Lecture 16 notes Colon and adaptations for herbivory

mesentery/ mesenteric vessels

Major functions of colon or large intestine
1. Absorbs water and ions to form solid feces
2. Storage of feces until removed- positive feedback evacuating colon
Major movements of Large intestine
1. Haustrations (bucket or scoop)
  1. Contraction of smooth muscle ring
  2. Simultaneous contraction of longitudinal s. Muscle
  3. Collectively causes bulging (haustration) of other parts of colon
  4. Results in turning over chyme like turning over soil with spade
2. Mass (propulsive) movements
  1. 1-3x per day
  2. 15 minutes after eating first meal of the day
  3. Series of contractions starting slowly then increasing rapidly forcing feces down the colon
  4. Series of mass movements persists for 10-30 mins
Defecation
1. Desire for defecation occurs when rectum is full- stretch receptors
2. Proceeds via positive feedback reflex
3. Anus lined with two sphincters
  1. Internal- under involuntary control
  2. External - under voluntary control (stays closed all the time)
Colonic bacterial flora
1. 300-1000 species live in our guts
2. Infants are born without many of these but colonized as pass thru the birth canal
3. Functions of these bacteria
  1. Ferment carbohydrates
  2. provide barrier to harmful bacteria
  3. Immune system
    1. Stimulate lymphoid tissue in gut mucosa to produce antibodies to harmful bacteria
    2. Have a role in making toll-like receptors (TLR’s)- proteins that recognize molecules on surface of infectious microbes
  4. Up tp 60% of fecal matter is dry

Other foregut fermenters- sheep, kangaroo

Other hindgut fermenters- horse, Chuckwalla (Sauromalus obesus), marine iguana, gopher tortoise, bunnies

Hindgut fermenters- how they absorb nutrients way back in their colon

Some have good absorption in caecum and LI
Others practice coprophagy!!!
Eating special type of feces “cecal feces”
Rabbit makes two types of feces
1. Normal waste feces
2. Cecal material- cecotropes

How do they do it?