GI Absorption Flashcards

1
Q

The three types of digestions are brought about by?

A

Luminal - Enzymes secreted into lumen by gland/stomach/pancreas

Membrane - anchored enzymes (enterocytes) into brush border (dig/absorb coupling)

Cytosol - intracellular cytosolic breakdown (of tri/dipeptides to AA)

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2
Q

Absorption - Explain process, and my what mechanisms

A

Lumen –> E-Cell –> blood/lymph

by Diffusion / FT/AT

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3
Q

Membrane Transport: Passive

A

Diffusion - down gradient

Facilitated - transport mediated by protein

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4
Q

Absorption of water is ___ and determined by ____. This is unidirectional. In the small intestines water can be absorbed against an osmotic pressure gradient by ______ EXPLAIN!

*helps reabsorbs water

A

passive; osmotic gradient; standing gradient osmosis

Active transport pumps sodium in to lateral intercellular space creating a local osmotic gradient. (passive Cl- entry too); water follows –> enters cell + capillary.

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5
Q

What two ways does water use to enter cell?

A

Paracellular - through leaky intestinal tight junctions

Transcellular - through cells

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6
Q

Osmolarity?

A

of chemical compounds dissolved in liquid.

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7
Q

Electrolyte absorption in GI (sodium, potassium, chloride, bicarbonate)

A

Na: - Actively (sec) transported (removed from cell cytosol using Na+ pump)
K: Passively in SI; Colon [c] based
Cl: Passively
HCO3: Absorbed in Jejunum., but NET secretion in GI - neutralize acid

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8
Q

Electrolyte absorption in GI (sodium, potassium, chloride, bicarbonate) NET

A

SI: net absorber of water and all electrolytes. net secretor of bicarbonate

C: net absorber of water, Na+, Cl-, but is a net secretor of K+ and HCO3-

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9
Q

Solvent Drag

A

Solutes dissolved in water that is absorbed get absorbed too. No gradients involved; form or paracellular transport.

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10
Q

Calcium absorption in GI is ____ in ____, Ca is also absorbed in the ____

A

active; duodenum only via Trans-cellular pathway; jejunum

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11
Q

Explain Ca++ absorption in GI: Transcellular Pathway?

What vitamin stimulates and enhances this process?

A

Ca++ enters (FD) binds to calbindin; then diffusion via Ca++ATPase & Ca/Na Exchanger

Vitamin D

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12
Q

Explain Ca++ absorption in GI: Paracellular Pathway?

Is this pathway dependent on vitamin D?

A

Transport in vesicles, does not involved vitamin d.

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13
Q

Where is Magnesium absorbed? active or passive transport?

A

Absorbed actively in the ileum - mechanism poorly described; minor passive transport

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14
Q

Iron depletion leads to ____ because. _____. What is it called when you have a genetic defect that causes excessive absorption of iron

A

anemia; iron is used in RBC synthesis

idiopathic hemochromatosis

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15
Q

What are the two types of Dietary IRON; how is each absorbed?

A

H: Enterocyte uptake (via FD) H.oxygenase splits –> free Fe

NH: Ferric/Ferrous in sol’n
⁃ Ferric not soluble in neutral pH
⁃ reduced to Ferrous via Vit C
⁃ Brush Border reductase uptake

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16
Q

What happens to iron once its inside the cell?

A

⁃ Stored Iron: Bound to form Ferritin (if needed) - irreversible

⁃ Transport Protein mediated transport through cytosol

17
Q

What happens to iron once its inside the cell?

A

Bound to transferrin moved to where it will be utilized - mostly liver

18
Q

Vitamins absorption in GI

A

Fat Soluble (ADEK) - Diffusion (in small intestines)

Water Soluble: FT and Na+ Dependent mechanism (sec AT)

19
Q

Explain Vitamin B12 absorbtion

A

salivary/gastric secretions have R proteins that bind free B12, and protect from gastric enzymes, in ileum R protein is degraded by pancreatic enzymes, and B12 is transferred to IF which protects against Pancreatic Enzymes; Ileum has IF-B12 complex receptors that mediated endocytosis –> enter HPC transferred by transcobalamin (stored in liver) IF - Intrinsic factor

20
Q

How can pancreatic issues lead to anemia?

A

if no pancreatic enzymes are present, degradation of R protiens of the R-B12 complex will not take place, and allow IF-B12 complex formation. There are no R-B12 receptors for uptake, so B12 will be lost in the stool