of the GIT?

Back 15

Ions

Front 16

Describe ptn releaseinto the lumen.

Back 16

50g as enz
30g as cells
Total: 80g of ptn/day
these ptns are broken into aa and enter the aa pool to be reutilized

Front 17

What is most of the absorption in the GIT?

Back 17

Reabsorption
->cst circulation btw the plasma and lumen of GIT

Front 18

What are the sites of exchange characterized by?

Back 18

1) Large surface areas
2) Intimate contact with blood vessels
->NO absorption in mouth, esophagus or stomach

Front 19

Which is the only GI organ that is essential to life?

Back 19

Small intestine
Where bulk of absorption takes place
Inner surface of SI = 600x outer surface area of SI

Front 20

Why does the inner surface of the SI have such a larfe area?

Back 20

Has many circular fold (inc surface area 3x)
Has villi (inc SA 30x)
Has microvilli (inc SA 600x)
->have more area then required, could remove half of SI and still have efficient absorption

Front 21

Describe the villus

Back 21

Outside in: columnar epithelium, capillary network, lacteal
Have arterial supply
Venous drain
Lymph vessels

Front 22

What are the postprandial blood flow and the lymph flow?

Back 22

Postprandial: 1-2L/min (to intestine, very fast)
Lymph: 1-2ml/min (slow)
->absorption takes place very rapidly from the eithelial cell to cap

Front 23

What is absorbed in the following areas:duodenum, jejunum, ileum?

Back 23

Duodenum: Iron, Ca2+, CHO (mostly), Ptns, lipids, Na+, H2O, a bit of bile acids (very little)
Jejunom: CHO, less:Ptns, lipids, Na+, H2O and a bit more of bile acids
Ileum: CHO, less Ptns, lipids, Na+, H2O. Only place fo Vit B12 and the majority of bile acids

Front 24

How are things transported?

Back 24

Simple Diffusion
Facilitated Diffusion
Active Transport
Pinocytosis
Osmosi: water always follows the osmotic gradient generated by movement of ions

Front 25

What limits absorption?

Back 25

->Need adequate digestion: activated enz, pH, ions
->Adequate site for absorption (ex: distal ileum required for VitB12 absorption)
->Adequate transit time for absorption
->Adequate co-factors (co-lipase, bile salts), transporters

Front 26

What are the distribution of the different carbs?

Back 26

Lactose: 6%
Lactose -> lactase
Starch: 60%
Stach--salivary amylase--> partially converted starch --pancreatic amylase--> e-dextrins (->isomaltase) or -> maltotriose (->maltase) or ->maltose (->maltase)
Sucrose: 30%
sucrose --> sucrase

Front 27

What these sugars broken down to?

Back 27

Lactase-> galactose + glucose
Maltase --> glucose x2
Sucrase --> Fructose + glucose

Front 28

What degrades protein?

Back 28

Pepsin
Pancreatic proteases
Ptn-> oligopeptides + free aa

Front 29

What happens to oligopeptides?

Back 29

Oligopeptides
↓
Peptidases (in the membrane)
↓ ---> aa
Small peptides ---> aa
Intracellular ↓ peptidases
aa

Front 30

What happens to the free aa that are broken down from ptns?

Back 30

Go to carrier mediated transport across the mb
Get aa

Front 31

What happens to aa that are broken down from ptns?

Back 31

go to the capillary

Front 32

Can oligopeptides be absorbed faster than free aa?

Back 32

Yes

Front 33

Describe fat digestion/

Back 33

Triglycerides ----> Monoglycerides + FFA
Enz: lipase, co-lapase, bile salts
Monoglycerides --> Glycerol --> Cap
Monoglycerides-->FFA --> FA, MG, LPL, Cholesterol, Vit A,D,E,K (micelle formed through bile salts)

Front 34

What is the transit time related to?

Back 34

Other fctnal activities of a given organ
<1 sec in the pharynx
a few seconds in the esophagus
minutes to hours in the stomach
several hours in the small intestine
hous to days in the large intestine

Front 35

What kind of waves are ass't with motor and secretory activity?

Back 35

Wave of secretory activity: preceding, accompanying and trailing behind the meal
Wave of motor activity which receives, accommodates and conveys meal

Front 36

What are the protective mechanisms?

Back 36

Mucin
Inactive protease, trypsin inhibitor
Gastric mucosal barrier (tight junctions)
Sphincters prevent reflux
Negatice fdbk inhibiton of gastrin (by release of somatostatins)
Neutralization of duodenal contents
MMC= housekeeper: interdigestive period, migratory motor complex