16 - Intestinal Absorption of Solutes and Amino Acids Flashcards Preview

GI / Hepatology > 16 - Intestinal Absorption of Solutes and Amino Acids > Flashcards

Flashcards in 16 - Intestinal Absorption of Solutes and Amino Acids Deck (36)
1

Lactose

Disaccharide
Glucose - Galactose

2

Lactase

Enzyme on brush border

Breaks Lactose down to Glucose & Galactose

Lactase expression decreases upon weaning

3

Lactose Intolerance

The inability to metabolize lactose.

No lactase (this is actually normal, without the mutation)

Lactose goes straight through to the colon. The bacteria in the colon eat the lactose and ferment it. This liberates H2, CO2, CH4!!

4

Mutation on Chromosome 2

Conveniently prevents the shutdown of lactase production, even after weaning.

Arose independently in northern Europe and east Africa.

5

Measuring Lactase Deficiency

Measure H2 in breath after giving lactose.

6

Fluid absorption by the gut

9L absorbed per day.

Majority of fluids absorbed in small intestine.

Colon plays role in water & Na+ retention.

7

Breakdown of fluid to absorb in the gut

2L intake

Endogenous secretions:
Saliva - 1.5L
Stomach - 2.5L
Bile - 0.5L
Pancrease - 1.5L
Intestines - 1.0L

8

Breakdown of fluid absorption sites in the gut

Small intestine - 7L
Colon & rectum - 1.9L

Remains in feces - 0.1L

9

Crypt-Villus Axis in Small Intestines - Absorption mechanisms

Electroneutral NaCl
Na+/H+ exchange
Parallel Na+/H+ and Cl-/HCO3- exchange

Solute-coupled Na+ transport
Na/Glucose
Na/Amino Acid

10

Crypt-Villus Axis in Small Intestines - Secretion Mechanisms

Chloride Channels
Bicarb Exchange

11

Surface-Crypt Axis in the Large Intestines - Absorption Mechanisms

Electrogenic Na+ (Apical ENaC)
Electroneutral NaCl
Short-Chain Fatty Acids
Potassium Channels

12

Surface-Crypt Axis in the Large Intestines - Secretion mechanisms

Chloride Channels
Potassium Channels

13

Luminal Water Content Control - What's up with that?

Maintains fluidity
Allows digestive enzymes to get in contact with food particles
Facilitates diffusion of digested nutrients across absorptive epithelium

Provides for normal transit of intestinal contents.
Imbalance = Diarrhea or constipation

Defense against infection
Tourist diarrhea

14

Jejunum - Transporters

Na+/H+ antiport at apical surface leads to acidic microclimate, but also takes sodium in.

Basolateral Na+/K+ antiport shuttles Na into the blood.

Also the H+ that was exported luminally has a bicarb that is exported basolaterally.

Net absorption of Sodium Bicarb + Sugar/AA

15

Ileum - Transporters

Luminal Na+/H+ antiport is decreasing.

HCO3-/Cl- antiport is increasing.

Microclimate disturbed. Fat poorly absorbed.

Cotransport of Na+ and Sugars!

Net NaCl absorption.

16

Colon - Transport

Na+ enters
K+ leaves

This is all controlled by aldosterone. The colon is the kidney of the GI system.

Na+/H+ exchange
Cl-/HCO3- exchange

KCl absorbed

17

Colon - Luminal loss of potassium

Flow-dependent.
There are K+ channels on both ends of the cell, so it depends on the luminal gradient.

You lose potassium in diarrhea

18

Crypt Cell - Transport

Basolateral:
Na+/K+ pump
Na+/K+/2Cl- import (essentially importing 1 NaCl and 1 KCl)

Apical:
Chloride channel

19

Crypt Cell - Chloride Channels

CFTR
Gating this channel gates how much water is or isn't secreted!

cAMP opens it!

Hormones modulate this (example: VIP)

Cholera toxin overproduces cAMP this way, permanently activating Adenylyl Cyclase.

20

CLC-2

Another (smaller) chloride channel in the colon.

Therapeutic target.

Chronic constipation - Open CLC-2 via Lubiprostone (Amitiza)

21

Lubiprostone

Opens CLC-2 channels to secrete more water in the colon.

Does not affect CFTRs

22

Treat cholera

Keep up with fluid loss via IV fluids until immune system can kill the cholera itself.

Measure the rice-water stool and make sure you're putting that much back in.

23

Cholera Buzz Words

Oysters
Travelers
Imported Food

24

How many cells make up a human?

10^13

25

How many microorganisms do we harbor

10^14 (10 times as many as we have cells of our own!)

26

Paneth Cells

Found at the base of the crypts

Provide innate immunity

27

Paneth Cells

Specialized for regulated secretion.

Have TLRs that recognize PAMPS

Contain α-Defensins

Secreted in response to bacteria or cholinergic stimuli

Long-lived cells!

Defend & nurture stem cells!!

Lots of RER

28

α-Defensins

Antibacterial proteins
Family of 6 proteins:
4 in PMNs
2 in Paneth cells (human defensins 5 & C, Cryptidin

Stored in zymogen granules:
Glycoprotein shell

Keep the lumen of the small intestine almost completely sterile.

29

Second defense in small intestine (other than Paneth cells)

Peyer's patches

30

Peyer's patches

Submucosal lymphoid follicles
Underlie mucosal domes

31

Mucosal dome

Place in the mucosa with no villi
Overlie Peyer's patches.
Contain M cells

32

M Cells

Not many villi.
Have a big cavity on the basement membrane, containing macrophages, APCs and Lymphocytes.

33

Transcytosis through an M-Cell

Pathogen transcytosed to the cavity where the antigens are directly presented to the immune cells (APCs, macrophages, lymphocytes).

Mediates early generation of immunity.

Almost pinocytosis-esque

34

M-Cells - Vulnerability.

HIV and some other pathogens use M-Cells to their advantage and jump right on in.

35

Intestinal Lymphocytes

High concentration Th cells (expressing CD4 & IL10)

Effector B cells differentiate into plasma cells, selectively secreting IgA via transcytosis

IgA absorbed to glycocalyx of enterocytes

Protects mucosa by immune exclusion

36

IgA Pathway

IgA created by B cells has special selectins telling it to adhere at the gut.

IgA dimers bind to basolateral IgA receptors and transcytose into the lumen. Part of the receptor is cleaved off with the IgA, protecting it from digestion in the lumen.