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GIGU test! > Digestion and absorption of the Gastrointestinal Tract > Flashcards

Digestion and absorption of the Gastrointestinal Tract Flashcards

1
Q

Characteristics of Lactose intolerance

A

Failure in ability to digest dairy carbohydrates

Brush border lactase enzyme activity is deficient or absent resulting in undigested and unabsorbed lactose

Low lactase activity: 75 percent oflactose can pass unabsorbed through the small intestine

Lactose converted to SCFAs and hydrogen gas thus producing acetate, butarate, and propionate

  • remains in lumen, holds H20 in lumen leading to osmottic diarrhea
  • Ferments into methane and H+ gas
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2
Q

What are the major sugars in human diet?

A

Primary: Sucrose, lactose, starch

Secondary: amylose, glycogen, EtOH/alcohol, lactic acid, pyruvic acid, pectins, destrins

Cellulose: no digestive enzymes

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3
Q

where does carbohydrate digestion occur? what enzymes are important in each location?

A

Mouth:

  • begins breaking down some starch
  • Salivary amylase (enzyme)
  • starch into maltose and 3-9 polymers of glucose

Small intestine:

  • most starch is broken down here
  • Pancreatic amylase
  • starch into maltose and 3-9 polymers of glucose
  • many disaccharides reach small intestine tract
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4
Q 
what does each compound break down into and what enzyme does it:
maltose
trehalose
lactose
sucrose
maltotriose
a-dextrins
A

Maltose: maltase
-glucose + glucose

Trehalose: trehalase
-glucose + glucose

Lactose: lactase
-glucose + galactose

Sucrose: sucrase
-glucose+ fructose

Maltotriose: sucrase
-glucose

a-dextrins: a-dextrinase
-glucose

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5
Q

what are the three transpors imporatant in absorption from the lumen of carbohydrates, and how does it leave the epithelial cell and enter the blood?

A

Na+/K+ ATPase creates concentration gradient to help facilitate diffusion

Secondary active transport for glucose and galactose (SG:T1)
-transports glucose and galactose from the lumen

Facilitated diffusion for fructose is GLUT5

all sugars to get into the blood is via GLUT2

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6
Q

How to test for Carbohydrate assimilation problems?

A

Following a fast give 25g of D-xylose and collect urine for next 5 hours

  • D-xylose can be absorbed but not utilized
  • if absorption is abnormal if less than 4g excreted in urine

other breath tests:

  • methane
  • isotopically labelled CO2 from different sugars
  • sucrose breath test
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7
Q

what are 5 different protein assimilation disorders?

A
  • chronic pancreatitis
  • Congenital trypsin absence
  • cystinuria
  • hartnup disease
  • cystic fibrosis
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8
Q

what is deficient in chronic pancreatitis?

A

deficiency in pancreatic enzymes: lack of proteases especially trypsinogen
-important for protein absorption

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9
Q

what is deficient in congenital trypsin absence?

A

absence of trypsin, all pancreatic enzymes are gone

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10
Q

what is deficient in cystinuria?

A

defect in the transporter (S:C3A1) or absence of di-basic AA transporter (SLC7A9)
-cysteine, lysine, arginine, ornithine are not reabsorbed at the proximal tubule

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11
Q

what is deficient in hartnups disease

A

Cannot absorb neutral AA
-autosomal recessive genetic disorder (SLC6A19) gene or a sodium dependent neutral amino acid transporter B(0)AT1)

symptoms:

  • diarrhea
  • mood changes and neurological problens
  • red, scaly skin
  • photosensitivity
  • high excretion of neutral amino acids (tryptopan)
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12
Q

what is deficient in cystic fibrosis?

A

CFTR gene that is a regulated Cl- channel on apical membrane of duct cells

  • pancreas problems persist
  • loss of HCO3- secretion
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13
Q

what enzymes are found at the stomach that break down protein?

A

Pepsin is secreted as pepsinogen, activated at ow pH

  • responsible for 10-20% of protein breakdown
  • not essential for protein digestion
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14
Q

what enzymes are found at the pancreas that break down protein? how are they released and how are they activated

A

Pancreatic enzymes are secreted as zymogens that are activated by either enterokinase (trypsinogen) or trypsin its self

Mostly breaks proteins down into di- and tripeptides, some amino acids

Enzymes: trypsin, chymotrypsin, carboxypeptidase, elastase

Trypsin and chymotrypsin break down small peptides

Carboxypeptidase cleaves AA into carboxyl ends

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15
Q

what enzymes are found at the small intestine that break down protein?

A

Enzymes: aminopokypeptidase, dipeptidases

amino acids, di and tri peptides are absorbed into enterocytes

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16
Q

How are proteins absorbed into the epithelial cell of the small intestine? how are peptides absorbed?

A

Seperated Na+ co-transporters for each amino acid type:

  • Neutral
  • acidic
  • basic
  • Imino

they are facilitated through diffusion based on the Na+/K+ ATPase estab;ishing a Na gradient

also the di- and tri-peptides are abosrbed via H+ cotranporters
-peptidase inside the cell will cleave to amino acids

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17
Q

How are proteins and peptides tranported from the epithelial cell into the blood?

A

Seperate facilitated diffusion mechanisms for each amino acid type:

  • neutral
  • acidic
  • basic
  • imino

same with dipeptides and tripeptides

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18
Q

Problems with Fat digestion and absorption: Celica Sprue characteristics?

A

Autoimmune disorder with hereditary component
-antibodies develop against a glutent component gliadin leading to destruction of small intestine villi and hyperplasia of the intestinal crypts

Malabsorption related to deficiencies in folate, iron, calcium, vitamins A, B12, and D

prevalence: most common in caucasions and persons of european ancestary, and women

GI symptoms: abdomina; pain, constipation, diarrhea, unexplained weith loss, vomiting, nausea, steatorrhea

other symptoms: tingling of extremities, rash, fatigue, seizures, bruising, bone fractures

Management: gluten free diet

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19
Q

what is the significance of the structure of the intestinal mucosa for its function?

A

Lumen surface of small intestine arranged in longitudinal folds of kerckring as well as villi and microvilli all contribute to increased surface area for absorption
-villi longest in duodenum

the Microvillar surface or brush border is site of activity of number of digestive enzymes
-barrie that must be transversed by nutrients, water and electrolytes

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20
Q

what are three cell types of intestinal epithelium?

A

Enterocytes: epitehlial cells

  • digestion,absorption,secretion
  • turnover rate 3-6 days
  • susceptible to irradiation and chemotherapy

Goblet cells: mucus secreting cells
-mucus provides physical,chemical and immunological protection

Paneth cells: part of mucosal defenses against infection
-secret agents that destroy bacteria or produce inflammatory responses

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21
Q

what are routes of passage into the enterocytes?

A

Pinocytosis: base of microvilli, major mechanism for uptake of protein

Passive diffusion: through pores in cell membrane, between cells

Membrane transporters:

  • facillitated diffusion
  • active transport
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22
Q

what are the barriers that solutes moving across enterocyes from the lumen to the blood have to cross?

A
  • Unstirred layer of fluid
  • Glycocalyx
  • apical membrane
  • cytoplasm of cell
  • basolateral membrane
  • basement membrane
  • wall of blood capillary/wall of lymphatic vessel
23
Q

why must fats be emulsified inorder to be digested and what does that?

A

Since fats are insoluble
-TAGS, diglycerides,monoglycerides,fatty acids,cholesterol esters, phospholipids

they must become emulsified inorder to become partially soluble

this is done by bile salts and lectithin

24
Q

Fat digestion and enzymes in the stomach?

A
  • lingual and gastric lipase act on TAGs
  • Dietary proteins perform emulsification here
  • 10% of TAG digestion
  • CCK: time is required, so CCK inhibits gastric emptying for more mixing along with activating gallbladder emptying
25
Q

Fat digestion and enzymes in the small intestine

A

Most digestion of lipids occurs in the small intestine
Bile salts emulsify the lipids
Pancreatic enzymes secreted into small intestine

Pancreatic lipase: secreted as active enzyme

  • inactivated by bile salts without colipase
  • colipase activated by trypsin, once activated displaces bile salts by binding to pancreatic lipase

Cholesterol ester hydrolase (secreted as active enzyme)

  • catalyzes production of free cholesterol
  • hydrolyzes triglycerides to glycerol

Phospholipase A2 (secreted as proenzyme activated by trypsin)

26
Q

5 steps in Fat absorption?

A

1) solubilization by micelles
2) diffusion of micellar content across apical membrane into the epithelial cell
3) Re-esterification
4) chylomicron formation
5) exocytosis of chylomicrons into lymphatics

27
Q

what happens if their is a lack of ApoB?

A

lack of ApoB leads to abetalipoproteinemia meaining there is no lipid absorption

28
Q

Problems with fat digestion and absorption: Pancreatic insufficiency?

A

failure to secrete proper amounts of pancreatic enzymes

29
Q

Problems with fat digestion and absorption: Zollinger-ellison syndrom

A
  • Gastrin secreting tumor of pancreas
  • increased H+ secretion by gastric parietal cells
  • overload of acid into duodenum
30
Q

Problems with fat digestion and absorption: Pancreatitis

A 
Pancreatic enzymes (Trypsin) become activated and self-digest the pancrease
-impaired HCO3 and enzyme secretions
31
Q

what are factors that can cause defects in bile salts?

A

ileal resection: total bile salt pool is reduced
-loss of enterohepatic recirculation of bile salts

small intestinal bacterial overgrowth (SIBO)

  • bacteria deconjugate bile salts, impairing micelle formation
  • severe bacterial overgrowth damages the intestinal mucosa
  • two main causes: too little gastric secretion and small intestine motility
32
Q

what does Small intestine bacterial overgrowth lead too? and how to detect

A

inappropriate growth of bacteria in small intestine, causes pain, bloating, gas, and diarrhea/constipation

can result in malabsorption issues, steatorrhea, vitamin/mineral deficiency

changes in pH result in improper activity of lipase enzymes in small intestine

Breath test: detect methane and hydrogen

33
Q

what vitamins are fat soluble and what are water soluble?

A

Fat soluble vitamins: A, D, E, K
-same absorption mechanisms as lipids

Water-soluble vitamins (B and C)
-most are absorbed via Na+ dependent cotransport, except Vitamin B12 forms complexes with other proteins to be absorbed: need R proteins and intrinsic factor and transcobalamin II

34
Q

what happens in a Vitamin B12 deficiency? what are some common causes of Vitamin B12 deficiency?

A

Pernicious anemia is caused by failure of red blood cell maturation when vitamin B12 is deficient
-important in DNA synthesis in red blood cells

Common causes is that the stomach does not produce enough IF:

  • Atropic gastritis: chronic inflammation of the stomach mucosa that leads to loss of parietal cells
  • Autoimmune metaplastic atrophic gastritis: immune system attacks IF protein or gastric parietal cells
35
Q

what are two surgical implications that lead to Vitamin B12 malabsorption?

A

Gastrectomy: loss of parietal cells which is a source of IF

Gastric Bypass: Exclusion of the stomach, duodenum and proximal jejunum alters absorption of vitamin B12

36
Q

How is calcium absorbed?

A

Calcium absorption depends on the presence of vitamin D (1,25-dihydroxycholecalciferol)

  • absorbed across enterocytes, but also reabsorbed in kidney
  • in small intestine, vitamin D-dependent Ca+ binding protein
  • Calcitrol and PTH govern
37
Q

what disease presents with Vitamin D deficiency?

A
  • Rickets (children)

- Osteomalacia (adults)

38
Q

How is iron absorbed?

A

Liver secrets apotransferrin into bile, enters duodenum

apotransferrin binds with free iron and with hemoglobin forming transferrin

Transferrin binds to receptors on membranes of intestinal epithelial cells, absorbed into cells via pinocytosis and later released

39
Q

Characteristics of electrolyte absorption?

A

The first step in this process is the absorption of solute, followed by the absorption of water

Absorbate is always isomotic, meaning that solute and water absorption occur in proportion to each other

40
Q

Electrolyte Absorption: small intestine

A

Jejunum: lots of sodium

Ileum: sodium absorbed, HCO3 secreted

41
Q

Electrolyte absorption Colon

A

Colon: Na absorption and K secretion

-aldosterone modulates

42
Q

how does chlorea affect the electrolyte absorption of the colon?

A

Chlorea increases cAMP resulting in increased Cl secretion

The resulting Cl- secretion is accompanied by secretion of Na+ and H20

Volume of fluid secreted into the intestinal lumen overwhelms the absorptive mechanisms of the small intestine and colon leading to massive secretory diarrhea

43
Q

Total absorption of the Proximal small intestine?

A
  • Fat
  • Sugars
  • Peptides and amino acids
  • iron
  • folate
  • calcium
  • water
  • electrolytes
44
Q

Total absorption of the middle small intestine

A
  • Sugars
  • peptides and amino acids
  • calcium
  • water
  • electrolytes especially sodium
45
Q

Total absorption of the distal small intestine

A
  • bile acids
  • Vitamin B12
  • water
  • electrolytes
46
Q

Total absorption of the colon

A
  • water
  • electrolytes
  • MCTs
  • calcium
  • amino acids
47
Q

Products of digestion, site of absorption, mechanism: Carbohydrate

A

Products of digestion: glucose, galactose, fructose

site of absorption: small intestine

Mechanism:

  • Na+ glucose transport,
  • Na+ galactose transport
  • Facillitated diffusion
48
Q

Products of digestion, site of absorption, mechanism: proteins

A

Products of digestion: Amino acids, dipeptides, tripeptides

site of absorption: small intestine

Mechanism:

  • Na+ amino acid transporter
  • H+ dipeptide and H+ tripeptide co transporter
49
Q

Products of digestion, site of absorption, mechanism: lipids

A

Products of digestion: fatty acids, monoglycerides, cholesterol

site of absorption: small intestine

Mechanism:

  • bile salts from micelles
  • diffusion of FA, MAG, and cholesterol
  • Reesterification in cell to TG and PLs, chylomicrons form and cell and transferred to lymph
50
Q

Products of digestion, site of absorption, mechanism: Water soluble vitamins and Vitamin B12

A

Products of digestion:
Small intestine
ileum

Mechanism:

  • Na+ dependent cotransporter
  • intrinsic factor
51
Q

Products of digestion, site of absorption, mechanism: Bile salts

A

site of absorption: ileum

mechanism:
- Na+ bile salt co transporter

52
Q

Products of digestion, site of absorption, mechanism: Ca+

A

site of absorption: small intestine

Mechanism:
-vitamin D dependent Ca+ binding protein

53
Q

Products of digestion, site of absorption, mechanism: Fe+

A

Products of digestion: Fe3+ reduced to Fe2+

Site of absorption: small intestine

Mechanism: Binds to apoferrintin in intestinal cells; binds to transferrin in blood

GIGU test! (40 decks)

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