Lecture 17: Water + Electrolytes Flashcards Preview

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Flashcards in Lecture 17: Water + Electrolytes Deck (51):
1

Define macro minerals

Essential inorganic elements with dietary needs of >100 mg/day

2

How are minerals absorbed and present in the body?

Ions = electrolytes

3

What are the electrolytes with the highest concentrations that dominate electrical properties of cells and membranes?

Na = EXTRAcellular

Cl = EXtracellular

K = INTRAcellular

4

What is sodium important for?

Water distribution

BP

Nerve/ muscle activity

5

What are food sources of sodium?

Soup

Bread

Pizza

Cheese

Cured meats

Salty snacks

6

What are food sources of chloride?

Soup

Bread

Pizza

Cheese

Cured meats

Salty snacks

7

What are important activities for Cl?

Water distribution

BP

Nerve functions

Gastric acid

8

Distinguish between the functions of villi vs. crypts - which predominates?

Villi = absorption

Crypts = secretion

Absorption = #1

9

Since sodium is too big to cross passively through epithelial barrier, what are the uptake pathways available for it?

Nutrient-dependent cotransport

Hydrogen-dependent (electroneutral) cotransport

Bile acid-dependent cotransport

Short chain fatty acid (SCFA)-dependent cotransport

Electrogenic channel

10

Where is nutrient-dependent sodium uptake important?

Villi in small intestine

11

What transporters are located on the apical and basolateral sides of the villus epithelial cell for nutrient-dependent sodium uptake?

SGLT-1: glucose + 2Na taken up into cell
(Apical)

Na,K ATPase: 3Na out, 2K in
(Basolateral)

12

Where is electroneutral sodium chloride uptake important?

Small intestine

Colon

13

What are important transporters in electroneutral NaCl uptake?

SLC26: Cl in, bicarbonate OUT to lumen
(Apical)

Na/H exchanger: Na in, H OUT to lumen
(Apical)

Chloride channel: Cl out
(Basolateral)

Na, K ATPase: K in, Na OUT
(Basolateral)

14

Describe sodium-dependent bile acid transportation

Na + bile salt taken up together from lumen, otherwise bile acid would not be able to get in since it's not membrane-permeable

15

Where is apical sodium-dependent bile acid transporter (ASBT) important?

Intestine = distal ileum

16

Where is epithelial sodium channel (ENaC) important?

Colon

17

What regulates epithelial sodium channel (ENaC) transport of sodium?

cAMP

18

What are the names of the players involved in electrogenic sodium uptake into the colon?

ENaC: sodium in from lumen
(Apical)

Na, K ATPase: K in, Na OUT
(Basolateral)

19

Where is sodium-coupled short chain fatty acid uptake important?

Colon

20

What are two active ways that epithelial cells in the colon take up short chain fatty acids?

**sodium-coupled monocarboxylate transporters (SMCT): 2 Na, fatty acid in, then fatty acid exits

H+-dependent monocarboxylate transporter (MCT): H+, short fatty acid IN, then fatty acid exits

21

Describe regional variation in active Na and Cl absorption in GI tract

Jejunum: Na-nutrient, Na-H

Ileum: Na-Cl, Na-nutrient, Na-bile acid

Cecum: Na, SCFA

Proximal colon: Na-Cl, Na-SCFA

Distal colon: Na

22

Compare locations of total intestinal Na absorption in GI tract

Duodenum/jejunum = Na/H & Na/solute
Proximal small intestine can occur w/o bicarb/Cl exchange

Ileum = Na/solute & Na-Cl coupled

Colon: Na-Cl coupled

Rectum: Na-Cl coupled, Na channel

23

Describe chloride secretion in crypts of small intestine and colon

Chloride is secreted into crypt lumen and generates water to flow out

This protects against microbes at the lumen

Sodium follows soon after

24

What is CFTR?

Cystic fibrosis transmembrane regulator

Transport ATPase that acts as a Cl ion channel

25

What activates CFTR?

cAMP-dependent protein kinase A (PKA)

26

What are food sources of potassium?

Fruits (bananas, oranges)

Vegetables (potatoes, beans, spinach, broccoli)

Dairy products (yogurt, milk)

Meat

27

What is potassium important for?

Nerve and muscle activity

Heart and BP regulation

28

Describe potassium absorption in the small intestine

Primarily passive

29

Describe potassium secretion and absorption in colon

Passive pathways

Active Potassium channels throughout colon

30

Describe potassium absorption in rectum

H/K ATPase: K uptake, H gets pumped out to lumen where it is neutralized by bicarbonate exchanged for absorbed Cl

31

Describe intestinal uptake of water

Passive along osmotic gradient

Passes easily through cell membranes

32

Where is the majority of water absorbed?

Small intestine = max capacity = 12 L

Colon = max capacity = 4-6 L

33

Name daily fluid loads of water in the GI tract

Oral

Saliva

Gastric juice

Bile

Intestinal secretion

Pancreatic juice

34

How does water get absorbed into intestines?

Follows major osmotically active salutes

35

What are the osmotically active solute?

Na

K

Cl

Glucose

36

Differentiate between K, Cl, glucose, and Na absorption with regards to their ability to drive the osmotic gradient

K and Cl do NOT drive gradient - absorption is mainly passive into intestine

Glucose and Na ARE the drivers of water absorption because they must be actively absorbed

37

What are the daily recommendations for K, Na, and Cl?

K = 4000 mg/day

Na = 2000 mg/day

Cl = 2000 mg/day

38

Describe the sodium-glucose cotransporter (SGLT-1)

Secondary active contra sport

2 Na, 1 glucose IN

Apical surface @ small intestine epithelial cells

39

What is GLUT-2 important for?

Can be inserted @ apical membrane if there is high load conditions to help absorb remaining glucose

40

What is GLUT?

Glucose transporter

41

What does GLUT do?

Uniporter for glucose or fructose

42

Whats the difference between GLUT 1-4 and GLUT 5?

GLUT1-4 = glucose

GLUT5 = fructose

43

Where is GLUT2 usually expressed?

Intestine

Liver

Pancreas

Kidney

44

Where is GLUT5 usually expressed?

Intestine

45

Where does glucose absorption mostly happen?

Jejunum

46

How does sodium uptake happen without glucose?

Small intestine:
Electroneutral Na-Cl absorption
Cotransport with bile acids


Colon:
Na-Cl absorption
Sodium channel (ENaC)
Cotransport w/ short chain fatty acids

47

How does diarrhea arise?

Increased solute secretion: excessive Cl secretion; infection + inflammation

Decreased solute absorption: diminished Na absorption; congenital defects in key transporters (ex: SGLT1)

Unabsorbable solutes in diet: osmotic agents

Loss of digestive capacity: lactase deficiency; villus loss in celiac disease

48

Describe ion transport in toxin-induced diarrhea

Toxins induce inc of cAMP

Decreased NaCl absorption (inhibition of Na/H exchanger)

Increase in Cl secretion leads to increased water output

Na-Nutrient absorption not affected - why oral rehydration solutions with Na, glucose ✅

49

What are key transport process in small intestine?

Na/glucose cotransport (SGLT1)

Facilitating transport of glucose (GLUT2)

Coupled, electroneutral exchange (Na/H and Cl/bicarbonate)

Sodium/bile acid cotransport (ASBT)

50

What are key transport processes in colon?

Coupled, electroneutral exchange (Na/H, Cl,HCO3)

Sodium channel (ENaC)

H/short chain fatty acid cotransport (MCT1)

51

Differentiate active uptakes in small intestine vs. colon

Small intestine = active uptake of glucose and Na
(K, Cl mostly passive)

Colon = active uptake of Na, K, and Cl
(Glucose normally not present)