4: Hsf B4: Digestion And Absorption

Front 1

What are the three major components of food?

Back 1

Carbs, fats, proteins

Front 2

What is the makeup of sucrose? Example?

Back 2

Disaccharide, cane sugar

Front 3

What are starches?

Back 3

Carbohydrates, large polysaccharides

Front 4

What is cellulose?

Back 4

Carbohydrate that can't be digested

Front 5

What are the minor components of carbohydrates?

Back 5

Amylose, glycogen, alcohol, lactic acid, pyruvic acid, pectins, dextrans

Front 6

What are triglycerides?

Back 6

Neutral fats

Front 7

What are the minor components of fats? (3)

Back 7

Phospholipids, cholesterol, cholesterol ester

Front 8

What are proteins?

Back 8

Long chains of amino acids

Front 9

What is hydrolysis?

Back 9

Splitting of a compound into fragments by the addition of water. Hydroxyl group is in one fragment, hydrogen atom in other.

Front 10

All three food groups are digested by the same basic process. What is this basic process and where does the difference lie?

Back 10

Hydrolysis. Difference is in the enzymes that catalyze the reaction.

Front 11

Why do large food molecules need to be digested before they can be absorbed?

Back 11

They're usually insoluble and too large for diffusion across membranes into the blood

Front 12

What are the two advantages of digesting food into smaller molecules?

Back 12

Usually soluble, small enough for absorption into the blood/later assimilation into tissues

Front 13

What are carbohydrates broken down into when they're digested?

Back 13

Monosaccharides

Front 14

What are proteins broken down into when they're digested?

Back 14

Small peptides and amino acids

Front 15

What are fats broken down into when they're digested?

Back 15

2 monoglycerides (-> glycerol) and fatty acids

Front 16

What are the two types of digestion, where do they occur, and what enzymes are involved?

Back 16

1) Luminal digestion - lumen of GI tract, enzymes from salivary gland, stomach, pancreas. 2) Membrane/contact digestion - enzymes from brush border of enterocytes (intestinal absorption cell)

Front 17

What digestive enzymes are secreted from the salivary glands? (2)

Back 17

Alpha amylase, lingual lipase

Front 18

What digestive enzyme is secreted from the stomach?

Back 18

Pepsin

Front 19

Where is amylase secreted from?

Back 19

Pancreas

Front 20

Where is trypsin secreted from?

Back 20

Pancreas

Front 21

Where is enterokinase secreted from?

Back 21

Intestinal mucosa

Front 22

Where is chymotrypsin secreted from?

Back 22

Pancreas

Front 23

Where is sucrase secreted from?

Back 23

Intestinal mucosa

Front 24

Where is maltase secreted from?

Back 24

Intestinal mucosa

Front 25

Where is carboxypeptidase elastase secreted from?

Back 25

Pancreas

Front 26

Where is lactase secreted from?

Back 26

Intestinal mucosa

Front 27

Where is lipase-colipase secreted from?

Back 27

Pancreas

Front 28

Where is phospholipase A2 secreted from?

Back 28

Pancreas

Front 29

Where is cholesterol esterase secreted from?

Back 29

Pancreas

Front 30

Where is alpha-dextrinase secreted from?

Back 30

Intestinal mucosa

Front 31

Where is amino-oligopeptidase secreted from?

Back 31

Intestinal mucosa

Front 32

Where is dipeptidase secreted from?

Back 32

Intestinal mucosa

Front 33

What enzymes digest starch and where do they come from?

Back 33

1) Alpha amylase in saliva (5% in mouth, 40% in stomach) 2) Pancreatic amylase in small intestine 3) Final digestion at brush border

Front 34

Where does lactose and sucrose digestion occur?

Back 34

Only at the brush border

Front 35

1) What is a key feature of the absorptive cells in the small intestine?
2) What are the three main elements in microvilli?

Back 35

1) Brush border with microvilli
2) Lacteal, venule, artery

Front 36

Out of the salivary gland, pancreas, and intestinal mucosa, where are:

1) Starches digested?
2) Proteins digested?
3) Fats digested?

Back 36

1) Salivary glands, stomach, pancreas, intestinal mucosa
2) Salivary glands, pancreas, intestinal mucosa
3) Salivary glands, pancreas only

Front 37

What enzyme is unique to the intestinal mucosa?

Back 37

Enterokinase

Front 38

1) What enzyme begins the digestion of starch? What digests it in the pancreas?
2) Where is starch digested?

Back 38

1) Alpha amylase in saliva in mouth, pancreatic amylase in pancreas
2) Mouth, stomach, lumen, small intestine. 5% in mouth, 40% in stomach by ptyalin, lumen of small intestine by pancreatic amylase, final digestion at brush border

Front 39

What are lactose and sucrose and where does their digestion take place?

Back 39

Disaccharides - at brush border ONLY.

Front 40

Ptyalin:

1) What is it?
2) How much starch does it digest?
3) What does it hydrolyze starch into?
4) How long is it active in the stomach?

Back 40

1) Alpha amylase
2) 20-40%
3) Maltose (disaccharide), glucose polymers 3-9 long
4) 1 hr, until pH <4

Front 41

Pancreatic amylase:

1) How much starch does it hydrolyze?
2) How does it compare to salivary amylase?
3) When does it complete digestion?

Back 41

1) 50-80% (more than mouth)
2) It's heartier and stronger
3) 15-30 minutes

Front 42

Describe the breakdown of:

1) Starches in general
2) Lactose
3) Sucrose

Back 42

1) Starches (ptyalin, pancreatic amylase) -> maltose/3-9 glucose polymers (maltase + alpha dextrinase @ brush border -> glucose (80%)

2) Lactose (lactase @ brush border) -> galactose (10%), glucose

3) Sucrose (sucrase @ brush border) -> fructose (10%), glucose

Front 43

1) Where does final digestion of carbohydrates occur?
2) What are the integral membrane proteins there?
3) What are the final products of digestion of carbs, and what % of the total product do they make up?

Back 43

1) Intestinal microvilli brush border
2) Maltase, lactase, sucrase
3) Water soluble monosaccharides - Glucose (80%, from breakdown of maltose, lactose, sucrose), galactose (10%, from breakdown of lactose), fructose (10%, from breakdown of sucrose)

Front 44

1) What two substances make up lactose?
2) What two substances make up sucrose?

Back 44

1) 1 galactose + 1 glucose
2) 1 fructose + 1 glucose

Front 45

1) What enzymes are responsible for digestion of proteins?
2) What are the three locations where digestion of proteins occurs, and what are the specific names of the proteases there?

Back 45

1) Proteases
2) GI lumen: stomach - pepsin, small intestine - endopeptidases, exopeptidases

Brush border - oligopeptidases, dipeptidases

Cytoplasm of mucosal cells - dipeptidases

Front 46

1) What is the first proteolytic enzyme that ingested proteins encounter? What cells secrete it?
2) When is this proteolytic enzyme inactive, and what activates it?
3) What is this enzyme important for, and what % of protein digestion does it do?

Back 46

1) Pepsin, secreted in pepsinogen form by chief cells of gastric gland.
2) Inactivate above pH 5.0 (in pepsinogen form), converted to pepsin (active form) by acidic pH (1.8-3.5) and pepsin (autocatalytic)
3) Digestion of collagen, 10-20% of protein digestion

Front 47

Enterokinase:

1) What is another name for it?
2) What is its function?
3) What secretes it and when is it secreted?
4) Is it a kinase?
5) What is the significance of enteropeptidase only being secreted in the small intestine?

Back 47

1) Enteropeptidase
2) Activates trypsinogen, converts it to trypsin
3) Crypts of Lieberkuhn in the duodenum's gland when food enters
4) NO!
5) Proenzymes aren't activated until they reach the small intestine

Front 48

What is the function of trypsin? What is special about it?

Back 48

Activates other proenzymes. It is autocatalytic (like pepsin).

Front 49

How quickly are proteolytic enzymes activated and destroyed? What destroys these proteolytic enzymes?

Back 49

Very quickly. Proteolytic enzymes digest themselves.

Front 50

1) Where are endopeptidases and exopeptidases found?
2) What is the difference between how they cleave?

Back 50

1) Small intestine
2) Endopeptidases cleave in the middle of the peptide chain, and they're specific for certain amino acids. Exopeptidases remove amino acids from the ends of polypeptide chains.

Front 51

What would happen if an extremely small amount of trypsinogen was converted to trypsin in the pancreas?

Back 51

It would digest the pancreas.

Front 52

1) What does trypsin inhibitor do?
2) What happens if the pancreas is damaged? What disease is caused?

Back 52

1) ACTIVELY prevents activation of trypsinogen in secretory cells, acini, ducts of pancreas
2) Damaged pancreas overwhelms the amount of inhibitor, you get activation of trypsinogen in pancreas. You get acute pancreatitis

Front 53

Why do you need trypsin inhibitor? Why isn't it enough to just have inactive trypsin?

Back 53

Just a small amount of trypsin sets off a cascade that activates trypsinogen that cleaves more trypsin, so it's just a bad cycle that needs to be strictly regulated.

Front 54

1) Where does a majority of protein digestion occur?
2) Describe the complete breakdown of proteins into amino acids, describing all the enzymes that are needed to break it down into its components

Back 54

1) Upper small intestine
2) Proteins (pepsin) -> polypeptides (trypsin, chymotrypsin) -> small polypeptides, AA (carboxypeptidase) -> single A.A. from carboxy ends of polypeptides OR small peptides, dipeptides, tripeptides.

Front 55

During protein digestion, how many single A.A.s are produced from protein vs. polypeptides/tripeptides/dipeptides?

Back 55

Very little single A.A's, because endopeptidases cleave at certain specific AAs and they usually aren't single and adjacent to each other.

Front 56

Describe the final stages of protein digestion (5 steps)

Back 56

1. Peptidases protrude through membrane of microvilli
2. Aminopolypeptidases/dipeptidases break down proteins into dipeptides, tripeptides, amino acids
3. Dipeptides/tripeptides/amino acids transported through the membrane
4. Cytosolic peptidases break them down farther
5. Everything turned into AA in minutes, pass through enterocyte and into blood.

Front 57

Where does the final conversion of proteins into AA occur?

Back 57

In the cytoplasm.

Front 58

1) Where does all of fat digestion occur?
2) What are the two basic steps of lipid digestion?

Back 58

1) Small intestine
2) a) Emulsification: large dietary triglycerides/fat (bile + agitation) -> emulsified fat b) Enzymatic digestion: emulsified fat (pancreatic lipase) -> fatty acids and 2-monoglycerides - both *diffuse* into enterocyte

Front 59

What do bile salt micelles act as?

Back 59

Transport medium for monoglycerides/fatty acids

Front 60

GI absorption - how much is absorbed?

1) Fluid
2) Sodium
3) Carbs/proteins
4) Fat
5) Where does a majority of absorption occur?
6) How many ml/day does the small intestine absorb vs. the colon?

Back 60

1) 8 L of fluid
2) 30 g
3) .5 kg
4) 1 kg
5) Small intestine
6) Small intestine = 8500 ml/day, colon = 400 ml/day

Front 61

What 3 things increase absorption in the small intestine, and by how much does each increase the SA? What is the total SA increase?

Back 61

1) Folds of Kerckring - 3x

2) Villi - 10x

3) Microvilli - 20x

1000x total increase in surface area.

Front 62

1) What makes water move inside or out of the gut lumen?
2) What happens if you have hyptonic chyme?
3) What happens if you have hypertonic chyme?

Back 62

1) Diffusion
2) It's dilute, water is absorbed
3) High concentration of ions - water enters intestine lumen

Front 63

1) Why is water secreted by the small intestine?
2) What are the two processes that establish an osmotic gradient?

Back 63

1) Lots of water is needed for digestion
2) a) Increased osmotic pressures from digestion of foodstuffs b) Crypt of Lieberkuhn cells actively secrete electrolytes that lead to water secretion

Front 64

1) What is water secretion by crypt cells driven by?
2) Describe the process

Back 64

1) Chloride secretion
2) cAMP activates Cl- channels, Na+ follows electrical gradient, H20 moves along osmotic gradients

Front 65

What are cyclic AMP dependent chloride channels also known as? Why?

Back 65

Cystic fibrosis transmembrane conductance regulator (CFTR). Mutations in ion channel cause cystic fibrosis, failure to produce sweat, digestive juices, mucous.

Front 66

1) How much sodium do you need to recover from intestinal secretions a day, and why?
2) How is sodium absorbed?
3) What stimulates Na transport mechanism during dehydration?
4) What happens to Cl- when Na+ is absorbed?

Back 66

1) 30 grams/day, rapidly absorbed to help absorb sugar and AA
2) *Actively transported across basal and basolateral membranes*, intracellular levels fall, sodium moves in through brush border, osmotic gradient brings water in through epithelial junctions
3) Aldosterone
4) Cl- absorption by diffusion, follows sodium

Front 67

What happens to cause absorption of bicarbonate ions?

Back 67

1) You bring Na+ into cell, secrete large amounts of H+ into lumen.
2) H+ binds with bicarbonate in secretions to form carbonic acid.
3) Carbonic anhydrase dissociates carbonic acid into water and CO2. 4) Water stays behind and CO2 enters the bloodstream.

Front 68

1) What system is used to absorb carbohydrates?
2) What are carbs absorbed as? What % of each is present?
3) How are glucose and galactose taken in?
4) How is fructose taken in?

Back 68

1) Active transport
2) Monosaccharides - glucose 80%, galactose 10%, fructose 10%
3) Sodium co-transport
4) Facilitated diffusion

Front 69

1) Where is Na+ transported in an epithelial cell in the small intestine, and by what process? What happens to the level of Na+ inside the cell?
2) How does glucose get into the cell?
3) How does galactose get into the cell?
4) How does fructose get into the cell and what is it converted to intracellularly?

Back 69

1) Active transport across basolateral membrane, depletes Na+ inside
2) Na+ transport is coupled to protein and glucose movement across the apical membrane
3) Same way - coupled with Na+ transport
4) Diffusion - glucose intracellularly

Front 70

Lactose intolerance:

1) Symptoms
2) Diagnosis
3) Cause

Back 70

1) Cramps, bloating, diarrhea
2) Feed lactose + look for glucose in plasma
3) Absence of brush border lactase

Front 71

How do you treat someone who has a lack of glucose/galactose carrier?

Back 71

Feed fructose

Front 72

1) What are the two ways amino acids can get into the body?
2) How does di and tri-peptide transport into the body differ from AA? Where are they hydrolyzed to AA?

Back 72

1) Secondary active transport (Na+ dependent), facilitated diffusion
2) Different than AA - absorbed faster, hydrolyzed to AA in cytoplasm

Front 73

Where do sugars, amino acids, and electrolytes go after being absorbed across the small intestine and colon?

Back 73

Hepatic portal circulation -> liver

Front 74

Map the conversion/route of triglycerides into the body.

Back 74

1) Triglyceride in, broken down into fatty acid/2-monoglyceride in duodenum
2) FA/monoglyceride passively diffuses into enterocyte, repackaged into triglyceride in SER
3) Triglyceride goes to Golgi, join cholesterol + phospholipid to make CHYLOMICRON
4) Exocytosed into basolateral space, into lacteals and lymph vessels
5) Short chain fatty acids (<12 C) are slightly soluble, diffuse across basolateral membrane into capillaries, go to liver for processing

Front 75

1) What does the large intestine absorb?
2) What does the proximal 1/2 of the colon do?
3) Distal 1/2?

Back 75

1) Salt and water
2) Proximal half reabsorbs
3) Distal half = storage colon

Front 76

1) What is the third leading cause of death worldwide?
2) What are the common causes?

Back 76

1) Diarrhea
2) Increased secretion/motility of large or small intestine. Infectious diarrhea due to viruses, bacteria, protozoa or ulcerative colitis

Front 77

1) What does vibrio cholera cause and how?
2) Prognosis
3) Treatment

Back 77

1) Cholera toxin binds GM1 ganglioside receptor, triggers endocytosis of toxin, toxin cleaved, activates Gsalpha subunit of GPCR through ADP ribosylation, locks G protein in GTP bound form. Stimulates adenylyl cyclase, cAMP -> activates cystic fibrosis transmembrane conductance regulator , stimulates secretion of water/electrolytes from crypt cells, lose 10L+ fluid/day
2) Untreated, 50% will die. Treated, 1% will die
3) Oral rehydration w/ glucose + solutions (glucose helps w/ reabsorption of sodium, water)

Front 78

What are the three lipases associated with digestion of dietary lipids?

Back 78

1) Pancreatic lipase (triglyceride -> 2-monoglyceride and FFA)

2) Cholesteral ester hydrolase (cholesterol ester -> cholesterol + fatty acid)

3) PLP A2 (lecithin -> lysolecithin)

Front 79

1) What does digestion do?
2) What does absorption do?
3) Once things are in the blood, what do they do?

Back 79

1) Break down large food molecules into smaller molecules
2) Uptakes molecules into the blood
3) Taken up by tissues and then assimilated to be used