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Flashcards in Gastrointetsinal absorption Deck (18)
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1
Q

Define digestion. What are the three types of digestion

A

Digestion is the breaking down of macromolecules into smaller components so they can be absorbed in the lumen of the GI tract

  1. Luminal- enzymes in the lumen of the GI tract
  2. Membrane or contact- Digestive enzymes synthesize by entercytes in the brush border of the GI lumen.
  3. Cytosol- intracellular cytosolic peptidases break down absorbed di/tri peptides into single AA acids
2
Q

Define absorption and how does it occur

A

Permeation of molecules from the lumen of the GI tract, through the epithelial cell (enterocyte) layer, into the blood and lymph vascular compartment.
• Occurs via diffusion, facilitated or active transport mechanisms across apical membrane.
• Enterocytes release absorbed nutrients into blood (e.g. amino acids, sugar) or lymphatic circulation (e.g. lipids) for delivery to sites of metabolism/utilization.

3
Q

Two common secondary transport in the GI tract

A

Active transport through secondary

Antiport- Na/Ca exchange

Symport-Na-glucose coupled

4
Q

Sites of absorption what are unique features of the SI

A

Features that increase the SA (absorptive surface) such as circular folds, villa, and microvilli. These can increase the SA by a factor of 600 compared to the simple tube of the small intestine.

Villa icnrease by 30x so imagine the damage of Celiacs and the inability to absorb

5
Q

Where are nutrients absorbed? Mostly in what specific part

A

ONLY in the SI

Majority of the carbds, proteins and lipids are in the Duodenum then the jejunum and least amount inte ileum

6
Q

Where is bile acids absorbed? mainly where?

A

Throughout the SI and LI

Mostly actively in the ileum and the uporcessed parts in the proximal part of the colon

7
Q

Breakdown of total amount of water intake

A

2 liters through diet

7 liters in GI sections

Lose 100mL (5%) through feces

SO the average absoprtion is about 9L

8
Q

How is water absorbed?

A

Generally passive and determiend by the differenes in osmolarity. (low to high osmolarity)

In the colon water can be absorbed in the absense or even against a gradient b/c the LI establishes a local gradient by extruding Na into thebasolateral space (blood) (Cl- follows for electronegative balance) so a gradient is established and water follows into the intercellular space .

9
Q

How does water move between the GI and circularoty system?

A

Either through transcellular(through epithelial cells) or paracellular(between epithelial cells/tight junctions)

Tight junctions in the GI tract are leaky and allow water and ions through (paracellular)

Solvent drag (paracellular)- large columes of water absorbed from lumen to blood with small solutes

10
Q

Na absorption

A

Acitvely in the jejunum ileium and colon

11
Q

K+ absorption and Cl-

A

K+- Mainly passively

Cl- absorbed througtout

HCO3–Absorbed in jejunum and secreted in ileum and colon

12
Q

Net absorption of SI and Colon

A

SI- net absorbtion of water, Na, CL, K ad net secretor of HCO3

LI- net absorb og water, Na+, Cl-, but is a net secretor of K+ and HCO3

13
Q

Dicuss calcium absorption

A

Calcium is Actively in the Duodenum and passively in the jejunum and ileum (ileum has the least absorption of calcium)

Active is transcellular- calcium enters cytosol of enterocytes and binds Ca to protein (calbindin) and they it is released through the Ca-ATPase out of the cell into circulation– this process is facilitated by Vitamin D. When low plasma Ca2+ Parathyoid hormone is converted and 25 Dhydrocy Vitamin D converted into 1-25 hydroxy vitamin D which stimulates the calium bindign proteins and Ca2+ ATPase

Passive is through paracellular (no cytosol) not under Vitamin D just dependent on the gradient

14
Q

Discuss absorption of magnesium

A

Active process is in the ileum but poorly described

Minor passive (paracellular)

15
Q

Discuss iron absroption

A

Too low can lead to anemia

Excessive absoprtion of iron through idiopathetic hemochromatosis

2 forms of iron 1/ Heme compound and 2. Non-heme

  1. Heme compound comes from meats and is absorbed by faciliated transport
  2. Non-heme iron- either Fe3+ (insoluble) or Fe2+– the apical membrance has na iron reductase that convert the 3+ intot he 2+ making it absorbable. THe iron doesn’t just diffuse it has Divalent Metal Transporter I from the lumen to the cytosol
16
Q

Define vitamins

A

organic substances needed in small quantities for normal metabolic function, growth and maintenance of the body

17
Q

Which ones are fat and water soluble? And discuss the difference in absorption

A

Fat (have to come from diet)- A, D, E, and K– absorbed by diffusion passively in the SI and make micelles

Water- C, B1, B2, B6, B12, biotin, choline folic acid and inositol– absorbed in the SI by Na-dependent or faciliated mechanisms

18
Q

Absorption of Vitamin B12

A

Gastric phase- B12 in binds to R proteins protected from the acidic stomach and an intrinsic factor.

Once it enters the SI the R protein is degraded but the intrinsic factor transfer it to the ileum

Intertinal Phase- the Vitamin B12 complex is absorbed at the terminal ileum via IF-B12 receptor