Exam 3 (Lecture 4) - Regulation of GI System Function 1

Question 1

List the 4 systems that regulate GI system function.

Answer 1

1) CNS (Central Nervous System)

2) ENS (Enteric Nervous System/GI Nervous System)

3) ΑNS (Autonomic Nervous System)

4) Enteroendocrine Cells (EECs) of GI Endocrine System

Question 2

How does the CNS regulate GI system function?

Answer 2

CNS:

  - Extrinsic control (outside of the gut)
  
  - Indirect regulation
  
  - CNS influence on the gut is mediated through the preganglionic 
     neurons of the ANS to stimulate or inhibit the ENS and GI
     endocrine system

Question 3

Describe the structures/functions of the enteric nerve plexuses of the ENS.

Answer 3

ENS is located within all GI organs
- intrinsic control (inside the gut)

  - ENS components (myenteric and submucosal plexuses)
  
  - Gut function is under direct regulation of ENS and GI endocrine
     system
         - intrinsic control allows the gut to regulate its functions 
            autonomously based on local conditions
                 - amount of type of food contained in the lumen
  
  - Coordination of GI function with the rest of the body is achieved 
     by integration of extrinsic and intrinsic influences

Two Major Enteric Nerve Plexuses:
- Myenteric (Auerbach) Plexus
- controls GI motility
- located between the inner circular and outer longitudinal
smooth muscle layers
- myenteric plexus of the SI generally shows a repeated
pattern of ganglia (oriented parallel to the axis of the circular
smooth muscle fibers; connecting nerve strands oriented
almost perpendicular to the ganglia)

  - Submucosal (Meissner) Plexus
        - controls GI function
        - Located in the submucosa

Question 4

List the peptide and nonpeptide neurocrines. Excitatory or inhibitory to GI tract function?

Answer 4

Peptide Neurocrines:
- Substance P (excitatory)
- Somatostatin (inhibitory)
- Vasoactive Intestinal Peptide
- inhibitory to gut muscle
- stimulatory to submucosal gland secretions

Nonpeptide Neurocrines:
- Acetylcholine (Ach) = excitatory
- Adenosine Triphosphate (ATP) = excitatory
- Nitric Oxide (NO) = inhibitory

Question 5

Describe the structure and function of the ANS. Parasympathetic Nervous System. Where is there an increase in blood flow? Decrease in blood flow? Sympathetic Nervous System: Where is there an increase in blood flow? Decrease in blood flow?

Answer 5

Sympathetic Nervous System:
- Thoracolumbar region (sympathetic trunk)
- Fight or Flight Response
- increase in blood flow to lungs, heart, and skeletal muscle
- decrease in blood flow to GI system and urinary system

Parasympathetic Nervous System:
- Cranial and sacral segments
- Rest and Digest
- increase in blood flow to digestive and urinary systems
- decrease in blood flow to lungs, heart, and skeletal muscle

Question 6

ANS - Parasympathetic and Sympathetic nervous system. What is the innervation pathway and which GI segments are innervated for the craniosacral and thoracolumbar divisions?

Answer 6

The GI tract receives extrinsic innervation from the autonomic NS.
1) Parasympathetic NS
- Cranio (brain stem) = brainstem to X (vagus)
- provides innervation from esophagus to transverse colon

      - Sacral (S1-S3 spinal cord segments to pelvic nerves)
         - provides innervation to terminal portions of colon

  2) Sympathetic NS
      - Thoraco (T1-T13 spinal cord segments)
         - T1-T13 to paravertebral ganglia (sympathetic chain) to 
            prevertebral ganglia (celiac ganglia)
               - provides innervation from esophagus to transverse col.

      - Lumbar (L1-L4 spinal cord segments)
         - L1-L4 to paravertebral ganglia to prevertebral ganglia
            (cranial and caudal mesenteric ganglia)
               - provides innervation to terminal portions of colon