Flashcards in Lecture 17: Water + Electrolytes Deck (51):
Define macro minerals
Essential inorganic elements with dietary needs of >100 mg/day
How are minerals absorbed and present in the body?
Ions = electrolytes
What are the electrolytes with the highest concentrations that dominate electrical properties of cells and membranes?
Na = EXTRAcellular
Cl = EXtracellular
K = INTRAcellular
What is sodium important for?
Nerve/ muscle activity
What are food sources of sodium?
What are food sources of chloride?
What are important activities for Cl?
Distinguish between the functions of villi vs. crypts - which predominates?
Villi = absorption
Crypts = secretion
Absorption = #1
Since sodium is too big to cross passively through epithelial barrier, what are the uptake pathways available for it?
Hydrogen-dependent (electroneutral) cotransport
Bile acid-dependent cotransport
Short chain fatty acid (SCFA)-dependent cotransport
Where is nutrient-dependent sodium uptake important?
Villi in small intestine
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
Na,K ATPase: 3Na out, 2K in
Where is electroneutral sodium chloride uptake important?
What are important transporters in electroneutral NaCl uptake?
SLC26: Cl in, bicarbonate OUT to lumen
Na/H exchanger: Na in, H OUT to lumen
Chloride channel: Cl out
Na, K ATPase: K in, Na OUT
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
Where is apical sodium-dependent bile acid transporter (ASBT) important?
Intestine = distal ileum
Where is epithelial sodium channel (ENaC) important?
What regulates epithelial sodium channel (ENaC) transport of sodium?
What are the names of the players involved in electrogenic sodium uptake into the colon?
ENaC: sodium in from lumen
Na, K ATPase: K in, Na OUT
Where is sodium-coupled short chain fatty acid uptake important?
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
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
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
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
What is CFTR?
Cystic fibrosis transmembrane regulator
Transport ATPase that acts as a Cl ion channel
What activates CFTR?
cAMP-dependent protein kinase A (PKA)
What are food sources of potassium?
Fruits (bananas, oranges)
Vegetables (potatoes, beans, spinach, broccoli)
Dairy products (yogurt, milk)
What is potassium important for?
Nerve and muscle activity
Heart and BP regulation
Describe potassium absorption in the small intestine
Describe potassium secretion and absorption in colon
Active Potassium channels throughout colon
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
Describe intestinal uptake of water
Passive along osmotic gradient
Passes easily through cell membranes
Where is the majority of water absorbed?
Small intestine = max capacity = 12 L
Colon = max capacity = 4-6 L
Name daily fluid loads of water in the GI tract
How does water get absorbed into intestines?
Follows major osmotically active salutes
What are the osmotically active solute?
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
What are the daily recommendations for K, Na, and Cl?
K = 4000 mg/day
Na = 2000 mg/day
Cl = 2000 mg/day
Describe the sodium-glucose cotransporter (SGLT-1)
Secondary active contra sport
2 Na, 1 glucose IN
Apical surface @ small intestine epithelial cells
What is GLUT-2 important for?
Can be inserted @ apical membrane if there is high load conditions to help absorb remaining glucose
What is GLUT?
What does GLUT do?
Uniporter for glucose or fructose
Whats the difference between GLUT 1-4 and GLUT 5?
GLUT1-4 = glucose
GLUT5 = fructose
Where is GLUT2 usually expressed?
Where is GLUT5 usually expressed?
Where does glucose absorption mostly happen?
How does sodium uptake happen without glucose?
Electroneutral Na-Cl absorption
Cotransport with bile acids
Sodium channel (ENaC)
Cotransport w/ short chain fatty acids
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
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 ✅
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)
What are key transport processes in colon?
Coupled, electroneutral exchange (Na/H, Cl,HCO3)
Sodium channel (ENaC)
H/short chain fatty acid cotransport (MCT1)