Functions of the Large Intestine
What are the 4 major functions of the large intestine?
- Absorb water and electrolytes - Absorb short chain fatty acids - Store and transport undigested material - Eliminate undigested material
When do mass movements occur?
- After meals - In response to gastrocolic reflex - In response to duodencolic reflex
In the large intestine, poor motility can lead to ____ and excess motility can lead to ____ :
- Constipation - Diarrhea
Intrinsic reflex is mediated by which control mechanism? What triggers the reflex?
- ENS - Poo entering the rectum
What is the purpose of spinal cord reflex in the defecation reflex?
- Greatly intensifies the intrinsic reflex.
What is the difference between haustral contractions and mass movements?
- Haustral: mix chyme to enhance absorption. Minimal propulsion. - Mass movements: propel fecal material.
To initiate defecation, pudendal nerve activity is (stimulated/inhibited) by higher brain centers.
- Inhibited to relax external sphincter.
Rectal distention initiates relaxation of the (internal/external) sphincter. This leaves pooping up to voluntary control of the (internal/external) sphincter.
- Internal - External
What kind of muscle makes up the internal and external sphincters?
- Internal: Smooth muscle (thickening of the circular smooth muscle) - External: Striated muscle that surrounds the internal sphincter.
What are the 3 levels of defecation control?
- Intrinsic reflex - Spinal cord reflex - Higher center involvement
What could happen if there was damage to/just above the S2-S4 region?
- Intrinsic reflex will still be intact. - Defecation reflex will be lost. - Manual stimulation may be necessary to complete the defecation process.
What are 2 factors that promote emptying of SI into colon?
- Pressure and chemical irritation of the ileum. - Fluidity of contents in the ileum.
What are 3 major functions of the colon microflora?
- Produce vit K, B1, B2 - Produce short chain fatty acids - Affect immune system
Which nerves supply sympathetic innervation to the proximal colon, the distal colon, and the rectum?
- Proximal: Celiac and Superior mesenteric ganglion - Distal: Inferior mesenteric plexus - Rectum: hypogastric plexus
Which nerves supply parasympathetic innervation to the proximal and distal colon?
- Proximal: Vagus - Distal: Pelvic nerves
To discourage defecation, pudendal nerve activity is (simulated/inhibited) by higher brain centers.
- Stimulated to contract external sphincter.
Why are Mass Movements considered to be modified peristalsis?
- They are not continuous like peristalsis is
How can mucus secretion be increased?
Parasympathetic stimulation
What factor may inhibit SI emptying into the colon?
Pressure or chemical irritation of the colon will activate/stimulate sphincter.
Which spinal cord levels provide sensory and motor fibers for defecation reflex?
S2 - S4
What is the function of the ileocecal junction?
Acts as a valve and a sphincter: - Valve: prevent backflow from colon to SI - Sphincter: regulate movement from SI into colon
Describe the haustra of the large intestine:
Ball like chambers that appear and disappear with the action of the longitundinal and circular muscle. - not fixed
The large intestine contains: - Crypts - Digestive enzymes - Villi
Crypts
