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Physiology > GIT 4 > Flashcards

GIT 4 Flashcards

1
Q

Differentiate digestion and absorption

A

Digestion- the enzymatic breakdown of food to components that can be absorbed

Absorption- the movement of nutrients, salts, and water across the GI epithelium into blood lymph

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2
Q

Describe intake of carbs in a western diet.

A

Intake of carbs(western diet)(250-800 g/day)

60%-polysaccharides (starch)

30%- sucrose, 10%- lactose (disaccharides)

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3
Q

Describe starch

A

Storage form of CHO

Plant-amylose(linear ) & amylopectin (branched)
Amylose-straight chain glucose polymer, glucose residues with a-1,4 linkages

 Amylopectin- branched glucose polymer a-1,4 linkages & a-1,6 linkages
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4
Q

What is the storage form of CHO in animals?

A

Glycogen

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5
Q

What is dietary fiber?

A

Bonds not broken by human enzymes in the small intestines. These carbohydrates cannot be absorbed and serve to increase fecal bulk. Increased bulk motility and increases frequency of defecation

  • soluble
  • insoluble
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6
Q

Describe disaccharides, oligosaccharides and monosaccharides

A

Disaccharides and oligosaccharides- derived from the breakdown of starch and other daily substrates

Monosaccharides- glucose, fructose and galactose are trabsported across the apical and basoateral membranes of small intestine enterocytes

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7
Q

What is the importance of dietary fiber?

A

Fiber is the non-digestible carbohydrate entities

Available polysaccharides (starch)- largely digestible in small intestines

  • Unavailable polysaccharides(non starch)- dietary fiber of plant origin (fruits, vegetables, cereals)
    • dietary Fiber composed of:
      • fibrous(cellulose and hemicellulose)
      • viscous (pectins and gums) forms
      • Lingins which are part of dietary fibers are aromatic polymers not carbohydrates and excreted
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8
Q

Colonic bacteria have enzymes that can degrade fiber….

A

Colonic bacteria have enzymes that can degrade fiber. Fiber is a major energy source for these bacteria

  • Dietary fiber affects innate hut immune response
  • lowers the incidence of several major diseases including coronary heart disease, diabetes mellitus, and colorectal cancer
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9
Q

What is lactose intolerance?

A
  • Absent brush border lactase
  • Unable to hydrolyze lactose and glucose and galactose for absorption
  • Non absorbed lactose and H2O remain in the lumen of the GI tract and cause osmotic diarrhea
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10
Q

How are monosaccharides absorbed in the small intestine ?

A

Polysaccharides are broken down by enzymes into simple monosaccharides

  • from microvilli of intestinal wall
  • Monosaccharides are hydrophilic transporters are needed to move these nutrients across these membranes

Na-K ATPase pump keeps intracellular Na low, maintaining the gradient to be used as a driving force

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11
Q

What is the function of apical membrane in cab absorption in the small intestine?

A

Glucose and galactose are actively cotransported with Na+ into the epithelial cells (SGLT1), secondary active transport

Fructose is transported exclusively by facilitated diffusion (GLUT5)

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12
Q

What is the function of basolateral membrane in the absorption of carbohydrates in the small intestine?

A

Glucose and galactose is transported by facilitated diffusion (GLUT 2)

Fructose is transported exclusively by facilitated diffusion (GLUT 2)

Most absorption in first 20% of small intestine

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13
Q

What is the most common starch form?

A

Starch is a polymer of glucose that exists in 2 forms. a-amylose is the minority form, consisting of long unbranched chains of a-1,4 linked glucose residues. The more common form of starch is a-amylopectin, which has numerous a-1,6 linked branch points.

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14
Q

Where is glycogen stored?

A

In the liver and skeletal muscle also has many a-1,6 linked branch points.

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15
Q

When does luminal digestion begin ?

A

Luminal digestion of starch begins with salivary amylase and is completed by pancreatic amylase. Both have pH optimal near 7. Salivary amylase remains active for a long time in the stomach within a food bolus, where it is buffered from gastric acidity. Amykasase breaks a-1,4 linkages at random to produce oligosaccharides of various lengths (known as DEXTRINS) many of which contain the a-1,4 linked oligosaccharides. Isomaltase is notable as the enzyme that breaks most of the a-1,6 branch points.

The remaining enzymes have primary substrates that are easy to predict from their names. In humans sucrose-isomaltase exists as a complex with 2 distinct subunits for each type of enzyme activity. All the sugars ultimately hydrolyze to one or more of the monomers, glucose, galactose and fructose (N.B. Trehalose is a a-1,1 linked dimer of glucose )

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16
Q

How does glucose uptake occur?

A

By secondary active transport. An inward Na+ gradient is maintained by the Na+/K+- ATPase in the basolateral membrane. Glucose entry is linked to 2 Na+ ions. This mechanism means that even very low concentrations of glucose in the lumen will not escape absorption

Galactose competes with equal affinity at the same carrier (SGLT1). SGLT-1 concentrates glucose/galactose in the cell and allows it to leave by facilitated diffusion using the carrier GLUT-2. The equivalent of over 20 pounds of sucrose could be transported via this mechanism this day

Fructose is not reabsorbed with Na+, but has its own facilitated diffusion process at the brush border membrane (GLUT 5). Once in the cell, fructose is also able to utilize the broad specificity carrier GLUT-2 in the basolateral membrane

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17
Q

Epidemiological data show that a diet high in dietary fiber (bulk) lowers the incidence of…

A

Several major diseases including coronary heart disease, diabetes mellitus, and colorectal cancer. Fiber consists of cellulose, hemicellulose, lignin, pectin, gums, and algal polysaccharides, which remain undigested. Low fiber diets are also associated with inactive colonic motility and infrequent stools

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18
Q

The primary bulking agents…

A

Are non starch polysaccharides. Resistant starch describes starch and products of its small intestinal digestion that arrive in the colon. It exists for various reasons, including chemical structure, cooking of food, chemical modification and how well food is chewed. Both fiber and resistant starch are subject to bacterial fermentation reactions in the colon. Short chain fatty acids (SFCAs) are important products of bacterial fermentation in the colon. The main SCFA’s are acetate, propionate and butyrate. SCFA’s are weak acids and there to prevent overgrowth of bacteria. A large proportion of SCFA are absorbed, constituting a significant source of calories in high fiber diets. SCFA’s are under greater scrutinity as. Protective agents since they increase colonic blood flow and help to maintain normal colonocyte phenotype

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19
Q

What causes flats?

A

Bacterial ferment reactions making gases including H2, CH4(methane), and CO2, and H2S

20
Q

How much proteins do we need a day?

A

50 g to supply all essential AA’s

21
Q

What is the optimum pH for pepsin?

A

1-3

22
Q

What does trypsin and chymotrypsin secreted from?

A

From pancreas(SI)(endopeptidases)

23
Q

What enzymes turn protein to peptides?

A

Pepsin, trypsin and chymotrypsin

24
Q

What enzymes are responsible for peptides to amino acids ?

A

Exopeptudases

Carboxypeptidases (pancreas)

Aminopeptidases (small intestine villi)

25
Q

Summarize how amino acids are absorbed

A

Active co-transport with Na+

Short chains alone using specific transporters

All in early stages of small intestine

26
Q

How can entire proteins be absorbed?

A

Endo and exocytosis to enter bloodstream

-Especially important in infants- Allows mothers antibodies to be transferred

27
Q

Summarize peptide absorption

A

Proteins become peptides—> forms di- and tripeptides cotransport with proton

  • Amino acids cotransport with Na+
  • Small peptides are carried intact across the cell by transcytosis

Peptidases convert peptides to amino acids within the cell before being transported to the liver

28
Q

Luminal digestion starts with PEPSIN in the stomach….

A

Partially digested proteins are acted on by 3 pancreatic enzymes Elastase, chymotrypsin and trypsin. These are defined as Endopeptidases, since they hydrolyze internal peptide bonds. The resulting oligopeptides are then attacked by the ECTOPEPTIDASES, which act from the carboxy terminus to remove one amino acid at a time. Carboxypeptidase B acts on products of Trypsin digestion. The major proteolytic brush border enzyme is AMINOOLIGOPEPTIDASE, though there are several other minor peptidases.

29
Q

What is the role of Kinetic advantage in digesting amino acids?

A

Most of the systems are cotransporters that couple amino acid entry to that of Na+ in the same way as that described for glucose. Others are facilitated diffusion carriers, which are Na+-independent. Surprisingly, an amino acid solution is reabsorbed more slowly than normal protein hydrolysate of equivalent nitrogen content. This phenomenon is called KINETIC ADVANTAGE and can be explained by the existence of carriers for small peptides, particularly dipeptides. As the amino acids carriers become saturated, small peptides continue to be absorbed via proton coupled di and tri peptide carrier molecule. Normal luminal digestion of proteins produces about 40% free amino acids and 60% as small peptides

30
Q

How much fats we need a day?

A

Between 25-160 g/day in Western diet

Most dietary fats consist of triglycerides

31
Q

How are fats digested in the mouth and stomach?

A

In mouth-lingual glands secrete acid lipases that digestsome fats in the optimal pH of 3.5 to 5.5

In stomach- mixing breaks lipids into droplets to increase the surface area for digestion by pancreatic enzymes. Gastric lipase also digests 20% of the total lipid hydrolysis. Most of lipids are digested by pancreatic lipases

32
Q

How are fats digested in the small intestine?

A

In small intestine- alkaline pancreatic lipase (pH 6-8) converts TG’s into Monoglycerols + fatty acids. Bile acids emulsify lipids, increasing surface area

PROBLEM: TG’s are insoluble in water. Lipids need to be micellized by bile salts

33
Q

Explain the digestion and absorption of fats

A
  1. Bile salts from liver coat fat droplets
  2. Pancreatic lipase and colipase break down fats into mono glycerides and fatty acids stored micelles
  3. Monoglycerides and fatty acids move out of micelles and enter cells by diffusion. Cholesterol is transported into cells by a membrane transporter.
  4. Absorbed fats combine with cholesterol and proteins in the intestinal cells to form chylomicrons
  5. Chylomicrons are released into the lymphatic system
34
Q

What is malabsorption ?

A

Syeatorrhea(fatty acid) more than 7g

  • Pancreatic disease-insufficient enzymes to digest the lipid
  • Hypersecretion of Gastrin - low pH inactivating pepsin
  • Ileal resection- depletion of bile acids
  • Reduced intestinal cells - reduced lipid absorption
35
Q

Describe pancreatic lipase

A

This is an Alkaline Lipase with an pH optimum of 6-8. It is present in large excess, such that only 10% of that secreted is typically hydrolyze ingested fats

36
Q

What is the function of Pancreatic lipase?

A

Produces monoglyceride and releases two free fatty acids from the parent triglyceride molecule. It is an unusual enzyme in that it acts at the oil/water boundary, but if it contacts the oil directly it becomes inactivated. Similarly bile salts replace pancreatic lipase from oil/water boundary if the enzyme is present on its own

To prevent this, CO-LIPASE is needed, which acts by displacing a bile salt molecule and providing a binding site for pancreatic lipase. Thus there is a complex interaction between lipase, bile salts and co-lipase

37
Q

What is the function of Phospholipase A2?

A

Which can degrade lecithins

38
Q

What is the function of Carboxyl ester lipase(nonspecific lipase)?

A

Which is able to hydrolyze cholesterol esters

39
Q

More than 7g per day of fatty acids in the stool indicates fat malabsorption…

A

Have many causes related to the different processes in fat assimilation. Emulsification is poor in patients with gastrectomy who have rapid dumping of ingested food into the small intestine. Given the large excess of pancreatic lipase, severe pancreatic dysfunction or duct obstruction is needed to hamper luminal digestion. Patients with hyper-secretion of gastric acid may have an acidic duodenal environment, inhibiting pancreatic lipase

40
Q

How do sodium and chloride enter intestinal cells?

A

Cross intestinal cells by either cellular or paracellular routes

-Tight junctions alter the membrane permeability. Small intestines is very ‘leaky’

  • Na+ moves into intestinal cells down the electrochemical gradient
    • Na+ pumped out the cell by Na-K pump
    • Na+ enters via:
      • passive diffusion
      • Na-glucose or Na-amino acid cotransport
      • Na-H exchange

Cl- follows by:

  • passive diffusion
  • Na-Cl cotransport
  • Cl-HCO3 exchange
41
Q

How is potassium and water absorbed?

A
  • K+ is absorbed by passive diffusion via paracellular route; small intestines
  • K+ is secreted in the colon
  • water absorption is secondary solute absorption
  • In colon, water permeability is reduced
42
Q

How can dehydration be treated?

A

Oral rehydration salts

  • Solutions contain both Na+ and glucose, which is absorbed via SGLT. 1
  • Sets up osmotic gradient for rehydration
43
Q

How are fat soluble vitamins absorbed?

A

Fat soluble A,D , E, K are incorporated into micelles

44
Q

How are water soluble vitamins transported?

A

Na+-dependent co-transported mechanisms

45
Q

Where is vitamin B12 absorbed?

A

In the ileum

Needs intrinsic factor

Deficiency created pernicious anemia

46
Q

Describe Calcium

A

Depends in the presence of active vitamin D 1,25- dihydroxycholecalciferol (kidney)

Induces the synthesis of intestinal Ca2+ binding protein calbindin D28K

-Deficiency results in rickets-children and osteomalacia- adults

47
Q

What are the effects of infant respiratory distress syndrome?

A

Increased work of breathing

  • Atelectasis and hyper expanded regions of lung
  • Poor gas exchange

Physiology (36 decks)

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