The Large Intestine & Defecation

Where is the large intestine and where does it start and end

The large intestine is in the abdominal cavity around the small intestine
it starts at the cecum and ends at the anal canal

How does the large intestine compare to the small intestine

it is shorter but wider

what are the 4 main funcitons of the large intestine

1. absorb water!!!

2. store indigestible food

3. propel feces to anaus

4. hosue good bacteria

What are the three unique features of the large intestine

teniae coli, haustra, epiploic appendages

Tenia coli

three bands of smooth muscle in the muscularis externa layer

Tenia coli (large intestines)

Haustra

pouches in the colon caused by muscle tone of teniae coli
muscle tone = slight constant activation

Haustra of large intestine

epiploic appendages

fat filled poucches that hangs off the serosa (most outer layer) of from transverse to sigmoid colon

omental (fatty) appendices / epiploic appendages

What are the two main parts of the large intestine

cecum → colon

Cecum of large intestine

cecum - and has what (2)

first segment of the large intestine

illeal papilla (connects to ileum of small intestine)+ appendix

What are the four parts of the colon in order

ascending, transverse ,descneding, sigmoid

What is a flexure and what are the two and why

a flexure is a bend

• right colic hepatic flexure → on the liver side (right)

• left colic splenic flexure → on the spleen side (left)

Rectum

Rectum contains

transverse rectal folds (rectal valves) → three curves and infoldings

also has goblet cells

anal canal

anal canal

final segment of the large intestines - ends at the anus

the mucosa folds into anal columns with anal sinuses in between

Superficial venous plexus

Hemorrhoidal veins part of the anal canal

Anus and what is it regulated by

the opening that feces exits

regulated by internal anal sphincter and external anal sphincter

Internal anal sphincter

smooth muscle of muscularis externa

External anal sphincter

skeletal muscle of pelvic diaphragm

Pathway of the large intestine

cecum - ascending colon → right hepatic flexure → transverse colon → left splenic flexure → descending colon → sigmoid colon → rectum → anal canal → anusTh

the large intestine houses and what two things do they do

gut microbiomes (microbiota) → helpful gut bacteria

• digest cellulose, pectin, and carbohydrates we can’t digest because we dont’t have the enzymes to do so

• help synthesize vitamin B and K

Vitamin K

synthesized by gut bacteria in large intestines → needed by liver to produce clotting proteins

Flatus and what 2 things cause it

intestinal gas that is expelled

• caused by swallowed air as well as bacteria

What are the two main large intestine mobility

haustral contractions and mass movements

Haustra contractions - what is it- what type of movement and what is it good for (often or not often)

Haustra = pouches → distension/stretching causes it to contract moving materail (feces) from one haustra pouch to another

• slow segmentation movement for churning and absorption of water and salt

every 30 min

Mass movement and what are they triggered by (2)

strong contractions 1-3 times a day
triggered by gastrocolic and duodenocolic reflexes

• filling of stomach (gastro) and duodenum → motility of colon

Mass movement vs haustra contractions

mass movements are stronger contractions and pushes materials further
while haustra contraction is slow segmentation for absorbtion and mixing

defecation pathway (what causes it, what reflex, what response → does what 2)

mass movement pushes feces into rectum → rectum fills → stretches/distension → spinal defecation reflex → parasympatheic response → peristalsis contraction of rectum and relaxation of internal anus sphincter

Why dont you immediately defecate

defacation only occurs if exteranl anal sphincter is voluntarily relaxed as well

Valsalva maneuver

abdominal contractions that increase pressure and compress rectum → helps defecation