5. Large intestine

Large intestine functions

Absorption (water and electrolytes) to form feces

Storage fecal matter until expulsion

Bacterial digestion (fermentation) forms gases and beneficial compounds

What are the names of the 2 movements of colon

Mixing contractions and propulsive movements

Mixing contractions

Haustrations, modified segmentation

Colon segmented into pouches called haustras which contract and relax to mix contents

This helps improve absorptions

Propulsive movements

Mass movements, modified peristalsis

Push fecal matter towards rectum

Regulation of movements (enteric NS + parasympathetic control)

ENS - controls digestive functions, regulates contractions of colon and coordinates movement

PNS - stim mass movements by activation of ENS, vagus and pelvic nerves increase motility, most active after eating

Regulation of movements (reflexes)

Gastrocolic - stomach fills with food, stimulates mass movement (expel old food to make space for new food)

Duodenocolic - food enters duodenum, stimulates mass movement (clear existing waste)

Defacation reflex

When rectum fills → stretch receptors signals spinal cord

Defacation reflex - involuntary control

Automatic (autonomous NS)

Internal anal sphincter relaxes - urge to defacate becomes noticeable

Increased peristalsis - sigmoid colon + rectum contract more forcefully, push feces to anus

Defacation reflex - voluntary control

Somatic NS - conscious control via pudendal nerve

External anal sphincter (choose to contract or relax)

Valsalva maneuver (straining to poop) - contraction abdominal muscles + diaphragm