Salt and Water Balance in the Intestine

Question 1

Describe the structure of the colon

Answer 1

Columnar
No villi
Crypts suck water out of faeces
Goblet cells secrete mucus => easy passage of faeces

Question 2

What are the properties of stool

• Normal water content
• Diarrhea water content
• pH
• Contents

Answer 2

Normal
-65-85% water

Diarrhea
->85% water

pH
-5-6 due to SCFA production to keep down pathogenic strains

Contents
-Bacteria, bile salts, electrolytes, enterocytes

Question 3

Describe water absorption

• main location
• method

Answer 3

Main location
-Jejunum

Method

• Follows ion absorption by osmosis, driven by Na
• Increased ion movement => increased water uptake => increased hydrostatic pressure => forces water out of cells
• Paraceullular, transcellular (APQ1-8)

Question 4

Describe how Na moves across the GI tract

• Proximal bowel
• Jejunum
• Ileum
• Colon

Answer 4

Proximal bowel
-NaH exchange

Jejunum
-NaAA/NaGlucose

Ileum
-NaCla contrasnport

Colon
-Na channels

ALL DRIVEN INTO ISS VIA NAKATPASE

Question 5

Describe how Cl, HCO3 moves across the GI tract

-Colon

Answer 5

Na transport => electrochemical gradient

=HCO3Cl exchange => HCO3 secretion

Question 6

What are the 3 types of diarrhea

-what are they each characterised by

Answer 6

Congenital
-HCO3Cl exchange faulty => Na secreted => no water uptake

Osmotic

• Inability to absorb non electrolytes/laxatives/hypermobility of intestines
• Osmotic gradient reversed

Bacterial

• Permanent AC activation => increased cAMP => increased Cl secretion
• NaH exchange inhibited => increased water secretion

Question 7

What is constipation

Answer 7

Slow movement, too much water uptake

Question 8

Name the roles of intestinal flora

Answer 8

Vitamin synthesis
Immune defense
Cross reactive antibody production
Tissue development
Fermentation
SCFA production

Question 9

Describe how intestinal flora achieves each of its functions

• Vitamin synthesis
• Immune defense
• Cross reactive antibody production
• Tissue development
• Fermentation
• SCFA production

Answer 9

Vitamin synthesis
-Vitamin K, B

Immune defense

• Prevent colonization by competing for nutrients
• Inhibits/kills non indigenous species

Cross reactive antibody production
-Production of AB that react to both flora and pathogens => prevent infection

Tissue development
-Stimulates caecal/lymphatic tissue development

Fermentation
-Break down fibre in colon

SCFA production

• Regulate gut hormone release
• Absorbed as energy source
• Influence food uptake/insulin sensitivity directly

Question 10

What are the 2 types of normal flora

Answer 10

Bacteroides
-Can cause infection if displaced into blood/tissue

Bifidobacteria
-Prevent colonization by pathogens