**3. GI-tract communications anatomy**

Before describing signaling pathways, we need to get a little familiar with the anatomy of the GI-tract and involved systems. Depending on the physiological structure of males and females, the structure of the pelvis will be different. Actually, the outlined subdivision of the pelvic connective tissue is identical in the male and female. The only difference is that in women the uterus is located between the bladder and the rectum and divides the pelvic peritoneum into two sacks, but this is not the case in the male pelvic cavity [64].

### **3.1 GI-tract neuroanatomy**

A complex set of nerve masses and fibers extending from the brainstem to the sacrum, together with neurons in the sympathetic and parasympathetic systems, control a variety of functions, including swallowing, digestion, and excretion. Intestinal-associated neurons and neural networks are generally classified as belonging to the enteric nervous system (ENS) [65], which is described in terms of function and action as follows:

*Large Association of GI Tract Microbial Community with Immune and Nervous Systems DOI: http://dx.doi.org/10.5772/intechopen.104120*

Actions:

Sympathetic �������! *catecholamines* **α-** or β-adrenergic receptors !

*postganglionic vasoconstrictor neurons secretion inhibitory neurons motility inhibitory neurons* 8 >>>< >>>: Parasympathetic ¼¼¼¼¼¼¼ **vagus nerve**) **Intestinal nerve innervation** ¼¼¼¼¼¼¼¼¼¼¼¼¼¼¼¼¼ **neurotransmitter acetylcholine**) **motility digestion secretory function** 8 >>>>< >>>>: 8 >>>>>>>< >>>>>>>:

The GI-tract is innervated through its connections to the CNS and by the ENS in the wall of the GI-tract, ENS works in coordination with the CNS reflex to the command center and in the neural pathways that pass through the sympathetic ganglia to control gastrointestinal function [66].
