L7 - Large Intestine

What is the primary site of nutrient absorption in the gastrointestinal tract?

The small intestine.

What are the primary functions of the large intestine?

active transport of sodium, coupled with osmotic absorption of water

What role do microbes in the large intestine play?

They produce vitamin K.

What is the maximum speed of semi-solid chyme progression in the large intestine

5-10 cm per hour (very slow)

What are the main types of motility in the large intestine

Segmental propulsion, kneading, and haustration

How does parasympathetic activity affect the large intestine

It increases activity

(If you’re chill, you can poo)

How often does mass movement occur in the large intestine

1-3 times per day (by peristaltic waves)

What is the main secretion of the large intestine and its function

Mucus; it acts as a protectant and adherent (protects wall of intestines from bacteria)

How does irritation of the large intestine affect water and electrolyte secretion

It increases secretion, leading to diarrhoea

What gets absorbed from the large intestines

Colon can absorb amino acids, fatty acids and peptides, Ions and water

How much water is excreted daily in faeces

50-100 mL per day

What complex carbohydrate is digested in the large intestine

Cellulose

What do bacteria in the large intestine ferment cellulose into

Short-chain fatty acids

What vitamins do gut bacteria produce

Vitamin K and vitamin B12.

What gases contribute to flatus?

Nitrogen (N₂), carbon dioxide (CO₂), hydrogen (H₂), methane (CH₄), and hydrogen sulfide

(Nasty Cats Hate Hunting Mice)

How much flatus is produced/swallowed daily

0.7 - 1 L/day

How much flatus is produced daily

400-700 mL per day

What makes up faeces content

Water, bacteria, bacterial waste, roughage, and bile pigments

(bacteria & bacterial waste since it is microorganisms (bacilli) that convert waste → faeces)

How does bacterial species abundance relate to inflammatory bowel disease (IBD)?

Differences in bacterial species abundance can differentiate IBD patients from healthy individuals.

How is secretion/absorption stimulated in the intestines

Non-absorbed CHO can’t be absorbed so it induces secretion

When colonic micro-biota breaks the CHO down into short chain FAs, absorption is stimulated to absorb the SCFAs

What is the primary function of sodium (Na⁺) absorption in the large intestine

It helps maintain electrolyte balance and water absorption

How is Na⁺ transported across the basolateral membrane

By an active sodium pump

What ion is exchanged with bicarbonate (HCO₃⁻) in the large intestine

butyrate (But⁻)

What is the significance of butyrate (But⁻) absorption in the large intestine

It serves as an energy source for colonocytes

(The But gives the colon energy!)

What bacterial byproduct is absorbed in the colon to provide energy for epithelial cells

Short-chain fatty acids (SCFAs) like butyrate

How does chloride (Cl⁻) move across the epithelial cells of the large intestine

It is absorbed through ion channels

Ampicillin is an antibiotic. How does it affect stool weight, consistency & breath H2 profile

Increases stool weight

Increase water output - can cause diarrhoea

Decreases breath H2 profile (breath hydrogen (H₂) test measures hydrogen gas (H₂) levels in exhaled breath, which is produced by gut bacteria - antibiotics would reduce gut bacteria → reduced H2 in the breath)

Effect of PEG (Polyethylene Glycol) & lactulose on stool water output

They both increases stool water output as they are laxatives (PEG more so than lactulose)

They can both cause osmotic diarhoea

(Put a PEG on your nose when someone takes PEG! If you Lack it you Lose!)

What can be added to standard therapy (rehydration solution) for diarrhoea to decrease time for the first stool to be formed

Rice flour & resistant starch would both decrease stool formation time

Is the rectum usually full/empty

empty

What happens that keep the rectum generally empty

Segmental contractions pass matter back to sigmoid colon

What triggers the urge to defecate

Mass movement filling the rectum

What is the reflex response to rectal filling

Relaxation of the internal anal sphincter and contraction of the external anal sphincters

How can defecation be voluntarily controlled

By relaxing the external anal sphincter and increasing intra-abdominal pressure

How has video endoscopy improved our understanding of the gut

It has enhanced knowledge of normal gut processes and revealed disease complications

What is the primary component of digestive secretions

water

Why do we say water absorption in the gut is highly efficient

Because most water is reabsorbed, minimizing excretion

What organ plays a primary role in osmotic homeostasis

The kidneys