GI tract introduction

Question 1

What are the basic processes of the GIT ?

Answer 1

Secretion - transfer of water and ions along with the release of synthesized materials by GI epithelial cells

Motility - movement of material through GIT

Digestion - mechanical and chemical breakdown of food into smaller absorbable units

Absorption - active or passive transfer of substances from the lumen of the GIT to the ECF

Question 2

Immune Processes

Answer 2

The gut forms a boundary between internal and external environments and is essential for innate immunity

the gut contains the largest accumulation of immune cells in the body (GALT) whose main function is oral tolerance

Question 3

Layers in the GIT TISSUE

Answer 3

1. Mucosa
2. Submucosa
   3.Muscularis
3. Serosa

Refer to GI TRACT INTRO PPT FOR FUNCTIONS

Question 4

Secretions which are released into the GUT

Answer 4

• digestive enzymes
• mucus
  -ions and water

Question 5

Exocrine glands

Answer 5

Glands contain a mix of serous and mucous cells in its acini that secrete a solution of pH 6.4

-salivary glands
-pancreas

functions of saliva :
- moistens mucous membranes
-facilitates the indigestion of food
-salivary amylase initiates carbohydrate digestion
- protective function as part of the innate immune system

Question 6

Regulation of GI function

Answer 6

GIT function is regulated by :
- the direct effect of luminal contents
- the actions of local mediators or hormones
the nervous system

Endocrine / paracrine and neuronal control is integrated to affect the activity of :
- epithelial cell activity
-visceral smooth muscle
-vascular smooth muscle of blood vessels
-exocrine glands and endocrine glands and cells

Question 7

Nervous supply to the GIT

Answer 7

Enteric Nervous system (ENS)
- contains sensory neurones
- inter-neurones
motor neurones

Autonomic nervous system (ANS)
-contains motor neurones
-sensory neurones
SYMPATHETIC SYSTEM
PARASYMPATHETIC SYSTEM

Question 8

Enteric nervous system

Answer 8

Two intramural plexuses control intrinsic regulation :
- myenteric plexus - contains motility
- submucosal plexus - controls secretion and blood flow to the GIT

Both use a wide range of neurotransmitters

contains sensory neurones that respond to :
- mechanical stimuli
(stretch)
- chemical stimuli (digestion products)

Question 9

Autonomic nervous system

Answer 9

Parasympathetic system :
- mostly cholinergic
- mostly excitatory

Sympathetic nervous system :
- mostly adrenergic
-mostly inhibitory

Both take part in extrinsic regulation

Question 10

Motility

Answer 10

movement and mixing is controlled by smooth muscle contraction and relaxation

• tonic contractions ;sustained for mins or hrs
• phasic contractions : rhythmic contraction-relaxation cycles

Question 11

MMC ( migrating motor complex )

Answer 11

cyclic, recurring motility pattern that occurs in the stomach and small bowel during fasting

Passage along gut initiates :
- short burst of gastric acid secretion
-short burst pancreatic juice secretion
-brief gallbladder contraction

Question 12

Peristalsis

Answer 12

Initiated during feeding

Progressive waves of contraction moving from one section of the GI tract to another

Leads to movement of bolus along the GIT

Bolus is a small rounded mass of a substance, especially of chewed food at the moment of swallowing

Likewise power propulsion are large amplitude contractions which help to :
- defence
- rapid clearance
-emesis
- clearance of long segments