3 - Ogranisation and functionf of GI system

What are the accessory organs of the GI system

Liver, Gallbladder and Pancreas

Produce buffers, enzymes and bile to facilitate digestion and absorption of nutrients

What are the functions of the GI

6 steps, 4 key processes

1. Ingestion

2. Motility

3. Digestion

4. Secretion

5. Absorption

6. Defecation

Describe the layers of the GI tract

Mucosa → submucosa → Muscularis → Serosa

Mucosa - Protection, absorption, secretion

Submucosa - Regulation (secretions), transport

Muscularis - Motility, mechanical digestion

Serosa - Protection

How is digestive activity regulated?

Regulated by extrinsic and intrinsic reflexes of the autonomic nervous system (ANS)

EXTRINSIC PATHWAYS via long reflexes:

• From GIT → Sensory afferent fibres project to CNS

• From CNS → motor efferent fibres to GIT

INTRINSIC PATHWAYS involve short reflexes via the Enteric Nervous System

Describe the two plexus that support regulation of digestive activity

both intrinsic pathways:

SUBMUCOSAL PLEXUS - in submucosal layer

• controls local blood flow and secretions, houses blood and lymphatic vessels

MYENTERIC PLEXUS - between circular and longitudinal muscle layers

• Facilitates motility and mechanical digestion

Know the integration of neural pathways

How do endocrine pathways regulate digestive activity

GUT HORMONES:

• stimulate digestive activity and secretions from the GI + accessory organs

• Integrate with appetite regulation pathways

What are the steps of Peristalsis

Peristalsis -

Adjacent sections contract and relax to propel food forward

In the esophagus, small and large intestines, mechanical digestion in stomach

What is segmentation

Non-adjacent sections contract and relax.

Slow movement + mechanical digestion

Mixes chyme with digestive secretions, increases exposure to epithelium for absorption