Lecom - Physiology 65: Digestion And Absorption In The Gi Tract

Front 1

Sucrose is broken down by __________ into ________ and _________?

Back 1

Sucrase into Fructose + Glucose

Front 2

Lactose is broken down by __________ into ________ and _________?

Back 2

Lactose into Galactose + Glucose

Front 3

Maltose is broken down by __________ into ________?

Back 3

Maltase into Glucose

Front 4

What enzymes are found in the enterocytes covering intestinal microvilli brush border?

Back 4

Sucrase, Lactase, Alpha-Dextrinoase, Maltase

Front 5

Ptyalin secreted from?

Back 5

Parotid Gland

Front 6

Ptyalin also know as?

Back 6

Salivary Alpha-Amylase

Front 7

Ptyalin Action?

Back 7

Hydrolyze starch into Maltose and other polymers of glucose with 3-9 subunits of glucose

Front 8

Ptyalin pH inactivation?

Back 8

Ptyalin is inactive at pH < 4.0

Front 9

Ptyalin % hydryolysis of starch?

Back 9

Usually accounts for 20-40% of starch hydrolysis usually into Maltose

Front 10

Pancreatic Alpha-Amylase

Back 10

Accounts for remaining starch hydrolysis, released from the pancreas

Front 11

Pepsin

Back 11

Peptic enzyme of stomach

Front 12

Pepsin pH inactivation?

Back 12

Most active at pH 2.0 - 3.0; Inactive at pH > 5.0

Front 13

Parietal (Oxyntic) Cells

Back 13

Secretes Hydrochloric Acid which has a pH at 0.8 pH; once mixed with secretions from non-oxyntic glandular cells pH goes to 2.0 - 3.0

Front 14

Pepsin really good at digesitng?

Back 14

Pepin able to digest Collagen (albuminoid type protein) which is a major constituent of meat CT.

Front 15

Pepsin accounts for what % of protein digestion?

Back 15

10 - 20% total protein digestion

Front 16

Most protein digestion occurs?

Back 16

Most protein digestion occurs by Pancreatic Enzymes working in the Duodenum and the Jejunum

Front 17

Action of Trypsin and Chymotrypsin?

Back 17

Split Protein Molecules into Polypeptides

Front 18

Action of Carboxypolypeptidase?

Back 18

Cleaves indvidual Amino Acids from Carboxyl ends of Polypeptides

Front 19

Action of Proelastase?

Back 19

Converts to Elastase which digests Elastin

Front 20

Last stage of protein digestion occurs where?

Back 20

Last stage of protein digestion occurs at the Enterocytes which line the villi of the brushborder of the Duodenum and Jejunum; Aminopolypeptidases and Dipeptidases

Front 21

What parts of Protein digestion can easily transport through the microvillar membrane to the interior of the Enterocytes?

Back 21

Amino Acids, Dipeptides and Tripeptides

Front 22

Which type of fats are the most abundant in the diet?

Back 22

Neutral fats, known as Triglycerides

Front 23

What are Triglycerides made up of?

Back 23

A glycerol nucleus and three fatty acid side chains

Front 24

Where are Triglycerides first digested and by what enzyme?

Back 24

Tryiglycerides are first digested in the stomach by lingual lipase (Only 10% of total fat digestion)

Front 25

Where is lingual lipase secreted?

Back 25

Lingual Lipase is secreted by the Lingual Gland in the mouth and swallowed with saliva

Front 26

What is emulsification?

Back 26

The first step in fat digestion, physically breaking down the fat globules into smaller sizes that the water soluble digestive enzymes can act on the globule surfaces. Begins by agitation in the stomach to mix the fat with products of stomach digestion.

Front 27

Where does the majority of emulsification occur?

Back 27

Majority of emulsification occurs at the Duodenum under the influence of Bile, made in the liver and stored in the gallbladder

Front 28

What makes up the Bile?

Back 28

Bile contains a large quanity of Bile Salts and the phospholipid Lechithin

Front 29

Describe the polarity aspect of Bile Salt and Lechitin?

Back 29

The polar parts of the bile salts and lecithin molecules are highly soluble in water, whereas most of the remaining portions of their molecules are highly soluble in fat. Therefore, the fat-soluble portions of these liver secretions dissolve in the surface layer of the fat globules, with the polar portions projecting. The polar projections, in turn, are soluble in the surrounding watery fluids, which greatly decreases the interfacial tension of the fat and makes it soluble as well.

Front 30

What enzyme is responsible for the digestion of lipids in the intestines?

Back 30

Pancreatic Lipase as well as lipase in the Enterocytes of the microville of the brush border

Front 31

End products of Triglyceride digestion?

Back 31

split by pancreatic lipase into free fatty acids and 2-monoglycerides

Front 32

What are micelles and how are they made?

Back 32

Micelles are small spherical, cylindrical globules 3 to 6 nanometers in diameter composed of 20 to 40 molecules of bile salt

Front 33

What actions do the micelles have?

Back 33

The small fat globule in the middle of a resulting micelle, with polar groups of bile salts projecting outward to cover the surface of the micelle, which allow the entire micelle globule to dissolve in the water of the digestive fluids and to remain in stable solution until the fat is absorbed into the blood. They also act as a transport medium to carry the monoglycerides and free fatty acids, both of which would otherwise be relatively insoluble, to the brush borders of the intestinal epithelial cells. There the monoglycerides and free fatty acids are absorbed into the blood, as discussed later, but the bile salts themselves are released back into the chyme to be used again and again for this "ferrying" process.

Front 34

Other lipids in the diet?

Back 34

Cholesterol in the diet is in the form of cholesterol esters, which are combinations of free cholesterol and one molecule of fatty acid. Phospholipids also contain fatty acid within their molecules. Phospholipids and Cholesterols are also "ferried" by Micelles

Front 35

Enzymes for Hydrolyzing Cholesterol Esters and Phospholipids?

Back 35

Two other lipases in the pancreatic secretion that free the fatty acids-the enzyme 1. cholesterol ester hydrolase to hydrolyze the cholesterol ester 2. phospholipase A2 to hydrolyze the phospholipid.

Front 36

Amount of various gastrointestinal secretions in liters?

Back 36

7 Liters

Front 37

Amount of typical ingested fluid?

Back 37

1.5 liters a day

Front 38

Amount of Absorption of fluids in GI tract a day?

Back 38

8 to 9 liters

Front 39

Amount of fluid that usually passes through the ileocecal valve into the colon that hadn't been reabsorbed a day?

Back 39

1.5 Liters

Front 40

Stomachs ability to Absorb?

Back 40

The stomach is a poor absorptive area of the gastrointestinal tract because it lacks the typical villus type of absorptive membrane, and also because the junctions between the epithelial cells are tight junctions. Only a few highly lipid-soluble substances, such as alcohol and some drugs like aspirin, can be absorbed in small quantities.

Front 41

What is the name of the many folds of the small intestinal mucosa? What is their function?

Back 41

Valvulae Conniventes or Folds of Kerckring; Folds extend circularly most of the way around the intestine especially well developed at the Duodenum and Jejunum..function is to increase surface area of the absorptive mucosa about threefold

Front 42

Villi

Back 42

Increase absorptive mucosa by 10-fold

Front 43

Each Villus has brush border

Back 43

Brush border consists of up to 1000 microvilli, increases the surface area by another 20-fold

Front 44

Functional Organization of Villus

Back 44

Central Lacteal surrounded by blood capillaries

Front 45

Absorption of water by Osmosis

Back 45

Water is transported through the intestinal membrane entirely by diffusion and obeys usual laws of osmosis

Front 46

Aldosterone effects on intestines?

Back 46

Within 1 to 3 hours aldosterone causes increased activation of the enzyme and transport mechanisms for all aspects of sodium absorption by the intestinal epithelium. Also causes secondary increases in absorption of Cl, Water and other substances.

Front 47

Absorption of Chloride ions in the Small Intestine in the upper part of the small intestines?

Back 47

Cl absorption is rapid and mainly by diffusion (absorption of sodium ions through the epithelium creates electronegativity in the chyme and electropositivity in the paracellular spaces between teh epithelial cells).

Front 48

Absorption of Chloride ions in the Small Intestine in the ileum and large intestine?

Back 48

Chloride is absorbed across the brush border membrane chloride bicarbonate exchanged; chloride exits teh cell on the basolateral membrane through chloride channels.

Front 49

Bicarbonate in the upper small intestines?

Back 49

Large quantities of bicarbonate reabsorbed due to large amounts be secreted in the duodenum in both pancreatic secretion and bile.

Front 50

How is Bicarbonate ion absorbed?

Back 50

Bicarbonate absorbed in an indirect way: when sodium ions are absorbed moderate amounts of hydrogen ions are secreted into the lumen of the gut in exchange for sodium. These hydrogen ions in turn combine with the bicarbonate ions to form Carbonic Acid (H2CO3) which then dissociates to form Water and Carbon Dioxide. Water remains in Chyme while CO2 is absorbed in blood and expired in lungs. This is known as an "active absorption of bicarbonate ions"

Front 51

Secretion of Bicarbonate Ions in the Ileum and Large intestine

Back 51

Epithelial cells of Villi in ileum and large intestine can secrete bicarbonate ions in exchange for absorption of Chloride ions...allows epithelium to neutralize acid products formed by bacteria

Front 52

Cholera

Back 52

Toxins of Cholera and other types of diarrheal bacteria can stimulate epithelial fold excretion of sodium chloride and water into the intestinal lumen so greatly that secretion overcomes absorption. Can cause water loss of 5 to 10 liters of water and NaCl as diarrhea each day.

Front 53

Cholera outcome?

Back 53

Within 1 to 5 days, many severely affected patients die from this loss of fluid alone

Front 54

Mechanism of Cholera Toxin

Back 54

Initiated by entry of cholera toxin into epithelial cells, stimulating formation of excess cyclic adenosine monophosphate, which opens a tremendous amount of Chloride channels, allowing chloride to flow rapdily out of the cell. Also with this action there is activation of the sodium pump which pumps sodium into the lumen. NaCl pull water into lumen as well.

Front 55

Cholera Treatment

Back 55

Life can be saved by administration of tremendous amounts of sodium chloride solution

Front 56

Calcium Absorption

Back 56

Calcium ions are actively absorbed into the blood especially from the duodenum and the amount is exactly controlled to supply the daily need of the body for calcium

Front 57

PTH and Vitmain D effect on Ca Absorption?

Back 57

PTH secreted by the parathyroid glands, activates Vitamin D, and activated Vitamin D in turn greatly enhances Calcium absorption.

Front 58

Iron Absorption

Back 58

Actively absorbed in the small intestines. (Discussed in chapter 32)

Front 59

Potassium, Magnesium, Phosphate absorption?

Back 59

Potassium, Magnesium, and Phosphate are actively absorbed through intestinal mucosa, in general monovalent ions are absorbed with ease and in great quantities. Bivalent ions are normally absorbed in only small amounts

Front 60

Absorption of Carbohydrates

Back 60

Aborption of carbohydrates is mainly in the form of monosaccharides only a small fraction are absorbed as disaccharides

Front 61

Most abundant of absorbed monosaccharides?

Back 61

Glucose, usually accounting for more than 80% of carbohydrate calories absorbed. Remaining 20% are galactose and fructose

Front 62

Through what mechanism are monosaccharides absorbed?

Back 62

Through active transporter

Front 63

Glucose transporter?

Back 63

Glucose is transported by a sodium co-transport, in the absence of Sodium transport in the intestines virtually no glucose can be absorbed

Front 64

Mechanism of Sodium-Glucose Co-Transporter

Back 64

Initially there is an active transport of sodium through the basolateral membrane of the intestinal epithelial cell that provides the eventual motive force for moving glucose through the membrane by Secondary Active-Transport

Front 65

Transport of Galactose

Back 65

Galactose, like glucose undergoes Secondary Active-Transport through sodium Co-Transporter

Front 66

Transport of Fructose

Back 66

Does not occur through Secondary Active Transport, but rather by Facilitated Diffusion, much of fructose entering cell becomes phosphorylated and then converted to glucose

Front 67

Rate of Transport of Fructose

Back 67

Because fructose is not co-transported with sodium, its overall rate of transport is only about one half that of glucose or galactose

Front 68

Absorption of Proteins as Dipeptides, Tripeptides and Amino Acids

Back 68

Most are transported through Secondary Active Transport with Sodium, a few are transported by a special membrane transport protein as facilitated diffusion.

Front 69

Absorption of Fats

Back 69

Lipids are membrane soluble and therefore leave the micelles and difuse directly through the membrane of the intestines

Front 70

Fat Absorption with and without Micelles

Back 70

In the presence of an abundance of Bile micelles about 97% of fat is aborbed in the absence only 40-50% can be absorbed

Front 71

Fats after Absorbed

Back 71

Fatty acids and Monoglycerides are taken up by the cell's Smooth ER where they are mainly used to form new Triglycerides that are subsequently released in the form of Chylomicrons to upward through the thoracic lymph duct into the circulating blood

Front 72

Direct Absorption of some Fatty Acids into the Portal Blood

Back 72

Small quantities of short and medium chain fatty acids are absorbed directly into the portal blood bypassing the Smooth ER and the Lymph

Front 73

Where does most of the absorption in the large intestine occur?

Back 73

The proximal one half of the colon, giving it the name of "Absorbing Colon", second half is principally for feces storage known as "Storage Colon"

Front 74

Large intestines Maximum Absorption Capacity

Back 74

Large intestines can absorb 5 to 8 liters of fluid and electrolytes a day, excess appears in feces as diarrhea

Front 75

Bacteria Action in Colon

Back 75

Numerous bacteia found in colon, bacterial activity results in Vitamin K, Vitamin B12, Thiamine, Riboflavin and various gases that contribute to flatus in teh colon including CO2, H2, and CH4

Front 76

Importance of Bacteria creating Vitamin K

Back 76

Bacteria formed Vitamin K especially important because amount of Vit K in food is normally insufficient to maintain adequate clotting

Front 77

Composition of Feces

Back 77

Normally 3/4s water and 1/4 Solid matter: 30% Dead Bacteria, 10-20% Fat, 10-20% inorganic matter, 2-3% protein, and 30% undigested roughage

Front 78

What causes the brown color of feces?

Back 78

Stercobilin and Urobilin, derivatives of bilirubin.

Front 79

What causes the odor of feces?

Back 79

Odor causes principally by products of bacterial action, odoriferous products include: indole, skatole, mercaptans, and hydrogen sulfide