The GI system is, at its base, a way for you to: get food, break it into absorbable parts, physically and chemically (through secretions), absorb all that you need from it, and then excrete it with other waste products, and it does this cleanly, safely, and by moving it to and from specialised organs for each function. It is a tube that is a conveyor belt, which does processes to the content of the belt at each step. your body puts stuff onto the belt and takes stuff off of the belt. what is on the belt is in the outside world and needs to be resorbed to be reused.
In essence
- Motility
- Secretion
- Digestion
- Absorption
Interrelation 
We need motility to move and crush food to smaller bits (digestion) and we also need motility to be able to push all the molecules up to the brush border to be absorbed as diffusion isnt great over long distances. We need secretion to digest everything molecularly, to make everything watery and slushey, and we need to secrete things to help absorption. we then need to absorb all the water and we secreted as well as we digest our secretions. We end up with a chart like this.
basic histology
- epithelial cellc
- lamina propria
- muscularis mucosae
- submucosal plexus
- circular muscel
- myenteric plexus
- longitudingal muscle
- Serosa
Enteric NS control git function - motility plus secretion
GIT hormones
can be endocrine (gastrin, cholecytokinin), paracrine(histamine, somatostatin) or autocrine ()